IS 13408 (Part 1) : 1992(Reaffirmed 2003)

Edition 1.1(2003-10)

B U R E A U O F I N D I A N S T A N D A R D SMANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG

NEW DELHI 110002

Price Group 12

© BIS 2003

Indian Standard

CODE OF PRACTICE FOR THE SELECTION, INSTALLATION AND MAINTENANCE OF ELECTRICAL APPARATUS FOR USE IN

POTENTIALLY EXPLOSIVE ATMOSPHERES (OTHER THAN MINING APPLICATIONS OR

EXPLOSIVES PROCESSING AND MANUFACTURE)

PART 1 GENERAL RECOMMENDATIONS

(Incorporating Amendment No. 1)

UDC 621.31-213.34 : 006.76

Electrical Apparatus for Explosive Atmospheres Sectional Committee, ET 22

CONTENTS

Section 1 General PAGE

1.2.3.4.5.6.

SCOPEREFERENCE STANDARDSDEFINITIONS AND EXPLANATION OF TERMSCLASSIFICATION OF HAZARDOUS AREASTYPES OF PROTECTIONLIGHT METALS AS CONSTRUCTIONAL MATERIALS

111234

Section 2 Selection of Apparatus7.8.

PROCEDURE FOR SELECTING ELECTRICAL APPARATUSINTERCONNECTION OF APPARATUS

46

Section 3 General Installation Recommendations9.

10.11.12.13.1415.16.17.18.19.20

GENERALACCESS FOR INSPECTIONPLANS AND RECORDSELECTRICAL RATINGSINSTALLATION OF APPARATUSINTEGRITY OF INSULATIONAUTOMATIC OVERCURRENT PROTECTIONEARTHING AND EARTH FAULT PROTECTIONISOLATIONEMERGENCY SUPPLIESWIRING SYSTEMSPORTABLE AND TRANSPORTABLE APPARATUS AND ITS CONNECTIONS

66666777777

10Section 4 Inspection, Maintenance and Testing

21.22.23.24.25.26.27.

GENERALPERSONNELISOLATION OF APPARATUSPRECAUTIONS CONCERNING THE USE OF IGNITING AGENCIESINITIAL AND PERIODIC INSPECTIONSINITIAL AND PERIODIC TESTINGMAINTENANCE RECOMMENDATIONS

10101010111212

Section 5 Properties of Flammable Liquids, Vapours and Gases28.29.30.31.32.33.34.35.36.

GENERALMELTING POINT AND BOILING POINTRELATIVE VAPOUR DENSITYFLASH POINTLIMITS OF FLAMMABILITYFLAMMABILITY RANGEEFFECT OF ENVIRONMENTS WITH OTHER THAN NORMAL ATMOSPHERIC CONDITIONSIGNITION TEMPERATUREGENERAL CONSIDERATION

131313131313141414

Section 6 Marking of Apparatus37.38.39.40.

GENERALMARKING REQUIREMENTS FOR APPARATUSEXAMPLES OF MARKING OF APPARATUSGENERAL NOTES ON MARKING

15151617

ANNEX A LIST OF REFERRED INDIAN STANDARDSANNEX B RELEVANT INTERNATIONAL, EUROPEAN AND BRITISH STANDARDS AND DETAILS OF

THE NATIONAL CERTIFYING AUTHORITY AND ITS CERTIFICATION STANDARDSANNEX C FRICTIONAL SPARKING RISKS WITH LIGHT METALS AND THEIR ALLOYSANNEX D DATA FOR FLAMMABLE MATERIALSANNEX E CALCULATION OF THE FLAMMABILITY LIMITS FOR A MIXTURE OF GASES

18

19212235

( Continued on third cover )

IS 13408 (Part 1) : 1992

1

Indian Standard

CODE OF PRACTICE FOR THE SELECTION, INSTALLATION AND MAINTENANCE OF ELECTRICAL APPARATUS FOR USE IN

POTENTIALLY EXPLOSIVE ATMOSPHERES (OTHER THAN MINING APPLICATIONS OR

EXPLOSIVES PROCESSING AND MANUFACTURE)

PART 1 GENERAL RECOMMENDATIONS

Section 1 General

1 SCOPE

1.1 This code gives recommendations forselection, installation and maintenance ofelectrical apparatus for use in areas wherepotentially explosive materials are generated,processed, handled, stored or otherwiseencountered.

1.2 Flammable or potentially explosivematerials in this standard include gases,vapours, mists and solids.

1.3 This standard applies to the following:a) thermal effects where those give rise to

danger in flammable or potentiallyexplosive atmosphere;

b) protection against overcurrent whererelevant to circuits in flammable orpotentially explosive atmospheres;

c) methods for switching and isolation ofelectrical systems where relevant tocircuits in flammable or potentiallyexplosive atmospheres.

1.4 This code does not cover the following:a) inherently explosive atmospheres, for

example, explosives manufacturing andprocessing;

b) underground mining application;c) dust atmospheres;d) areas where abnormal atmospheric

conditions occur;e) the effects of static electricity and high

frequency electromagnetic radiation.NOTE — Detailed guidance on protection against risksdue to static electricity may be found in IS 7689 : 1989.

1.5 This standard is applicable to all newpermanent installations and, where resonably

practicable, to existing installations. Therecommendations for maintenance areapplicable to all installations.

1.6 The recommendations of the standard arealso applicable to those installations that aresemi-permanent or temporary but alternativesafety measures and procedures may need to beadopted to achieve the same level of safety asthat recommended in this standard.

NOTES

1 This standard does not give guidance on methods ofprotection against electric shock, the effects of lightning( see IS 2809 : 1969 ), ignitions sources other than thoseassociated with electrical apparatus or toxic risks. Thetoxic risks associated with flammable materials apply toconcentrations that are usually very much less than thelower flammable limit.

2 Annex B contains, for information, a list of relevantinternational, European and British Standards,together with details of the national certifying authorityand its certification standards.

2 REFERENCES

The list of Indian Standards given in Annex Ais a necessary adjunct to this standard.

3 DEFINITIONS AND EXPLANATION OF TERMS

3.0 For the purpose of this part and of the otherparts of the code generally, the followingdefinitions shall apply.

NOTE — Further definitions that are particularlyrelevant to specific types of protection are included inthe appropriate parts of this code of practice.

3.1 Explosive Atmospheres

A mixture of flammable gas or vapour with airunder atmospheric conditions in which, afterignitions, combustion rapidly spreadsthroughout the unconsumed mixture.

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3.2 Mist

A free suspension in air of droplets of a liquidwhose vapour is flammable in free suspensionin air.

3.3 Hazard

The presence, or the risk of the presence, of anexplosive atmosphere.

3.4 Hazardous Area

An area in which explosive atmospheres are, ormay be expected to be, present in quantitiessuch as to require special precautions for theconstruction and use of electrical apparatus.

3.5 Non-Hazardous Area

An area in which explosive atmospheres are notexpected to be present in such quantities thatspecial precautions for the construction and useof electrical apparatus are necessary.

3.4 Flash Point

The lowest temperature at which sufficientvapour is given off from a flammable materialto form an explosive atmosphere.

3.7 Ignition Temperature

The lowest temperature of a flammable gas orvapour at which ignition occurs when tested asdescribed in IS 7820 : 1975.

NOTE — Ignition temperature was formally known asautoignition or spontaneous ignition temperature.

3.8 Accessible Surface

A surface to which an explosive atmosphere hasaccess, and that is not explosion protected otherthan by temperature limitation.

3.9 Maximum Surface Temperature

The highest temperature attained underpractical conditions of operation within therating of the apparatus (and recognizedoverloads, and including defined faultconditions, if any, associated therewith) by anaccessible surface the exposure of which to anexplosive atmosphere may involve a risk.

3.10 Temperature Class (T Class)

One of six values of temperature allocated toelectrical apparatus derived from a system ofclassification according to the maximumsurface temperature of the apparatus.

3.11 Apparatus Group and Sub-Group

Group or sub-group assigned to apparatusdepending on its suitability for use with specificgases.

An apparatus group or sub-group may be usedwith flammable materials of a lesser risk

sub-group subject only to considerations oftemperature and chemical compatibility.

3.12 Protection

3.12.1 Type of Protection

The measures applied in the construction ofapparatus or part of apparatus to preventignition of surrounding explosive atmosphereby such apparatus.

NOTE — Formerly it was common for an individualitem of apparatus to employ one type of protection only;increasingly apparatus may now employ two or moretypes of protection. Thus a rotating machine mayincorporate a motor carcase in type of protection ‘d’(flameproof enclosure) and a terminal box in type ofprotection ‘e’ (increased safety). It has become commonusage to refer to ‘explosion-protected’ apparatus ratherthan to any one type of protection ( see also Section 2 ).

3.12.2 Enclosure Protection

The measures applied to the enclosures ofapparatus to provide degrees of protection for :

a) persons against contact with live ormoving parts inside the enclosure andprotection for the apparatus againstingress of solid foreign bodies;

b) the apparatus against the ingress ofliquids.

3.12.3 Electrical Protection

The measures applied to circuits to control theeffects of overload and overcurrent.

4 CLASSIFICATION OF HAZARDOUS AREAS

This code of practice is based on the concept ofdealing with the risk of fire and explosion byarea classification. This concept recognizes thediffering degrees of probability with whichconcentrations of flammable gas or vapour mayarise in installations in terms of both thefrequency of occurrence and the probableduration of existence on each occasion.

The detailed considerations that should betaken into account in area classification aredescribed in IS 5572 (Part 1) : 1978. Forcompleteness, the definitions appropriate toarea classification are repeated here.

Zone 0 Zone in which an explosive gas-airmixture is continuously present, orpresent for long periods.

Zone 1 Zone in which an explosive gas-airmixture is likely to occur in normaloperation.

Zone 2 Zone in which an explosive gas-airmixture is not likely to occur innormal operation, and if it occurs itwill exist only for a short time.

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It should be noted that this area classificationdeals only with risks due to flammable gasesand vapours and, by implication, flammablemists. In a non-hazardous area normalelectrical techniques apply.

When the hazardous areas of a plant have beenclassified, the remainder will be defined asnon-hazardous.

5 TYPES OF PROTECTION

There are at present eight accepted types ofprotection for electrical apparatus for use inhazardous areas. A description of each type isgiven in Table 1. The relevant equipmentspecifications, where they exist, should bereferred to for precise definitions of the type ofprotection.

Table 1 Types of Protection

Type of Protection

Title Description Reference toIndian Standards

‘d’ Flameproof A method of protection where the enclosure for electricalapparatus will withstand an internal explosion of theflammable gas or vapour (for which it is designed) which mayenter it, without suffering damage and withoutcommunicating the internal flammation to the externalflammable gas or vapour for which it is designed, through anyjoints or structural openings in the enclosure.

IS 2148 : 1981

‘i’ Intrinsically safe apparatus or system

A protection technique based upon the restriction of electricalenergy within apparatus and in the interconnecting wiring,exposed to a potentially explosive atmosphere, to a levelbelow that which can cause ignition by either sparking orheating effects. Because of the method by which intrinsicsafety is achieved it is necessary that not only the electricalapparatus exposed to the potentially explosive atmospherebut also other (associated) electrical apparatus with which itis interconnected is suitably constructed.

IS 5780 : 1980

‘p’ Pressurization continuous dilution and pressurised rooms

A method of protection using the pressure of a protective gasto prevent the ingress of an external flammable atmosphereto a space which may contain a source of ignition and, wherenecessary, using continuous dilution of an atmosphere withina space which contains a source of emission of gas which mayform an explosive atmosphere.

IS 7389 (Part 1) : 1976

‘e’ Increasedsafety

A method of protection by which additional measures areapplied to an electrical apparatus to give increased securityagainst the possibility of excessive temperatures and of theoccurrence of arcs and sparks during the service life of theapparatus. It applies only to an electrical apparatus, no partsof which produce sparks or arcs or exceed the limitingtemperature in normal service.

IS 6381 : 1972

‘n’ Type of protection n

A type of protection applied to an electrical apparatus suchthat, in normal operation, it is not capable of igniting asurrounding explosive atmosphere, and a fault capable ofcausing ignition is not likely to occur.

IS 8289 : 1976

‘s’ Special protection

A concept for those types of electrical apparatus that, by theirnature, do not comply with the constructional or otherrequirements specified for apparatus with established typesof protection, but which nevertheless can be shown, wherenecessary by test, to be suitable for use in hazardous areas inprescribed zones.

‘o’ Oil-immersed

A method of protection where electrical apparatus is madesafe by oil-immersion in the sense that flammable gases orvapours above the oil or outside the enclosure will not beignited.

IS 7693 : 1975

‘q’ Sand-filled A method of protection where the enclosure of electricalapparatus is filled with a mass of powdery material such that,if an arc occurs, the arc will not be liable to ignite the outerflammable atmosphere.

IS 7724 : 1975

NOTE — Other types of protection are under consideration internationally. These may include type of protection ‘h’hermetically sealed and type of protection ‘m’ encapsulation.

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6 LIGHT METALS AS CONSTRUCTIONAL MATERIALS

6.1 Particular consideration should be given tothe location of an apparatus that incorporateslight metals in the construction of its enclosure.

The propensity of such materials to give rise tosparking that is incentive under conditions offrictional contact has been well established.Reference should be made to Annex C forfurther detailed guidance.

Section 2 Selection of Apparatus

7 PROCEDURE FOR SELECTING ELECTRICAL APPARATUS

7.1 General

Hazardous area apparatus should be selectedfor use in accordance with each of the followingcriteria as appropriate:

a) classification of area;

b) temperature classification;

c) apparatus sub-grouping;

d) environmental conditions.

Selection procedures according to the abovecriteria are recommended in 7.2 to 7.5.

Special considerations may be required for anon-hazardous area apparatus that isassociated with hazardous area apparatus ( seeappropriate Indian Standards for intrinsicsafety and increased safety apparatus,respectively ).

7.2 Selection According to Classification of Area

Reference should be to IS 5572 (Part 1) : 1978for details of area classification which results inthe division of the hazardous area into one ormore zones.

7.2.1 Having established the zones, the types ofprotection to be applied to the electricalapparatus should be selected in accordancewith Tables 2A and 2B.

Table 2A Selection of Apparatus According to Zone of Risk

Zone Type of Protection Reference to IS

0 ‘ia’ IS 5780 : 1980

1 Any explosion protectionsuitable for Zone 0 and‘d’‘ib’‘o’ ( see Note 1 )‘p’ ( see Table 2B )‘q’‘s’

IS 2148 : 1981IS 5780 : 1980IS 7693 : 1975IS 7389 (Part 1) : 1976IS 7724 : 1975

—

2 Any explosion protectionsuitable for Zones 0 or 1 and‘e’ ( see Note 2 )‘n’ ( see Note 2 )‘p’ ( see Table 2B )

IS 6381 : 1972IS 8289 : 1976IS 7389 (Part 1) : 1976

NOTES

1 Oil-immersed apparatus may be used only in case its security will not be impaired by tilting or vibration of theapparatus.

2 For outdoor installations, the apparatus with type of protection ‘e’ and ‘n’ should be used with enclosures providing atleast the following degree of protection in accordance with IS 4691 : 1985:

a) IP 55 where there are uninsulated conducting parts internally, and

b) IP 44 for insulated parts.

