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					This document has been provided so that a standardized format would be available as an example of an AIHA Guideline. Its content is NOT intended to be used as a practice guideline. AIHA Guideline - 2009

Temporary Ventilation of Confined Spaces

Approved - 2009

American Industrial Hygiene Association

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This document has been provided so that a standardized format would be available as an example of an AIHA Guideline. Its content is NOT intended to be used as a practice guideline.

Foreword
{Any introductory information goes here. This section is not part of the guideline.}

Committee Members
Mike Harris, Ph.D., CIH Lindsay Booher, CIH, CSP Stephanie Carter, CIH

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This document has been provided so that a standardized format would be available as an example of an AIHA Guideline. Its content is NOT intended to be used as a practice guideline.
Zandra Walton, CIH

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This document has been provided so that a standardized format would be available as an example of an AIHA Guideline. Its content is NOT intended to be used as a practice guideline.
AIHA Guideline 2009

AIHA Guideline – Temporary Ventilation of Confined Spaces
1. Purpose  constantly changing environment that arises during repair work in confined spaces. In situations in which there are not enough openings for adequate ductwork or not enough space for a local exhaust duct for each welder, supplied air respiratory protection may be the only practical solution. However, supplied air respirator line entanglement is a real problem and should be avoided if feasible.

The purpose of this guideline is to summarize selected fundamentals for installing temporary mechanically-assisted ventilation for control of airborne contaminants during hotwork in confined spaces. Examples of successful ventilation applications are also provided. 2.
Scope

This guide applies to the temporary ventilation for hotwork in confined spaces. Examples in Appendix B are derived from ventilation of vessels in petrochemical plants but the concepts will be useful in virtually all facilities. This publication is not intended as a comprehensive guide to OSHA compliance nor is it designed to address topics such as metal fume and toxic gas health effects, heat stress, radiation, confined space entry procedures and lockout/tagout. The user is encouraged to review applicable standards before commencing work in any confined space. In addition to reviewing the procedures described herein, the reader should note the following cautions:  Field testing of airflow and personal air monitoring are strongly recommended to verify the efficiency of any exhaust system. Continuous monitoring of airborne exposures may be necessary due to the complex and

This guideline is intended for use by industrial hygienists, safety professionals, project supervisors, project planners, confined space entry supervisors (qualified persons) and others whose responsibilities include providing a healthful workplace with confined spaces. 3. Definitions & Abbreviations

For the purposes of this guideline document, the following terms and definitions apply. The AIHA "Glossary of Terms" should be referenced for any terms not defined in this section. 3.1 Axial fan: A fan in which the airflow from entry to exit is predominately parallel to the axis of rotation. Centrifugal fan: A fan in which the air is turned from parallel to the axis of rotation on entry to a direction tangential to the arc described by the tips of the rotating blades or vanes.

3.2

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This document has been provided so that a standardized format would be available as an example of an AIHA Guideline. Its content is NOT intended to be used as a practice guideline.
3.3 Confined Space: 3.3.1 A space that a) is large enough and so configured that an employee can bodily enter and perform assigned work; b) has limited or restricted means for entry or exit; and c) is not designed for continuous human occupancy. (See OSHA 1910.146). 3.3.2 An enclosure that contains an oxygen deficiency, where the oxygen concentration is less than 19.5%. Examples include storage vessels and tanks, process and reactor vessels, furnaces, boilers, drums, ventilation ducts, hoppers and manholes. 3.3.3 [29 CFR 1910.252 (c)] Spaces within which hotwork is being performed that meet any of the following three criteria: a). the work space is less than 16 feet high. B). the volume of the space is less than 10,000 cubic feet per welder, or c). the work areas contain/include partitions, structural barriers or other barriers that significantly obstruct air flow (such as baffles, trays, or limited access openings). 3.4 Eductors: Air powered devices, which use Venturi effects to move air. A device that withdraws a fluid by aspiration and mixes it with another fluid. 2. Using water, steam or air to induce the flow of other fluids from a vessel. Any nozzle or nozzle like device through which a fluid is forced into a chamber or passage. May sometimes be referred to as "air horns" or "air movers". 3.5 Grade D Breathing Air: Air that meets the requirements defined by the Compressed Gas Association Commodity Specification for Air (1989). 3.6 Hotwork: The process of thermal joining and cutting. Hotwork activities include torch cutting, all forms of welding, brazing and soldering and arc gouging. 3.7 Local exhaust devices: Lengths of flexible ducting connected to an air-moving device. 3.8 Makeup air: Outdoor air supplied to replace exhausted air brought through a ventilation system without previous circulation in the system. 3.9 Mechanical ventilation: The process of supplying and removing air by mechanical means to and from any space. 3.10 Natural ventilation - The movement of outdoor air into a space through openings or through non-powered ventilators or by infiltration. 3.11 Supplied air respiratory protection: A respirator that supplies the respirator user with breathing air from a source independent of the ambient atmosphere, and includes supplied-air respirators (SARs) and selfcontained breathing apparatus (SCBA) units. 3.12 Venturi: A constriction in a pipe, tube or flume consisting of a tapered inlet, a short straight constricted throat and a gradually tapered outlet; fluid velocity is greater and pressure is lower in the throat area than in the main conduit upstream or downstream of the venturi; it can be used to measure flow rate, or to draw another fluid from a branch into the main fluid stream. 4. Referenced Documents 1. Code of Federal Regulations (1996), 29 CFR Part 1910, Subpart 146 (Permit Required Confined Spaces). Washington, DC: Government Printing Office, Federal Register. 2. Code of Federal Regulations (1996), 29 CFR Part 1910, Subpart Welding, Cutting and Brazing – General Industry). Washington,

