The fire scene temperature for fire rescue operations is generally 600℃～1000℃, and the radiant heat is 115 kW/(m²·s)～200 kW/(m²·s), so the fire suit needs to have good thermal insulation performance to minimize the heat damage to the wearer within a certain period of time. When the fire suit is between the heat source and the protected fire fighter, the heat will be transferred to the inside of the fire suit through the combined effect of heat conduction, convection and radiation. Due to the reflection effect of the fabric surface and the absorption effect of the fabric, it has a certain thermal insulation performance.
The thermal conductivity of fabric fibers is much greater than the thermal conductivity of air, so when heat is transferred from the outside to the inside of the fire suit, there is a certain lag compared to the direct transfer of the same distance and time in the air. The number of layers of fire suit fabric, fabric properties, body shape and wearing status all have an impact on the thickness of the air layer. A smaller thickness of the air layer under the clothes has too little resistance to heat energy, which is easy to cause second-degree burns on the skin; but an excessively large air layer thickness will produce a thermal convection effect and promote heat transfer.
The thermal insulation performance of fire suits is closely related to the thermal conductivity of fiber raw materials, the structural design of fire suits, and the structure of fabrics and linings. In the selection of fire suit fibers, textile fibers with poor thermal conductivity are selected to make it difficult for the heat from external heat sources to be transferred to human skin, thereby improving the thermal insulation of fire suits. In the structural design of fire suits, openings and sutures with leakage are minimized as much as possible, and fire suit fabrics with appropriate tightness are selected to reduce the direct channels for heat from the environment to be transferred inward, thereby achieving the purpose of optimizing the thermal insulation performance of fire suits; the closer the thickness of the air layer is to a reasonable value, the greater the heat transfer resistance and the better the thermal insulation performance.