Principles of Explosion Protection - IRANELECTRICALiranelectrical.com/wp-content/uploads/Principles-of-Ex-Protection.pdf · Fundamental principles of explosion protection 6 Explosive

Principles ofExplosion Protection

1CEAG Sicherheitstechnik GmbH

Foreword 3

The history of explosion protection 4

Fundamental principles of explosion protection 6

Explosive atmosphere 6Ignition sources 6Flash point 7

Primary and secondary explosion protection 8

Potentially explosive atmospheres 9

Zone classification 9Zone 0 9Zone 1 9Zone 2 10Zone 20 10Zone 21 10Zone 22 10

EC directives on explosion protection 11

Directive 94/9/EC of the European Parliament and Council dated March 23rd, 1994 (ATEX) 12

Scope of application 12Essential safety requirements 13Groups and categories of apparatus 14Putting in circulation and commissioning of apparatus 15Procedures in event of unsafe apparatus 15Marking 15Provisional arrangements 15

CE marking 16

Apparatus safety law (GSG) 18Decree concerning the putting into circulation of apparatus and protectivesystems for use in potentially explosiveatmospheres – explosion protectiondecree (ExVO) 18New version of the decree concerningelectrical installations in potentially explosive atmospheres (ElexV) 18Standards 19Zone classification 20Explosion protection document 21

Electrical apparatus for use in potentiallyexplosive atmospheres 22

Principles 22

Types of protection for explosion-protected apparatus 24

General requirements acc. to EN 50 014 24

Oil immersion “o“: EN 50 015/VDE 1070/0171, Part 2 25

Pressurization “p“:EN 50 016/VDE 0170/0171, Part 3 25

Sand filling “q“:EN 50 017/VDE 0170/0171, Part 4 26

Flameproof enclosure “d“:EN 50 018/VDE 0170/0171, Part 5 27

Combined types of protection 27

Increased safety “e“: EN 50 019/VDE 0170/0171, Part 6 28

Encapsulation “m“:EN 50 028/VDE 0170/0171, Part 9 29

Intrinsic safety “i“:EN 50 020/VDE 0170/0171, Part 7 30

Technical terms 30Fundamental data 30Limiting ignition curves 31Categories of intrinsically safe and associated electrical apparatus 31Constructional requirements 32Types of limiting modules 32Isolation of intrinsically safe circuitsfrom non-intrinsically safe circuits 32Apparatus for intrinsicallysafe air cuits 32Types of limiting modules 32Isolation of intrinsically safe circuits from non-intrinsically safe circuits 32Design of intrinsically safe circuits 33Working on and testing of intrinsically safe circuits 33

Intrinsically safe electrical systems “i“EN 50039 / VDE 0170/0171, Part 10

Technical terms 34

Cap lamps for use in mines susceptible to firedamp EN 50033/VDE 0170/0171, Part 14 35

Technical terms 35

Zone 0 apparatus 36

Zone 2 apparatus 37

Type of protection “n“EN 50 021/VDE 0170/0171, Part 16 37

Electrical apparatus for use in areas withinflammable dusts 39

Ignition sources 39Electrical apparatus for use in areas with inflammable dust with protection by the enclosure 39

Electrical installations in potentially explosive atmospheres 41

Obligations of the manufacturer 41Obligations of the installer 41Obligations of the operator 41

Table of Contents


Setting-up of electrical installations in potentially explosive atmospheres 42

Safety-related data for potentially explosive gas atmospheres 42Division of potentially explosive atmospheres into zones 42Temperature class – Explosion group 43Atmospheric conditions 43Selection of electrical apparatus 44Fundamental installation requirements 45Electrical protection and monitoring devices 46Cables 46Additional requirements 46

Maintenance and repair of explosion-protected apparatus 48

Rules, regulations and decrees 48Special safety measures 48Installation 50Maintenance 50Repairs 51

Definition of potentially explosive atmospheres and requirements for explosion-protected apparatus on the world market 53

NEC 53Table of comparison NEC IEC/EN 53

IP degrees of protection 55

Table 1 Procedure for the assessment of the zone classification acc. to ElexV, EX-RL and VDE 0165 56

Table 2Explosion protection at a glance 57

Annex 1 Sample of an expert’s certificate acc. to §9 ElexV 58

Annex 2Sample of an expert’s certificate acc. to §10 ElexV (old) 59

Annex 3Sample of an installation certificate 60

Annex 4Sample of a hot work permit 61

Annex 5Bibliography 62

Annex 6Harmonized standards to directive 94/9/EC 63


Foreword

This publication provides a brief survey of theessential aspects of explosion protection. Thestatutory regulations, the VDE specifications andthe Employers’ Liability Insurance Associationdirectives define the obligatory duties of manu-facturers, installers and operators of electricalinstallations in explosive atmospheres.At the end of this publication there is a list ofliterary references for the interested reader.

The history of explosion protection

In 1909 Concordia Elektrizitäts-Aktiengesell-schaft, later called CEAG, began to manufacturefiredamp protected electrical miners lamps forthe mining industry. Up to that time, only lampswith a naked flame had been available. The firstcontributions regarding safety had been made in1815 by the English chemist, Sir Davy whodeveloped an oil lamp which prevented the pro-pagation of the flame through a close meshedscreen.

The fundamental experiments made by Dr.-Ing.e.h. Carl Beyling, a mining engineer, relating tosafety against firedamp of specially protectedelectrical motors and apparatus in coal mineswas a decisive step in the development ofexplosion protection. The governing design prin-ciples of firedamp protection devices on electri-cal machines, transformers and switchgeardating from 1912 were based on the results ofthese experiments. As protective measures, thefollowing types of protection were accepted:

• Flameproof enclosure (at that time called closed encapsulation)

• Plate encapsulation• Oil immersion• Close meshed screen

Since 1924 only incandescent lamps were per-mitted for lighting hazardous areas, the luminouselement of which was hermetically sealed. Theincandescent lamps had to be protected withstrong glass bells which also tightly enclosed thelampholder.

Light switches had to be installed outside of thehazardous locations, and in the case of a failureor the lack of explosion protected lighting,access to these locations was only permittedwith safety lamps. Therefore, in general electricalinstallations in hazardous locations were dispen-sed with.

Machines containing slip rings or commutatorshad to be designed so that the slip ring or com-mutator space was at least enclosed andthoroughly purged under overpressure withextraneous air or a suitable gas. Purging had tostart prior to switching on the machine, or themachine had to have a flameproof enclosure.This requirement applied to any locations whichwere subject to the hazard of gas or vapour/airmixtures.

The guiding principles issued in 1935 on themounting of electrical installations in hazardousproduction areas and storage rooms (VDE0165/1935) was to be the first German regulati-ons on the protection of hazardous installations.

The fundamental revision of these regulationsbegan with the VDE regulations 0171 ”Con-structional regulations for explosion protectedapparatus” which finally came into force in 1943.They provided the manufacturers of electricalequipment for use in explosive atmosphereswith the necessary documents for a safe designand construction. This regulation not onlydescribed the individual types of protection andtheir scopes of application, but also included anumber of constructional specifications andintroduced the identification marking (Ex) forthose electrical apparatus made in compliancewith it.

The governing principles and specifications ofthe VDE regulations 0165 and 0171 constitutedthe basis of the police decree dated Oct. 13,1943 for electrical apparatus in hazardous loca-tions and in mines subject to the hazard of fire-damp. The police decree primarily aimed at themanufacturers of electrical apparatus. It laiddown that explosion protected electrical equip-ment was only allowed to be put in circulation,installed and operated, if it conformed to the so-called VDE regulations and had successfullypassed the type and routine tests specified wit-hin.

The factory inspectorate division was chosen tobe the competent authority to define whatextent a room or plant might be subject to the hazard of explosion.

The decree of 1963 regarding electrical installati-ons in explosive atmospheres (ExVO), today cal-led ElexV, not only imposed the obligation tohave the explosion protected apparatus testedby the Federal Physico-Technical Institute (Phy-sikalisch-Technische Bundesanstalt PTB) or theMining Test Station (BVS), but also the obliga-tion to obtain the design approval from the aut-horities of the competent federal state.

Miner’s lamp



Research papers by

C. Beyling, mining engineer

In 1975 the Council of the European Communityissued basic directives on explosion protection.The European standards for hazardous areaswere worked out by CENELEC, the Europeancommittee for electrotechnical standardization.In Germany the new European standards EN 50014 to EN 50 020 were adopted as VDE stan-dards as part of the national standards works.These new standards DIN EN 50014 to50020/VDE 0170/0171 part 1 to 7, designatedas VDE regulations, came into force on May 1st,1978, and the new statutory provisions on July1st, 1980.

