Thermal Protective Performance (TPP) is a test that indicates the amount of protection a material or material system provides against both convective and radiant heat. To determine actual time to burn, the TPP score is divided in half and the resulting number is the time, in seconds, that human tissue reaches second degree burn in a flash over situation. The NFPA 1971 (2013 edition) standard requires a TPP of 35 Cal/cm2, which is the equivalent of 17.5 seconds to second degree burn.