Flameproof enclosures are not gas tight, and a gas or vapour will enter the enclosure through joints or cable entries. Since these enclosures are designed to contain components which are an ignition source, ignition of the gas may occur, and the resulting explosion pressure can reach a peak value in excess of 10 Bar (150psi). IIC gases have a greater explosion pressure than IIB or IIA gases, typically up to 13 Bar for hydrogen).
The enclosure must therefore be strong enough to contain this explosion pressure, and the gaps at the joints and threads of cable entries must be long and narrow to help cool the flames/ hot gases to prevent transmission of the internal explosion to a flammable atmosphere outside the enclosure.