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This document has been provided so that a standardized format would be available as an example of an AIHA Guideline. Its content is NOT intended to be used as a practice guideline.
DC: Government Printing Office, Federal Register. 3. Code of Federal Regulations (1996), 29 CFR Part 1926, Subpart 353 (Ventilation and Protection in Welding, Cutting and Heating – Construction). Washington, DC: Government Printing Office, Federal Register. 4. Code of Federal Regulations (1996), 29 CFR Part 1910 Subpart 134 (Respiratory Protection). Washington, DC: Government Printing Office, Federal Register. 5. Significance & Uses 6. Ventilation Requirements Federal regulations establish several criteria for ventilating confined spaces for hotwork. The following OSHA criteria from the General Industry Standard 29 CFR 1910.252 (c) define spaces that require ventilation:    The work space is less than 16 feet high. The volume is less than 10,000 cubic feet per welder. Work areas where there are partitions, structural barriers or other barriers that significantly obstruct air flow (such as baffles, trays, or limited access openings).

Hotwork operations can result in the generation of a hazardous atmosphere in a confined space, even though that space may have been found safe for entry prior to beginning the work. Commonly found contaminants that may be generated during hotwork include contaminants from surface coating and residues such as:  Paint: Paints may contain lead and cadmium. Pyrolysis products may also be a concern.  Plating: Chemicals used in plating processes include chromium, nickel, copper and zinc.  Process residue: Sulfur compounds from sour crude or external sulfur accumulations in gasfired furnaces may be present.  Degreasers: The presence of fluorocarbons should cause particular concern.  Fluorides may be released when Shielded Metal Arc Welding is employed.
Note: no attempt has been made to identify all the chemicals that may be found in a space during all processes.

The same standard describes the following ventilation options:  Provide a least 2,000 cubic feet per minute (cfm) of airflow for each active welder. - OR  Provide each welder with a local exhaust device. These local exhaust device must be capable of maintaining a velocity of 100 feet per minute (fpm) toward the air intake.

This guide applies to the temporary ventilation for hotwork in confined spaces. However, ventilation alone may not be sufficient, especially when elevated concentrations of toxic metals may be present. Atmospheric testing and/or personal air monitoring is strongly recommended to ensure that the ventilation application is effective. The need for respiratory protection in addition to mechanical ventilation must be determined by the results of atmospheric testing and/or personal air monitoring for the contaminants of concern while the work is progressing in the confined space.

Air moving devices may be used to remove contaminants by pulling air out of a space or by pushing air into a space. Both of these methods will replace contaminated air with clean air and are equally acceptable as long as the air entering the confined space is of adequate quality. Replacement air should not be a source of airborne contaminants; those potentially present include:        Carbon monoxide from generators, air compressors and vehicles. Carbon monoxide and/or metal fumes from hotwork outside the vessel. Paint and cleaning solvent vapors. Silica from adjacent blasting operations. Lead from paint removal work. Asbestos or insulation work. Nearby process sources.