3 A substantial saving in cost may be achieved by using apparatus with type of protection ‘n’ in Zone 2 areas.

Table 2B Minimum Actions of Failure of Protective Gas For Type of Protection ‘p’( Clause 7.2.1 )

AreaClassification

Enclosure Does not Contain Ignition-Capable Apparatus

Enclosure Contains Ignition-Capable Apparatus

Zone 1

Zone 2

Alarm

No action required

Alarm and switch off

Alarm

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7.3 Selection According to Temperature ClassificationWhen selecting apparatus according totemperature classification, the maximumsurface temperature of the T class of theapparatus (or, where the apparatus is markedwith a particular maximum surfacetemperature, that temperature) should notexceed the ignition temperature of the gases orvapours involved.7.3.1 In certain cases, temperatures higherthan that of the marked temperature class canbe permitted, for example, for smallcomponents such as transistors or resistors,provided it is proved by tests or otherexperimental evidence that there is no risk ofdirect or indirect flammation, deterioration ordeformation by such high temperatures.7.3.2 A T class is assigned to apparatus on thebasis of temperature rise tests assuming thatthe apparatus may be used in an environmentwith an ambient temperature not exceeding40°C. In special cases, apparatus may bedesigned on request to operate in anenvironment with a temperature of more than40°C. In this case the designed maximumpermitted temperature of the environment willbe clearly marked on the apparatus. TheT class will have been assigned on the basis oftemperature rise tests and the assumption thatthe apparatus may operate at temperatures upto the designed maximum permittedtemperature of the environment.7.3.3 When apparatus, which has had a T classassigned assuming a 40°C maximum ambienttemperature, is to be used at a higherenvironmental temperature, for example,because it is mounted on a hot surface, themaximum surface temperature of theapparatus should not exceed the ignitiontemperature of the gases or vapours likely to bepresent. It is also important to check with themanufacturer on the suitability of theapparatus to operate at these highertemperatures. For example, when apparatus isto be mounted under pipe-lagging, it isvirtually unaffected by the air temperature, butmay fail due to heat from the pipe.7.3.4 The permitted maximum surface tempe-ratures classified according to IS 13346 : 1992are given in Table 3.

7.3.5 An example can be given of therelationship between T class and ignition

temperature. Cyclohexane has an ignitiontemperature of 259°C and, therefore, assuminga maximum environmental temperature of40°C, apparatus with a temperature class T2(that is, 300°C) would not be suitable whereasapparatus with a temperature class of T3 (thatis 200°C) would be suitable.

NOTE — In special cases, apparatus can be markedwith a particular temperature as well as one of the six Tclasses. For example, in the case cited above if theapparatus were marked with a temperature of 259°C, aswell as the temperature class of T2, it would still besuitable for use in areas where a potentially explosiveatmosphere of cyclohexane might form.

7.4 Selection According to Apparatus Sub- Grouping

In the new groupings, agreed internationally,Group I is reserved for apparatus for minessusceptible to methane (firedamp) and istherefore outside the scope of this standard.Group II is reserved for apparatus for use in allother places where there may be potentiallyexplosive atmospheres and as appropriate issub-grouped IIA, IIB and IIC.

7.4.1 It should be noted that apparatussub-grouping is applied to the technique ofprevention of flame transmission andlimitation of energy. Apparatus with type ofprotection ‘s’ may be subject to sub-groupingwhere it used one or more of these techniques.The protective features of other types ofprotection apply equally to all industrial gases,subject only to temperature classification;apparatus sub-grouping is not thereforenecessary ( see also Section 6 ).

7.4.2 Apparatus may be protected by one ormore types of protection which may requireapparatus sub-grouping. Such apparatus willbe marked as described in 40.4. In thesecircumstances, the apparatus should beselected according to the apparatus sub-groupto which the flammable materials that may bepresent are allocated.

7.4.3 Apparatus should be used only withmaterials allocated to the appropriateapparatus sub-group, as indicated in Table 6( see Annex D ), whose ignition temperaturesare not less than the maximum temperature ofthe T class certified for the apparatus.Apparatus certified for a particular sub-groupmay also be used with materials allocated to alower risk sub-group, subject again toconsiderations of temperature classification.

7.4.4 It will sometimes be found necessary touse electrical apparatus in applications wherematerials may be present that have not yetbeen allocated to a sub-group. In thesecircumstances, expert advice should beobtained on the sub-group allocation of thematerials in question.

NOTE — In IS 2148 : 1981 and IS 9570: 1980 flammablegases and vapours are grouped or classified,respectively, according to the experimental data forlimiting safe gaps or igniting currents measured underprecisely specified conditions. In the case ofIS 9570 : 1980 many materials are classified according

Table 3 Relationship Between T Class and Maximum Surface Temperature

T Class Maximum Surface Temperature°C

T1T2T3T4T5T6

450300200135100

85

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to their chemical similarity with gases and vapours thatare already classified on the basis of experimental data.Neither method of grouping takes into account the needfor surface temperature classification, since ignitiontemperatures generally are not related to othercombustion characteristics. It is therefore inaccurate toassume that any particular apparatus complying withthe design requirements for a group of gases could beused safely with all materials allocated to that group.For this reason, instead of grouping gases, an apparatusitself is now grouped according to design criteriaspecified in the appropriate Indian Standards such asIS 6381 : 1972 and IS 8289 : 1976.

7.5 Selection According to Environmental ConditionsApparatus and its component parts should beconstructed so as to guard against electricaland mechanical failure in the intendedconditions of use. The integrity of someelectrical apparatus may be effected when

required to operate under temperature orpressure conditions outside those for which theapparatus has been constructed. In suchconditions further advice should be sought.7.5.1 Particular attention should be given to theneed for protection against the weather, theingress of liquids and particulate matter,corrosion, the effect of solvents and the effect ofheat from adjacent plant ( see also 27.3 to 27.5 ).

8 INTERCONNECTION OF APPARATUSThe safety of individual pieces of apparatusmay be influenced by any other apparatus withwhich it is interconnected. For such systemconsiderations, reference should be made toappropriate standards covering individualprotection concepts.

Section 3 General Installation Recommendations

9 GENERAL9.1 In addition to any recommendations theremay be for installation in non-hazardous areas,further recommendations for installations inhazardous areas as a consequence of the natureof the environment and that are generallyapplicable to all types of protection aredescribed in 10 to 20.

9.2 The explosion protection of someinstallations, for example, those using electricsurface heating, pressurization ‘p’, etc, isdependent on the overall design of the finishedsystem. In such cases, the appropriate designcodes or standards should be used for guidanceto carry out the installation ( see B-3 ).

9.3 Alterations to apparatus or systems mayinvalidate any certificate or otherdocumentation relating to that apparatus orsystem. Such alterations should be made onlywith the agreement of the occupier inconsultation with the manufacturer whereappropriate.9.4 There may be special requirements listed inthe certification documents ( see 40.2 ) that willaffect the method of installation. Installers andoccupiers should satisfy themselves that suchconditions are properly met.

10 ACCESS FOR INSPECTIONInstallations should be designed and theapparatus and materials installed with a viewto providing ease of access for inspection andmaintenance.

11 PLANS AND RECORDSFor each site a responsible person shouldmaintain and make available plans or recordsof the following items:

a) the classification and extent of hazardousareas together with the other informationas recommended in IS 5572 (Part 1) : 1978;

b) records sufficient to enable the explosionprotected equipment to be maintained inaccordance with its type of protection; and

c) the type, route and details of undergroundcables.

12 ELECTRICAL RATINGS12.1 Electrical apparatus and materials shouldbe installed, used and maintained within theirelectrical ratings for power, voltage, current,frequency, duty and such other characteristicswhere non-compliance might jeopardize thesafety of the installation.12.2 In respect of electrical apparatus fromoverseas suppliers, because of the differingnature of the supply networks, special careshould be taken that:

a) the voltage and frequency rating areappropriate to the supply system on whichthe apparatus is to be used; and

b) the temperature classification has beenestablished for the correct voltage,frequency, etc.

13 INSTALLATION OF APPARATUS13.1 All apparatus should be installed with dueregard to the possibility of external mechanicaldamage affecting the type of protection of theapparatus. Where equipment is to be installedin areas of high mechanical risk, additionalmeasures such as the provision of guards forlight transmitting parts, may be necessary.However, additional measures should notimpair the integrity of the type of protection.13.2 Special installation conditions apply toany type of certified explosion protectedapparatus where the certificate number has asuffix marking of ‘B’ or ‘X’. The certificationdocuments should be studied to ascertain theconditions of installation. The manufacturersshould also have provided clear installationinstructions.

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14 INTEGRITY OF INSULATIONCare should be taken during installation tomaintain the degree of electrical insulationprovided by the construction of the apparatusso that the possibility of accidental sparking orarching is avoided.

15 AUTOMATIC OVERCURRENT PROTECTIONIn general, all circuits and apparatus inhazardous areas should be provided withautomatic means of disconnection in the eventof overcurrent (short circuit and overload)conditions. However, apparatus with particulartypes of protection may have additional and/oralternative requirements, and reference shouldbe made to the recommendations in theappropriate Indian Standard. Suitableprotection should be fitted where there is adanger that three-phase apparatus may besubjected to excess current during single-phaseoperation.

16 EARTHING AND EARTH FAULT PROTECTION16.1 Earthing of Power SystemsGenerally earthing of power distributionsystems should be in accordance with therecommendations of IS 3043 : 1987.In typical industrial systems, for example415 V and 440 V, earth fault protection may beafforded by the overcurrent protective devices.However, where the earth loop impedance is toohigh for that method to be adopted, it will benecessary to provide earth fault protection byother means such as residual current devices.Smaller rating systems do not require residualcurrent devices.In higher voltage systems, for example, 3.3 kVand 6.6 kV, apparatus should have earth faultprotection in addition to overcurrent protection.If environmental conditions could lead toaccelerated degradation of earth loop paths,anti-corrosive protection should be provided orthe earth loop impedance values decreasedaccordingly.16.2 Earthing of Intrinsically Safe Electrical Systems/Apparatus ‘i’Detailed recommendations will be covered laterin a separate standard.16.3 Lightning ProtectionRecommendations for lightning protection aregiven in IS 2309 : 1969.16.4 Electrostatic PhenomenaRecommendations for the avoidance of ignitionrisks due to static electricity are given inIS 7689 : 1989.16.5 Cathodic ProtectionRecommendations for cathodic protectionsystems are given in IS 8062 (Part 1) : 1976.

16.6 Protective Multiple Earthing (PME)Where the power supply is directly from asystem that is protected by PME, specialprecautions may be required within thehazardous area and specialist advice should besought.16.7 Interconnection of Earthing SystemsThe power, lightning, and static earthingsystems, where they exist in the same area,should be effectively connected together toensure as far as possible that all metal work ina particular area is at the same potential underall conditions.

17 ISOLATION17.1 At a suitable point or points outside thehazardous area there should be single ormultiple means of isolating mains supplies tothe hazardous area.17.2 A means of isolation of each circuit orgroup of circuits, to include isolation of theneutral, should be provided. Where the meansof isolation is located inside the hazardous areait should be provided with an appropriate typeof protection.17.3 Labelling should be provided immediatelyadjacent to each means of isolation to permitrapid identification of the circuit or group ofcircuits thereby controlled. There should beeffective measures to prevent the restoration ofsupply to the apparatus whilst the risk ofexposing live conductors to an explosiveatmosphere continues.

18 EMERGENCY SUPPLIESSpecial precautions should be taken in theprovision of emergency supplies to electricalapparatus (for example emergency lighting,critical instruments, valves) that may berequired to operate during periods of powerfailure.

19 WIRING SYSTEMS19.1 GeneralThe types of wiring that in principle may beused for installations in hazardous areas aredescribed in this clause. The detailedrecommendations for permitted types of cableand their accessories are described in IS 5571 :1979.For a Zone 0 installation, cabling will be eitherpart of an ‘ia’ systems or as recommended fortype of protection ‘s’ for Zone 0.Types of wiring and systems that should beused in Zone 1 and 2 areas are:

a) cables drawn into screwed, solid drawn orseam welded steel conduit; and

b) cables that are otherwise suitablyprotected against mechanical damage.

NOTE — The sheath of a metal sheathed cable shouldnot be used as the neutral conductor.

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Examples of the types of cable which are inaccordance with the recommendations of (b) are:

1) thermoplastic or elastomer insulatedscreened or armoured cable without a loadsheath and with polyvinylchloride (PVC)polychroprene (PCP) or similar sheathoverall;

2) cables enclosed in a seamless aluminiumsheath with or without armour, with anouter protective sheath ( see also Annex C );

3) mineral insulated metal sheathed cable( see also Annex C );

4) thermoplastic or elastomer insulatedflexible cable or cord with a flexiblemetallic screen or armour and a PVC, PCPor similar sheath overall; and

5) thermoplastic insulated cable withsemi-rigid sheath.

For type of protection ‘1’ (intrinsic safety) andfor apparatus used in Zone 2 only, other cablesmay be used.19.2 General Installation Recommendations for Wiring Systems

19.2.1 The wiring entry to the apparatusshould maintain the integrity of the type ofprotection of the apparatus.19.2.2 Unused cable entries in electricalapparatus should be closed with plugs suitablefor the type of protection of the apparatus.19.2.3 Where accessories (for example, ajunction box) are used for the interconnection ofcable, only those accessories that are suitablefor the zone concerned should be used.19.2.4 Electrical continuity between metallicenclosures and conduit, armour or cablesheaths and armour, or across any joints in thecoduit or armour, should be maintained by theintegrity of the joint itself. If external bondingis in certain circumstances necessary, it shouldpreferably be connected directly across thejoint.19.2.5 Where circuits traverse a hazardousarea in passing from one non-hazardous area toanother, the wiring in the hazardous areashould be in accordance with therecommendations of this code.19.2.6 Except for trace heating, fortuitouscontact between conduit or the metallicarmouring/sheathing of cables and pipe work orequipment containing flammable gases, vapouror liquids should be avoided. The insulationprovided by a non-metallic outer sheath on acable will usually be sufficient to avoid this.19.2.7 Wiring should be installed, so far as ispracticable, in positions that will prevent itsbeing exposed to mechanical damages and(with the exception of trace heating cables) tothe effects of heat and to corrosive or solventagencies. Where exposure of this nature isunavoidable, appropriate protective measuresshould be taken.

19.2.8 All apparatus connections and wiringwhose functions are not immediately apparentshould be clearly marked to enable theirrelationship to any associated apparatus,connections and wiring to be clearly recognized.19.2.9 Where cables or conduit pass through afloor, wall, partition or ceiling that forms a gasor fire barrier, the hole provided for themshould be made good with cement or similarincombustible material to the full thickness ofthe floor, wall, partition or ceiling. Alter-natively, cable glands or cable transits may beused for this purpose.19.2.10 Where trunking, ducts, pipes ortrenches are used to accommodate cables,precautions should be taken to prevent thepassage of flammable gases, vapours or liquidsfrom one area to another and to prevent thecollection of flammable gases, vapours orliquids in trenches. Such precautions mayinvolve the sealing of trunking, ducts and pipesand the adequate ventilation or sand filling oftrenches.19.2.11 For terminal connections to fixedapparatus that may be required to be moved asmall distance (for example, motors on slidsrails), cables arranged to permit the necessarymovement without detriment to the cable, orone of the types of cable suitable fortransportable apparatus may be used. Ifflexible conduit is used, it and its fittingsshould be so constructed and assembled thatdamage to the cable consequent upon its use isavoided. Adequate earthing or bonding shouldbe maintained other than by means of theflexible conduit.19.2.12 Where an overhead line provides poweror telecommunication services to apparatus ina hazardous area it should be terminated in anon-hazardous area and the service continuedby cable. Suitable surge protection apparatusshould be fitted at or near the terminal point.The armouring or metal sheathing of the cableshould be electrically continuous, and the endadjacent to the point of connection with theover-head line should be bonded to the earthelectrode of the surge protection apparatus. Inaddition the armouring or metal sheathingshould be independently earthed as near aspossible to the lighting protective system, ifany, associated with the hazardous area ( seeIS 2309 : 1969).19.3 Environmental Factors Affecting Choice of Wiring System19.3.1 Insulating materials may be attacked bycertain chemicals, and where contact may besufficiently long that deterioration could resultfrom such exposure, then consideration shouldbe given to the use of a protective sheath.19.3.2 Where cables may be subjected toexcessive flexing, consideration should be givento the avoidance of fracture, for example, whenusing mineral insulated cable, by forming thecable into a loop close to the point oftermination.

