OSHA's highly hazardous chemical list: does your shop qualify?

Last updated 2026-07-11

What is OSHA's highly hazardous chemical list?

OSHA's highly hazardous chemical list is Appendix A to 29 CFR 1910.119, the Process Safety Management (PSM) standard. It names 137 chemicals, each paired with a threshold quantity (TQ) in pounds. When a process at your facility holds a listed chemical at or above that threshold, PSM applies. The compliance load that follows is heavy.

OSHA promulgated the list in 1992 alongside the PSM rule itself ^[1]. It covers three kinds of dangerous substances: toxics (chlorine, ammonia, hydrogen cyanide), flammables (propane, hydrogen, ethylene oxide), and reactives (allyl chloride, trimethylamine). Some chemicals are on the list because of catastrophic accidents. The 1984 Bhopal disaster, which killed thousands after a methyl isocyanate release, pushed U.S. process safety regulation forward ^[2].

There's also a separate clause at 29 CFR 1910.119(a)(1)(ii) covering flammable liquids and gases at 10,000 pounds on-site in a process. This one catches substances that never appear by name: large propane systems, natural gas handling, fuel-oil storage tied to a covered process.

Don't confuse this list with HazCom (GHS) under 29 CFR 1910.1200, which covers hazard communication for basically every chemical in your workplace. PSM is a separate, far more demanding standard built for large inventories with catastrophic-release potential. You can have flawless HazCom compliance and zero PSM obligation. You can also trigger PSM with a single tank of the wrong substance.

Which 137 chemicals are on the OSHA PSM list, and where can I find them?

The full list lives in Appendix A of 29 CFR 1910.119, free on OSHA's website ^[1]. Here's a representative sample with thresholds, because the numbers swing wildly from one chemical to the next.

Chemical	TQ (lbs)	Common industrial use
Ammonia (anhydrous)	10,000	Refrigeration, agriculture
Chlorine	1,500	Water treatment, chemical mfg
Hydrogen	10,000	Welding, fuel cells
Hydrogen cyanide	1,000	Chemical synthesis
Hydrogen fluoride	1,000	Metal pickling, petrochemical
Propylene oxide	10,000	Plastics, sterilization
Ethylene oxide	5,000	Sterilization, plastics
Methyl isocyanate	250	Pesticide manufacturing
Phosgene	500	Chemical manufacturing
Sulfur dioxide (anhydrous)	1,000	Refrigeration, paper mfg
Vinyl chloride	5,000	PVC manufacturing
Trimethylamine	10,000	Fishing, chemical synthesis

Methyl isocyanate, the Bhopal chemical, carries the lowest threshold on the list at 250 pounds. Phosgene sits at 500. Chlorine at 1,500 pounds is a common trigger for water treatment plants and pool chemical suppliers.

Flammable liquids and gases not named individually get a blanket TQ of 10,000 pounds under the general flammables clause. Store more than 10,000 pounds of propane in a single connected process and you're covered, even though propane never appears by name in Appendix A.

Look up the exact CAS numbers in Appendix A, because chemical naming is sloppy. "Ammonia" by itself can mean several forms. OSHA lists anhydrous ammonia at 10,000 pounds. Aqueous ammonia solutions are a different animal, and some concentrations get handled under EPA's RMP rule instead ^[3].

How do I know if my shop hits a threshold quantity?

The test is easy to state and harder to run. For each process at your facility, add up the maximum amount of each Appendix A chemical that could be present at one time. If that total meets or beats the listed TQ, PSM applies to that process.

The word "process" carries most of the weight. OSHA defines it at 29 CFR 1910.119(b) as "any activity involving a highly hazardous chemical including any use, storage, manufacturing, handling, or on-site movement of such chemicals, or combination of these activities." Two tanks physically connected, or two tanks where a failure in one could affect the other, count as one process ^[4]. That framing catches people off guard. You can't split a 12,000-lb ammonia system into two 6,000-lb "systems" on paper and call yourself under the 10,000-lb TQ.

A few things drop out of the calculation. Retail facilities (selling to end consumers) are exempt. Normally unoccupied remote facilities are exempt. Fuel used in a non-process context, like the propane running your forklift fleet in a separate area, generally doesn't count toward a manufacturing process TQ. That last one gets genuinely tangled, and OSHA's letters of interpretation address specific fact patterns ^[4].

