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.

June 6, 2024

Allison Skidd
Sr. Manager, Global Regulatory Affairs
Rheem Manufacturing Company
1100 Abernathy, Ste. 1400
Atlanta, GA 30328

Dear Allison Skidd:

Thank you for your inquiry to the Occupational Safety and Health Administration (OSHA) regarding aggregating the weight of a Category 1 flammable gas in equipment on site in one location and compliance with OSHA’s Process Safety Management (PSM) Standard, 29 CFR § 1910.119. This letter constitutes OSHA's interpretation only of the requirements discussed and may not be applicable to any questions not delineated within your original correspondence. Your paraphrased scenario, questions, and OSHA’s response are below:

Background: On May 6, 2021, the Environmental Protection Agency (EPA) published a Final Rule listing R‒452B, R‒454A, R‒454B, R‒454C, and R‒457A as acceptable substitutes, subject to use conditions, for use in residential and light commercial air conditioning and heat pumps.1 These refrigerants are flammable and are classified as belonging to ANSI/ASHRAE Standard 34 safety group A2L.2 The listed substitutes are refrigerant blends; Section 6.1.3 of the ANSI/ASHRAE Standard 34 requires the LFL of refrigerant blends to be measured at 73.4 °F [23.0 °C] and 14.7 psia [101.3 kPa]. These refrigerant blends meet the definition of a Category 1 flammable gas in Section 1910.119(a)(1)(ii).

In the manufacturing plant, after assembly of the mechanical components, refrigerant is charged to an air conditioner or heat pump. These pre-charged pieces of air conditioners and heat pumps are then stored in a warehouse or a distribution center before shipment to customers. Such pieces of pre-charged air conditioners and heat pumps are unconnected but co-located.

Question: Is the storage of pre-charged air conditioners and heat pumps in a warehouse or distribution center subject to OSHA’s PSM Standard, 29 CFR § 1910.119, if the aggregate weight of the refrigerant, a flammable gas, in the stored pre-charged equipment on the premises exceeds the threshold quantity (TQ) of 10,000 pounds?

Response: Yes. For the reasons listed below, what you describe is a PSM-covered process.

Section 1910.119(a) Application states that the PSM standard applies to:

A process which involves a Category 1 flammable gas (as defined in 1910.1200(c)) or a flammable liquid with a flashpoint below 100°F (37.8°C) on site in one location, in a quantity of 10,000 pounds (4535.9 kg) or more except for...

  1. A process
    Section 1910.119(b) defines a "process" as "any activity involving a highly hazardous chemical (HHC) including any use, storage, manufacturing, handling, or the on-site movement of such chemicals, or combination of these activities." In the warehouse or a distribution center there is a covered activity, such as storage and on-site movement (e.g., forklifts moving pre-charged pieces of air conditioners and heat pumps). This meets the definition of a process.

  2. which involves a Category 1 flammable gas (as defined in 1910.1200(c)) or a flammable liquid with a flashpoint below 100 °F (37.8 °C)
    The PSM standard refers to the definition of "flammable gas" in 29 CFR § 1910.1200(c). The Hazard Communication standard, 29 CFR § 1910.1200, defines flammable gas as "a gas having a flammable range with air at 20°C (68 F) and a standard pressure of 101.3 kPa (14.7 psi)." Appendix B states that Category 1 flammable gases are:

    Gases, which at 20°C (68°F) and a standard pressure of 101.3 kPa (14.7 psi):
    (a) are ignitable when in a mixture of 13% or less by volume in air; or
    (b) have a flammable range with air of at least 12 percentage points regardless of the lower flammable limit.

    The refrigerants you describe are Category 1 flammable gases which are PSM-covered HHCs.