By means of this statutory order now calledElexV, the expertise of the testing establish-ments and the design approval are replaced bya type sample test. The type sample test is car-ried out by any authorized testing establishmentof the member states of the EU. The certificatesof conformity and inspection granted on thebasis of said test are mutually acknowledged astype sample test certificates by all member sta-tes of the EU.

The directive 94/9/EC for the harmonization sta-tutory provisions of the member states relatingto apparatus and protective systems for useaccording to the rules in potentially explosiveatmospheres, issued on March 23, 1994 by theEuropean Parliament and Council, will substituteany directives concerning explosion protectionexisting on a European level as from July 1st,2003. The European Parliament determinedMarch 1st, 1996 as the date for conversion ofthis new directive into national law.

On December 12th1996 the directive 94/9/ECwas converted into national law by the seconddecree concerning the equipment safety lawand the changes relating to the equipmentsafety law by the explosion protection decree(ExVO). With this decree the acetyl decree, VbFand Elex were also assimilated with the Euro-pean law. On account of a transition period uptill June 30th, 2003, manufacturers, testing aut-horities and operators were now confronted withvarious decrees that were similarly worded.

On January 28th, 2000 the second importantdirective relating to explosion protection waspublished in the official gazette of the Europeancommunities. The directive 1999/92/EC relatingto minimum requirements for the improvementof the health protection and the safety ofemployees who may be endangered by potenti-ally explosive atmospheres was issued onDecember 16th, 1999 by the European Parlia-ment and council. Here the final date laid downfor the conversion of this new directive intonational law was June 30th, 2003.


Fundamental principles ofexplosion protection

Explosive atmosphere

An explosive atmosphere is built up of a mixtureof inflammable gases, vapours, mists or dustswith air, including the usual constituents such ashumidity. After ignition, a reaction in the explo-sive atmosphere is automatically propagatedunder atmospheric conditions (currently onlydetailed in VDE 0165 (2/91) and in the ExRL).

Atmospheric conditions are total pressures ran-ging from 0.8 to 1.1 bar and temperatures of themixture from -20° to + 60°C. The Europeandirectives and their implementary decrees are,however, based on this definition.

In addition to this, the risk of explosion existswhen two other conditions are fulfilled at thesame time:

• The proportion of inflammable matter is sohigh that an explosive mixture can be formed.

• There is an ignition source in the same areathat can ignite the mixture.

Such a mixture is capable of exploding when inatmospheric conditions its concentration is wit-hin certain limits specific to the type of sub-stance. The lower explosive limit defines theconcentration up to which a mixture is not yetcapable of exploding. The upper explosive limitdefines the concentration up to which the mix-ture is capable of exploding. In conditions otherthan atmospheric, the explosion limits change.As the proportion of oxygen increases, e. g. theupper explosive limit is raised.

Generally, the explosive limits are indicated inpercent by volume. Percent by volume, abbre-viated %/vol., means the volume percent of thecombustible matter in the mixture. The lowerexplosive limit of hydrogen is 4.0 % by volume,and the upper explosive limit 75.6 % by volume.The safety coefficients define quantitative dataabout the properties of most of the known sub-stances.

If, in the event that an explosive mixture is igni-ted, people are directly or indirectly endangered,this is then classed as a potentially explosiveatmosphere. Whether or not an atmosphere ispotentially explosive can be roughly assessed. Inenclosed rooms, regardless of their size, 10 lit-res of explosive atmosphere are already consi-dered hazardous. If the volume of the room isless than 100 m3, this also applies to smallerquantities.

Ignition sources

Ignition sources that can cause an explosion,are:• Electric sparks and arcs, e. g.

– when circuits are opened and closed,– when electrostatically charged components

are discharged,– at the contact points of switchgear,– when cables are ruptured,– in the event of a short-circuit, or electric

compensating currents• mechanical sparks produced by friction,

impact and grinding• hot surfaces such as live conductors in

windings of motors, heat conductors,bearings, shaft bushings

• electrostatic charges as a result of a separating process involving at least onechargeable substance. (Running down of foilsover rollers, driving belts, filling andemptying of liquids and powdery substances.)

Although of minor importance, the following igni-tion sources should also be mentioned:• glowing particles • flames• compression and shock waves e. g. when

vacuum flasks and fluorescent lamps break• electromagnetic waves in the optical region of

the spectrum• ultrasonics: causes temperature rise• radiation

– high-frequency– radioactive radiation– X-radiation

• chemical reactions


Flash point

An explosion hazard can also result when aninflammable liquid evaporates at the surface.This results in a vapour/air mixture which, undergiven conditions, forms an explosive atmos-phere.

In order to do so, the temperature must havereached the flash point of the liquid. The flashpoint is the lowest temperature at a pressure of1013 hPa (normal air pressure) at which vapoursdevelop in such a quantity that an inflammablemixture forms above the liquid.

In accordance with the ”Technical directive oninflammable liquids” (TRbF), inflammable liquidsare divided into four classes according to theirflash points:

If they are whirled up, inflammable dusts whichare evenly distributed in a layer of less than 1 mm and at normal room heights can alsocompletely fill a whole room with an explosivedust/air mixture.

More details on this subject can be found in thechapter ”Potentially explosive atmospheres”.

Class of hazard Flash point

AI < 21° C

AII 21 to 55° C

AIII > 55 to 100° C

B < 21° C, at 15° C soluble in water

Oil terminal


Primary and secondaryexplosion protection

Avoiding the danger of an explosion is alwayspreferable to any protection against explosion.An explosion can be prevented, if the creation ofan explosive atmosphere can be excluded.Measures to this end are summarized under theheading Primary Explosion Protection.

Avoidance of inflammable substancesInflammable substances should, whenever pos-sible, be substituted by substances that are notcapable of forming an explosive mixture.

Observance of the flash pointHere distinction is made between two procedures.

Raising the flash pointThe flash point of an inflammable liquid must beat least 5 K above the processing temperatureor the room temperature. In the case of water-soluble, inflammable substances this can beachieved by adding water.

Lowering the processing temperatureWith this method it is necessary to apply techni-cal measures (e.g. cooling) to ensure that theprocessing temperature is always at least 5-10K lower than the flash point. It is, however,necessary to keep faults, standstills, leakagesand other influence factors safely under control.

Limitation of the concentrationThe build-up of an explosive atmosphere can beprevented if it is possible to limit the concentra-tion of a substance to the range below the loweror above the upper explosive limit. This can frequently be achieved with gases. Dif-ficulties arise in the event of gas leaks or if theignition range has to be passed when the plantis started or switched off. With liquid substances, the concentration isusually kept below the lower explosive limit,since it requires a very high effort to keep theconcentration in the upper range.Such measures cannot be applied for dusts,since it is practically impossible to achieve aneven distribution.

InertisationIf the proportion of oxygen in a mixture is lessthan 10 percent by volume, then, as a generalrule, an explosive mixture does not exist. Inorder to reach such a low proportion, so-calledinert gaseous substances such as nitrogen, car-bon dioxide, water steam or halogenatedhydrocarbon are added to the mixture until thedesired concentration is obtained.If the percent by volume of the inert gas to theinflammable gas is in the minimum ratio of 25:1,an explosive atmosphere cannot build up,regardless of the quantity of air added.

VentilationThe formation of a hazardous explosive atmos-phere can be prevented or restricted by ventila-tion. In rooms above ground level and withoutspecial ventilation, the air is renewed by naturalventilation once per hour. By way of compari-son, the exchange of air in cellar rooms takes upto 2.5 hours. The concentration of the mixturecan, however, only be calculated, if the escapingquantity per unit of time of an inflammable sub-stance is known and if an equal distribution canbe assumed.

The natural flow conditions in a room can beassessed by an expert on ventilation, who willthen usually recommend an artificial ventilation.Compared to natural ventilation, it ensures theexchange of larger quantities of air and a morecarefully directed air flow. Moreover, the con-centration occurring can be determined with aconsiderably higher degree of reliability. On theother hand, the drawback of a ventilation bytechnical means is that it needs constant servi-cing. In addition to this, precautions have to betaken in case the installation should operate at alower output or fail altogether.

Explosion-proof designThe explosion-proof design is a constructionalmeasure which does not prevent an explosion,but restricts its effect to a harmless degree. Theapparatus must be designed in such a way thatit withstands the maximum explosion pressureand, in extreme cases, even the detonationpressure. With pipes and other long stretched-out constructions a detonation is easily possible.If the explosion-proof design is not able to with-stand the increased pressure, effective pressurerelief must be provided.

