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NOTICE: This is an OSHA Archive Document, and may no longer represent OSHA Policy. It is presented here as historical content, for research and review purposes only.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

"This document was published prior to the publication of OSHA's final rule on Ergonomics Program (29 CFR 1910.900, November 14, 2000), and therefore does not necessarily address or reflect the provisions set forth in the final standard."

July 7, 1994

Mr. Jerry T. Fields
Director, Safety & Health
Boise Cascade Corporation
One Jefferson Square
Boise, Idaho 83728

Dear Mr. Fields:

This is in response to your April 21 letter, requesting interpretation of the Process Safety Management (PSM) of Highly Hazardous Chemicals (HHCs) standard, 29 CFR 1910.119 with respect to a wood digestion process containing multiple toxic and flammable liquid HHCs as described in the scenario below. Your questions and our responses follow.

Scenario: Various wood species are used as a base stock either in chipped or in wood dust form and combined with cooking liquors (containing sodium sulfides) under heat and pressure. This process separates useable cellulose fiber from the wood matrix. Byproduct materials produced incidental to the process include the toxic chemicals: Hydrogen Sulfide and Methyl Mercaptan and the flammable liquids: Dimethyl Sulfide, Dimethyl Disulfide, Methanol and Turpentine. The process may be accomplished in batch or continuous methods. All such processes are enclosed while in progress. The aforementioned process HHCs undergo separation. Turpentine is then stored in atmospheric tanks without chilling or refrigeration. In most cases, most of the turpentine is separated and stored in a bulk tank or tanks for subsequent sale as a commodity material. In some cases, a quantity of turpentine is used as a fuel in a lime kiln.

Question 1:

Is 10,000 pounds (4535.9 kg) or greater amount of turpentine stored in atmospheric tanks without benefit of chilling or refrigeration as described in our letter excepted from PSM coverage by 1910.119(a)(1)(ii)(B)?


There is insufficient information in your letter to provide a definite yes or no answer to your question. The following clarification is provided to assist you in this determination. The method of storage of flammable liquids is but one consideration which must be evaluated to determine whether or not a flammable liquid at or above the threshold quantity is subject to the PSM standard. Merely to store a flammable liquid in tanks at atmospheric pressure without benefit of chilling or refrigeration is not in itself sufficient reason to remove a process from coverage. Although the standard provides a conditional exception for such storage, such substances are covered if, for example, they are part of a "process", as defined in the standard, which include activities in addition to storage and associated transfer or if they are sited in near proximity to a hazardous process and thus might become involved in a catastrophic event.

Question 2:

Is 10,000 pounds or greater amounts of turpentine stored in atmospheric tanks without benefit of chilling or refrigeration when used as a hydrocarbon fuel in a lime kiln excepted from PSM coverage by 1910.119(a)(1)(A)?


Based on the information provided in your letter we can provide you only with a conditional answer to your question. In order to be excluded from coverage by the 1910.119(a)(10)(ii)(A) exception, a hydrocarbon fuel, for example, turpentine, contained in a process, must be used solely for workplace consumption as a fuel, for example to fire a lime kiln and must not be part of a process containing another highly hazardous chemical covered by the PSM standard.

The following additional clarifications are intended to assist you in determining whether a process or processes is or are covered by the PSM standard.

First of all, compliance with the PSM standard is determined on a worksite by worksite basis. Secondly, by the definition of "process" at 1910.119(b), a process is defined by activities including any use, storage, manufacturing, handling or the on-site movement or combination of these activities. Also, by this definition, a process includes any group of vessels which are interconnected and separate vessels which are located such that a highly hazardous chemical could be involved in a potential release. The definition of "process" is discussed further on page 6372 of the preamble to the Final Rule, a copy of which is enclosed for your use. Lastly, the threshold quantity or greater amounts of flammable liquids contained in a process covered by the PSM standard is based on the aggregate amount of all flammable liquids, for example, turpentine, methyl sulfide, methyl disulfide and/or methanol contained in a process at any one time.

We appreciate your interest in occupational safety and health. If we can be of further assistance, please do not hesitate to contact us.


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