The flame retardancy index includes after flame time, afterglow time, char length, melting, dripping, and thermal protection performance.
After flame time: under the specified test conditions, the time for the material to continue to burn with flame after removing (igniting) the fire source. The shorter the burning time is, the shorter the burning time with flame is, which can reduce the burn of flame to the human body and avoid the continuous spread of flame.
Afterglow time: under the specified test conditions, when the flaming combustion is terminated, or when the fire source is removed (ignited), the material continues to burn without flame. Smoldering combustion has the characteristics of slow reaction speed, not easy to extinguish, strong concealment, and so on. When the external conditions are satisfied, smoldering combustion can quickly transform to open fire and cause secondary burns to the human body. The longer the smoldering time is, the weaker the protective function is.
Char length: the maximum length of material damage area in a specified direction under specified test conditions. The larger the damage length is, the smaller the protection area is.
Melting and dripping: generally, synthetic fibers are flammable and fusible, and the viscous liquid or droplets will adhere to human skin quickly, causing deep burns. Therefore, melting and dripping are not allowed in flame retardant overalls.
Thermal protection performance: the thermal value of second-degree burn caused by fabric. The higher the value is, the stronger the thermal protection performance of the fabric is, and the stronger the protection function to the human body is.