p406-407:Layout 1 15/5/07 12:59 Page 2
i Technical Information
MULTIPLE TYPES OF PROTECTION
Hazardous Area
Hazardous area electrical equipment may incorporate more than one type of protection. The
external marking plate should indicate the overall protection, which will determine the installation
PROCEDURE FOR SELECTING ELECTRICAL APPARATUS
requirements. For example a piece of equipment having an Exd contact device with Exe
terminations may be marked EExde IIc T6.
Electrical apparatus should be selected for use in a hazardous area in accordance with each of the
following criteria:
ENVIRONMENTAL CONDITIONS
(a) The type of proection of the apparatus in relation to the area classification of the
hazardous area;
When selecting apparatus, special care should be taken to ensure that the apparatus and its
(b) The temperature classification of the apparatus in relation to the ignition temperature of
component parts are constructed so as to guard against electrical and mechanical failure in the
the gases and vapours involved;
intended conditions of use.
(c) The Apparatus Gas group (where applicable) in relation to the relevant properties of the
gases and vapours involved;
Particular attention should be given to the need for protection against the weather, the ingress of
(d) The apparatus construction and enclosure in relation to the environmental conditions.
liquids and particulate matter, corrosion, the effect of solvents and the effect of heat from
(It should be noted that Exd [Flameproof] Apparatus is not necessarily inherently
adjacent plant.
‘weatherproof’).
Note: Where in addition to hazardous gases the area is subject to dust deposition the thickness of
which cannot effectively be controlled and/or where the dust could form an explosible
CLASSIFICATION OF HAZARDOUS AREAS
concentration, in addition to the protection category discussed below, account should be taken of
It should be noted that classified areas were formerly called ‘divisions’, whereas now they are
the effect due to surface insulation on the temperature classification of the apparatus, also the
called ‘zones’.
smouldering temperature of the dust. (See also BS6467).
Zone 0 In which an explosive gas-air mixture is continuously present, or present for long
periods.
Zone 1 In which an explosive gas-air mixture is likely to occur in normal operation.
Ventilation
Zone 2 In which an explosive gas-air mixture is not likely to occur in normal operation, and if it
occurs will exist only for a short time.
SELECTING THE CORRECT FAN
It will be noted that this area classification deals only with risks due to inflammable gases and
vapours and, by implication, flammable mists.
How much ventilation is required?
It does not deal with dusts, for which area classification is being developed.
In a non-hazardous area normal electrical techniques generally apply.
By implication an area that is not classified Zone 0, 1 or 2 is deemed to be non-hazardous and
This depends on: Size of Room Amount of Use
where normal industrial electrical equipment may be used.
Type of Room Existing Regulations
Builing Regulations say that mechanical ventilation must provide at least 3 air changes per hour in
SELECTION OF APPARATUS ACCORDING TO ZONE OF RISK
sanitary accommodation and must also run for at least 15 minutes after the room has been
Zone 0 Zone 1 Zone 2
vacated.
Type of Protection Type of Protection Type of Protection
Ex ‘ia’ Any type of protection suitable Any type of protection suitable
Bathrooms require 54m
3
(or 15 l/s) when in use.
Ex ‘s’ (specially certified for for Zone 0 and for Zone 0 and 1 and
Suggested Air Changes Per Hour at Normal Conditions
use in Zone 0) Ex ‘d’ Ex ‘N’ or ‘n’
Ex ‘ib’ Ex ‘o’
Ex ‘p’ Ex ‘q’
Banks 2-4 Kitchens (Domestic) 10-15
Ex ‘e’
Bathrooms 8-10 Kitchens (Commercial) 25-40
Ex ‘s’
Bedrooms 2-5 Laboratories 5-10
Cafés 10-12 Offices 5-7
Apparatus suitable for Zone 1 can be used in Zone 2 subject to the usual temperature and gas
Clubs 12-14 Pubs/Bars 12+
group classification restrictions where applicable.
Factories 8-10 Restaurants 10-15
The type of protection will also be designated ‘EEx’ where equipment if certified to the harmonised Garages 6-8 Shower Rooms 15-20
European Standards. Hairdressing Salons 10-15 Toilets 6-10
TYPES OF PROTECTION
How to Choose the Correct Extract Fan
Type of protection ‘d’ (flameproof)
Effective ventilation, conforming to Building regulations, depends on the selection of a fan or fans
Enclosures are designed to withstand an internal explosion of flammable gas or vapour without
of the correct size and capacity. To do this, you need only consider:
suffering damage or allowing the gas or vapour surrounding the enclosure to ignite.
Type of protection ‘e’ (increased safety)
a) The cubic capacity of the area to be ventilated.
Apparatus designed in such a way as to give increased security against the possibility of sparking
or excessive temperatures.
b) The required number of air changes per hour. Multiplying the cubic capcity by the number of
Type of protection ‘N’ or ‘n’ (type N or n)
air changes determines the optimum fan capacity required.
Similar in basic concept to type ‘e’ above but also includes methods of protecting sparking or high
temperature devices.
NOTE: To convert feet to metres x .3048 To convert metres to feet x 3.28
Note: this is still only a UK accepted concept and is restricted to Zone 2 applications.
Type of protection ‘i’ (intrinsic safety)
Example Room Size Air Changes Air Movement
Apparatus is designed in such a way as to restrict the energy within the apparatus to a level below
that which can cause ignition by either sparking or excessive temperatures.
Bathroom/Toilet
Type of protection ‘p’ (pressurization and continuous dilution)
2.5 x 2 x 2.5 = 12.5m
3
8 12.5 x 8 = 100 = 1 x M12/5T
This system uses air or inert gas to maintain positive pressure to prevent the entry of flammable
8 x 6.5 x 8 = 416 cu ft or 1 x M12/5AT
gas or vapour into the enclosure or room. Another method is to reduce the volume of gas or vapour
within the enclosure or room below the explosive gas-air mixture level by dilution from a clean
Domestic Kitchen
external source.
3 x 2.5 x 2.5 = 18.75cm
3
10 18.75 x 10 = 185 1 x V15/6
Type of protection ‘o’ (oil immersion)
10 x 8 x 8 = 640 cu ft or 1 x V15/6AI
Apparatus in which ignition of flammable gas or vapour is prevented by immersion of the live or
sparking apparatus in oil.
Restaurant
Type of protection ‘q’ (sand-filled)
7 x 5 x 105m3 10 105 x 10 = 1050 = 2 x V30/12AR
A similar method to oil immersion above but the media is usually granular quartz.
23 x 16.5 x 10 = 3795 cu ft or 2 x V30/12ARI
Type of protection ‘m’ (encapsulation)
Apparatus in which the parts which can cause ignition of flammable gas or vapour by sparking or
Fans Used with Ducting
heat are prevented from so doing by encapsulation.
Type of protection ‘s’ (special protection) If fans are used with ducting, it is important to remember that long lengths of ducting will reduce
This concept is used to permit certification of designs of apparatus that do not comply with the the fan’s performance.
standards of established concepts above, but can be shown by test to be suitable for use. As a rule, when long lengths of ducting are required, Centrifugal Fans need to be selected.
Please Note: All prices shown exclude V.A.T.
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