Explosive Gas Area Classifications

- Aug 24, 2017-

Typical gas hazards are from hydrocarbon compounds, but hydrogen and ammonia are common industrial gases that are flammable.

Class I, Division 1 classified locations
An area where ignitable concentrations of flammable gases, vapors or liquids can exist all of the time or some of the time under normal operating conditions. A Class I, Division 1 area encompasses the combination of Zone 0 and Zone 1 areas.

Zone 0 classified locations
An area where ignitable concentrations of flammable gases, vapors or liquids are present continuously or for long periods of time under normal operating conditions. An example of this would be the vapor space above the liquid in the top of a tank or drum. The ANSI/NEC classification method consider this environment a Class I, Division 1 area. As a guide for Zone 0, this can be defined as over 1000 hours/year or >10% of the time.[4]

Zone 1 classified location
An area where ignitable concentrations of flammable gases, vapors or liquids are likely to exist under normal operating conditions. As a guide for Zone 1, this can be defined as 10–1000 hours/year or 0.1–10% of the time.[4]

Class I, Division 2 or Zone 2 classified locations
An area where ignitable concentrations of flammable gases, vapors or liquids are not likely to exist under normal operating conditions. In this area the gas, vapor or liquids would only be present under abnormal conditions (most often leaks under abnormal conditions). As a general guide for Zone 2, unwanted substances should only be present under 10 hours/year or 0–0.1% of the time.[4]

Unclassified locations
Also known as non-hazardous or ordinary locations, these locations are determined to be neither Class I, Division 1 or Division 2; Zone 0, Zone 1 or Zone 2; or any combination thereof. Such areas include a residence or office where the only risk of a release of explosive or flammable gas would be such things as the propellant in an aerosol spray. The only explosive or flammable liquid would be paint and brush cleaner. These are designated as very low risk of causing an explosion and are more of a fire risk (although gas explosions in residential buildings do occur). Unclassified locations on chemical and other plant are present where it is absolutely certain that the hazardous gas is diluted to a concentration below 25% of its lower flammability limit (or lower explosive limit (LEL)).