Class II

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

equipment operation.

2. In which gases or vapors are normally prevented, by positive mechanical ventilation, from

forming ignitable concentrations and which might become hazardous through failure or

abnormal operation of the ventilating equipment

3. That are adjacent to a Class I Division 1 location and to which ignitable concentrations of

gases or vapors might occasionally be transmitted unless such transmittal is prevented by

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

against ventilation failure are provided.

The fine-print note #2 to NEC Section 500-5(b) describes a number of areas and occupancies

normally classified as Class I Division 2 locations. For example, piping systems without valves,

meters, and devices do not usually cause a hazardous condition, even though they carry flammable

liquids, because they are considered a contained system. Therefore, the surrounding area can be

classified as a Class I Division 2 location.

5.3.2 CLASS II

A Class II location is defined in NEC Section 500-6 as an area where combustible dust presents a fire

or explosion hazard. Class II locations are divided into two divisions based on the normal presence

or absence of dust.

5.3.2.1 CLASS II DIVISION 1

A Class II Division 1 location is one:

1. In which combustible dust is in the air under normal operating conditions in quantities

sufficient to produce explosive or ignitable mixtures;

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 electrical equipment, operation of protective devices, or other

causes; or

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

quantities. (See Table 5-6.)

5.3.2.2 CLASS II DIVISION 2

A Class II Division 2 location is one where:

1. Combustible dust is not normally in the air in quantities sufficient to produce explosive or

ignitable mixtures;

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