A lot of PSM/RMP covered processes utilize ventialtion as an engineering control within the process. And if this is the case, then OSHA and EPA require the facility to have supporting documentation to show that the ventilation will do what it it intended to do.
Here is what OSHA stated in a 2003 LOI…
…You requested clarification of the documentation requirements for “Ventilation system design,” described under 29 CFR 1910.119(d)(3)(i)(E), at these facilities: 1) natural gas compression and/or processing facilities; 2) anhydrous ammonia terminals including pressure vessel storage; 3) natural gas liquid (NGL) terminals including pressure vessel storage; and 4) gasoline/diesel terminals, including tank storage.
Scenario: You included the following proposals to meet the requirements:
1. Where ventilation is used to declassify or alter the Electrical Area Classification (EAC) of a building, the company EAC standard (currently API 500) should be documented as the design basis of the ventilation. The documentation should include all assumptions and calculations used.
2. Where a hydrocarbon process is housed within a building, the building should be ventilated and the design basis for the ventilation must be documented. The documentation should include what code or standard was used as the design basis as well as all assumptions and calculations. A process would include, but is not limited to pumps, piping, and/or storage of flammable liquids or NGLs. Ventilation may be mechanical or natural (vents and louvers).
3. The code or standard must be appropriate and supportable for the process in question. Some examples are:
1. “Structure or Building Ventilation,” NFPA 58, 2001 Edition, Section 7.2.2, could be supported as appropriate for buildings at the end of the propane terminals.
2. “Ventilation,” NFPA 30, 2000 Edition, Section 5.3.4, could be supported as appropriate for buildings at most Refined Products facilities.
3. “Building Ventilation,” Williams Gas Pipelines Standard For Compressor Facility Design (FDS-1, Issue #1), Section 5.2.4, could be supported as appropriate for buildings at gathering facilities.
EXCEPTIONS:
1. NGL Sample Containers: So long as the total weight of NGLs stored in a building in sample containers awaiting shipment is less than 300 pounds, no ventilation requirements exist for these containers. (See NFPA 58, 2001 Edition, Section 5.3.2.1.)
2. Refined Products Sample Bottles: So long as the total volume of Refined Products stored in a building in sample containers awaiting shipment is less than 10 gallons, no ventilation requirements exist for these containers. (See NFPA 30, 2000 Edition, Section 4.5.5.3.)
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4. Where an ammonia process is housed within a building, the building should be ventilated and the design basis for the ventilation must be documented. A process would include, but not be limited to, refrigeration, pumping, piping, and/or storage. Ventilation may be mechanical or natural (vents and louvers). The code or standard must be appropriate and supportable for the process in question. For example, the International Institute of Ammonia Refrigeration (IIAR) Bulletin 111, “Guidelines for Ammonia Machinery Room Ventilation,” 1992 Edition, could be supported as appropriate for buildings housing ammonia refrigeration processes.
Also, NFPA states the following when using ventialtion to declassifiy an area that would otherwise be a HAZLOC:
3.3.1 Adequate Ventilation. A ventilation rate that affords either 6 air changes per hour, or 1 cfm per square foot of floor area, or other similar criteria that prevent the accumulation of significant quantities of vapor–air concentrations from exceeding 25 percent of the lower flammable limit.
5.4 Unclassified Locations.
5.4.1 Experience has shown that the release of ignitible mixtures from some operations and apparatus is so infrequent that area classification is not necessary. For example, it is not usually necessary to classify the following locations where combustible materials are processed, stored, or handled:
(1) Locations that have adequate ventilation, where combustible materials are contained within suitable, well-maintained, closed piping systems
(2) Locations that lack adequate ventilation, but where piping systems are without valves, fittings, flanges, and similar accessories that may be prone to leaks
(3) Locations where combustible materials are stored in suitable containers
(4) Locations where the use of combustible liquids, or flammable liquids or gases, will not produce gas or vapor sufficient to reach25 percent of the lower flammable limit (LFL) of that combustible material.
5.4.2 Locations considered to have adequate ventilation include the following:
(1) An outside location
(2) A building, room, or space that is substantially open and free of obstruction to the natural passage of air, either vertically or horizontally. (Such areas could be roofed over with no walls, could be roofed over and closed on one side, or could be provided with suitably designed windbreaks.)
(3) An enclosed or partly enclosed space provided with ventilation equivalent to natural ventilation. (The ventilation system must have adequate safeguards against failure.)
5.4.3 Open flames and hot surfaces associated with the operation of certain equipment, such as boilers and fired heaters, provide inherent thermal ignition sources. Electrical classification is not appropriate in the immediate vicinity of these facilities. However, it is prudent to avoid installing electrical equipment that could be a primary ignition source for potential leak sources in pumps, valves, and so forth, or in waste product and fuel feed lines.
5.4.4 Experience indicates that Class IIIB liquids seldom evolve enough vapors to form ignitible mixtures even when heated, and are seldom ignited by properly installed and maintained general-purpose electrical equipment.
5.4.5 Experience has shown that some halogenated liquid hydrocarbons, such as trichloroethylene; 1,1,1-trichloroethane; methylene chloride; and 1,1-dichloro-1-fluoroethane (HCFC-141b), which do not have flash points, but do have a flammable range, are for practical purposes nonflammable and do not require special electrical equipment for hazardous (classified) locations.