According to the NEC, there are three types of hazardous locations. The first type of hazard is one which is created by the presence of flammable gases or vapors in the air, such as natural gas or gasoline vapor. When these materials are found in the atmosphere, a potential for explosion exists, which could be ignited if an electrical or other source of ignition is present. The Code writers have referred to this first type of hazard as Class I. So, a Class I Hazardous Location is one in which flammable gases or vapors may be present in the air in sufficient quantities to be explosive or ignitable. Some typical Class I locations are:
Petroleum refineries, and gasoline storage and dispensing areas;
Dry cleaning plants where vapors from cleaning fluids can be present;
Spray finishing areas;
Aircraft hangars and fuel servicing areas; and
Utility gas plants, and operations involving storage and handling of liquified petroleum gas or natural gas.
All of these are Class I . . . gas or vapor . . . hazardous locations. All require special Class I hazardous location equipment.
of an explosive gas atmosphere, as follows:
Zone 0
Area in which an explosive gas atmosphere is present continuously or for long periods or frequently.
Zone 1
Area in which an explosive gas atmosphere is likely to occur in normal operation occasionally.
Zone 2
Area in which an explosive gas atmosphere is not likely to occur in normal operation but, if it does occur,
will persist for a short period only.
Non hazardous area (safe area )
A non hazardous area is an area in which an explosive atmosphere is not expected to be present.