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19.3.3 Where electrolytic corrosion of metalsheath may result from contact with walls orother surfaces to which the cable is attached, itshould be kept clear of such surfaces or coveredwith a protective sheath.19.4 Conduit SystemsWhere used, screwed heavy gauge steelconduit, solid drawn or seam welded, should bein accordance with the requirements of IS 9537(Part 2) : 1981.Such screwed steel conduit systems aresatisfactory for many situations but should notbe used where vibration may cause fracture orloosening of joints or where excessive stressmay be imposed as a result of its rigidity ofwhere corrosion or excessive internal con-densation of moisture is likely to occur. In suchcircumstances, flexible conduit of very heavymechanical strength should be used.Where a run of conduit, irrespective of size,passes from a hazardous area to anon-hazardous area, a stopper box or sealingdevice should be inserted at the hazardous areaboundary or, failing this, on the side remotefrom the hazardous area.

NOTE — The use of a sealing device is essential to themaintenance of certain types of protection.

Elbows of the solid types may be used for theimmediate connection of conduit to apparatus.Surface mounted conduit should be supportedby spacing saddles.All joints in an assembly of conduit should beprepared before or after assembly so that thedevelopment of rust is inhibited and earthcontinuity and bonding is maintained.All bends in conduit should be machine-madeand rounded so as to facilitate drawing in ofcables.For additional requirements for conduitsystems that are relevant to particular types ofprotection, appropriate standards may bereferred to.

19.5 Cable Systems19.5.1 GeneralConductors may be copper or aluminium butplain aluminium should not be used forconductors with cross-sectional areas less than16 mm2 ( see also C-7 for precautions on the useof aluminium in Ex ‘d’ flameproof enclosures).

Cable runs should, where practicable, beuninterrupted. Where discontinuities cannot beavoided, the joint should be encapsulated ormade in a compound-filled joint box or beprotected in accordance with the requirementsof the zone.Certain types of protection require specifictypes of cable glands. Compression type glandswould serve the purpose as the cables would beterminated in a terminal box. Direct entrywithout a terminal box shall be treated as aspecial case.

Attention is drawn to the need to preventtransmission of flammable liquids or gasesfrom a hazardous to a non-hazardous areathrough the interstices of cables terminating inapparatus (for example pressure switches orcanned pumps) into which such fluids areintroduced. Under fault conditions (forexample, diaphragm or can failure) the fluidmay be released inside the apparatus underconsiderable pressure against whose effects itmay be difficult to seal the cable interstices.Apparatus of this kind should be deliberatelyvented to atmosphere, but if this is not possible(for example, a type ‘d’ enclosure) a specialsealing joint or length of mineral insulatedmetal sheathed cable should be introduced inthe cable run.All cables should be provided with adequatemechanical protection. Cables should beadequately supported throughout their length,care being taken to avoid excessive pressurewhen cleats are used. Horizontal cables may becarried on support or cable trays or throughprotective troughs or tubes. Rising cablesshould be clipped, cleated or otherwise attachedto suitable supports that provide adequatemechanical protection and support.Where single core metal sheathed or armouredcables are used, precautions should be taken toavoid dangerous sheath voltages or currents.19.5.2 PVC Covered and/or Insulated CablesAttention is drawn to the fact that as thetemperature decreases, PVC becomesincreasingly stiff and brittle with the resultthat, if PVC cables are bent too sharply or arestruck at temperatures of about 0°C or lower,there is a risk for most PVC cables of shatteringthe PVC. Therefore, it is advisable to store PVCcable at temperatures above 0°C for at least24 h prior to installation ( see 19.3.1 ).19.5.3 Paper Insulated CablesWhere paper insulated armoured cables areused, and particularly where such cables maybe exposed to high temperature, preferenceshould be given to non-draining cable. In thecase of other types of paper insulated armouredcables, vertical runs should be avoided.Cable boxes should, if necessary, be arrangedfor sealing the cable insulation and should beprovided, as necessary, with adequate meansfor ensuring the earth continuity of metallicsheath and/or armour.Adequate arrangements should be made toensure that cable boxes can be completely filledwith the necessary compound or insulating oilaccording to their design,19.5.4 Mineral Insulated Metal SheathedCablesCable terminations should incorporate a sealfor the cable insulation and, where necessary,means of ensuring adequate earth continuity.

NOTE — Certain types of protection require specifictypes of seal.

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Seals in which compound is used should not beexposed to temperature that may, in the courseof normal working, affect the satisfactoryfunctioning of such compound.Where there is a risk of mineral insulatedcables being exposed to excessive voltages suchas inductive surges, surge suppression shouldbe fitted. Where surge suppression devices areinstalled in hazardous areas, they should besuitably exposition protected.19.5.5 Aluminium Sheathed CablesAluminium sheathed cables, unless sheathwith a protective covering, should not beinstalled in contact with walls or floors.Consideration should be given to the avoidanceof frictional contact with such cables ( seeAnnex C ).

20 PORTABLE AND TRANSPORTABLE APPARATUS AND ITS CONNECTIONSApparatus other than fixed apparatus shouldhave a type of protection appropriate to thezone(s) of use. During use such apparatusshould not be transferred from a zone of lowerrisk to a zone of higher risk unless it is suitablyprotected for the higher risk. Additionally, theapparatus group and T class should be

appropriate to all of the gases and vapours inwhich the apparatus may be used.

NOTE — Ordinary industrial portable or transportableapparatus, welding equipment, etc, should not be usedin a hazardous area unless its use is undertaken undera controlled procedure and the specific location has beenassessed to ensure that potentially flammable gas orvapour is absent.

Should plugs and sockets be in a hazardousarea, they should be suitable for use in theparticular zone of risk and should havemechanical and/or electrical interlocking toprevent danger during insertion or removal ofthe plug.In many cases the type of cable to be used willbe stated on the apparatus certificate. In caseswhere this is not so, the cable should besuitable for rough usage and other adverseenvironmental conditions (for example,elevated temperatures, presence of solvents). Itshould also be suitable for the circuit protectivearrangements (for example, where earthmonitoring is used, the necessary number ofconductors should be included). Where theapparatus needs to be earthed, the cable mayinclude an angular earthed flexible metallicscreen in addition to the earth conductor.

Section 4 Inspection, Maintenance and Testing

21 GENERAL21.1 To minimize the risk of ignition of anexplosive atmosphere by electrical apparatus,efficient inspection, maintenance and testing ofthe apparatus, systems and installations areessential. It should be noted that correctfunctional operation does not itself indicateconformity with the recommendations for thesafe use of apparatus. The general recommen-dations for inspection, maintenance and testingthat are applicable to all types of protection aredescribed in 22 to 27.22 PERSONNEL22.1 The inspection, testing, maintenance,replacement and repair of apparatus, systemsand installations should be carried out only bypersons whose training includes instruction onthe various types of protection involved.Appropriate refresher training should be givenfrom time to time.

23 ISOLATION OF APPARATUS23.1 No apparatus should be opened in ahazardous area other than apparatus with typeof protection ‘i’ (intrinsic safety) and non-incendive apparatus until it has beendisconnected from its source of supply ( see 17 )and effective measures, such as the locking ofthe disconnector in the open position or fuseremoval, have been taken to prevent its beingmade alive before re-assembly. Particularattention should be paid in the case of anapparatus that may be live even after it has

been disconnected from a source of supply.Where heavy rotating machinery is involved,the back e.m.f. of such plant should beconsidered and precautions will usually need tobe taken to ensure that the apparatus, or anyapparatus associated with it, is not openeduntil the rotating plant is stationary. Mostpower capacitors are fitted with dischargeresistors and it should be noted that these takea finite time to bring the terminal voltage to aharmless value.23.2 Where for purpose of electrical testing it isessential to restore the supply before theapparatus is re-assembled, then this workwould be under a controlled procedure and thespecific location assessed to ensure thatpotentially flammable gas or vapour is absent.For the testing of intrinsically safe electricalapparatus and systems see IS 5780 : 1980.

24 PRECAUTIONS CONCERNING THE USE OF IGNITING AGENCIES24.1 No operation involving the use of an openflame or other source of ignition should beattempted in a hazardous area until theconditions have been made safe by the controlof the flammable material that may give rise tothe risk. Such operations should be undertakenonly on the issue of a gas free certificate,confirming that adequate control measureshave been taken and that tests have been madeand will be repeated at sufficiently frequentintervals to ensure that safe conditions aremaintained.

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25 INITIAL AND PERIODIC INSPECTIONS25.1 All electrical apparatus, systems andinstallations should be inspected prior tocommissioning to check that the selection andinstallation is appropriate and in accordancewith IS 5571 : 1979. Examples of some of theitems which should be included in an initialinspection are given in Table 4.25.2 Following any replacement, repair, modifi-cation or adjustment, the items concernedshould be inspected, to check that theappropriate recommendations of the code havebeen maintained.25.3 If at any time there is a change in the areaclassification or in the characteristic of theflammable material used in the area, or if anyapparatus is moved from one location toanother, a check should be made to ensure thatthe type of protection, apparatus group andT class, where appropriate, are suitable for therevised conditions.25.4 The extent, complexity and frequency ofinspection of apparatus, systems andinstallations when in use should be determinedby those whose training and experience willenable them to recognize any potential hazardsand who are familiar with the local environ-mental conditions and use.

25.5 The frequency of inspection depends onthe type of equipment, the factors governing itsdeterioration, and the finding of previousinspections. Examples of factors which canaffect the deterioration of apparatus orotherwise lead to an unsafe condition are givenin Table 5.

25.6 It is, therefore, recommended that oncethe apparatus has been taken into use, initialintervals between inspections should be of areasonably short duration and that a system beestablished to enable subsequent inspectionintervals to be reviewed and modified in thelight of operational experience. Whereinspection intervals and methods are alreadyestablished and are found by experience to besatisfactory for similar apparatus andenvironments, these may continue to be used.It is recommended that an inspection recordsystem be operated so that the review ofinspection frequencies is effective.

25.7 When large number of similar items suchas luminaires, junction boxes, etc, are installed,it may be feasible to carry out inspections on asample basis provided that the degree ofsampling in addition to the inspectionfrequency is subjected to review.

Table 4 Example of Schedule for Initial Inspection( Clause 25.1)

Initial Inspection Items

Apparatus appropriate for the area classificationCorrect temperature classificationAppropriate apparatus group or sub-groupCorrect circuit identificationMaintenance of integrity of enclosureCable entries and stoppers, etc, are completeElectrical connections are tightSatisfactory earthingCorrect rating of apparatus and componentsDamage to installationAdequate environmental protection (e.g. against weather, mechanical damage)No unauthorized modifications

NOTE — Items are not listed in any order of priority. Where integrity of type of protection is dependent on electricalprotection, this should be checked initially.

Table 5 Example of Schedule for Subsequent Inspections( Clause 25.5 )

Factors Affecting Integrity of Apparatus, Systems and InstallationsCorrosion of enclosures, fixings, cable entries, etcUndue accumulation of dust and dirtLoose electrical connections including those for earthingLoose fixings, glands, conduit, stoppers, etcCondition of enclosure gaskets and fasteningsLeakage of oil or compoundCondition of bearingsInadvertent contact between rotating and fixed partsIntegrity of guardsIncorrect lamp ratings or typeUndue vibrationMalfunction of relays and protective devicesUnauthorized modifications or adjustmentsInappropriate maintenance, e.g. not in accordance with manufacturer’s recommendations

NOTE — Items are not listed in any order of priority. Where integrity of type of protection is dependent on electricalprotection, this should be checked initially.

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26 INITIAL AND PERIODIC TESTING26.1 All electrical apparatus, systems andinstallations should be tested prior tocommissioning and these tests should includethe following:

a) insulation resistance measurement;b) earth electrode resistance measurement;c) earth loop impedance measurement; andNOTE — It may be advantageous to make the earth loopimpedance measurement with both a substantial currentand with an intrinsically safe tester to enable themeasurement to be made with the intrinsically safetester alone for subsequent tests and to allow thoseresults to be compared with the initial test results. Itshould be noted that tests made with an intrinsically safetester may not necessarily identify certain badconnections because of the low test current.

d) operation and setting of protective devices.The results of all tests should be recorded andincluded in the record of inspections describedin 25.26.2 The testing of apparatus, systems andinstallations when in use should be carried outby those whose experience will enable them torecognize the potential hazards and who arefamiliar with local environmental conditionsand use.26.3 Test procedures should be designed tocause the minimum disturbance to theinstallation or system.26.4 Diagnostic testing and recording of resultsof such functions as time, operating voltage,circuit resistance, insulation resistance, etc,should be used where possible to show trends inelectrical condition and to aid the determinationof both the nature and frequency of subsequenttests and inspections.26.5 The frequency of testing depends on thetype of equipment or system, the factorsgoverning its deterioration and in particular thefinds of previous tests. Factors which may affectthe deterioration of apparatus are identified inTable 6 and as these should be taken intoaccount in determining the frequency ofinspection, the frequency of testing will not begreater than, and in fact may be less than, thefrequency of inspection for the relevantapparatus or system. The frequency of testingshould be established and reviewed in a mannersimilar to that recommended for the inspection.26.6 Testing in continuously operating plantand on similar apparatus or systems may beundertaken on a sample basis subject to reviewsimilar to that recommended for inspectionsconducted on a sample basis.26.7 Tests should be made in such a way thatthe safety devices used in low energy or lowvoltage apparatus and circuits are not subject todamage by excess voltage. For testingintrinsically safe electrical systems ‘i’ seeIS 5780 : 1980.26.8 Test should be undertaken under acontrolled procedure to ensure that the specificlocation has either been assessed for the absenceof a flammable gas or vapour or that the testmethod is non-incendive.

27 MAINTENANCE RECOMMENDATIONS27.1 Alterations to ApparatusThe general condition of all apparatus should benoted periodically as recommended in 25 andappropriate remedial measures should be takenwhere necessary. Care should be taken,however, to maintain the integrity of the type ofprotection provided for the apparatus; this mayrequire consultation with the originalmanufacturer. Replacement parts should be inaccordance with the conditions of certification.No alteration that might invalidate thecertificate or other document relating to thesafety of apparatus should be made to anyapparatus without appropriate approval.27.2 Maintenance of Flexible CablesFlexible cables, flexible conduits and theirterminations should be inspected at regularintervals and should be replaced if found to bedamaged or defective.27.3 Precautions Against CorrosionMetallic enclosures of apparatus should wherenecessary, be treated with an appropriateprotective coating as a precaution againstcorrosion, the frequency and nature of suchtreatment being determined by theenvironmental conditions.

NOTE — For special precautions concerning the use ofcertain protective materials (e.g. on the flange faces of Ex‘d’ flameproof apparatus) reference should be made toIS 2148 : 1981.

27.4 CleanlinessAll parts of installations should be kept cleanand free from accumulations of dust anddeleterious substances.27.5 Precautions Against Excessive Temperature RiseApparatus should be kept of free from dustdeposits of such a nature as could causeexcessive rise in temperature.When replacing lamps in luminaires the correctrating and type should be used for excessivetemperature rise may result.The etching, painting or screening of lighttransmitting parts may lead to excessivetemperatures.27.6 Withdrawal from ServiceShould it be necessary for maintenancepurposes to withdraw apparatus, etc, fromservice, the exposed conductors should beterminated in an appropriate certifiedenclosure; alternatively, the cable may beprotected adequately by insulating the ends ofthe conductors and isolating the cable from allsources of power supply. Should the apparatusbe permanently withdrawn from service,associated wiring should be removed or,alternatively, otherwise correctly terminated inan appropriate certified enclosure.27.7 Fastenings and ToolsWhere special bolts and other fastenings orspecial tools are required, these items should beavailable and should be used.

