Bsi bs en 50281 1 2 1999 (2002)

13979 fm BRITISH STANDARD BS EN 50281 1 2 1999 Incorporating Amendments Nos 1 and 2 and Corrigendum No 1 Electrical apparatus for use in the presence of combustible dust — Part 1 2 Electrical apparatu[.]

Electrical apparatus for

use in the presence of

combustible dust —

Part 1-2: Electrical apparatus protected

by enclosures — Selection, installation

and maintenance

The European Standard EN 50281-1-2:1998, with the incorporation of

amendment A1:2002, has the status of a British Standard

ICS 29.260.20

This British Standard, having

been prepared under the

direction of the

Electrotechnical Sector

Committee, was published

under the authority of the

Standards Committee and

comes into effect on

15 May 1999

© BSI 1 November 2002

December 1999 BS EN 50281-1-1 and BS EN 50281-1-2 supersede

BS 6467-1:1985 and BS 6467-2:1988 which will be withdrawn on 2003-06-30 The UK participation in its preparation was entrusted by Technical Committee GEL/31, Electrical apparatus for explosive atmospheres, to Subcommittee GEL/31/20, Apparatus for use in the presence of ignitable dust, which has the responsibility to:

A list of organizations represented on this subcommittee can be obtained on request to its secretary

Cross-references

The British Standards which implement international or European

publications referred to in this document may be found in the BSI Catalogue

under the section entitled “International Standards Correspondence Index”, or

by using the “Search” facility of the BSI Electronic Catalogue or of British

Standards Online

This publication does not purport to include all the necessary provisions of a contract Users are responsible for its correct application

Compliance with a British Standard does not of itself confer immunity from legal obligations.

— aid enquirers to understand the text;

— present to the responsible European committee any enquiries on the interpretation, or proposals for change, and keep the UK interests informed;

— monitor related international and European developments and promulgate them in the UK

Summary of pages

This document comprises a front cover, an inside front cover, the EN title page, pages 2 to 13 and a back cover

The BSI copyright notice displayed in this document indicates when the document was last issued

Sidelining in this document indicates the most recent changes by amendment

Amendments issued since publication

10763 October 1999 Indicated by a sideline

10856 Corrigendum May 2000 Correction to EN foreword, second paragraph

13979 1 November 2002 Revision of 8.2

ICS 29.260.20 Incorporates Corrigenda August 1999 and

December 1999 Descriptors:

English version

Electrical apparatus for use in the presence of

combustible dust — Part 1-2: Electrical apparatus protected by enclosures —

Selection, installation and maintenance

(includes amendment A1:2002)

Matériels électriques destinés à être utilisés en

présence de poussières combustibles —

Partie 1-2: Matériels électriques protégés par

enveloppes — Sélection, installation et

entretien

(inclut l’amendement A1:2002)

Elektrische Betriebsmittel zur Verwendung in Bereichen mit brennbarem Staub —

Teil 1-2: Elektrische Betriebsmittel mit Schutz durch Gehäuse — Auswahl, Errichten und Instandhaltung

(enthält Änderung A1:2002)

This European Standard was approved by CENELEC on 1998-09-01

Amendment A1 was approved by CENELEC on 2001-12-01

CENELEC members are bound to comply with the CEN/CENELEC Internal

Regulations which stipulate the conditions for giving this European Standard

the status of a national standard without any alteration Up-to-date lists and

bibliographical references concerning such national standards may be obtained

on application to the Central Secretariat or to any CENELEC member

This European Standard exists in three official versions (English, French,

German) A version in any other language made by translation under the

responsibility of a CENELEC member into its own language and notified to the

Central Secretariat has the same status as the official versions

CENELEC members are the national standards bodies of Austria, Belgium,

Czech Republic, Denmark, Finland, France, Germany, Greece, Iceland, Ireland,

Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden,

Switzerland and United Kingdom

CENELEC

European Committee for Electrotechnical Standardization Comité Européen de Normalisation Electrotechnique Europäisches Komitee für Elektrotechnische Normung

Central Secretariat: rue de Stassart 35, B-1050 Brussels

© 1998 CENELEC All rights of exploitation in any form and by any means reserved worldwide for

This European Standard was prepared by the

Technical Committee CENELEC TC 31, Electrical

apparatus for explosive atmospheres The text of the

draft was submitted to the Unique Acceptance

Procedure and was approved by CENELEC

EN 50281-1-2 on 1998-09-01

This European Standard was prepared under a

mandate given to CENELEC by the European

Commission and the European Free Trade

Association and only those sections of this standard

which refer to equipment requirements support the

essential health and safety requirements of the EC

Directive 94/9/EC

This European Standard is to be read in conjunction

with EN 50281-1-1:1998

The following dates have been fixed:

