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Explosion-proof instruments for explosive gas environments include: Category I: Explosion-proof instruments for use in coal mines; Category II: Explosion-proof instruments for use in factories. Instruments used in explosive hazardous areas must have the capability, during operation, to prevent the ignition of the explosive mixtures surrounding them. Explosion-proof instrument equipment that meets the requirements can be of the flameproof type, increased safety type, intrinsically safe type, positive pressure type, oil-flushing type, sand-flushing type, spark-free type, sealed type, special explosion-proof type, and dust explosion-proof type. Maximum surface temperature of explosion-proof instruments: For intrinsically safe types, the maximum surface temperature refers to the surface of the enclosure; for other explosion-proof types, it refers to the surfaces that may come into contact with explosive mixtures. For Class I explosion-proof instruments, when measures are taken to prevent the accumulation of coal dust, the maximum surface temperature shall not exceed 450°C; in the presence of coal dust deposits, the maximum surface temperature shall not exceed 150°C. The maximum surface temperatures for Class II explosion-proof instruments are as follows: Group T1 – 450°C, Group T2 – 300°C, Group T3 – 200°C, Group T4 – 135°C, Group T5 – 100°C, Group T6 – 85°C. When such instruments are used in areas with flammable dust and dust accumulates on their surfaces, the allowable maximum surface temperature should be calculated based on the combustible temperature of the dust layer. The various types of explosion-proof instruments, such as flameproof type, increased safety type, intrinsically safe type, positive pressure type, oil flushing type, sand flushing type, spark-free type, sealed type, special explosion-proof type, and dust explosion-proof type, should be selected based on the actual circumstances. They cannot be used together.