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 https://www.osha.gov.

May 25, 1994

Mr. Sam Mannan
Jones and Neuse, Inc.
Suite 300
912 Capitol of Texas Highway
South Austin, Texas 78746

Dear Mr. Mannan:

This is in response to your December 6, 1993 letter, requesting an interpretation of the Process Safety Management (PSM) of Highly Hazardous Chemicals, 29 CFR 1910.119, standard. In your letter you identified an explosive device consisting of a shocktube containing an explosive core and a blasting cap. These components which are manufactured elsewhere are delivered to the worksite where they are used to manufacture the explosive device, the primary or common purpose of which is to function by explosion. The shocktube undergoes cutting, coiling and sealing and then a blast cap (with an antistatic device) is crimped onto the shocktube. Your specific questions with respect to this explosive manufacturing process which is covered by the PSM standard and our responses follow.

Question 1:

What types of hardware that see contact with explosives are covered by the PSM rule? The hazard of shocktube detonation alone is none and the shocktube is not destroyed. Associated mechanical equipment does not have pressure vessels, storage tanks, piping systems, relief or vent systems, and devices or pumps.


The employer is required to determine the extent of the process used to manufacture the explosive device described above. A covered process may include equipment within the facility which may or may not contact the explosive, or explosive device components, during the manufacturing activity. Note that the process hazard analysis required by 1910.119(e) of the PSM standard would verify the scope of process coverage within the facility including manufacturing hardware and associated equipment. A copy of the PSM Final Rule is enclosed for your use.

Question 2:

Does the rule specify the limit of process equipment that must be included in a mechanical integrity program?


No. As noted approximately halfway down the middle column on page 6389 of the preamble to the PSM Final Rule, OSHA believes that certain equipment is critical to process safety. At least the equipment specified in paragraph (j)(1) must be subject to the requirements of 1910.119(j). However, if an employer deems additional equipment to be critical to the safety of a particular process, that employer should consider that equipment to be covered by 1910.119(j) and treat it accordingly.

Question 3.

If there is no threshold quantity for explosives, what about explosives used for research and development?


Only the manufacture of explosives is covered by the PSM standard. The activity of "use" (see the 1910.119(b) definition of process) does not apply to explosives unless the explosive is otherwise covered by the PSM standard as a flammable liquid or gas as described at 1910.119(a)(1)(ii) or as a highly hazardous chemical listed in Appendix A.

Question 4:

The delay area has mixing equipment items that are not pressure vessels. Is this type of equipment covered?


The response to question 1 applies.

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


H. Berrien Zettler, Deputy Director
Directorate of Compliance Programs