The National Electric Code (NEC) has established a system that identifies hazardous locations according to Classifications and Divisions. Hazardous locations are defined as areas “where fire or explosion hazards may exist due to flammable gases or vapors, flammable liquids, combustible dust, or ignitable fibers or flyings.”
Each of the three hazardous classifications defined by the NEC (Class I, Class II, Class III), can be further subcategorized into two divisions. Division 1 includes normal operating conditions. Division 2, on the other hand, involves abnormal operating conditions.
A Class I Area is hazardous due to flammable gases or vapors. A Class I, Division I area includes locations where a flammable gas or vapor can exist:
- Continuously, intermittently or periodically during normal operations
- Frequently due to repair, maintenance or leakage
A Class I, Division 2 Area is an area where hazardous liquids, vapors or gases are:
- Adjacent to Class I areas
- Normally confined within closed containers or closed systems from which they can escape only in the case of accidental rupture or breakdown of such containers or systems
- Normally prevented by positive mechanical ventilation and which may become hazardous through failure or abnormal operation of the ventilation equipment.
Examples of Class I areas include:
- Operations involving storage and handling of liquified petroleum gas or natural gas
- Petroleum refineries
- Gasoline storage and dispensing areas
- Spray finishing areas
- Utility gas plants
- Aircraft hangers
Class II and Class III areas are not generally encountered in the oil and gas industry. Class II Areas are hazardous due to the presence of combustible dust, while Class III Areas present dangers from easily ignitable fibers and flyings.