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The Dangerous Substances and
Explosive Atmospheres Regulations 2002 (DSEAR) require employers to control
the risks to safety from fire and explosions
Many
workplaces may contain explosive or potentially explosive atmospheres.
Examples
include places where work activities create or release flammable gases or
vapours, such as vehicle paint spraying, or in workplaces handling fine
organic dusts such as grain flour or wood.
Employers must classify
areas where hazardous explosive atmospheres may occur into zones.
The
classification given to a particular zone, and its size and location,
depends on the likelihood of an explosive atmosphere occurring and its
persistence if it does. Schedule 2 of DSEAR contains descriptions of the
various classifications of zones for gases and vapours and for dusts.
GASES VAPOURS & MISTS
DUSTS
EQUIPMENT CATEGORY
|
Zone 0 |
Zone 20 |
Category 1
|
|
A place in which an explosive atmosphere consisting of a mixture
with air of dangerous substances in the form of gas, vapour or mist
is present continuously or for long periods or frequently. |
A place in which an explosive atmosphere in the form of a cloud of
combustible dust in air is present continuously, or for long periods
or frequently. |
|
Zone 1 |
Zone 21 |
Category 2 |
|
A place in which an explosive atmosphere consisting of a mixture
with air of dangerous substances in the form of gas, vapour or mist
is likely to occur in normal operation occasionally |
A place in which an explosive atmosphere in the form of a cloud of
combustible dust in air is likely to occur in normal operation
occasionally. |
|
Zone 2 |
Zone 22 |
Category 3 |
|
A place in which an explosive atmosphere consisting of a mixture
with air of dangerous substances in the form of gas, vapour or mist
is not likely to occur in normal operation but, if it does occur,
will persist for a short period only. |
A place in which an explosive atmosphere in the form of a cloud of
combustible dust in air is not likely to occur in normal operation
but, if it does occur, will persist for a short period only |
|
Notes: Layers,
deposits and heaps of combustible dust must be considered as any
other source which can form an explosive atmosphere. "Normal
operation" means the situation when installations are used within
their design parameters. |
Notes: Category
1 equipment can also be used in zones 1 and 21. Category 1 and
2 equipment can be used in zones 2 and 22. |
The Employer must undertake a Risk
Assessment to identify the zone applicable. To identify equipment suitable
for the specified zone the user should check that the equipment supplied is
appropriate by reference to
-
Classification of the hazardous
area zones, shown in the table above
-
Temperature class or ignition
temperature of the gas or vapour involved according to the table below
|
Temperature Classification |
Maximum Surface Temperature, °C |
Ignition Temperature of gas mists or vapour, °C |
|
T1 |
450 |
>450 |
|
T2 |
300 |
>300 |
|
T3 |
200 |
>200 |
|
T4 |
135 |
>135 |
|
T5 |
100 |
>100 |
|
T6 |
85 |
>85 |
Electrical
equipment for use in explosive atmospheres should be marked with:
-
CE Mark
-
Explosion
protection symbol Ex in a hexagon,
-
Symbol of
the Group: I = Mining products, II = Non-Mining
products
-
Equipment
category number see zoning table overleaf
1 =
Category 1
2 =
Category 2
3 =
Category 3
= G
(concerning explosive atmospheres caused by gases, vapours or mists)
= D
(concerning explosive atmospheres caused by dust)
= G
D (concerning explosive atmospheres caused by
gas/vapour/mist/dust)
o oil
immersion
p
pressurisation
q
powder filling
d
flameproof enclosure
e
increased safety
ia or ib
intrinsic safety
m
encapsulation
-
Explosion
groups 1, 11A, 11B, 11C if optional protection
d ia, ib or q
-
If
temperature rating part of selection criteria a T marking, see
Temperature Table above.
These indicate
limitations to safe use. Other information necessary for safe use may
also be marked.
for example:
II
1 G EEx T4
Non-Mining products, Group II, Category 1 for use in gas/vapour/mist
atmospheres, max temp 135°C
II 3 D EEx T5
Non-Mining products, Group II, Category 3 for use in dust atmospheres, max
temp 100°C
Employers and those
installing equipment should consider the marking and documentation provided
with Ex equipment when it is being installed.
All products must be
also marked with:
-
name and
address of the manufacturer,
-
designation
of series or type,
-
serial
number (if any)
-
the year
of construction.
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