OSHA Hazard Information Bulletins
Classification of Ammonium Perchlorate

September 25, 1991

Office of Field Programs
Directorate of Technical Support
Hazard Information Bulletin on the Classification of Ammonium Perchlorate

The San Francisco Regional Office brought to our attention a potential problem due to the inconsistency among different authorities in the classification of ammonium perchlorate (AP) as an oxidizer or as an explosive. Since there are differences in the classification by different Federal and State jurisdictions, the question of proper classification for the purpose of safe handling, storage and transportation in the workplace is at issue.


Ammonium perchlorate (NH4CLO4) is a white crystalline substance. It is a powerful oxidizing material. It is stable in pure form at ordinary temperature, but decomposes at a temperature of 150°C or above. It becomes an explosive when mixed with finely divided organic materials. AP exhibits the same explosive sensitivity to shock as picric acid (Class A explosive). Sensitivity to shock and friction may be great when contaminated with small amounts of some impurities such as sulfur, powdered metals and carbonaceous materials. AP may explode when involved in fire.1


OSHA Standards

29 CFR 1910.109(a)(3) is OSHA's definition of explosive. It references the Department of Transportation (DOT) regulation, 49 CFR Chapter I, regarding the classification of explosives.

Department of Transportation Standards

DOT classifies AP either as an oxidizer or high explosive under the DOT standard 49 CFR 172.101 "Hazardous Material Table." This table is for domestic uses and does not specify particle size for AP. DOT 49 CFR 172.102 "Optional Hazardous Materials Table" lists AP with average particle size under 45 microns as explosive for the purpose of international shipping.

Current DOT regulations require the shipper to classify hazardous materials. It is our understanding from DOT that if AP is intended to be used as an explosive, or if the shipper has doubt that it could be explosive, the shipper must send samples to either the Bureau of Mines (BOM) or the Bureau of Explosives (BOE) for testing and classification. DOT has revised its standards to require that for AP to be classified as an explosive, it must meet the United Nations (UN) Tests and Criteria, Recommendation on the Transportation of Dangerous Goods. The distinction between AP as explosive and as oxidizer is based on test results. Laboratory testing is required in making the classification determination. The revised DOT standards will be effective on October 1, 1991. However, DOT has authorized immediate compliance with the amended regulations.

Department of Defense (DOD)

DOD is authorized to classify military explosives. Commercial explosives, however, must be classified and approved by DOT. DOD Hazardous Material Classification Procedure is similar to the United Nations Classification Procedure. UN classifies explosives as Class 1 materials. Under Class 1 there are six divisions:

Division 1.1 Substances and articles which have a mass explosion hazard.

Division 1.2 Substances and articles which have a projection hazard but not a mass explosion hazard.

Division 1.3 Substances and articles which have a fire hazard and either a minor blast hazard or a minor projection hazard or both, but not a mass explosion hazard.

Division 1.4 Substances and articles which present no significant hazard.

Division 1.5 Very insensitive substances which have a mass explosion hazard.

Division 1.6 Extremely insensitive articles which do not have a mass explosion hazard.

The UN Class 5 materials are oxidizing substances and organic peroxides. The following are Class 5 divisions:

Division 5.1 Oxidizing substances.

Division 5.2 Organic peroxides.

According to the DOD Explosives Safety Board, AP manufactured at 200 microns has been tested and classified as UN Class 5, Division 5.1 oxidizer. The U.S. Army currently classifies AP with particle size under 15 microns as Class 1, Division 1.1 explosive. AP with particle size over 15 microns and stored near explosive materials is classified as Class 1, Division 1.3 explosive. The Army classifies 200 microns AP as Class l, Division 1.4 explosive when it is located in an explosive area.

Bureau of Alcohol, Tobacco and Firearms (BATF)

In 1975 BATF published an explosive materials list which contained AP. Based on industry and DOD test data received, BATF concluded in April, 1976 that AP having nominal particle size less than 15 microns is an explosive material. Before April, 1976, BATF used 45 microns as the cutoff.

State of Utah OSHA

The State of Utah OSHA considers AP to be an explosive material regardless of its size. Utah defines explosive materials as "These include explosives, blasting agents and detonators. The term includes, but is not limited to dynamite and other high explosives, slurries, emulsions, water gels, blasting agents, black powder, pellet powder, initiating explosives, detonators, safety fuses, squibs, detonating cord, igniter cord, igniters, pyrotechnics, pyrotechnic compositions, fireworks (special and Common), ammunition, propellent and propellent compositions."


Since 1910.109(a)(3) references DOT regulations, OSHA must follow the most current DOT classification of hazardous materials. Compliance with any other Federal or State regulations may or may not be adequate for the purpose of 1910.109(a)(3) requirements.


Our recommendations for the classification of AP are as follows:

  1. AP is a Class 5.1 oxidizer unless the manufacturer classifies it as a Class 1 material (explosive).
  2. AP is an explosive if a sample is sent to BOM for testing according to the UN test criteria for explosive, and was found to meet the requirements as a Class 1 material and accepted by DOT. However, we recommend that samples be taken only by individuals specifically trained to handle potentially explosive materials.


  1. NFPA 49-1975, Hazardous Chemical Data, Fire Protection Guide on Hazardous Material, 1986.

1 The Directorate of Technical Support issues Hazard Information Bulletins (HIBs) in accordance with OSHA Instruction CPL 2.65 to provide relevant information regarding unrecognized or misunderstood safety and health hazards, and/or inadequacies of materials, devices, techniques and engineering controls. HIBs are initiated based on information provided by the field staff, studies, reports, concerns expressed by safety and health professionals, employers and the public. Information is compiled based on a comprehensive evaluation of available facts, literature and in coordination with appropriate parties. HIBs do not necessarily reflect OSHA policy.