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Section 5 Properties of Flammable Liquids, Vapours and Gases

28 GENERAL28.1 Available data applicable only to the use ofelectrical apparatus in hazardous areas aregiven in Table 6 ( see Annex D ) for thoseflammable gases and vapours that have beenallocated to apparatus groups. The physicalproperties of these materials that have to beconsidered when the degree of risk appropriateto a particular application or installation isbeing assessed are defined and discussed in 29to 35 in the same order as that in which theyare given in Table 6 [ see also IS 5572(Part 1) : 1978 ].28.2 Properties of the materials given inTable 6 are generally for materials in the pureform and may be different if there areimpurities or where there are mixtures ofmaterials. In such cases expert advice shouldbe sought. For descriptions of the concepts oftemperature classification and apparatusgrouping, see 7.3 and 7.4.

29 MELTING POINT AND BOILING POINT29.1 The melting and boiling points have theirusual meanings, and the data listed in Table 6apply at standard atmospheric pressure.

30 RELATIVE VAPOUR DENSITY30.1 The relative vapour density of a materialis the mass of a given volume of the material inits gaseous or vapour form compared with themass of an equal volume of dry air at the sametemperature and pressure. It is often calculatedas the ratio of the relative molecular mass ofthe material to the average relative molecularmass of air (the value of the latter beingapproximately 29).

31 FLASH POINT31.1 GeneralThe flash point of a material is the minimumtemperature at which it gives off sufficientvapour to form a flammable mixture with airnear the surface of the material or within theapparatus used for flash point determination.31.1.1 Flash point data are normally associatedwith materials in the liquid phase. There are afew materials, however, that give off sufficientvapour in the solid phase to form flammablemixtures with air. For those materials andthose that sublimate (i.e. pass from solid tovapour without the normal intermediate liquidphase), flash point data will be associated withthe materials in their solid form.31.1.2 The test apparatus used for themeasurement of flash point is normally one oftwo types, of which there are several variants.These are called generally open cup and closedcup flash point testers. For most liquids theflash point determined by the closed cupmethod is slightly lower (in the region of 5% to10% when measured in °C) than thatdetermined by the open cup method. Flash

points measured by the more sensitive closedcup method are, therefore, normally used andare given in Table 6.31.2 Materials having High Flash PointsSome materials have such high flash pointsthat they do not form flammable mixtures withair at normal ambient temperatures, evenwhen exposed to the sun in tropical locations.These should not be discounted as ignitionhazards, however, since exposure to a suitablyhot surface or use of the material at a tem-perature above its flash point may create aflammable mixture locally, which may beignited by the same hot surface or analternative ignition source. It is thereforenecessary to consider the limitation of surfacetemperatures even when materials of highflash point are being processed.31.2.1 It should be noted also that materialshaving high flash points may be used inprocesses involving high temperatures andpossibly high pressures. The normal oraccidental release to the atmosphere ofcompounds under such conditions may presentlocal explosion risks that would not normally beassociated with high flash point materials.Materials having high flash points can formflammable mixtures with air at subatmosphericpressure.31.3 Classification of Flash PointsIn some industries, it has been foundconvenient to group materials into prescribedranges of flammability according to their flashpoints to facilitate safe handling. In certainapplications, legislation specifies the limits forthese ranges.

32 LIMITS OF FLAMMABILITY32.1 All combustible gases and vapours arecharacterized by flammable limits betweenwhich the gas or vapour mixed with air iscapable of sustaining the propagation of flame.

32.2 The limits are called the lower flammablelimit (LFL) and the upper or flammable limit(UFL) and are usually expressed aspercentages of the material mixed with air byvolume. They are also sometimes, expressed asmilligrams of material per litre of air. Whereappropriate, both sets of data are included inTable 6.

33 FLAMMABILITY RANGE

33.1 The range of gas or vapour mixtures withair between the flammable limits over whichthe gas/air mixture is continuously flammableis called the flammability range. Gas/airmixture outside this range are, therefore,non-flammable under normal atmosphericconditions. Concentrations above the UFL infree atmospheric conditions cannot becontrolled and further dilution with air willproduce mixtures within the flammabilityrange.

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34 EFFECT OF ENVIRONMENTS WITH OTHER THAN NORMAL ATMOSPHERIC CONDITIONS34.1 It should be noted that the data given inTable 6 apply only to mixtures of flammablegases and vapours with air under normalconditions of atmospheric temperature andpressure or at suitably elevated temperatures ifthe flash point of the vapour is above thenormal ambient temperature. Caution shouldbe exercised therefore in assessing theexplosivity of gas or vapour with air underenvironmental conditions that are other thannormal. It is possible here to give only generalguidance on the influence of changes intemperature, pressure and oxygen content ofthe mixture.34.2 Generally, the effect of increasedtemperature of pressure is to lower the LFLand to raise the UFL. Reduction in temperatureor pressure has the opposite effect.34.3 An increase in oxygen content of a gasmixture, compared with a mixture of theflammable gas or vapour with air only, haslittle or no effect on the LFL but generallyresults in an increase UFL. The increase in theupper limit depends on the degree of oxygenenrichment and may be substantial. Thus, theeffect generally of an increase in oxygencontent is to broaden the flammability range.

35 IGNITION TEMPERATURE35.1 The ignition temperature of a material isthe minimum temperature under prescribedtest conditions at which the material will igniteand sustain combustion when mixed with air atnormal pressure, without initiation of ignitionby spark or flame.35.2 The ignition temperature, formerly knownas the auto-ignition or spontaneous ignitiontemperature, should be clearly distinguishedfrom the flash point. In the latter case, ignitionis initiated by a small flame simply todetermine that a flammable mixture exists. Inthe former, ignition is a consequence ofchemical reactions initiated on account of thetemperature of the local environment and maytherefore in practice be a result of thetemperature of hot surfaces adjacent to theflammable atmosphere.35.3 The majority of ignition temperatureslisted in Table 6 have been determined with thetest apparatus and procedure described inIS 7820 : 1975 or with equivalent testapparatus. Where a determination by a methodother than that in IS 7820 : 1975 provides theonly data available, the classification may beregarded as provisional only and has been, forguidance, enclosed in parentheses in Table 6.35.4 The direct result of established ignitiontemperatures is to limit the surfacetemperatures of electrical apparatus inhazardous areas so that these do not present anignition risk. Formerly permitted surfacetemperatures were limited to a certainproportion of the measured ignitiontemperature (commonly 80%) to provide a

factor of safety. It is now generally accepted,however, that the sensitivity of the recognizedtest methods is such that the temperatures ofunprotected surfaces of electrical apparatusmay safely be allowed to rise to the ignitiontemperature of the gas or vapour that presentsthe explosion risk. Where more than oneflammable material may be present in aparticular application, the surface temperatureshould be limited to the lowest value of theignition temperatures of the combustiblesconcerned or the ignition temperature of theparticular mixture as determined by test.However where there is a possibility of catalyticinteraction between the components or wheremixtures of hydrogen, moisture orhydrocarbons with carbon monoxide occur, thesurface temperature may need to be less thanthe lowest ignition temperature of theindividual components.35.5 It should be noted that the value forignition temperature is dependent on themethod chosen for its measurement. Inparticular, factor such as the geometry,dimensions and materials of the test apparatusinfluence the measured ignition temperature.Care should be exercised, therefore, if theignition temperature data contained in thisstandard are applied to equipment other thanelectrical apparatus.

36 GENERAL CONSIDERATIONS36.1 Relation Between Ignition Temperature and Maximum Surface Temperature

The vapour given off from a flammable liquidwill form a flammable mixture with air,provided the temperature of the liquid is at orabove its flash point. The flammable mixturemay then be ignited by one of severa1 means: aflame, a suitable frictional spark, an electricalspark of sufficient energy or a hot surface. If, onthe other hand, the local ambient temperatureand that of the electrical apparatus, etc, arebelow the flashpoint, the vapour will eventuallycondense to a mist of liquid droplets and spreadas such both through the atmosphere and overthe surfaces of the apparatus. It is in the latterrespect that adequate resistance to chemicalattack may be particularly important.36.1.1 For ignition by a hot surface, the surfacetemperature has generally to be greater thanthe ignition temperature of the flammablematerial. Therefore, to ensure that ignition byhot surfaces does not occur, it is necessary thatthe temperature of all unprotected surfacesexposed to the gas or the vapour/air mixtureshould not be greater than the ignitiontemperature. This has led to the concept oftemperature classification described in 7.3.

NOTE — Surfaces that are catalytically active canignite vapours at temperatures lower than the normalignition temperature.

36.2 Mixtures of Materials

Single-component flammable materials are notoften encountered in practice. Most frequently,mixtures of two or more materials are present,in ratios that may vary between prescribed

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limits. Consideration has then to be given tothe characteristics required for electricalapparatus in the light of the properties of eachindividual component present. Often this willimpose no difficulty since, by the nature of theprocess, the various materials will possesssimilar chemical properties and, often, similarcombustion properties.36.2.1 There are occasions, however, when thisis not the case. The materials may be ofdifferent gas classifications or have widelydifferent ignition temperatures. In these cases,it is possible to give only the most general ofrules for guidance. In general it should beassumed that, at some time during the processor the life of the plant, the component in themixture having the most demanding of thecharacteristics being considered (e.g. the gasclassification, the flammable limits, the flashpoint or ignition temperature) will be presentas the largest proportion of the mixture, andthe electrical installation should be designedaccordingly.36.2.2 However, this can impose limitationsthat may be severe, and further considerationof the relative rates and quantities of thematerials used in the process and the degree ofcontrol thereof may be required. Somerelaxation may then be possible, but expertadvice should always be sought in thesecircumstances.36.2.3 Particular consideration should be givento those materials whose behaviour may beanomalous. It is known, for example, thatcarbon monoxide, with which Group IIAapparatus may be safely used, may be added inconsiderable quantity to hydrogen without

altering the group of apparatus, namely GroupIIC, that has to be used with this lattercompound. Carbon monoxide also exhibitsunusual behaviour under other test conditions.For example, it has been shown that theaddition of moisture to mixtures of carbonmonoxide with air to the point of saturationserves to change the gas classification for thismaterial from Group IIA to Group IIB. Thischange in gas classification is also observed ifmethane is added to carbon monoxide in theproportion 15 : 85 methane to carbon monoxide.36.2.4 When the individual components ofmixtures and their proportions of the totalmixture are precisely known or can besustained, it is often possible to calculate theresultant flammable limits for the mixture withair. Examples of this care described inAnnex E. However, if the mixture ispredominantly carbon monoxide, expert adviceshould be sought.36.3 MistsThe characteristics described in this standardapply to mixtures of gases and vapours onlywith air. The distinction to be drawn between agas and a vapour in this context is simply thatthe latter may be in contact with its liquidphase at normal temperature and pressure,whereas a gas cannot be liquefied under normalatmospheric conditions. In practice, mistsconsisting of clouds of condensed vapour canalso occur. In general, the characteristicsdescribed in this standard should be consideredapplicable to mists, since local ignition sourcesor hot surfaces generally may serve to restorethe condensed material to its vapour phase.

Section 6 Marking of Apparatus

37 GENERAL37.1 It has been agreed internationally, thatthe letters ‘Ex’ should be used to indicateexplosion protection and that this symbolshould be accompanied by a lower case better toindicate the type of protection used. The lettercode is described in 5.37.2 The marking requirements for the varioustypes of explosion protected apparatus shall bein accordance with IS 13346 : 1992.

38 MARKING REQUIREMENTS FOR APPARATUS38.1 The general marking requirementsdescribed in this clause are intended to aid theuser in identifying the type of protection and toassist identification of the particular explosionrisk for which the apparatus is suitable.38.2 The marking requirements include thefollowing :

a) Identification of the manufacturer. Themanufacturer may be identified by nameor trademark.

b) The manufacturer’s name or typedesignation for the apparatus.

c) The certifying authority mark and thecertificate number.

d) identification of the type of protection( see 39 ).

e) The apparatus sub-group, if applicable.The system of marking for indicatingapparatus sub-grouping is described in 39.

f) The T class or maximum surfacetemperature. This requirement isdescribed in 7.3.

g) Any other, relevant information, will nor-mally include voltage and current ratings,under prescribed conditions wherenecessary, and such other information asmay be necessary for the satisfactoryoperation of the apparatus.

38.3 The marking includes, therefore, not onlythe manufacturer’s name and rating data withwhich all electrical apparatus should normallybe marked, but also sufficient additionalinformation to indicate the suitability of theapparatus for use in particular flammableatmospheres. This is explained in 39 and 40.

IS 13408 (Part 1) : 1992

16

39 EXAMPLES OF MARKING OF APPARATUS39.1 GeneralThe following examples are included toillustrate the application and interpretation ofthe marking requirements. They do notrepresent all the variations of marking that arepossible, nor is it intended to include in theseexamples all the marking requirements thatare usually specified. More detailed markingrequirements that are relevant to particulartypes of protection are described in theappropriate standard and in the relevantapparatus standards.39.2 Flameproof Enclosure ‘d’The marking on apparatus with type ofprotection ‘d’ will normally include thefollowing:

a) The symbol for the type of protection ‘d’;b) The apparatus group and sub-group; andc) The temperature classification.

For example, EExd IIB T5 indicates that theenclosure complies with Group IIBrequirements and that the apparatus has atemperature classification of T5.39.3 Increased Safety Apparatus ‘e’The marking on apparatus with type ofprotection ‘e’ will normally include thefollowing to indicate compliance with therequirements of IS 6381 : 1972:

a) The symbol for the type of protection ‘e’;b) The apparatus group; andc) The temperature classification.

For example, EEx e II T3 indicates that theapparatus may be used safely with allflammable gases and vapours allocated toapparatus Group II, subject to a temperatureclassification of T3.39.4 Intrinsic Safety ‘i’39.4.1 Intrinsically Safe ApparatusIntrinsically safe apparatus can be category ‘ia’or ‘ib’ and may be suitable for connection toexternal circuits subject to certain possiblelimitations on their characteristics.The marking on apparatus with type ofprotection ‘i’ will normally include the followingto indicate compliance with the requirements ofIS 5780 : 1990:

a) The symbol for the type of protection ‘i’and the apparatus category;

b) The apparatus group and sub-group; andc) The temperature classification.

For example EEx ia IIC T5 indicates that theapparatus group is IIC and that the apparatushas a temperature classification of T5.

Additionally, there may be marking to indicatethe limiting characteristics of external circuits,e.g.Lext = 12 µH, Cext = 1 200 pF, Umax = 28 V.The second mark indicates the limiting valuesof inductance, capacitance and voltage of theexternal circuits which may be connected to theapparatus to maintain its safe use under theconditions indicated by the first mark.39.4.2 Associated Electrical ApparatusAssociated electrical apparatus installed in anon-hazardous area can be category ‘ia’ or ‘ib’.This limitation in its use is denoted on themarking by enclosing the applicable symbols insquare brackets.

The marking on such apparatus includes thefollowing:

a) The symbols of the type of protection ‘i’and the apparatus category; and

b) The apparatus group and sub-group.For example, (EEx ib) IIC indicates compliancewith IS 5780 : 1980. There is no requirement tomark an apparatus temperature classificationsince the apparatus is installed in anon-hazardous area.39.4.3 Intrinsically Safe Electrical System ‘i’Certified intrinsically safe electrical systems ‘i’which comply with all the requirements forIS 5780 : 1980 will be marked as described in40.4.1 and additionally will be marked in astrategic position with the letters SYST.For intrinsically safe electrical systems ‘i’complying with the requirements of IS 5780 :1980 which have not been certified, markingwhich permits positive identification of thesystem and reference for the relevant systemdescription will normally be applied.39.5 Type of Protection ‘n’The marking in accordance with IS 8289 : 1976on this apparatus will normally include thefollowing to indicate compliance with therequirements of that standard:

a) The symbol of the type of protection ‘n’and the apparatus category;

b) The apparatus group; andc) The temperature classification.

