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					                      OPERATING AND MAINTENANCE GENERAL PROCEDURES

 Operations &
 Maintenance                                        INDEX                                    Page 1 of 2


  OM - 10       Abandonment or Inactivation of Facilities

  OM - 20       Testing of Gas Mains

  OM - 30       Notification of Gas Supply and Distribution Facility Shutdowns, Isolations or Stopoffs

  OM - 50       Investigation of Accidents and Failures

  OM - 60       Leakage Control

  OM - 64       Leak Reporting

  OM - 66       Corrosion Control

  OM - 70       Odorization

  OM - 72       Responding to a Gas Odor                                                                   192-93

  OM - 74       Operating Pressures

  OM - 80       Prevention of Accidental Ignition

  OM - 82       Pressure Conversion Plans (Uprating)

  OM - 90       Purging Procedures

  OM - 92       Purging Details

  OM - 94       Purging Gas Services

  OM - 96       Inside Service Atmospheric Corrosion Inspection and Leak Survey




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                        OPERATING AND MAINTENANCE GENERAL PROCEDURES                                   OM - 10

  Operations &
  Maintenance               ABANDONMENT OR INACTIVATION OF FACILITIES                                 Page 1 of 4


     1. DEFINITIONS

         a. Main: A distribution line that serves as a common source of supply for more than one
            service line.

         b. Service line: A distribution line that transports gas from a common source of supply
            to:

              •   a customer meter or the connection to a customer’s piping, which ever is further
                  downstream, or;
              •   the connection to a customer’s piping if there is no meter.


     2. ABANDONMENT OF MAINS

         Each main abandoned in place shall be physically disconnected from all sources and supplies of gas.
         Every abandoned part shall be purged of gas in accordance with O&M Procedure 4.6.8 unless the
         volume of gas is so small that there is no potential hazard.
         All open pipe ends of abandoned mains shall be capped, plugged, or otherwise effectively sealed. All
         abandoned gate boxes shall be removed or filled.


     3. ABANDONMENT OF SERVICES

         Each service abandoned in place shall be disconnected or cut off at or close to the main as practical
         and;

              •   Any opening in the main or the open end of the segment of the service line left thereto
                  is sealed; and
              •   The service line is purged of gas, except when the volume of gas is so small that there
                  is no potential hazard; and
              •   The open end of the disconnected service line near the main and traversing to the
                  premises is sealed.

         An inactive service must be cut-off and abandoned as noted above regardless of its’ material being
         plastic, or the fact that it might be cathodically protected if the service is;

              •   in, or close to, an excavation of another facility; or
              •   located in, or close to, buildings being demolished; or
              •   discovered to be leaking gas; or
              •   unrecorded and/or previously unknown after being discovered during the course of
                  performing leak surveys, maintenance, or inspection of pipeline facilities.




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                        OPERATING AND MAINTENANCE GENERAL PROCEDURES                               OM - 10

  Operations &
  Maintenance               ABANDONMENT OR INACTIVATION OF FACILITIES                             Page 2 of 4


     4. INACTIVE SERVICES

         Whenever a service line becomes an inactive service line, one of the following must be promptly
         implemented:

         •    The valve that is closed to prevent the flow of gas to the customer must be provided with a
              locking device or other means designed to prevent the opening of the valve by persons other than
              those authorized by the operator;
         •    A mechanical device or fitting that will prevent the flow of gas must be installed in the
              service line or in the meter assembly;
         •    The customers’ piping must be physically disconnected from the gas supply and the open
              pipe ends sealed; or,
         •    The operator’s pipe must be physically disconnected at some point other than the source of
              gas supply and the open pipe end sealed.


     5. ABANDONMENT OF VAULTS

         Vaults to be abandoned shall be removed or filled with a suitable compacted material and the surface
         made to conform to its immediate surroundings or restored to its original condition.


     6. RECORDS

         Records of inactive service lines shall be maintained including location, date service line became
         inactive and date service line was installed.
         Records of services, which have been abandoned, shall be maintained for not less than five (5) years
         from date of abandoned or longer time as deemed appropriate.


     7. REVIEW OF RECORDS

         An annual review shall be made of the gas customer’s records. Every customer’s meter showing no
         consumption for 12 consecutive months shall be listed and a determination made as to whether each
         such meter should be:

         •    Removed,
         •    Shut off; or
         •    Allowed to remain “live”.




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  Operations &
  Maintenance              ABANDONMENT OR INACTIVATION OF FACILITIES                               Page 3 of 4


         Records of inactive gas services shall be reviewed at least once in each calendar year to determine
         which of such inactive services having no planned future use should be abandoned.
         An inactive service line installed on or before July 31, 1971, and which becomes inactive after
         August 8, 1985, shall be abandoned not later than five years after the most recent inactivation date,
         provided, however, that if the operator can demonstrate that such service line in plastic or, steel
         which is cathodically protected in accordance with 49 CFR 192.463 and 49 CFR 192.455(a)(1) and
         (2), then such service shall be abandoned not later than ten years after the most recent inactivation
         date.
         A service line which was installed after July 31, 1971, and which becomes inactive after August 8,
         1985, shall be abandoned not later than ten years after the most recent inactivation date.


     8. REPORTS

        An annual report shall be sent to the Department of Telecommunications and Energy prior to March
        15th of each year indicating the total number of inactive service lines on December 31st of the
        preceding calendar year, and the number of inactive service lines abandoned during the preceding
        year.




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                        OPERATING AND MAINTENANCE GENERAL PROCEDURES                                     OM - 20

  Operations &
  Maintenance                                TESTING OF GAS MAINS                                       Page 1 of 4


     PRESSURE TEST REQUIREMENTS FOR MAINS

     1. Safety
        Personnel and public safety will be the priority concern when performing a pressure test. Properly
        installed positive restraint end caps or fused or welded end caps will be used during the test.
        Situations that require the use of non-positive restraint end caps will be approved by the Area
        Manager or Director prior to installation. In the event a non-positive restraint end cap is approved, it
        must be properly secured according to the proper procedure for installing and welding a restraint
        assembly. At all times, when any mechanical end cap is used, personnel will be directed to evacuate
        the trench and stand clear of the downstream side of the end cap while the line is pressurized.
        Precautions will be taken to secure the area downstream of the end cap to protect the public.

         In the event any mechanical end cap, positive or non-positive restraint, leaks during the pressure test
         the line will be blown down completely prior to personnel entering the excavation to make
         adjustments on the end cap.

     2. General
         The test medium will normally be air, inert gas or water.

         Mains will be pressure tested according to Items 3 through 8 of this section. Once the main is               Stds.
                                                                                                                      Comm.
         pressurized to the test pressure, the test medium source must be disconnected.

         Mains may be tested in sections. For steel mains, standard weld caps of the same pipe schedule as
         that being tested or flat plate test heads with the thickness and fabrication method indicated in the
         company standards manual should be welded to the ends of the section to be tested. All welds must
         be the same strength and quality as other pipe joints. Upon completing the test, the weld caps or flat
         plate test head, including the weld, shall be cut off from the test section. Mechanical couplings,
         either positive or non-positive restraint, will not be used for testing unless previously approved by
         the area Manager or Director. In the event a mechanical coupling is approved, positive restraint end
         caps will be installed or non-positive restraint end caps will be used with the required restraint
         assembly.

         If the main is not to be immediately placed in service, air or inert gas may be left in the main at a
         reduced pressure as directed by the Director of Distribution. Otherwise upon completion of testing,
         the main or section shall be blown down, properly purged, and placed in service.

         Tie-in connections shall be soap tested at the available line pressure.

     3. Steel Mains to be Operated Below 100 psig
         Steel mains to be operated below 100 psig shall be tested for tightness to at least 90 psig for at least
         one hour. Loss of pressure due to leakage during the test is not permitted.

         If the main is over 1,000 feet in length it shall be tested to at least 90 psig for at least 24 hours. For
         this test, a recording pressure gauge shall be used. Loss of pressure due to leakage during the test is

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  Operations &
  Maintenance                                 TESTING OF GAS MAINS                                    Page 2 of 4


         not permitted.
         A record of the test shall be kept for the life of the pipeline.

     4. Steel Mains to be Operated Between 100 psig and 200 psig (Inclusive) and at a Hoop Stress of
        Less Than 30% of SMYS
         Steel mains to be operated between 100 psig and 200 psig (inclusive) and at a hoop stress of less
         than 30% of SMYS shall be inert gas, air or hydrostatically tested for tightness to 1.5 times the
         MAOP for at least four hours. Loss of pressure due to leakage during the test is not permitted.

         Steel mains 1,000 feet or more in length shall be tested to the above requirements for at least 24
         hours. Loss of pressure due to leakage during the test is not permitted.

         If the main is to be stressed in excess of 20% SMYS during the test and inert gas or air is the test
         medium, a leak test must be made between 100 psig and 20% SMYS or the line walked to check for
         leaks while hoop stress is held at approximately 20% SMYS.

         Calibrated recording instruments verified by dead weight instruments are to be used and the
         recording submitted to the Massachusetts Department of Telecommunications and Energy for
         certification that the steel main, as defined, may be operated at a pressure which is equal to the test
         pressure divided by a factor of 1.5. The pressure test may be witnessed by the D.T.E.
                                                                                                                    Stds.
                                                                                                                    Comm.
         See paragraph 8 for required records.

     5. Steel Mains to be Operated Above 200 psig and at a Hoop Stress of Less Than 30% of SMYS
         Steel mains to be operated above 200 psig and a hoop stress of less than 30% of SMYS shall be inert
         gas, air or hydrostatically tested for tightness to 1.5 times the MAOP for at least eight hours. Loss of
         pressure due to leakage during the test is not permitted.
         Steel mains 1,000 feet or more in length shall be tested to the above pressure requirements for at
         least 24 hours. Loss of pressure due to leakage during the test is not permitted.

         If the main is to be stressed in excess of 20% SMYS during the test and inert gas or air is the test
         medium, a leak test must be made between 100 psig and 20% SMYS or the line walked to check for
         leaks while hoop stress is held at approximately 20% SMYS.

         Calibrated recording instruments verified by dead weight instruments are to be used and the
         recording submitted to the Massachusetts Department of Telecommunications and Energy for
         certification that the steel main, as defined, may be operated at a pressure which is equal to the test
         pressure divided by a factor of 1.5. The pressure test may be witnessed by the D.T.E.

         See paragraph 8 for required records.

     6. Steel Mains to be Operated at a Hoop Stress of 30% or More of SMYS
         Steel mains to be operated at a hoop stress of 30% or more of SMYS, shall be strength tested in


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                        OPERATING AND MAINTENANCE GENERAL PROCEDURES                                 OM - 20

  Operations &
  Maintenance                                 TESTING OF GAS MAINS                                  Page 3 of 4


         accordance with 49CFR 192.505 and 192.515.
         See paragraph 8 for required records.

     7. Plastic Mains to be Operated Below 100 psig
         Plastic mains to be operated below 100 psig shall be tested to 1.5 times the MAOP or for at least one
         hour. The test pressure shall be limited to 3 times the design pressure of the pipe. The temperature
         of thermoplastic material must not exceed 100ºF during the test. Loss of pressure due to leakage
         during the test is not permitted.

         Plastic mains 1,000 feet or more in length shall be tested to the above pressure requirements for at
         least 24 hours. For this test, a recording pressure gauge shall be used. Loss of pressure due to
         leakage during the test is not permitted.

         A record of the test shall be kept for the life of the pipeline.

     8. RECORDS
         A record of each test performed on pipelines to operate at or above 100 psig shall be made and
         retained for the life of the pipeline. The record must contain at least the following:

         a. The operator's name, the name of the operator's employee responsible for making the test, and         Stds.
            the name of any test company used.                                                                    Comm.

         b. The test medium used.
         c. The test pressure.
         d. The test duration.
         e. The pressure recording charts, or other record of pressure readings.
         f. Elevation variations, whenever significant for the particular test.
         g. Leaks and failures noted and their disposition.




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  Maintenance                    TESTING OF GAS MAINS                Page 4 of 4


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                        OPERATING AND MAINTENANCE GENERAL PROCEDURES                                 OM - 30

  Operations &              NOTIFICATION OF GAS SUPPLY AND DISTRIBUTION
  Maintenance               FACILITY SHUTDOWNS, ISOLATIONS OR STOPOFFS                              Page 1 of 4



     This procedure is applicable to all scheduled, unscheduled and emergency isolation or shutdown of Gas
     Supply and Distribution facilities. Its intent is to provide for communication and coordination of
     operations activities among the Customer Service, Distribution and Gas Supply departments such that
     system safety, integrity and reliability are maintained.

     1. SCHEDULED FACILITY SHUTDOWNS, ISOLATIONS AND STOPOFFS IN
        CONJUNCTION WITH MAINTENANCE, REPAIRS OR CONSTRUCTION ACTIVITIES

         a. General Requirements

              Advance notification shall be provided to all operating departments at the earliest opportunity
              when scheduling shutdowns, isolations, cutouts, tie-ins, pressures adjustments or stopoffs
              involving or affecting any gas transmission or distribution facilities, exclusive of individual
              service lines

              The notification shall include, but not necessarily be limited to the following:
              • Description of the proposed work.
              • Area affected.
              • Approximate duration of the work.
              • Name of the responsible supervisor or foreman.

              System Analysis and Gas Control shall review all proposed work to assess the potential affect on
              system reliability and integrity and provide a written response to all operating departments
              approving, disapproving or setting conditions for performance of the proposed work. The review
              shall include but not necessarily be limited to system modeling under the proposed conditions
              and confirmation of system piping configuration and supply sources in the affected area. The
              proposed work shall not proceed until such approvals have been granted and any conditions are
              satisfied.

               System Analysis shall copy Gas Control on responses to all requests for preliminary evaluation
              of proposed shutdowns, isolations, cutouts, tie-ins or stopoffs.

              Operations will fill out the “Daily System Schedule” at least one day in advance of the scheduled
              work and forward to Gas Control.

              Gas Control shall maintain and distribute the “Gas Operations Daily Report” along with a
              daily/weekly schedule of all proposed work.

         b. Gas Supply Facilities

              Gas Control shall provide advance notification of proposed Gas Supply facility work via memo
              or e-mail to the appropriate Distribution and Service area Managers and System Analysis
              Engineer, followed by telephone communication to confirm receipt.


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                        OPERATING AND MAINTENANCE GENERAL PROCEDURES                                OM - 30

  Operations &              NOTIFICATION OF GAS SUPPLY AND DISTRIBUTION
  Maintenance               FACILITY SHUTDOWNS, ISOLATIONS OR STOPOFFS                             Page 2 of 4


              Immediately prior to shutting down a take station, district regulator or transfer facility the
              responsible Gas Supply Field Supervisor shall notify Gas Control by radio, telephone or Nextel.
              Gas Control shall review current system status and confirm authorization to proceed with the
              work.

              In addition to advance notification and confirmation, Gas Control shall notify the appropriate
              Distribution and Service Managers by radio, telephone or Nextel immediately prior to removing
              take stations, district regulators or transfer stations from service.

