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Standard Interpretations - Table of Contents
• Standard Number: 1910.119; 1910.119(a)(1)(ii); 1910.119(b)

May 21, 2009

Mr. Mark R. Kaster
Dorsey & Whitney LLP
50 South Sixth Street, Suite 1500
Minneapolis, MN 55402-1498

Dear Mr. Kaster:

Thank you for your January 29, 2009 letter to the Occupational Safety and Health Administration (OSHA) Directorate of Enforcement Programs. You have specific questions regarding the application of the Process Safety Management (PSM) standard, 29 CFR 1910.119, in three flammable liquid handling scenarios. This letter constitutes OSHA's interpretation only of the requirements discussed and may not be applicable to any question not delineated within your original correspondence.

Two of your paraphrased questions and our responses are provided below. As communicated by telephone by a member of my staff, OSHA intends to issue a compliance directive that should address the remainder of your questions.

Question: Is the total mass of a mixture consisting of a fine, non-soluble, non-combustible solid combined with a flammable liquid considered when determining if a threshold quantity (TQ) is present in a process? The mixture is stipulated to meet the definition of "liquid" in 29 CFR 1910.106(a)(17), to have a flash point less than 100oF, and to contain less than 99% non-combustible components.

Reply: A process containing flammable liquids or gases is subject to the requirements of 29 CFR 1910.119 if it meets the criteria for flammables specified in 29 CFR 1910.119 (a)(1)(ii):

"A process which involves flammable liquid or gas (as defined in 1910.1200(c) of this part) on site in one location, in a quantity of 10,000 pounds (4535.9 kg) or more..."

A flammable liquid is defined in 29 CFR 1910.1200(c)(iii) as:

"Liquid, flammable" means any liquid having a flashpoint below 100 deg. F (37.8 deg. C), except any mixture having components with flashpoints of 100 deg. F (37.8 deg. C) or higher, the total of which make up 99 percent or more of the total volume of the mixture.

Because the mixture in question meets the definition of a liquid and has a flashpoint of less than 100oF, it is a flammable liquid. A process containing 10,000 pounds or more of the mixture would be covered under the PSM standard.

For the specific example you give of a mixture containing 2,000 pounds of fine, non-soluble, non-combustible solid, and 8,000 pounds of a flammable liquid, if the mixture as a whole meets the 29 CFR 1910.1200(c)(iii) definition of a flammable liquid, then the total amount of flammable liquid is 10,000 pounds, even if some component(s) of the mixture alone would not meet the required flash point.

Question: Process A is a PSM covered process using flammable liquids in excess of the threshold quantity. Process A supplies a "metered" flow rate of flammable product through pumps and small diameter piping to Process B, which contains less than the threshold quantity of flammable material and is located under one roof, but separated by distance and fire walls, from Process A. It is stipulated that an event in one location would not be expected to directly involve or impact the other. Both processes utilize multiple controls and monitoring to prevent a release of flammable liquid.

Sub-question a:Is Process B a PSM process?

Reply a:Because Process A and Process B are interconnected, Process B is a PSM covered process because together with Process A it meets the definition of a process in 29 CFR 1910.119(b) ("Any group of vessels which are interconnected and separate vessels that are located such that a highly hazardous chemical could be involved in a potential release shall be considered a single process") and contains 10,000 pounds or more of flammable liquid (emphasis added).

Sub-question b:Does the OSHA interpretation of the PSM standard published June 7, 2007, in the Federal Register or the Preamble to the PSM standard support the interpretation that the Process B is not a PSM process? Please explain.

Reply b: The June 7, 2007 Federal Register interpretation supports OSHA's position that Process B is a PSM covered process.

The interpretation states that "on site in one location" means that "the standard applies when a threshold quantity (TQ) of a highly hazardous chemical (HHC) exists within contiguous areas under the control of an employer...in any group of vessels that are interconnected, or in such proximity that the HHC could be involved in a potential catastrophic release..." (emphasis added). 72 Fed Reg 31435 (June 7, 2007). The interpretation further states that interconnected vessels need not be closely co-located to form a process, and that "...there is no additional requirement on OSHA to show the potentiality of a release with respect to interconnected (as opposed to separate) vessels. Rather, the PSM standard presumes that all aspects of a physically connected process can be expected to participate in a catastrophic release." Id. at 31457.

Therefore, as a result of the interconnection between Process A and Process B, the June 7, 2007, interpretation supports that Process B is a PSM covered process.

Please note that while controls may be required under other elements of the PSM standard to control hazards, the presence or absence of controls does not affect whether or not a process is covered. The scope and application paragraph (29 CFR 1910.119(a)(1)) of the PSM standard establishes coverage based on the existence of a process as defined by 29 CFR 1910.119(b). Neither the "application" paragraph, nor the definition of "process," states or implies that controls can limit the extent or boundaries of a PSM covered process. OSHA has stated this position in other enforcement policy documents.1, 2

Thank you for your interest in occupational safety and health. We hope you find this information helpful. 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 interpretation 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 may update our guidance in response to new information. To keep apprised of such developments, you can consult OSHA's website at http://www.osha.gov.

If you have any further questions, please call the Office of General Industry Enforcement at 202-693-1850.


Richard E. Fairfax, Director
Directorate of Enforcement Programs

1  AKZO-Nobel Chemicals - Limits of a Process;Memorandum for Patricia Clark, Regional Administrator, 2/28/1997; "Engineering and administrative controls required by the PSM standard to prevent catastrophic release of a covered HHC may not be used to determine the extent of a process as defined in 1910.119(b)."  [Return to Text]

2 OSHA Letter of Interpretation: Highly Hazardous Chemicals as it applies to what constitutes the boundaries of a process, Barker, 04/28/1994. "Question 2. If the storage tank is considered part of the covered process, would the storage tank be considered part of the process if it could be isolated from the process by a valve? Reply: Yes. The storage tank would be considered part of the process whether of not the tank could be isolated by valve closure."   [Return to Text]

Standard Interpretations - Table of Contents

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