Which Explosion-Proof Level Is Higher, BT5 or BT4

The BT5 explosion-proof rating is considered high.

Class And Level	Ignition Temperature And Group
-	T1	T2	T3	T4	T5	T6
-	T＞450	450≥T＞300	300≥T＞200	200≥T＞135	135≥T＞100	100≥T＞85
I	Methane
IIA	Ethane, Propane, Acetone, Phenethyl, Ene, Aminobenzene, Toluene, Benzene, Ammonia, Carbon Monoxide, Ethyl Acetate, Acetic Acid	Butane, Ethanol, Propylene, Butanol, Acetic Acid, Butyl Ester, Amyl Acetate Acetic Anhydride	Pentane, Hexane, Heptane, Decane, Octane, Gasoline, Hydrogen Sulfide, Cyclohexane, Gasoline, Kerosene, Diesel, Petroleum	Ether, Acetaldehyde, Trimethylamine		Ethyl Nitrite
IIB	Propylene, Acetylene, Cyclopropane, Coke Oven Gas	Epoxy Z-Alkane, Epoxy Propane, Butadiene, Ethylene	Dimethyl Ether, Isoprene, Hydrogen Sulfide	Diethylether, Dibutyl Ether
IIC	Water Gas, Hydrogen	Acetylene			Carbon Disulfide	Ethyl Nitrate

All units are rated at IIB level. However, T4 equipment has a maximum surface temperature limit of 135°C, whereas T5 equipment is limited to 100°C. Lower maximum surface temperatures indicate greater safety. Thus, equipment compliant with BT5 standards is also compatible with BT4, but the reverse does not apply.