              The responsible gas supply field supervisor shall notify Gas Control by radio, telephone or
              Nextel as soon as possible after completion of the work. Gas Control shall then notify the
              appropriate area Manager of Distribution and Customer Service via telephone.

         c. Distribution Facilities
              The responsible Distribution area Manager or designated Field Supervisor or Planning and
              Scheduling Supervisor shall provide advance notification of Distribution work to Gas Control
              and the System Analysis Engineer via memo or e-mail, followed by telephone communication to
              confirm receipt. The Gas Control Supervisor shall be responsible for informing the Director,
              Manager, other Gas Control Supervisors and appropriate area Field Supervisors in Gas Supply.
              The responsible Distribution Field Supervisor shall notify Gas Control and the Service area
              Manager by radio, Nextel or telephone immediately prior to performing a scheduled shutdown,
              isolation, cutoff, tie-in or stopoff. Gas Control shall review current system status, confirm
              authorization to proceed with the work, notify the appropriate Gas Supply Field Supervisor via
              radio, telephone or alpha page and record the activity in the Gas Control Activity Log.
              The responsible Distribution Field Supervisor shall notify Gas Control by radio or telephone as
              soon as possible after completion of the work. Completion of the work shall be entered in the
              Gas Control Activity Log.

     2. PLANNED FACILITY SHUTDOWNS IN CONJUNCTION WITH ENGINEERED
        PROJECTS
         Engineered projects involving facility shutdowns, isolations or stopoff s shall be reviewed and
         discussed by the responsible operating personnel during the planning stages of the project.
         The responsible Engineer shall distribute plans, drawings, sketches, procedures and any other
         information necessary to ensure that all operating departments are aware of the project scope and
         system impact and are prepared to make any necessary changes in system operation during project
         implementation.
         Projects involving facility shutdowns, isolations or stopoffs shall not commence without the
         concurrence of the operating departments.
         In addition to the project review process, the department responsible for project implementation shall
         provide notifications as described in Section 1.

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                       OPERATING AND MAINTENANCE GENERAL PROCEDURES                                OM - 30

  Operations &             NOTIFICATION OF GAS SUPPLY AND DISTRIBUTION
  Maintenance              FACILITY SHUTDOWNS, ISOLATIONS OR STOPOFFS                             Page 3 of 4



     3. EMERGENCY SHUTDOWNS, ISOLATIONS AND STOPOFFS
         Emergency and unscheduled shutdowns, isolations and stopoffs shall be made only after an assessment
         of the impact on system operation and consideration of the safety of personnel, customers and the
         general public. Emergency shutdowns shall be performed only after consultation and coordination
         with Gas Control unless there is immediate danger of injury to personnel or damage to NSTAR or
         third party property.
         Service Dispatch must be notified of all emergencies as outlined in the NSTAR Gas Emergency
         Plan.
         Notification of shutdowns, isolations and stopoffs in the event of system emergencies shall be
         provided to other operating departments as soon as possible utilizing the most effective
         communications available under the circumstances.
         Company radios shall be utilized for emergency communication whenever possible to provide the
         widest range of notification.




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  Maintenance         FACILITY SHUTDOWNS, ISOLATIONS OR STOPOFFS      Page 4 of 4


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                        OPERATING AND MAINTENANCE GENERAL PROCEDURES                                 OM - 50

  Operations &
  Maintenance                 INVESTIGATION OF ACCIDENTS AND FAILURES                               Page 1 of 2


     This procedure pertains to the investigation, analysis and reporting of incidents involving gas and/or
     company owned pipeline facilities and resulting in personal injury, property damage, and/or interruption
     of service. Determination of the causes of such accidents and failures are essential for the purpose of
     preventing or minimizing the possibility of recurrence.

     1. PROCEDURE FOR THE FIRST SERVICEMAN OR CREW PRESENT OR ASSIGNED
        TO INVESTIGATE

         a. Take appropriate “make safe” action to prevent further injury and damage. Avoid becoming a
            casualty yourself.

         b. If personal injuries have been sustained in connection with the operation of company property:

              (1) Obtain medical service by the most direct method.
              (2) If an ambulance is needed, follow the procedure, which will procure one most quickly.
              (3) In the meantime, First Aid Treatment in accordance with the Company’s first aid procedures
                  may be given to injured persons.

         c. After steps have been taken to care for the injured and protect the public, the employee shall
            notify his Supervisor and advise him of the situation. If the Supervisor cannot be reached call the
            Company’s Accident Investigator, the Department Manager, or higher authority. If a radio
            equipped vehicle is available the call may be relayed through the Dispatcher.

         d. As soon as possible, preferably in private, write down the names of witnesses, what happened,
            what was found, and what was done.

         e. If pressed for an explanation of causes of the accident, advise the questioner that there will have
            to be more investigation before the complete answer will be known.

         f. Cooperate with public authority as requested.


     2. PROCEDURE FOR THE SUPERVISOR

         a. Arrange for additional manpower, equipment and materials as needed on the job.

         b. Notify the persons designated by management of the incident and of your actions. Do this at
            once in case of serious accident.

         c. Follow through; ask instructions if in doubt.




     3. GENERAL INSTRUCTIONS

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                         OPERATING AND MAINTENANCE GENERAL PROCEDURES                                OM - 50

  Operations &
  Maintenance                 INVESTIGATION OF ACCIDENTS AND FAILURES                                Page 2 of 2



         Any incident involving personal injury or property damage may result in a claim against the
         Company. It is essential, therefore, that each incident be reported promptly and with sufficient detail
         so that persons, not otherwise familiar with the incident, may visualize it and attempt to determine its
         cause. Employees should keep this in mind, and after doing everything possible for the injured, they
         should immediately start to obtain information for a complete report. Follow this procedure:

         a. Secure names and addresses of all witnesses. Even the testimony of late arrivals is often
            valuable. Be patient and courteous in this work.

         b. Avoid any disputes or discussion with any unauthorized individual as to the cause of the
            incident.

         c. Describe the incident as accurately as you can. Sketches and measurements made at the scene of
            the incident are often very useful. The description should answer the following questions:

              1)   What happened?
              2)   Exact time and date?
              3)   Where?
              4)   Who was injured? (Note name and address)
              5)   What was done for the injured?
              6)   How did the accident happen?

         d. Note particularly any unusual circumstances or conditions pertinent to the incident.

         e. Preserve any tool, device, piece of equipment or material for laboratory examination, where
            appropriate, for the purpose of determining the cause of the failure to minimize a similar
            occurrence in the future.

         f. The field report becomes the basis of all later reports to be made and care in its preparation will
            help reduce accident cost and prevent recurrence.




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                      OPERATING AND MAINTENANCE GENERAL PROCEDURES                              OM - 60

Operations &                                                                                   Page 1 of 9
Maintenance                                LEAKAGE CONTROL


  1. GENERAL

  The following is the established procedure for leakage surveys, leak classification, action criteria, and
  reporting. When evaluating any gas leak, the initial step is to determine the perimeter of the leak area.
  When the perimeter extends to a building wall, the investigation will continue into the building.
  Activities described in these procedures shall be conducted by qualified contractors or qualified NSTAR
  personnel.


  2. DEFINITION OF TERMS

      a. Building: Any structure, which is normally or occasionally entered by humans for business,
         residential or other purposes, and in which gas could accumulate.

      b. Building of Public Assembly: A building where persons would gather for a public event. These
         buildings would include schools, churches, hospitals, theaters, arenas, etc.

      c. Business District: Areas with pavement from building wall to building wall and/or where the
         principal commercial activity of the city or town takes place.

      d. Class Location: Pipeline location defined and classified in accordance with D.O.T. Minimum
         Federal Safety Standards, Title 49 CFR Part 192.5.

      e. Combustible Material: A flammable gaseous material consisting of organic compounds such as
         methane, benzene, etc.

      f. Confined Space: A confined space means any space which has a limited means of access and
         egress, has adequate size and configuration for employee entry, is not designed for continuous
         employee occupancy and where the atmosphere may be deficient in oxygen content or is subject
         to the accumulation of toxic or flammable contaminants.

      g. Distribution Main: A line that serves as a common source of gas supply for more than one
         service line.

      h. Gas Detector: An instrument capable of detecting and measuring the percentage concentration
         of combustible gas in air.

      i     Gas Facilities: All company operated gas lines and related appurtenances.

      j.    Leak: The unintentional escape of gas from containment.




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                      OPERATING AND MAINTENANCE GENERAL PROCEDURES                                OM - 60

Operations &                                                                                     Page 2 of 9
Maintenance                                 LEAKAGE CONTROL



      k. Leak Classifications:

            1. Class 1 Leak - A leak that represents an existing or probable hazard to persons or property
               and requires immediate repair or continuous action until the conditions are no longer
               hazardous.
            2. Class 2 Leak - A leak that is recognized as being non-hazardous at the time of detection, but
               justifies repair based on possible future hazard.
            3. Class 3 Leak - A leak that is non-hazardous at the time of detection and can be reasonably
               expected to remain non-hazardous.

      l.    Leak Survey: A search for possible gas leakage in any area where gas facilities exist, or where a
            gas leak is reported or suspected.

      m. LEL: The lower explosive limit, as indicated on a combustible gas indicator, expressed as a
         percentage of gas in air.

      n. Pipeline: A natural gas main or transmission line with an MAOP greater than 200 psig,
         including, but not limited to pipe, valves and other appurtenances attached to the pipe (220 CMR
         109.03).

      o. Reading: A repeated measure of gas indicated on a gas detector. Where the reading is in a
         confined space, consideration should be given to the rate of dissipation when the space is opened
         or ventilated for the test and the rate of accumulation when the space is closed.

      p. Service Line: A distribution line which transports gas from a common source of supply to an
         individual customer, to two adjacent or adjoining residential or small commercial customers, or
         to multiple residential or small commercial customers served through a meter header or
         manifold. A service line ends at the outlet of the customer meter or at the connection to a
         customer’s piping, whichever is further downstream, or at the connection to customer piping if
         there is no meter.

      q. Station Piping: For the purposes of leak surveying, this includes all underground gas pipes and
         appurtenances within the property lines of regulator stations and other gas operating installations.

      r. Substructure: Any man-made structure, tunnel, passageway, or other confined space below
         ground level where gas could accumulate.

  3. PRIORITIES

      a. Surveillance and repair activities shall be based on such factors as:

            1. The volume, gas-air concentration, and source of the escaping gas.
            2. The size and occupancy of the area where the leakage could occur, and the proximity to
               structures both above and below ground.


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            3. The presence of any substructure or other underground facility that could affect the migration
               or accumulation of gas.
            4. Soil or surface conditions that could affect the migration of gas.
            5. The proximity to sources of ignition.
            6. Public awareness and reaction to the leak situation.
            7. Soil movement caused by landslides, earthquakes, etc., where external stresses on the
               pipeline may cause leakage.

      b. After consideration of the above factors, repair priority will be in the order of Class 1, Class 2, and
         Class 3.

  4. LEAK CLASSIFICATION AND ACTION CRITERIA

      The following examples of leak conditions and possible action are to be used as guidelines and are
      not exclusive.

      The judgment of company personnel at the scene is of primary importance in determining the
      classification of a leak and the action to be taken.

      a. Class 1 - Classification

            1. Any leak which, in the judgment of company personnel at the scene, is regarded as an
               immediate hazard.
            2. Any indication of gas, which has migrated into or under a building or structure.
            3. Any reading below ground or which has emanated from below ground at the outside wall of
               a building.
            4. Escaping gas, which has ignited.
            5. Any reading of 80% LEL, or greater, in a confined space.
            6. Any reading of 80% LEL, or greater, in a non-gas substructure from which gas would likely
               migrate to the outside wall of a building.
            7. Any reading of 40% LEL, or greater, under a sidewalk which extends to a building wall in
               wall-to-wall paved area.

      b. Class 1 - Action Criteria

            Take immediate and continuous action until the hazard no longer exists. Such action may include
            (but is not limited to or restricted to the order in which they are listed) one or more of the
            following:

            1. All identified conditions of a hazardous nature to persons or property shall be promptly made
               safe and permanent repairs instituted.
            2. Evacuate the premises and notify the area Manager or Director of the situation.
            3. Vent the leakage.
            4. Remove sources of ignition.
            5. If burning, prevent the spread of the fire but not necessarily extinguishing burning gas.

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            6. Eliminate the source of gas by closing valves or other means.
            7. Restrict public access into the area, including rerouting traffic.
            8. Notify police and fire departments.

            On all Class I leaks, the sources of escaping gas must be identified and addressed with either
               temporary or permanent repairs

      c. Class 2 - Classification

            1. Any leak which, in the judgment of company personnel at the scene, is of sufficient
               magnitude to justify periodic monitoring.

            2. Any leak which, under frozen or other adverse soil conditions, would likely migrate to the
               outside of a building wall.
            3. Any leak under the street of a wall-to-wall paved area that has a substantial enough spread to
               indicate the possibility of migrating to the outside wall of a building.
            4. Any reading between 20% LEL and 80% LEL in a confined space.
            5. Any reading between 20% LEL and 80% LEL in a non-gas substructure.
            6. Any reading on a pipeline operating at 20% SMYS, or greater, in a Class 3 or 4 location.

      d. Class 2 - Action Criteria

            Monitor on a periodic basis, the frequency depending on the location and magnitude of the leak.
            Schedule repair as necessary.

      e. Class 3 - Classification

            All other leaks which are determined to be non-hazardous at the time of detection and can be
            expected to remain non-hazardous.

      f. Class 3 - Action Criteria

            Reevaluate during next scheduled survey or until leak is reclassified or no longer results in a
            reading.

  5. FREQUENCY OF PERIODIC LEAK SURVEYS
     Periodic leak surveys shall coordinated, scheduled and tracked by the Compliance and Corrosion
     group and shall be performed by qualified contractors or NSTAR personnel or both as required.
     a. Monthly Survey

            Redacted




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      b. Quarterly Survey

            Mains in place or on structures where anticipated movement or external loading could cause
            failure or leakage will be surveyed at intervals not exceeding 4 ½ months, but at least four times
            per calendar year [Ref. 49 CFR 192.721 (b)].

            During these surveys observations will be made of surface conditions on and adjacent to the
            pipeline right-of-way for indications of leaks, construction activity, and other factors which may
            affect safety and operation. Above ground piping will, in addition, be visually inspected for signs
            of damage, physical movement or external loading that could cause failure or leakage

      c.    Semi-Annual Survey

            Redacted

      d. Annual Survey

            1. Business district - A leakage survey with leak detector equipment shall be conducted in
               business districts ,including tests of the atmosphere in gas, electric, telephone, sewer, and
               water system manholes, at cracks in pavement and sidewalks, in gas boxes, and at other
               locations providing an opportunity for finding gas leaks. The survey shall include tests for
               gas leakage and visual inspection of NSTAR-owned inside service piping to the outlet of the
               meter or the connection to the customer’s piping, whichever is further downstream.

               In areas where effectively prescribed and supervised surveys of manholes (electric,
               telephone, etc.) and vaults is conducted and offers more frequent coverage. Such a survey
               procedure may be substituted.

