By Daniel Madrzykowski
Introduction
Over the past 50 years, changes in construction materials, construction methods, insulation, and furnishings have changed the means and the speed of fire growth within a structure. Both experiments and Line of Duty Death (LODD) investigations have demonstrated the importance of understanding of how ventilation affects fire behavior. Fires in today’s fire environment, fueled predominantly by synthetic materials, commonly become ventilation-limited. How, where, and when a fire receives oxygen greatly affects the fire dynamics and the resulting thermal environment inside the structure.
During the same 50-year period, the tactics firefighters use on the fire ground have also changed, largely due to the improvements in protective equipment and clothing firefighters rely on to enter high-temperature atmospheres considered immediately dangerous to life or health (IDLH). Just as the use of synthetic materials has overtaken the use of natural materials such as cotton, wool, or wood in homes, the same trend is true for firefighter protective clothing and equipment. In the past, firefighting coats were wool-lined and had an outer layer of cotton canvas or rubber. Firefighters protected their feet and legs with long rubber boots. Hoses used to be cotton-jacketed with rubber liners. Today, the firefighter has the most-advanced protective ensemble and the widest range of tools and equipment for fighting fire than ever before. The synthetic materials currently used in firefighting gear have improved performance over natural materials in many ways.
However, in the aftermath of firefighter LODDs and Line of Duty Injuries (LODIs), the question of the protective capabilities of firefighter protective clothing and safety equipment arises. Although firefighter protective clothing and safety equipment has been improving over the years, how do these improvements align with the changes in the firefighter’s workplace? In other words, have the hazards of the structural fire increased? If so, are the current thermal performance standards for firefighter protective clothing and safety equipment appropriate for the current operational environment? This study serves as a step toward addressing the question of how well we understand the thermal conditions in the firefighters ’ operational environment.
The study is composed of these four tasks.
- Literature Review and Defining the Operational Environment. Provide a comprehensive review of available literature related to thermal conditions in the firefighter operational environment. Determine extent of the operational environment in a structural fire incident, including location and exposures. Possible locations to consider include rooms, hallways, stairwells, and exterior of structure.
- Gap Analysis. Determine gaps in available information about thermal conditions in the operational environment.
- Thermal Scenarios. Identify conceptual thermal scenarios that can form the technical basis for test standards. These should include a quantitative description of the operational environment based on information from previous tasks.
- Final Report. Synthesize the information gathered in the completion of the previous tasks to develop a comprehensive description of the firefighter equipment operational environment based on the available information. The description of the operational environment should use terms that can be communicated to users (i.e., firefighters).
Summary
The goal of this study was to review the available literature to develop a quantitative description of the thermal conditions that firefighters and their equipment are exposed to in a structural fire environment. The thermal exposure from the modern fire environment was characterized by reviewing fire research studies and fire ground incidents that provided insight and data to develop a range of quantification. This information was compared with existing standards for firefighting PPE and equipment to generate a sense of the gap between known information and the need for improved understanding. The comparison of fire conditions with the thermal performance requirements of firefighter PPE and equipment demonstrates that the equipment a firefighter wears or uses can fail in a fire in a compartment under certain conditions.
It is clear that fire can generate thermal environments that exceed the capabilities of firefighter PPE and equipment that are available today. Since the 1970s, the NFPA, researchers, the fire service, and manufacturers have been working together to improve and optimize the protective capabilities of the PPE and equipment. Optimization is a key word. Gear could be built to withstand higher heat transfer rates, but most solutions result in the addition of weight, reduced breathability, increased heat stress, some loss of functionality, and increased cost, so a fireproof suit with fireproof safety equipment is not likely to be available anytime soon. Because potential solutions could be more harmful to firefighters than the current hazards at most fire scenes, a careful, holistic analysis is needed before implementing changes to the standards.
The review pointed out that:
- The accepted pairing of gas temperature ranges with a corresponding range of heat fluxes does not reflect all fire conditions. In some cases, the heat flux exceeds the hazard level of the surrounding gas temperature and vice versa.
- Thermal conditions can change within seconds. Experimental studies and incidents were identified in which firefighters would be in thermal conditions that were safe for operation based on the temperature and heat flux, but a change in their environment exposed the firefighters to conditions that could exceed the protective capabilities of their PPE and equipment.
- Gas velocity is not explicitly considered within the thermal performance requirements. PPE and equipment tested with a hot air circulating (convection) oven are exposed to gas velocities of approximately 1.3 m/s (3 mph). The convected hot gas flows within a structural fire could be in the range of 2.2 m/s (5 mph) to 9.0 m/s (20 mph). If the firefighter were located in the exhaust portion of a flow path while operating above the level of the fire, the hot gas velocity could be higher. The increase in hot gas velocity would serve to increase the convective heat transfer rate to the PPE, the equipment, and the firefighter, reducing the safe operating time within the structure.
- Based on the limited data available, it appears the effectiveness of currently available protective clothing enables firefighters to operate routinely in conditions above and beyond the routine conditions measured in the fire ground exposure studies conducted during the 1970s.
The fire service and fire service standards communities could benefit from: 1) an improved understanding of real-world fire ground conditions using modern sensor and data acquisition methods for monitoring the firefighting environment; 2) an improved understanding of the impact of convection on the capabilities of PPE and equipment; and 3) an effort to harmonize or balance the thermal exposures in components of firefighter protective clothing and safety equipment.
Fire officers and chiefs must consider the capabilities of the protection that their firefighters have when determining the strategies and tactics for a fire attack to ensure the gear is within the design operating environment, and to maintain the safety factor it provides in case of an emergency.
Daniel Madrzykowski with the UL Firefighter Safety Research Institute, Columbia, MD
Acknowledgments
The author would like to thank the Fire Protection Research Foundation for their support of this study, especially Dan Gorham for his guidance on the needs of the technical committees that have requested this information. In the course of conducting this research, the author contacted several libraries and archives to locate some of the material used in the literature search. The author would like to acknowledge the assistance of Edward Metz and his staff at the National Emergency Training Center Library, Justine Wagner of the UL Archive, Joy Rodowicz of NFPA’s Charles S. Morgan Technical Library, and Wayne Powell and Frank Schmersal of the National Fire Heritage Center.
The full report can be found at this link:
http://www.nfpa.org/News-and-Research/Fire-statistics-and-reports/Research-reports/For-emergency-responders/Fire-Fighter-Equipment-Operational-Environment-Evaluation-of-Thermal-Conditions.