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Light fittings for use in Hazardous areas have the following characteristics. They are sealed to prevent the ingress of the liquid, gas or dust, lens for lamp, protection of a robust impact resistant material. They have a seal or machined face to ensure resistance to liquid, dust or gas, or a quenching flame path. Light fittings have different grades of protection depending on their construction and intended purpose. Some fittings are classified according to their IP Ingress Protection rating as it is designated.
What constitutes a hazardous area: in some contexts it could be a badly lit step, however, we consider it an area in which a flammable material, gas or vapour must be mixed in the correct proportion with air and within this mixture a spark or heat is present, sufficient to ignite the mixture. When Light fittings and other electrical apparatus are to be installed in a Hazardous Area it is essential that the decision maker takes measures to reduce the likelihood of an explosion by the correct selection of the equipment to be installed in that area. As the gases and vapours liable to be present are rated according to ignition temperature, Flash point and lower explosive limit, this information must be on hand when making your light fitting selection.
Gases also have a gas group classification, namely Group I, Group IIA, Group IIB and Group IIC, where Methane falls in the category Group I, while Hydrogen is a Group IIC gas, together with Acetylene.
The general classification of the area is then Zone 1 and 2 for gases and vapours and volatile liquids present in the air Zone 21 for combustible dusts, metallic and non-metallic and also fibres in suspension in the air Zone 22 dust and easily combustible fibres, not normally in suspension in the air, but are present in sufficient quantities to produce a combustible mixture.
A common fault of the light fitting purchaser is the non-specification of the gland type required for the installation which has to be compatible to the type of cable and the core diameters.
There are different glands available for steel armoured cable and for sheathed cables. Also cables should be of the flame retardant type if for exposed usage and if not sand covered.
Of the more common type of light fittings available for the Zone 1 situation are those designated and enclosed in:
i) Flameproof or explosion proof Ex "d" housings.
ii) Increased Safety Ex "e".
Although both are suitable for use in this type of atmosphere there is a world of difference in their construction format.