               The business districts shall be outlined on a map. The map shall be revised as conditions
               warrant. [Ref. 49 CFR 192.723 (b)(1); 220 CMR 101.06 (21)(a)]

            2. Buildings of Public Assembly - A leakage survey shall be conducted at least once annually at
               schools, churches, hospitals, theatres and arenas and shall include tests for gas leakage and
               visual inspection of gas facilities in the immediate area of the service entrance, including all
               NSTAR-owned inside service piping to the outlet of the meter or the connection to the
               customer’s piping, whichever is further downstream. [Ref. 220 CMR 101.06 (21)(d)]

            3. Pipelines with an MAOP in Excess of 200 PSIG – Leakage surveys of Pipelines with an
               MAOP in excess of 200 psig shall be conducted at least once each calendar year but at
               intervals no greater than 15 months utilizing flame ionization detectors or equivalent devices.
               [Ref. 220 CMR 109.13 (5)]

               The following is a list of Pipelines with an MAOP in excess of 200 psig:




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                CAMBRIDGE

                    INFORMATION HAS BEEN REDACTED


                HOPCO

                    INFORMATION HAS BEEN REDACTED


                SOUTHBORO/WORCESTER

                    INFORMATION HAS BEEN REDACTED

      e. Every Two Years

            1. Mains in areas not included in business districts. [Ref. 220 CMR 101.06 (21)(b)]

      f. Every Three Years

            Cathodically unprotected metallic distribution lines located outside business districts and subject
            to D.O.T. Pipeline Safety Regulations part 192.465(e) on which electrical surveys for corrosion
            are impractical shall be leak surveyed at least once every three (3) calendar years at intervals not
            exceeding thirty-nine (39) months.

      g. Every Five Years

            All other service lines not covered in Section 5, Items a to f, will be surveyed at least once every
            five (5) calendar years at intervals not exceeding 63 months. This survey will include 20% of the
            service lines each year and shall include tests for gas leakage and visual inspection of NSTAR-
            owned inside service piping to the outlet of the meter or the connection to the customer’s piping,
            whichever is further downstream. [Ref. 49 CFR 192.723 (b)(2).]

      h. Additional Leak Surveys

            The following is to be used as a guide for conducting additional leak surveys as frequently as
            experience and technology indicate necessary:

            1. Surveys during winter months when frost heave could result in leakage.
            2. Yearly survey in lieu of two-year survey of entire distribution system in addition to the
               principal business districts. This survey may be performed at a faster rate than the two-year
               survey. It may involve driving in the normal traffic lanes on both sides of the street.
            3. Interim patrols to locate leaks after or during outside construction in the area of gas lines,
               prior to street resurfacing, and as a result of past leak history or corrosion information.


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            4. Leakage surveys on NSTAR-owned inside service piping shall be conducted whenever a
               qualified employee visits a customer location for the purposes of exchanging meters,
               performing utilization equipment maintenance, repairs or relights or for other reasons.

  6. LEAK SURVEY METHODS

      a. The method used for leakage surveys shall include one or more of the following:
         1. Gas detector survey using combustible gas indicators
         2. Flame ionization equipment
         3. Infrared equipment
         4. Other industry accepted and proved equipment

      b. When conducting scheduled surveys the following guidelines will be observed unless otherwise
         directed:

            1. Mobile surveys will be performed with a mobile unit at a speed of not more than 5 MPH.
               The detection instrument will be set on the low scale (0-10 PPM). The survey will be
               conducted on both sides of the street wherever possible.
            2. Walking surveys will be performed using a portable flame ionization unit, or other industry
               accepted equipment, walking in the sidewalk area parallel to the main and along the
               foundation of the building, and criss-crossing the land between the main and the structure. In
               the case of a vacant lot, the same pattern will be followed using common sense to establish a
               bound area. The probe of the instrument will be held as close to the ground as possible while
               walking. This survey shall encompass all buildings and lots on a given street unless
               otherwise noted.
            3. Building of Public Assembly surveys will include tests for gas leakage and visual inspection
               of the gas facilities in the immediate area of the service entrance including all NSTAR-
               owned inside service piping to the outlet of the meter or the connection to the customer’s
               piping, whichever is further downstream. Tests will be conducted with a combustible gas
               indicator or other industry accepted equipment.
            4. Bridge and other exposed pipe surveys will be performed by walking the designated areas
               using a portable flame ionization unit or other industry accepted equipment. While
               conducting the survey the detection probe will be placed as close to the pipe as possible.
            5. Surveys conducted in a principal business district will involve the testing of the atmosphere
               in available street openings including electric, telephone, sewer, drain, and water system
               manholes, catch basins, at cracks in pavement and sidewalks, boxes including gas boxes, and
               at other locations providing the opportunity for finding gas leaks. These surveys shall also
               include tests for leakage on NSTAR-owned inside service piping to the outlet of the meter or
               the connection to the customer’s piping, whichever is further downstream These tests will be
               performed using a combustible gas indicator, flame ionization equipment, or other industry
               accepted equipment.
            6. Outside surveys will not be performed under wind and weather conditions, which would
               adversely affect the ability of the survey unit to accurately detect the presence of leaks.




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            7. When the person conducting a scheduled survey detects any leak determined to be
               potentially hazardous and classified as a Class I, they will immediately notify the appropriate
               personnel and remain at the location of the leak. This person will continue to pinpoint the
               source of the leak until properly relieved by a supervisor.

  7. FOLLOW-UP INSPECTION

      The adequacy of leak repairs will be checked before backfilling. The perimeter of the leak area will
      be checked with a combustible gas indicator. Where there is residual gas in the ground after the
      repair of a Class 1 leak, a follow-up inspection will be made as soon as practical after allowing the
      soil atmosphere to vent and stabilize, but in no case later than one month following the repair. In the
      case of other leak repairs, the need for a follow-up inspection will be determined by qualified
      personnel.

      In order to facilitate a follow-up inspection, the amount of residual gas from a Class I leak must be
      recorded on the reverse side of Leakage Control Report OD 374.

  8. RECORDS

      a. Leak survey records for the MIT Service Line, Transmission Lines and Pipelines with an MAOP
         in excess of 200 psig shall be kept as long as the segment involved remains in service. [Ref 49
         CFR 192.709]

      b. All other leak survey records identified in this operating and maintenance plan shall be
         maintained for at least six (6) years in accordance with Compliance Agreement DPU 03-PL-19.

      c. Records for each leak survey conducted by leak survey contractors shall include sufficient
         information to determine the following at a later date:

            1.   The type of survey and date it was conducted.
            2.   The personnel conducting the survey and whom they represent.
            3.   The area or buildings surveyed.
            4.   Location of all leak indications found.

      d. In the event of a leak, the qualified leak survey contractor or Distribution supervisor conducting
         the survey will complete Leakage Control Report OD 374 (see attached). In the New Bedford
         and Plymouth districts qualified and trained technicians may also complete the Leakage Control
         Report. In addition to the above information the following will be recorded:
         1. The method of survey.
         2. The percent of gas or LEL.
         3. The leak classification.
         4. A sketch providing the location of the underground leak or a detailed description of an above
             ground leak.
         5. Time reported (Class 1).


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      e. Leak repair records on all lines will be kept on file for at least six (6) years. Records for each
         leak repair completed by Distribution will include:

            1. Information required on the reverse side of Leakage Control Report OD 374.
            2. Person responsible for repair.
            3. A sketch of the exact location of the repair and any other pertinent information regarding
               underground leaks.
            4. Description of repairs made on above ground leaks.
            5. Method used to repair the leak.
            6. Percentage of residual gas after the repair of a Class I leak.

      f. Records for leak surveys conducted by qualified service personnel shall be maintained in the
      Pipeline Compliance System. Records of leaks repaired by the service department shall be
      maintained in the Advantex MDSI system for a period of not less than six (6) years.

      g. Records for leak surveys conducted by qualified Distribution personnel shall be recorded
      manually and entered into PCS.


9. OTHER COMBUSTIBLE MATERIAL IN SOIL

      If the source of the gas leak can not be found after a thorough investigation by a Leak Surveyor or by
      a Distribution Crew, one potential cause that must be considered is the presence of other combustible
      material in the soil.
      Once it has been determined the source of the combustible material in the soil is not from our
      facility, the appropriate public safety office will be notified.




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     This part prescribes requirements for the reporting of gas leaks that are not intended by the operator and
     that require immediate or scheduled repair of failures by persons engaged in the transportation of gas.

     1. Telephonic Report (800-424-8802)

         a. At the earliest practical moment following discovery, each operator shall give notice of incidents
            which:

              (1)   Involved a release of gas from a pipeline and

                    (a)   A death, or personal injury necessitating in-patient hospitalization; or
                    (b)   Estimated property damage, including cost of gas lost, of the property of others, or
                          both of $50,000 or more.

              (2)   Is significant in the judgment of the operator even though it did not meet the criteria of
                    paragraph (1).

         b. Notice of a leak need not be given if only the criteria of (2) above was met, and if it occurred
            solely as a result of, or in connection with planned or routine maintenance or construction.

         c. Reports, if needed, will require the following information:

              (1)   Names of operator and person making report and their telephone numbers.
              (2)   The location of the incident
              (3)   The time of the incident.
              (4)   The number of fatalities and personal injuries, if any.
              (5)   Other significant facts known by the operator that are relevant to the cause of the leak or
                    extent of the damages.


     2. Incident Report - Distribution System

         a. Each operator of a distribution system shall submit Department of Transportation Form RSPA-F-
            7 100.1 as soon as practicable but not more than 30 days after detection of an incident required to
            be reported by 1 above.

         b. When additional relevant information is obtained after the report is submitted, the operator shall
            make supplementary reports as deemed necessary with a clear reference by date and subject to
            the original report.

         c. Mail to applicable jurisdiction.

          (1) State (2 copies).
          (2) Director, Office of Pipeline Safety, Department of Transportation.
     3. Written Annual Report - Distribution System

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         a. Each operator of a distribution system shall submit an annual report on Department of
            Transportation Form RSPA-F-7 100.1.

         b. Annual report must be submitted for the preceding calendar year not later than March 15th.




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    This procedure pertains to the cathodic protection monitoring and corrosion control on steel, cast iron
    and ductile iron mains and services. All activities described in these procedures shall be performed by
    qualified contractors or NSTAR personnel as noted for each activity.

    1. Monitoring Existing Cathodic Protection Systems
       The following minimum inspections shall be performed in the specified intervals and prompt
       remedial action taken to correct any deficiencies indicated by the inspections. Monitoring and
       inspection activities shall be coordinated by the Compliance and Corrosion group and conducted
       by qualified contractors in the Worcester, Southboro, Somerville and Hyde Park districts. In the
       New Bedford and Plymouth districts monitoring and inspection activities will be performed by
       NSTAR Distribution Planning personnel and supplemented as needed by qualified contractors.

       a.    Each pipeline that is under cathodic protection must be tested at least once each calendar
             year, but with intervals not exceeding 15 months to determine whether the cathodic
             protection meets the requirements of 49 CFR 192.463. Exceptions to this requirement
             include separately protected short segments of mains or transmission lines not in excess of
             100 feet in length or separately protected service lines. These lines shall be inspected on a
             sampling basis with at least 10% of the protected structures, distributed over the entire
             system surveyed each calendar year. A different 10% shall be surveyed each subsequent
             year such that the entire system is tested in each 10-year period.

       b.    Each cathodic protection rectifier or other impressed current power source shall be
             inspected six times each calendar year but with intervals not exceeding 2 1/2 months to
             insure that it is operating.

       c.    Each reverse current switch, each diode and each interference bond whose failure would
             jeopardize structure protection must be electrically checked for proper performance six
             times each calendar year but with intervals not exceeding 2 ½ months. All other interference
             bonds shall be checked at least once each calendar year but with intervals not exceeding 15
             months.

    2. Remedial Measures for Corroded Pipe
       a.  General
           Whenever any portion of a buried pipeline is exposed, the exposed portion shall be
           examined for evidence of external corrosion if the pipe is bare or if the coating is
           deteriorated. If external corrosion requiring remedial action is found the pipe shall be
           examined circumferentially and longitudinally beyond the exposed portion to determine
           whether additional corrosion requiring remedial action exists in the vicinity of the exposed
           portion. The examination shall be performed by qualified NSTAR Distribution personnel
           and recorded on an Activity Report. Qualified contractors may be utilized to perform
           examinations and shall document the results of any examination in a report format
           acceptable to the Company.

             Unprotected pipelines shall be reevaluated not less than every 3 years at intervals not
             exceeding 39 months and cathodically protected in areas in which active corrosion is found.

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             On distribution lines areas of active corrosion may be determined by means other than
             electrical survey including review and analysis of leak repair and inspection records,
             corrosion monitoring records, exposed pipe inspection records and the pipeline
             environment.

       b.    Cast Iron and Ductile Iron Pipe
             Each segment of cast iron or ductile iron pipe on which general graphitization is found to a
             degree where a fracture or any leakage might result shall be replaced. Each segment of cast
             iron or ductile iron pipe on which localized graphitization is found to a degree where any
             leakage might result must be replaced or repaired, or sealed by internal sealing methods
             adequate to prevent or arrest any leakage.

       c.    Distribution Lines
             Except for cast iron or ductile iron pipe each segment of generally corroded distribution line
             pipe with a remaining wall thickness less than that required for the MAOP of the pipeline or
             a remaining wall thickness less than 30% of the nominal wall thickness must be replaced
             with plastic pipe or cathodically protected coated steel pipe. Corroded pipe may also be
             repaired by a method that reliable engineering tests and analysis show can permanently
             restore the serviceability of the pipe. Corrosion pitting so closely grouped as to affect the
             overall strength of the pipe is considered general corrosion.

             Except for cast iron or ductile iron pipe each segment of distribution line pipe with localized
             corrosion pitting to a degree where leakage may result must be repaired or replaced.

    3. Internal Corrosion Control
       a.   Corrosive gas may not be transported by pipeline, unless the corrosive effect of the gas on
            the pipeline has been investigated and steps have been taken to minimize internal corrosion.

       b.    Whenever any pipe is removed from a pipeline for any reason, the internal surface shall be
             inspected for evidence of corrosion by qualified NSTAR Distribution personnel or qualified
             contractors if required. If internal corrosion is found, the adjacent pipe shall be investigated
             to determine the extent of internal corrosion. Pipe segments exhibiting internal corrosion
             shall be replaced with plastic or cathodically protected coated steel pipe.

    4. Atmospheric Corrosion Control
       General
       Each pipeline or portion of pipeline that is exposed to the atmosphere shall be cleaned and coated
       with a material suitable for the prevention of atmospheric corrosion.

       Protection from atmospheric corrosion is not required on pipelines for which it can be
       demonstrated by test, investigation or experience appropriate to the environment of the pipeline
       that corrosion will only be a light surface oxide or will not affect the safe operation of the pipeline
       before the next scheduled inspection. However, protection from atmospheric corrosion is
       recommended for all exposed pipelines.


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       Monitoring
       Each onshore pipeline or portion of pipeline that is exposed to the atmosphere shall be inspected
       for evidence of atmospheric corrosion at least once every three (3) calendar years, but with
       intervals not exceeding 39 months. During inspections particular attention shall be given to pipe
       at soil-to-air interfaces, under thermal or acoustic insulation, under disbonded coatings, at pipe
       supports, in splash zones, at deck and wall penetrations and in spans over water.
       This inspection requirement shall apply to all company-owned piping, including service piping
       inside a building to the downstream side of the meter or the connection to the customer-owned
       piping, whichever is further downstream. Inspections for atmospheric corrosion may be
       performed by qualified NSTAR Distribution or Service personnel or qualified contractors as
       assigned.
       Records pertaining to inside atmospheric corrosion inspections shall be maintained for at least six
       (6) years in accordance with the Compliance Agreement DPU 03-PL-19.

    5. Corrosion Control Records
       General

       Records and maps shall be maintained to show the location of cathodically protected piping,
       cathodic protection facilities, galvanic anodes and neighboring structures bonded to the cathodic
       protection system. Records and maps showing a stated number of anodes, installed in a stated
       manner or spacing need not show specific distances to each buried anode. These records shall be
       retained for as long as the pipeline remains in service.