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This document has been provided so that a standardized format would be available as an example of an AIHA Guideline. Its content is NOT intended to be used as a practice guideline.
The OSHA General Industry and Construction standards [29 CFR 1910.252(c) and 29 CFR 1926.353(c)] require local exhaust ventilation or supplied air respiratory protection when performing hotwork in a confined space which involves the following substances:       Fluorine compounds - check fluxes and rod coatings. Zinc Lead Cadmium Mercury Beryllium - local exhaust and supplied air respirators are required. overcome, the less air is moved. If the air will not move as fast as the fan blades, the blades operate inefficiently. Airflow restrictions in confined spaces may include:  Equipment components in the confined space; e.g., brackets, trays, pipes.  Maintenance or construction materials erected in the confined space; e.g., tube and clamp scaffolds, scaffold boards, fire blankets.  Obstructions in the makeup air manway; e.g., attendant's body, weather enclosures around manways, local exhaust ducts, welding cables, and load-in and load-out operations.  Insufficient number of makeup air manways. It is best to have at least one makeup air manway for each air moving device.  Air hoses supplying the fans or eductors that are excessively long will cause a reduction in air pressure and volume delivered to these air moving devices. Reductions are also likely if numerous workers are using air-powered equipment driven by the same compressor. These factors can result in a reduction of air pressure at the air moving devices by as much as 50%.  Fans are often "hung" on vessel flanges with wire. The "short-circuiting" of airflow that results when air passes through the gap between the fan and the flange can be eliminated by securing the fan with a bolt and clamp. 8. Local Exhaust Ventilation (LEV)

The OSHA General Construction standard [29 CFR 1926.353(c)] requires local exhaust ventilation or supplied air respiratory protection when performing hotwork in a confined space which involves the following:   Chromium Stainless steels - when using inert gas metal arc (MIG) processes.

7. Mechanical Air Movement These are two types of widely used air moving devices for ventilating confined spaces: fans and venturi-type eductors. Fans are generally air or steam driven or electrically powered. Eductors are always air powered and rely on venturi-effects to move air. Centrifugal fans, which are generally electricallydriven, are designed to overcome higher static pressures than axial flow fans. Centrifugal fans are particularly useful for local exhaust systems which have static pressure losses due to long duct runs, tight bends, etc. Factors Affecting Air Moving Device Performance The more restrictions an air moving device must 7.1

When dilution ventilation will not be sufficient to remove the contaminants produced by hotwork, LEV may be a suitable means of controlling contaminant concentrations. Circumstances in which local exhaust would be appropriate include:

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This document has been provided so that a standardized format would be available as an example of an AIHA Guideline. Its content is NOT intended to be used as a practice guideline.
    Vessels in which only one manway has been opened for the hotwork operations. Confined spaces which do not offer a feasible way to attach an air moving device. Confined spaces with interior obstructions that may decrease ventilation effectiveness. Work with metals such as nickel, chromium, zinc, lead, beryllium, or cadmium. (Note: This is not an exhaustive list.) Instead of running many small ducts from an air moving device to the inside of the vessel, consider the use of a single large duct with a plenum or manifold to distribute the air within the vessel. When many welders work in a space at the same time, the installation of temporary local exhaust systems with a duct for each welder can be a challenge. Consider the following items:   Keep duct runs as short as possible. Long runs of duct reduce air flow. Air flow losses can be minimized by use of smooth ducting with large radius bends (elbows). However, flexible ducting is more commonly used for temporary ventilation systems. Flexible ducting tends to collapse at sharp bends, and this type of duct run should be as straight as possible.

Local exhaust is only effective when it captures and removes welding fumes and gases at the source as they are emitted during the hotwork process. Air velocity into the local exhaust inlet must be at least 100 fpm at the source of the fumes or gases to be effective and to comply with applicable OSHA standards. This usually requires that the inlet be placed within 12" (or less) of the source. The maximum acceptable distance from the hood intake to the arc/flame is a function of the duct diameter and the air flow through the duct (see Table 1). The values in the table assume that the duct is fitted with a simple flange (3" wide) around the duct inlet. If non-flanged hoods are used, 25% more cfm will be required to achieve the same capture distances. The use of flanges in all situations is difficult because flanged hoods may be awkward to handle in tight spaces. Flanges also tend to become bent or damaged due to rough handling. When many welders work in a space at the same time, the installation of temporary local exhaust systems with a duct for each welder can be a challenge. Consider the following items:   Keep duct runs as short as possible. Long runs of duct reduce air flow. Air flow losses can be minimized by use of smooth ducting with large radius bends (elbows). However, flexible ducting is more commonly used for temporary ventilation systems. Flexible ducting tends to collapse at sharp bends, and this type of duct run should be as straight as possible.

9. Bibliography
Confined Space Entry; An AIHA Protocol Guide American Conference of Governmental Industrial Hygienists (ACGIH): Industrial Ventilation, A Manual of Recommended Practice, 23rd ed. Cincinnati, OH: ACGIH, 1998. Talty, J.T. (ed): Industrial Hygiene Engineering: Recognition, Measurement, Evaluation, and Control, 2nd ed. Park Ridge, NJ: Noyes Publications, 1988. Advanced Industrial Hygiene Engineering, US DHHR, National Institute for Occupational Safety and Health, Cincinnati, Ohio, 1986. Guide to Occupational Exposure Values, American Conference of Governmental Industrial Hygienists, Cincinnati, Ohio, 1995 1995-1996 Threshold Limit Values and Biological Exposure Indices, American Conference of Governmental Industrial Hygienists, Cincinnati, Ohio, 1995 Welding Health and Safety Resource Manual, American Industrial Hygiene Association, Fairfax, VA,

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This document has been provided so that a standardized format would be available as an example of an AIHA Guideline. Its content is NOT intended to be used as a practice guideline.
1984.