For example, Ex n II T3 indicates that theapparatus may be used safely in Zone 2 areaswith all flammable gases and vapours allocatedto apparatus Group II, subject to a temperatureclassification of T3.39.6 Other Types of ProtectionThe types of protection that have not beenincluded in the examples in 39.2 to 39.5 willnormally be marked in accordance with similarrules.

IS 13408 (Part 1) : 1992

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40 GENERAL NOTES ON MARKING

40.1 General

In 40.2 to 40.4 some of the finer details ofmarking requirements that have not beenindicated in the examples in 39.2 to 39.4 areexplained.

40.2 Certificate Number

The certificate number may refer to a singledesign or to a range of apparatus of similardesign. The same number may also be used formodifications to the original design.

Where the certificate number is followed by ‘X’,it indicates that special conditions for safe useapply, and therefore particular attentionshould be paid to certification documents beforeapparatus is selected.

The certificate number may also be followed by‘S’. This suffix indicates that the apparatus somarked is suitable for installation in a safearea only, but that it may form part of acertified system.

40.3 Ex component Approval

Component parts or sub-assemblies formingpart of certified apparatus may be the subject ofseparate component certificates. Thisprocedure is called ‘component approval’.Approval Ex components will generally bemarked in accordance with the rules describedin 37 to 39, with the addition of the letter ‘U’

after the approval number, but will notnormally carry the testing house certificationmark.

40.4 Multiple Types of Protection

40.4.1 Increasingly, electrical apparatus forhazardous areas may incorporate more thanone type of protection. The examples in 40.4.2and 40.4.3 serve to illustrate the markingrequirements that will normally be applied.

40.4.2 A flameproof apparatus such as a motormay incorporate an increased safety terminalbox. In this case, where each type of protectionis readily and separately identifiable, eachenclosure will normally be marked accordingly.

40.4.3 An apparatus with type of protection ‘e’(increased safety) overall may incorporatesparking contacts protected by a flameproofenclosure (type of protection ‘d’). In this case,the types of protection that are used internallycannot be identified by external examinationother than by inspection of the marking plate.The external marking will indicate the overallprotection, which will determine theinstallation requirements, and may indicatethe additional protective features in asecondary manner. For example, an increasedsafety apparatus with internal flameproofenclosure having a T3 temperatureclassification would normally be marked asfollows:

EEx e d IIC T3.

IS 13408 (Part 1) : 1992

18

ANNEX A( Clause 2 )

LIST OF REFERRED INDIAN STANDARDS

IS No. Title2148 : 1981 Flameproof enclosures for

electrical apparatus ( secondrevision )

2309 : 1969 Code of practice for theprotection of buildings andallied structures againstlighting ( first revision )

3043 : 1987 Code of practice for earthing5571 : 1979 Guide for selection of electrical

equipment for hazardous areas( first revision )

5572(Part 1) : 1978

Classification of hazardousareas (other than mines) forelectrical installations: Part 1Areas having flammable gasesand vapours ( first revision )

5780 : 1980 Specification for intrinsicallysafe electrical apparatus andcircuit ( first revision )

6381 : 1972 Constructions and testing ofelectrical apparatus with typeof protection ‘e’

IS No. Title7689 : 1989 Guide for control of undesirable

static electricity ( firstrevision )

7820 : 1975 Method of test for ignitiontemperatures

8062(Part 1) : 1976

Code of practice for cathodicprotection of steel structures :Part 1 General principle

8289 : 1976 Electrical equipment with typeof protection ‘n’

9570 : 1980 Classification of flammablegases or vapours with airaccording to their maximumexperimental safe gaps andminimum ignition current

9537(Part 2) : 1981

Conduits for electricalinstallations: Part 2 Rigid steelconduits

13346 : 1992 General requirements for theelectrical apparatus for use inexplosive atmospheres.

IS 13408 (Part 1) : 1992

19

ANNEX B( Clause 1.6, Note 2 )

RELEVANT INTERNATIONAL, EUROPEAN BRITISH STANDARDS ANDINDIAN STANDARDS AND DETAILS OF THE NATIONAL CERTIFYING

AUTHORITY AND ITS CERTIFICATION STANDARDS

B-1 EN50014 to EN50020 and EN50039 havebeen prepared by CENELEC TechnicalCommittee 31. These standards representtechnical texts accepted by 17 CENELECMember National Committees (including theUK), in the three official CENELEC languages,and which carry the strict obligation to be im-plemented as a national standard, unaltered inpresentation or content. This has been done bypublishing BS 5501: Parts 1 to 7 and Part 9,which are identical to EN 50 014 to EN 50 020and EN 50 039, respectively ( see B-3 ).

B-2 STANDARDS PRODUCED BY THE INTERNATIONAL ELECTROTECHNICAL COMMISSION (IEC)As part of a continuing process towardsinternational standardization, many countriesincluding the UK participate in theInternational Electrotechnical Commission(IEC). This organization produces recommen-dations which are intended to form the basis forthe national standards of each participatingcountry. As specifications for each type ofprotection and ancillary subjects are developed,these are published in a sequential series ofstandards each of which is a part of IECPublication 79 ( see also B-3 ). The followingparts of Publication 79 have already beenpublished:

The following IEC Standards cover relatedtopics:

B-3 RELEVANT INDIAN STANDARDS

Indian Standards relevant to the use ofelectrical apparatus in hazardous areas are asfollows:

79 Electrical apparatus for explosive gasatmospheres

79-0 Part 0 General requirements79-1 Part 1 Construction and test of

flameproof enclosures of electricalapparatus

79-1A First supplement Appendix D: Methodof test for ascertainment of maximumexperimental safe gap

79-2 Part 2 Pressurized enclosures79-3 Part 3 Spark test apparatus for

intrinsically-safe circuits79-4 Part 4 Method of test for ignition

temperature79-4A First supplement

79-5 Part 5 Sand-filled apparatus79-6 Part 6 Oil-immersed apparatus79-7 Part 7 Construction and test of

electrical apparatus, type of protection‘e’

79-8 Part 8 Classification of maximumsurface temperatures

79-9 Part 9 Marking79-10 Part 10 Classification of hazardous

areas

79-11 Part 11 Construction and test ofintrinsically-safe and associatedapparatus

79-12 Part 12 Classification of mixtures ofgases or vapours with air according totheir maximum experimental safe gapsand minimum igniting currents

79-13 Part 13 Construction and use of roomsor buildings protected by pressurization

IEC 34 Rotating electrical machinesPart 5 Classification of degrees ofprotection provided by enclosures forrotating machines

IEC 144 :1963

Degrees of protection of enclosure forlow-voltage switchgear and control-gear (= BS 5420 : 1977)

IEC 529 :1976

Classification of degrees of protec-tion provided by enclosures (= BS5490 : 1977)

IS 692 : 1973 Paper insulated lead-sheathedcables for electricity supply( second revision )

IS 694 : 1977 PVC insulated cables forworking voltages up to andincluding 1 100 volts ( secondrevision )

IS 1554(Part 2) : 1981

For working voltages from3.3 kV up to and including11 kV ( first revision )

IS 2147 : 1962 Degrees of protection providedby enclosures for low-voltageswitchgear and controlgear

IS 2148 : 1981 Flameproof enclosures ofelectrical apparatus ( secondrevision )

IS 2206(Part 1) : 1984

Flameproof electric lightingfittings: Part 1 Well glassedand bulk-hood type

IS 2667 : 1976 Fittings for rigid steel conduitsfor electrical wiring

IS 2772 : 1982 Non-flameproof miningtransformers for use belowground ( first revision )

IS 13408 (Part 1) : 1992

20

B-4 BIS CERTIFICATION MARKING SCHEME

B-4.1 The certification of electrical apparatusfor use in hazardous areas is being done by theBureau of Indian Standards, New Delhi (BIS)under well defined system of inspection, testingand quality control during preparation. Thissystem, which is devised and supervised by BISand operated by the producer, has the furthersafeguard that the apparatus carrying BIScertification mark are continuously checked byBIS for conformity to that Standard.

IS 4691 : 1985 Degrees of protection providedby enclosures for rotatingelectrical machinery ( firstrevision )

IS 5571 : 1979 Guide for selection of electricalequipment for hazardous areas( first revision )

IS 5572 : 1978 Classification of hazardousareas (other than mines) forelectrical installation : Part 1Areas having flammable gasesand vapours ( first revision )

IS 5780 : 1980 Intrinsically safe electricalapparatus and circuits ( firstrevision )

IS 6381 : 1972 Construction and testing ofelectrical apparatus with typeof protection ‘e’

IS 7389(Part 1) : 1976

Pressurized enclosures ofelectrical apparatus for use inexplosive atmospheres: Part 1Pressurized enclosures with nointernal source of flammablegas or vapour

IS 7689 : 1974 Guide for control of undesirablestatic electricity

IS 7693 : 1975 Oil immersed electricalapparatus for use in explosivegas atmospheres

IS 7724 : 1975 Sand-filled protection ofelectrical equipment for use inexplosive atmospheres

IS 7820 : 1975 Method of test for ignitiontemperatures

IS 8062(Part 1) : 1976

Code of practice for cathodicprotection of steel structures :Part 1 General principles

IS 8224 : 1976 Electric lighting fitting fordivision 2 areas

IS 8289 : 1976 Electrical equipment with typeof protection ‘n’

IS 9537(Part 1) : 1980

General requirements

IS 9537(Part 2) : 1981

Rigid steel conduits

IS 9628 : 1980 Three-phase induction motorswith type of protection ‘n’

IS 9968(Part 1) : 1981

For working voltages up to andincluding 1 100 volts

IS 12309 : 1989 Code of practice for theprotection of buildings andallied structures againstlightning ( second revision )

IS 13408 (Part 1) : 1992

21

ANNEX C( Clause 6.1 )

FRICTIONAL SPARKING RISKS WITH LIGHT METALS AND THEIR ALLOYS*

C-1 The risk of ignition due to frictionalsparking, which though present with ferrousand certain other metals is sufficientlyimprobable to be discounted, may besufficiently severe when certain light metalsand their alloys are involved that specialconsideration has to be given to their use,particularly in the more hazardous areas. It isgenerally recognized that the recommendationsin C-2 to C-7 should be noted.

C-2 It has been clearly established thatincendive frictional sparking can occur incircumstances where certain light metals ortheir alloys are brought into suitable contactwith other materials, particularly when theother material is an oxygen carrier such asrust. Suitable safeguards have therefore to betaken to prevent the occurrence of suchfrictional contact in circumstances where aflammable atmosphere may be present, as thesimultaneous occurrence of the two sets ofcircumstances, could lead to ignition.

C-3 As with other ignition risks, the firstsafeguard is to avoid the occurrence offlammable atmospheres and to site theapparatus whenever practicable in locationswhere such atmospheres are not likely to occur.

C-4 For rigidly mounted electrical apparatuswith light metal enclosures and aluminiumarmoured or sheathed cable sited in Zone 2areas, the frictional sparking risk may bedisregarded except in those particularcircumstances where heavy impact might alsoinitiate the release of flammable material. Thisapplies also in Zone 1 areas, unless the impactrisk is high, when the use of light metalenclosures or aluminium protected cablesshould be avoided unless they are providedwith a robust protective covering. Suchapparatus and cables should not be used onZone 0 areas.

C-5 Portable and transportable apparatus withlight metal or light alloy enclosures that areotherwise unprotected against frictionalcontact should not be taken into hazardousareas unless special precautions are taken toensure safety. Such precautions may include aspecial permit to work in the assured absenceof a flammable atmosphere, though moresatisfactory safeguards may be taken by, forexample, coating the apparatus with a suitableabrasion resistant material. When suchcoatings are used they should be subject toregular and careful inspection. The continueduse of the apparatus should not be permitted ifinspection reveals that the protective materialhas become damaged to the extent that theunderlying protected metal is visible, until suchdamage has been satisfactorily repaired.

These precautions should be adopted even forapparatus intended for use in Zone 2 areasonly, since it may be difficult in practice toprevent the transfer of’ unprotected portableapparatus to an area of greater risk.

C-6 Provided that the protective cowls for lightmetal fans on motors are designed so that theyare not readily deformed, such fans may beused in Zone 1 and Zone 2 areas since othermodes of failure (e.g. bearing failure) are morelikely to create a source of ignition. If plasticfans or cowls are used as alternatives, theyshould be of anti-static material.

C-7 Until further information is available, theuse of alumimum conductors in flameproofenclosures should be avoided in those caseswhere a fault leading to potentially severearcing involving the conductors may occur inthe vicinity of a plain flanged joint. Adequateprotection may be afforded by suitableconductor and terminal insulation to preventthe occurrence of faults or by using enclosureswith spigot or threaded joints.

*The term ‘light metal’ refers to such materials as aluminium, magnesium and titanium which are characterized bytheir ability when finely divided to react exothermically with atmospheric oxygen and, as a result, to ignite a flammableatmosphere. The term ‘light alloy’ refers to an alloy containing at least 50% of a light metal by atomic proportions.

IS 13408 (Part 1) : 1992

22

ANNEX D( Clause 7.4.3 )

DATA FOR FLAMMABLE MATERIALS

D-1 INTRODUCTIOND-1.1 The data for Table 6 has been obtainedfrom a number of references which appear inthe bibliography ( see D-8 ). Some minorvariations in the data appear when referencesare compared but usually the discrepancy issufficiently small to be ignored. The valuescontained in Table 6 are indicative only. Forexample, naptha and kerosine are generalterms not precisely defining the composition ofthe substance concerned. In addition,impurities can affect various properties. It isrecommended therefore that further checks bemade on the properties of the particularmaterial involved in the application concerned.The notes in D-2 to D-9 relate to thedescription of the data in Table 6.

D-2 CHEMICAL STRUCTURED-2.1 The work ‘mixture’ in col 2 of Table 6indicates the material is a mixture of materials.

D-3 FLASH POINTSD-3.1 The value given is the closed cupmeasurement. When this data is not availablethe open cup value is given. Open cup valuesare enclosed in brackets. The symbol < (lessthan) indicates that the flash point is below thevalue stated, this value probably being thelimit of the apparatus used.

D-4 FLAMMABLE LIMITSD-4.1 Where flammability data is presentedmaterials with flash points above 40°C, thedeterminations have been made at an elevatedtemperature sufficient to give the quotedconcentration.

D-5 IGNITION TEMPERATURE AND T CLASSD-5.1 The preferred data is that recorded inIEC Publication79-4A (Indian Standard yet tobe prepared). In the absence of such data, thevalues given are the lowest reported from classapparatus tests. When the lowest reported is inother unspecified apparatus, the value isenclosed in brackets. Knowledge of the ignitiontemperature allows the choice of the apparatusT class suitable for the flammable material tobe made. The T class is given in brackets whenthe lowest reported ignition temperature wasdetermined in unspecified apparatus orapparatus other than glass apparatus.

D-6 GROUP AND SUB-GROUP FOR APPARATUS WITH FLAMEPROOF ENCLOSURED-6.1 The groups are the result of maximumexperimental safe gap (MESG) determinations,except for values in brackets. These values areestimates based on chemical similarity. Thereis no lower limit to Group IIC and, therefore,

each compound in Group IIC should beconsidered individually.

D-7 NOTES ON SOME INDIVIDUAL MATERIALS

D-8 BIBLIOGRAPHY

Further data on the properties of flammablematerials may be found in the followingreferences, some of which were used in thecompilation of the tables.