       Records of each test, survey, or inspection shall be maintained by the Compliance and Corrosion
       group in sufficient detail to demonstrate the adequacy of corrosion control measures or that a
       corrosive condition does not exist. These records shall be retained for at least 5 years, except
       those related to cathodic protection testing and testing to determine areas of active corrosion (49
       CFR 192.465 (a) and (e)) and records related to internal corrosion inspection and repairs (49 CFR
       192.475 (b), which shall be retained as long as the pipeline remains in service.




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  Operations &
  Maintenance                                   ORDORIZATION                                         Page 1 of 2


     This procedure pertains to the odorization of gas distributed through gas mains and services.

     1. Odorization

        a.    All combustible gas distributed, regardless of pressure, shall have a distinctive odor of
              sufficient intensity so that a concentration of 0.15% gas in the air (i.e. one part of the
              odorized gas in 666 parts of otherwise uncontaminated air) is readily perceptible to the
              normal or average olfactory sense of a person coming from fresh uncontaminated air into a
              closed space containing said concentration of odorized gas in air.


     2. Odorant Characteristics

        a.    Odorant shall be harmless to humans, non-toxic and non-corrosive to piping materials.

        b.    Odorant shall not be soluble in water to an extent greater than 2.5 parts by weight of the
              odorant to 100 parts by weight of water.

        c.    Upon burning, the products of combustion from the odorant shall be non-toxic to a person
              breathing air containing these products of combustion and shall not be corrosive or harmful
              to materials normally exposed to such products of combustion.


     3. Odorization Equipment

        a.    Equipment used to introduce odorant into the piping system shall be designed such that
              there will be no wide variations in the level of odor in the gas.


     4. Sampling of Gas for Odor level

        a.    Periodic sampling of combustible gases shall be conducted to arrive at the proper
              concentration of odorant. Sampling shall be performed with an instrument capable of
                                                                                                                   192-93
              determining the percentage of gas in air at which the odor becomes readily detectable.


     5. Records

        a.    Retain a record for five (5) years of odor sampling, which includes the date, location, name
              of operator and the sample’s test results.




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  Operations &
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     1. GENERAL:

        An odor complaint should be considered a Class 1 leak until proven otherwise.

        The first employee arriving at the scene of a report of a natural gas odor shall immediately notify
        dispatch and do whatever can be done with reasonable personal safety to discern the source of
        the odor and assess the extent to which actions are needed to protect the public. If the source of
        the odor is found to be a leak, any responsible company employee is authorized to evacuate an
        area if in their judgment, life or property is in jeopardy. On location of the source of odor,
        employees should not attempt to control the gas at the point of discharge without help unless the
        following conditions are met:

        1. The gas is blowing freely into the atmosphere and the work can be performed safely and
           without breathing oxygen deficient air.

        2. The escape of gas can be safely controlled by a method such as closing a valve or by using
           sealing compound, tape, a wooden plug, or other suitable means.

        As soon as practical, the employee in charge should request help from the local police and fire
        departments and on their arrival, should make NSTAR presence known to police and/or fire                   Stds.
        department representatives or other appropriate individuals. If applicable, the employee should            Comm.
        explain how the cause of the gas odor is to be contained and discuss any additional assistance or
        action that may be needed to protect the public. Also, additional company assistance should be
        arranged for as required, including claims and public information personnel.

     2. ODORS AND EMERGENCY LEVELS:

        If the cause of the odor is found to be a leak that meets the criteria of the levels listed below, it
        should be acted upon based on normal procedure including judgment and experience. Otherwise,
        action criteria as described in Section 4.0 of OM-60 (contained in the General Procedures
        section) should be followed.

              Level 1

              Situations that can be handled by the supervisor on duty or on-call: the availability of
              personnel, equipment, tools and material needed at the scene shall be determined by the
              supervisor and reported to the area manager immediately for situations such as:

              a. Odor complaint calls involving less than ten (10) customers (civil, municipal or news
                 media not involved).

              b. Significant odor with no report of ignition, explosion, evacuation or serious damage.

              c. Odor calls that are persistent for 50 hours.
              Level 2

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                        OPERATING AND MAINTENANCE GENERAL PROCEDURES                                 OM - 72

  Operations &
  Maintenance                            RESPONDING TO A GAS ODOR                                   Page 2 of 2



              Situations that can be handled principally by personnel within the report area affected as
              determined by the area manger based upon information obtained in the field. The area
              manager shall notify his director or the Vice President of Operation immediately who will
              then notify New Customer Connect, Gas Control and Gas Central Service managers.
              Situations for a Level 2 condition are defined as:

              a. Interruption of gas supply affecting service to ten (10) or more customers.

              b. Explosion or fires where gas may be involved.

              c. Situations, which require taking a main supply line out of service.

              d. Situations where damage to Company or other property is anticipated to exceed $5,000.

              Level 3

              Situations that require manpower of facilities beyond the capabilities of area personnel and
              those situations which may result in the need to conserve gas in the system in order to             Stds.
              prevent or delay a major interruption. Such situations could result in the implementation of        Comm.

              the Company Load Curtailment Policy, Mutual Assistance Program (Appendix A of the
              Emergency Plan) or the shutting off of an area.




       Issued                Revised                Revised                Revised                 Revised
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                       OPERATING AND MAINTENANCE GENERAL PROCEDURES                                 OM - 74

  Operations &                                                                                     Page 1 of 2
  Maintenance                              OPERATING PRESSURES


     This procedure applies to the determination of safe operating pressures.


     1. Maximum Allowable Operating Pressures (MAOP)

         a.   Where definite records regarding the installation and testing of a particular pipeline are not
              available, it shall be assumed that the highest actual operating pressure to which the pipeline
              was subjected between July 1, 1965 and July 1, 1970, is the MAOP for that pipeline.

         b.   Where a. above shall apply and a higher operating pressure is desired, that pressure may be
              established through compliance with OM-82.

         c.   Where definite records regarding the installation and testing of a particular pipeline are
              available, the MAOP shall be determined by dividing the recorded test pressure by a factor of
              1.5 for steel or plastic pipe.

         d.   Cast iron pipe in which there are un-reinforced bell and spigot joints may not, under any
              circumstances, be operated above 25 psig.

         e.   In no case may the operating pressure exceed the weakest element in the pipeline or any
              equipment, which will be subjected to that operating pressure.

         f.   If personal judgment, based on a pipeline’s corrosion and operating history, should indicate
              that the safe operating pressure is less than the allowable operating pressure, then that
              judgment shall be established as the MAOP until the situation can be corrected. Over pressure
              protection must be supplied if the MAOP can be exceeded.


     2. Maximum and Minimum Operating Pressure - Low-Pressure Distribution System

         a.   For the purpose of these standards, a low-pressure distribution system is one which the
              pressure in the main is equal to or less than 2 psig.

         b.   The maximum and minimum allowable operating pressures shall be limited to those which will
              ensure the safe and continued operation of any properly connected and adjusted low pressure
              gas burning equipment.

         c.   For good operation the pressure range downstream of the meter should be between 4” w.c. and
              14” w.c. unless the customer’s equipment is designed to operate outside the range.




     3. Maximum Allowable Operating Pressure - Intermediate and High-Pressure Distribution

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  Operations &                                                                                   Page 2 of 2
  Maintenance                             OPERATING PRESSURES


         Systems

         a.   Intermediate pressure distribution systems may be operated at pressures not to exceed 60 psig,
              provided the system is equipped with overpressure protection and each service is equipped
              with a service regulator as described in NSTAR Gas Material Specification M-300 or M301
              and installed in accordance with NSTAR Gas Construction Standards C-314, C-316 or C-320.

         b.   High pressure distribution systems may be operated above 60 psig but less than 100 psig
              provided the system is equipped with overpressure protection equipment as described in
              NSTAR Gas Material Specification M-300, or M-301, M-303 and installed in accordance with
              NSTAR Gas Construction Standards C-314, C-316 or C-320 and C-216.

         c.   High pressure distribution systems may be operated at or above 100 psig but less than 200 psig
              provided the system is equipped with overpressure protection equipment as described in
              NSTAR Gas Material Specification M-300 or M-301, M-303, M-305 and installed in
              accordance with NSTAR Gas Construction Standards C-314, C-316 or C-320, and C-218.

         d.   Any high-pressure distribution system designed to be operated above 200 psig will be designed
              for the specific MAOP by the Engineering department.




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                        OPERATING AND MAINTENANCE GENERAL PROCEDURES                                  OM - 80

  Operations &
  Maintenance                     PREVENTION OF ACCIDENTAL IGNITION                                   Page 1 of 2


     1. General

         When work is performed in any structure or area where the presence of gas may be expected to
         constitute a hazard of fire or explosion the person in charge shall preplan the work to include steps to
         minimize the danger of accidental ignition of gas, including the following:

         a.    No smoking.

         b.    No open flames.

         c.    A fire extinguisher, preferably of the dry powder type, must be readily available in close
               proximity to the work site, i.e. not left on the truck. More than one may be necessary,
               depending on the scope of the operation.

         d.    An electrical bond shall be placed across a point where an unpurged metallic pipe is to be cut
               or separated to prevent a spark. Plastic pipe shall be grounded to eliminate static electrical
               charge.

         e.    When the work to be done is such that gas could be released and accumulate to a hazardous
               concentration the workmen:

               (1)   Shall use supplied air respiratory protective equipment. In a confined space the workmen
                     shall wear a safety harness with an attached, tended and secured lifeline unless the
                     probability of entanglement would present a greater hazard to the individual.

               (2)   Shall not carry matches, lighters or flints on their persons.

               (3)   Should wear apparel having anti-static and fire resisting qualities.

         f.    Shut off the supply of electricity (including telephone equipment), unless all electrical wiring,
               fixtures and equipment are explosion proof.

         g.    Open frame motors or other electrical apparatus, which may cause sparks, shall not be used in
               areas where gas is likely to be present in the atmosphere.


     2. In Structures

         a.    Provide ventilation so that the concentration of gas in air is kept to a minimum.

         b.    Where searching for gas leaks, or entering unlighted places where gas may be present, use only
               approved electric battery flashlights or hand lanterns.

         c.    Concentrations of combustible gas in air must be reduced to a minimum before entering a
               confined space.

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                       OPERATING AND MAINTENANCE GENERAL PROCEDURES                                   OM - 80

  Operations &
  Maintenance                    PREVENTION OF ACCIDENTAL IGNITION                                   Page 2 of 2


     3. On Customers’ Premises

         a.   Smoking on customers’ premises is not permitted.

         b.   A pipe containing gas under pressure shall not be opened inside the customers’ building except
              where special precautions to prevent the escape of unsafe quantities of gas have been taken.

         c.   It is the duty of the workmen to determine by a test that meter, meter fit and house piping are
              tight before leaving a turn-on job. He also has the duty to see that all lines are purged of air and
              that all pilots and burners are working properly.

         d.   Services shall not be purged into the customer’s building.

         e.    Under no circumstances shall employees test for leaking gas with a match or flame, nor shall
              they permit others to make such a test.

     4. In Open Air

         a.   When a hazardous amount of gas is being vented into open air, each potential source of
              ignition must be removed from the area.

         b.   Barricades and warning signs shall be used where needed to keep unauthorized persons safely
              away from the work site.

         c.   Since gases blowing to atmosphere can generate static charges and objects against, which the
              gas is directed may collect and discharge such static charges; blowing gas should be prevented
              wherever possible.

     5. Welding and Cutting

         a.   Gas or electric welding or cutting may not be performed on pipe or on pipe components that
              contain a combustible mixture of gas and air.

         b.   Empty drums or tanks, which have contained flammable materials; shall be purged by filling
              with water before cutting or welding.




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                       OPERATING AND MAINTENANCE GENERAL PROCEDURES                                   OM - 82

  Operations &
  Maintenance                  PRESSURE CONVERSION PLANS (UPRATING)                                  Page 1 of 2


     1. General

         The maximum allowable operating pressure (MAOP) of a pipeline shall be established through the
         procedure outlined in OM-74. Where an increase in the present MAOP is desired, follow the
         procedure outlined below.


     2. Preparations

         a.   Review the design, operating and maintenance history and the previous pressure tests, when
              available, of the pipeline to be uprated to determine if the proposed increase can be safely
              applied to the pipeline. Where sufficient records are not available to make this determination
              new calculations must be made.

         b.   Prepare a written plan or checklist detailing the procedures to be followed in performing the
              actual uprating.

         c.   Wherever necessary, take adequate precautions to insure that existing mechanical fittings on
              the pipeline are secured from pull-out and that anchors on bends or dead ends are sufficient for
              the uprated pressure.

         d.   Perform a leak survey of the entire pipeline and repair any significant or potentially hazardous
              leaks.

         e.   Repair, replace, or alter any portion or component of the pipeline which might become unsafe
              at the elevated pressure.

         f.   If the uprating of the MAOP of the pipeline shall produce a pressure in the main or connected
              service line which is to be higher than the pressure supplied to the customer’s appliances a
              service regulator shall be installed on each service line and tested to insure proper operation. If
              the uprated pressure of the pipeline is to exceed 60 psig, overpressure protection shall be
              installed on each service line in accordance with OM-74.


     3. Uprating Procedure

         After completing steps a. through f. above, the actual uprating procedure may proceed as follows:

         a.   Isolate the pipeline to be uprated from other sections, which will continue to be operated at the
              lower pressure.

         b.   Gradually increase the pressure in the pipeline in increments of 10 psig or 25% of the total
              pressure increase, whichever produces the fewer number of increments. In any case, there must
              be at least two approximately equal incremental increases.
         c.   If the pipeline is being uprated from a low pressure system to some higher pressure requiring

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                        OPERATING AND MAINTENANCE GENERAL PROCEDURES                                  OM - 82

  Operations &
  Maintenance                   PRESSURE CONVERSION PLANS (UPRATING)                                 Page 2 of 2


               service regulators on each service the first incremental pressure increase must be at least equal
               to the minimum operating pressure of the new service regulators.

         d.    Hold the pressure at each incremental increase long enough to allow adequate time to check for
               leaks and repair any that are found to be potentially hazardous.

         e.    Recheck regulators for proper operation.


     4. Limitations

         Under no circumstances may the MAOP of any pipeline be raised, through the procedure outlined
         above, to a new MAOP, which would exceed that which might be established for a new segment of
         pipeline constructed of the same materials in the same location.


     5. Records

         Retain all records relating to job preparation, investigation, and all work and pressure tests
         performed on the uprated pipeline for the life of the pipeline.




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                        OPERATING AND MAINTENANCE GENERAL PROCEDURES                                  OM - 90

  Operations &
  Maintenance                                PURGING PROCEDURES                                      Page 1 of 12


     1. General
     The purpose of this procedure is to provide a basic guide for performing purging of mains into or out of
     service. Where more detailed information on purging is desired, see OM-92 and PURGING
     PRINCIPLES AND PRACTICE - American Gas Association Catalog No. XK0775.

     All gas lines being placed into or taken out of service, and within which a flammable mixture of gas and
     air might accumulate and have sufficient volume to become hazardous, must be purged to a safe
     condition to ensure against accidental ignition. For lines being taken out of service, purge immediately
     after blowdown.

     The medium used for purging may either be air, gas, or an inert gas, preferably nitrogen (N2).

     Before starting to purge, check to see that all valves are in the correct position, al1 appurtenances are in
     operating condition and that the main is completely isolated from all other mains and services. Under no
     conditions shall a line be purged into a cellar or other confined space.

