UFC 3 -430-11
14 February 2001
3-7.2
Hazardous Locations. Hazardous locations are defined by NFPA-70,
National Electric Code. Enclosures must be rated for the location in which they will be
installed. Cost savings may be achieved by relocating an enclosure from a hazardous
location to a non-hazardous one. A summary of hazardous area classifications follows.
3-7.2.1
Class Definition
Class I - Gases and Vapors
Class II - Combustible Dusts
Class III - Easily Ignitable Fibers or Flyings
Classes I and II are applicable to boiler plants; class III is not.
3-7.2.2
Division Definition
Division 1 - Normally hazardous
Division 2 - Not normally hazardous
Division 1 is usually not applicable to boiler plants except for coal handling
and fuel storage areas. Division 2 is often applicable.
3-7.2.3
Group Definition
Group A - Acetylene
Group B - Hydrogen and other gases of equivalent hazard
Group C - Ethylene and other gases and vapors of equivalent hazard
Group D - Natural gas, gasoline, other gases and vapors of equivalent
hazard
Group E - Meta l dusts
Group F - Coal dust
Group G - Agricultural and plastic dusts
Groups A, B, C, E, and G are not applicable to boiler plants. Groups D and F
are applicable.
3-7.3
Special Considerations. When specifying enclosures note the following:
3-7.3.1 Maintenance. Class I, Group D, Division 2 can be met by either providing an
explosion proof enclosure or by providing a non-explosion proof enclosure and purging
it with air. The non-explosion proof enclosure is less expensive (initial cost) but requires
an air supply and more attention in that a constant air purge must be maintained. This
long -term maintenance is expensive. Therefore, to keep maintenance to a minimum,
specify the enclosure as explosion proof. Only exceptionally large equipment should be
considered for a Class 1, Group D, Division 2 constant air-purge system, where the life
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