Here's a practical first pass for most small shops:

1. Pull your chemical inventory (your SDS binder, or whatever backs your hazard communication program). 2. Cross-reference each chemical against Appendix A of 1910.119 by CAS number, not by name. 3. For any match, check your maximum on-hand quantity in a single connected process against the listed TQ. 4. For flammables not on the list, sum the maximum pounds in a connected system and compare to 10,000.

If you're anywhere near a threshold, get an independent process safety professional to review before you make a coverage call. The penalty stakes are too high to guess.

What shops are most likely to trigger PSM coverage?

Few small shops trigger PSM. The ones that do are usually surprised. Here's where the risk piles up.

Refrigeration-heavy operations are a leading trigger. Ammonia refrigeration at 10,000 lbs (roughly 1,600 gallons of anhydrous ammonia) is one of the most common PSM triggers in food processing, cold storage, and large commercial HVAC. A mid-sized cold storage warehouse can hold that easily. Thousands of ammonia refrigeration systems are covered nationally, and OSHA runs a National Emphasis Program aimed straight at them ^[5].

Water and wastewater plants using chlorine gas get caught often. A single one-ton chlorine cylinder holds 2,000 pounds, so one cylinder already tops the 1,500-lb TQ. Switching to sodium hypochlorite (liquid bleach) is a big reason many small water systems dropped chlorine gas. The liquid form isn't on Appendix A at typical use concentrations.

Agriculture and co-ops handling anhydrous ammonia for fertilizer are on the list too. A 10,000-lb nurse tank is a standard size. Store or handle that at one location as part of a connected process and you qualify.

Chemical distributors and manufacturers are the obvious candidates. So is a plastics shop with a large ethylene oxide sterilizer, a semiconductor fab using hydrogen fluoride, or a paper mill using sulfur dioxide.

Who almost never qualifies: auto repair shops, restaurants and commercial kitchens, small fabrication shops, most construction sites, and general retail. Their quantities are too small. Lockout/tagout and HazCom are your standards there, not PSM.

What does OSHA PSM compliance actually require if I qualify?

PSM is one of OSHA's most demanding standards. The 14 elements of 29 CFR 1910.119 read like a full management system:

1. Process Safety Information (PSI): documented info on hazards, technology, and equipment 2. Process Hazard Analysis (PHA): systematic team review of hazards (HAZOP, What-If, and similar) 3. Operating Procedures: written, current, and accessible to employees 4. Training: initial and refresher training on the PSI and procedures 5. Contractors: pre-qualification, on-site safety practices, and injury tracking for contract workers 6. Pre-Startup Safety Review: for new or modified processes 7. Mechanical Integrity: inspection and testing programs for critical equipment 8. Hot Work Permit: controlled ignition source management 9. Management of Change: formal review before any process modification 10. Incident Investigation: root cause analysis of incidents 11. Emergency Planning and Response: tied to 29 CFR 1910.38 12. Compliance Audits: at least every three years, with retained findings 13. Trade Secrets: access rules for employees and contractors 14. Employee Participation: written plan for worker involvement

Building a PSM program from scratch for a newly covered process usually takes months and often needs outside consultants. The three-year compliance audit isn't optional; the standard requires it. OSHA's PSM inspection procedures are detailed, and they produce real citations even for well-meaning employers who miss documentation requirements ^[6].

Willful or repeat PSM violations can run up to $161,323 per violation as of the 2025 penalty schedule ^[7]. When a process safety incident kills someone, criminal referrals are possible under the OSH Act's general provisions.

If your shop is edging toward a PSM threshold, weigh whether process redesign beats building a full program. Cutting inventory, switching to a safer substitute, or reengineering to stay under the TQ can be more practical than the whole PSM apparatus. That's not dodging the rules. That's inherently safer design, and OSHA treats it as legitimate.

Is the EPA's RMP list the same as OSHA's PSM list?

No, and confusing the two costs money. The EPA's Risk Management Program (RMP) rule at 40 CFR Part 68 has its own list of regulated substances with its own thresholds ^[3]. The two programs overlap a lot but don't match.

