There are many places where an explosive mixture of air and gas
or vapour is, or may be present continuously, intermittently or as
a result of an accident. These are defined as hazardous areas by BS
EN 600079, the code of practice for installation and maintenance of
electrical apparatus in potentially explosive atmospheres.
Hazardous areas are common in petroleum and chemical engineering
plants and in factories processing and storing gases, solvents,
paints and other volatile substances.
Electrical equipment for use in these areas needs to be designed
so that it cannot ignite an explosive mixture, not only in normal
operation but also in fault conditions. There are a number of
methods available to achieve this but one of the most common is
Flameproof equipment is contained in a box so strong that an
internal explosion will neither damage the box nor be transmitted
outside the box. The surface must remain cool enough not to ignite
the explosive mixture.
When flameproof equipment is interconnected, flameproof wiring
must be used. This method is most valuable when high power levels
are unavoidable but it is not acceptable for areas in which an
explosive gas/air mixture may be continuously present or present
for long periods.
For this reason, Apollo fire detectors are made intrinsically
safe rather than flameproof. Intrinsically safe equipment operates
at such low power and with such small amounts of stored energy that
it is incapable of causing ignition:
- In normal conditions
- With a single fault
- With a combination of any two faults
In any of these conditions, every component must remain cool
enough not to ignite the gases for which it is approved.
Apollo offer intrinsically safe (IS) detectors in the XP95 and