Hazardous Areas Classification

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European hazardous areas classifications in zones, protection types, temperature codes and codes

Hazardous areas outside North America are classified by gas groups and zones.

Zones are used to define the probability of the presence of flammable materials.
Groups classify the exact flammable nature of the material.

Protection Types are used to denote the level of safety for the device. Equipment approved receives a temperature code indicating the maximum surface temperature of the equipment.

Zones

The zone defines the probability of hazardous material being present in an ignitable concentration in the surrounding atmosphere.

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 for short periods 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 very short time due to an abnormal condition.

Protection Types

Different protection techniques are used to address the hazardous zones.

		Zone
Ex d	Flameproof (Explosion proof) Enclosure	1, 2
Ex e	Increased Safety	1, 2
Ex ia	Intrinsically Safe	0, 1, 2
Ex ib	Intrinsically Safe	1, 2
Ex o	Oil Immersion	2
Ex p	Pressurized Apparatus (Purged Apparatus)	1, 2
Ex q	Powder Filling (Sand Filling)	2
Ex m	Encapsulation	1, 2
Ex n or Ex N	Non incentive or/and normally no sparking circuits	2

Flameproof (Explosion proof) Enclosure

All electrical circuits are enclosed in a house strong enough to contain any explosion or fire that may take place on the inside.

Increased Safety

Electrical circuits incorporates special measures to reduce the probability of excessive temperatures and the occurrence of arcs and sparks in normal service.

Intrinsically Safety

The electrical energy available in circuits and equipment, is limited to a level to low to ignite the most easily ignitable mixtures in a hazardous area.

Intrinsically safe barriers, as Zener, are installed in the circuit to limit current and voltage in the hazardous areas to avoid sparks or hot spots under fault conditions.

Hazardous Area Types of Protection

Temperature Codes

A mixture of air and hazardous gases may ignite by coming in contact with a hot surface. An ignition depends on surface area, temperature and the concentration of the gas.

Certified equipment are tested for maximum temperature ratings by approval agencies. Equipment for Group II receives a temperature code indicating the maximum surface temperature.

Temperature Code	^oF	^oC
T1	842	450
T2	572	300
T3	392	200
T4	275	135
T5	212	100
T6	185	85

The coding is based on a 104 ^oF (40 ^oC) ambient temperature.

The automatic ignition temperature can be found in IEC 79-4.

Critical Temperature Parameters For Dust Explosions

Groups

Electrical equipment are divided into two groups where Group I covers equipment used in mines and Group II covers all other applications. Group II is subdivided into three subgroups where the specific hazardous materials within each group can be found in CENELEC EN 50014.

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.
Group IIB	For application in above ground installations where hazards due to ethylene may exist.
Group IIC	For application in above ground installations where hazards due to hydrogen or acetylene may exist.