Archive Notice - OSHA Archive

NOTICE: This is an OSHA Archive Document, and may no longer represent OSHA Policy. It is presented here as historical content, for research and review purposes only.

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

September 29, 1993

Mr. Joseph C. Caporossi, Director
Safety, Health & Emergency Response
Cytec Industries
Five Garret Mountain Plaza
West Peterson, N.J. 07424

Dear Mr. Caporossi:

This is in response to your August 26 letter, requesting interpretation of the Process Safety Management (PSM) of Highly Hazardous Chemicals standard, 29 CFR 1910.119. In your letter you requested clarification on whether the scheduling and prioritizing on a "worst-first" basis of Process Hazard Analyses (PHA's) of covered processes would comply with the PSM standard in the following scenario.


A manufacturing site has six process units in it. All six process units use raw materials and produce products covered by 1910.119. Each of the six process units has subunits such as storage for raw materials, reactors, distillers, separators and end product storage. PHA's are conducted on the subunits per a schedule by which no less than 25 percent of the subunits for each process will be completed by 5/26/94, 50 percent by 5/26/95, 75 percent by 5/26/96 and 100 percent by 5/26/97. The PHA's on all subunits will be completed by 5/26/97, which is the PHA completion deadline specified in the PSM standard. The PHA schedule is based on a prioritization of the subunits within a process unit. Thus, for each process unit, no less than 25 percent of the subunits will be completed by 5/26/94, no less than 50 percent by 5/26/95, no less than 75 percent by 5/26/96 and no less than 100 percent by 5/26/97. The most hazardous process subunits in each process unit will have PHA's completed first. This approach will accelerate hazard identification and correction on a "worst-first" basis.

Our response:

The preceding PHA scenario would be acceptable to OSHA for the purpose of meeting the completion schedule requirements of 1910.119(e). The following information is provided to assist you.

Employer determination and documentation of the priority order for conducting PHA's at a worksite is required by 1910.119(e)(1). The basis for determining this priority order is a rationale which includes such considerations as the extent of the process hazard, number of potentially affected employees, age of the process, and operating history of the process. The "worst-first" basis you intend to use must incorporate this rationale.

PHA's must be "conducted as soon as possible" but not later than the schedule addressed in your letter. An employer must be prepared to demonstrate (through documentation including records which are maintained and otherwise) to OSHA that PHA's could not be completed before the percentage completion deadlines specified in 1910.119(e)(1).

Thank you for your interest in occupational safety and health. If we may be of further assistance please feel free to contact us.


Roger A. Clark, Director
Directorate of Compliance Programs