Secondary explosion protectionAfter all the possibilities of primary explosionprotection have been exhausted, there can stillbe areas where a hazardous explosive atmos-phere occurs. These areas are called hazard-ous areas or potentially explosive atmospheres.Secondary explosion protection with protectivemeasures against ignition that render ignitionsources ineffective applies for such areas.Secondary explosion protection encompassesall electrical apparatus for use in hazardousareas.

Examples for the avoidanceof inflammable substances

Inflammable Substitutesubstance

Inflammable solvents Hydrous solutionsand detergents

Inflammable Non-inflammablepulverized filling substancessubstances


Potentially explosiveatmospheres

Zone classification

Potentially explosive atmospheres are dividedinto six zones. The classification depends on theprobability of the build-up of a potentially explo-sive atmosphere. In addition, distinction is madebetween inflammable gases, vapours and mistson the one hand, and inflammable dusts on theother.Which explosion protected electrical apparatusmay be used in the individual zones?

Zone 0Zone 0 mainly encompasses areas such as theinside of enclosed containers, pipes and appa-ratus which contain inflammable liquids. Therespective operating temperature lies above theflash point. The potentially explosive atmospherelies above the surface of the liquid and not in theliquid. Most gases of inflammable liquids areheavier than air and spread in a similar way toliquids. Cavities such as pits or pump sumpscan usually accommodate these explosivegases for longer periods, so that here it is alsonecessary to expect a zone 0 area.

With apparatus for zone 0, ignition sourcesmust be protected against explosion even if theoccurrence of failures is only rare. Hence, theapparatus must meet the following require-ments:Should one type of protection fail or shouldtwo faults occur simultaneously, still be suffi-cient protection against explosion must still beensured.

The constructional requirements EN 50284 (VDE0170/0171, Part 12-1) state that the necessaryexplosion protection is attained if the apparatus

• is built in accordance with the type of protec-tion ”ia” to EN 50 020, or

• conforms to at least one type of protectionaccording to EN 50 015 to EN 50 020, and ifthe scope of the protective measures includesa second independent type of protection.

For example, flameproof luminaires were addi-tionally pressurized, or intrinsically safe appara-tus were additionally encapsulated acc. to EN50 028. According to the directive 94/9/EC,apparatus for zone 0 must comply with thecategory 1G.In zone 0 the hazard of an ignition due to elec-trostatic charge is particularly high. For this rea-son the relevant standard DIN EN 50 284 con-tains extremely detailed requirements thatexceed the requirements of DIN EN 50 014.

Zone 1Inflammable or explosive substances are made,processed or stored in zone 1. This includes thearea surrounding charging doors and in theclose vicinity of filling and discharging facilities,the vicinity of fragile equipment, pipes andglands on pumps and slides that do not sealadequately. It is likely that an ignitable concen-tration will occur during normal operation. Igni-tion sources that occur during normal, trouble-free operation and those that usually occur inthe event of operational failures, must be explo-sion-proof.The chapter ”Electrical apparatus for use inpotentially explosive atmospheres” describes theindividual types of protection. According to thedirective 94/9/EC, zone 1 apparatus must com-ply with the category 2G.

Ex-protected torch for use in zone 0: specially certified

for the increased requirements in this hazardous area

Zone classification to EN 50 014

Ex-protected control switch and ex-protected safety

switch with pipe fixing, certified for use in zones 1 and 21

Inflammable gases, vapours and mists

Zone 0 An area in which an explosivegas atmosphere is presentcontinuously or for longperiods

Zone 1 An area in which an explosivegas atmosphere is likely tooccur occasionally duringnormal operation

Zone 2 An area in which an explosiveatmosphere is likely to occuronly rarely and then only fora short period

Inflammable dusts

Zone 20 An area in which an explosiveatmosphere due to a mixtureof dust with air is present con-tinuously, for long periodsor frequently

Zone 21 An area in which an explosiveatmosphere due to mixtures ofdust with air is to be expectedoccasionally and for shortperiods

Zone 22 An area in which an explosiveatmosphere due to whirled-updust deposits is not to beexpected. However, if such anatmosphere should occur,then in all probability onlyoccasionally and for shortperiods


Zone 2Zone 2 encompasses areas around zone 0 andzone 1, as well as areas around flanged jointson pipelines in enclosed rooms. Furthermore, itincludes such areas in which, due to natural orforced ventilation, the lower explosive limit isonly reached in exceptional cases, such as theenvironment of outdoor installations. Zone 2 applies to areas where inflammable orexplosive substances are manufactured or sto-red. The probability that an ignitable concentra-tion will occur is rare and then exists only for ashort period.

During normal, trouble-free operation, ignitionsources must be explosion-proof.The use of all apparatus that satisfies the requi-rements for zone 0 and zone 1 apparatus is per-mitted.According to the directive 94/9/EC, apparatusfor zone 2 must comply with the category 3 G.

Zone 20Apparatus for zone 20 shall be specially appro-ved for this purpose, e.g. grain silos. Construc-tional requirements for apparatus for this zonewhere protection is afforded by the surroundingenclosure can be found in DIN EN 50281-1-1.Further standards, e.g. for apparatus in the typeof protection Intrinsic Safety, are being prepa-red. According to the directive 94/9/EC, appara-tus for zone 20 must comply with the category1D.

Zone 21Among others, zone 21 encompasses mills,warehouses for coal or grain, and the area sur-rounding filling stations. Here explosive clouds ofdust can develop due, for example, to the occa-sional of dust escaping from the opening. Therisk of hazards due to dust deposits is oftenunderestimated. Explosive dust/air mixtures candevelop due to the formation of a smoulder spotor of a low temperature carbonization gas, aswell as due to the deflagration of a low tempera-ture carbonization gas or to the whirling-up ofgas caused by glowing combustion. Accordingto the directive 94/9/EC, apparatus for zone 21must comply with the category 2D.

Zone 22Under normal operating conditions it is notnecessary to expect the occurrence of an explo-sive dust/air mixture in zone 22. It is only neces-sary to expect an explosive atmosphere due, forexample, to whirled-up dust deposits in theevent of a breakdown. According to the directive94/9/EC, apparatus for zone 22 must complywith the category 3D. According to the DIN/EN50281-1-1, in the event that conductive dustsare present in an installation, the apparatus usedmust comply with the category 2D.

Detailed information on all zones can be found inthe chapter ”Erection and operation of electricalinstallations in potentially explosive areas”.

Ex-protected fluorescent light fitting with electronic bal-

last for use in zones 2 and 22


fied by a ”notified body”. Another new features isa description of the hazardous areas in workpla-ces with potentially explosive atmospheres and,as a result of it, graded safety features for the”apparatus” being used. Since the new directive was formulated inaccordance with the ”New Approach” of the EC,this involved the introduction of the manufactu-rer’s declaration of conformity in conjunctionwith a CE marking of the products for explosionprotected apparatus as well.A detailed explanation with regard to the direc-tive 94/9/EC is included in the chapter ”Directive94/9/EC of the European Parliament and Coun-cil of March 23rd, 1994”.

The opposite chart shows a brief comparison ofthe main differences between the rulings accor-ding to the old and the new directive.

Directive 79/196/EEC Directive 94/9 EC– ATEX 100a –

Scope Electrical apparatus Electrical and non-electrical apparatus and protective systems

Potentially explosive gas Potentially explosive gasatmospheres and dust atmospheres

Distinctivecommunitymark for the freemovement of goods

Certificate Certificate of conformity Manufacturer’s declaration Inspection certificate of conformityby a notified body The basis is a type

certificate issued bythe notified body

Quality assurance Not referred to Requiredsystem

Fields of application Regulated by standards Direct regulationand construction of in the directivethe apparatus – Apparatus groups

– Apparatus categories – Basic safety requirments

Marking of apparatus Regulated by standards Laid down in the directive

Free trade within the EuropeanCommunity

The basis for the free movement of goods withinthe European trade area was established in thearticles of association of the EEC.

Article 100a of the contract

New version of Article 95A series of European standards for explosionprotected apparatus was drawn up by the Euro-pean Standards Committee for electrical appa-ratus (CENELEC) to provide the basis for theenforcement of the requirements. The directive79/196/EEC of the European committee provi-ded the legal basis.

This ”old” directive was restricted to explosion-protected electrical apparatus and the regulati-ons that were required for the free movement ofgoods. By rigidly referring to the European stan-dards, the normative basis for the certification ofexplosion-protected electrical apparatus wasregulated by ”notified bodies”.