Roughly 77 of OSHA's 137 PSM chemicals also appear on EPA's RMP list, but the threshold quantities sometimes differ. Flammable substances sort into EPA's Program 1, 2, or 3 tiers differently than they hit OSHA's single PSM threshold. Some chemicals are on EPA's list but not OSHA's, and the reverse.

Trigger OSHA PSM and you very likely trigger EPA RMP too. Facilities that trip both face inspections from two federal agencies under two enforcement regimes. The paperwork overlaps enough that many facilities build one integrated PSM/RMP program, but the obligations stay legally distinct.

EPA updated the RMP rule in 2024 with new requirements around accident prevention and safer technology and alternatives analysis (STAA) for Program 3 processes ^[3]. Those changes add to the EPA side even when OSHA PSM stays put.

For most small businesses, the first question is whether you trigger either rule at all. Once you know you do, the integrated-versus-separate documentation question belongs to an environmental health and safety (EHS) attorney or a process safety engineer, not to a weekend spreadsheet.

What are the OSHA penalties if I'm covered and not compliant?

OSHA raises its penalty caps every year for inflation. For 2025, the maximum per serious violation is $16,131. Willful or repeat violations reach $161,323 each ^[7]. PSM inspections routinely turn up multiple violations, so total exposure from one inspection climbs into six figures fast.

OSHA runs a National Emphasis Program (NEP) for PSM facilities, which means inspectors trained in process safety run targeted inspections at covered sites ^[5]. These aren't casual walk-arounds. They go straight to your Process Hazard Analysis documentation, your mechanical integrity records, and your management of change logs. Documentation gaps get penalized even when nothing has blown up.

The failure OSHA sees most in small covered facilities isn't malice. It's not knowing they were covered in the first place. That's cold comfort when the citation lands.

The general duty clause (Section 5(a)(1) of the OSH Act) can also reach chemical hazards that fall short of a TQ but still count as recognized serious dangers. Falling just under a threshold doesn't buy you immunity if conditions at your facility present a clear and recognized hazard.

Not sure whether you're covered? Request a free OSHA consultation through your state's On-Site Consultation Program. A consultation visit doesn't trigger enforcement, and it can't produce a citation. Contact information is on OSHA's website ^[8].

How does PSM relate to other OSHA chemical safety standards?

PSM sits at the top of OSHA's chemical safety stack. Below it are standards that reach far more workplaces.

Hazard communication (29 CFR 1910.1200) applies to nearly every workplace that touches a chemical. It requires Safety Data Sheets (SDS), container labeling, and employee training. A shop with one bottle of acetone needs HazCom. PSM is a separate obligation that only fires at the Appendix A thresholds.

Substance-specific standards under 29 CFR 1910 Subpart Z cover individual chemicals at lower exposure levels. Asbestos (1910.1001), benzene (1910.1028), formaldehyde (1910.1048), and lead (1910.1025) each carry their own permissible exposure limits, monitoring, and medical surveillance rules. They apply whether or not PSM is triggered.

The Hazardous Waste Operations and Emergency Response (HAZWOPER) standard at 29 CFR 1910.120 covers workers in hazardous waste cleanup and emergency response. If a PSM-covered facility also handles hazardous waste or runs an emergency response team, HAZWOPER training stacks on top of PSM.

For small shops holding chemicals well below PSM thresholds, put your energy into a solid HazCom program, reliable SDS access, good engineering controls, and appropriate PPE. That combination handles the vast majority of chemical hazards a typical small business faces. If you want an organized starting point for the written program side, SafetyFolio's safety program generator can build a HazCom and chemical safety program in a structured way without the PSM overhead.

One number for scale: OSHA estimates roughly 250,000 workers at about 30,000 U.S. facilities are covered by PSM ^[1]. That's a thin slice of the workforce, so most readers here won't qualify. If you do, it matters enormously.

How do I do a basic self-audit to determine PSM applicability?

Start with a plain chemical inventory audit. The initial screening doesn't need a consultant. It needs honesty about what you actually have.

First, list every chemical in your facility by CAS number. Your SDS files for HazCom already carry CAS numbers, so this data should exist. If it doesn't, your HazCom program has a hole to patch before you worry about PSM.

Second, compare each CAS number to Appendix A of 29 CFR 1910.119 ^[1]. OSHA publishes the full list online. For any match, record the listed threshold quantity.