Fire Protection Associated (London). Fire andrelated properties of industrial chemicals,reprinted 1974.

National Fire Protection Association (Boston,Mass). Fire protection guide on hazardousmaterials, seventh edition, 1978.

Hilado, C.J. and Clark, S.W. Auto-ignitiontemperatures of organic chemicals. ChemicalEngineering, September 4 1972, 75.

Acetylene Type ‘d’ apparatus for use withacetylene is grouped IIC, butadditional requirements forsuch apparatus for use with thisgas are specified in BS5501 : Part 5. (correspondingIndian Standard does notinclude recommendations forapparatus for acetylene gas).

Carbondisulphide

Group IIC apparatus shouldonly be used with carbondisulphide when the freevolume of the enclosure is lessthan 100 ml. For large volumes,the apparatus should besubjected to special test.

Coke oven gas This is a mixture of hydrogen,carbon monoxide, and methane.If the sum of the concentrationsof hydrogen and carbonmonoxide is less than 75%,Group IIB flameproof apparatusis required, otherwise GroupIIC. For all concentrations,intrinsically safe apparatusshould be Group IIC.

Ethyl nitrate It is recommended thatapparatus of type of protection‘d’ is not used in the presence ofethyl nitrate.

Methane Industrial methane includesmethane mixed with not morethan 15% by volume ofhydrogen.

Xylene The ignition temperature ofo-xylene is 464°C, and ofp-xylene is 528°C.

IS 13408 (Part 1) : 1992

23

Publications of the Engineering Sciences DataUnit (UK) (A list of properties is inpreparation).

Whessoe Technical Computing Services,CHEMSTOR, Chemical and Hazard EnquiryService.

Mullins, B.P. Spontaneous ignition of liquidfuels, AGARD 1955.

Lunn, G.A. and Phillips, H.A. Summary ofexperimental data on the maximumexperimental safe gap, SMRE Report T2, 1973.

Nabert, K. and Schon, G. Safety characteristicsof combustible gases and vapours, DeutschesEichverlag, 1963 ( revised 1980 ).

Toxic and Hazardous Industrial ChemicalsSafety Manual, 1975/76 (Japan).

Coward, H.F. and Jones, G.W. Limits offlammability of gases and vapors. US Bureau ofMines Bulletin 503, 1952.

Zabetakis, M.G. Flammability characteristicsof combustible gases and vapors. US Bureau ofMines Bulletin 627, 1965.

IS 13408 (P

art 1) : 1992

24

Table 6 Data for Flammable Materials for Use with Electrical Equipment( Clauses 7.4.3, 28.1, 28.2, 29.1, 31.2, 32.2, 34.1, 35.3, Annex D-1.1 and D-2.1 )

Name Formula

Mel

tin

g P

oin

t

Bo

ilin

g P

oin

t

Rel

ati

ve

Va

po

ur

Den

sity

Fla

sh P

oin

t

Ign

itio

nT

emp

era

ture

Min

imu

m I

gn

itin

gC

urr

ent

T C

lass

of

Su

ita

ble

Ap

pa

ratu

s

Ap

pa

ratu

s G

rou

p

Flammable Limits

v/v m/v

LFL UFL LFL UFL

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14)

C °C °C °C % % mg/l mg/l °C mA

Acetaldehyde

Acetic acid

Acetic anhydride

Acetone

Acetonitrile

Acetyl chloride

Acetylene ( see D-7 )

Acrylonitrile

Allyl alcohol

Allyl chloride

Allylene

Ammonia

Amphetamine

Aniline

Benzaldehyde

Benzene

Blue water gas

l-bromobutane

Bromoethane

Buta-1, 3-diene(Butadiene)

CH3CHO

CH3COOH

(CH3 CO)2O

(CH3)2CO

CH3CN

CH3COCL

CH=CH

CH2=CHCN

CH2=CHCH2OH

CH2=CHCH2CL

CH3C=CH

NH3

C6H5CH2CH(NH2)CH3

C6H5NH2

C6H5CHO

C6H6

Mixture

CH3(CH2)2CH2 Br

C2H5 Br

CH2=CHCH=CH2

–123

17

–73

–95

–45

–112

–81

–82

—

–135

–103

–78

—

–6

–26

–6

—

–112

–119

–109

20

118

140

56

82

51

–84*

77

—

45

–23

–33

200

184

179

80

—

102

38

–4

1.52

2.07

3.52

2.0

1.42

2.7

0.9

1.83

—

2.64

1.38

0.59

4.67

3.22

3.66

2.7

—

4.72

3.75

1.87

–38

40

54

–19

5

4

—

–5

21

–20

—

—

<100

75

65

–11

—

<21

<–20

—

4

5.4

2.7

2.15

—

5.0

1.5

3

—

3.2

1.7

15

—

1.2

1.4

1.2

—

2.5

6.7

2.1

57

16

10

13

4.4

—

100

17

—

11.2

—

28

—

8.3

—

8

—

—

11.3

12.5

73

100

—

60

16

—

—

65

—

105

28

105

—

—

60

39

—

230

300

25

1 040

430

—

310

—

—

—

380

—

360

—

200

—

—

—

270

—

—

510

290

140

485

(334)

535

523

390

305

480

—

485

—

630

—

617

190

560

—

265

510

430

—

—

—

—

—

—

24

—

—

—

—

—

—

—

—

—

—

—

—

65

T4

T1

(T2)

(T1)

T1

T2

T2

T1

—

T1

—

T1

—

T1

T4

T1

T1

T3

T1

T2

IIA

IIA

IIA

IIA

IIA

(IIA)

IIC

IIA

IIA

IIA

(IIB)

IIA

(IIA)

(IIA)

(IIA)

IIA

(IIC)

(IIA)

(IIA)

IIA

*Sublimation temperature.

IS 13408 (P

art 1) : 1992

25

Table 6 ( Continued )

Name Formula

Mel

tin

g P

oin

t

Bo

ilin

g P

oin

t

Rel

ati

ve

Va

po

ur

Den

sity

Fla

sh P

oin

t

Ign

itio

nT

emp

era

ture

Min

imu

m I

gn

itin

gC

urr

ent

T C

lass

of

Su

ita

ble

Ap

pa

ratu

s

Ap

pa

ratu

s G

rou

p

Flammable Limits

v/v m/v

LFL UFL LFL UFL

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14)

C °C °C °C % % mg/l mg/l °C mA

Butane

Butanone(Ethyl methyl ketone)

Butan-1-ol(l-butanol)

Butyl acetate

Butyl glycolate(butyl hydroxyacetate)

Butyle styrene

Butylamine

Butyldigol

Butyraldehyde

But-l-ene(l-butene)

But-2-ene(2-butene)

Carbon disulphide ( see D-7 )

Carbon monoxide ( see D-7 )

Chlorobenzene

l-chlorobutane

Chloroethane

C4H10

C2H5COCH3

CH3(CH2)2CH2OH

CH3COOCH2(CH2)2CH3

HOCH2COOC4H9

C6H5C(CH2)3 = CH2

C4H9NH2

CH3 (CH2)3OCH2CH2OCH2CH2OH

CH3CH2CH2CHO

CH2 = CHCH2CH3

CH3CH = CHCH3

CS2

CO

C6H5Cl

CH3 (CH2)2CH2Cl

C2H5Cl

–138

–86

–89

–77

—

—

–104

88

–97

–185

—

–112

–205

45

–123

–136

–1

80

118

127

356

—

63

231

75

–6

4

46

–191

132

78

12

2.05

2.48

2.55

4.01

4.45

—

2.52

5.59

2.48

1.95

1.94

2.64

0.97

3.88

3.2

2.22

–60

–1

29

22

61

—

<–9

78

<–5

—

—

–20

—

28

<0

—

1.5

1.8

1.7

1.4

—

—

—

—

1.4

1.6

1.7

1.0

12.5

1.3

1.8

3.6

8.5

11.5

9.0

8

—

—

—

—

12.5

10

9

60

74.2

7.1

10

15.4

37

50

43

58

—

—

—

—

42

35

—

30

145

60

65

95

210

350

350

360

—

—

—

—

380

235

—

1 900

870

520

390

400

365

505

340

370

—

—

(312)

225

230

385

(325)

102

605

637

(460)

510

80

—

—

—

—

—

—

—

—

—

—

—

90

—

—

—

T2

T1

T2

T2

—

—

T2

T3

T3

T2

(T2)

T5

T1

T1

(T1)

T1

IIA

IIA

IIA

IIA

(IIB)

IIB

IIA

IIA

IIA

IIA

IIB

IIC

IIB

(IIA)

IIA

(IIA)

IS 13408 (P

art 1) : 1992

26

Table 6 ( Continued )

Name Formula

Mel

tin

g P

oin

t

Bo

ilin

g P

oin

t

Re

lati

ve

Va

po

ur

Den

sity

Fla

sh P

oin

t

Ign

itio

nT

em

per

atu

re

Min

imu

m I

gn

itin

gC

urr

ent

T C

lass

of

Su

ita

ble

Ap

pa

ratu

s

Ap

pa

ratu

s G

rou

p

Flammable Limits

v/v m/v

LFL UFL LFL UFL

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14)

C °C °C °C % % mg/l mg/l °C mA

2-chloroethanol(Chloroethanol)

Chloroethylene(Vinyl chloride)

Chloromethane

Chloromethylmethylether(Chlorodimethyl ether)

1-chloropropane(N-Chloropropane)

2-chloropropane(iso-chloropropane)

α-Chlorotoluene(Benzyl chloride)

1-chloro-2, 3-epoxypropane (Epichlorhydrin)

Coal tar naphtha

Coke oven gas ( see D-7 )

Cresol

Crotonaldehyde

Cumene

Cyclobutane

Cycloheptane

CH2ClCH2OH

CH2=CHCl

CH3Cl

CH3OCH2Cl

C3H7Cl

(CH3)2CHCL

C6H5CH2Cl

OCH2CHCH2CL

Mixture

Mixture

CH3C6H4OH

CH3CH=CHCHO

C6H5CH(CH3)2

–70

–154

–98

–103

–123

—

–39

–57

—

—

11

–75

–97

–91

—

129

–14

–24

60

37

47

179

116

—

—

191

102

152

13

119

2.78

2.15

1.78

—

2.7

2.7

4.36

3.30

—

—

3.73

2.41

4.13

1.93

3.39

55

—

—

—

–18

–32

60

(40)

—

—

81

13

36

—

<–21

5.0

3.8

10.7

—

2.8

2.6

1.2

—

—

—

1.1

2.1

0.88

1.8

—

16

29.3

13.4

—

10.7

11.1

—

—

—

—

—

15.5

6.5

—

—

160

95

150

—

70

—

55

—

—

—

45

—

—

42

—

540

770

400

—

300

—

—

—

—

—

—

—

—

—

—

425

470

625

—

(592)

520

585

—

272

—

555

(230)

420

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

T2

T1

T1

—

(T1)

T1

T1

—

T3

—

T1

(T3)

T2

—

—

(IIA)

IIA

IIA

(IIA)

(IIA)

IIA

(IIA)

IIA

(IIA)

(IIA)

IIB

(IIA)

(IIA)

(IIA)

IS 13408 (P

art 1) : 1992

27

Table 6 ( Continued )

Name Formula

Mel

tin

g P

oin

t

Bo

ilin

g P

oin

t

Re

lati

ve

Va

po

ur

Den

sity

Fla

sh P

oin

t

Ign

itio

nT

em

per

atu

re

Min

imu

m I

gn

itin

gC

urr

ent

T C

lass

of

Su

ita

ble

Ap

pa

ratu

s

Ap

pa

ratu

s G

rou

p

Flammable Limits

v/v m/v

LFL UFL LFL UFL

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14)

C °C °C °C % % mg/l mg/l °C mA

Cyclohexane

Cyclohexanol

Cyclohexanone

Cyclohexene

Cyclohexylamine

Cyclopentane

Cyclopropane

Decahydronaphthalene

Decane

Dibutyl ether

Dichlorobenzene

1, 1-dichloroethane

1, 2-dichloroethane(ethylene dichloride)

1, 1-dichloroethylene(Vinylidene chloride)

1, 2-dichloroethylene

1, 2-dichloropropane

Diethyl ether

Diethyl ketone

C10H22(Approx)

(C4H9)2O

C6H4Cl2

CH3CHCl2

CH2ClCH2Cl

CH2=CCl2

ClCH=CHCl

CH3CHCLCH2CL

(C2H5)2O

C2H5COC2H5

7

24

–31

–104

–118

–93

–127

–43

–30

–95

–18

–98

–36

—

–122

80

–116

—

81

161

156

83

134

47

–33

196

173

141

179

57

84

37

33

96

34

—

2.9

3.45

3.38

2.83

3.42

—

1.45

4.76

4.9

4.48

5.07

3.42

3.42

3.4

3.55

3.9

2.55

—

–18

68

43

<–20

32

–37

—

54

96

25

66

–10

(5)

–18

–10

15

<–20

(55)

1.2

1.2

1.4

1.2

—

—

2.4

0.7

0.8

1.5

2.2

5.6

6.2

7.3

9.7

3.4

1.7

—

7.8

—

9.4

—

—

—

10.4

4.9

5.4

7.6

9.2

16

15.9

16

12.8

14.5

36

—

40

—

53

—

—

—

40

40

—

48

130

225

—

—

220

160

50

—

290

—

380

—

—

—

185

280

—

460

750

660

—

—

650

690

1 100

—

259

300

419

(310)

290

(380)

495

260

205

185

(640)

440

(413)

(570)

(440)

555

170

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

75

—

T3

T2

T2

(T2)

T3

(T2)

T1

T3

T3

T4

(T1)

T2

(T2)

(T1)

(T2)

T1

T4

—

IIA

(IIA)

IIA

(IIA)

(IIA)

IIA

IIA

(IIA)

IIA

IIB

(IIA)

(IIA)

IIA

IIA

(IIA)

(IIA)

IIB

IIA

IS 13408 (P

art 1) : 1992

28

Table 6 ( Continued )

Name Formula

Mel

tin

g P

oin

t

Bo

ilin

g P

oin

t

Re

lati

ve

Va

po

ur

Den

sity

Fla

sh P

oin

t

Ign

itio

nT

em

per

atu

re

Min

imu

m I

gn

itin

gC

urr

ent

T C

lass

of

Su

ita

ble

Ap

pa

ratu

s

Ap

pa

ratu

s G

rou

p

Flammable Limits

v/v m/v

LFL UFL LFL UFL

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14)

C °C °C °C % % mg/l mg/l °C mA

Diethyl oxalate

Diethyl sulphate

Diethylamine

2-diethylaminoethanol

Diethyldichlorosilane

Dihexyl ether

Di-isobutylene

Di-isopropyl ether

Dimethyl ether

Dimethylamine

Dimethylaniline

Dimethylformamide(Formdimethylamide)

1, 4-dioxane

1, 3-dioxolane

Dipentyl ether(di-n-amylether)(Diamethyl ether)

Dipropyl ether

Ditertiary butyl peroxide

1, 2-epoxypropane(Propylene oxide)

(COOC2H5)2

(C2H5)2SO4

(C2H5)2NH

(C2H5)2NC2H4OH

(C2H5)2SiCl2

(CH3(CH2)5)2O

C2H5CH(CH3)CH(CH3)C2H5

((CH3)2CH)2O

(CH3)2O

(CH3)2NH

C6H3(CH3)2NH2

HCON(CH3)2

(C5H11)2O

(C3H7)2O

(CH3)3COOC(CH3)3

–41

–25

–50

—

—

–43

–106

–86

–141

–92

2

–61

10

–26

–69

–122

—

—

180

208

56

161

—

227

105

69

–25

7

194

152

101

74

170

90

—

—

5.04

5.31

2.53

4.04

—

6.43

3.87

3.52

1.59

1.55

4.17

2.51

3.03

2.55

5.45

3.53

—

—

76

104

<–20

(60)

