Management of Change (MOC) – Interpreting the OSHA Regulations
The first challenge is to define a “covered process”. OSHA 1910.119 states that the process safety management regulations are applicable under the following circumstances:
- This section applies to the following:
- A process which involves a chemical at or above the specified threshold quantities listed in appendix A to this section;
- A process which involves a flammable liquid or gas (as defined in 1910.1200(c) of this part) on site in one location, in a quantity of 10,000 pounds (4535.9 kg) or more except for:
- Hydrocarbon fuels used solely for workplace consumption as a fuel (e.g., propane used for comfort heating, gasoline for vehicle refueling), if such fuels are not a part of a process containing another highly hazardous chemical covered by this standard;
- Flammable liquids stored in atmospheric tanks or transferred which are kept below their normal boiling point without benefit of chilling or refrigeration.
- This section does not apply to:
- Retail facilities;
- Oil or gas well drilling or servicing operations; or,
- Normally unoccupied remote facilities.
Certain words in paragraph (a) are augmented with definitions in paragraph
Atmospheric tank means a storage tank which has been designed to operate at pressures from atmospheric through 0.5 p.s.i.g. (pounds per square inch gauge, 3.45 Kpa).
Facility means the buildings, containers or equipment which contain a process.
Highly hazardous chemical means a substance possessing toxic, reactive, flammable, or explosive properties and specified by paragraph (a)(1) of this section.
Normally unoccupied remote facility means a facility which is operated, maintained or serviced by employees who visit the facility only periodically to check its operation and to perform necessary operating or maintenance tasks. No employees are permanently stationed at the facility.
Facilities meeting this definition are not contiguous with, and must be geographically remote from all other buildings, processes or persons.
Process means any activity involving a highly hazardous chemical including any use, storage, manufacturing, handling, or the on-site movement of such chemicals, or combination of these activities. For 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 Venn-diagram interpretation of the applicability of the PSM regulations appears in Figure 1.
The unshaded regions in Figure 1 represent exemptions from the PSM regulations. A process that isn’t covered by the PSM regulations is comparatively cheaper to operate since the cost of compliance with the PSM regulations is zero. So, there’s an obvious interest in clearly understanding when a process is covered and when it isn’t. While Figure 1 appears clear conceptually, whether a process is covered, or not, is often determined by nuances in the meaning of the words describing the regions. Numerous requests were made of OSHA to clarify the meaning of every concept listed in paragraph (a), above. What follows is a comprehensive compilation of comments from various Standards Interpretations issued by OSHA in the years beginning in 1992.
Some of the following discussion involves results of legal cases and judgments. In many instances OSHA lost its case. But losing a case often has more to do with semantics and legal process issues, than the validity of the underlying regulations. The following discussion emphasizes OSHA’s intent as much as possible, since understanding the intent of the PSM regulations is critical to implementing good process safety management.
Figure 1. Venn diagram illustrating the meaning of “covered process”. The shaded regions are covered processes; the unshaded regions are not covered processes according to OSHA 1910.119.
The notion of “process” is fundamental to any interpretation of the PSM standard.
The definition of “process” in §(b) includes many items: “use, storage, manufacturing, handling, or the on-site movement of such chemicals”. This becomes an issue when, for example, when the amount of chemical in storage and the amount of chemical in manufacturing are each less than the threshold amounts in Appendix A, but the total is greater than the threshold amount. An employer may wish to separate storage from manufacturing in order to avoid the necessity of PSM compliance. While it may be possible to enact sufficient barriers and controls to keep various uses separate, OSHA indicated that the employer has a substantial burden to demonstrate that different uses of the same chemical in a facility do not and cannot interact with each other.
Flammable liquids stored in “atmospheric tanks” are exempted by §(a)(1)(ii)(B), provided they are not connected to anything this isn’t just storage and transfer. Once tanks are connected to a usage that is beyond storage and transfer, then the tanks are included as part of the process. This is true regardless of the presence of valves or other controls that may be used to separate or direct fluid flows.
There may still be confusion regarding the boundaries of a process, for certain applications that are not really the focus of the PSM regulations, but still may be covered by the regulations (e.g. on-site final assembly of explosives immediately prior to use). In these cases, a process hazards analysis can be used to determine the scope of process coverage[5, 6].
(b) Process – “Interconnected”
b) continues with the concept of interconnectedness, “any group of vessels which are interconnected…shall be considered a single process.”
If several vessels are interconnected, and only one of them has greater than a threshold quantity of an HHC, then there’s high probability that all of the interconnected vessels would be considered a single process, and subject to PSM.
The connection between vessels need not be rigid piping. OSHA has interpreted each of the following to be a legitimate connection:
- “a closed double block and vent in a pipeline (that is, a pipeline containing two closed valves, between which is a vent which is open to the air)”, even though such an arrangement is considered an energy isolating device under lockout/tagout §1910.147(b) ,
- a temporary flex hose running between two vessels,
- a conveyor moving between two pieces of equipment, even if the equipment pieces are separated by a large distance, and even if the conveyed material is neither flammable nor an Appendix A material,
- a pipe used to supply a vessel, but which is removed when the process actually occurs.
This concept of “interconnected” is critical since utility systems (e.g. steam, plant air), which wouldn’t be covered by PSM in isolation, would likely be covered once connected to a covered process[9, 10]. This is reasonable since failure of a utility system may contribute to a catastrophic release, or inhibit the mitigation of a release once it occurred. A PHA may be used to determine which aspects of a utility system are to be covered by PSM.
