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 or 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.

Common IMESAFR Terminology:

1. Exposed Site (ES) – A location exposed to the potential hazardous effects from an explosion at a potential explosion site. ESs include inhabited buildings and highways.
2. Potential Explosion Site (PES) – The location of a quantity of explosives that will create a blast, fragment, thermal, or debris hazard in the event of an explosion of its contents. PESs include explosives storage magazines.
3. Individual Risk (P_f) – Sum of all significant risks to an individual in an ES from all PESs.
4. Group Risk (E_f) – Sum of all individual risk in a group.
5. Risk-Based Evaluation Distance (RBED) - The distance required from a PES to meet either the applicable quantity/distance requirements or the IMESAFR calculated distance from a PES at which the individual risk of fatality for a single person in the open for 8,760 hours per year does not exceed 1E-08.

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.
   a. Include the version used to create the file.
   b. Include an overlay image (if used).
   c. The RBED must include all ESs that fail ATF’s quantity and distance requirements, and those that meet the ATF quantity/distance requirements but that still affect the risk outputs.
   d. Include all PESs at the storage location.
    
2. Site map that shows the locations of, and distances between all PESs and ESs.
   a. The address of the storage location or GPS coordinates if there is no address or if the address does not sufficiently identify the storage location.
   b. Use the same magazine identifier (e.g. Magazine #1) on the site map and in the IMESAFR computer file.
   c. Identify all natural and artificial barricades.
    
3. ES Information
   a. Photos and addresses of all inhabited buildings.
   b. For residences with an unknown number of occupants, industry members should create 3 groups of exposed personnel:
        i.    Group 1 – The average number of residents per household for the city where the ES is located (based on U.S. Census Bureau data) for 6,570 hours per year.
        ii.   Group 2 – 10 people present for 36 hours per year (10 additional people in the residence for 3 hours per month).
        iii.  Group 3 – 3 additional people present for 104 hours per year (3 people in the residence for 2 hours per week).
   c. Name, speed limit, and traffic count for each highway.

4. PES information:
   a. Photos of all PESs.
   b. For underground PESs, please include the depth (from surface) of the PES.

5. 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).
    
6. “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 (P_f) and group risk (E_f) 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 people within each exposed site must be lower than 1E-06. The group risk for all people from all potential explosion sites must be lower than 1E-05.

Approved variances to use IMESAFR contain a condition that requires the industry member to conduct a new IMESAFR evaluation:

1. In the six months preceding expiration of its Federal explosives license or permit;
2. When there are significant changes to exposed sites on its premises or in the area surrounding its premises (e.g. new inhabited buildings);
3. Before adding magazines, changing locations of magazines, or otherwise increasing your storage capacity; and
4. When ATF requests a new evaluation.

The industry member must apply for an amended variance when any new IMESAFR evaluation results in an increase to any individual risk or to the group risk. Industry members must notify ATF when they add magazines and/or increase their storage capacity at the storage site. Reevaluations must use the latest IMESAFR version.

ATF encourages industry members who want to learn more about IMESAFR to contact IME and/or APT. Industry members interested in IMESAFR training can find more information at:  https://www.apt-research.com/products/imesafr/.  Industry members who have questions regarding ATF’s variance process should contact ATF’s Explosives Industry Programs Branch at eipb@atf.gov or 202-648-7120.