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NOTICE: This is an OSHA Archive Document, and may no longer represent OSHA Policy. It is presented here as historical content, for research and review purposes only.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

December 3, 1992

Mr. David A. Day
107 Barley Mill Drive
Greer, South Carolina 29651

Dear Mr. Day:

This is in response to your July 14 letter to Mr. Rolland Stroup, a member of my staff requesting interpretations of the Occupational Safety and Health Administration (OSHA's) standard on Process Safety Management (PSM) of Highly Hazardous Chemicals. Please accept our apologies for the delay in responding.

In your letter you requested that OSHA clarify whether the PSM standard would apply to the storage of pentane in excess of 10,000 pounds (4535.9 kg) in a tank where the pentane is neither chilled nor refrigerated to keep it below its boiling point and the tank pressure does not exceed 0.5 psi (3447.3 newtons per square meter) guage. We need additional information to determine applicability of the PSM standard. Please advise us how the pentane is used at the site, and how it is transferred. Also, since the boiling point of pentane is 97 degrees F, please advise how it is kept below that temperature on hot days. Please feel free to contact us for any further request for interpretation. Your careful consideration of the "process" definition in the PSM standard is recommended. Please note that a process may include not only storage and associated transfer activities but also, interconnected use, manufacturing, handling and on-site movement activities.

Also, in your letter you requested that OSHA clarify whether the following process is exempt from coverage by the PSM standard. A process involves n-propyl alcohol and n-propyl acetate used as solvents for printing inks. The solvents are stored in above ground tanks and are piped inside the building where the solvents are distributed into individual five gallon (18.9 liter) containers where the inks are mixed. These flammable liquids are stored in atmospheric tanks and transferred while being kept below their boiling point without benefit of chilling or refrigeration. Please advise us of the capacity of the storage tanks and if the five gallon (18.9 l) containers are directly connected to the incoming flammable liquids during the dispensing process. Are the containers then moved prior to the mixing?

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


Roger A. Clark,
Directorate of Compliance Programs