Hazardous Area Protection Guide
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A Guide to the Selection of Electrical Equipment for Installation in Hazardous Areas
The information below is given as a guide to enable the users of this catalogue to select the correct hazardous area equipment for their application. It should not be used to define the nature of hazardous areas, this is a task for experienced professionals in the field of hazardous area definition. Nor should it be used as replacement for the very detailed standards which cover the installation of electrical equipment in hazardous areas.
--What conditions are required for an explosion?
There are three elements required in order to create a hazardous area.
2. A flammable medium for example gases, vapours, mists and dusts.
3. A source of ignition of sufficient energy and /or a rise in temperature.
--What is an explosive atmosphere?
An explosive atmosphere is created when air and an flammable medium mix such that a rise in temperature or an electrical spark produces an explosion.
--What is a potentially explosive atmosphere?
An atmosphere is defined as potentially explosive when in its normal state it is not explosive but there exists the possibility that in abnormal circumstances it will become explosive. For example in the case of a gas leak or the vapourisation of a fluid leak.
An explosive atmosphere needs a minimum energy for ignition. The energy produced by arcs and sparks are many times greater than this minimum.
--Self Ignition Temperature
An explosive atmosphere can self ignite if the local temperature rises above the so-called self ignition temperature. This temperature is different for different flammable mediums.
-The classification of hazardous areas-
--Gases, Vapours, Mists and Dusts.
Explosive atmospheres are caused by a mixture of gases, vapours, mists dusts and air. If the explosive atmosphere is caused by gases, vapours and mists the hazardous area is coded G. If the explosive atmosphere is caused by dusts the hazardous area is coded D.
Explosion protected electrical equipment is classified in terms of the ignition temperature, the ignition capability and flame transmission capacity of the explosive atmosphere in which it is designed to operate.
In the first instance equipment is divided into two groups dependingon its location above or below ground.
Group I Electrical equipment for use below ground in areas susceptible to firedamp.
Group II Electrical equipment for all other areas.
Group II equipment is further divided into three sub groups depending on the ignition and flame transmission characteristics of the explosive hazard.
These sub-groups are designated IIA, IIB and IIC.Zones
-The probability of an explosive atmosphere occurring.-
Zone 0 defines an area in which an explosive atmosphere caused by a mixture of air and gases, vapours and mists is present continuously for long periods or very frequently.
Zone 1 defines areas in which an explosive atmosphere caused by a mixture air and gases, vapours and mists is expected to occur occasionally.
Zone 2 defines areas in which an explosive atmosphere caused by a mixture of air and gases, vapours and mists is unlikely and if it should occur it will be for a short time and then only rarely.
Zone 20 defines an area in which an explosive atmosphere caused by a cloud of combustible dust and air is present continuously for long periods or very frequently.
Zone 21 defines areas in which an explosive atmosphere caused by a cloud of combustible dust and air is expected to occur occasionally.
Zone 22 defines areas in which an explosive atmosphere caused by a cloud of combustible dust and air is unlikely and if it should occur it will be for a short time and then only rarely.
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