IMESAFR Variances

The regulations at 27 CFR 555.206 require the storage of high explosives and blasting agents to meet the minimum specified distances to inhabited buildings, highways, passenger railways, ammonium nitrate storage, and other explosives storage magazines prescribed in the tables of distances at 27 CFR 555.218 and 555.220. These requirements are based on the net explosives weights in the magazines, their distances to exposed sites (e.g., inhabited buildings), and barricading.

The Institute of Makers of Explosives Safety Analysis for Risk (IMESAFR) is based on quantitative risk assessment methods that assess the risk to the public from various explosives operations. IMESAFR is a program developed by APT Research, Inc. (APT) in collaboration with the IME. The program has its roots in the Safety Analysis for Risk (SAFER) software originally developed by APT for the U.S. Department of Defense for assessing risk in its explosives operations. Like the tables of distances noted above, IMESAFR takes into account explosives weights and types, distances to exposed sites, and barricading; but it also uses additional information such as magazine and building construction, magazine orientation, and numbers of persons in exposed sites to assess the risk to the public. ATF has determined that the IMESAFR quantitative risk assessment tool provides a valid method for evaluating risk from explosives storage magazines to persons within inhabited buildings and in vehicles on highways. ATF has therefore approved variance requests from industry members who show good cause to exceed the maximum allowable explosives weights in 27 CFR 555.218 and 555.220 based, in part, on the evaluation of the explosives storage site using IMESAFR.

In order for ATF to efficiently and effectively evaluate IMESAFR variance requests, industry members are encouraged to submit the following information with their request:

  1. IMESAFR computer file.
  2. Site map including the locations of all explosives storage magazines.
  3. Distances between all magazines and all exposed sites (e.g., inhabited buildings, highways) that fail ATF’s quantity and distance requirements, and those that meet the ATF quantity/distance requirements but that potentially affect the risk outputs.
  4. Explosives storage magazine information:

    a. Photos of all magazines.

    b. Magazine description worksheets or description of each magazine.

    c. Desired net explosives weight and the type/class of explosive materials for each magazine

    d. Distances between magazines (if not on the site map).
  5. Photos and addresses of all inhabited buildings included under item 3.
  6. Highway information:

    a. Name of all highways included under item 3.

    b. Speed limit and traffic count for each highway.
  7. Additional policies and procedures the industry member has in place that exceed ATF’s regulatory requirements, and that help reduce risk (e.g., employee training programs, self-inspections.)
  8. “Good cause” (as required in 27 CFR § 555.22) for the proposed alternate procedure.

ATF will evaluate each variance request based on, among other factors, the IMESAFR-calculated individual risk (Pf) and group risk (Ef) to all individuals within all exposed sites, and the additional policies and procedures the industry member has in place that help reduce risk. The individual risk for persons within each exposed site must be lower than 1E-06. The group risk for all persons from all potential explosion sites must be lower than 1E-05.

Approved variances to use IMESAFR typically contain a condition that the industry member must provide ATF with a reevaluation of the storage site every three years and whenever changes occur. Such a reevaluation must use the latest IMESAFR version and take into account any significant changes to exposed sites on your premises or in the area surrounding your premises (e.g., new or modified public roads or inhabited buildings). Additionally, any changes to the magazine locations or changes in the net explosives weight requires a reevaluation. The variance expiration date coincides with the renewal date of the explosives license or permit.

ATF encourages industry members who want to learn more about IMESAFR to contact IME and/or APT. Industry members who have questions regarding ATF’s variance process should contact the Explosives Industry Programs Branch at or 202-648-7120.

Last Reviewed December 20, 2022