—

75

(2)

–28

—

—

63

58

11

(2)

(57)

<21

18

–37

—

—

1.7

—

—

—

—

1.4

3.7

2.8

1.2

2.2

1.9

—

—

—

—

—

—

—

10.1

—

—

—

—

21

27.0

14.4

7.0

15.2

22.5

—

—

—

—

—

—

—

50

—

—

—

—

—

38

52

60

—

70

—

—

—

—

—

—

—

305

—

—

—

—

—

520

270

350

—

820

—

—

—

—

—

—

—

310

—

—

185

(305)

(416)

—

(400)

370

(440)

379

—

170

170

170

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

(T2)

—

—

T4

(T2)

(T2)

—

(T2)

T2

(T2)

T2

—

T4

T4

T4

—

IIA

IIA

(IIA)

(IIA)

IIC

(IIA)

(IIA)

IIA

IIB

IIA

(IIA)

IIA

IIB

(IIB)

(IIA)

(IIB)

IIB

IIB

IS 13408 (P

art 1) : 1992

29

Table 6 ( Continued )

Name Formula

Mel

tin

g P

oin

t

Bo

ilin

g P

oin

t

Re

lati

ve

Va

po

ur

Den

sity

Fla

sh P

oin

t

Ign

itio

nT

em

per

atu

re

Min

imu

m I

gn

itin

gC

urr

ent

T C

lass

of

Su

ita

ble

Ap

pa

ratu

s

Ap

pa

ratu

s G

rou

p

Flammable Limits

v/v m/v

LFL UFL LFL UFL

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14)

C °C °C °C % % mg/l mg/l °C mA

Ethane

Ethanethiol(Ethyl mercaptan)

Ethanol

Ethanolamine

2-ethoxyethanol

Ethoxyethyl acetate

Ethyl acetate

Ethyl acetoacetate

Ethyl acetylene

Ethyl acrylate

Ethyl benzene

Ethyl cyclobutane

Ethyl cyclohexane

Ethyl cyclopentane

Ethyl formate

Ethyl methacrylate

Ethyl methyl ether

Ethyl nitrate ( see D.7 )

Ethyldigol

CH3CH3

C2H5SH

C2H5OH

NH2CH2CH2OH

C2H5OCH2CH2OH

CH3COOCH2CH2OC2H5

CH3COOCH2CH3

CH3COCH2COOC2H5

C2H5C=CH

CH2 =CHCOOC2H5

C2H5C6H5

HCOOCH2CH3

CH2=CCH3COOC2H5

CH3OC2H5

CH3CH2ONO2

CH3CH2OCH2CH2OCH2CH2OH

–183

–148

–144

10

—

—

83

—

—

<–75

–95

—

—

—

–80

—

—

–112

—

–87

35

78

172

135

156

77

180

—

100

135

—

131

103

54

240

8

89

202

1.04

2.11

1.59

2.1

3.1

4.6

3.04

—

—

3.45

3.66

2.0

3.87

3.4

2.55

3.9

2.087

3.14

4.62

—

–20

12

85

95

47

–4

(84)

—

9

15

<–16

14

1

<–20

(20)

—

10

94

3.0

2.8

3.3

—

1.8

—

2.1

—

—

1.8

1.0

1.2

0.9

1.1

2.7

—

2.0

4.0

—

15.5

18

19

—

15.7

—

11.5

—

—

—

6.7

7.7

6.6

6.7

16.5

—

10.1

—

—

37

70

67

—

—

—

75

—

—

74

44

—

—

—

80

—

49

—

—

195

460

290

—

—

—

420

—

—

—

—

—

—

—

500

—

255

—

—

515

295

425

—

235

380

460

295

—

—

431

210

262

260

440

—

190

—

—

70

—

75

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

T1

T3

T2

—

T3

T2

T1

T3

—

—

T2

T3

T3

T3

T2

—

T4

—

—

IIA

IIA

IIA

(IIA)

IIB

IIA

IIA

IIB

IIB

IIB

(IIA)

(IIA)

(IIA)

IIA

(IIA)

IIA

(IIB)

—

IIA

IS 13408 (P

art 1) : 1992

30

Table 6 ( Continued )

Name Formula

Mel

tin

g P

oin

t

Bo

ilin

g P

oin

t

Re

lati

ve

Va

po

ur

Den

sity

Fla

sh P

oin

t

Ign

itio

nT

em

per

atu

re

Min

imu

m I

gn

itin

gC

urr

ent

T C

lass

of

Su

ita

ble

Ap

pa

ratu

s

Ap

pa

ratu

s G

rou

p

Flammable Limits

v/v m/v

LFL UFL LFL UFL

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14)

C °C °C °C % % mg/l mg/l °C mA

Ethylene

Ethylene diamine(Diaminoethane)

Ethylene oxide

Formaldehyde

Formic acid

2-furaldehyde(Furfuraldehyde)

Furan

Heptane

Heptan-1-ol(1-Heptanol)

Heptan-2-one(Amyl methyl ketone)

Hept-2-one(2-Heptene)

Hexane

Hexan-2-one(Butyl methyl ketone)

Hydrogen cyanide

Hydrogen sulphide

Hydrogen ( see D.7 )

CH2=CH2

NH2CH2CH2NH2

HCHO

HCOOH

C7H16

C7H15OH

CH3CO(CH2)4CH3

CH3(CH2)3CH=CHCH3

CH3(CH2)4CH3

CH3CO(CH2)3CH3

HCN

H2S

H2

–169

8

–112

–117

—

—

—

–91

–34

–35

—

–95

–56

—

–86

–259

–104

116

11

–19

101

161

—

98

176

151

—

69

28

26

–60

–253

0.97

2.07

1.52

1.03

1.6

3.3

—

3.46

4.03

3.94

—

2.97

3.46

0.90

1.19

0.07

—

34

—

—

68

60

60

–4

60

(49)

<0

–21

23

–18

—

—

2.7

—

3.7

7

—

2.1

—

1.1

—

—

—

1.2

1.2

5.6

4.3

4.0

34

—

100

73

—

19.3

—

6.7

—

—

—

7.4

8

40

45.5

75.6

31

—

55

87

—

—

—

46

—

—

—

42

50

—

60

3.3

390

—

1 820

10

—

—

—

280

—

—

—

265

330

—

650

64

425

385

440

424

(520)

315

—

215

—

—

—

233

(530)

(538)

270

560

45

—

40

—

—

—

—

75

—

—

—

75

—

—

—

21

T2

T2

T2

T2

(T1)

T2

—

T3

—

—

—

T3

(T1)

(T1)

T3

T1

IIB

IIA

IIB

IIB

IIA

IIA

IIA

IIA

IIA

(IIA)

IIA

IIA

(IIA)

IIB

(IIB)

IIC

IS 13408 (P

art 1) : 1992

31

Table 6 ( Continued )

Name Formula

Mel

tin

g P

oin

t

Bo

ilin

g P

oin

t

Rel

ati

ve

Va

po

ur

Den

sity

Fla

sh P

oin

t

Ign

itio

nT

emp

era

ture

Min

imu

m I

gn

itin

gC

urr

ent

T C

lass

of

Su

ita

ble

Ap

pa

ratu

s

Ap

pa

ratu

s G

rou

p

Flammable Limits

v/v m/v

LFL UFL LFL UFL

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14)

C °C °C °C % % mg/l mg/l °C mA

4-hydroxy-4-methylpenthan-2-one(Diacetyl alcohol)

Isopentane

Isopropyl nitrate

ISO-octane

Kerosine

(RS)-p-mentha-1, 8-diene(Dipentene)

Metaldehyde

Methane (firedamp)

Methane (industrial)( see D-7 )

Methanol

2-methoxyethanol

Methyl acetate

Methyl acetoacetate

Methyl acetylene

Methyl acrylate

Methyl cyclobutane

Methyl cyclohexane

CH3COCH2C(CH3)2OH

(CH3)2CHCH2CH3

(CH3)2CHONO2

(CH3)2CHCH2C(CH3)3

Mixture

C10H16

(C2H4O)4

CH4

CH4

CH3OH

CH3OCH2CH2OH

CH3COOCH3

CH3CO2CH2COCH3

CH3C=CH

CH2=CHCOOCH3

–47

—

—

—

—

–75

246*

–182

—

–98

–86

–99

—

—

<–75

—

–127

166

—

105

—

150

175

112+

–161

—

65

124

57

170

–23

80

—

101

4.0

—

—

—

—

4.66

6.07

0.55

—

1.11

2.63

2.56

4.0

1.4

3.0

—

3.38

58

<–51

20

–21

38

42

36

—

—

11

39

–10

67

—

–3

—

–4

1.8

—

2

—

0.7

0.7

—

5

—

6.7

2.5

3.1

—

1.7

2.8

—

1.15

6.9

—

100

—

5

6.1

—

15

—

36

14

16

—

—

25

—

6.7

—

—

—

—

—

—

—

—

—

73

80

95

—

—

100

—

45

—

—

—

—

—

—

—

—

—

350

630

500

—

—

895

—

—

680

—

175

411

210

237

—

595

—

455

285

475

280

—

—

—

260

—

—

—

—

—

—

—

85

—

70

—

—

—

—

—

—

—

T1

—

T4

T2

T3

—

—

T1

T1

T1

T3

T1

T3

—

—

—

T3

(IIA)

IIA

(IIB)

IIA

(IIA)

IIA

(IIA)

I

IIA

IIA

IIB

IIA

(IIA)

IIB

IIB

(IIA)

(IIA)

*In an enclosed vessel.†Sublimation temperature.

IS 13408 (P

art 1) : 1992

32

Table 6 ( Continued )

Name Formula

Mel

tin

g P

oin

t

Bo

ilin

g P

oin

t

Re

lati

ve

Va

po

ur

Den

sity

Fla

sh P

oin

t

Ign

itio

nT

em

per

atu

re

Min

imu

m I

gn

itin

gC

urr

ent

T C

lass

of

Su

ita

ble

Ap

pa

ratu

s

Ap

pa

ratu

s G

rou

p

Flammable Limits

v/v m/v

LFL UFL LFL UFL

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14)

C °C °C °C % % mg/l mg/l °C mA

Methyl cyclohexanol

Methyl cyclopentane

Methyl formate

Methyl methancrylate

2-methyl propan-l-ol[Butanol (ISO)]

Methyl styrene

Methylamine

4-methylpentan-2-one(Iso-butyl methyl ketone)

Morpholine

Naphtha

Naphthalene

Nitrobenzene

Nitroethane

Nitromethane

1-nitropropane

Nonane

Nonanol

n-Hexanol

Octaldehyde

C7H13OH (isomer not stated)

HCOOCH3

CH2=CCH3COOCH3

(CH3)2CHCH2OH

C9H10 (isomer not stated)

CH3NH2

(CH3)2CHCH2COCH3

Mixture

C10H8

C6H5NO2

C2H5NO2

CH3NO2

C3H7NO2

C9H20

C9H19OH

C6H13OH

C7H15CHO

–38

—

–100

—

–108

—

–92

–80

–3

—

80

6

–90

–29

–108

–54

—

–45

—

168

72

32

—

107

172

–6

116

128

35

218

211

115

101

131

151

178

157

163

3.95

2.9

2.07

—

2.55

4.1

1.07

3.45

3.0

2.5

4.42

4.25

2.58

2.11

3.06

4.43

4.97

3.5

4.42

68

—

<–20

(10)

—

57

—

16

(40)

–6

77

88

27

36

49

30

75

63

52

—

—

5

—

1.7

0.7

5

1.4

—

0.9

0.9

1.8

—

—

—

0.8

0.8

1.2

—

—

—

23

—

10.9

—

20.7

7.5

—

6

5.9

—

—

—

—

5.6

6.1

—

—

—

—

120

—

—

—

60

—

—

—

45

90

—

—

—

37

—

—

—

—

—

570

—

—

—

270

—

—

—

320

—

—

—

—

300

—

—

—

295

—

450

—

408

(495)

430

(459)

(310)

290

528

480

410

415

420

205

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

T3

—

T1

—

(T2)

(T1)

T2

(T1)

(T2)

T3

T1

T1

T2

T2

T2

T3

—

—

—

(IIA)

(IIA)

IIA

IIA

IIA

(IIA)

IIA

IIA

IIA

(IIA)

(IIA)

IIA

IIB

IIA

IIB

(IIA)

(IIA)

IIA

(IIA)

IS 13408 (P

art 1) : 1992

33

Table 6 ( Continued )

Name Formula

Mel

tin

g P

oin

t

Bo

ilin

g P

oin

t

Re

lati

ve

Va

po

ur

Den

sity

Fla

sh P

oin

t

Ign

itio

nT

em

per

atu

re

Min

imu

m I

gn

itin

gC

urr

ent

T C

lass

of

Su

ita

ble

Ap

pa

ratu

s

Ap

pa

ratu

s G

rou

p

Flammable Limits

v/v m/v

LFL UFL LFL UFL

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14)

C °C °C °C % % mg/l mg/l °C mA

Octane

Octanol

Paraformaldehyde

Paraldehyde

Pentane (mixed isomers)

Pentane-2, 4-dione(Acetyl acetone)

Pentanol (mixed isomers)

Pentylacetate(Amyl acetate)

Petroleum

Phenol

Propane

Propanethiol(Propyl mercaptan)

Propan-1-ol

Propan-2-ol

Propene(Propylene)

Propyl acetate

Propylamine

Pyridine

CH3(CH2)6CH3

C8H17OH

poly (CH2O)

(CH3CHO)3

C5H12

CH3COCH2COCH3

C5H11OH

CH3COOC5H11

Mixture

C6H5OH

CH3CH2CH3

C3H7SH

CH3CH2CH2OH

(CH3)2CHOH

CH2=CHCH3

CH3COOCH2CH2CH3

CH3(CH2)2NH2

Mixture

–56

–16

—

12

130

–23

–78

–78

—

41

–188

—

–126

–86

–185

—

–101

–42

126

195

25

124

36

140

138

147

—

182

–42

—

97

83

–48

—

32

115

3.93

4.5

—

4.56

2.48

3.5

3.04

4.48

—

3.24

1.56

—

2.07

2.07

1.5

—

2.04

2.73

13

81

70

17

<–20

34

34

25

<–20

75

—

—

15

12

—

14

<–20

17

1.0

—

—

1.3

1.4

1.7

1.2

1.0

—

—

2.0

—

2.15

2.0

2.0

—

2.0

1.8

3.2

—

—

—

8.0

—

10.5

7.1

—

—

9.5

—

13.5

12

11.7

—

10.4

12.0

—

—

—

70

41

—

44

60

—

—

39

—

50

—

35

—

49

56

—

—

—

—

240

—

380

550

—

—

180

—

340

—

210

—

260

350

210

—

300

235

285

340

300

375

—

605

470

—

405

425

(455)

—

(320)

550

—

—

—

—

73

—

—

—

—

—

70

—

—

—

—

—

—

—

T3

—

T2

T3

T3

T2

T2

T2

—

T1

T1

—

T2

T2

(T1)

—

(T2)

T1

IIA

IIA

IIB

(IIA)

IIA

IIA

IIA

IIA

(IIA)

(IIA)

IIA

(IIB)

IIB

IIA

IIA

IIA

IIA

(IIA)

IS 13408 (P

art 1) : 1992

34

Table 6 ( Concluded )

Name Formula

Mel

tin

g P

oin

t

Bo

ilin

g P

oin

t

Re

lati

ve

Va

po

ur

Den

sity

Fla

sh P

oin

t

Ign

itio

nT

em

per

atu

re

Min

imu

m I

gn

itin

gC

urr

ent

T C

lass

of

Su

ita

ble

Ap

pa

ratu

s

Ap

pa

ratu

s G

rou

p

Flammable Limits

v/v m/v

LFL UFL LFL UFL

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14)

