Division 2

DOE-HDBK-1092-2004

NEC Article 100 defines a flammable liquid as one that has a flashpoint below 38C (100F) or

one whose temperature is raised above its flashpoint. Flashpoint is the lowest temperature to

which a combustible or flammable liquid may be heated before sufficient vapors are driven off

and the liquid will flash when brought into contact with a flame, arc, spark, or another ignition

source. (See Section 1-3 of NFPA 497M for more details.)

5.3.1.2 DIVISION 2

NEC 500.5(B)(2) defines Class I Division 2 locations as those:

1. In which flammable liquids or gases are handled, processed, or used, but where such

materials are normally confined in closed 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 equipment operation.

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

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 500.5 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 500 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 11 Division 1 location is one:

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

sufficient to produce explosive or ignitable mixtures;

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

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

hazardous quantities. (See Table 5-6.)

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