Annexes designated “informative” are given for

information only

In this standard, Annex A is informative

Foreword to amendment A1

This amendment to the European Standard

EN 50281-1-2:1998 was prepared by the Technical Committee CENELEC TC 31, Electrical apparatus for explosive atmospheres — General requirements The text of the draft was submitted to the Unique Acceptance Procedure and was approved by CENELEC as amendment A1 to EN 50281-1-2:1998

on 2001-12-01

The following dates were fixed:

Contents

Page

7 Selection of dust ignition protected

8 Selection of radiating equipment 8

9 Selection of ultrasonic equipment 9

10 Installation requirements 9

12 Inspection and maintenance 12 Annex A (informative) Examples for dust layers with excessive thickness with the requirement of

— latest date by which the

EN has to be

implemented at national

level by publication of an

identical national

standard or by

endorsement (dop) 1999-09-01

— latest date by which

national standards

conflicting with the EN

have to be withdrawn (dow) 2003-06-30

— latest date by which the amendment has to be implemented at national level by publication of an identical national standard

or by endorsement (dop) 2002-12-01

— latest date by which national standards conflicting with the amendment have to be withdrawn (dow) 2004-12-01

Combustible dust can be ignited by electrical apparatus in several main ways:

— by surfaces of the apparatus that are above the ignition temperature of the dust concerned The temperature at which a dust ignites is a function of the properties of the dust, whether the dust is in a cloud or layer, the thickness of the layer and the geometry of the heat source;

— by arcing or sparking of electrical parts such as switches, contacts, commutators, brushes, or the like;

— by discharge of an accumulated electrostatic charge;

— by radiated energy (e.g electromagnetic radiation);

— by mechanical sparking or frictional sparking or heating associated with the apparatus

In order to avoid ignition hazards it is necessary that:

— the temperature of surfaces on which dust can be deposited, or which would be in contact with a dust cloud, is kept below the temperature limitation specified in this standard;

— any electrical sparking parts, or parts having a temperature above the temperature limit specified in this standard:

— are contained in an enclosure which adequately prevents the ingress of dust, or

— the energy of electrical circuits is limited as to avoid arcs, sparks or temperatures capable of igniting combustible dust;

— any other ignition sources are avoided

Where the apparatus has to meet other environmental requirements, for example, protection against ingress of water and resistance to corrosion, the method of protection used shall not adversely affect the integrity of the enclosure

The protection specified in this standard will not provide the required level of safety unless the electrical apparatus is operated within its rating and is installed and maintained according to the relevant codes of practice or requirements, for example in respect of protection against over-currents, internal short circuits, and other electrical faults In particular, it is essential that the severity and duration of an internal or external fault be limited to values that can be sustained by the electrical apparatus without damage

1 Scope

This European Standard is applicable to electrical apparatus protected by enclosure and temperature limitation for use in areas where combustible dust may be present in quantities which could lead to a fire

or explosion hazard

This standard gives guidance on the selection, installation and maintenance of electrical apparatus

NOTE EN 50281-1-1 specifies requirements for the construction and testing of electrical apparatus.

The ignition protection is based on the limitation of the maximum surface temperature of the enclosure and

on the restriction of dust ingress into the enclosure by the use of “dust-tight” or “dust-protected” enclosures The application of electrical apparatus in atmospheres that may contain explosive gas as well as

combustible dust, whether simultaneously or separately, requires additional protection measures

The principles of this standard can also be followed when combustible fibres or flyings cause a hazard This standard does not apply to dusts of explosives which do not require atmospheric oxygen for

combustion, or to pyrophoric substances

This standard is not applicable to electrical apparatus for use in mines susceptible to firedamp; nor does it take account of any risk because of an emission of flammable or toxic gas from the dust

This standard does not include other types of protection and is only applicable to protection by enclosure and temperature limitation

2 Normative references

EN 50014, Electrical apparatus for potentially explosive atmospheres — General requirements.

EN 50281-1-1, Electrical apparatus for use in the presence of combustible dust — Part 1-1: Electrical

apparatus protected by enclosures — Construction and testing.

EN 50281-2-1, Electrical apparatus for use in the presence of combustible dust — Part 2-1: Test methods —

Methods for determining the minimum ignition temperatures of dust.

EN 60079-14, Electrical apparatus for explosive gas atmospheres — Part 14: Electrical installations in

hazardous areas (other than mines).

(IEC 60079-14:1996)

EN 60529, Degrees of protection provided by enclosures (IP Code)

(IEC 60529:1989)

EN 61241-2-2, Electrical apparatus for use in the presence of combustible dust — Part 2: Test methods —

Section 2: Method for determining the electrical resistivity of dust in layers

(IEC 61241-2-2:1993 + corr May 1994)

HD 384 (series), Electrical installations of buildings

(IEC 60364 series)

ISO 4225, Air quality — General aspects — Vocabulary.

