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.



September 21, 2000

Mr. Gregory M. Adams
Assistant Departmental Engineer
County Sanitation Districts of Los Angeles County
Office Engineering Department
P.O. Box 4998
Whittier, CA 90607-4998

Dear Mr. Adams:

Thank you for your March 9, 1998 letter to the Occupational Safety and Health Administration's (OSHA's) [Directorate of Enforcement Programs (DEP)]. You have questions regarding OSHA's Process Safety Management of Highly Hazardous Chemicals; Explosives and Blasting Agents Standard (PSM), 29 CFR 1910.119. Please be aware that this response may not be applicable to any question(s), situations, statements, etc., not delineated within your original correspondence. Your specific question is related to methane collection systems at wastewater treatment plants (WWTPs) or publicly owned treatment plants (POTWs). We apologize for the delay in our response.

The methane collection systems you described include anaerobic digesters which are utilized to collect methane gas from the biological conversion of organic wastes. Often large to mid-sized systems contain in aggregate more than 10,000 pounds of methane.The anaerobic digesters are interconnected and provide methane as a fuel for on-site boilers, pump engine drivers, gas turbines, etc. All the methane from the anaerobic digesters is used on-site solely as a fuel.

Question: Are the methane collection systems described above covered by OSHA's PSM standard?

Response: The response to your question has two aspects: jurisdictional and technical. We address both below.

Technical: There is insufficient information provided related to the quantity of methane in the process you described to determine PSM coverage. However, we will answer your question by assuming a threshold quantity or greater amount (TQ) of a highly hazardous chemical (HHC) exists in the process you described.

The process you described is a PSM-covered process based on the following:



  1. A PSM-covered HHC exists in your process - methane is a flammable gas [29 CFR 1910.119(a)(1)(ii)]; and
  2. An assumed TQ of methane exists in your process. If this assumption is not correct, your process is not covered by PSM because it does not contain a TQ.

However, since the methane is used solely for workplace consumption as a fuel, your PSM-covered process is excepted from the standard, see 29 CFR 1910.119(a)(1)(ii)(A). Simply, you are not required to implement the requirements of PSM to the process you described.

Please note, if the methane is a part of a process containing another HHC covered by PSM then the methane would be considered part of that covered process and no exemption would result. In other words, the methane would not qualify for the exception if the methane fuels equipment used to heat another PSM-covered process.

As you stated in your letter, other PSM HHCs common to this type facility include chlorine, sulfur dioxide, ammonia and propane. As stated above, if other HHCs exists at your facilities, you may be required to comply with PSM for your entire methane system based on the methane system's interconnection and/or proximity to other covered HHCs. If your PSM-covered methane system is not excepted you may be required to comply with PSM as required in the discussion on the jurisdictional aspect below.

Jurisdictional: As you are with the County Sanitation District of Los Angeles, CA, your waste treatment facilities in question are probably POTW facilities. Most POTWs are operated by municipalities. While Federal OSHA does not have direct jurisdiction over employees of State and local governments, twenty-five States, including California, administer their own occupational safety and health programs under plans approved by OSHA. These States are required to adopt and enforce occupational safety and health standards which are at least as effective as those promulgated by OSHA and must extend their coverage to public sector employees. Therefore, both public sector employees of POTWs and any contract employees who perform operations, maintenance, or other PSM-covered activities, would be covered by the State's PSM standard. California has adopted a PSM standard which is similar to the Federal standard. For more information on California's enforcement of its standard, I suggest you contact:

[Division of Occupational and Health
455 Golden Gate Avenue, 10th Floor
San Francisco, CA 94102
Phone: (415) 703-5100
Fax: (415) 703-5135]

For members of your association located in a Federal OSHA jurisdiction with no State Plan, the level of coverage is somewhat different. Because Federal OSHA does not have jurisdiction over employees of government entities, including municipal workers, OSHA does not enforce the provisions of the PSM standard with respect to the municipal workers who work at PSM-covered facilities in states in a Federal OSHA jurisdiction. However, should government entities in states with Federal OSHA jurisdiction utilize contractors to work on a covered PSM process including POTWs, the contract employees would be covered by the OSH Act. Based on the type and extent of their work activities, contract employers are required to comply with those elements of the standard for which they can control hazards related to specific requirements of PSM. At a minimum contract employers would be required to comply with the Contractor Responsibility provisions of PSM, found at 29 CFR 1910.119(h)(3).

Thank you for your interest in occupational safety and health. We hope you find this information helpful. Please be aware that OSHA's enforcement guidance is subject to periodic review and clarification, amplification, or correction. Such guidance could also be affected by subsequent rulemaking. In the future, should you wish to verify that the guidance herein remains current oraccess the referenced information, you may consult OSHA's website at
http://www.osha.gov. If you have any further questions, please feel free to contact the [Office of General Industry Enforcement at (202) 693-1850].


Richard E. Fairfax, Director
[Directorate of Enforcement Programs]

[Corrected 6/2/2005]