     When purging long lines with an appreciable difference in elevation, the inert gas should be introduced
     at the lower end of the line.

     2. Purging Small Diameter Mains                                                                                 Stds.
     For purging mains less than 4 inch in diameter and less than 500 feet long it is permissible to make a          Comm.
     direct replacement of gas with air to purge out of service or air with gas to purge into service.

     To minimize mixing of air and gas a lineal velocity of at least 200 feet per minute in the main must be
     maintained. The minimum flow of air or gas to satisfy this condition is shown below for common small
     diameter mains.


                    TABLE 2A: DIRECT REPLACEMENT FLOW RATE REQUIREMENTS

                            Nominal                           Minimum c.f.m. of Air or Gas
                           Size (Inches)                      to Maintain at Least 200 f.p.m.

                               11/4                                         5.0
                               11/2                                         5.0
                                2                                           5.0
                                3                                           10.0


     NOTES
     1. Values given will provide at least the minimum vent velocity required when using a 1-inch diameter
        vent stack.


     The velocity of gases at vent outlet shall be maintained at 10 to 12 feet per second to be sure that the exit

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  Operations &
  Maintenance                                PURGING PROCEDURES                                        Page 2 of 12


     velocity is greater than the rate of flame travel in a combustible mixture of air and gas. For this method of
     purge use a 1 (one) inch vent line and a riser length of at least 7 feet - 0 inches above ground level. This
     size will provide adequate velocities at the vent outlet when using a 100 to 125 c.f.m. street air compressor
     or if merely using the required c.f.m. of air or gas as listed above. It is permissible to increase the vent size
     as long as the following minimum flow rates are maintained: 1¼ inch - 6.25 c.f.m., and 1½ inch - 8.5
     c.f.m. and 2-inch - 14.0 c.f.m.

     3. Purging Larger Diameter Mains
     For short but large diameter mains, i.e., less than 500 feet long and 4-inch diameter and larger, complete
     filling of the pipe with an inert gas is recommended. A volume of 10% to 50% more inert gas than the
     total volume of the line, added at a velocity of at least 100 f.p.m. in the main will ensure complete filling,
     the cubic feet per running foot of some common pipe diameters are listed below:

                              TABLE 3a: COMPLETE FILL PURGING METHOD

                                                                            Minimum c.f.m. of Inert Gas
                      Nominal                 Cubic Feet Per                   to Maintain at Least
                    Size(Inches)              Running Foot                         100 f.p.m.
                                                                                                                         Stds.
                         4                          .09                                   15                             Comm.

                         6                          .2 1                                 20
                         8                          .36                                   40
                                                                                        Note 2
                        10                           .57                                  60
                        12                           .82                                  80
                        16                          1.31                                 130
                        18                          1.67                                 210

     Multiply the appropriate value for a given pipe diameter times the length of line and add 50% to the
     calculated volume to determine the amount of inert gas to be used.

     Using the complete fill purge method, an injection rate of at least 100 feet per minute is necessary to
     prevent mixing. See Section 4 for a method to determine injection rate. The 2-inch diameter vent riser
     shall extend at least 7 feet - 0 inches above ground level.

     NOTES
     1. Values given will also provide the minimum 10 f.p.s. vent velocity required at the outlet of a 2-inch
        diameter vent stack.

     2. Do not withdraw more than 50 c.f.m. from the N2 cylinder to prevent freezing. One cylinder of N2 at
        2200 PSIG = 200 c.f. at atmospheric pressure.

     For mains 500 feet or longer and 4 inch diameter or larger purging, using an inert gas slug to separate the
     gas from the air is recommended. The purge must immediately follow the insertion of the inert gas slug
     since a delay of as little as three minutes will destroy the effectiveness of the slug.

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  Operations &
  Maintenance                                PURGING PROCEDURES                                       Page 3 of 12



     The following table provides necessary information required to purge various main sizes and lengths by
     the slug method using N2 cylinders. Data has been selected to provide adequate slug velocity in the main
     and sufficient velocity at the vent outlet when using a 2 inch diameter vent set at least 7 foot - 0 inches
     above the ground level.

                           TABLE 3b: N2 PURGE DATA USING SLUG METHOD

                                              N2 PURGE TABLE

                                 Injection       Slug                     Cubic Feet of N2 per Length
                Nominal            Rate         Velocity                           of Main
              Size (Inches)       (c.f.m)       (f.p.m)           500     1000    2000      5000 10000

                      4            15              170             10       20        20         20         20
                      6            20              100             30       30        30         40         40
                      8            40              100             70       70        80         90        120       Stds.
                                  Note 1                                                                             Comm.

                    10             60              100            130      140       150       180         230
                    12             80              100            280      300       340       370         400
                    16            130              100            580      630       700       790         850
                    18            210              125            740      850       970      1100        1200

     The N2 table is based upon maintaining a slug of at least 100 feet in length at end of purge.

     To provide additional safety it is recommended that double the amount of N2 indicated be used.

     4. Determining Injection Rate Measurement of Gas, Nitrogen or Air
     A common method of determining the injection rate and velocity of the purge media is by measuring the
     pressure drop across a restriction, such as an orifice, in the purge line. Using a 3/4 or P/+ inch diameter
     hose at a given length can be adequate substitute. The following table provides pressure drop
     information when using a 50-foot purge hose for various injection rates.

     NOTES
     Do not withdraw more than 50 c.f.m. from one N2 cylinder to prevent freezing. One cylinder of N2 at
     2200 PSIG = 200 c.f. at atmospheric pressure.




                           TABLE 4: INJECTION RATE PRESSURE DROP DATA

          Injection
            Rate                 Pressure Drop Across                     Pressure Drop Across

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  Operations &
  Maintenance                               PURGING PROCEDURES                                      Page 4 of 12


           (c.f.m)     ¾ inch Diameter 50 feet Hose (PSIG)       1¼ inch Diameter 50 feet Hose (PSIG)

                              Gas           N2 or Air                      Gas          N2 or Air
                5              1.0             1.3
               10              2               2.7
               15              3               4
               20              4               5
               40              9             11
               60             15             18
               80             21             26
              130             39             49                              6               9
              210             76             92                             12              18


     5. Sample N2 Slug Purge Procedure
     Purge a 12-inch diameter, 2,000 feet main into service.                                                       Stds.
                                                                                                                   Comm.
     a. Table 3a on Page 2 indicates an N2 flow requirement of at least 80 c.f.m.

     b. Table 3b on Page 3 indicates that at least 340 c.f. of N2 will be required to establish the proper
        length of slug.

     c. Table 4 above indicates that a pressure drop of 26 PSIG through 50 feet of 3/4 inch diameter hose is
        required to provide the flow rate required in step a.

     To complete the purge, using the above information, manifold at least 3 full N2 cylinders (600 c.f.) to
     the ¾ inch diameter 50-foot long hose. Open the manifold control valve and establish a 26 PSIG
     pressure drop across the hose. Continue the injection for at least 5 minutes (80c.f m. x 5 minutes = 400
     c.f.) and then open the natural gas supply valve and maintain a continuous flow until 100% gas is
     measured at the 2-inch diameter vent stack outlet.

     6. Inert Purge Gases
     Inert gases commonly available for purging are composed primarily of carbon dioxide or nitrogen. Since
     neither of these gases will support life, inhalation of abnormal concentrations should be avoided, as the
     oxygen may thereby be reduced sufficiently to cause oxygen starvation or smothering. For the same
     reason, do not enter trenches, valves pits, manholes, and the like where inert gas is being vented. This is
     also one reason for the specification of adequate vents in purging operations. Inert gases made up of
     combustion products also may contain carbon monoxide in sufficient quantities to have toxic effects.



     7. Supplemental Purging Table
     This table is a quick reference guide to the nitrogen slug method of purging 4-inch through 12-inch
     diameter from 500 feet through 20,000 feet in length. For more complete information see OM-92. Once
     the nitrogen slug has been injected, the purge medium (using natural gas to purge into service or

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  Operations &
  Maintenance                               PURGING PROCEDURES                                     Page 5 of 12


     compressed air to purge out of service) must follow immediately to prevent break-up of the slug. Where
     there is a significant difference in elevation of the pipeline being purged, the purge operation should be
     set up and conducted from the lowest end of the main. To prevent accidental ignition from a static
     electricity discharge, a #10 copper wire should be installed from the nitrogen tank or tank manifold to
     the main.




                                                                                                                  Stds.
                                                                                                                  Comm.




     8. Use of Nitrogen (N2) Cylinders for Purging
     CYLINDER SPECIFICATIONS:

                                                 Nitrogen (N2) Tank

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  Operations &
  Maintenance                               PURGING PROCEDURES                                     Page 6 of 12




         Weight when full (lbs.)                       149 lbs.
         Weight of gas (lbs.)                           16 lbs.
         Pressure when full (PSIG)                    2,200 psig
         Volume at atmospheric pressure
           and 70°F (c.f.)                           226 Cu. Ft.


     HANDLING CYLINDERS:

     Cylinders should be handled carefully even if empty. They should not be dropped, struck by other
     objects or used for supports or rollers.

     Never lift cylinders by slings, caps or electric magnets. A platform, cage or suitable stand should be
                                                                                                                   Stds.
     used when cylinders are handled by hoisting equipment.                                                        Comm.


     Before moving a cylinder, close the valve and install a protective cap, and keep the cap in place over the
     valve when the cylinder is not in use.

     If a cylinder is frozen to the ground, warm (not boiling) water may be poured onto the frozen area to
     loosen the cylinder. Do not pry under valves or protective caps.

     A cylinder may be raised from a horizontal to a vertical position by the protective cap after making
     certain that it is properly hand-tightened. Do no use valve protection caps for lifting cylinders from one
     vertical position to another.

     Store cylinders in well protected, well ventilated, dry locations, away from sources of heat and
     combustible materials; avoid storage in subsurface locations. Cylinders should be stored away from
     elevators, stairs and gangways, where they might be knocked over or damaged by passing or falling
     objects.

     Secure cylinders in the upright position and in assigned storage areas prominently posted with names of
     gases. Segregate cylinders of nonflammable nitrogen (N2) apart from stored oxygen or fuel gas
     cylinders.

     Cylinders may be stored in the open, but in all cases should be protected against extremes in temperature
     (screened against direct rays of the sun and sheltered from accumulations of ice and snow.)
     It is required that a cylinder be condemned when it leaks or when corrosion, denting, bulging or
     evidence of rough usage exists to the extent that the cylinder is likely to be weakened appreciably.
     Remove the leaking cylinder out of doors to a well-ventilated location. Notify the gas supplier and
     follow his instructions as to the return of the cylinder. Return doubtful cylinders to the supplier for re-

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  Operations &
  Maintenance                               PURGING PROCEDURES                                       Page 7 of 12


     inspection.

     Use cylinders in the order received from the supplier. Empty cylinders should be marked "MT" (empty),
     segregated from full cylinders and promptly returned to the supplier. Keep valves closed and protective
     caps in place on empty cylinders.

     In use, the cylinder should be directly connected to the equipment being purged either with metallic
     tubing, or pipe. If such a direct connection is not made, electrically bond the cylinder so as to dissipate
     any static charge.

     For bonds and ground connections use #10 AWG, bare, stranded copper wire.

     Securely fasten cylinders to a permanent object or bundle together when in use. As many cylinders as
     practical should be manifold together to avoid delays when exchanging cylinders during the purge. The
     manifold piping must be sufficiently flexible to be able to avoid stress from distortion during usage and      Stds.
     should have adequate strength to contain the gas pressure up to the point of expansion in the piping           Comm.
     being purged.

     USING NITROGEN (N2) CYLINDERS:

     The cylinder may be held in any convenient position when in use since it is always in the gaseous state.

     The cylinder manifold, main connection and component parts may be made with threaded fittings. Since
     the pressure in the cylinder is as much as 2200 PSIG high pressure steel forged fittings should be used,
     such as those shown in the following drawing and material list.

     For flows of nitrogen (N2) less than 50 c.f.m. a regulator should be used to reduce the pressure to that
     which will produce the desired flow. When flows are greater than 50 c.f.m. the capacity of the regulator
     should be considered or it should be omitted from the piping system.

     Note that unregulated pressures can be in excess of 2000 PSIG.




          FIGURE 1: TYPICAL NITROGEN N2 PURGE MANIFOLD (MAIN INTO SERVICE)




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                       OPERATING AND MAINTENANCE GENERAL PROCEDURES                                OM - 90

  Operations &
  Maintenance                                 PURGING PROCEDURES                                  Page 8 of 12




                                                                                                                 Stds.
                                                                                                                 Comm.




    1    Standard N2 Cylinder                               NOTES

    2    ½" Needle Valve (3000 lb. rating)              a. The arrangement shown is used when flow rate
                                                           is to be established as described in paragraphs
    3    Press. Regulator when req'd. (3000 lb.            1 through 6.
         rating - 0 to 100 PSIG setting)
                                                        b. For alternate method of establishing flow rate
    4    Relief Valve (3000 lb. rating -100                as described in OM-92 a hose or rigid piping
         PSIG setting)                                     manifold to main connection may be used.
                                                           Each cylinder must have a 0-2500 PSIG
    5    Press. Gauge (0-100 PSIG)                         pressure gauge connected down stream of the
                                                           cylinder control valve.
    6    Press. Gauge (0-2500 PSIG)
                                                        c. If a non-metallic hose connection is used
    7    Shut-Off (M-51 or M-351)                          between the manifold and gas main a #10
                                                           AWG, bare, stranded, copper bond wire must
    8    Air Compressor Hose (50 ft.)                      be installed as shown.

    9    Typical 3000 lb. Forged Steel Fitting          d. The pressure ratings and capacities of all
                                                           components must be properly selected.
    10   Typical Sch. 80 (min.) steel pipe
     The purging arrangement shown on Page 8 provides a satisfactory method of controlling high N2 flow
     rates. Injection is through a high-pressure ½" pipe manifold with a single ½" needle valve for regulating
     the flow. All fittings in the manifold, to and including the ½" needle valve are rated for 3000 PSIG.

       Issued               Revised               Revised                 Revised                Revised
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  Operations &
  Maintenance                               PURGING PROCEDURES                                      Page 9 of 12


     Several cylinders can be connected in parallel, and the one valve used for regulating and flow. Flows as
     great as 700 cu. ft. per minute have been obtained through this type of manifold. However, it is
     recommended that additional manifolds with throttle valve be used for rates over 500 cu. ft. per minute.

     Freezing may occur between the throttle valve and the cylinder, at temperatures below 32°F. This
     freezing tends to occur first at the cylinder control valve orifice, and begins when the withdrawal rate is
     about 50 cu. ft. per minute.




                                                                                                                   Stds.
                                                                                                                   Comm.




     9. Purging Examples
     PURGING INTO SERVICE



       Issued               Revised                Revised                 Revised                 Revised
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                       OPERATING AND MAINTENANCE GENERAL PROCEDURES                                 OM - 90

  Operations &
  Maintenance                              PURGING PROCEDURES                                     Page 10 of 12




                                                                                                                  Stds.
                                                                                                                  Comm.