Third, figure the maximum quantity of each Appendix A chemical your facility could hold in a single connected process. Use purchase records, tank capacities, and piping diagrams, more than what happens to be on hand today. TQ calculations run on maximum inventory, not average.

Fourth, run the same analysis for flammable liquids and gases not on Appendix A against the 10,000-lb generic flammable threshold.

Fifth, write down your findings and keep them. If you conclude you're not covered, that conclusion has to hold up if OSHA ever asks. A simple spreadsheet with CAS number, maximum quantity, applicable TQ, and your determination beats no record at all.

If any chemical sits at 50% or more of its TQ, treat it as a near-miss and ask whether process changes are worth it. PSM thresholds don't graduate. The standard applies or it doesn't. But creeping toward a threshold with no plan is exactly how facilities get blindsided after an expansion or a new contract.

For broader OSHA compliance, including what OSHA covers and how inspections run, a grounding in the basics saves time. Good incident report and recordkeeping habits feed your PSM compliance too, since incident investigation is one of PSM's 14 required elements.

What does OSHA say about flammable liquids and the 10,000-pound threshold?

The flammable liquid and gas provision at 29 CFR 1910.119(a)(1)(ii) stretches PSM coverage past the 137 named chemicals. It reaches any flammable liquid or gas with a flash point below 100 degrees F, or any flammable gas, held in a process above 10,000 pounds ^[1].

That definition sweeps in a lot of everyday materials: propane, natural gas, butane, pentane, and more. A propane storage system with several tanks manifolded together clears 10,000 lbs without much trouble. At roughly 4.2 lbs per gallon of liquid propane, a 2,400-gallon system crosses the line.

OSHA has issued letters of interpretation on what counts as a "process" for flammables. The question that decides it is whether separate vessels are interconnected or interdependent enough that a release from one could affect another ^[4]. Tanks on a common header are generally one process. Tanks physically separated and used in fully independent operations are more likely to be treated separately, but get that determination in writing if you're relying on it.

LPG dealers who fill customer cylinders operate differently than a manufacturer with a stationary propane system. Retail facilities are explicitly exempt from PSM at 29 CFR 1910.119(a)(2)(i), though the definition of retail gets murky when a distributor also blends or manufactures on site.

If flammables are your main concern, the National Fire Protection Association's NFPA 58 (LP gas) and NFPA 55 (compressed gases) govern storage quantities and separation distances independent of OSHA PSM ^[11]. Those fire code limits can kick in at far lower quantities than the 10,000-lb TQ, so they may be the binding constraint even for shops that never hit PSM coverage.

What training do employees need if we're covered by PSM?

PSM's training requirements at 29 CFR 1910.119(g) are specific and documented. Every employee who operates a covered process must be trained on an overview of the process and its operating procedures before being assigned to it. They have to understand the safety and health hazards, emergency operations including shutdown, and safe work practices ^[10].

Refresher training is required at least every three years, or sooner if a review says so. The employer has to document each employee's training and the means used to verify the employee understood it. That verification piece trips people up. Sign-in sheets aren't enough. You need evidence of comprehension: a written test, a practical demonstration, or a signed acknowledgment that goes past mere attendance.

Contractors working on or near a covered process get their own requirements under 29 CFR 1910.119(h). The employer has to evaluate contractor safety programs, document contractor injuries and illnesses during on-site work, and make contractors aware of fire, explosion, and toxic release hazards tied to the job.

For general chemical safety training outside PSM, OSHA training in HazCom, emergency response, and PPE use is required no matter your PSM status. An OSHA 30 course for supervisors covers the regulatory framework across standards, which is useful context even though it won't stand in for PSM-specific training.

Building out your overall training infrastructure? SafetyFolio's safety program generator can map which standards apply to your workforce and create the written program foundation your training sits on.

Are there exemptions that might exclude my facility from PSM even if I have listed chemicals?

Yes. OSHA wrote several exemptions into 29 CFR 1910.119(a)(2), and they matter for shops on the boundary.

Retail facilities are exempt. OSHA defines retail as a facility that sells highly hazardous chemicals mostly to end users for personal or business consumption, not for resale. A hardware store selling propane cylinders to homeowners is retail. A distribution center selling propane in bulk to other businesses for resale generally isn't.