3 Definitions

For the purpose of this European Standard, the following definitions apply

3.1

dust

small solid particles in the atmosphere which settle out under their own weight, but which may remain suspended in air for some time (includes dust and grit as defined in ISO 4225)

3.2

combustible dust

dust that can burn or glow in air and could form explosive mixtures with air at atmospheric pressure and normal temperature

3.3

conductive dust

a dust with electrical resistivity equal to or less than 103W·m

3.4

explosive dust atmosphere

mixture with air, under atmospheric conditions, of flammable substances in the form of dust or fibres in which, after ignition, combustion spreads throughout the unconsumed mixture (see IEV 426-02-04)

3.5

ignition temperature of a dust layer

the lowest temperature of a hot surface at which ignition occurs in a dust layer of specified thickness on this hot surface

3.6

ignition temperature of a dust cloud

the lowest temperature of the hot inner wall of a furnace at which ignition occurs in a dust cloud in air contained therein

3.7

dust ignition protection

all relevant measures specified in this standard (e.g dust ingress protection and surface temperature limitation) applied to electrical apparatus to avoid ignition of a dust layer or cloud

3.8

dust-tight enclosure

an enclosure capable of preventing the ingress of all observable dust particles

3.9

dust-protected enclosure

an enclosure in which the ingress of dust is not totally prevented but dust does not enter in sufficient quantity to interfere with the safe operation of the equipment Dust shall not accumulate in a position within the enclosure where it is liable to cause an ignition hazard

3.10

maximum surface temperature

the highest temperature which is attained by any part of the surface of electrical apparatus when tested under the defined dust free conditions

NOTE This temperature is attained under the test condition Increasing the layer thickness can increase this temperature due to the thermal insulation properties of dust.

3.11

maximum permissible surface temperature

the highest temperature a surface of electrical apparatus is allowed to reach in practical service to avoid ignition The maximum permissible surface temperature will depend on the type of dust, its layer

thickness, and the application of a safety factor

NOTE For details see clause 6.

4 Area classification

Equipment placed in areas outside the main dust hazard zones, but which may be temporarily subjected

to a dust-laden atmosphere occasionally by a failure in the plant or any untoward happening shall be dust protected and have a surface temperature limitation below the dust ignition temperatures

To determine the extent of measures necessary to avoid effective ignition sources, the hazardous places shall be classified into zones based on the frequency and duration of occurrence of a hazardous explosive atmosphere

A place in which an explosive atmosphere is not expected to occur in such quantities as to require special precautions shall be regarded as non-hazardous within the meaning of this standard

These areas, the dust hazard zones and the surrounding fringe zone, are designated Zone 20, 21 and 22 respectively, with the following definitions:

Layers, deposits and heaps of combustible dust shall be considered as any other source which can form an explosive atmosphere

4.1 Zone 20

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

NOTE In general these conditions, when they occur, arise inside containers, pipes and vessels etc.

4.2 Zone 21

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

NOTE This zone can include, among others, places in the immediate vicinity of, e.g powder filling and emptying points and places where dust layers occur and are likely in normal operation to give rise to an explosive concentration of combustible dust mixture with air.

4.3 Zone 22

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

NOTE This zone can include, among others, places in the vicinity of equipment, protective systems and components containing dust, from which dust can escape from leaks and form dust deposits, (e.g milling rooms, in which the dust escapes from the mills and then settles).

Layers, deposits and heaps of combustible dusts outside the containment shall be avoided Where such accumulations of dust cannot be avoided, the surface temperature of the apparatus to be installed in such

areas shall be reduced to a safe level as specified in clause 6.

5 Selection of apparatus

The apparatus shall be selected taking into account the following conditions:

— ignition temperatures of a dust layer determined for a 5 mm layer thickness as specified in

EN 50281-2-1;

— maximum surface temperature measured under dust free conditions as specified in EN 50281-1-1,

clause 10;

— maximum permissible surface temperature for apparatus, in the presence of dust clouds as specified

in 6.1 and having dust layers up to 5 mm thickness calculated as specified in 6.2.1;

— construction of enclosure meeting the general requirements as specified in EN 50281-1-1, clauses 4 and 6;

— dust tightness tested by the method specified in EN 60529 for Category 1 (using artificial depression) meeting the requirements of:

6 Temperature limitation

The maximum surface temperature permitted for apparatus operating in any zone shall be determined by the deduction of a safety margin from the minimum ignition temperature of the dust concerned, when tested in accordance with the methods specified in EN 50281-2-1 (or IEC 61241-2-1) for both dust clouds and layers up to 5 mm thickness

The following rules for temperature limitation shall be applied independently of the zone in which the apparatus is intended to be used

