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Introduction To Arc Flash Hazard Requirements

VIEWS: 15 PAGES: 42

									     ICC Spring Meeting 2008 – Tradewinds Resort – 11 March 2008




                      Introduction To
Arc-Flash Hazard Requirements
         Of NFPA 70E
                               And
         Arc-Flash Calculation
                                Per
                    IEEE 1584a


Philip Cox, PE - Memphis Light, Gas And Water – Memphis, Tennessee
ICC Spring Meeting 2008 – Tradewinds Resort – 11 March 2008


                      Brief History Of NFPA 70E

                1976 A committee, “Electrical Safety 
                Requirements for Employee 
                Workplaces”, was formed with the 
                specific purpose to ʺassist OSHA in 
                preparing electrical safety standards that 
                would serve OSHAʹs needs.ʺ 

                1983 The third edition was published 
                and included parts 1 and 2 and a new 
                part 3 ‘Safety Related Maintenance 
                Requirements’.
ICC Spring Meeting 2008 – Tradewinds Resort – 11 March 2008


                     Brief History Of NFPA 70E

                1995 The fifth edition was published.  
                Major revisions included the concepts of 
                ‘Limits of Approach’ and ‘Flash 
                Protection Boundary’.

                2000 The sixth edition was published.
                Emphasis was placed on ‘Personal 
                Protection Equipment’ and a new part 4 
                ‘Safety Requirements for Special 
                Equipment’ was added. 
ICC Spring Meeting 2008 – Tradewinds Resort – 11 March 2008


                2004 (Seventh Edition)

                     Name change to ‘NFPA 70E, 
                     Standard for Electrical Safety in the 
                     Workplace’ ‐ Major changes 
                     emphasize safe work practices.

                     Since OSHA is about safety in the 
                     workplace, OSHA has started to 
                     emphasize 70E. Also, working on 
                     live parts was now considered to be 
                     ‘The last alternative work practice’.
                     Working on energized equipment 
                     now requires a ‘Work Permit’.
ICC Spring Meeting 2008 – Tradewinds Resort – 11 March 2008


                2004 (Seventh Edition)

                     NFPA 70E‐2004, Part II 2‐1.3.3 Flash 
                     Hazard Analysis.  “Flash hazard 
                     analysis shall be done before a 
                     person approaches any exposed 
                     electrical conductor or circuit part 
                     that has not been placed in an 
                     electrically safe work condition”.
ICC Spring Meeting 2008 – Tradewinds Resort – 11 March 2008

                Code Of Federal Regulations (OSHA)

                    29 CFR 1910.333 – “Live electrical 
                    parts that an employee may be 
                    exposed shall be de‐energized unless 
                    additional or greater hazards are 
                    introduced.”

                    29 CFR 1910.335 – “Employees 
                    working in areas where potential 
                    electrical hazards exist shall be 
                    provided with and shall use 
                    personal protective equipment.”

                    OSHA is citing NFPA 70E in injury 
                    investigation and fine assessment.
ICC Spring Meeting 2008 – Tradewinds Resort – 11 March 2008




Are The Requirements Of NPFA 70E and 
OSHA Valid Concerns From A 
Technical Standpoint Regarding Worker 
Safety?

Or, Are These Concerns Over‐Stated 
And “Just Make Getting Work Done”
More Difficult For the Employer And 
The Worker?
   ICC Spring Meeting 2008 – Tradewinds Resort – 11 March 2008


An Example:                     277/480V MLGW 
                                Network Transformer 
                                Vault With ~200kA Of 
                                Available Fault Current 
                                At Bus Connection

                                IEEE C57.12.44, Standard 
                                For Secondary Network 
                                Protectors, Requires A 
                                Fault Withstand For 1 
                                Second In Duration.

 How Much Energy Is That?
   ICC Spring Meeting 2008 – Tradewinds Resort – 11 March 2008


This  Much Energy Will Lift Which Of The 
Following Objects Approximately 27 Feet?




