“It’s very hard for all of us, when we’ve committed ourselves to a particular interpretation, to change our minds.”  — Donald Johanson

We were recently asked if a steam boiler was a PSM-covered process. The answer seemed obvious. No, steam boilers, themselves, are not covered under the Occupational Safety and Health Administration’s Process Safety Management (PSM) standard (29 CFR 1910.119). But not wanting to leave it at that, we clarified. “Some steam boilers might need to be included within the boundaries of a PSM-covered process.”

The problem with that clarification is how useless it is as a practical matter. If a boiler might need to be included, then it might not need to be included. What do you do with “maybe”?

When Is A Boiler Absolutely, Certainly, Unambiguously Not Covered Under PSM?

A steam boiler is never covered under the PSM standard when it is in a facility that otherwise does not have a process covered by the PSM standard. So, a boiler in an office building that supplies the steam for space heating is not covered.

A boiler at a manufacturing plant that does not use or store any of the listed toxics in Appendix A of the standard, or any flammable liquid or gas? Not covered.

A boiler in a chemical process that uses or stores both toxics listed in Appendix A and flammable liquids, but none more than the threshold quantity (TQ)? Not covered.

Our confidence in these assertions comes from paragraph (a) of the standard, where it tells us that the standard applies to a process involving a chemical at or above the TQs listed in Appendix A (water is not one of those listed toxic chemicals) or a process involving more than 10,000 pounds of flammable liquids with a flash point less than 100°F or Category 1 flammable gases. A typical liquid fuel for boilers is fuel oil. The most volatile, Fuel Oil No. 1, is formulated to avoid being covered, with a flash point in the range of >100°F to 162°F, so it is not covered. Neither is Fuel Oil No. 2, No. 4, or No. 6, all of which have even higher flash points.

Natural gas, on the other hand, which is almost pure methane, is a Category 1 flammable gas. However, no boiler, even the biggest in the world, will ever contain more than 10,000 pounds of natural gas in its combustion chamber. That much natural gas is over 237,000 standard cubic feet.

The Fuel Exception

To further make the case is the hydrocarbon fuel exception, also in paragraph (a). This states that hydrocarbon fuels (fuel oil and natural gas, for example, but not ethanol) used solely for workplace consumption as a fuel are an exception to the application of the PSM standard.

But there is an exception to the exception:

“…if such fuels are not a part of a process containing another highly hazardous chemical covered by this standard.” High hazardous chemicals (HHCs)—those listed in Appendix A or flammable chemicals—are only covered if they exceed the TQ of that chemical in the process. So, the standard is saying that there is a fuel exception except when the fuel is used in an otherwise covered process.

We’ve always understood the exception to the exception to mean that there is not an exception when a hydrocarbon used as a fuel is also used as a reactant in a process. But that is a matter of interpretation, and OSHA gets to interpret its own regulations, at least until a judge says their interpretation is not supported by the language of the regulation. And even then, another judge may later determine that the first judge was “egregiously wrong from the start”.

The Definition of a Process

The real sticking point in this world of “maybe” is OSHA’s (and by extension, the EPA’s) definition of a process. To refresh, a process is any use, storage, manufacturing, handling, or the on-site movement of chemicals, or combination of these activities. By this definition, warehousing is a process. The regulatory definition of a process goes on to say:

“For the purposes of this definition, any group of vessels which are interconnected and separate vessels which are located such that a highly hazardous chemical could be involved in a potential release shall be considered a single process.”

A boiler that is not used in a covered process but is close enough to a covered process that a failure of the boiler could potentially result in the release of a hazardous chemical would be considered part of the process, and so would be covered under the PSM standard.

As for the interconnectedness of boilers and the processes they heat, OSHA addressed that early in one of their PSM letters of interpretation. It’s important to note that all of OSHA’s standard interpretations are preceded by this statement:

OSHA requirements are set by statute, standards and regulations. Our interpretation letters explain these requirements and how they apply to particular circumstances, but they cannot create additional employer obligations. This letter constitutes OSHA’s interpretation of the requirements discussed. Note that our enforcement guidance may be affected by changes to OSHA rules. Also, from time to time we update our guidance in response to new information. To keep apprised of such developments, you can consult OSHA’s website at https://www.osha.gov.

On January 8, 1993, Roger A. Clark wrote that “applicability of the PSM standard is determined with respect to each worksite, on a site by site basis.” But then it went on to toss out the idea of a “site-by-site” determination by categorically stipulating that a “boiler used to provide heat to a process covered by the PSM Standard is considered part of the covered process.” There. Settled. There was no discussion of whether the boiler was fired, a waste-heat recovery steam generator, or electrically heated, or whether it presented any hazard of a potential release of a highly hazardous chemical.

The AkzoNobel Letter

A few years later, however, OSHA issued a memorandum of interpretation about the limits or boundaries of covered process. Known as the AkzoNobel interpretation, John B. Miles wrote on February 28, 1997, that employers can determine the boundaries of a covered process by performing a three-step analysis. To paraphrase, the three steps consist of

  1. Begin by considering all vessels that are interconnected and separate vessels that are co-located as a single process.
  2. Determine whether this single comprehensive process contains at any particular time a quantity of an HHC that exceeds the TQ.
  3. Include any aspect of the single process that contains the HHC as part of the covered process. Aspects of the single process that do not contain the HHC but could cause a release of an HHC or interfere with mitigating the consequences of an HHC release are also part of the covered process. Otherwise, they are not.

Not so settled, then. The newer interpretation requires and allows a site-by-site determination by the employer. That said, however, OSHA hasn’t relegated its older, January 8, 1993, letter of interpretation to the archives.

When Is A Boiler Absolutely, Certainly, Unambiguously Covered Under PSM?

A steam boiler is always covered under the PSM standard when it is located immediately adjacent to a process covered by the PSM standard, such that a failure at the boiler could potentially result in the release of an HHC.

A steam boiler is always covered under the PSM standard when the steam is directly in contact with a process covered by the PSM standard, for example for sparging, purging, inerting, or as a reactant. This is true, whether the boiler is adjacent to the process or not.

A steam boiler is always covered under the PSM when the steam provided by the boiler is required to either keep the process in a safe state or to take the process to a safe state in the event of a dangerous process upset.

Other Situations Require Analysis

Whether you rely on the 1993 guidance – a “boiler used to provide heat to a process covered by the PSM Standard is considered part of the covered process” – or the 1997 guidance – interconnected equipment that “cannot cause a HHC release or interfere with the mitigation of the consequences of a HHC release, and the equipment does not itself contain a TQ or greater amount of a HHC, then such equipment could safely be considered outside the limits or boundaries of the covered process” will determine whether your boiler is part of a covered process or not.

What to Do?

A steam boiler is not a PSM-covered process, but it may be a part of a PSM-covered process. First, however, there must be a PSM-covered process. With that as a starting point, you will not need to justify including the boiler within the boundaries of your PSM-covered process. OSHA inspectors are not going to challenge such a conservative approach.

On the other hand, if you want to exclude your boiler from the boundaries of your PSM-covered process, then it will be on you to document your justification for excluding it.


  • Mike Schmidt

    With a career in the CPI that began in 1977 with Union Carbide, Mike was profoundly impacted by the 1984 tragedy in Bhopal and has been working on process safety ever since.