     2000 feet of 8” pipe
        (1) Install vent stack and leave valve open.
        (2) Install temporary connection to inject nitrogen. Table shows that two cylinders of nitrogen will
             be needed.
        (3) Inject nitrogen while maintaining a pressure of 18psig or higher at the nitrogen manifold using a
             ¾” diameter hose 50’ long.
        (4) Inject natural gas immediately following the nitrogen, closing nitrogen manifold valve as gas
             bypass valve is opened. Progress of the purge may be monitored with a combustible gas
             indicator, CGI at the vent stack sample point.
        (5) Stop injection of gas when combustible gas indicator at vent indicates essentially 100 percent
             gas.
        (6) Close vent.
        NOTE:
        If tie-in is done after purging, the following precautions should be observed to keep air from entering
        line.
             (a) If possible, a very slight positive internal pressure should be maintained while joining pipe.
             (b) When a pipe is opened to the atmosphere, the open ends should be immediately covered by
                 some appropriate closure.



       Issued               Revised                Revised                Revised                Revised
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                       OPERATING AND MAINTENANCE GENERAL PROCEDURES                                OM - 90

  Operations &
  Maintenance                              PURGING PROCEDURES                                    Page 11 of 12


     PURGING OUT OF SERVICE




                                                                                                                 Stds.
                                                                                                                 Comm.




     2000 feet of 8” pipe
        (1) Install vent stack and leave valve closed.
        (2) Install connections and hoses to inject nitrogen and air. Table shows that two cylinders will be
            needed.
        NOTE:
            To maintain a minimum purge velocity for air injection, see table, 56cfm of air injection is
            required. A compressor with this capacity is required.
            A pressure of 18psig at the nitrogen manifold will provide the required injection rate through the
            50 feet of ¾” I.D. hose.
        (3) Isolate pipe segment to be purge; blow down to atmospheric pressure and open vent stack valve.
        (4) Inject cylinders of nitrogen, maintaining a pressure of 18psig on the nitrogen manifold.
        (5) Inject air immediately following the nitrogen, closing the nitrogen manifold as the air valve is
            opened. Progress of the purge may be monitored with an instrument to monitor oxygen meter at
            the vent stack.
        (6) Stop injection of air when oxygen indicator at vent indicates 20.8 percent oxygen or higher.
        (7) Close vent.


       Issued               Revised               Revised                 Revised                Revised
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    Date By               Date By                Date By                 Date By               Date By
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  Operations &
  Maintenance                     PURGING PROCEDURES                Page 12 of 12


                                 THIS PAGE LEFT BLANK




                                                                                    Stds.
                                                                                    Comm.




       Issued          Revised         Revised          Revised     Revised
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                        OPERATING AND MAINTENANCE GENERAL PROCEDURES                                  OM - 92

  Operations &
  Maintenance                                  PURGING DETAILS                                       Page 1 of 12


     1. GENERAL

         For simplified purging methods and for using Nitrogen (N2) for purging see OM-90. For purging
         pressure vessels, tanks, etc., or for more detailed information on purging mains see PURGING
         PRINCIPLES AND PRACTICE - American Gas Association Catalog No. XK0775.

         Purging is the replacement of one gas by another gas. In an enclosed space, such as a pipeline, this
         takes place by two distinct actions, namely displaced and mixing. Most purging operations are
         combinations of displacement and dilution actions. Three different purging procedures will be
         covered:

         a. Direct displacement of air with gas, or gas with air.
         b. Inert purging by complete filling with inert gas.
         c. Inert purging using a slug to separate the gas from the air.

         All gas lines being placed into or taken out of service and within which a flammable mixture of gas
         and air might accumulate, must be purged to a safe condition to ensure against accidental ignition.
         For lines being taken out of service purge immediately after blowdown.

         The medium used for purging may be either air, gas, or an inert gas, preferably nitrogen (N2). An          Stds.
         inert gas must be used to purge 500 foot or longer segments of 4 inch or larger pipe. When purging         Comm.
         long lines with an appreciable difference in elevation, the nitrogen should be introduced at the lower
         end of the line.

         The purging operation is not complete until the reading on a combustible gas indicator shows either
         0% on the LEL scale for taking a line out of service or 100% on the percent gas scale for placing a
         line in service. See C-702, page 2 for a discussion on combustible gases.

         Before starting a purge, check to see that all valves are in the correct position and all appurtenances
         are in operating condition.

         Under no condition may a line be purged into a cellar or other confined space. See OM-94 for
         procedures for purging gas services.

         Proper safety precautions shall be taken to guard against toxic conditions, accidental ignition, and
         the escape of noxious odors. As in any gas distribution work, adequate fire extinguishing equipment
         shall be readily available on the job site and within easy reach of the personnel. See safety standard
         C-701 for prevention of accidental ignition.




     2. DIRECT DISPLACEMENT OF GAS OR AIR

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                        OPERATING AND MAINTENANCE GENERAL PROCEDURES                                   OM - 92

  Operations &
  Maintenance                                   PURGING DETAILS                                       Page 2 of 12



         To minimize the mixing of medium being introduced with the gas or air in the line and to form as
         short a length of mixture within the flammable range as possible, the velocity of entrance of the
         purge medium should be as high as is practical. At least 100 lineal feet per minute must be
         maintained, however, 200 feet per minute or greater is preferable. See Table 1 for flow rates
         required for air or gas, to maintain a rate of flow of at least 100 lineal feet per minute within various
         size lines.

         A minimum exit velocity of 10-12 lineal feet per second must be maintained at the vent outlet to be
         sure that the velocity of gas is greater than the flame front velocity. See Table 2 for sizing of vent
         stack.


                                           TABLE 1
                             MINIMUM FLOW OF PURGE MEDIA REQUIRED

         Nominal Size             I.D.           Main Content             Minimum c.f.m. to inject Gas to
          (Inches)               Inches           c.f. per ft.             Maintain at Least 100 f.p.m.

              1¼                  1.380               .010                               2.0                         Stds.
              1½                  1.610               .014                               3.0                         Comm.
               2                  2.067               .023                               5.0
               3                  3.068               .051                               8.0
               4                  4.026               .088                              10.0
               6                  6.187               .208                              20.0
                                 Note 1
               8                  8.125               .360                              40.0
              10                 10.250               .573                              60.0
              12                 12.250               .819                              80.0
              16                 15.50               1.310                             130.0
              18                 17.50               1.670                             210.0


     NOTES

     1. Freezing begins when withdrawal rate exceeds 50 c.f.m. from one nitrogen cylinder. Therefore, a
        manifold must be used.

     2. A similar table in OM-90, Page 2, is designed for the minimum allowable velocity of 100 f.p.m. but
        is based upon using a 10 foot long, 2 inch diameter vent stack. When using the above table be sure
        to check Table 2, Pages 3 and 4, to verify that the vent velocity is between 10 f.p.s. and 450 f.p.s. for
        the vent stack size to be used.


                                                    TABLE 2

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                          OPERATING AND MAINTENANCE GENERAL PROCEDURES                                        OM - 92

  Operations &
  Maintenance                                         PURGING DETAILS                                     Page 3 of 12


                             FLOW RATES, VELOCITIES THROUGH VENT PIPES
                              AND PRESSURES LOSS THROUGH 10 FOOT LONG
                               VENT PIPES FOR AIR OR NITROGEN AND GAS



                                    1" Vent                          1" Vent                           1" Vent
                                  Press. Loss                      Press. Loss                       Press. Loss
    Flow Rate         Flow Vel. Inches Water            Flow Vel. Inches Water            Flow Vel. Inches Water
  c.f.h. c.f.m.        ft./sec. Air or N2 Gas            ft./sec. Air or N2 Gas            ft./sec. Air or N2 Gas

    100      1.7         4.7                               2.7                               2.0
    200      3.3         9.3                               5.3                               3.9
    300      5.0        13.9                               8.0                               5.9
    400      6.7        18.5                              10.7                               7.9
    500      8.3        23.1                              13.4                               9.8
   1000     16.7        46.3                              26.7                              19.6
   1500     25.0        69.4                              40.1                              29.5
   2000     33.3        92.6         10.5       6.7       53.4         2.7          1.7     39.3       1.0        0.6
   2500     41.7       115.8         16.4      10.5       66.8         4.2          2.7     49.0       1.6        1.0    Stds.
   3000     50.0       138.9         23.6      15.1       80.1         6.0          3.8     58.8       2.3        1.5    Comm.

   3500     58.3       162.1         32.1      20.5       93.5         8.2          5.2     70.6       3.1        2.0
   4000     66.7       185.2         42.0      26.9      106.8        10.7          6.8     78.4       4.1        2.6
   4500     75.0       208.4         53.1      34.0      120.2        13.5          8.6     88.2       5.2        3.3
   5000     83.3       231.5         65.6      42.0      133.5        16.7         10.7     98.0       6.4        4.1
   6000     100.0      277.8         94.5      60.5      160.2        24.0         15.4    117.6       9.2        5.9
   7000     116.7      324.1        128.6      82.3      186.9        32.6         20.9    137.2      12.5        8.0
   8000     133.3      370.4                  107.5      213.6        42.6         27.3    156.8      16.3       10.4
   9000     150.0      416.7                             240.3        53.9         34.5    176.4      20.6       13.2
  10000     166.6                                        267.0        66.6         42.6    196.0      25.5       16.3
  15000     250.0                                        400.5       149.9         95.9    294.0      57.3       36.7
  20000     333.3                                                                          392.0     101.9       65.2
                                                                                           Note 1
  25000     416.7                                                                          490.0                101.9


 NOTES

 1.    At a velocity of approximately 450 ft./sec. the gas reaches critical flow across the shut-off valve.

 2.    Flow velocity at the vent stack outlet must be at least 10 to 12 ft./sec.




                                                 TABLE 2 (Continued)


       Issued                   Revised                 Revised                     Revised              Revised
12/17/04      DCW
      Date By                  Date By                  Date By                    Date By             Date By
                        OPERATING AND MAINTENANCE GENERAL PROCEDURES                                        OM - 92

  Operations &
  Maintenance                                      PURGING DETAILS                                         Page 4 of 12


                           FLOW RATES, VELOCITIES THROUGH VENT PIPES
                            AND PRESSURE LOSS THROUGH 10 FOOT LONG
                             VENT PIPES FOR AIR OR NITROGEN AND GAS



                                  1" Vent                         1" Vent                         1" Vent
                                Press. Loss                     Press. Loss                     Press. Loss
    Flow Rate       Flow Vel. Inches Water           Flow Vel. Inches Water          Flow Vel. Inches Water
  c.f.h. c.f.m.      ft./sec. Air or N2 Gas           ft./sec. Air or N2 Gas          ft./sec. Air or N2 Gas

    100    1.7        1.2                               0.54                              0.31
    200    3.3        2.4                               1.1                               0.63
    300    5.0        3.6                               1.6                               0.94
    400    6.7        4.8                               2.2                               1.3
    500    8.3        6.0                               2.7                               1.6
   1000   16.7       11.9                               5.4                               3.1
   1500   25.0       17.9                               8.1                               4.7
   2000   33.3       23.8           0.2      0.1       10.8                               6.3
   2500   41.7       29.8           0.4      0.3       13.5                               7.8                             Stds.
   3000   50.0       35.7           0.6      0.4       16.2          0.1                  9.3                             Comm.

   3500   58.3       41.7           0.8      0.5       18.9          0.1                 10.9
   4000   66.7       47.6           1.0      0.6       21.6          0.1                 12.4
   4500   75.0       53.6           1.2      0.8       24.3          0.1      0.1        14.0
   5000   83.3       59.5           1.5      1.0       27.0          0.2      0.1        15.5
   6000   100.0      71.4           2.2      1.4       32.4          0.3      0.2        18.6
   7000   116.7      83.3           3.0      1.9       37.8          0.4      0.3        21.7        0.1
   8000   133.3      95.2           3.9      2.5       43.2          0.5      0.3        24.8        0.1
   9000   150.0     107.1           5.0      3.2       48.6          0.6      0.4        27.9        0.1         0.1
  10000   166.6     119.0           6.1      3.9       54.0          0.7      0.5        31.0        0.2         0.1
  15000   250.0     178.5          13.8      8.8       81.0          1.6      1.0        46.5        0.4         0.3
  20000   333.3     238.0          24.5     15.7      108.0          2.9      1.9        62.0        0.7         0.5
  25000   416.7     297.5          38.3     24.5      135.0          4.5      2.9        77.5        1.1         0.7
  30000   500.0     357.0          55.2     35.3      162.0          6.5      4.2        93.0        1.6         1.0
  35000   583.3     416.5          75.2     48.1      189.0          8.9      5.7       108.5        2.1         1.3
                    Note. 1
  40000   666.7     476.0          98.2     62.8      216.0        11.6       7.4       124.0        2.8         1.8
  50000   833.3     595.0                   98.2      270.0        18.1      11.6       155.0        4.3         2.6

 NOTES

 1. At a velocity of approximately 450 ft./sec. the gas reaches critical flow across the shut-off valve.
    Under this condition the noise level at a distance of 10 feet exceeds 110 dB.

 2. Flow velocity at the vent stack outlet must be at least 10 to 12 ft./sec.
    3. INERT PURGING BY COMPLETE FILLING WITH INERT GAS


       Issued                 Revised                 Revised                 Revised                 Revised
12/17/04      DCW
    Date By                 Date By                  Date By                 Date By                 Date By
                        OPERATING AND MAINTENANCE GENERAL PROCEDURES                                  OM - 92

  Operations &
  Maintenance                                   PURGING DETAILS                                      Page 5 of 12


         An inert purge may be accomplished by filling the entire line with the inert gas. A volume of 10% to
         50% more inert gas than the total volume of the line added rapidly will insure complete filling. Use
         the pipe content column of Table 1 to determine the volume of nitrogen required. Multiply cubic
         feet per foot of pipe times the length of the line to get volumetric content. This multiplied by 1.1 to
         1.5 will give the nitrogen requirement.

         Vent gases should be analyzed to make sure that the line has been filled with inert gas and the
         specified end point has been reached. (The end point is that concentration of inert gas in the line
         being purged, that the addition of more air if the line is being purged out of service, or more gas if
         being purged into service will not result in the formation of a flammable mixture). See Table 3 for
         end points.

                                TABLE 3: END POINT CONCENTRATIONS

                      Nitrogen End Points                                Oxygen End Points
                    For Purging Into Service                       For Purging Into Service with N21.

              Combustible      Percent N21. required              Combustible         Percent of Oxygen             Stds.
                               to render mixtures                                     below which no                Comm.
                               non-flammable                                          mixture is flammable
              Methane                 49                          Methane                    9.7
              Ethane                  55                          Ethane                     8.8
              Propane                 54                          Propane                    9.1

                      Nitrogen End Points                            Combustive Gas End Points
                     For Purging Into Service                      For Purging Into Service with N21.

                                  Note 1.
              Combustible      Percent N2 required to             Combustible         Percent of Combustible
                               render mixtures non-                                   below which no mixture
                               flammable when air is                                  is flammable when air
                               added in any amount                                    is added in any amount

              Methane                  89                         Methane                    11
              Ethane                   95                         Ethane                      5
              Propane                  95                         Propane                     5


     NOTES

     1. Includes a 20% Safety Factor.


     4. INERT PURGING USING A SLUG TO SEPARATE THE MEDIA BEING INTERCHANGED



       Issued                Revised                Revised                 Revised                Revised
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                       OPERATING AND MAINTENANCE GENERAL PROCEDURES                                  OM - 92

  Operations &
  Maintenance                                  PURGING DETAILS                                      Page 6 of 12


         Prevention of flammable mixtures, without complete displacement with inert gas can be accomplished
         by maintaining a slug of inert gas between the air and combustible gas. This slug must be long
         enough to allow for some mixture at each end of the slug.