   A. This Coast Guard Helicopter (Wt)
     ICC Spring Meeting 2008 – Tradewinds Resort – 11 March 2008


This  Much Energy Will Lift Which Of The 
Following Objects Approximately 27 Feet?




B. Five (5) North American T6 “Texans” (Wt)
    ICC Spring Meeting 2008 – Tradewinds Resort – 11 March 2008


This  Much Energy Will Lift Which Of The 
Following Objects Approximately 27 Feet?

                          C. The Statue Of Liberty
                                (Not Including The Foundation, But
                                Including the Helicopter)
   ICC Spring Meeting 2008 – Tradewinds Resort – 11 March 2008


This  Much Energy Will Lift Which Of The 
Following Objects Approximately 27 Feet?

                            D. The Space Shuttle
                                At Maximum Take Off Weight
                                Including Two Solid Rocket Boosters
                                And A Full External Fuel Tank
   ICC Spring Meeting 2008 – Tradewinds Resort – 11 March 2008


This  Much Energy Will Lift Which Of The 
Following Objects Approximately 27 Feet?

                            D. The Space Shuttle
                           If You Said –

                             “D – The Space Shuttle”, 
                             Weighing Approximately  4.5 Million Pounds (f),

                               You Would Be Correct!


                           Helicopter – 13,000’; 5 ‐T6s – 4,300’; Statue Of Liberty – 270’
ICC Spring Meeting 2008 – Tradewinds Resort – 11 March 2008



     Should You Be Concerned?
ICC Spring Meeting 2008 – Tradewinds Resort – 11 March 2008



     Should You Be Concerned?




                     Yes !
   ICC Spring Meeting 2008 – Tradewinds Resort – 11 March 2008




Some “Not‐So‐Fun” Facts

  Electric Arcs Can Generate Temperatures Exceeding 
  35k°F (19k+°C)

  Copper Boils At 4650°F (2565°C)

  Vaporized Copper Expands By A Factor Of 67,000!
    ICC Spring Meeting 2008 – Tradewinds Resort – 11 March 2008




Some “Not‐So‐Fun” Facts

A 50 kA Arc Fault Can Create:

   Sound Pressure Levels  Of 165 dB

   Pressure Waves Can Exceed More Than 3,600 Lbs/Ft2
   Which Can Propel A Worker Several Feet!
   ICC Spring Meeting 2008 – Tradewinds Resort – 11 March 2008




Some “Not‐So‐Fun” Facts

  Shrapnel And Molten Metal Are Propelled At 
  Velocities Greater Than 700 MPH

  There Are ~30,000 Non‐Fatal Electrical Shock 
  Accidents Per Year

  There Are ~1000 Fatalities Per Year Due To 
  Electrocution 

  ~2000 People Require Treatment At Burn Centers 
  Due To Arc Flash Burns
   ICC Spring Meeting 2008 – Tradewinds Resort – 11 March 2008




So What Is Required ?

  Training
  ‐ Provided By The Employer
  ‐ Implemented By The Employee
  ‐ Classroom & “On The Job”
  ‐ Includes Documentation Of Training
                      (Chapter 1 ‐ General Requirements)
ICC Spring Meeting 2008 – Tradewinds Resort – 11 March 2008



Employer Required To Establish An 
Electrical Safety Program
   The intention is to instill safety principles and 
   controls, and prevent injury and death.

   Any time an employee is near any exposed live 
   parts that operate at greater than 50 volts, a 
   hazard/risk evaluation procedure must be done.

   If live parts are not de‐energized, work can only be 
   performed by written permission.

   And, the obvious, lockout‐tagout procedures shall 
   be followed when working on dangerous 
   equipment.
   ICC Spring Meeting 2008 – Tradewinds Resort – 11 March 2008


General Philosophy Of Mitigation Of 
Injuries Due To Arc Flash Hazards

  De‐Energize Equipment Whenever Possible

  When It Is Not Possible To De‐Energize Equipment, 
  Limit Arc Energy To The Worker By:

     Reducing Available Fault Current
     Reducing Arc Time
     Increasing Distance From Arc Fault
     Use Appropriate  Levels Of PPE
     Use Arc Blankets/Barriers
     Use Equipment Designed To Mitigate Arc Flash 
    ICC Spring Meeting 2008 – Tradewinds Resort – 11 March 2008


Mitigation By PPE

   The Intent Of The Appropriate PPE Level Is To 
   Limit Burns To (Curable) Second Degree Burns 
   With A 95% Survival Rate.

