Gas and Vapours
Hazardous Area Zones
Hazardous Areas are defined by three main criteria
-The type of hazard
-The likelihood of the hazard being present in flammable concentrations
-The (auto) ignition temperature of the hazardous material
The type of hazard (groups)
Gases and Vapours are categorised in terms of their ignition energy or the
maximum experimental safe gap (in respect of flameproof protection). This categorisation leads to the Gas Groups:
Group IIC is the most severe group. Hazards in this group can be ignited very easily indeed.
Equipment marked as suitable for Group IIC is also suitable for IIB and IIA.
Equipment marked as suitable for IIB is also suitable for IIA but NOT for IIC.
If equipment is marked, for example, Ex e II T4 then it is suitable for all subgroups IIA, IIB and IIC.
There are three zones for gases and vapours:
Zone 0 Flammable atmosphere highly likely to be present – may be present for long periods or even continuously
Zone 1 Flammable atmosphere possible but unlikely to be present for long periods
Zone 2 Flammable atmosphere unlikely to be present except for short periods of time – typically as a result of a process fault condition.
Zone zero is the most severe zone (the highest probability of flammable atmosphere presence). Equipment for this zone needs to be very well protected against providing a source of ignition.
When electrical equipment is used in, around, or near an atmosphere that has flammable gases or vapours, flammable liquids, combustible dusts, ignitable fibres or flying, there is always a possibility or risk that a fire or explosion might occur. Those areas where the possibility or risk of fire or explosion might occur due to an explosive atmosphere and/or mixture is often called a hazardous (or classified) location/area.
What is an explosive atmosphere?
An explosive atmosphere is defined as a mixture of dangerous substances with air, under atmospheric conditions, in the form of gases, vapours, mist or dust in which, after ignition has occurred, combustion spreads to the entire unburned mixture.
Explosive atmospheres can be caused by flammable gases, mists or vapours or by combustible dusts. If there is enough of the substance, mixed with air, then all it needs is a source of ignition to cause an explosion.
Explosions can cause loss of life and serious injuries as well as significant damage. Preventing releases of dangerous substances, which can create explosive atmospheres, and preventing sources of ignition are two widely used ways of reducing the risk. Using the correct equipment can help greatly in this.
Where can explosive atmosphere’s be found?
Many workplaces may contain, or have activities that produce, explosive or potentially explosive atmospheres. Examples include places where work activities create or release flammable gases or vapours, such as vehicle paint spraying, chemical stores, filling stations, vehicle workshops, LPG installations and storage facilities, clinics and hospitals or in workplaces handling substances that can cause flammable gases or vapours.