Flammable liquids and gases don't have to appear on Appendix A to trigger PSM. Under 29 CFR 1910.119(a)(1)(ii), a process is covered if it involves a Category 1 flammable gas or a flammable liquid with a flashpoint below 100 °F (37.8 °C) in a quantity of 10,000 pounds or more on site in one location. Two exceptions apply: hydrocarbon fuels used solely for workplace consumption as a fuel, and flammable liquids stored in atmospheric tanks or transferred while kept below their normal boiling point without chilling or refrigeration. Most coverage questions come down to two things these letters answer: what gets added together toward the 10,000-pound threshold, and how far the atmospheric storage exception really reaches.
What OSHA Has Said
Jun 6, 2024
Pre-charged air conditioners stored in warehouses
Rheem asked whether a warehouse holding pre-charged air conditioners and heat pumps, charged with A2L refrigerants that meet the Category 1 flammable gas definition, is a PSM process. OSHA said yes once the refrigerant in co-located units totals 10,000 lb. Storage and forklift movement are covered activities, and units close enough to be involved in the same release, such as a building fire, are aggregated. OSHA also restated that sprinklers and administrative controls may not be considered when setting process boundaries.
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Jun 28, 2019
Aerosol cans in a distribution center
A warehouse stored consumer aerosol cans (shaving cream, hair spray) with butane, isobutane, and propane propellants. OSHA held the small amounts in each can must be aggregated across co-located cans, and if the total exceeds 10,000 lb it is a PSM-covered process. Compliance with NFPA 30B and the fire code does not decide coverage, but those codes can serve as RAGAGEP once covered. OSHA also said short periods when inventory dips below the threshold do not eliminate coverage unless the employer controls inventory below it.
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Dec 19, 2018
Upstream facilities that recover natural gas liquids
OSHA's 2000 enforcement stay for oil and gas production does not cover facilities that recover natural gas liquids, such as mechanical refrigeration units, JT plants, or stabilizers upstream of a gathering system. Those are in an industry code included in the original PSM rulemaking, so OSHA will enforce PSM where they contain 10,000 lb or more of flammable gases or liquids. OSHA also pointed operators to EPA's RMP rule.
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Jun 4, 2018
Positive displacement pumps in flammable liquid service
Writing to a Fluor engineer, OSHA explained that the atmospheric storage exception is limited to tanks and transfer piping not connected to a process or process vessel, so it does not cover pumps feeding a process. OSHA also said a Safety Instrumented System designed to ANSI/ISA-84.00.01 (IEC 61511) is acceptable in place of the pressure relief 1910.106 requires on PD pumps, treated as a de minimis violation, while ordinary non-SIS interlocks are not.
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Sep 9, 1993 · Archived
LPG, nearby tanks, and the atmospheric storage exception
A nine-question letter on an aerosol filling operation. Key points: LPG over 10,000 lb feeding a filling building is covered; nearby atmospheric flammable liquid tanks become part of the process if an incident in the LPG process could reasonably involve them, assuming the event happens despite PSM controls; atmospheric tanks with feeder connections to a process are covered, while bulk transfer terminals without them are not; mixing, blending, and on-site movement remove the storage exception. OSHA also confirmed that dilute solutions such as 30% hydrochloric acid are not covered as anhydrous hydrogen chloride.
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⚡ Key Compliance Takeaway
The flammables threshold is 10,000 pounds of Category 1 flammable gas or flammable liquid with a flashpoint below 100 °F, not just what's on Appendix A. Add up everything that is interconnected or close enough to be involved in the same release, including small containers on warehouse racks, and do not count on sprinklers or procedures to shrink the boundary. The atmospheric storage exception only covers storage and transfer to storage. Once a tank feeds a process, or the material is mixed, blended, or moved on site, assume PSM applies.
