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.

January 31, 1994

L. Dave McLean
Strategic Operations
Thiokol Corporation
P.O. Box 689, M/S DOO
Brigham City, Utah 84302-0689

Dear Mr. McLean:

This is in response to your September 28 letter, requesting interpretation of the Process Safety Management (PSM) of Highly Hazardous Chemicals standard, 29 CFR 1910.119. Please accept our apology for the delay in responding. Your questions and our responses follow.

Question 1: Is the manufacture of solid propellant rocket motors covered by 1910.119?

Reply: The PSM standard covers the manufacturing of solid propellant rocket motors to be used for propulsion when such motors are classified as Class A, Class B and Class C explosives by the Department of Transportation (DOT). Please note that DOT now classifies explosives by number designation. See the 49 CFR 173.53 table (enclosed) which compares old and new designations.

Question 2: Is the manufacture of flares to be used for battlefield illumination or for heat source protection of aircraft covered by 1910.119?

Reply: The PSM standard applies to the manufacturing of flares when such flares are classified as explosives by DOT, as noted in the reply to question 1 above.

Question 3: Except for Ammonium Perchlorate (AP) no other ingredient used in our processes is listed in Appendix A. However, several explosive compounds are, namely HMX and nitroglycerin. We receive both from other manufacturers. We do process both. In the case of HMX we dry and grind batches up to 5000 lbs in quantity and we blend nitro with other ingredients for insertion into our propellant mixes. In accordance with paragraph three and four of your letter of September 17, we now interpret that these processes are not covered as the end product is not intended to explode and because the HMX and nitro are "manufactured elsewhere and delivered to the weapon manufacturing worksite". Is that a correct assumption?

Reply: The PSM standard applies not only to employers who initially manufacture explosive materials, including Nitroglycerin and CycloTetraMethylene-TetraNitrimine (HMX) but also to employers who further process such explosives as described above. Also, the PSM standard applies to manufactured end products classified as explosive by DOT as noted previously. The OSHA letter of September 17 to which you refer in your question is being revised to clarify that the definition of explosive includes those classified as such by DOT. This revised PSM letter of interpretation will be sent to you separately.

Question 4: We store more than the threshold quantity of AP so we understand that it is a covered process. We process the AP by grinding but never greater than threshold quantities therefore that is not a covered process. The ground AP is added to our propellant mixes but never greater than threshold quantities so that is not a covered process. But in the case of our larger motors, numerous mixes are cast into a single motor which has a total accumulation of AP, as one ingredient of the mixes, which does not exceed the threshold quantity. Is this, propellant casting, a covered process?

Reply: Ammonium Perchlorate (AP) may be covered as a reactive and also as an explosive highly hazardous chemical. A process containing 7500 pounds (3401.9 kgs) or greater quantity of AP is covered by the PSM standard as a reactive highly hazardous chemical (See Appendix C). Also, the process activity of manufacturing any amount of explosive, classified as such by DOT, is covered by the PSM standard as discussed in our replies to your other questions.

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


Roger A. Clark, Director
Directorate of Compliance Programs