Hazardous Areas
are locations where the potential for fire or explosion exists
because of gases, dust, or easily ignitable fibers or flyings
in the atmosphere.
In North America, hazardous areas are separated by classes,
divisions, and groups to define the level of safety required for
equipment installed in these locations. Classes define the general
form of the flammable materials in the atmosphere. Divisions define
the probability of the presence of flammable materials. Groups
classify the exact flammable nature of the material.
In Europe and countries outside of North America, classification
of hazardous areas is accomplished differently. Zones are used
to define the probability of the presence of flammable materials.
Protection Types denote the level of safety for the device. Groups
classify the exact flammable nature of the material. These groups
are separated differently than North American Groups. Temperature
Identifications convey the maximum surface temperature of the
apparatus based on 104° F (40° C) ambient. These temperature codes
are selected carefully not to exceed the ignition temperature
of the specific gas or vapor to be encountered in the application.
Some classifications are not shown here. For further detailed
information, see specific standards published by approval organizations.
Classifications Inside North America
| Class I |
Flammable gases or vapors are present in the air in quantities
sufficient to produce explosive or ignitable mixtures. |
| Class II |
Combustible or conductive dusts are present. |
| Class III |
Ignitable fibers or flyings are present, but not likely to
be in suspension in sufficient quantities to produce ignitable
mixtures. (Group classifications are not applied to this
class.) |
| Division 1 |
The substance referred to by class is present during normal
conditions. |
| Division 2 |
The substance referred to by class is present only in abnormal
conditions, such as a container failure or system breakdown. |
| Group A |
Acetylene |
| Group B |
Hydrogen (or gases of equivalent hazard) |
| Group C |
Ethylene (or gases of equivalent hazard) |
| Group D |
Gasoline (or gases of equivalent hazard) |
| Group E |
Metal Dust |
| Group F |
Coal Dust |
| Group G |
Grain Dust |
Classification Outside North America
| Zone 0 |
Area in which an explosive gas-air mixture is continuously
present or present for long periods. |
| Zone 1 |
Combustible or conductive dusts are present.Area in which
an explosive gas-air mixture is likely to occur in normal
operation. |
| Zone 2 |
Area in which an explosive gas-air mixture is not likely to
occur, and if it occurs it will only exist for a short time. |
| |
|
Zone |
| d |
Flameproof (Explosion proof) Enclosure |
1,2 |
| e |
Increased Safety |
1,2 |
| ia |
Intrinsic Safety |
0,1,2 |
| ib |
Intrinsic Safety |
1,2 |
| o |
Oil Immersion |
2 |
| p |
Pressurized Apparatus (Purged Apparatus) |
1,2 |
| q |
Powder Filling (Sand Filling) |
2 |
| m |
Encapsulation |
1,2 |
| n |
Normally Nonsparking and/or Nonincendive Circuits) |
2 |
| |
°F |
°C |
| T1 |
842 |
450 |
| T2 |
572 |
300 |
| T3 |
392 |
200 |
| T4 |
275 |
135 |
| T5 |
212 |
100 |
| T6 |
185 |
85 |
| Group I |
For application in below ground installations (mines) where
methane (firedamp) and coal dust may be present. |
| Group IIA |
For application in above ground installation where hazards
due to propane may exist. This group most closely matches
the North American Group D. |
| Group IIB |
For application in above ground installations where hazards
due to ethylene may exist. This group most closely matches
the North American Group C. |
| Group IIC |
For application in above ground installations where hazards
due to hydrogen or acetylene may exist. This group most
closely matches the North American Groups A and B. |
|