Gardner Denver Reavell H5000 Series, Operator'S Handbook Manual

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SAFETY
PAGE 15
1.9.5 PRODUCTION METHODS
There are two main types of protection against explosion occurring in hazardous areas; INTRINSIC
SAFETY and FLAMEPROOF . There are various levels of the latter, brief descriptions and options
available are as follows:-
1.9.5.1 INTRINSIC SAFETY (IS)
This is based on the principle of restricting the electrical energy available in circuits in the hazardous
area such that any sparks or hot surfaces that may occur as a result of electrical faults are toop weak
to cause ignition.
The useful power is about 1 watt which is sufficient for most modern instrumentation. I.S. is therefore
inherently safe as evidenced by the fact that it is the only technique that is accepted for Zone 1 (high
risk) hazardous areas.
It is also safer for personnel since the voltages are low and it allows field equipment to be maintained
and calibrated ‘live’ without the need to obtain a gas-free certificate. I.S. equipment is light in weight
and can be inter-connected by ordinary instrument cabling.
Note: Intrinsic safety is only suitable for low power duties such as cut-out or control switches.
Although I.S. classified solenoid valves are available for some duties they are expensive
.
1.9.5.2 FLAMEPROOF
Flameproof equipment must be used for electric motors and solenoid valves. There are varying
degrees of protection in this category which are described below.
Flameproof EExd
A type of protection in which the parts which can ignite an explosive atmosphere are placed in an
enclosure which can withstand the pressure developed during an internal explosion of an explosive
mixture and which prevents the transmission of the explosion to the explosive atmosphere
surrounding the enclosure.
Increased Safety Eexe
The method of protection by which additional measures are applied to electrical equipment so as to
give increased security against the possibility of excessive temperatures and of the occurrence of
sparks and arcs during the service life of the apparatus, It applies only to equipment no parts of which
produce sparks or arcs or exceeds the limiting temperature in normal service.
Non Sparking ExN
A type of protection applied to electrical apparatus such as that, in normal operation, it is not capable
of igniting a surrounding explosive atmosphere and a fault capable of causing ignition is not likely to
occur.
Pressurised Eexp
Protection is given by subjecting the equipment’s internal parts to a positive pressure relative to the
surroundings so that the potential explosive atmosphere cannot penetrate the equipment in service.
Continuous flushing or compensation for leakage must be arranged. It is also necessary to provide
shut-down switches to operate in the event of failure to maintain the positive pressure.