The ”new” directive 94/9/EC regulates the requi-rements for ALL apparatus and protectivesystems for use in potentially explosive atmos-pheres. In addition, the directive now includesthe ”Basic safety requirements” for explosion-protected apparatus. Manufacturers of explo-sion-protected apparatus must provide evidenceof a quality assurance system that is to be veri-

EC directives on explosion protection


Set-up of the directive 94/9/EC

Disposing part

Chapter Clause Heading

I 1 – 7 Scope of application, putting in circulation and free movement of goods

II 8 – 9 Conformity assessment procedures

III 10 – 11 CE marking of conformity

IV 12 – 16 Concluding provisions

Annexes

I Criteria of decision for the classification of groups of apparatus in categories

II Essential safety and health requirements for the conception and construction of apparatus and protective systems for use in potentially explosive atmospheres

III Module: EC- type-examination

IV Module: Quality assurance of the production

V Module: Inspection of the products

VI Module: Conformity with the design

VII Module: Quality assurance of the product

VIII Module: Internal production control

IX Module: Individual test

X CE marking and contents of the EC certificate of conformity

XI VMinimum criteria to be taken into account by the member states for the authorization of testing laboratories

Directive 94/9/EC of theEuropean Parliament and Council dated March 23rd, 1994- ATEX directive –

The purpose of this directive is the assimilationof the statutory stipulations of the member sta-tes of the European Union concerning apparatusand protective systems for use in potentiallyexplosive atmospheres.

As of July 1st, 2003 it will substitute any existingdirectives concerning explosion protection on aEuropean level. The European Parliament fixedJuly 1st, 1996 as the date for the conversion ofthe new directive into national law.

The four chapters of the disposing part are sub-divided into 16 clauses. In the chapters refe-rence is made to the annexes I to XI, whichinclude 7 modules

Scope of applicationThe directive, also known as the ATEX directive,applies to apparatus and protective systemsthat are designed for use in potentially explosiveatmospheres. Safety devices and controlsystems for use outside of potentially explosive

atmospheres also come under this directive.This applies when such devices are required forthe safe operation of apparatus and protectivesystems or contribute to it. The definitions for some terms relating to explo-sion protection in this directive are different tothose found in the International Electro-technicalDictionary.Apparatus and protective systems designed foruse in hazardous areas:

Apparatus is machinery, equipment, stationaryor portable devices, control units and parts ofequipment, as well as warning and preventivesystems that, either individually or in combina-tion, are designed for the generation, transmis-sion, storage, measurement, control and con-version of energy and for the processing ofmaterials that feature inherent ignition sourcesand are, therefore, capable of causing an explo-sion.

Protective systems are all devices that imme-diately stop an explosion in its very beginningand/or limit the area covered by an explosion.They that are put in circulation as independentsystems. The components of the apparatusdefined above are not regarded as protectivesystems.

Components are those parts that are requiredfor the safe operation of apparatus and protec-tive systems without, however, fulfilling an inde-pendent function.

An explosive atmosphere is a mixture of airwith inflammable gases, vapours, mists or dustsunder atmospheric conditions in which, afterignition has occurred, the process of combus-tion is propagated to the whole unconsumedmixture.

In a potentially explosive atmosphere theatmosphere can become explosive due to localand operational conditions.

The scope of application of this directive doesnot include:• medical equipment designed for use in

medical areas,• apparatus and protective systems with which

an explosion hazard is only possible if explosives or chemically unstable substancesare present,

• apparatus intended for use in domestic andnon-commercial surroundings in which anexplosive atmosphere can only rarely be formed, and then only as a result of an inadvertent leakage of fuel,

• personal protective outfits,• ocean-going vessels and mobile offshore

plants, as well as the equipment on board of these vessels or plants,

• vehicles and the associated trailers that areexclusively intended for the transportation of people by air, road, rail, or water, andtransportation means designed for the transport of goods by air, public road andrailway systems, or water. Vehicles intendedfor use in potentially explosive atmospheresare not excluded and,


• possibly, products for military purposes, if thisis deemed necessary by any of the memberstates of the European Union.

In order to make it easier to furnish proof that apiece of apparatus or a protective system con-forms to these requirements, uniform standardswill have to be established on a European level.This applies, in particular, to the non-electricalfield of explosion protection. In the past stan-dards only existed for electrical apparatus inEurope. These standards, if not already in exi-stence, will describe the conception, design andtesting of apparatus and devices. Compliancewith these standards ensures that a productconforms to the basic requirements of the direc-tive 94/9/EC. These standards will be drawn upby the European Standardization Committee(CEN) and the European Committee for Electro-technical Standardization (CENELEC).The German interests will be represented by theGerman Institute for Standardizaton (DIN) andthe German Electrotechnical Commission (DKE).

Groups and categories of apparatusApparatus is subdivided into groups and cate-gories:Apparatus group I applies to apparatus formining operations above ground and underground that may be endangered by methanegas and/or inflammable dusts.Apparatus group II applies to apparatus foruse in all other areas that can be subject tothe hazard of an explosive atmosphere. The apparatus group I is subdivided into thecategories M1 and M2:

Essential safety requirementsA product is considered to be safe, if, when it isused as directed, the essential safety and healthrequirements for the conception and the designof apparatus and protective systems accordingto the directive are fulfilled. With regard to associated equipment, the basicsafety requirements only apply inasmuch as theyare necessary for a safe and reliable functioningand handling of this equipment in order toensure the explosion protection.

Group of apparatus II with potential ignition source

Apparatus category 1 Apparatus category 2 Apparatus category 3

Electricalapparatus

yes no

Motorwith internalcombustion

EC-Type Examination

Documentationfrom a notified body

Documentationfrom manufacturer

Essential safety and health requirements

Internal production control

yes

no


Category Apparatus Group II

1 The apparatus is intended for use in areas in which an explosiveatmosphere is present continuously or for long periods or fre-quently.Even if apparatus failures only occur infrequently, the apparatus mustensure the required degree of safety and feature such explosion pro-tection measures that• if one constructional protective measure fails, at least one other

independent constructional protective measure ensures the required degree of safety, or

• if two independent faults occur in combination, the required degreeof safety is still ensured.

2 The apparatus is intended for use in areas in which an explosiveatmosphere occurs occasionally.Even in the case of frequent apparatus failures or faulty conditions thatare normally to be expected, the constructional explosion protectionmeasures ensure the required degree of safety.

3 The apparatus is intended for use in areas in which no occurrence ofan explosive atmosphere due to gases, vapours, mists or whirled-updust is to be expected. If, however, it occurs, then in all probabilityonly rarely or for a short period.During normal operation the apparatus ensures the required degree ofsafety.

The apparatus group II is subdivided into the categories 1, 2 and 3:

Category Apparatus Group I

M 1 The apparatus must continue to work even in the event of infrequent failures coinciding with an existing explosive atmosphere and must fea-ture such protective measures against explosion that• if one constructional protective measure fails, at least one other

independent constructional measure will ensure the required safety, or

• if two independent faults occur in combination, the required safety is still ensured.

M 2 If an explosive atmosphere occurs, it must be possible to switch off the apparatus.The constructional explosion-protection measures ensure the requireddegree of safety during normal operation, even under severe operatingconditions and, in particular, in cases of rough handling and changingenvironmental influences.

Group IIII 1G Category 1 (Zone 0 apparatus) (G = gases, vapours, mists)



Group IIII 1D Category 1 (Zone 20 apparatus) (D = dust)




Apparatus, protective systems or devices areregarded as unsafe if, when used for their inten-ded purpose, they represent an imminent dan-ger to the safety of people, domestic animals orgoods.

The member state is required to notify the com-mission of the European Union of such measu-res and to give the reasons for its decision. Thecommission will immediately contact the com-panies concerned and inform all member statesif these measures has are justified. If the fault is the result of a standard, a commit-tee will deal with it. Great importance is attachedto the uniformity of the practical implementation.The standing committee will review questionsrelating to the application of this directive.

MarkingEach piece of apparatus and each protectivesystem must be marked in a clear and indeliblemanner with the following minimum data: • manufacturer’s name and address • CE marking• designation of the series and of the type• serial number, when required• the year of construction• the community marking for explosion-

protected apparatus in accordance with the directive 76/117/EEC in conjunction with the marking relating to the category

• the letter ”G” for apparatus group II for areasin which explosive mixtures of gas, vapour or mist with air mixtures are presentand/or the letter ”D” for areas where anexplosive atmosphere can form due to dust.

In addition and where required, any details thatare indispensable for the safety of operation alsohave to be affixed.

Provisional arrangementsBetween March 1st, 1996, the date on whichthe directive first applies, and complete harmo-nization from July 1st, 2003, there is a transitio-nal period during which both the old regulationsand the new directive can be applied. This longtransitional period facilitates the introduction ofthe new quality assurance system according tothe directive for the manufacturer. For the userof the apparatus, the apparatus marking mustclearly show whether the ”old” or the ”new”directive was applied.

