Definitions cont'd - hdbk10920286

DOE-HDBK-1092-98

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 of

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:

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

1. 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

2. 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

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

NOTE: Combustible dusts which are electrically nonconductive include dusts produced in the

handling and processing of grain and grain products, pulverized sugar and cocoa, dried egg and

milk powders, pulverized spices, starch and pastes, potato and woodflour, oil meal from beans

and seed, dried hay, and other organic materials which may produce combustible dusts when

processed or handled. Dusts containing magnesium or aluminum are particularly hazardous and

the use of extreme caution is necessary to avoid ignition and explosion.

b. Class II, Division 2--A Class II, Division 2 location is a location in which:

1. combustible dust will not normally be in suspension in the air in quantities sufficient to

produce explosive or ignitable mixtures, and dust accumulations are normally insufficient

to interfere with the normal operation of electrical equipment or other apparatus; or

2. dust may be in suspension in the air as a result of infrequent malfunctioning of handling or

processing equipment, and dust accumulations resulting therefrom may be ignitable by

abnormal operation or failure of electrical equipment or other apparatus.

NOTE: This classification includes locations where dangerous concentrations of suspended dust

would not be likely but where dust accumulations might form on or in the vicinity of electric

equipment. These areas may contain equipment from which appreciable quantities of dust would

escape under abnormal operating conditions or be adjacent to a Class II Division 1 location, as

described above, into which an explosive or ignitable concentration of dust may be put into

suspension under abnormal operating conditions.

Class III locations--Class III locations are those that are hazardous because of the presence of easily

ignitable fibers or flyings but in which such fibers or flyings are not likely to be in suspension in the

air in quantities sufficient to produce ignitable mixtures. Class 111 locations include the following:

B-26