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.

February 23, 1995

Mr. Steve Neville
Safety and Health Program Development
Analyst Steve Neville Associates
144 Ocean Terrace Indialantic, FL 32903

Dear Mr. Neville:

This is in response to your letter of November 18, 1994, in which you have requested clarification on how the Occupational Safety and Health Administration (OSHA) would address the use of natural gas or liquid propane gas used in an after-burner to remove volatile organic carbon (VOC) air contaminants.

From the information you have provided, we understand that your process involves the use of natural gas as a source of fuel for incineration of VOC contaminants.

Please be advised that the Process Safety Management of Highly Hazardous Chemicals Standard (PSM), 29 CFR 1910.119, applies to:

(i) A process that involves a chemical at or above the threshold quantities listed in appendix A of 1910.119;

(ii) A process that involves a flammable liquid or gas (as defined in 1910.1200(c)) on site in one location, in a quantity of 10,000 pounds or more.

The applicability of 1910.119 is controlled by the quantities used of the chemicals that are listed in appendix A, or the 10,000 pounds of the flammable liquid or gas. An exception is made for hydrocarbon fuels, such as those used for heating or vehicle use, if their use is not part of a covered process.

Your letter neither quantified the hazardous contaminants being processed in the incinerator, nor the flammable liquid being stored on-site for incineration. In addition, we do not have a detailed description of your after-burning process. Therefore, the applicability of 1910.119 to your process could not be determined.

With regard to your second question that pertains to the applicability of OSHA's regulations to vapor concentrations above the lower explosive limit (LEL), please be advised that OSHA's regulations apply to workers' protection. OSHA's regulations do not address concentrations within the vapor generating enclosure and/or within the exhaust plenum, so long as no workers are exposed and no danger of explosion exists.

Thank you for your interest in occupational safety and health. If we could be of further assistance, please contact us.


John B. Miles, Jr., Director
Directorate of Compliance Programs