| Explosion-proof equipment is generally required in environments where there
is an expected or possible presence of flamable gas(es). These locations
might include: petroleum refineries, engine spaces, aircraft hangars, grain
storage or processing*, mines* etc.
Generally any equipment to be used in such a location must not ever create
a spark or flame which would be capable of initiating a larger fire or
explosion.
It is generally difficult to ensure that (e.g.) a switch or motor can
never internally create any spark or that potentially flamable gasses can not
enter such a device. Therefore the design of explosion-proof
equipment generally assumes that an explosive mixture of gasses could enter
the device and may try to ensure:
- Cases will not be breached in the event of an internal explosion
- Continuous venting (possibly with inert gas)
- Maintenance of positive pressure
- Use of inherently safe components / design
This can be achieved by a combination of ensuring the case is strong enough
to withstand any pressure which might be developed and appropriately strong
seals on any moving parts. The use of inherently safe components is a
relatively new approach to ensuring safety in hazardous environments,
involving higher assurance in the design.
A number of other steps are important wherever there is a high risk of fire
or explosion. Eliminating sources of sparks (from static, grinding etc) may
be achieved with proper grounding. Obviously activities such as welding
must not be undertaken in such environments. Also non-sparking tools are
advised, usually this dictates use of beryllium-copper, bronze and
other non-ferous metals.
* Dust explosions most often include: wood, grain, resin / plastic, starch and
some metals (aluminum, magnesium)
References:
NFPA: http://www.nfpa.org
Mark's Standard Handbook for Mechanical Engineers
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