C °C °C °C % % mg/l mg/l °C mA

P-cymene

Styrene

Tetrafluoroethylene

Tetrahydrofuran

Tetrahydrofurfuryl alcohol

Tetrahydrothiophen

3a, 4, 7, 7a-tetrahydro-4,7-methanoindene(Dicyclopentadiene)

Thiophen

Toluene

Toluidine

Triethylamine

α, α, α-trifluorotoluene(Benzotrifluoride)

Trimethylamine

Trimethylbenzene

1, 3, 5-trioxane

Turpentine

Vinyl acetate

Vinyl chloride

Xylene ( see D-7 )

CH3C6H4CH(CH3)2

C6H5CH=CH2

CF2=CF2

CHCH=CHCH2CHCHCH=CHCHCH2

C6H5CH3

CH3C6H4NH2

(C2H5)3N

C6H5CF3

(CH3)3N

C6H3(CH3)3

Mixture

CH3COOCH=CH2

CH2=CHCl

C6H4(CH3)2

–70

–31

—

–108

—

—

—

—

–95

–16

–115

—

–117

–45

62

—

—

—

–25

177

145

—

64

178

—

—

84

111

200

89

102

3

165

115

149

—

—

144

4.62

3.6

—

2.49

3.52

—

—

2.90

3.18

3.7

3.5

5.0

2.04

4.15

3.11

—

—

—

3.66

47

30

—

–17

70

—

(32)

–1

6

85

0

12

—

—

(45)

35

–7

—

30

0.7

1.1

—

2.0

1.5

—

—

—

1.2

—

1.2

—

2.0

—

3.6

0.8

—

—

1.0

5.6

8.0

—

11.8

9.7

—

—

—

7

—

8

—

11.6

—

29

—

—

—

6.7

—

45

—

46

60

—

—

—

46

—

50

—

49

—

135

—

—

—

44

—

350

—

360

410

—

—

—

270

—

340

—

285

—

1 110

—

—

—

335

435

490

—

224

280

—

—

—

535

480

—

—

(190)

470

410

254

—

—

464

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

T2

T1

—

T3

T3

—

—

—

T1

T1

—

—

(T4)

T1

T2

T3

—

—

T1

(IIA)

(IIA)

IIB

IIB

IIB

IIA

IIA

IIA

(IIA)

(IIA)

(IIA)

IIA

IIA

(IIA)

IIB

(IIA)

IIA

IIA

IIA

IS 13408 (Part 1) : 1992

35

ANNEX E( Clause 36.2.4 )

CALCULATION OF THE FLAMMABLE LIMITS FOR A MIXTURE OF GASESNOTE — This annexure may be helpful for use with IS 5572 (Part 1) : 1978.

E-1 LIMITS FOR SAMPLE MIXTURES

E-1.1 General

Frequently, explosion risks arise from mixturesof flammable materials with air. Though onlythe most general of rules can be indicated forensuring the safe use of electrical apparatuswith mixtures of gases, it is often desirable tobe able to establish with some degree ofconfidence the flammable limits for suchmixtures in order that local explosion risk canbe avoided. A method that may be used tocalculate the flammable limits of most mixturesof flammable gases is described in E-1.2.Though this method achieves a satisfactorydegree of accuracy for most applications, it isalways advisable to apply caution where theexpected total concentration of combustible isnear to the calculated value for the appropriateflammable limit. Particular care should also betaken in circumstances where catalytic effectsbetween individual components of a mixtureare suspected. General purpose calculationscannot take such effects into account.

E-1.2 Method of Calculation

The method of calculation is based on a simplerelationship due to Le Chatelier connecting thelower flammable limits for any two gases in airwith the lower limit for any mixture of them.The relationship is expressed by the followingequation:

where

N1 and N2 are the lower flammablelimits in air for each combustible gasseparately (in %); and

n1 and n2 are the percentages of eachgas present in any mixture of them thatis itself a lower limit mixture.

The formula indicates, for example, that amixture of air, carbon monoxide and hydrogenthat contains one-quarter of the amount ofcarbon monoxide and three-quarters of theamount of hydrogen necessary to form lowerlimit mixtures with air independently (i.e.one-quarter of 14% approximately and three-quarters of 4% respectively) will itself be alower limit mixture.

The formula may be generalized to apply to anynumber of gases. Thus:

The formula may be applied also to upper limitmixtures with suitable redefinition of the termsn1, etc, and N1, etc.

The equation may be rendered more useful asfollows. (It is assumed that the terms used areconsistent, i.e. they are all lower limit mixturesor they are all upper limit mixtures).

Let P1, P2, P3, etc, represent the proportions ofeach combustible gas present, ignoring air andinert gases, so that :

P1 + P2 + P3 +........ = 100

and let L represent the flammable limit(upper or lower, as appropriate) so that:

L = n1 + n2 + n3 +...

since n1/L = Pl/100, then substituting inequation (2)

L/100 ( P1/N1 + P2/N2 + P3/N3 ... ) = 1

and therefore

E-1.3 Example

As an example of the use of this equation,consider the determination of the lower limitfor a gas mixture representative of natural gas.

The natural gas might comprise

methane in the proportion of 80% ( P1 )

(lower limit 5.32%)

ethane in the proportion of 15% ( P2 )

(lower limit 3.22%)

propane in the proportion of 4% ( P3 )

(lower limit 2.37%)

butane in the proportion of 1% ( P4 )

(lower limit 1.85%)

The lower flammable limit of this mixture withair would be:

n1N1-------

n2N2-------+ 1=

n1N1-------

n2N2-------

n3N3------- + + + 1=

L 100P1N1-------

P2N2-------

P3N3------- ......+ + +

------------------------------------------------------=

L 10080

5.32----------- 15

3.22----------- 4

2.37----------- 1

1.85-----------+ + +

------------------------------------------------------------------- 4.55%==

IS 13408 (Part 1) : 1992

36

E-2 LIMITS FOR COMPLEX INDUSTRIAL GAS MIXTURES

E-2.1 Method of Calculation

A flammable gas mixture encountered in manyindustrial processes comprises hydrogen,carbon monoxide, methane, nitrogen, carbondioxide and oxygen. The procedure to be usedfor calculating the flammable limits for mixtureof these gases is as follows:

a) The composition of the mixture is firstrecalculated on an air-free basis. Theamount of each gas is expressed thereforeas a percentage of the total air-freemixture.

b) A somewhat arbitrary dissection of theair-free mixture developed from step (a) ismade into simpler mixtures, each of whichcontains only one flammable gas and partor all of the nitrogen and carbon dioxide.

c) The appropriate limits for each of themixtures obtained from step (b) areobtained from available data ( see Fig. 1and 2, which give available data for theflammable limits of hydrogen, carbonmonoxide, methane, ethane and benzenewith various amounts of carbon dioxideand nitrogen as inert diluent components).

d) The limits of the air-free mixture are thancalculated from the data for the dissectedmixtures obtained in step (c) usingequation (6), were P1, P2, P3, etc, are theproportions of the dissected mixtures, inpercentages, and N1, N2, N3 etc, are theirrespective limits.

e) From the limits of the air-free complexmixture thus obtained, the limits of theoriginal complex mixture which includedair can be deduced.

E-2.2 Example

The following is an example of the step-by stepcalculation outlined in E-2.1.

a) The constituent components of the gasmixture are indicated in Table 7. Thecomposition of the air-free mixture,indicated in the third col of the table, maybe calculated as follows:The amount of air in the mixture is 2.8 ×100/20.9 or 13.4%. The air-free mixture istherefore 86.6% of the whole. When theoriginal proportions of carbon dioxide,carbon monoxide, methane and hydrogenare divided by 86.6 and multiplied by 100,the air-free percentages are obtained. Thenitrogen percentage is the differencebetween 100 and the sum of thesepercentages.

b) The flammable gases are paired with theinert gases to form separate mixtures, asshown in Table 8.

c) The flammable limits for the separate ordissected mixtures, taken from Fig. 1, areindicated in col 7 and 8 of Table 8.

d) The values for the flammable limits ofthese simpler mixtures and for thepercentages of the air-free mixture that

Table 7 Components of the Industrial Gas Mixture

Constituent Components of Industrial Gas

Mixture

Composition Composition Calculated on Air-Free Basis

% %

Carbon dioxide

Oxygen

Carbon monoxide

Methane

Hydrogen

Nitrogen

13.6

2.8

4.3

3.3

4.9

70.9

15.9

0.0

5.0

3.8

5.7

69.6

Table 8 Flammability Limits of Simpler Mixtures[ Clause E-2.2 (b) ]

FlammableMaterial

Amount of Flammable

Material

Carbon Dioxide

Nitrogen Total Ratio of Inert to

Combustible Gas

FlammableLimits from

Fig. 1

Lower Higher

(1) (2) (3) (4) (5) (6) (7) (8)

% % % % % %

Carbon monoxide 5.0 — 17.5 22.5 3.5 61.0 73.0

Methane 3.8 — 20.9 24.7 5.5 36.0 41.5

Hydrogen5.7

3.02.7

—15.9

31.2—

34.218.6

10.45.9

50.032.0

76.064.0

Total 14.5 15.9 69.6 100.0 — — —

IS 13408 (Part 1) : 1992

37

FIG. 1 LIMITS OF FLAMMABILITY OF HYDROGEN, CARBON MONOXIDE, AND METHANE CONTAINING VARIOUS AMOUNTS OF CARBON DIOXIDE AND NITROGEN

FIG. 2 LIMITS OF FLAMMABILITY OF ETHANE, ETHYLENE AND BENZENE CONTAINING VARIOUS AMOUNTS OF CARBON DIOXIDE AND NITROGEN

IS 13408 (Part 1) : 1992

38

each of these simpler mixtures represents( see col 5 of Table 8 ) permit calculation ofthe flammable limits for the complexair-free mixture. Thus, the lowerflammable limit (LF) (in %) is given by thefollowing equation:

The upper flammable limit (UFL) (in %) isgiven by the following equation:

e) As the air-free mixture is 86.6% of thecomplete sample mixture, the flammablelimits in air for the sample mixture are43 × 100/86.6 and 61 × 100/86.6, or 50%and 70% respectively. Thus, the originalsample will be flammable within thelimits of 50% and 70% in air.

E-2.3 Further Information

Further notes of the limitations of thesecalculations and the precautions that should betaken with such calculations are available ( seeCoward, H.F. and Jones, G.W. Limits offlammability of gases and vapors. US Bureau ofMines Bulletin 503, 1952).

LFL 10022.561

----------- 24.736

----------- 34.250

----------- 18.632

-----------+ + +------------------------------------------------------------------- 43%==

UFL 10022.573

----------- 24.741.5----------- 34.2

76----------- 18.6

64-----------+ + +

------------------------------------------------------------------- 61%==

Standard Mark

The use of the Standard Mark is governed by the provisions of the Bureau of IndianStandards Act, 1986 and the Rules and Regulations made thereunder. The Standard Mark onproducts covered by an Indian Standard conveys the assurance that they have been producedto comply with the requirements of that standard under a well defined system of inspection,testing and quality control which is devised and supervised by BIS and operated by theproducer. Standard marked products are also continuously checked by BIS for conformity tothat standard as a further safeguard. Details of conditions under which a licence for the use ofthe Standard Mark may be granted to manufacturers or producers may be obtained from theBureau of Indian Standards.

( Continued from second cover )

FOREWORDThis Indian Standard (Part 1) was adopted by the Bureau of Indian Standards, after the draftfinalized by the Electrical Apparatus for Explosive Atmospheres Sectional Committee had beenapproved by the Electrotechnical Division Council.Many industrial processes involve the generation, processing, handling and storage of flammableand potentially explosive gases, vapours and mists. Where such materials may be presentappropriate precautions have to be taken to design or locate electrical apparatus so that electricalarcs, sparks, hot surfaces or frictional sparks produced by such apparatus do not cause ignition.Several techniques are available for the protection of electrical apparatus situated in hazardousareas. These techniques are described in this code which takes into account the developments thathave taken place in area classification and the design, manufacture and use of electrical apparatusfor hazardous areas.The following standards on the selection, installation and maintenance recommendationsappropriate to the types of protection that may be used to achieve safe operation of equipment inpotentially explosive atmospheres shall be prepared in due course. This would provide basicrecommendations applicable to all other standards:

a) Installation and maintenance requirements for electrical apparatus with type of protection ‘d’Flameproof enclosure.

b) Installation and maintenance requirements for electrical apparatus with type of protection ‘i’Intrinsically safe electrical apparatus and systems.

c) Installation and maintenance requirements for electrical apparatus protected bypressurization ‘p’ and by continuous dilution, and for pressurized rooms.

d) Installation and maintenance requirements for electrical apparatus with type of protection‘e’. Increased safety.

e) Installation and maintenance requirements for electrical apparatus with type of protection ‘n’.This code of practice is prepared from Doc : 85/21906 DC Code of practice for electrical apparatusfor explosive atmospheres (of Technical Committee GEL/114 Electrical Apparatus for ExplosiveAtmosphers) issued for comments by British Standards Institution, U.K.This edition 1.1 incorporates Amendment No. 1 (October 2003). Side bar indicates modification ofthe text as the result of incorporation of the amendment.

PAGE

Table 1Table 2ATable 2BTable 3Table 4Table 5Table 6Table 7Table 8

TYPES OF PROTECTION

SELECTION OF APPARATUS, ACCORDING TO ZONE OF RISK

MINIMUM ACTIONS ON FAILURE OF PROTECTIVE GAS FOR TYPE OF PROTECTION ‘p’RELATIONSHIP BETWEEN T CLASS AND MAXIMUM SURFACE TEMPERATURE

EXAMPLE OF SCHEDULE FOR INITIAL INSPECTION

EXAMPLE OF SCHEDULE FOR SUBSEQUENT INSPECTIONS

DATA FOR FLAMMABLE MATERIALS FOR USE WITH ELECTRICAL EQUIPMENT

COMPONENTS OF THE INDUSTRIAL GAS MIXTURE

FLAMMABILITY LIMITS OF SIMPLER MIXTURES

3445

1111243636

FIGURE 1 LIMITS OF FLAMMABILITY OF HYDROGEN, CARBON MONOXIDE AND METHANECONTAINING VARIOUS AMOUNTS OF CARBON DIOXIDE AND NITROGEN 37

FIGURE 2 LIMITS OF FLAMMABILITY OF ETHANE, ETHYLENE AND BENZENE CONTAININGVARIOUS AMOUNTS OF CARBON DIOXIDE AND NITROGEN 37

Bureau of Indian Standards

BIS is a statutory institution established under the Bureau of Indian Standards Act, 1986 to promoteharmonious development of the activities of standardization, marking and quality certification of goods andattending to connected matters in the country.

Copyright

BIS has the copyright of all its publications. No part of these publications may be reproduced in any formwithout the prior permission in writing of BIS. This does not preclude the free use, in the course ofimplementing the standard, of necessary details, such as symbols and sizes, type or grade designations.Enquiries relating to copyright be addressed to the Director (Publications), BIS.

Review of Indian Standards

Amendments are issued to standards as the need arises on the basis of comments. Standards are alsoreviewed periodically; a standard along with amendments is reaffirmed when such review indicates that nochanges are needed; if the review indicates that changes are needed, it is taken up for revision. Users ofIndian Standards should ascertain that they are in possession of the latest amendments or edition byreferring to the latest issue of ‘BIS Catalogue’ and ‘Standards : Monthly Additions’.

This Indian Standard has been developed from Doc : No. ET 22 (3045)

Amendments Issued Since Publication

Amend No. Date of Issue

Amd. No. 1 October 2003

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