Thermal Performance of Self-contained Breathing Apparatus Facepiece Lenses Exposed to Radiant Heat Flux

Résumé du livre

Fire fighters are exposed to highly variable thermal environments including elevated temperatures, convective heat flux, and radiant heat flux, which can put a significant burden on personal protective equipment. Thermally degraded and melted self-contained breathing apparatus (SCBA) facepieces have been identified as a contributing factor in certain fire fighter fatalities and injuries in the United States. At the current time, standard performance tests for SCBA facepieces are conducted at less severe thermal conditions than other components of a fire fighter's ensemble and equipment. In order to better understand the level of thermal performance of the SCBA facepiece lens and to develop an improved performance test method, facepieces were exposed to controlled and well characterized elevated thermal environments. In these experiments, SCBA facepieces were exposed to radiant heat fluxes of 2 kW/m2 to 15 kW/m2 from a natural gas fired radiant panel apparatus. The facepieces were mounted on a headform and instrumented with thermocouples to measure the temperatures of the exterior lens surface, the interior lens surface, inside the facepiece, on the headform, and in the airway of the headform during exposure. Heat flux to the headform was also measured during the exposures. Airflow through the mouth and respiratory system was simulated using a breathing apparatus, with the air to the mask supplied by an SCBA, at an average flow rate of 40 L/min at 24 breaths/min. The pressure inside the facepiece was measured during the experiments. During the experiments, the facepiece lenses sustained various degrees of thermal damage, ranging from no visible damage to the formation of crazing, bubbles, holes, and protuberant deformations. The maximum temperatures measured on the exterior of the lenses were approximately 290 °C, while the maximum airway temperatures were approximately 55 °C. An incident radiant heat flux of 15 kW/m2 was selected as representative of fire fighter exposure and as a useful test criterion for evaluating the performance of the SCBA facepiece lenses. Measurement of internal facepiece pressure was found to be a valuable method for determining the effect of holes on firefighter air supply duration and breathing protection. All of the SCBA facepieces tested exhibited holes in the lens in less than 5 min of exposure to 15 kW/m2 of incident heat flux. Although much was learned about conditions associated with thermal degradation of SCBA facepiece lenses, more research and development are needed to understand the thermal degradation of facepiece lenses and to develop equipment that better resists the radiant heat fluxes encountered by the fire service during structure fires. These experiments were conducted with support in part by the Department of Homeland Security Science and Technology Directorate and the United States Fire Administration.