         The purge must immediately follow the insertion of the inert gas slug or a new slug must be injected.
         A delay of approximately three minutes will destroy the effectiveness of the slug.
         The initial slug length required for purging of given diameter pipe is dependent primarily upon the
         length of the pipe and the velocity of the slug within the pipe. See Table 4 for volume of nitrogen
         required for inert slug for various pipe sizes, lengths, and injection rates. An automatic factor of
         safety results from using Table 4 because a mixture of 85% or more of nitrogen with natural gas
         cannot be made to burn regardless of the amount of air present, therefore, the effective length of non-
         combustible slug is the length of any pure nitrogen plus the length of mixture including more than
         85% nitrogen.
         The same amount of inert gas, as a slug, is used if a main is being purged into or out of service.

         The following chart shows the safe limits of a natural gas-nitrogen mixture with air.                     Stds.
                                                                                                                   Comm.
                              FIGURE 1: NATURAL GAS, AIR, AND NITROGEN MIXTURES




     EXAMPLE

     If a mixture contains 83 percent nitrogen and 17 percent natural gas, the lower flammable limit of the
     mixture in air would 31 percent; the upper flammable limit 40 percent.


                                                      TABLE 4


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12/17/04      DCW
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                           OPERATING AND MAINTENANCE GENERAL PROCEDURES                                   OM - 92

  Operations &
  Maintenance                                         PURGING DETAILS                                    Page 7 of 12


     Pipe            Slug                 Injection      N2 Tank      C.F.of N2            C.F.of N2      C.F.of N2
     Size           Velocity                Rate         Manifold     Slug for              Slug for       Slug for
   (Diam.)          Ft./Min.               C.F.M.        Required    500'Main             1000'Main      2000'Main
                                           Note a.
      4"             100                    10             1        10 c.f.               10 c.f.       20 c.f.
      6"             100                    20             1        30 c.f.               30 c.f.       30 c.f.
      8"             100                    40             1        70 c.f.               70 c.f.       80 c.f.
     10"             100                    60             2        130 c.f.              140 c.f.      150 c.f.

     12"             100                   80              2        10 c.f.               300 c.f.      340 c.f.
     12"             125                  100              3        30 c.f.               270 c.f.      300 c.f.
     12"             150                  120              3        10 c.f.               240 c.f.      260 c.f.
     12"             175                  140              3        30 c.f.               200 c.f.      220 c.f.

     16"             100                  130              3        10 c.f.               630 c.f.      700 c.f.
     16"             125                  160              4        30 c.f.               550 c.f.      620 c.f.
     16"             150                  200              5        10 c.f.               470 c.f.      520 c.f.
     16"             175                  230              5        30 c.f.               400 c.f.      450 c.f.

     18"             125                  210              5        10 c.f.               850 c.f.      970 c.f.
     18"             150                  250              6        30 c.f.               690 c.f.      750 c.f.
     18"             175                  290              7        10 c.f.               550 c.f.      620 c.f.
     18"             200                  340              8        30 c.f.               450 c.f.      500 c.f.
                                                                                                                        Stds.
                                                                                                                        Comm.
     Pipe            Slug                 Injection      N2 Tank      C.F.of N2            C.F.of N2     C.F.of N2
     Size           Velocity                Rate         Manifold     Slug for              Slug for      Slug for
   (Diam.)          Ft./Min.               C.F.M.        Required    5000'Main            10000'Main    20000'Main
                                           Note a.
      4"             100                    10             1        20 c.f.               20 c.f.       30 c.f.
      6"             100                    20             1        40 c.f.               50 c.f.       70 c.f.
      8"             100                    40             1        90 c.f.               120 c.f.      160 c.f.
     10"             100                    60             2        180 c.f.              230 c.f.      280 c.f.

     12"             100                   80              2        370 c.f.              400 c.f.      430 c.f.
     12"             125                  100              3        330 c.f.              350 c.f.      390 c.f.
     12"             150                  120              3        290 c.f.              310 c.f.      340 c.f.
     12"             175                  140              3        250 c.f.              270 c.f.      290 c.f.

     16"             100                  130              3        790 c.f.              850 c.f.      910 c.f.
     16"             125                  160              4        700 c.f.              750 c.f.      810 c.f.
     16"             150                  200              5        590 c.f.              640 c.f.      700 c.f.
     16"             175                  230              5        530 c.f.              570 c.f.      610 c.f.

     18"             125                  210              5        1110 c.f.             1200 c.f.     1300 c.f.
     18"             150                  250              6        850 c.f.              940 c.f.      1000 c.f.
     18"             175                  290              7        700 c.f.              770 c.f.      820 c.f.
     18"             200                  340              8        550 c.f.              600 c.f.      650 c.f.


   NOTES
   a. Only 50 C.F.M. of N2 can be withdrawn per cylinder before freezing begins. In order to inject nitrogen
       flow rates in excess of 50 C.F.M. multiple cylinder manifolds are used. See OM-90 page 8 for the proper
       arrangement of components in fabricating the manifold. See OM-90 page 3 paragraph 4 or OM-92 page 9
       paragraph 6 regarding methods used to measure and control the injection rate.
     5. FIRE SCREENS ON VENT PIPES


       Issued                   Revised                 Revised                 Revised                 Revised
12/17/04      DCW
    Date By                    Date By                  Date By                Date By                 Date By
                       OPERATING AND MAINTENANCE GENERAL PROCEDURES                                 OM - 92

  Operations &
  Maintenance                                  PURGING DETAILS                                     Page 8 of 12


         If the velocity of flow is greater than the speed of the flame travel, fire screens should not be
         necessary. However, screens may be used to protect against unpredictable conditions or unforeseen
         interruptions in the supply of inert gas while purging from gas to air.
         Fire screens, in addition, tend to prevent flashback should flammable mixture become ignited.
         Fire screens are generally 50 to 60 mesh wire screen installed between pipe flanges with at least 4
         times the area of the vent pipe; for example 4 inch flanges on 2 inch diameter pipe.
         The disadvantages accompanying the use of fire screens include:
         a. There is no assurance that flame will not strike back through the screen. If the gas issuing from
            the pipe should become ignited, the center of the screen could become hot enough to ignite the
            gas-air mixture approaching the screen.
         b. The mesh may become clogged with condensate and dust. The condensates may be volatile oils
            or water. This can be quite troublesome and constant attention should be given to the screen. If
            condensates collect, it may be possible to dislodge them by tapping the screen lightly, or it may
            be necessary to remove the screen for cleaning or replacement.
                                                                                                                  Stds.
         c. Plugged screens will decrease the flow of the purged mixture and may stop it entirely, unless         Comm.
            constant attention is given to keeping them clean and open.
         On those occasions where flaring might be necessary due to excessive volumes of gas to be purged,
         the vent line may be equipped with a double safety fire screen of 50-60 mesh between 4 inch
         diameter flanges, as shown in the following drawing:
                                                                  FIGURE 2: FIRE SCREEN



         1    2" Steel Pipe (M-251)
        2     4" x 2" Concentric Reducer
        3     4" Flanges with 50-60 Steel
              Mesh Between
        4     4" Steel Pipe (M-251) Spool




     6. DETERMINING INJECTION RATE MEASUREMENT OF NITROGEN


       Issued               Revised                Revised                 Revised               Revised
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    Date By                Date By                Date By                Date By                Date By
                       OPERATING AND MAINTENANCE GENERAL PROCEDURES                                OM - 92

  Operations &
  Maintenance                                 PURGING DETAILS                                     Page 9 of 12


         To establish the amount of N2 withdrawn from a standard cylinder install a 0 to 2500 PSIG or similar
         pressure gauge on the outlet side of the outlet control valve of each cylinder. By noting the rate of
         pressure decrease on the gauge, the chart shown below will indicate the rate of withdrawal. Note
         from the slope of the line on the chart that a 100 PSIG drop in pressure will cause 10 c.f. of N2 to
         flow from the cylinder.

                            FIGURE 3: N2 CYLINDER PRESSURE VS. VOLUME




                                                                   Cylinder Manifolds
                                                                   When cylinders are Manifolded-
                                                                   multiply the volumes shown in
                                                                   the chart by the number of                    Stds.
                                                                   cylinders in he manifold.                     Comm.




     PROCEDURE
     The steps for obtaining the proper N2 flow (based upon a velocity of 100 f.p.m.) using a standard
     cylinder at 2200 PSIG are as follows:
       a. From Table 1, Page 2 obtain the minimum flow rate (c.f.m) of N2 for the diameter of main to be
          purged into or out of service.
       b. From Table 4, Page 7, obtain the minimum volume (c.f.) of N2 for the diameter and length of main
          to be purged.
       c. Determine the pressure drop in the cylinders for delivering the necessary volume as determined
          form step b. by using the above chart or by multiplying the volume by 10.
       d. Determine the period of time it should take for the pressure in the cylinders to drop as determined
          from step c. by dividing the volume obtained in step b. by the flow rate obtained in step a. (For
          alternate method see OM-90, Page 3)

     6. DETERMINING INJECTION RATE MEASUREMENT OF NITROGEN (Continued)


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  Operations &
  Maintenance                                 PURGING DETAILS                                    Page 10 of 12


         Example: Slug Method

                      To Purge a 6 inch diameter, 1600 foot long main into or out of service.

         1. Injection flow Rate
                Go to Table 1, page 2 to find the minimum nitrogen (N2) flow rate required for a 6 inch
                main - 20.0 c.f.m.

         2. Volume of Slug
               Go to Table 4, page 7, to find the volume of nitrogen necessary to create the proper size
               (length) of slug - 30 cu.ft.

         3. Cylinder Pressure Drop
               Multiply the volume of the slug by 10 to obtain the N2 cylinder gage drop in pressure
               required to release the volume of 30 c.f. from the cylinder. 30 x 10 = 300 psig cylinder
               pressure drop.

         4. Injection Timing
                Divide the volume required by the injection rate required to determine the amount of             Stds.
                                                                                                                 Comm.
                time in which to inject the proper amount of nitrogen at the determined flow rate, which
                will keep the slug together.
                                      (30 cu.ft. ϊ 20 c.f.m. = 1.5 minutes).

         Therefore, to obtain the proper slug length and velocity a pressure drop of 300 PSIG must take place
         in 1.5 minutes. It can be seen from Table 2, Page 3, that a 1 inch diameter vent stack will provide a
         satisfactory exit velocity. Air or gas must immediately follow the N2 slug at about the same flow
         rate. The vent should be continuously monitored with a combustible gas indicator to be sure that the
         final conditions of 100% air for purging out of service and 100% gas for purging into service are
         met.

         NOTES

         1. To obtain the minimum number of cylinders required for a purge, divide the minimum volume
            (from step b.) by 200 c.f.

         2. The pressure drop for each cylinder will be based upon the volume being withdrawn from that
            cylinder.

         3. See OM-90, Page 8 for typical N2 manifold, main connection and vent stack.

         Reference:
         Most of the composition, charts and tables presented herein are taken directly or adapted from
         PURGING PRINCIPLES AND PRACTICE - American Gas Association, Catalog No. XK0775.

     7. SAFETY PRECAUTIONS WITH INERT PURGE GASES


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  Operations &
  Maintenance                                 PURGING DETAILS                                     Page 11 of 12


         Inert gases commonly available for purging are composed primarily of carbon dioxide or nitrogen.
         Since neither of theses gases will support life, inhalation of abnormal concentrations should be
         avoided, as the oxygen may thereby be reduced sufficiently to cause oxygen starvation or
         smothering. For the same reason, men should not enter trenches, valve pits, manholes, and the like
         when inert gas is being vented. This is also one reason for the specification of adequate vents in
         purging operations, particularly those, which should be carried out inside buildings or other enclosed
         areas. It is necessary in such cases to carry vents outside of the buildings and away from windows
         and doors. Inert gases made up combustion products also may contain carbon monoxide in sufficient
         quantities to have toxic effects.


                                                  WARNING

                     EXTREME PRECAUTIONS SHOULD BE OBSERVED WHEN
                      WORKING WITH OXYGEN DEFICIENT ATMOSPHERES

         Immediate Effects of Breathing Oxygen Deficient Atmospheres
                                                                                                                  Stds.
         As blood passes through the lungs it gives up carbon dioxide and accepts oxygen through the thin         Comm.

         walls of tiny air sacs. Blood, which becomes enriched in oxygen in the lungs then takes less than 10
         seconds to reach the brain.

         When an individual takes a few breaths of gas containing NO OXYGEN (pure nitrogen for example)
         the lungs fill with a gas containing no oxygen. Blood in the lungs cannot receive oxygen because
         none has been inhaled. In fact the blood gives up whatever residual oxygen it may be carrying.
         Blood severely depleted in oxygen then flows to the brain, where tissues become oxygen deficient.
         The result is swift unconsciousness because brain tissue is the body component most sensitive to the
         lack of oxygen. Within 5 seconds after inhaling only a few breaths of oxygen-free gas there is a
         rapid drop in oxygen content in the blood. Coma follows a few seconds later. Symptoms or
         warnings are generally absent but even if present do not permit the victim to take adequate corrective
         action. Death follows in 2-4 minutes.


                                                  FIRST AID

         Persons suffering from lack of oxygen should quickly be moved to areas with normal atmosphere.
         Assisted respiration and supplemental oxygen should be given if the victim is not breathing. NOTE:
         COMA DUE TO LACK OF OXYGEN IS NOT ALWAYS FATAL. KNOW, PRACTICE AND
         USE CARDIOPULMONARY RESUSCITATION (CPR) TECHNIQUES.




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  Maintenance                      PURGING DETAILS                  Page 12 of 12


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                        OPERATING AND MAINTENANCE GENERAL PROCEDURES                                  OM - 94

  Operations &
  Maintenance                               PURGING GAS SERVICES                                     Page 1 of 2


     Services shall not be purged into service until testing has been completed as outlined in C-245. All gas
     piping shall be fully purged and the pilots lighted before leaving the premises.

     For services which are 2" nominal diameter or less, and not more than 125 feet in length, purging is
     usually done after the meter fit is installed, fuel lines are connected and an open flame appliance is ready
     to be lighted. The easiest and safest method is to hold a lighted match over the appliance burner and to
     control the flow by adjusting the burner valve until the flame is steady.

     A suggested method for purging the gas piping to an appliance not having an open flame is to disconnect
     the pilot piping at the outlet of the pilot valve. Piping shall not be purged into the combustion chamber or
     an appliance.

     The open end of the piping systems being purged shall not discharge into confined spaces or areas where
     there are sources of ignition unless precautions are taken to perform this operation in a safe manner by
     ventilation of the space, control of purging rate and elimination of all hazardous conditions.

     For services larger than 2" nominal diameter or longer than 125 feet, or if for other reasons purging
     cannot be accomplished in the above described manner, the service shall be purged by bleeding the gas
     through a hose to atmosphere outside the customer’s building, making sure that gas does not blow back
     into the building. Purging shall be continued until 100% gas is obtained at the hose discharge.                Stds.
                                                                                                                    Comm.
     The remainder of the piping and appliances shall be purged as described above.




       Issued               Revised                 Revised                 Revised                Revised
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  Operations &
  Maintenance                    PURGING GAS SERVICES                Page 2 of 2


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                     OPERATING AND MAINTENANCE GENERAL PROCEDURES                                 OM - 96

 Operations &                INSIDE SERVICE ATMOSPHERIC CORROSION
 Maintenance                       INSPECTIONAND LEAK SURVEY                                     Page 1 of 7


    1. GENERAL

       This procedure applies to the inspection for atmospheric corrosion and survey for gas leakage on
       NSTAR-owned inside service piping. It describes the process for managing the program,
       organizational responsibilities, scheduling and performing inspections and surveys and follow-up
       actions required when inside service piping is inaccessible when an inspection is attempted.

