Total Heat Loss
THL: Adopted in the NFPA 1971 2000 Edition to address firefighter
heat stress. It measures the ability of the garment to allow heat to pass
through it’s 3 layers, away from the body. Minimum requirement is 205
W/m2.
THL vs TPP
Both THL and TPP tests are taken on all 3 layers of the garment
together.
THL (Total Heat Loss) – In short, breathability.
Lighter / thinner garments = Higher THL (Comfort)
TPP (Thermal Protection Performance) – Thermal Insulation.
Thicker/heavier Garment = Higher TPP