Although "flameproof" and "explosionproof" designs are technically different, they both use the same principles. They rely on the physical enclosure to contain any ignition in a safe manner. This makes them the only containment technique concerned with containment, rather than prevention, of an explosion.
Contrary to popular belief, flameproof enclosures are not totally sealed. They are not completely sealed against flammable gas entry, nor are they totally sealed against the explosion leaving the enclosure.
Instead, they rely on the correct mating of metal-to-metal surfaces, such as flanges and threads, to quench any flame front before it leaves the enclosure. By the time the explosion leaves the container, it is too cold to cause any subsequent ignition outside the enclosure.
Flameproof enclosures may also use other flame barriers, such as metal sinters, to contain the flame front. Sinters, for example, allow gases to pass through into the enclosure while preventing a flame front from escaping.
Flameproof enclosures have the advantage of not requiring any limitations on the power or construction of the electronics inside the device. This makes them highly useful for high-power equipment that cannot be protected in another manner.
However, in order to contain the significant pressures and temperatures, they often must be constructed of materials such as aluminum, steel, and heavy glass, which makes them expensive to manufacture. Therefore, enclosing large pieces of equipment in flameproof enclosures may not be cost-effective. They also often have a size limitation beyond which they can no longer safely contain an explosion.
Testing flameproof enclosures involves practical testing to determine if an internal explosion causes an external one, as well as pressure tests several times higher than the actual expected worst-case pressure. This type of testing is accurate, but time-consuming and costly.
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Go to Certification Standards.
Go to Understanding ATEX.
Go to Understanding IEC 60079.
