Definitions Applicable to 29 CFR 1926 Subpart K cont'd

DOE-HDBK-1092-2004

accidental rupture or breakdown of such containers or systems, or in case of abnormal

operation of equipment; or

2. in which ignitable 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

3. that is adjacent to a Class 1, Division 1 location, and to which ignitable 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 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 I--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:

B-25