Explosion-proof markings describe how electrical or mechanical equipment can safely operate in hazardous environments.
Let’s take Ex d IIB T4 Gb as an example and break it down step by step.
Ex is the universal symbol indicating compliance with explosion-proof standards such as IEC 60079 or GB3836. These standards ensure the equipment has been tested and certified by authorities like PCEC, ATEX, or IECEx.
d stands for Flameproof type. The enclosure is strong enough to contain any internal explosion and prevent flames or hot gases from igniting the surrounding atmosphere.
II means the equipment is suitable for gas environments other than underground mining. Group I covers mining applications, while Group II applies to general industrial areas, and Group III is for dust environments.
B refers to the gas subgroup, representing the ignition characteristics of gases.
Group IIA is the least ignitable (e.g., propane), IIB is medium (e.g., ethylene), and IIC is the most ignitable (e.g., hydrogen or acetylene).
Equipment rated for a higher group can also be used in lower groups.
T4 indicates that the maximum surface temperature of the equipment will not exceed 135°C, preventing ignition of gases with higher ignition temperatures.
Finally, Gb specifies the Equipment Protection Level (EPL).
“Gb” means high protection, suitable for Zone 1, where explosive gases are likely to occur occasionally.
“Ga” would represent very high protection for continuous exposure (Zone 0), while “Gc” is for enhanced protection in infrequent exposure (Zone 2).
In short, Ex d IIB T4 Gb means a flameproof device designed for gas environments, safe for ethylene-class gases, with a surface temperature below 135°C, and protection suitable for Zone 1 installations.
