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Two Journal Articles Improve Understanding of SCBA Facepiece Thermal Degradation and Thermal Exposure Classification

May 31, 2024

Two peer-reviewed journal articles led by the Fire Safety Research Institute (FSRI), part of UL Research Institutes, were recently published in the Journal of Fire Sciences. The first article, Thermal Degradation of Self-Contained Breathing Apparatus Facepiece Lenses Under Radiant Thermal Loads, evaluates how different models of self-contained breathing apparatus (SCBA) facepieces degrade under intense heat. The second article, Toward Improved Thermal Exposure Classes for Structural Firefighters, analyzes the results of this study along with full-scale experimental data to propose expanding thermal exposure classifications from three to six classes. Both articles contribute to the body of evidence of thermal exposures to operating firefighters.

Newer SCBA facepiece models provide more protection to firefighters

Across the U.S., fire departments use a range of SCBA facepiece models. Some were manufactured to align with older editions of the NFPA 1981 standard, while others incorporate modern technology aligned with more recent editions. Despite how critical SCBAs are to protecting firefighters on the job, the SCBA facepiece lens is often considered the weakest point of the personal protective equipment (PPE) ensemble. Reports from the National Institute for Occupational Safety and Health have also noted that SCBA performance may have played a role in line-of-duty deaths where thermal conditions rapidly changed.

To better understand how much protection the facepiece models offer firefighters, FSRI tested three different facepieces meeting various editions of NFPA 1981 standards. Two models complied with the 2007 edition, and one model complied with the 2013 edition. Researchers tested the facepieces at four heat flux intensities: 5, 10, 15, and 20 kW/m2 for up to 30 minutes or until holes were formed. These higher heat flux values were included to simulate emergency situations, although most firefighting operations typically encounter intensities between 5 and 10 kW/m2. The researchers monitored the facepieces for signs of thermal degradation, including crazing, bubbling, and hole formation. 

Representative images of thermal degradation of the SCBA facepiece: Crazing (left), bubbling (center), and hole formation (right).
Representative images of thermal degradation of the SCBA facepiece: Crazing (left), bubbling (center), and hole formation (right).

The results demonstrated that:

  • Thermal degradation can start to occur when facepiece lenses are subjected to heat fluxes between 5 and 10 kW/m2. 
  • Thermal degradation can impact vision clarity and potentially compromise protection in older SCBA models. 
  • The newer facepiece lens model takes significantly longer to show signs of thermal degradation compared to older models. 
  • The newer facepiece model reaches a higher maximum temperature, likely because of the extended time the heat is applied.

“This study examines a range of SCBA facepieces and highlights how changes in national standards have improved the thermal performance of the SCBA. Our results showed that SCBAs meeting current versions of NFPA 1981 are more resistant to thermal degradation, providing more protection for the firefighter.” - Richard Kesler, research engineer, FSRI

Taking it one step further: Expanding firefighter thermal exposure classifications

Recent bench-scale and full-scale data suggest there are several subsets of thermal operating classes that define the environment in which firefighters work. Existing thermal classifications date back to the 1970s. They reflect the PPE standards of that era (i.e., the 1973 ​​Standard on Protective Ensembles for Structural Fire Fighting and Proximity Fire Fighting) as well as the fire environment, which included homes furnished with natural materials. Based on changes in the fire environment, insights from the SCBA facepiece thermal degradation study, and experimental data from full-scale experiments such as the Size-up and Search & Rescue project, the researchers suggest expanding the thermal exposure classifications from three to six categories. 

The original classification was broken down into three classes: Routine, Ordinary, and Emergency. FSRI researchers demonstrated that more granularity is needed in both the Ordinary and Emergency categories of exposure. The creation of Ordinary I and II classes as well as Emergency I, II, and III classes keeps the relative criticality of the original designations while offering firefighters better information about the operational thresholds of each class. These updated categories better illustrate the realities of the firefighting environment and the responses of firefighters to that environment.

Thermal Exposure Classification Graph illustrating three to six categories
Modified thermal exposure classifications.

“The original thermal classes were proposed approximately 50 years ago. This study focuses on updating those classes to better reflect both the changes to the environment to which firefighters respond and the equipment they wear for protection.” - Craig Weinschenk, principal research engineer, FSRI

Improving SCBA facepiece performance and thermal exposure classification for enhanced firefighter safety

The combined findings from these studies offer implications for advancing firefighter safety. The first study quantifies the thermal performance of SCBA facepieces designed to meet more demanding specifications. The data show that modern facepieces provide a higher level of protection for the firefighter. This information supports the continued development of the SCBA facepiece as well as the creation of SCBA-related policies and procedures that promote firefighter health and safety. The updated thermal classes reflect a proactive approach to demonstrating the thermal thresholds of modern PPE. They also paint a better picture of the realities of the firefighting environment and the responses of firefighters to that environment, supporting fire departments and researchers alike. 

Read the two peer-reviewed journal articles:

  1. Thermal degradation of self-contained breathing apparatus facepiece lenses under radiant thermal loads
  2. Toward improved thermal exposure classes for structural firefighters

This research builds on work conducted at the Illinois Fire Service Institute and the National Institute of Standards and Technology. This work was supported by the Department of Homeland Security Federal Emergency Management Agency’s Assistance to Firefighters Grant Program under the Fire Prevention and Safety Grants: Research and Development (EMW-2017-FP-00628).

About the Journal of Fire Sciences:

The Journal of Fire Sciences is a leading, peer-reviewed international journal for the reporting of new and significant fundamental and applied research within the fire safety science community. Its overall content is generally aimed toward the prevention and mitigation of the adverse effects of fires involving combustible materials. 

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