Glass Hazards Analysis (GHA)
Safety Management Services, Inc. (SMS) regularly performs GHAs on facilities using a variety of tools and technical guidance documents. The general approach is to evaluate each building located within inhabited building distance (IBD) of a potential explosion site (PES) using a checklist. A completed checklist is provided to our customer for each building evaluated and includes any deficiencies in the building’s glass type and installation. All required or implemented mitigation actions to bring the building into compliance are assembled in an appendix to facilitate work orders or integrating into a service contract. A window is considered compliant if it withstands the worst-case expected overpressure or 3.5 psi, whichever is lower. This approach correlates well with DA PAM 385-64 that, for windows within IBD, directs that “An engineering analysis will be made to determine the type of blast-resistant glass required to withstand the expected overpressure.”
Windows, skylights, and glass panels within IBD are evaluated to determine whether they meet the required criteria to resist expected blast pressures. SMS performs a physical assessment of all glass within buildings out to IBD blast hazard arcs and determines their blast pressure capacity in accordance with Unified Facilities Criteria (UFC) 3-340-02, Structures to Resist the Effects of Accidental Explosion, 5 December 2008. Where glass blast pressure capacity did not exceed the expected overpressure from an explosive event from nearby PES, mitigation actions are recommended. During the evaluation, the team focuses on worst-case explosive events in evaluating window and glass response. For a given PES, this worst-case event is the expected overpressure resulting from the entire NEW involved in an event. However, in some cases, window failure is not the major hazard of concern. Consideration is also given during our evaluation to the fact that although considerable damage is expected at maximum net explosive weight (NEW), the NEW involved in any incident is nearly always less than the maximum. Consequently, the mitigation steps recommended reflect these real-world expectations that personnel at less than intraline distance (ILD) may be subject to lower pressures and thus consideration of mitigating the glass hazard is warranted.