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.

July 16, 2024

Mr. Thomas A. Adams
1502 Inverness Road
Lynn Haven, FL 32444

Dear Mr. Adams:

Thank you for your letter to the Occupational Safety and Health Administration's (OSHA), Directorate of Enforcement Programs. You have questions about the application of OSHA standards to the Department of Defense's (DoD's) Air Force facilities and whether "oxygen- deficient atmosphere," as defined in OSHA's Respiratory Protection Standard, 29 CFR 1910.134, should be used to configure heating, ventilation, and air conditioning (HVAC) systems for occupant safety in military facilities. You were also contacted by my staff for additional explanation related to your questions. This letter constitutes OSHA's interpretation only of the requirements herein and may not be applicable to any questions not delineated within your original correspondence. Your questions have been paraphrased, followed by our response.

Background: You state that as a Senior Mechanical Engineer for HVAC systems in Air Force facilities, you are responsible for setting design standards for mechanical systems in the facilities (primarily office buildings but also childcare, emergency operations, & dormitory-type buildings). In this capacity, you sometimes use HVAC systems that may expose facility occupants to the system's refrigerant (as would happen if a refrigerant line inside the facility would rupture or become disconnected). Therefore, you limit the amount of refrigerant for a system to protect occupants in the event of an accidental release of refrigerant from these systems by following the safety guidelines published by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE). You state that the Air Force relies on the ASHRAE standard 15/34-2002 (Safety Standard for Refrigeration Systems and Designation and Safety Classification of Refrigerants) definition of oxygen deficient environment of 18% oxygen (which is equivalent to 140,000 ppm or 14% concentration of refrigerant).

Question 1: Do OSHA standards apply to DoD's Air Force facilities, specifically the definition of "oxygen-deficient atmosphere" in OSHA's Respiratory Protection Standard, 29 CFR 1910.134, which says, "Oxygen deficient atmosphere means an atmosphere with an oxygen content below 19.5% by volume"?

Response: In accordance with Executive Order 12196, issued February 26, 1980, and Basic Program Elements for Federal Employee Occupational Safety and Health Programs and Related Matters, 29 CFR Part 1960, military personnel and uniquely military equipment systems and operations are excluded from OSHA coverage. However, OSHA retains jurisdiction over workplaces and operations comparable to those of private sector industries and civilian employees are covered by OSHA when working on equipment, systems and operations that are not uniquely military, as explained in the section on Military Personnel, Equipment, and Operations in Chapter 13 of OSHA's Field Operations Manual. This includes employees of private contractors performing work under federal government contracts.

Where civilian employees are covered by OSHA standards, as explained above, they are subject to all requirements in OSHA's Respiratory Protection Standard, 29 CFR 1910.134, including those addressing exposure to oxygen-deficient atmosphere. According to 29 CFR 1910.134(d)(2)(iii), all oxygen-deficient atmospheres must be considered immediately dangerous to life and health (IDLH). However, in an oxygen deficient atmosphere, if the employer demonstrates that under all foreseeable conditions, the oxygen concentration can be maintained within the ranges specified in Table II of the standard (i.e., for the altitudes set out in the table), an atmosphere-supplying respirator may be used.

Question 2: Should DoD Air Force facilities continue to protect occupants to the ASHRAE prescribed Oxygen Deprivation Limit (ODL) of 18% oxygen (140,000 ppm), or should we adopt the 29 CFR 1910.134 limit of 19.5% oxygen?

Response: OSHA does not have any standards for building ventilation systems and refrigerant safety for oxygen deficiency levels related to building occupants' safety. As explained in the response to Question 1 above, certain civilian employees of the DoD are subject to OSHA's Respiratory Protection Standard and the associated requirements for protection against oxygen- deficient conditions during regular work activities and during emergency situations, including those involving refrigerants. Oxygen-deficient atmospheres may potentially be created if refrigerants are used in sufficient quantities in the workplace (e.g., in cold storage facilities, medical laboratories) and may pose risks to workers, such as asphyxiation, in the event of a leak or containment failure.

OSHA does not enforce the ASHRAE standard, which is a consensus standard, and cannot comment on or verify the requirements in the ASHRAE standard, or on your understanding of the ODL definition in the standard, including your associated calculations equating the ODL to 18% oxygen for a refrigerant concentration of 140,000 ppm. We recommend that you contact ASHRAE for clarification of its ODL and the oxygen levels it prescribes as safe for facility occupants, as related to the use of a refrigerant or other gases in HVAC systems.

Thank you for your interest in occupational safety and health. I hope you find this information helpful. OSHA's requirements are set by statute, standards, and regulations. Letters of interpretation do not create new or additional requirements but rather explain these requirements and how they apply to particular circumstances. This letter constitutes OSHA's interpretation of the requirements discussed. From time to time, letters are affected when the Agency updates a standard, a legal decision impacts a standard, or when changes in technology affect the interpretation. To ensure that you are using the correct information and guidance, please consult OSHA's website at https://www.osha.gov. If you have further questions, please feel free to contact the Office of Health Enforcement at (202) 693-2190.

Sincerely,

Scott C. Ketcham, Director
Directorate of Enforcement Programs