6.1 Temperature limitations because of the presence of dust clouds

The maximum surface temperature of the apparatus shall not exceed two-thirds of the ignition

temperature in °C of the dust/air mixture concerned

Tmax= 2/3 TCl

6.2 Temperature limitation because of the presence of dust layers

6.2.1 Dust layers up to 5 mm thickness

The maximum surface temperature of the apparatus when tested to the method given in EN 50281-1-1,

clause 10 shall not exceed a value of 75 K below the minimum ignition temperature for 5 mm layer

thickness of the dust concerned

Tmax = T5 mm p 75K

where

TCl is the ignition temperature of a cloud of dust

where

T5 mm is the ignition temperature of 5 mm layer of dust

6.2.2 Dust layers above 5 mm up to 50 mm thickness

Where there is a possibility that dust layers in excess of 5 mm up to 50 mm may be formed on apparatus, the maximum permissible surface temperature shall be reduced accordingly The reduction in maximum permissible surface temperature of apparatus used in the presence of dusts having ignition temperatures

in excess of 250 °C for a 5 mm layer shall be in accordance with the graph in Figure 1

NOTE Before applying the information in this graph, reference should be made to EN 50281-2-1 (or IEC 61241-2-1).

Laboratory investigation shall be carried out for apparatus where the ignition temperature of a 5 mm layer

is below 250 °C, or there is any doubt concerning the application of the graph

6.2.3 Dust layers of excessive thickness

Where it cannot be avoided that a dust layer of excessive thickness is formed on top of an apparatus or around the sides and bottom of an apparatus, or where the apparatus is totally submerged in the dust, due

to the thermally insulating effect, a much lower surface temperature may be necessary

NOTE See informative annex A for examples of “excessive layers”.

6.3 Apparatus to be submitted to laboratory investigation

— apparatus covered by dust layers in excess of 50 mm on their top section;

— apparatus covered by layers of any thickness greater than 5 mm, e.g formed around the sides and bottom of the apparatus;

— apparatus completely submerged in dust

Laboratory investigation may include tests and/or recognized calculation schemes

Key

1 Maximum permissible surface temperature of apparatus °C

2 Ignition temperature of a 5 mm layer

3 Thickness of layer mm

Figure 1 — Reduction in maximum permissible surface temperature for increasing

depth of dust layers

A report of such laboratory investigation shall normally include all details of application such as:

— type of dust (electrically conductive or non conductive see EN 61241-2-2);

— ignition temperature of the dust layer;

— extent and thickness of the dust layer that may be formed around the apparatus;

— preferred values of layer thickness to be investigated are:

— maximum amount of dust that the apparatus can retain;

— apparatus completely submerged in the dust;

— measures to limit the power input;

— measures to control the inherent temperature

6.4 Maximum permissible surface temperature

The lower of the values obtained in 6.1, 6.2 and 6.3 shall determine the maximum permissible surface

temperature of the apparatus to be used

7 Selection of dust ignition protected apparatus

The apparatus shall be designed and tested to meet the relevant requirements of EN 50281-1-1 and its

maximum surface temperature shall be within the limits given in clause 6 of this standard, depending on

the possible build-up of dust layers

The special requirements for Zone 20 can be met by a system of power limitation, with or without inherent temperature control, which shall be investigated under simulated working conditions

NOTE Apparatus for measurement and control techniques (e.g instrumentation, sensors, controls) are typical applications under dust, of excessive layers.

Power engineering apparatus (such as motors, luminaires, plugs and sockets) shall wherever practicable

be placed outside Zone 20 areas or if used at all be submitted to special investigation

8 Selection of radiating equipment

For equipment radiating in the optical spectral range that is to be installed in the hazardous area all

relevant requirements of this standard including clause 8 shall be applied.

For equipment installed outside of, but radiating into, the hazardous area only the requirements of clause 8

need be applied

NOTE Protective measures against ignition hazards due to radiation in any frequency range (e.g ultrasonic, ionizing, radio frequency, spectral) are presently under investigation The latest results of research and standards need to be applied when using radiating equipment.

8.1 Ignition process

In the case of laser radiation (for example, signalling, telemeters, surveying, range-finders) the energy or power density even of the unfocussed beam at long distances may be so great that ignition is possible Particularly intense focussing may cause temperatures of far above 1 000 °C at the focal point

Consideration shall be given to the possibility that the equipment itself producing the radiation (for example, lamps, electric arcs, lasers, etc.) may be an ignition source

Conductive Cat 1 D

Temperature limitations because of the presence of

uncontrollable and excessive thickness as specified in 6.2.3 and 6.3

Cat 1 D

or Cat 2 D

Cat 1 D

IP 6X

or Cat 2 D Non

conductive Cat 1 D Temperature limitations because of the presence of

uncontrollable and excessive thickness as specified in 6.2.3 and 6.3

Cat 1 D

or Cat 2 D

Cat 1 D

or Cat 2 D

or Cat 3 D