Depending on where in the world you work, you are following one of two standards.
Those areas, where the possibility or risk of fire or explosion occur due to an explosive atmosphere is called Hazardous area.
Zone system is the IEC standard used in Europe and the rest of the world.
Class- Division System NEC/CEC standard mostly followed in North America.
Hazardous areas as per Zones System classified as
Gas Zone: Zone 0, Zone 1 and Zone 2.
Dust Zone: Zone 20, Zone 21 and Zone 22.
Hazardous areas as per Class-Division System can be classified as Class, Division, and Group.
Zone System (Gas)
Zone 0:An area in which flammable atmosphere is continuously present for long periods of time. As a guide for zone 0, this can be defined as over 1000 hours/year or> 10% of the time.
Zone 1:An area in which flammable atmosphere exists intermittently or periodically under normal operating conditions. As a guide for zone 1, this can be defined as over 10 – 1000 hours/year or 0.1 – 10%of time.
Zone 2:An area in which the flammable atmosphere is likely to occur if it occurs only exists for short periods of time. As a guide for zone 1, this can be defined as over 1 – 10 hours/year or 0 – 1% of the time.
Zone System (Dust)
Zone 20:An area in which combustible dust, ignitable fibers, flyings are continuously present continuous or for long periods of time.
Zone 21: An area in which combustible dust, ignitable fibers, flyings are likely to occur under normal operating conditions.
Zone 22:An area in which combustible dust, ignitable fibers, flyings are not likely to occur under normal operating conditions., do so only for short periods of time.
Group 1: Mines
The flammable mixture of gases naturally occurring in mine.
Group 2: Explosive gas.
A: Atmosphere contains propane, acetone, benzene, butane, methane, petrol, Hexane.
B: Atmosphere contains Ethylene, Propylene Oxide, Ethylene oxide, Butadiene, Cyclopropane.
C: Atmosphere contains Acetylene, Hydrogen, Carbon disulfide gases or vapors of equivalent hazard.
Group 3: Explosive dust.
A: Atmosphere containing combustible flyings.
B: Atmosphere containing non-conductive dust.
C: Atmosphere containing conductive dust.
Class: The class defines the general nature of hazardous material in the surrounding atmosphere.
Class 1: Flammable gas
Class 2: Ignitable Dust
Class 3: Ignitable fiber or flying things in the air.
Division: This is based on the probability of the hazardous atmosphere.
Div 1: Indicates that hazardous material has a high probability of producing explosion due to it being presence continuously, intermittently or periodically.
Div 2: Indicates that hazardous material has a low probability of producing explosion due to its presence only during abnormal operating conditions.
Group: This is based on the presence of Type of hazardous material
Group A: Atmosphere containing Acetylene.
Group B: Hydrogen, Butadiene
Group C: Ethylene, Cyclopropane
Group D: Propane. Hexane, Methanol
Group E: Atmosphere containing combustible metal dust such as magnesium, Aluminum, bronze, Chromium, Titanium, Zinc.
Group F: Atmosphere containing carbonaceous dust Carbon black, coal black, charcoal, coal or coke dusts.
Group G: Flour, Grain, Starch, Wood, Plastics, and Chemicals.