Hazardous Area Equipment
Classification of hazardous areas
Explosive gas atmospheres AS 2430.1
Combustible dusts AS/NZS 61241.3 (AS 2430.2)
Specific occupancies AS 2430.3
Group II Flammable gas, vapour or mist
Combustible dusts
Zone classification
Zone 0 Continuously hazardous (protection technique allowed)
Exia intrinsic safety
Zone 1
Frequently hazardous (protection technique allowed)
Exib intrinsic safety
Exd flameproof
Exe increased safety
Exp pressured or purged
Exv
ventilation
Exs special protection
Zone 2 Infrequently hazardous (protection technique allowed)
Exn Non-sparking
Group II Classification (protection technique allowed)
DIP dust - excluding ignition proof:- the new DIP standard
will reflect 3 zones for dust areas, zone 20, 21 and 22.
Dust Area Zones
Gas/Vapour area Zones
Group II hazardous area zones
The classification of ZONE is a complex problem but
the main factors to consider are:
• The probability of the presence of gas
• The quantity and duration of hazardous vapour
• The amount of ventilation
• The nature of gas: lighter or heavier than air
The consequence of an explosion:
The division of plant or parts of plant into zones is generally undertaken by the supervisory authority in that industry
in tandem with process engineers / chemists at the design and or construction stage.
Group classification
Hazardous area equipment is specified in terms of the types of gases present, being:
Group I For mining applications
Group II For general industry
Equipment must be categorised as being suitable for use with gases in Group II industries.
Group I equipment has a representative gas of Methane and all equipment used in underground mining applications fall into this category Any other equipment will be Group II classified.
As shown in the table below. Group II is
again segmented into three different representative gas groups, Propane, Ethylene and Hydrogen. Groups IIA, IIB and IIC respectively.
As stated these are only representative gases where in fact there are many different types of gases one can be presented with when classifying equipment.
Temperature classification
Temperature classification takes into account the ignition temperature of the flammable gases present in the
particular environment.
Ambient temperatures are of course considered in this appraisal, however circumstances which may increase this surface temperature must also be taken into account.
For example, an enclosure shall over a period of time, collect a layer of dust on its surfaces. This shall increase the units overall operating and surface temperatures, to a point where if it
rises to a point nearing the flash or combustion point of surrounding gases, liquids or dusts, then an explosive situation would occur.
For Group I classified electrical equipment, where coal dust can form a layer, the maximum
surface temperature shall not exceed 150 °C. If this layer can be avoided through sealing or protection from the ingress of dust, the internal surfaces must not exceed 450 °C.
In respect to Group II electrical equipment,
temperatures are classified as per the following table.
Temperature classes T1 to T6 (AS 1280.1) are used for all protection techniques, and correspond to the electrical devices maximum operational temperature.
The better the equipment, the lower the rated surface temperature. In other words a rating of T4 is better than that of T2.
Therefore, those items certified as being T6, can be used in T1, T2, T3, T4, T5 and T6 gases. Whereas a T2
certification only allows a piece of equipment to be used
in T1 and T2 gases.
Zone protection techniques
A "protection technique" is a specific process which negates one of the three components of combustion.
The table below includes some other standards which are relevant to hazardous areas.
Explosion protection techniques
INGRESS PROTECTION (IP)
RATINGS TO AS 1939 (IEC 529)
This is protection for electrical apparatus against physical contact, foreign bodies
and ingress of water. The degree of protection is stipulated by using the abbreviation IP (Ingress Protection) and two identification numbers according to the following ingress table.
The first numeral indicates protection of
persons against access to dangerous parts and protection of internal equipment against the ingress of solid objects.
The second numeral indicates protection of internal equipment against harmful ingress of water.
IP 4 3
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