AT4 A、T4
CT5 - C、T5
A and c stand for places where dangerous substances are found. Generally speaking, in China, propane gas is the representative of Class C places, and hydrogen and acetylene are the representatives of Class C places.
T stands for temperature, * * * is divided into six grades, T 1, T2. . . . T6
T4 represents that the surface temperature is less than 135 degrees;
T5 stands for low surface temperature 100 degrees.