Putting in circulation and commissioning of productsThe member states must not forbid, restrict orimpede the putting in circulation and commissio-ning of apparatus, protective systems and devi-ces that conform to the terms of this directive.Similarly. the putting in circulation of compo-nents covered by a certificate of conformitymust not be forbidden, restricted or impeded ifthey are to be built into a piece of equipment ora protective system in line with this directive.

The EU member states assume conformity withthis directive and with the conformity asses-sment procedures, if the apparatus, protectivesystems and devices are accompanied by theEC certificate of conformity, and if the productsare provided with the CE mark. Products that do not yet meet the requirementsof this directive, may be displayed at exhibitions,fairs and demonstrations, if a visible label clearlypoints to the fact that it will not be possible topurchase the product until compliance with thedirective has been ensured.

Procedure in the event of unsafe productsShould a member state discover that any appa-ratus, protective systems or devices with CEmark are unsafe, it can withdraw these from themarket and forbid their being put in circulation orcommissioning, or restrict their free circulation.

Marking examples:

S. Nr.: D 123456 2000 II 2 G 0102


CE marking

Products that fall within the scope of givendirectives must be provided with the CE markingby the manufacturer. This refers to products thatare covered by the directives according to thenew concept, that include requirements relatingto the technical properties of products. These EC directives constitute binding regulati-ons of the ”European Union”. That means thatthe compliance with these requirements is thecondition for marketing the products in Europe.When a product is provided with the CE mark,the conformity of the product with the relevantbasic requirements of all directives applicableto the products is confirmed. The marking is,therefore, an imperative requirement for the put-ting in circulation of the products within theCommunity, as well as in the country of origin.

The CE marking is only meant as evidence ofthe conformity with the directives for the supervi-sing authorities. It is, however, often mistaken asa quality mark and is, therefore, also requestedwithout a legal basis by the users.

The following directives are of special impor-tance for electrical apparatus:

• Directive 73/23/EECElectrical apparatus for use within defined voltage limits

• Directive 89/336/EEC Electromagnetic compatibility

• Directive 89/392/EEC Safety of machinery

• Directive 91/263/EEC Telecommunication equipment

• Directive 94/9/ECApparatus and protective systems for use inpotentially explosive atmospheres

When assessing which directives must beapplied to explosion-protected apparatus,it is necessary to differentiate between whetherthese directives are to be applied generally oronly to certain products.

• Directive 73/23/EECThis directive does not apply to ”Electricalapparatus for use in explosive atmospheres” (Exclusion as per annex II of the directive)

• Directive 89/336/EECThis directive is to be applied to any productsthat may cause electromagnetic interferencesor the operation of which may be impaired bysuch interferences

• Directive 89/392/EECArticle 1, clauses 4 and 5 of the directiveclearly state that this directive is notto beapplied to explosion-protected electrical apparatus

• Directive 91/263/EECThis directive applies to ”Electrical apparatusfor use in explosive atmospheres” onlyto avery limited extent. (Products for connection to the public tele-communication network)

• Directive 94/9/ECThis directive is to be applied to all products(including non-electric products) for use in apotentially explosive atmosphere

In addition to marking products with the CEmark, the manufacturer must issue a declarationof conformity for the product. This declaration ofconformity must clearly state

which directive was applied and accordingto which standards the tests were carriedout.

At present, due to the fact that the various direc-tives came into force at different times and tran-sitional periods have been determined, thedeclaration of conformity is the only means toclearly discern which directive was taken as abasis for the CE marking (e. g. directive94/9/EC, applicable as of: March 1st, 1996;obligatory application as of: July 1st, 2003).

As explained in the first paragraph, this allapplies to directives according to the new con-cept. Unlike for many other products, directivesfor explosion-protected apparatus already exi-sted at a very early date. Thus, the Europeaninterstate market had already been establishedfor these products.

Directives 76/117/EEC; 79/196/EEC;82/130/EEC

These directives defined as the distinctivemark for the putting into circulation of explosion-protected apparatus within the whole commu-nity.

Now, as a result, until 2003 (general obligatoryapplication of the directive 94/9/EC) the follo-wing special situation relating to explosion-pro-tected electrical apparatus:

Apparatus manufactured and certified in accor-dance with the old directive on explosion pro-tection, and simultaneous obligatory applicationof the EMC directive:

marking and certificate of conformityissued for the product by a testing labora-tory, and, at the same time, the CE markingaccording to the EMC directive and themanufacturer's declaration of conformity

Apparatus in accordance with the new directiveon explosion protection and simultaneous appli-cation of the EMC directive:

CE marking and comprehensive manufac-turer’s declaration of conformity

Type label according to new ATEX directive 94/9/EC

eLLK 92036/36CEAG Sicherheitstechnik GmbH, Senator-Schwartz-Ring 26, 59494 Soest

PTB 96 ATEX 2144 110-254 V 50-60 Hz

EEx ed IIC T4 110-230 V DC

Lampe: G13-81-IEC-1305-2 Ta ≤ 50 °C

PTB Nr. Ex-92.C.1801 X

Type label according to previous directive

eLLK 92036/36CEAG Sicherheitstechnik GmbH

EEx ed IIC T4 110-254 V 50-60 Hz

Lampe: G13-IEC-1305-2 110-230 V DC

Ser. Nr.: D189115 Tu ≤ 50 °C


Conformity assessment procedure

Apparatus Group I and II I and II I and II II

Category M 1 and 1 M 2 and 2 M 2 and 2 3

Field of • any apparatus • electrical apparatus • other apparatus • any apparatus application • if applicable • if applicable, • components (*) • safety and control

safety and safety and devicescontrol devices control devices • components (*)

• components (*) • components (*) • independent protective systems • I.C.-engines

Combination of EC type sample EC type sample Internal production Internal productionprocedures acc. test to annex III test to annex III control acc. to control acc. toIto the annexes plus quality plus quality annex VIII annex VIIIIII to IX ass. of production ass. of product plus submitting of

acc. to annex IV acc. to annex VIII technical documents or inspection of or conformity with to the designated products acc. to annex V design IV test lab

Alternative: Individual EC test acc. to annex IX

(*) Components without CE mark

Conformity assessment procedure forapparatus according to directive94/9/ECDepending upon the conformity assessmentprocedure to be applied, a notified body can beactive during the design and engineering phase,during the production phase or during both pha-ses. The applicable evaluation procedure is laiddown in the directive 94/9/EC in relation to theproduct, the apparatus group and the apparatuscategory.

Apparatus groups I and II, apparatuscategory M1 and 1In order to be permitted to affix the CE markingto his product, the manufacturer must arrangefor the following procedures to be carried out:

• EC-type examination by a notified bodyand

• either an inspection of the quality assu-rance for the production process or

• an inspection of the products.

Apparatus groups I and II, apparatuscategory M2 and 2With internal combustion motors and electricalapparatus, in order to be permitted to affix theCE marking on the product, the manufacturermust arrange for the following procedures to becarried out and/or ensure the following measu-res:

• EC-type examination by a notified bodyand

• either guarantee of constructional confor-mity or

• verification of the required quality level bymeans of the quality assurance procedurefor the products.

The internal production control procedure shallbe applied for all other apparatus in thesegroups and categories.

Apparatus group II, apparatus category 3In order to be permitted to affix the CE markingto the product, the manufacturer shall apply theinternal production control procedure.

The EC declaration of conformity must be inclu-ded with all products or batches of identical pro-ducts that are put into circulation. This does notapply for the report issued by the notified bodyas part of the inspection of the quality assurancesystem of the manufacturer or for the EC-typeexamination certificate.


The Equipment Safety Law(GSG)

As of January 1st, 1993 electrical apparatus forhazardous areas are covered by the equipmentsafety law. Untill then, the requirements for thequalification of equipment were based on theFactory Act (GewO), the statutory regulations(RVO) and the Equipment Safety Law. This dualresponsibilty hasbeen eliminated.

Now all measures relating to the in circula-tion of technical equipment are comprisedin the Equipment Safety Law. These measures serve for the protection ofemployees and consumers in accordance withthe harmonized right in the European Union.

If you are, however, looking for “hazardousareas” in the equipment safety law, you will notfind them. Instead of these it quotes “installati-ons requiring supervision”. These also include“electrical installations in particularly endangeredlocations”.

The equipment safety law now makes it possiblethat the safety requirements for installations andparts of these requiring supervision are enforcedupon the manufacturers and importers. Apartfrom that, it is now easier to implement ECdirectives relevant to the putting in circulation.

