Thermal Performance of SelfContained Breathing Apparatus Facepiece Lenses Exposed to Radiant Heat Flux

Abstract

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/m 2 to 15 kW/m 2 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/m 2 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/m 2 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

Characterizing a Firefighter’s Immediate Thermal Environment in Live-Fire Training Scenarios

“…It has been reported that surface cracking of a firefighter's SCBA facepiece can begin to occur at temperatures around 180°C and at an exposure to a heat flux of 5 kW/m 2 for a minimum of 12 min [35]. Firefighter radios begin to experience performance problems (drift of signal frequency, failure to transmit, etc.)…”

“…According to Putorti et al, an SCBA facepiece can begin to bubble when exposed to a heat flux of 5 kW/m 2 for approximately 12 min or 7 kW/m 2 for 6 min [35]. During Exposure 1, bubbling of the facepiece began to occur after roughly 9 min of Class I and Class II heat flux exposures (average of 1.1 kW/m 2 ) followed by less than 9 min of Class III heat flux exposures containing an average of 5.0 kW/m 2 .…”

“…The apparatus was modified to provide for a range of heat flux exposures from 1 kW/m 2 to 20 kW/m 2 for testing firefighter protective equipment [33][34][35].…”

A study on the effect of repeat moderate intensity radiant exposures on SCBA facepiece properties

“…However, exposures below these levels -that may result in structural changes to the lens yet provide minimal visual indications of damagewere not studied. In their conclusions, Putorti et al suggested that "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" [21].…”

“…To follow up these experiments, NIST developed a laboratory based radiant heat exposure protocol for testing SCBA facepieces [21]. Putorti et al conducted a series of laboratory experiments, which examined the thermal performance of polycarbonate SCBA facepieces under a variety of radiant heat flux levels, with a focus on severe conditions where lens degradation and/or failure may occur on the order of 10 minutes.…”