       Atmospheric corrosion inspections described in these procedures are required by 49 CFR 192.481
       and leakage surveys are required by 49 CFR 192.723. The inspections and surveys are performed in
       compliance with the aforementioned regulations and pursuant to the Consent Order and Compliance
       Agreement entered into by NSTAR Gas in the matter of DPU 03-PL-19.

    2. DEFINITIONS

       The following definitions apply for the purposes of this inspection program:

       Advantex: Mobile data scheduling software utilized to schedule inspections and surveys

       ATM and Leak Survey Letter: One of several letters for the purpose of contacting customers to
       make appointments to perform inspections

       CGI Notice: A “door hanger”, tag or card left by a company technician or contractor when they
       have been unable to access an inside service location to conduct an inspection or survey. The CGI
       Notice advises the customer that an attempt has been made to perform an inspection or survey and
       requests that the customer contact the company to schedule an inspection.

       CIS: Customer Information System

       Concealed Piping: Piping located behind finished walls or ceilings that cannot be seen or accessed
       to perform atmospheric corrosion inspections or leak surveys

       Inspection: Visual examination of NSTAR-owned piping and meter assemblies for the presence of
       atmospheric corrosion

       Leak Survey: A search for possible gas leakage in any area where gas facilities exist or where a gas
       leak is reported or suspected

       Obstructed Piping: Piping that cannot be accessed to perform atmospheric corrosion inspections or
       leak surveys due to the presence of debris, boxes, locked doors, barricades, fences or other obstacles

       PCS: Pipeline Compliance System database used to identify, schedule and record completed
       inspections




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 Operations &                INSIDE SERVICE ATMOSPHERIC CORROSION
 Maintenance                       INSPECTIONAND LEAK SURVEY                                      Page 2 of 7


       Service Line: A distribution line which transports gas from a common source of supply to an
       individual customer, to two adjacent or adjoining residential or small commercial customers, or to
       multiple residential or small commercial customers served through a meter header or manifold. A
       service line ends at the outlet of the customer meter or at the connection to the customer’s piping,
       whichever is further downstream, or at the connection to customer piping if there is no meter.

    3. IDENTIFICATION OF REQUIRED INSPECTIONS

       The Pipeline Compliance System (PCS) contains the list of inside service locations identified by
       address and premise ID and establishes the inspection due date at 36 months from the last inspection.
       Completed inspections will be recorded in PCS by scheduled download from Advantex, download
       from Allegro handheld devices or entered manually.

       The listing of outstanding inspections due in the current year will be updated periodically to reflect
       completed inspections. Throughout the year the inspection program will be monitored to ensure annual
       target attainment.

    4. INSPECTION PROCESS

       4.1 Business Districts
       Leak surveys on NSTAR-owned inside service piping located in buildings within a Business District
       will be conducted at least once each calendar year at intervals not exceeding fifteen (15) months.
       Atmospheric corrosion inspections will be conducted at least once every three (3) calendar years at
       intervals not exceeding thirty-nine (39) months. To the extent possible both the atmospheric
       corrosion inspection and leak survey will be conducted during the same visit. They will be
       conducted by qualified contractors in conjunction with scheduled leak surveys of the buried mains
       and services within the Business Districts.
       Existing procedures will be followed to report leaks or “poor” or “immediate hazard” conditions
       discovered during an inspection or survey.

       4.2 Buildings of Public Assembly
       Leak surveys on NSTAR-owned inside service piping located in Buildings of Public Assembly will
       be conducted at least once each calendar year at intervals not exceeding fifteen (15) months.
       Atmospheric corrosion inspections will be conducted at least once every three (3) calendar years at
       intervals not exceeding thirty-nine (39) months. To the extent possible both the atmospheric
       corrosion inspection and leak survey will be conducted during the same visit. They will be
       conducted by qualified contractors in conjunction with scheduled leak surveys of the service line to
       the Building of Public Assembly. Existing procedures will be followed to report leaks or “poor” or
       “immediate hazard” conditions discovered during an inspection or survey.

       4.3 Balance of System
       Atmospheric corrosion inspections on NSTAR-owned inside service piping at locations other than
       Buildings of Public Assembly and locations outside Business Districts will be conducted at least
       once every three (3) calendar years at intervals not exceeding 39 months. Leak surveys of NSTAR-
       owned inside service piping will be conducted at least once every five (5) calendar years at intervals

     Revised              Revised                Revised                 Revised                Revised
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   Date By               Date By                Date By                 Date By               Date By
                       OPERATING AND MAINTENANCE GENERAL PROCEDURES                                 OM - 96

 Operations &                  INSIDE SERVICE ATMOSPHERIC CORROSION
 Maintenance                         INSPECTIONAND LEAK SURVEY                                     Page 3 of 7


       not exceeding sixty (60) months. Existing procedures will be followed to report leaks or “poor” or
       “immediate hazard” atmospheric corrosion conditions discovered during an inspection or survey.

       Atmospheric corrosion inspections and leak surveys will be conducted utilizing one or both of the
       methods described below:

             4.3.1 Canvas Process
             Before scheduling inspections at locations not planned for a meter exchange, qualified NSTAR
             technicians may visit service locations on geographically grouped streets to perform inspections
             and leak surveys. The technician will record meter numbers for all meters connected to a single
             service at multi-meter or multi-address locations, confirm inside / outside meter location and
             record the results of the atmospheric corrosion inspection and leak survey. Data will be recorded
             manually, or on a laptop computer, or hand held data collection device based on availability.

             Unsuccessful inspection attempts will be recorded by the NSTAR technicians and a CGI Notice
             left requesting the customer to contact the Company to schedule an inspection.

             If the customer fails to respond to the CGI Notice additional attempts will be made to contact the
             customer to make a good faith effort to perform the required inspections and leak surveys and
             comply with the applicable regulations. These additional attempts are described in Section 6.0 of
             these procedures.

             4.3.2 Scheduled Inspections
             Scheduled atmospheric corrosion inspections and leak surveys may be performed by qualified
             NSTAR technicians in conjunction with scheduled meter exchange appointments or by
             appointments scheduled in response to a CGI Notice, follow-up letter or outbound telephone call
             to the customer.

             Technicians will record meter numbers for all meters connected to a single service at multi-meter
             or multi-address locations, confirm inside / outside meter location and record the results of the
             atmospheric corrosion inspection and leak survey. Data will be recorded in Advantex, manually,
             on a laptop computer, hand held data collection device or appropriate written form based on
             availability.

    5. CGI FOLLOW-UP PROCESS

       If a customer does not respond within approximately 30 days after a CGI Notice has been left during
       an unsuccessful inspection attempt letter ATM #1 will be sent to the customer, requesting that they
       contact the company to schedule an inspection. Planning and Scheduling will initiate the letter in CIS
       and CIS will record that a letter has been sent.

       If the customer does not respond to letter ATM #1 within approximately 30 days a second letter
       ATM #2 will be sent to the customer, noting previous attempts to gain access. The letter will be
       initiated by Planning and Scheduling, recorded in CIS and sent by certified mail.


     Revised                Revised                Revised                Revised                Revised
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   Date By                Date By                 Date By                Date By                Date By
                     OPERATING AND MAINTENANCE GENERAL PROCEDURES                                   OM - 96

 Operations &                INSIDE SERVICE ATMOSPHERIC CORROSION
 Maintenance                       INSPECTIONAND LEAK SURVEY                                       Page 4 of 7


       If no response to the CGI Notice and the two ATM letters is received no further attempts to schedule
       an inspection will be made in the current cycle. The next inspection due date will be set in PCS to 36
       months from the due date of the current cycle.

    6. APPOINTMENT BY LETTER PROCESS

       Upon completion of the canvas process letters may be sent to any remaining customers outside the
       canvassed areas that require an inspection in the current year and are not scheduled for a meter
       exchange. The letter will request the customer to contact the Company to schedule an inspection.

       Planning and Scheduling will initiate the letter, ATM #3, requesting that the customer contact the
       Company by telephone to schedule an inspection. Letters will be initiated and recorded in CIS.

       If the customer does not respond within approximately 30 days Planning and Scheduling will initiate
       a second letter, ATM #2, noting previous attempts and again requesting that the customer contact the
       Company to schedule an inspection. Letters sent will be initiated and recorded in CIS.

       If no response is received from the customer within approximately 30 days after letter ATM #2 is
       sent, Planning and Scheduling will initiate a final letter, ATM #4, noting previous attempts,
       requesting that the customer contact the Company to schedule an inspection and advising the
       customer that this is the final attempt to contact them to perform the required inspections. The letter
       will be initiated and recorded in CIS and sent by certified mail.

       If no response to the three ATM letters is received no further attempts to schedule an inspection will
       be made in the current inspection cycle. The next inspection due date will be set in PCS to 36 months
       from the due date of the current cycle.

    7. OBSTRUCTED PIPING PROCESS

       If a complete inspection and leak survey cannot be completed due to obstructed piping the technician
       shall advise the customer and request access to all NSTAR-owned inside service piping. If
       unobstructed access cannot be provided the technician shall complete as thorough an inspection and
       leak survey as possible and document the cause of the incomplete inspection in Advantex. The
       technician shall request that the customer take whatever actions are necessary to provide access and
       then contact the Company to schedule a follow-up inspection.

       If the customer does not contact the Company within approximately 30 days after the initial
       inspection Planning and Scheduling will initiate letter ATM #5, which indicates that obstructions
       prevented inspection during the initial visit. The letter will request that the customer clear the
       obstruction and contact the Company to schedule a follow-up inspection. The letter will be initiated
       and recorded in CIS.

       If the customer does not respond to letter ATM #5 within approximately 30 days Planning and
       Scheduling will initiate letter ATM #6. The letter will note that obstructions prevented inspection
       during the initial visit, previous attempts to contact the customer to schedule a follow-up

     Revised              Revised                 Revised                 Revised                Revised
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   Date By               Date By                 Date By                Date By                 Date By
                     OPERATING AND MAINTENANCE GENERAL PROCEDURES                                  OM - 96

 Operations &                INSIDE SERVICE ATMOSPHERIC CORROSION
 Maintenance                       INSPECTIONAND LEAK SURVEY                                      Page 5 of 7


       inspection.and advise the customer that this is the final attempt to contact them to schedule the
       required inspection. The letter will be initiated and recorded in CIS and sent by certified mail

       If no response to the two ATM letters is received and telephone contact is unsuccessful, no further
       attempts to schedule an inspection will be made in the current inspection cycle. The next inspection
       due date will be set in PCS to 36 months from the due date of the current cycle.

    8. CONCEALED PIPING

       If a complete inspection and leak survey cannot be completed due to concealed piping the technician
       shall advise the customer that permanent walls, ceilings or other structures have prevented a
       complete inspection. If access cannot be provided the technician shall complete as thorough an
       inspection and leak survey as possible and document the cause of the incomplete inspection in
       Advantex.

    9. ORGANIZATIONAL RESPONSIBILITIES

       9.1 Customer Care
       Customer Care is the point of contact for customers responding to notices and letters sent by NSTAR
       requesting access to inside service piping to perform inspections and surveys:
           • Answer inbound calls from customers responding to CGI Notices and follow-up ATM letters
           • Schedule inspections in Advantex in response to customer calls

       9.2 Compliance and Corrosion
       Compliance and Corrosion has overall responsibility for coordination, tracking and monitoring and
       reporting progress of the inside service atmospheric corrosion and leak survey program:
           • Maintain records of inside service locations in PCS
           • During the three years from September 2008 through August 2011 update PCS to identify
               and record multiple meters on the same inside service to establish a database of inside
               services
           • Identify inside services requiring inspection in current year via PCS
           • Schedule and manage inspections in Business Districts and Buildings of Public Assembly
           • Prepare maps, documents and data collection equipment to support canvassing of designated
               areas
           • Maintain database containing completed inspections in PCS
           • Monitor PCS database to ensure completed inspection data is transferred from Advantex to
               PCS as scheduled
           • On a monthly basis or other frequency deemed appropriate update listing of inside services
               requiring inspection in the current year
           • Develop and submit semi-annual reports to MA DPU for each of the five years through 2013
               listing by municipality, the total number of inside service line segments or inside meter sets
               that have been leak surveyed and the number of leaks found
           • Develop and submit semi-annual reports to MA DPU for each of the three years through
               2011 listing by municipality, the total number of inside service line segments or inside meter

     Revised              Revised                Revised                 Revised                Revised
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   Date By               Date By                Date By                 Date By                Date By
                      OPERATING AND MAINTENANCE GENERAL PROCEDURES                               OM - 96

 Operations &                INSIDE SERVICE ATMOSPHERIC CORROSION
 Maintenance                       INSPECTIONAND LEAK SURVEY                                     Page 6 of 7


                sets that have been inspected for atmospheric corrosion, the number requiring remedial
                action to maintain protection against atmospheric corrosion and the number of completed
                repairs

       9.3 Gas Distribution
           • Perform inspections when assigned, canvassing designated areas identified by Compliance
              and Corrosion
           • Record completed inspection data
           • Confirm meter location (inside / outside)
           • Record the location and date of unsuccessful inspections due to obstructed piping
           • Leave CGI Notice at locations when unable to gain entry to perform inspections
           • Record the location and date of unsuccessful attempts to perform inspections
           • Deliver completed inspection data and records of unsuccessful inspection attempts to
              Compliance and Corrosion for incorporation in the PCS database
           • Report leaks and atmospheric corrosion conditions requiring immediate remedial action to
              the area Service or Planning and Scheduling Supervisor as appropriate in accordance with
              existing procedures
           • Take corrective action to remediate “poor” atmospheric corrosion conditions identified
              during inspections within 30 days. Corrective action may include coating application,
              relocating customer meters from inside to outside or replacing or renewing entire service line
              as appropriate

       9.4 Gas Service
           • Perform inspections in conjunction with meter exchanges, odor investigations, utilization
              equipment maintenance or all other work whenever at a customer location
           • Perform inspections when assigned, canvassing designated areas identified by Compliance
              and Corrosion
           • Perform inspections scheduled through Advantex
           • Record completed inspection data in Advantex
           • Investigate and repair leaks discovered during inspections; if unable to make repairs, refer to
              the area Service or Planning and Scheduling Supervisor in accordance with existing
              procedures
           • Record leak repair information in Advantex and document in accordance with OM-60
           • Record results of atmospheric corrosion inspection in Advantex in accordance with existing
              procedures
           • Report atmospheric corrosion conditions requiring immediate remedial action to the area
              Service or Planning and Scheduling Supervisor as appropriate in accordance with existing
              procedures

       9.5 Planning and Scheduling
           • Initiate follow-up letters to customers at established intervals when no response is received
              after technicians leave a CGI Notice or no response is received to previous letters requesting
              access for inspection


     Revised              Revised                Revised                Revised                Revised
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                       OPERATING AND MAINTENANCE GENERAL PROCEDURES                                  OM - 96

 Operations &                  INSIDE SERVICE ATMOSPHERIC CORROSION
 Maintenance                         INSPECTIONAND LEAK SURVEY                                   Page 7 of 7


             •   Maintain database containing records of attempts to contact customers to schedule
                 inspections




     Revised                Revised               Revised                Revised               Revised
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