Table 1 OSHA Local Exhaust Guidelines Taken from 29 CFR 1910.252
Distance from Arc Minimum Airflow Through Duct 150 cfm 275 cfm 425 cfm 600 cfm Duct Diameter

4" to 6" 6" to 8" 8" to 10" 10" to 12"

3" 3.5" 4.5" 5.7"

Note 1: 100 fpm velocity may not be adequate for situations with significant cross drafts or when the process creates high velocity air currents as would be the case with arc gouging.) Note 2: While some welders using inert gas shielded processes may protest that 100 fpm at the arc will adversely affect weld quality, field testing shows that this generally not the case. Exceptions to this generalization may include welding titanium and welding processes requiring the use of backing gases.

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This document has been provided so that a standardized format would be available as an example of an AIHA Guideline. Its content is NOT intended to be used as a practice guideline.
Appendix A: Measuring Airflow Through a Vessel Field measurement requires a pocket calculator, measuring tape and air velocity instrument. Calculations are made using the following formula: Q = VA Where: Velocity (V) in feet per minute (fpm) Area (A) in square feet (sq.ft.) For circular openings, the formula to derive A is A = pr2 Air flow (Q) in cubic feet per minute (cfm) is the quantity of air passing through a manway Measure the average makeup air velocity (in fpm) entering the vessel through each opening. Makeup air entering the vessel is measured because the air moving devices, when used to “pull” air through the vessel, usually make the exhaust air too turbulent for effective measurement. Note: When identifying and selecting intake air openings for airflow measurement, consider the possible effects of "short-circuiting" which may be present. If short-circuiting is suspected, it may be prudent to test the air flow pattern using smoke tubes to ensure that the 2,000 cfm per welder criterion is a appropriate for the situation under investigation. If short-circuiting is suspected but cannot be excluded, use of local exhaust ventilation is likely the better choice. Measure the largest openings first. Since most of the air will pass through the larger openings, they will account for the majority of the makeup air entering the vessel. If the confined space is supplied with pressurized makeup air (from portable air conditioners or heaters), pierce the flexible ducting to measure the air flow velocity and repair the hole with duct tape. Multiply the average airflow velocity for each opening by the cross-sectional area (in sq.ft.) of the opening to obtain the quantity of make-up air (in cfm) entering the confined space. Finally, add the makeup air quantities for each opening in the vessel. Note: The ACGIH Industrial Ventilation, A Manual of Recommended Practice recommends up to twenty measurements along two 10 point transects at 90 ° to each other. This document provides the details of accurate air velocity measurements which provide spacing for circular openings which will provide equal areas (Figure 9). For rectangular openings, 16 measurements are recommended (Figure 9). The average velocity may be calculated by averaging the measurements for a given opening.

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This document has been provided so that a standardized format would be available as an example of an AIHA Guideline. Its content is NOT intended to be used as a practice guideline.
Example #1: A single fan is mounted on a manway near the top of a vessel, and makeup air is entering through a manway (40" diameter) near the bottom of the vessel at an average velocity of 370 fpm. Determine the amount of make up air.
Determine the cross sectional area (A). Using the formula: A = r2 Radius = ½ diameter = 20" = 1.67' A = (3.1416)(1.67)2 = 8.7 ft2 Calculate the air flow (Q) in cfm: Using the formula: Q = VA Q = 370 fpm x 8.7 sqft = 3,245 cfm

In this example, 3,245 cfm dilution ventilation is supplied to the vessel. Remembering that one active welder is allowed for each 2,000 cfm dilution ventilation entering the confined space, only one welder may work in this space. Example #2: For the same space, if there is still one fan on the upper manway, but there are now two 40" manways available for makeup air. What is the amount of make-up air if the average velocity is 280 fpm through one manway and 310 fpm through the other?
The cross sectional area for the two 40" manways is 8.7 sq.ft. (See Example #1) The air flow in cfm: 280 fpm x 8.7 sqft = 2,456 cfm Plus 310 fpm x 8.7 sqft = 2,719 cfm Total: 5,175 cfm

In this example, 5,175 cfm dilution ventilation is supplied to the vessel and two welders may work simultaneously in this space.

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This document has been provided so that a standardized format would be available as an example of an AIHA Guideline. Its content is NOT intended to be used as a practice guideline.

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