Decree concerning the puttinginto circulation of apparatusand protective systems for usein potentially explosive atmos-pheres – explosion protectiondecree (ExVO)

§1 Scope §2 Definitions§3 Safety requirements§4 Conditions for putting into circulation§5 CE conformity marking§6 Breaches of the regulations§7 Provisional regulations

The decree concerning explosion protectiondirectly converts the directive 94/4/EC intonational law. It applies for all apparatus, protec-tive systems, safety and control devices for usein and for potentially explosive atmospheres.The range of application for such apparatus(including non-electrical apparatus) applies toapparatus that features an inherent potentialignition source and can cause an explosion.Such apparatus, protective systems and devicesmay only be put into circulation if they fulfil therequirements of the directive 94/9/EC. The legis-lative body has granted a transition period up toJune 30th, 2003. Until this time apparatus maybe put into circulation according to the law fromMarch 23rd, 1994.

New version of the decree con-cerning electrical installationsin potentially explosive atmos-pheres (ElexV)

§1 Scope§2 Definitions§3 General requirements, authorization

for the issue of technical regulations§4 Further requirements§5 Exceptions§6 Federal installation§7 Measures for the prevention of an

explosive atmosphere§8 (omitted)§9 Repair of apparatus§10 (omitted)§11 Non-application of §9§12 Tests§13 Operation§14 Test certificates§15 Experts§16 Supervision of federal installations§17 Damages§18 German committee for explosion-

protected electrical installations§19 Provisional regulations§19a (omitted)§20 Breaches of regulations§21 (omitted)§22 (omitted)Annex (to §3, para. 1)

The second decree relating to the EquipmentSafety Law and the amendment of decrees rela-ting to the Equipment Safety Law converted theproduct requirements of the directive 94/9/ECinto national law by means of the ExVO andchanged the decrees that previously regulatedthe electrical explosion protection. Due to thetransition period up to June 30th, 2003, instal-lers and operators must now, depending uponrequirements, take two different decree textsinto consideration.The ElexV regulates the installation and opera-tion of electrical apparatus in potentially explo-sive atmospheres.The product requirements of the old ElexV (§8 –omitted) have been transferred to the ExVOdecree. Therefore, the ElexV now contains ope-rating instruction only. According to the new §3electrical installations in potentially explosiveatmospheres must be assembled, installed andoperated in keeping with the latest technologicaldevelopments. They may only be put into opera-tion if they comply with the explosion protectiondecree, that is with the directive 94/9/EC. All fur-ther paragraphs are described in the followingchapters.The legislative body (BMA) specifies standardsto Elex V in an administration regulation.


Specification of standards as defined by § 2 of the general administration regulation to ElexVPromulgation 5 of the BMA dated September 25th, 1996-IIIb5-35471-

The following standards (VDE specifications) according to § 2 of the general administration regulation to the decree concerning electricalinstallations in potentially explosive atmospheres (ElexV) dated February 27th, 1980 (Federal Gazette No. 43 dated March 1st, 1980) are listed:

1. Standards (VDE specifications) that were drawn up and passed by committees of the German Electrotechnical Commission in DIN and VDE (DKE)

DIN VDE 0105 Part 4 September 1988DIN VDE 0105 Part 9 May 1986DIN VDE 0107 October 1994DIN VDE 0165 February 1991DIN VDE 0170/0171 Part 1 A 102 March 1988DIN VDE 0170/0171 Part 13 November 1986DIN VDE 0848 Part 3 March 1985DIN VDE 0147 Part 1 (DIN 57147 Part 1) September 1983DIN VDE 0147 Part 2 August 1985

2. Standards (VDE specifications) that were taken over as national standards by the DKE from the European Standardization Committee CENELEC, with the exception of No. 3.

DIN VDE 0170/0171 Part 1 (EN 50014) March 1994DIN VDE 0170/0171 Part 2 (EN 50015) January 1995DIN VDE 0170/0171 Part 3 (EN 50016) May 1996DIN VDE 0170/0171 Part 4 (EN 50017) February 1995DIN VDE 0170/0171 Part 5 (EN 50018) March 1995DIN VDE 0170/0171 Part 6 (EN 50019) March 1996DIN VDE 0170/0171 Part 7 (EN 50020) April 1996DIN VDE 0745 Part 101 (EN 50053 Part 1) December 19871

DIN VDE 0745 Part 102 (EN 50053 Part 2) September 19901


DIN VDE 0750 Part 1 (EN 60601 Part1) December 19911

3. Standards (VDE specifications) that are referred to as European standards in a directive of the Council of the EC for the harmoniza-tion of the statutory regulations of the member states concerning electrical apparatus for use in potentially explosive atmospheres.

DIN VDE 0170/0171 Part 1 (1978) (EN 50014) incl. A1, A 2, 3 & 4 (May 1984) & A5 January 1987DIN VDE 0170/0171 Part 2 (1978)(EN 50015) incl. A 1 September 1980DIN VDE 0170/0171 Part 3 (1978)(EN 50016) incl. A1 September 1980DIN VDE 0170/0171 Part 4 (1978)(EN 50017) incl. A1 September 1980DIN VDE 0170/0171 Part 5 (1978)(EN 50018) incl. A1, A2 (May 1984) & A3 January 1987DIN VDE 0170/0171 Part 6 (1978)(EN 50019) incl. A1, A2 (July 1984) & A3 January 19872

as well as A4 July 1990A 5 May 1992DIN VDE 0170/0171 Part 7 (EN 50020) incl. A1 (September 1980) & A2 as well as January 19872

A 3 March 1992A 4 April 1992A 5 April 1992DIN VDE 0170/0171 Part 9 (EN 50028) July 1988DIN VDE 0170/0171 Part 10 (EN 50039) April 1982DIN VDE 0745 Part 100 (EN 50050) January 1987DIN VDE 0745 Part 101 (EN 50053 Part 1) December 19873



This promulgation replaces the promulgation of the Federal Minister for Labour and Social Order dated November 10th, 1994, Az.IIIb 6-35471 (Federal labour journal 1/1995, Page 42).

1 Only those paragraphs relating to the use fall under this number2 According to this edition of the standard, the notified bodies according to § 8, Para. 1, No. 1 of the

”old” ElexV may only certify electrical apparatus until 19963 Only those paragraphs relating to the products fall under this number

(Extract from the Federal Labour Journal 4/1998, Page 77)


These specified standards are now to be takeninto consideration for the installation and opera-tion of electrical apparatus in explosion-protec-ted installations.. In addition to this, the latesttechnological developments as reflected in theharmonized standards must also be considered.

Directive 1999/92/EC of the European Par-liament and Council dated December 16th,1999Structure of the directive 199/92/EC

Ruling part

Section Article HeadingI 1-2 General requirementsII 3-9 Duties of employer

3 Prevention of and protec-tion against explosions

4 Assessment of the explo-sion risks

5 General obligations6 Coordination obligations7 Areas with explosive

atmospheres8 Explosion protection

document9 Special regulations relating

to working materials andplaces of work

III 10-15 Other requirements

AnnexesI Classification of areas in which explo-

sive atmospheres can be present1. Areas in which explosive atmospheres

can be present 2. Classification of potentially explosive

atmospheres

II A Minimum requirement for theimprovement of the safety andhealth protection of employeeswho could be endangered byexplosive atmospheres

1. Organizational measures2. Explosion protection measures

B Criteria for the selection of appa-ratus and protective systems

III Warning signs for marking areasin which explosive atmospherescan occur

The aim of the European directive is to lay downminimum requirements for the improvement ofthe health protection and safety of employeeswho could be endangered by explosive atmos-pheres. The national legislative bodies are obli-ged to implement these requirements, but mayalso lay down additional measures on a nationalbasis.

Scope:The scope of application covers the areas inwhich employees can be endangered by explo-sive atmospheres. Here an explosive atmos-phere is defined as being a mixture of inflamma-ble gases, vapours, mists or dusts with air.

Reductions and assessment of explosionrisksIt is the duty of the employer to carry out mea-sures according to the following order of prece-dence:1. Prevention of explosive atmospheres,

where possible by the substitution of materi-als.

2. Prevention of the ignition of explosiveatmospheres.

3. Reduce harmful effects to a minimum.This concept is already known in Germany dueto the explosion protection directives of theemployers’ liability insurance association and ithas been put into practice for many years. Thenew aspect of this directive is the systematicmethod according to which the measures arelaid down and documented.After assessment of all the remaining explosionrisks, whereby the interaction of installations, thematerials being used, the processes and theirpossible interactions were taken into considera-tion, measures for the safety of employees atwork must be laid down to ensure their healthand safety at all times. Here special require-ments are imposed regarding the coordinationduties of the employer at the place of work.