Normally unoccupied remote facilities are exempt. A small chemical storage depot that's unstaffed except for periodic visits may qualify, depending on the facts. OSHA has defined "normally unoccupied" through letters of interpretation, and the exemption is narrow ^[4].

Oil and gas well drilling and servicing operations are exempt. That one matters for oilfield services companies.

Flammable liquids stored in atmospheric tanks, or transferred, and kept below their normal boiling point without chilling or refrigeration are also excluded under 29 CFR 1910.119(a)(1)(ii)(B). This is the ambient-storage exclusion for flammables, and it pulls a lot of ordinary fuel storage out of PSM.

Hydrocarbon fuels used solely as fuel are generally excluded too, which is why the propane feeding your space heaters or forklifts usually doesn't count unless it's part of a covered manufacturing process.

These exclusions interact in non-obvious ways. A grain operation drying with direct-fired propane burners fed by a large tank might argue the fuel exclusion applies. Whether it does turns on whether the propane system counts as a "process" under PSM definitions. This is exactly the kind of question where an OSHA letter of interpretation, or a call to a process safety professional, saves you from an expensive mistake.

Frequently asked questions

Where can I find the full OSHA highly hazardous chemical list?

The complete list of 137 chemicals with threshold quantities is in Appendix A of 29 CFR 1910.119, free on OSHA's website. Search '1910.119 Appendix A' on osha.gov, or find it in the Electronic Code of Federal Regulations at ecfr.gov. The list includes CAS numbers for each substance, which is the most reliable way to match chemicals in your facility.

Does my auto body shop or welding shop qualify for PSM?

Almost certainly not. Auto body and welding shops don't store chemicals anywhere near OSHA's PSM thresholds. Acetylene cylinders, paint solvents, and welding gases in shop-scale quantities fall well short of the 1,500 to 10,000-lb thresholds. Your chemical compliance focus belongs on HazCom (SDS binder, labeling, training), respiratory protection if needed, and proper flammable storage per NFPA 30.

Does PSM apply to anhydrous ammonia on a farm or at an agricultural co-op?

It can. Anhydrous ammonia has a TQ of 10,000 lbs under Appendix A. A single standard nurse tank holds about 1,000 gallons, roughly 5,000 lbs, so two connected tanks could top the threshold. Agricultural retail facilities selling ammonia to farmers may qualify for the retail exemption, but co-ops that store and distribute large quantities need to check carefully. OSHA has pursued PSM citations against agricultural facilities.

What's the difference between OSHA PSM and EPA RMP?

Both regulate highly hazardous chemicals at threshold quantities, but they come from different agencies with different lists and thresholds. OSHA PSM protects workers (29 CFR 1910.119); EPA RMP protects the surrounding community (40 CFR Part 68). Many facilities trigger both, and EPA updated its RMP rule in 2024 with stricter requirements. The compliance documents overlap, but they're legally separate obligations enforced by separate agencies.

Do threshold quantities apply to the whole facility or just one process?

The TQ applies per process, not per facility. OSHA defines a process as any activity involving a highly hazardous chemical, including physically connected or interdependent equipment. Two separate, independent processes at one facility get evaluated separately. But two tanks on a common piping header are typically one process, so you can't split systems on paper to slip under the TQ.

Can I avoid PSM by keeping quantities just under the threshold?

Managing inventory to stay below a TQ is legal if it reflects real operations. But it has to be genuine. OSHA looks at the maximum inventory that could be present, not the average. If your process design needs more chemical than you're claiming, you can't just say you'll never fill the tank past a certain level without engineering controls or procedural limits that are verifiable and enforced.

What is OSHA's National Emphasis Program for PSM?

OSHA's PSM National Emphasis Program (NEP) directs targeted inspections at covered facilities, especially refining, petrochemicals, and refrigeration. Inspectors trained specifically in process safety run these. The NEP (CPL 03-00-010) focuses on program quality, more than whether documents exist. Facilities in covered industries should expect harder inspections than a routine compliance check.

How often does OSHA inspect PSM facilities?

