"Fire fighters are exposed to highly variable environments including elevated temperatures and convective and radiant thermal 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. The SCBA facepiece lens is often considered the weakest component of a fire fighter's ensemble in high heat conditions, but the level of thermal performance of the facepiece lens is not well understood. These experiments, conducted by the National Institute of Standards and Technology (NIST), demonstrated a range of realistic thermal exposures and environmental conditions, which can result in thermal degradation and even catastrophic failure of facepieces. SCBA facepieces were exposed to thermal environments from propane-fueled calibration experiments and furnished townhouse fire experiments. The rooms and the facepieces were instrumented to measure temperatures of the environment and the facepieces. The fire experiments lasted 5 min to 10 min and produced ceiling temperatures of approximately 500 °C (932 °F) to 750 °C (1382 °F) in the room adjacent to the fire. A heat flux gauge was also installed next to the facepieces and measured peak heat fluxes from approximately 2 kW/m2 to 55 kW/m2. Eight facepieces were tested in six different experiments, with three facepiece lenses showing evidence of thermal degradation from the exposure. Maximum exterior lens temperatures were as high as 300 °C (572 °F) in these cases. The environments that caused the failures were identified in an attempt to characterize the thermal performance of SCBA facepieces. Constant airflow at 40 L/min was introduced into three of the facepieces to study if there is a cooling effect associated with breathing. The facepieces with airflow did have a slightly increased temperature difference between the interior and exterior lens surfaces as compared to facepiece lenses without airflow in the same experiment. Although much was learned about conditions associated with thermal degradation of SCBA facepiece lenses, more experiments are needed to understand the thermal degradation and more definitively predict the conditions that are likely to cause a facepiece lens failure. These experiments were conducted with the support of the Chicago Fire Department, the Department of Homeland Security, and the U.S. Fire Administration."
National Institute of Standards and Technology Technical Note 1724
National Institute of Standards and Technology: http://www.nist.gov/