Does OSHA PSM Apply to Your Facility?

By the Aetso Technical engineering team · Reviewed November 2026 · 8 min read

OSHA's Process Safety Management standard, 29 CFR 1910.119, applies to processes, not to entire companies. Determining whether a process is covered is the first, and one of the most consequential, decisions in a PSM program. This article summarizes the main tests; the regulation and OSHA's interpretations govern.

Test 1: Highly hazardous chemicals (Appendix A)

A process is covered if it involves a chemical listed in Appendix A of the standard at or above its threshold quantity (TQ). Appendix A lists well over one hundred toxic and reactive chemicals. Examples include anhydrous ammonia (10,000 lb), chlorine (1,500 lb), and hydrogen fluoride (1,000 lb). Concentration matters for some entries; for example, aqueous ammonia solutions are listed only above a stated concentration.

Test 2: Flammable liquids and gases

A process is also covered if it involves 10,000 pounds or more of a flammable liquid or gas on site in one location, except:

• Hydrocarbon fuels used solely for workplace consumption as a fuel (for example, propane for comfort heating or gasoline for vehicle refueling), if they are not part of a process containing another highly hazardous chemical covered by the standard; and
• Flammable liquids stored in atmospheric tanks or transferred, which are kept below their normal boiling point without benefit of chilling or refrigeration.

Exempt facilities

The standard does not apply to retail facilities, oil or gas well drilling or servicing operations, or normally unoccupied remote facilities.

What is a "process"?

PSM defines a process broadly: any activity involving a highly hazardous chemical, including use, storage, manufacturing, handling or on-site movement, or a combination of these. Interconnected vessels, and separate vessels located such that a highly hazardous chemical could be involved in a potential release, are considered a single process. This is why the aggregation of inventories across tanks, piping and equipment matters so much in the calculation.

A practical determination process

1. Inventory chemicals

   List every hazardous material on site, with maximum intended inventory and concentration.

2. Screen against Appendix A and flammability criteria

   Check each material against the list and flammable definitions.

3. Define process boundaries

   Identify interconnections and co-located equipment that could be involved in a single release.

4. Aggregate quantities

   Sum inventory within each process boundary, including piping and equipment holdup.

5. Apply exemptions and exceptions

   Document the basis for any exclusion carefully.

6. Document the determination

   Record assumptions, so the determination can be revisited when inventories or equipment change.

PSM and EPA RMP

EPA's Risk Management Program rule (40 CFR Part 68) has its own list of regulated substances and thresholds, which differ from PSM's. A process can be covered by one, both or neither. Processes subject to PSM that exceed RMP thresholds are generally Program 3 under RMP. See our RMP page, including the current status of RMP rulemaking.

When to revisit applicability

• Inventory increases, new storage or new raw materials
• New interconnections between previously separate systems
• Acquisition of a facility or change in operations
• Changes in regulation or OSHA interpretation