Archive Notice - OSHA Archive

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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

January 16, 1996

Mr. K.S. Dreux
McDermott, Will & Emery
1850 K Street, N.W.
Washington, DC 20006-2296

Dear Mr. Dreux:

This is response to your letter of August 25, 1995 requesting interpretation of the 29 CFR 1910.119, Process Safety Management (PSM) of Highly Hazardous Chemicals (HHC's) standard. Your process scenario and question and our reply follow.

Scenario: Through a documented inventory plan, an inventory of less than 9000 pounds of a flammable liquid is maintained in a storage tank. The flammable liquid is hard piped to a valve station. As batches of the mixture are made, a temporary hose is attached to the valve station, and approximately 4200 pounds of the flammable liquid are transferred to a mix tank and mixed with 6000 pounds of inert solids. The flammable liquid is added as the mix tank's agitator is operating. The resulting liquid-solid mixture has the same flashpoint as the flashpoint of the flammable liquid (i.e., less than 100 degrees F), and the combined weight of the liquid and inert solids is greater than 10,000 pounds. The entire operation from the storage to the mix tank has less 10,000 pounds of flammable liquids in it. The mix tank always has less than 10,000 pounds of flammable liquid in it.

Question: Is the process described in the scenario above covered by the PSM standard?

Reply: Based on the information you have provided, the process you have described falls outside the scope of the PSM standard. The standard applies to processes which involve flammable liquids or gases in quantities of 10,000 pounds (4535.9 kg) or more. The process you describe does not meet the specified threshold quantities in Appendix A of the standard.