It is conceivable that interconnected “aspects” of a process (e.g. downstream of the use of HHCs) do not contain any HHCs, nor could they contribute to a release, nor could they interfere with mitigating the consequences of a release elsewhere. The onus is on the employer to conduct a rigorous analysis demonstrating that an interconnected process aspect is not capable of contributing to a release or its consequences. This analysis does not provide a perpetual exemption, since changes in the plant may invalidate the analysis, thereby making those process aspects subject to the PSM standard.
(b) Process – Close Proximity
While it’s understandable that interconnected vessels may be involved in, or contribute to, a catastrophic release of HHCs, it’s also plausible that vessels that are located near each other may participate in a catastrophic release, simply due to their proximity even without being interconnected.
b) also includes the concept of close proximity, “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 number of interpretations supported the view that containers, vessels and piping in close proximity, which can contribute to a release of HHCs, are considered part of a single process[8, 14, 15].
It’s clear from this discussion about the meaning of the word “process”, that the PSM standard definition of “process” may differ dramatically from local notions of what the boundaries of a particular process are.
At the same time (1992) that the PSM regulation appeared in the Federal Register, the regulations covering explosives were modified to ensure that explosives manufacturing is covered by the PSM regulations, “The manufacture of explosives…shall also meet the requirements contained in §1910.119” .
The purpose of explosives is to…explode! So, it would be nonsensical for the “use” of explosives to be covered by PSM—and the use isn’t covered, just the manufacture.
Some confusion ensued, since neither 1910.109 nor 1910.119 make any reference to threshold quantities of explosives. OSHA responded that “the synthesis of chemicals to create any amount [emphasis mine] of explosives is considered to be explosives manufacturing and is covered by the PSM standard”[17, 18]. Other interpretations agree.
Manufacturing of explosive devices, not just explosive chemicals, is also covered by the PSM standard:
As a hypothetical example, an employer obtains an explosive device manufactured by another employer. This explosive device is a subassembly for a missile which is manufactured by the employer. Both employers must comply with the PSM standard.
A less dramatic example is the manufacture of automobile air bag inflation modules. These contain materials which are listed as Class B explosives by the Department of Transport, which are covered by the PSM standards. Consequently manufacture of these modules is subject to PSM standards.
In contrast, simply using explosive devices in the manufacture of products that are not intended to explode, e.g. automobiles, is not covered by the PSM standard. Similarly, in aircraft manufacture:
OSHA did not intend that the PSM standard apply to the installation of explosive devices, such as explosive bolts… ejection seat rocket motors … into larger finished products or devices that are not intended to explode. 
Repackaging explosives into, say, different size packages “is considered to be storage and handling activities [of explosives] which are not covered by the PSM standard”[23, 24]. It’s important that no further processing, mixing, blending or other changes take place for this exemption to hold[24, 25]. Explosives are handled quite differently than other HHCs since repackaging the latter actually is indeed regulated by the PSM standard.
(a)(1)(i) Highly hazardous chemicals
A number of inquiries have been made to OSHA regarding chemicals not on the list in Appendix A. Invariably OSHA’s response has been that if it’s not on the Appendix A list, then it’s not covered by §(a)(1)(i) of the PSM standard[27, 28].
Chemicals that are not listed in Appendix A may still present potential hazards. For instance, neither sodium hydrosulfite (powder) nor aluminum powder are in Appendix A, but a mixture of the two is very reactive with water. A fatal accident, involving this mixture and water that had leaked from a cooling system prompted OSHA to recommend, “A process safety analysis should be done for all materials with a catastrophic potential, even if they are not covered by the Process Safety Standard.”
(a)(1)(i) Highly hazardous chemicals – mixtures and solutions
Solutions of nine chemicals in Appendix A become subject to the PSM regulations when they exist in greater than prescribed concentrations. For example, hydrogen peroxide is subject to PSM if the concentration is greater than 52% by weight, and the amount is greater than 7,500 pounds. Below 52% concentration, any amount of hydrogen peroxide is permitted.
Many chemicals are procured in aqueous solution form. When the concentration to trigger coverage under PSM is not stated in the Appendix A, then the usual commercial concentration or reagent concentration applies, whichever is less.
Also, many of the highly hazardous chemicals listed in Appendix A of the PSM regulation are used in aqueous solution form. Although they may trigger PSM compliance (when used in greater than threshold quantities) in their unmixed form, they may not trigger PSM compliance in solution. Appendix A of the PSM regulation is quite explicit about when solutions of highly hazardous chemicals trigger PSM compliance[30-34]: e.g. “Ammonia solutions (> 44% by weight)”. Solutions of related chemicals, not listed in Appendix A, such as ammonium chloride, do not trigger the need for PSM compliance.
This effectively creates a “low concentration solution exemption.” But note that fluids may become flammable once in solution, in which case the Appendix A criterion (§(a)(1)(i) no longer governs whether the process is covered; instead, the flammable liquid or gas criterion, §(a)(1)(ii), governs whether the process is covered[32, 35].
When an HHC solution is identified in Appendix A, then the entire weight of the solution (including the water) is included when determining whether threshold quantities are exceeded.
A further complication arises when the aqueous solutions of HHCs are unstable, in the sense that the HHC will come out of solution (e.g. Chlorine dioxide in water) unless properly contained. In the event of a breach of the containment system, the HHC may come out of solution, and create a greater than threshold amount of HHC. The employer has an obligation to ensure that controls are in place to prevent this from happening, otherwise the process is subject to PSM regulations.
And finally, although an HHC in aqueous solution at concentrations below Appendix A limits and below commercial/reagent concentrations would not trigger PSM compliance due to dilution, it still may trigger PSM compliance if it’s a flammable or explosive mixture.