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. The National Institute of Standards and Technology (NIST), conducted experiments and detailed findings which demonstrated a range of realistic thermal exposures and environmental conditions, which can result in thermal degradation and even catastrophic failure of facepieces.