Types and Definition of Hazardous Locations:
Class I, Division I
Locations in which hazardous concentrations of flammable gases or vapors exist continuously, intermittently, or periodically under normal operating conditions.
Class I, Division II
Locations in which volatile flammable gases are hazardous liquids, vapors or gases will normally be confined within closed containers or closed systems from which they can escape only in case of accidental rupture or breakdown of such systems or containers, or in case of abnormal operation of equipment.
Class II Locations
Locations which are hazardous because of the pressure of combustible dust.
Class III Locations
Location in which easily ignitable fibers or materials producing combustible flyings are present.
Atmosphere containing acetylene.
Atmospheres containing hydrogen or gases or vapors of equivalent hazards such as manufactured gas.
Atmospheres containing ethyl ether vapors, ethylene, or cyclopropane.
Atmospheres containing gasoline, hexane, naptha, benzine, butane, alcohol, benzol, lacquer solvent vapors, or natural gases.
Atmospheres containing metal dust, including aluminum, magnesium, and their commercial alloys, and other metals of similar hazardous characteristics.
Atmospheres containing carbon black coal or coke dust.
Atmospheres containing flour, starch, or grain dusts.
Explosion- Proof Enclosure
Explosion-proof enclosure means an enclosure for electrical apparatus which is capable of withstanding, without damage, an explosion which may occur within it, of specified gas or vapor, and capable of preventing ignition of specified gas or vapor surrounding the enclosure from sparks or flames from explosion of specified gas or vapor within the enclosure.
To make a system explosion-proof, the enclosure must be capable of withstanding an explosion, and the system must be installed per national electrical code for hazardous locations.
Intrinsically Safe Equipment
Intrinsically safe equipment and wiring are incapable of releasing sufficient electrical energy under normal or abnormal conditions to cause ignition of specific hazardous atmospheric mixture. Abnormal condition will include accidental damage to any part of the equipment or wiring, insulation, or other failure of electrical components, application of overvoltage, adjustment and maintenance operations, and other similar conditions.
Equipment built for this requirement is designed with low energy storage components as outlined in ISA procedure RP12-2. Several advantages to the intrinsic safety approach are listed below. These advantages
have to be weighed against the initial higher purchase price. Today it is estimated that 60 percent of these types of installations are classified as intrinsically safe.
· Lower installation cost.
· Less operator-dependent to maintain a safe system.
· Easier to maintain and repair.
· Accessible to repair without special precautions before opening the unit.