OSHA doesn't publish a fixed inspection frequency for PSM facilities, but covered sites under the NEP get prioritized scheduling. Beyond programmed NEP inspections, any complaint, referral, or incident at a covered facility triggers a visit. Separately, the PSM standard itself requires the employer to run a compliance audit at least every three years, which is distinct from OSHA enforcement.

What happens if I discover my facility should have been under PSM but wasn't?

Self-disclosure lands better than OSHA finding the gap during an inspection. Contact your state OSHA On-Site Consultation Program first; that visit is confidential and citation-free. Then build a plan to reach compliance, document it, and move forward. Hiding the situation or ignoring it carries far greater risk than fixing it head-on. An EHS attorney can help with voluntary disclosure if needed.

Are compressed gas cylinders at my shop counted toward PSM thresholds?

It depends on what's in them and how they're used and connected. A single chlorine cylinder at 150 lbs sits below the 1,500-lb TQ. Ten interconnected chlorine cylinders on a common manifold could tell a different story at 1,500 lbs total. Cylinders held for retail sale and not consumed in a manufacturing process may fall under the retail exemption. Evaluate each case against the process definition and the applicable TQ.

Does PSM apply to construction sites?

PSM (29 CFR 1910.119) is a general industry standard and doesn't directly apply to construction work governed by 29 CFR Part 1926. OSHA can still cite construction employers under the General Duty Clause for recognized chemical hazards. And if a construction project involves a covered process at a PSM facility, the facility's contractor provisions at 1910.119(h) reach the construction firm's workers.

What does a Process Hazard Analysis (PHA) actually involve?

A PHA is a structured team review of a covered process to find hazards, weigh the consequences of failures, and recommend safeguards. Common methods include HAZOP (hazard and operability study), What-If analysis, Failure Mode and Effects Analysis (FMEA), and fault tree analysis. The team must include at least one person with engineering experience in the process and one worker with hands-on process experience. PHAs must be updated at least every five years.

What's the cheapest legitimate way to start PSM compliance for a small covered facility?

Start with Process Safety Information: gather all existing documentation on chemical hazards (SDS files), process technology, and equipment specs. You likely already hold much of it for HazCom and maintenance. Then hire a qualified process safety engineer for the Process Hazard Analysis, the element most likely to need specialized skill. OSHA's free On-Site Consultation can flag gaps before you spend on full program development.

Sources

1. OSHA, 29 CFR 1910.119 Process Safety Management of Highly Hazardous Chemicals (including Appendix A): Appendix A lists 137 highly hazardous chemicals with threshold quantities; the PSM standard was promulgated in 1992; OSHA estimates roughly 250,000 workers at about 30,000 U.S. facilities are covered
2. U.S. Chemical Safety and Hazard Investigation Board, Bhopal background: The 1984 Bhopal disaster, involving methyl isocyanate, accelerated development of U.S. process safety regulation
3. EPA, Risk Management Program (RMP) Rule, 40 CFR Part 68: EPA's RMP list has its own regulated substances and thresholds distinct from OSHA's PSM list; the rule was updated in 2024 with new STAA requirements
4. OSHA, Letters of Interpretation on the PSM standard, 29 CFR 1910.119: OSHA interprets connected or interdependent equipment as a single process, and addresses retail, remote-facility, and fuel-use exemptions through letters of interpretation
5. OSHA, National Emphasis Program for PSM Covered Facilities, CPL 03-00-010: OSHA's PSM NEP targets covered facilities including ammonia refrigeration systems with specially trained inspectors
6. OSHA, Process Safety Management enforcement and inspection procedures: OSHA's PSM inspections review PHA, mechanical integrity, and management of change records and produce citations for documentation gaps
7. OSHA, Penalties (2025 penalty schedule): Maximum penalty per serious violation is $16,131; willful or repeat violations reach $161,323 per violation as of 2025
8. OSHA, On-Site Consultation Program for small businesses: OSHA's free On-Site Consultation Program provides confidential safety reviews that cannot result in citations
9. OSHA, PSM Standard 29 CFR 1910.119(g) Training requirements: PSM requires initial training before assignment to a covered process and refresher training at least every three years with documented verification of comprehension
10. NFPA, NFPA 58 Liquefied Petroleum Gas Code: NFPA 58 governs LP gas storage and separation distances, which can apply at lower quantities than OSHA's 10,000-lb PSM threshold