Definitions cont'd - hdbk10920266

DOE-HDBK-1092-98

containers or closed systems from which they can escape only in case of accidental rupture

or breakdown of such containers or systems, or in case of abnormal operation of equipment;

b. in which hazardous concentrations of gases or vapors are normally prevented by positive

mechanical ventilation, and which might become hazardous through failure or abnormal

operations of the ventilating equipment; or

c. that is adjacent to a Class I, Division 1 location, and to which hazardous concentrations of

gases or vapors might occasionally be communicated unless such communication is

prevented by adequate positive-pressure ventilation from a source of clean air, and effective

safeguards against ventilation failure are provided.

NOTE: This classification usually includes locations where volatile flammable liquids or flammable

gases or vapors are used, but which would become hazardous only in case of an accident or of

some unusual operating condition. The quantity of flammable material that might escape in case

of accident, the adequacy of ventilating equipment, the total area involved, and the record of the

industry or business with respect to explosions or fires are all factors that merit consideration in

determining the classification and extent of each location.

Piping without valves, checks, meters, and similar devices would not ordinarily introduce a

hazardous condition even though used for flammable liquids or gases. Locations used for the

storage of flammable liquids or a liquefied or compressed gases in sealed containers would not

normally be considered hazardous unless also subject to other hazardous conditions.

Electrical conduits and their associated enclosures separated from process fluids by a single seal

or barrier are classed as a Division 2 location if the outside of the conduit and enclosures is a

nonhazardous location.

Class II locations--Class II locations are those that are hazardous because of the presence of

combustible dust. Class II locations include the following:

Class II, Division 1. A Class II, Division 1 location is a location:

a. In which combustible dust is or may be in suspension in the air under normal operating

conditions, in quantities sufficient to produce explosive or ignitable mixtures; or

b. where mechanical failure or abnormal operation of machinery or equipment might cause

such explosive or ignitable mixtures to be produced, and might also provide a source of

ignition through simultaneous failure of electric equipment, operation of protection devices,

or from other causes, or

c. in which combustible dusts of an electrically conductive nature may be present.

NOTE: This classification may include areas of grain handling and processing plants, starch plants,

sugar-pulverizing plants, malting plants, hay-grinding plants, coal pulverizing plants, areas

where metal dusts and powders are produced or processed, and other similar locations which

contain dust producing machinery and equipment (except where the equipment is dust-tight or

vented to the outside). These areas would have combustible dust in the air, under normal

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