  3. on site in one location
    The definition of "process" in the PSM standard, includes any "separate vessels which are located such that a HHC could be involved in a potential release".3 OSHA intended for the PSM standard to apply to "vessels in close proximity such that the release of an HHC in one could trigger a chain reaction in the others."4 A single process containing a TQ of an HHC includes a co-located process and is subject to the PSM requirements. For co-located equipment to be considered a PSM-covered process, there must be a reasonable probability that an event such as an explosion or fire would affect unconnected equipment which contain at least a TQ of HHC. In general, unconnected equipment must be evaluated by the employer to determine if they would interact during an incident, and if such a reasonable condition exists these vessels would be included in the boundaries of PSM-covered process.5

    When determining PSM coverage and the extent of the process, an employer may not consider engineering controls such as sprinkler systems and administrative controls.6,7

    Based on your description that the pieces of equipment are co-located, there is a reasonable probability that a fire in the warehouse or distribution center could result in a release of HHC contained in the separate equipment. The co-located equipment described in your scenario would therefore meet the PSM standard’s definition of a "process."8

  4. in a quantity of 10,000 pounds (4535.9 kg) or more
    The aggregated quantity of flammable gas exceeds the TQ of 10,000 pounds.

  5. except for
    No PSM exemptions apply in the scenario described.

In your letter, you noted potential contradictions between interpretations. The referenced interpretations are not contradictory as they both state that HHCs in co-located vessels, which could be involved in the same release, must be aggregated to determine whether a TQ exists. In the situation referenced in your letter, units "sufficiently close together," such as units occupying the same fire area, "that they could be involved in the same release," such as a structural fire in the distribution center, are to be aggregated and to be considered co-located.9,10

Thank you for your interest in occupational safety and health. We hope you find this information helpful. OSHA requirements are set by statute, standards, and regulations. Our interpretation letters explain these requirements and how they apply to 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 http://www.osha.gov. If you have further questions, please feel free to contact the Directorate of Enforcement Programs at (202) 693-2100.

Sincerely,

Scott C. Ketcham, Acting Director
Directorate of Enforcement Programs

1 Protection of Stratospheric Ozone: Listing of Substitutes Under the Significant New Alternatives Policy Program; 86 F.R. 24444 (May 6, 2021).

2 Designation and Safety Classification of Refrigerants. ANSI/ASHRAE Standard 34‒2019. Atlanta, GA: American Society of Heating, Refrigerating, and Air Conditioning Engineers, 2019.

3 1910.119(b) - 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 [emphasis added].

4 72 FR 31453-31457, Interpretation of OSHA's Standard for Process Safety Management of Highly Hazardous Chemicals (6/7/2007) - https://www.osha.gov/laws-regs/federalregister/2007-06-07
"Accordingly, OSHA modified the definition of "process" to include the concepts of "interconnection" and "co-location" with addition of the language, "any group of vessels which are interconnected or separate vessels which are located such that a highly hazardous chemical could be involved in a potential release shall be considered a single process." 29 CFR 1910.119(b). OSHA stated in the final rule that this definition, when read in conjunction with the application section, establishes the standard's intended coverage, (57 FR 6372). Therefore, a "single process" containing a TQ of an HHC includes an "interconnected" or closely co-located process".

5 OSHA Letter of Interpretation - Boundaries of a PSM-Covered Process... - https://www.osha.gov/laws-regs/standardinterpretations/2014-05-02, 05/02/2014

6 OSHA Letter of Interpretation - PSM applicability to warehousing flammable liquids and other HHCs ... - https://www.osha.gov/laws-regs/standardinterpretations/2002-02-01, 2/01/2002

7 OSHA Letter of Interpretation - Akzo-Nobel Chemicals - Limits of a Process - https://www.osha.gov/laws-regs/standardinterpretations/1997-02-28, 2/28/1997

8 OSHA Letter of Interpretation - Boundaries of a PSM-Covered Process... - https://www.osha.gov/laws-regs/standardinterpretations/2014-05-02, 05/02/2014

9 72 FR 31453-31457, Interpretation of OSHA's Standard for Process Safety Management of Highly Hazardous Chemicals (6/7/2007) - https://www.osha.gov/laws-regs/federalregister/2007-06-07

10 OSHA Letter of Interpretation - PSM and Aerosol (Flammable Gas) Containers Stored ... - https://www.osha.gov/laws-regs/standardinterpretations/2019-06-28, 6/28/2019