Circuit breaker cont'd - hdbk109220040232

DOE-HDBK-1092-2004

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 1, 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 operating conditions, in quantities sufficient to produce explosive or

ignitable mixtures. 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

B-6