   It Does Not Attempt To Prevent Injuries Completely

   Second Degree Burns Can Result At A Skin 
   Temperature Of 80°C (176°F) Exposure For 0.1s, 
   Approximately 1.2 Calories/Cm2

   Third Degree Burns Can Result At a Skin 
   Temperature Of 95°C (203°F) Exposure For 0.1s
         ICC Spring Meeting 2008 – Tradewinds Resort – 11 March 2008


Hazard/Risk Levels & PPE

     Typically Arc‐Flash Energy Is Described By 
     Calories/Cm2, or Joules/Cm2
Hazard/Risk       Arc‐Flash (Energy) Rating Of PPE      Typical FR Clothing 
 Category                  [Calories/Cm2]                 Requirements

     0                          < 2                       Untreated Cotton
     1                          < 4                      FR Shirt & FR Pants
                                                     Cotton Underwear, FR Shirt 
     2                          < 8
                                                             & FR Pants
                                                     Cotton Underwear, FR Shirt, 
     3                          < 25
                                                      FR Pants & FR Coveralls
                                                     Cotton Underwear, FR Shirt, 
                                                       FR Pants, Double Layer 
     4                          < 40
                                                      Switching Coat & Double 
                                                       Layer Switching Pants
    ICC Spring Meeting 2008 – Tradewinds Resort – 11 March 2008


Typical Risk/Hazard Category 2

                          Face Shield ‐ Eye Protection

                          Balaclava – Face, Neck, Ears, Etc.

                          8 Cal/Cm2 Coveralls ‐
                                      W/FR Shirt & Pants

                          Heavy Duty Insulated Leather 
                          Work Boots
    ICC Spring Meeting 2008 – Tradewinds Resort – 11 March 2008


Typical Risk/Hazard Category 3

                              Face Shield/Arc Flash Hood 
                              – Eyes, Face, Neck, Ears, Etc.

                              25+ Cal/Cm2 Coveralls ‐
                              ‐ W/FR Shirt & Pants

                              Heavy Duty Insulated 
                              Leather Work Boots
    ICC Spring Meeting 2008 – Tradewinds Resort – 11 March 2008


Typical Risk/Hazard Category 4


                                Face Shield/Arc Flash Hood 
                                – Eyes, Face, Neck, Ears, Etc.

                                40+ Cal/Cm2 Coveralls ‐
                                ‐ W/FR Shirt & Pants

                                Heavy Duty Insulated 
                                Leather Work Boots
    ICC Spring Meeting 2008 – Tradewinds Resort – 11 March 2008



Approach Boundaries
    ICC Spring Meeting 2008 – Tradewinds Resort – 11 March 2008


Approach Boundaries
                            1. Flash Protection Boundary

                                     An approach limit at a 
                                     distance from exposed 
                                     live parts within which 
                                     a person could receive a 
                                     second degree burn.
    ICC Spring Meeting 2008 – Tradewinds Resort – 11 March 2008


Approach Boundaries
                           2. Limited Approach Boundary

                                     An approach limit at a 
                                     distance from exposed 
                                     live part within which a 
                                     shock hazard exists.
    ICC Spring Meeting 2008 – Tradewinds Resort – 11 March 2008


Approach Boundaries
                        4. Restricted Approach Boundary

                                     An approach limit at a 
                                     distance from exposed 
                                     live part within which a 
                                     increased risk of shock, 
                                     due to electrical arc over 
                                     combined with 
                                     inadvertent movement, 
                                     for personnel working 
                                     in close proximity to a 
                                     live part.
    ICC Spring Meeting 2008 – Tradewinds Resort – 11 March 2008


