PSM Boundaries

Applying sound process safety practices beyond the regulatory boundary is often smart. However, calling everything “PSM” can create unnecessary obligations, muddy the actual boundary, and weaken the program. The critical distinction is:

• PSM-covered: legally subject to 29 CFR 1910.119.

• PSM-managed: voluntarily controlled using some or all PSM principles.

• Safety-critical support: may not contain an HHC but can cause, prevent, or mitigate an HHC release—and therefore may actually fall within relevant PSM requirements.

OSHA coverage is determined by the physical and functional facts, not by what the company calls the equipment. Voluntarily putting an asset on a “PSM equipment list” does not automatically make it legally covered. Conversely, labeling equipment “non-PSM” does not exclude it if it is interconnected, sufficiently co-located, or capable of causing or worsening an HHC release.

How the boundary is actually determined

Under OSHA’s definition, the covered process includes:

• Activities involving an HHC or Category 1 Flammable Liquid or Gas at or above the threshold quantity.

• Interconnected vessels and equipment.

• Separate, co-located vessels that could be involved in the same potential release.

• Non-HHC aspects that could cause an HHC release or interfere with prevention or mitigation.

OSHA’s current enforcement guidance describes a three-part analysis:

1. Identify interconnected and potentially interacting co-located equipment.

2. Determine whether the resulting process contains a threshold quantity.

3. Evaluate non-HHC aspects to determine whether their failure could cause a release or impair mitigation.

For example, nitrogen inerting, instrument air, cooling, electrical supply, control systems, SIS/ESD equipment, relief disposal, or fire protection may require PSM treatment even though those systems do not contain the covered chemical. OSHA specifically uses nitrogen inerting as an example. OSHA’s 2024 PSM enforcement directive (Scenario B-14).

A valve, double block and bleed, shutdown procedure, alarm, or other active control generally cannot be used to declare interconnected equipment outside the process. OSHA presumes that interconnected equipment can participate in a release. Passive physical separation can sometimes support a separate-process determination for otherwise unconnected equipment. OSHA boundary interpretation

The risk of indiscriminately applying PSM

Indiscriminately applying PSM to non-covered equipment can blur the actual regulatory boundary, create unnecessary audit findings, overload the MOC system, inflate inspection and action-item backlogs, and divert resources from equipment that presents true catastrophic risk. When nearly every change or asset is treated as PSM-critical, employees may begin viewing PSM as excessive paperwork, weakening engagement and compliance where it matters most. Overly broad internal procedures and equipment designations can also create conflicting records, unintended corporate obligations, and evidence that the company recognized specific hazards or adopted standards it did not consistently follow.

For equipment that is actually covered, OSHA can enforce the internal standards the employer selected or adopted, to include your RAGAGEPs. OSHA’s guidance expressly discusses citations when an employer fails to follow its selected internal standard or inspection practice. OSHA RAGAGEP enforcement guidance

That does not mean every voluntary rule for non-covered equipment becomes enforceable under PSM. It means careless terminology and poorly written scope statements can make the company’s position much harder to defend.

The better structure

I use three clearly documented categories:

1. Regulatory PSM-covered process

   Subject to every applicable requirement of 1910.119.

2. PSM-critical support equipment

   Equipment or systems whose failure could cause, prevent, or worsen an HHC release. Apply the relevant elements for PHA analysis, PSI, MOC, MI, testing, training, or procedures, based on function.

3. Non-covered high-hazard equipment

   Managed under a separate company process safety or operational risk standard. The company can still use PHAs, MOC, PSSR, MI, incident investigation, or emergency planning without representing that OSHA PSM coverage exists.

Companies should also distinguish the regulatory boundary from the PHA study boundary. A PHA should consider utilities, external events, adjacent equipment, human actions, and off-boundary hazards. OSHA specifically expects PHAs to consider those factors. Studying an external hazard does not necessarily mean every external asset becomes covered, although equipment that can cause or interfere with mitigation may be part of the covered process. OSHA PSM rulemaking explanation

My bottom-line position is:

Be broad in hazard analysis, precise in regulatory boundary determination, and selective in applying lifecycle controls.

The biggest mistake is not being conservative. It is using “PSM” as a generic synonym for “important equipment” and then losing the ability to explain what is legally covered, what is functionally critical, and what is voluntarily managed.