Zone classification

The areas in which explosive atmospheres canoccur must be subdivided into zones accordingto Annex I of the directive. Here gases anddusts are each divided into three zones accor-ding to the probability of their occurrence.

Inflammable gases, vapours or mists:

Zone 0An area in which an explosive atmosphere com-prising a mixture of air with inflammable gases,vapours or mists is present for long periods orfrequently.

Zone 1An area in which an explosive atmosphere com-prising a mixture of air with inflammable gases,vapours or mists can form occasionally undernormal operating conditions.

Zone 2An area in which an explosive atmosphere com-prising a mixture of air with inflammable gases,vapours or mists does not normally occur oronly occurs for a short period under normaloperating conditions.


Inflammable dusts:

Zone 20An area in which an explosive atmosphere in theform of a cloud of inflammable dust found in theair can be present for long periods or fre-quently.

Zone 21An area in which an explosive atmosphere in theform of a cloud of inflammable dust found in theair can form occasionally under normal ope-rating conditions.

Zone 22An area in which an explosive atmosphere in theform of a cloud of inflammable dust found in theair normally does not occur or occurs for ashort period only under normal operating con-ditions.

With inflammable dusts it is also necessary toconsider the layers, deposits and accumulationsas a cause for possible explosive atmospheres.Normal operation is understood as being wheninstallations are being used according to thespecified parameters.

Explosion protection document

After the employer has classified the zones andmarked these areas in accordance with Annex IIIof the directive, he then has to issue the explo-sion protection document. First all the ascertai-ned explosion risks and the measures taken (pri-mary explosion protection) are documentedhere, together with the zone classification. Thisis followed by the documentation of the measu-res according to Annex IIA relating to the fulfil-ment of the minimum requirements. This inclu-des the areas of installations located in the non-potentially hazardous atmospheres that arenecessary for the safety of the potentially explo-sive atmosphere.

Annex II AMinimum requirements for the improvement ofthe safety and health protection of employeeswho can be endangered by explosive atmos-pheres.

1. Organizational measures- Appropriate instruction of employees- Written instructions and work release

notes• If necessary, written instructions for work

assignment• Work release system for hazardous tasks• Work release by authorized person

2. Explosion protection measures- Rendering any escaped Ex-atmosphere

harmless- Design according to the highest risk

potential- Avoidance of all ignition hazards

(e.g. static charge of persons)- Taking into operation if authorized in the

explosion document - Installation and operation according to

lowest explosion risk- If necessary, warning of Ex-atmosphere

(visual/acoustical)- Provision of escape facilities- Initial inspection by qualified person- Measures for risk assessment

• Hazards due to power failures• Manual operation of apparatus and protective

systems• Safe reduction of stored energy

Annex II BCriteria for the selection of apparatus and pro-tective systems

Unless otherwise specified in the explosion pro-tection document taking into account the riskevaluation, apparatus and protective systemsare selected in accordance with directive94/9/EC.

Zone Category0 or 20 11 or 21 1 or 22 or 22 1, 2 or 3

Annex IIIWarning sign for marking areas in which explo-sive atmospheres can occur.

In addition to these measures, it is necessary todocument how the place of work and the wor-king materials, including the warning sign, aresafely designed, serviced and operated. Themeasures for the safe use of working materialsare also to be documented in accordance withdirective 89/655/EEC.Before work is commenced, this documentmust be drawn up and revised in such a waythat any significant changes, extensions or rear-rangements of the place of work, the workingmaterials or the work process are taken intoconsideration.

Special regulations for working materials andplaces of work- up to 30.06.03 working materials to (All A)- from 01.07.03 new working materials (All A+B)- from 01.07.03 new places of work to (All)- up to 30.06.03 rearrange old places of work- from 01.07.03 rearrange places of work in the event of changes


Electrical apparatus foruse in potentially explosiveatmospheres

There is a certain interrelation between the limit-ing gap widths and the ratio of minimum ignitioncurrent. In order to be able to classify gases andvapours to meet the requirements of explosionprotection, it is, therefore, sufficient to defineonly one of the two properties for most of theindustrially employed gas/air and vapour/air mix-tures. Annex A to VDE 0170/0171/part 1/3.94 -DIN EN 50 014 states the classification of anumber of industrially important gases andvapours according to their limiting gap widthand their minimum ignition current.

PrinciplesDivision into explosion groupsIt would not be economical to construct allexplosion-protected electrical apparatus to meetthe most stringent requirements with regard toignition temperature, explosive force and ignitioncapability of the gases. For this reason, electricalapparatus is divided into explosion groups andtemperature classes. Group I: encompasses electrical apparatus

for underground mines that are sus-ceptible to the hazard of firedamp,e.g. coal mines

Group II: encompasses electrical apparatusfor all other hazardous areas

Sub-division of the explosion groupsaccording to the explosive force andminimum igniting currentA sub-division into A, B and C is prescribed forsome types of protection for Group II electricalapparatus. For flameproof enclosures it is basedon the maximum experimental safe gap (MESG),and for intrinsically safe apparatus on the mini-mum igniting current (MIC).

Maximum experimental safe gap(MESG)In the case of electrical apparatus in which arcsor sparks occur during normal operation, anexplosive atmosphere that has penetrated intothe enclosure can be ignited. However, the pro-pagation of an already initiated ignition from wit-hin the enclosure to the surrounding atmos-phere can be prevented if the flame is forced topass through narrow gaps. As it passes throughthe gap, heat is taken away from the flame andthe temperature is reduced to such a degreethat combustion no longer takes place and theflame is extinguished. With electrical apparatusin the type of protection "Flameproof enclosure”the classification of the gases and vapoursbased on the maximum experimental safe gap(MESG) are carried out in testing vessels with agap length of 25 mm. The testing vessel descri-bed in the IEC publication 60079-1 A must beused as the standardization method for determi-ning the MESG.

Minimum ignition current (MIC)As far as intrinsically safe electrical apparatusare concerned, gases and vapours are classifiedaccording to their ratio of minimum ignition cur-rent. In order to ignite an explosive atmosphere,the ignition spark must contain a minimumenergy content. The necessary minimum energycontent is a specific property of the ignitablegases and vapours. A criterion for this is theratio of the minimum ignition current (MIC) to theminimum ignition current of laboratory methane.The MIC is determined according to a standardi-zed method and must be carried out with appa-ratus as defined in EN 50 020 annex B.

Explosion Limiting gap Ratio ofgroups width minimum

in mm ignition current

II A > 0,9 > 0,8

II B 0,5 to 0,9 0,45 to 0,8

II C < 0,5 < 0,45


Ignition temperature and temperatureclasses

The maximum surface temperature of the elec-trical apparatus must not reach the ignition tem-perature of the potentially explosive atmosphere.The ignition temperature of an inflammable sub-stance is determined by means of a test appara-tus. It is the lowest temperature on a heated wallat which the inflammable substance will justabout ignite in a mixture with air. The ignitiontemperature of liquids and gases is determinedaccording to the method defined in DIN 51 794.The determination of the ignition temperature ofinflammable dusts is specified in the IEC publi-cation IEC 61241-2-1.The ignition temperatures of the different mixtu-res vary considerably. Whereas a mixture of airwith town gas will only ignite at 560 °C, a mixture of air and petrol will already ignite at ca.250 °C.This classification makes it possible to take eco-nomical aspects into account for the design ofthe electrical apparatus. The requirements rela-ting to the construction increase with the ascen-ding order of the letters marking the explosiongroups. The requirements relating to the admis-sible temperature of the surfaces that come intocontact with the explosive atmosphere(decrease in surface temperature), rise with theascending order of the numerals for the tempe-rature classes. It is, therefore, left to the manu-facturer to decide the requirements accordingto which he wants to design and be permitted tomark his explosion-protected electrical appara-tus. It goes without saying that apparatus thatfulfils the requirements of temperature class T3,is also suitable for use in explosive atmospheresin the temperature classes T1 and T2.

Classification of maximum surface temperatureson group II electrical apparatus

Temperature Max. admiss. surface temperature Ignition temperatures in °Cclass in °C of the apparatuses of inflammable substances

T 1 450 > 450

T 2 300 > 300 ≤ 450

T 3 200 > 200 ≤ 300

T 4 135 > 135 ≤ 200

T 5 100 > 100 ≤ 135

T 6 85 > 85 ≤ 100

Classification of gases and vapours in explosion groups and temperature classes

T 1 T 2 T 3 T 4 T 5 T 6

I Methane

II A Acetone Ethylalcohol Petrol AcetaldehydeEthane I-amyl acetate Diesel fuel EthyletherEthylacetate n-butane Aviation fuelAmmonia n-butylalcohol HeatingBenzol oilsAcetic acid n-hexaneCarbonmonoxideMethanolPropaneToluene

II B Town gas Ethylen(lamp gas)

II C Hydrogen Acetylene Carbondisulphide


Types of protection for explosion-protected apparatus

General requirements acc. toEN 50 014

According to the European standard DIN EN 50014 (VDE regulations 0170/0171/part 1) explosion-protected apparatus can bedesigned to meet the requirements of varioustypes of protection. Here, seven types of protec-tion based on different principles are taken intoconsideration.

