NEC FLAMMABLE CONDITIONS BASIC INFORMATION AND TUTORIALS

The National Electrical Code addresses hazardous conditions that create the potential for fires to occur. Environments that pose fire or combustion hazards are listed in Articles 500-510. Requirements covering specific types of facilities that pose additional hazards, such as bulk storage plants or motor fuel dispensing locations, are explained in Articles 511-516.

NEC Section (C)(2)(1) describes Class II, Division 2 locations classifications. These are listed as:

1. Locations where some combustible dust is normally in the air but where abnormal operations may increase the suspended dust to ignitable or explosive levels.

2. Locations where combustible dust accumulations are normally not concentrated enough to interfere with the operation of electrical equipment unless an “infrequent equipment malfunction” occurs that increases the level of dust suspended in the air.

3. Locations where combustible dust concentrations in or on electrical equipment may be sufficient to limit heat dissipation or that could be ignited by failure or abnormal operation of electrical equipment.

A variety of airborne environmental conditions that require classification are listed in Article 500. Class I covers locations specified in Sections [500.5(B)(1)] and [500.5 (B)(2)] where flammable gases or vapors are present, or could exist in the air in high enough quantities that they could produce explosive or ignitable mixtures. Section [500.5(B)(1) FPN 1] provides examples of locations usually included in Class I as the following:

1. Where volatile flammable liquids or liquefied flammable gases are transferred from one container to another.

2. Interiors of spray booths and areas in the vicinity of spraying and painting operations where volatile flammable solvents are used.

3. Locations containing open tanks or vats of volatile flammable liquids.

4. Drying rooms or compartments for the evaporation of flammable solvents.

5. Locations with fat and oil extraction equipment that uses volatile flammable solvents.

6. Portions of cleaning and dyeing plants where flammable liquids are used.

7. Gas generator rooms and other portions of gas manufacturing plants where flammable gas may escape.

8. Pump rooms for flammable gas or for volatile flammable liquids that are not adequately ventilated.

9. The interiors of refrigerators and freezers where flammable materials are stored in open or easily ruptured containers.

10. All other locations where ignitable concentrations of flammable vapors or gases are likely to occur in the course of normal operations.