Page 23 - Electrical Installation in Hazardous Area

2 Electrical installations in hazardous areas

Senghennyd colliery - 191 3

An underground firedamp (methane) explosion caused a roof fall which cut
off over 400 miners from a shaft in a burning section of the colliery. Most
of them died from the resulting suffocation.

Flixborough - 1974

A modification to a process plant, said by the accident report not to have
been properly considered, was identified as causing a major release of
flammable gas resulting in an immense aerial explosion. Loss of life on the
plant was mercifully low (probably because it was Saturday) but damage to
the plant and surrounding residential and other properties was significant.

Piper Alpha - 1988

This oil platform was effectively destroyed by a gas explosion which
resulted from a major release of gas suggested to be due to erroneous
process operation. The initial and subsequent explosions and fire effectively
prevented controlled evacuation of the platform and heavy loss of life was
caused.

Texaco Pembroke refinery - 1994
A major vapour explosion occurred leading to a major fire which was
extremely difficult to extinguish. The refinery burned for a considerable
time with consequent adverse effects on the local environment. Casualties
were light but the refinery suffered considerable damage.
The above examples clearly demonstrate the dangers present, particu-
larly in locations where escape of personnel is difficult and it is essential,
therefore, that all involved have an understanding of the technology used
to minimize the risk of explosion.

1.2 Technological approach

The objective of the technology associated with the use of electrical
equipment in potentially explosive atmospheres is to reduce the risk of
an explosion to an acceptable level. To have an explosion three elements
are necessary - namely fuel, oxygen and a source of ignition (see Fig. 1.1).
Oxygen is present in air to a sufficient extent to support combustion and
cannot normally be excluded, which leaves only the fuel and ignition
sources as elements to which influence can be applied. This has formed