A Guide to the Selection of Electrical Equipment for Installation in Hazardous Areas
The information below is given as a guide to enable the users of this catalogue to select the correct hazardous area equipment for their application. It should not be used to define the nature of hazardous areas, this is a task for experienced professionals in the field of hazardous area definition. Nor should it be used as replacement for the very detailed standards which cover the installation of electrical equipment in hazardous areas.
What conditions are required for an explosion?
There are three elements required in order to create a hazardous area.
2. A flammable medium for example gases, vapours, mists and dusts.
3. A source of ignition of sufficient energy and /or a rise in temperature.
What is an explosive atmosphere?
An explosive atmosphere is created when air and an flammable medium mix such that a rise in temperature or an electrical spark produces an explosion.
What is a potentially explosive atmosphere?
An atmosphere is defined as potentially explosive when in its normal state it is not explosive but there exists the possibility that in abnormal circumstances it will become explosive. For example in the case of a gas leak or the vapourisation of a fluid leak.
An explosive atmosphere needs a minimum energy for ignition. The energy produced by arcs and sparks are many times greater than this minimum.
Self Ignition Temperature
An explosive atmosphere can self ignite if the local temperature rises above the so-called self ignition temperature. This temperature is different for different flammable mediums. Self ignition temperatures for a range of commonly found flammable gasses and dust are given in Table 1 and 2.
Typical self ignition temperatures for Gases
|Gas||Temp + °C|
Typical self ignition temperatures for Dust
|Dust||Temp + °C|
Gases, Vapours, Mists and Dusts.
Explosive atmospheres are caused by a mixture of gases, vapours, mists dusts and air. If the explosive atmosphere is caused by gases, vapours and mists the hazardous area is coded G. If the explosive atmosphere is caused by dusts the hazardous area is coded D.
Explosion protected electrical equipment is classified
in terms of the ignition temperature, the ignition capability and flame
transmission capacity of the explosive atmosphere in which it is designed
In the first instance equipment is divided into two groups dependingon its location above or below ground.
Group I Electrical equipment for use below ground in areas susceptible to firedamp.
Group II Electrical equipment for all other areas.
Group II equipment is further divided into three sub groups depending on the ignition and flame transmission characteristics of the explosive hazard.
These sub-groups are designated IIA, IIB and IIC.Zones
Typical self ignition temperatures for Dusts
|Acetic acid||Carbon disulphide|
Zone 0 defines
an area in which an explosive atmosphere caused by a mixture of air and
gases, vapours and mists is present continuously for long periods or very
Zone 1 defines areas in which an explosive atmosphere caused by a mixture air and gases, vapours and mists is expected to occur occasionally.
Zone 2 defines areas in which an explosive atmosphere caused by a mixture of air and gases, vapours and mists is unlikely and if it should occur it will be for a short time and then only rarely.
Zone 20 defines an area in which an explosive atmosphere caused by a cloud of combustible dust and air is present continuously for long periods or very frequently.
Zone 21 defines areas in which an explosive atmosphere caused by a cloud of combustible dust and air is expected to occur occasionally.
Zone 22 defines areas in which an explosive atmosphere caused by a cloud of combustible dust and air is unlikely and if it should occur it will be for a short time and then only rarely.
Defenition of zones
|Type of hazard||G||D||G||D||G||D|
The ignition temperature is the lowest temperature
on the surface at which an explosive atmosphere will ignite. Gases and
dusts have been divided into temperature classes according to their ignition
temperatures so that electrical equipment can be further sub-divided into
six temperature classes T1 to T6. The temperature classes are shown in
Note. The maximum operating surface temperature of a piece of electrical equipment must always be below the ignition temperature of the explosive mixture, see Table 6 below.
|Temperature Class||Maximum Surface Temperature °C|
Self Ignition Temperature and Temparature Classes
|Self Ignition Temperature °C||Temperature Class of the Equipment|
|85° ≤ T ≤ 100 °c|
|100° ≤ T ≤ 135 °c|
|135° ≤ T ≤ 200 °c|
|200° ≤ T ≤ 3 00 °c|
|300° ≤ T≤ 450 °c|
Electrical equipment for hazardous areas is designed to comply with different fault levels depending on the Zone in which the equipment is to be installed. These fault levels are designated as Categories 1, 2 and 3. Their relationship with the zones, the potential for an explosive atmosphere and the type of explosive atmosphere is shown in Table 7.
Relationship between zones and equipment categories
|Type of hazard||G||D||G||D||G||D|
Because hazardous area electrical equipment is very often used in hostile atmospheric environments the standards call for minimum levels of protection against water and dust. For example the minimum level set is IP54 however in the case of dust hazards the minimum level ingress protection is set at IP64. The range of IP levels are shown in Table 8.
IP Rating IPXY
|X Protected From||Y Protected From|
|1||Solids < 50mm diam||1||Water dripping vertically|
|2||Solids < 12.5mm diam||2||Water dripping at 15 deg|
|3||Solids < 2.5mm diam||3||Spray water at 60 deg|
|4||Solids < 1mm diam||4||Splash water from any direction|
|5||Dust protected||5||Jet water from any direction|
|6||Dust tight||6||Powerful water jets from any direction|
|7||Water when submerged for limited time|
|8||Water when submerged for an indeterminate time|
The ATEX standards call for
the manufacturers of hazardous area electrical equipment to label their
products with the following information. A typical label for a flood light
is shown for reference.
1. Name of manufacturer
2. Product type code
3. Address of manufacturer
4. Year of manufacture
5. Marking in accordance with directive 94/9/EC II 3 GD – group II location, category 3 equipment, for gas and dust hazards
6. Marking in accordance with European standards EEx nR II T – built and tested to European standards, type of protection, explosion group, temperature class
7. CE marking together with notified body registration number
8. Notified testing body and reference number
9. Serial number
10. Technical data
11. Ingress protection
We specialise in the manufacture and supply of the following products for hazardous areas: