Defense Threat Reduction Agency – Fire Hazards Analysis

Sigma Science is developing Fire Hazard Analyses (FHA) for the Defense Threat Reduction Agency (DTRA) under a $2 million, 3.5-year (09/2020–03/2024 with options) task order contract. Sigma is developing three U.S. Air Force (USAF) Facility Fire Hazard Analyses (FHA) in accordance with USAF requirements for Air Force Global Strike Command Nuclear Weapons facilities at the Ellsworth Air Force Base, the Minot Air Force Base, and the Kirtland Airforce Base. FHAs for these facilitates, as described in FC 4-420-07F, Section 8-3.5.1, include an assessment of the risk from fire and related hazards in relation to existing or proposed fire safety features to ensure the facility can be safely controlled and stabilized during and after a fire. New facility [Ellsworth AFB Weapon Generation Facility (WGF)-F] design FHAs are being initiated early in the design phase to ensure an acceptable level of protection is being incorporated into the design. In addition to the three FHAs, during Option Period 2, DTRA increased our scope to perform two additional reviews of the Ellsworth AFB WGF-F FHA at the 95% design and final design for this new facility.

The FHAs developed for DTRA include the following tasks:

• Performing timed egress analysis for the facility, and documenting Required Safe Egress Time (RSET) for exit access routes. Safe egress is provided by evaluating a combination of: 1) discharge to the exterior of the facility, 2) horizontal exits to adjacent fire areas, and 3) protected areas of refuge. Sigma is analyzing unmitigated fire scenarios (meeting the definition of MPFL as described in FC 4-420-07F, Appendix C), to determine the critical Heat Release Rate (HRR) for fires in each compartment in terms of Available Safe Egress Time (ASET), based on fixed tenability acceptance criteria (Temperature, Visibility, CO Concentration). Tools that are being used in the development of the Design FHA include fire modeling such as those developed by the National Institute of Standards (NIST).
• Identifying credible scenarios beginning with identifying Initial Conditions (ICs). Typical initial conditions include facility subdivision by fire rated construction as fire area boundaries and identifying the actual number of assigned personnel and expected number of visitors during operations, maintenance, and testing activities. Sigma then creates a Hazard Identification (HID) table, identifying energy sources such as lightning, electrical systems, heat producing appliances, hot work, etc. This HID Table was used to populate a list of candidate Maximum Credible Events (MCEs), using What If type Hazard Analysis (HA).
• Identifying fire protection controls for minimizing risk to life safety. Fire protection controls are considered based on the defense in depth philosophy presented in FC 4-420-07F, Section 8-3.3.9. Independent layers of defense-in-depth are composed of suites of candidate controls that function in parallel to reduce risk. Candidate control analysis is performed for each candidate MCE. Sigma is evaluating reductions in probability or consequence based on the effectiveness and reliability of controls considered, following a hierarchy of controls.
• Identifying Maximum Credible Events (MCEs) based on mitigated risk. At this stage of the fire hazard analysis, fire events are classified as credible, physically meaningful events, mitigated by the those features of the existing design that have been determined to by the most reliable and effective for ensuring safe egress. Final calculations of mitigated consequence for all MCEs are then based on the acceptance criteria provided by the Cognizant Office of Responsibility [i.e., Fractional Effective Dose (FED) methodology]. Sigma then establishes functional requirements for credited fire protection controls. If any mitigated events exceed the acceptance criteria and no additional reasonable prevention or mitigation can be identified, those scenarios are identified/highlighted for the government to determine if additional analysis is required.
• Documenting the fire analysis, risk analysis and modeling outputs in a report titled “Pre-Decisional Fire Hazards Analysis for the Facility”. Sigma worked closely and cooperatively with DTRA on the development of the template for the FHA report considering guidance in FC 4-420-07F. After incorporating comments, Sigma delivers a final Design FHA that establishes a robust and defensible baseline to the Cognizant Office of Responsibility, facilitates interdisciplinary coordination, and integrates fire protection requirements into design documentation/programs.

Key accomplishments under this contract include:

• Transmitted the 65% Ellsworth AFB WGF-F FHA to DTRA on June 27, 2022, on schedule.
• On schedule to submit the Minot AFB FHA by March 31, 2023.
• On schedule to submit the Kirkland AFB KUMMSC FHA by September 29, 2023.