Technical Documentation: Fire Detectors used in hazardous areas
P-DET/EX/RCE/PM5/GKa/110995 6 Autronica Fire and Security AS
1.2 Ex-classifications
The risk of explosion is different for different gas types and areas where the gas
is expected to be present. Therefore classifications of gases into Groups and
areas into Zones are necessary.
Group classification is concerning the type of gas which is (or is expected to
be) present in the hazardous area. Two criteria are of value when the gas is to
be classified.
a) The gas grade of explosion hazard, and
b) The ignition energy necessary to make the gas explode.
Zone classification is, as the name indicates, based upon the zones surrounding
the gas source.
Classifications are indicated by type description. The example below shows the
type:
Exib/IIC, which is, by the way, the claims Autronica set to the products used in
hazardous areas.
Ex - means that the equipment is intended for use in hazardous area.
(EEx is European standard)
i - means that the equipment is intrinsically safe.
b - means that the equipment must be used in zone 1 or 2.
(a - is zone 0, 1 and 2)
II - means that the equipment is intended for group II, which covers
nearly all purposes. (Group I is Mining Industry, mainly).
C - means that the equipment is build to withstand the most extreme
claims with respect to safety. (Ignition energy less than 20 µ -
joule and surface temperature less than 85°C).
The drawing below shows the distribution of zones around gas sources. The
right illustration shows a simple concentric arrangement, while the left one
illustrates a tank under loading or unloading. The expansion of zones 1 and 2
along the base is due to the fact that the gas has a higher density than the air.
In most of the industry buildings where danger of explosion exist, the main part
of the hazardous area is characterised as Zone 2.
Note that USA and Canada have different zone classification, such that their
"Division 1" covers Zone 0 and Zone 1. "Division 2" covers Zone 2.
Ex-
classifications
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