Approach Boundaries
                        4. Prohibited Approach Boundary

                                     An approach limit at a 
                                     distance from exposed 
                                     live part within which 
                                     work is considered the 
                                     same as making contact 
                                     with the live part.
ICC Spring Meeting 2008 – Tradewinds Resort – 11 March 2008
    ICC Spring Meeting 2008 – Tradewinds Resort – 11 March 2008


Determination Of Hazard/Risk Category

   HRC For Typical Worker Areas & Tasks Can Be 
   Found In NFPA 70E – Table 130.7(C)(9)(a)
      ICC Spring Meeting 2008 – Tradewinds Resort – 11 March 2008


Determination Of Hazard/Risk Category
   Or Can Be Calculated By Various Methods In IEEE 
   1584, Such As:
    ICC Spring Meeting 2008 – Tradewinds Resort – 11 March 2008


Determination Of Hazard/Risk Category

   Flash Protection Boundary Can Also Be Calculated 
   By Methods In IEEE 1584, Such As:
ICC Spring Meeting 2008 – Tradewinds Resort – 11 March 2008


                NFPA 70 (National Electrical Code)
                110.16 ‐ Flash Protection. Switchboards, 
                panelboards, industrial control panels, 
                meter socket enclosures, and motor 
                control centers that are in other than 
                dwelling occupancies and are likely to 
                require examination, adjustment, 
                servicing, or maintenance while 
                energized shall be field marked to 
                warn qualified persons of potential 
                electric flash arc hazards. The marking 
                shall be located so as to be clearly 
                visible before examination, adjustment, 
                servicing, or maintenance of equipment.
        ICC Spring Meeting 2008 – Tradewinds Resort – 11 March 2008



                    Required Marking




ANSI Z535
        ICC Spring Meeting 2008 – Tradewinds Resort – 11 March 2008


                      Work Permit
            Must include At Least These 11 Items

1. A description of the circuit and equipment to be worked 
   on and their location.
2. Justification of why the work must be performed in an 
   energized condition.
3. A description of the safe work practices to be employed.
4. Results of the shock hazard analysis.
5. Determination of the shock protection boundaries.
6. Results of the flash hazard analysis.
         ICC Spring Meeting 2008 – Tradewinds Resort – 11 March 2008


                     Work Permit
           Must include At Least These 11 Items

7. The Flash Protection Boundary.
8. The necessary personal protection equipment (PPE) to 
   safely perform the assigned task.
9. Means employed to restrict the access of unqualified 
   persons from the work area. 
10. Evidence of completion of a job briefing, including a 
    discussion of job‐specific hazards.
11. Energized work approval by safety officer, 
    management, owner.
     ICC Spring Meeting 2008 – Tradewinds Resort – 11 March 2008




   Job Briefing & Checklist
Identify: The hazards, the voltage levels, skills required, other 
voltage sources, unusual work conditions, number of people 
needed, shock and flash protection boundaries, available 
incident energy, and any other information that might be 
relevant.

Ask: Can the equipment be de‐energized? Are backfeeds
possible? Is a standby person required? Any other pertinent 
questions.

Check: Job Plans, single line diagrams and other prints, safety 
procedures, vendor information, special conditions that might 
exist at your facility.  
     ICC Spring Meeting 2008 – Tradewinds Resort – 11 March 2008




   Job Briefing & Checklist
Know: What the job is, who is in charge, and who else might 
need to know what is going on.

Think: About unexpected events, Lock out ‐ Tag out – Test, and 
TEST again, Install grounds, install barriers, and think about 
what is going on.  Be present, because electricity can be 
dangerous.

And finally, prepare for an emergency: Is a CPR person 
available?  Is emergency equipment available?  Where are the 
fire extinguishers?  Where are the shut off devices located?  Is
there a two way radio available?  Can you dial 911?
ICC Spring Meeting 2008 – Tradewinds Resort – 11 March 2008




                       End

								
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