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.

December 30, 1993

Mr. J. A. Dzwierzynski
Director of Engineering
11 Apollo Drive
Whippany, N.J. 07981

Dear Mr. Dzwierzynski:

This is in response to your letters of June 29 and August 11, requesting interpretation of the Process Safety Management (PSM) of Highly Hazardous Chemicals, 29 CFR 1910.119, standard. Specifically, you requested clarification on whether the PSM standard applies to your ethylene oxide (ETO) facilities at the Spartanburg, South Carolina and El Paso, Texas work sites. Please accept our apology for the delay in responding.

In your letter you described the preceding facilities as buildings, each containing an inside ETO storage room and an adjacent ETO process area. We understand that the inside storage room and the process area of the facility in combination could contain 5000 pounds or more of ETO. Also, you indicated that less than 5000 pounds (2267.95 kgs) of ETO would be in the inside storage room or in the process area at any particular time. From the blueprint accompanying your letter, we understand a sterilizer area to be connected to the process area by pipelines which transport ETO. If the process area and the sterilizer area contain a combined quantity of 5,000 pounds or more of ETO, then we consider the combination to be one process covered by the PSM standard.

We initially consider the entire facility including storage, sterilizer and process area to be one process covered by the PSM standard. If an effective barrier is created to isolate the storage area, then it may be considered as not a part of the process. In your August 11 letter you provided additional information which disclosed that the inside storage room and the process area in the ETO facilities are constructed with 100 pounds per square feet (psf), or 488.2. kgs per square meter, blast resistant walls and 20 psf (97.64 kgs per square meter) blast relieving panels which comply with the Factory Mutual (FM) standard, FM 792. Also, you disclosed that the facilities meet all National Electrical Code (N.E.C.) and Fire Marshall requirements.

Work site processes containing threshold quantities, that is, 5000 pounds or greater amount of ETO are covered by the PSM standard. When an effective barrier to protect against gas transfer and permeation and fire/explosion hazards is installed between the inside storage room and the process area and areas communicating thereto, the ETO containers and the ETO process described above would be considered separate processes if they are not interconnected. The ability to serve as an effective barrier must be determined not only on the basis of boundary construction itself but also on the integrated construction of boundary walls, ceilings and floors with the building. Special attention must be directed at boundary penetrations, such as those for electrical wiring and heating, ventilation and air conditioning ducts. Extreme caution must be undertaken if door accesses through the barrier are contemplated. The effectiveness of the barrier must be reevaluated on a periodic basis.

When the employer intends that the containers of ETO in the inside storage room and the adjacent ETO process be separate processes, then he must be capable of demonstrating (through documentation, including records which are maintained), to OSHA that the barrier built between the two areas is effective in preventing the transfer of toxic gas and the effects of fire/explosion.

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


Roger A. Clark, Director
Directorate of Compliance Programs