Electrical apparatus for hazardous areas mustconform to the general terms of the Europeanstandard EN 50 014 and to the specific require-ments for the type of protection for which theyare built. Particularly harsh operating conditions,the effects of moisture, high ambient temperatu-res and other special stresses might possiblyrequire additional measures.Special requirements listed in the standard mustbe observed for enclosures made of plasticsand light alloys. Special requirements apply to: • locks and fixings,• bushings and connecting pieces,• Cables and conduit entries

In accordance with the requirements of the stan-dards electrical apparatus built according toEuropean standards must be subjected to atype test by an independent testing station andto a routine test by the manufacturer. The typetest establishes whether the technical docu-ments (description and drawings) and the testsamples are in conformity with the respectivestandards. The mechanical strength is verifiedby an impact and drop test.

Compliance with admissible surface and windingtemperatures is verified by measurements. Spe-cial tests are specified for• the surface resistance,• the verification of the thermal resistance of

plastic,• the thermal shock resistance of glass parts of

luminaires and inspection windows.

Explosion-protected electrical apparatus mustbe marked in a clearly visible position. Accordingto EN 50 014 it is not necessary to certify ormark apparatus where none of the values of 1.2 V, 0.1 A, 20 µJ or 25 mW is exceeded.

Explosive atmosphere Explosive atmosphere Explosive atmosphere

Oil immersion ”o” – EN 50 015 Pressurization ”p” – EN 50 016 Sand filling ”q” – EN 50 017


Generalrequirements


Flameproof enclosure ”d” – EN 50 0158 EN 50 014 Increased safety ”I” – EN 50 019

Explosiveatmosphere


”n”

Intrinsic safety ”I” – EN 50 020 Encapsulation ”m” – EN 50 028 ”n” – EN 50 021

Sandfilling

inert gas

Oil filling

Pottingcompund

Types of protection


Oil immersion ”o”EN 50 015/VDE 0170/0171, Part 2Definition: A type of protection for electrical appa-ratus where the complete electrical apparatus orparts of electrical apparatus are rendered safeby immersing them in oil, so that the explosiveatmosphere cannot come into contact with thepotential ignition source.With this type of protection, the ignition source isso deeply immersed in an oil-filled enclosure thata transmission of the flame to the area above theoil level is prevented. This requires that the ther-mal output fed to the oil, the thermal energy andthe resulting energy density be taken intoaccount.

This type of protection is chiefly applied to swit-chgear and transformers. With such switchgear,the switching arc is drawn in oil and does not,therefore, come into contact with the explosivemixture. Besides making sure that a sufficient oillevel is provided in any operating position of theswitchgear, the use of a suitable oil that must notdecompose as a result of the switching arc is ofspecial importance. In addition to this, care hasto be taken to ensure that the temperature of theswitchgear does not rise too high. An increasedoil temperature could, in turn, become an ignitionsource. The long term quality of the oil must alsobe monitored, as soot changes the properties ofthe oil.

Oil-immersed switchgear was widely used by thechemical industry for the local switching ofmotors. As a result of the transition to remotecontrols and an increase in the number ofinterlocks, it has lost much of its significance.Nowadays oil-immersed switches are only instal-led in exceptional cases. Moreover, the use of oil-immersed switches for portable equipment is notpermitted. They also require a lot more mainten-ance. Repairs are more difficult, because the oilbox has to be removed prior to starting. This isoften undesirable inside the work area.

Pressurization ”p”EN 50 016/VDE 0170/0171, Part 3The type of protection Pressurization preventsthe penetration of an explosive atmosphere intothe enclosure containing electrical apparatus.This is achieved by means of an inert gas insidethe enclosure that is maintained at a pressureabove that of the surrounding atmosphere. Theoverpressure of at least 0.5 mbar can be main-tained with or without continuous purging withinert gas. As a rule, air serves as an inert gas. Previously,this type of protection was called separateventilation ”f”.There are two types of pressurization: • Pressurization with continuous purging• Pressurization with leakage compensation

The inert gas must be enter into or exit theenclosure outside of the hazardous area. Withboth types, the enclosure of the apparatus andall its ducts must be purged prior to operationby a volume of gas that equals the five-foldvolume of the enclosure. During operation theoverpressure must be monitored and, if theoverpressure drops, a warning signal given orthe apparatus switched off. Normally, a flow gauge is used in conjunctionwith a time lag relay to monitor the purging. Thetime lag relay starts running at the same time aspurging. As soon as the required volume of inertgas has flown through, the time lag relay relea-ses the switching-on of the apparatus that isbuilt into the enclosure. If the purging fails orthere is a drop in the overpressure during opera-tion, the flow gauge or a manometer closes acontact which switches off the apparatus orgives a warning signal.The encapsulation of the apparatus must con-form to a minimum degree of protection IP 40 toEEN 60529. It must prevent the propagation offlames, sparks or ignitable particles to thepotentially explosive atmospheres.

Examples for pressurization ”p”• Electrical machinery with higher rating • Switch cabinets• Control panels• Switch rooms• Transformers• Measuring instruments• Resistor instruments• Liquid starters• Luminaires• Current and voltage transformers• Communication devices

Example of pressurized apparatus


Ex-floodlight for high pressure lamps: flameproof

enclosure in combination with a terminal compart-

ment in type of protection ”increased safety”

Sand filling ”q”EN 50 017/VDE 0170/0171, Part 4With the type of protection Sand filling, theenclosure of an electrical apparatus is filled witha fine-grained filling material. This prevents thedevelopment of an arc inside the enclosure thatcould ignite the explosive atmosphere surroun-ding the enclosure. In addition to this, neither anignition caused by flames nor an ignition as aresult of increased temperatures on the enclo-sure surface should be possible.

With this type of protection the enclosure isgenerally filled with quartz sand that has to meetspecific requirements with regard to the grainsize, purity, moisture content and disruptivestrength. A filling material other than quartz ispermitted if it conforms to the requirements. Theenclosure must preferably be made of metal.Other materials are only permitted if theirmechanical and thermal properties have beensubjected to a test and described in detail. Inany case, the resistance to pressure must beverified by a static pressure test.

The built-in electrical components must be ade-quately insulated, irrespective of the insulatingeffect of the filling material. With naked live partsthere must be sufficient space between theparts and between the parts and the enclosurewall.

The filling material is compressed, whereby,depending on the built-in instruments and requi-rements, the layers of filling material must have aspecified thickness. A perforated metal sheetmay be laid in the filling as a screen to reducethe thickness of the layers.

Examples for sand filling ”q”:• capacitors• bell transformers• control circuits with hot or sparking parts• electronic apparatus

Flameproof enclosure ”d”EN 50 018/VDE 0170/0171, Part 5With this type of protection those parts that arecapable of igniting an explosive atmosphere arebuilt into a flameproof enclosure that withstandsthe explosion pressure if an inflammable mixtureis ignited inside it. In this way a transmission ofthe explosion to the explosive atmosphere sur-rounding the enclosure is prevented

The flameproof enclosure principle can be com-pared to a one-way street • an explosive atmosphere can penetrate into

the enclosure of the electrical apparatus,• but, in the event of an explosion inside the

enclosure, a transmission of the explosion tothe outside is prevented.

The flameproof enclosures generally featurejoints for the reduction of the high gas pressurethat is generated in the event of an explosion.These joints have two functions. On the onehand, the reduction of the gas pressure, and, onthe other hand, the cooling down of the tempe-rature of the explosion gas being releasedthrough the joint to such a degree that an explo-sive atmosphere surrounding the flameproofenclosure is not ignited.

A series of experiments was carried out todetermine the gap dimensions for each type ofexplosive so that the flammable atmospheresurrounding the atmosphere is not ignited.Information on the determination of the maxi-mum gap widths can be found in the section"Fundamental principles of explosion protec-tion”.

The type label of the flameproof apparatus mustshow the explosion group. Group II C apparatuscan also be operated in areas for the groups IIBand II A, and group II B in areas for group II A.

The temperature class of apparatus indicatesthe permitted limiting temperature up to whichthe outer surfaces of such apparatus may rise.

The type of protection "d” is often used formotors and switchgear. Very little heat is gene-rated in switchgear, so that during operation thesurface temperature of the enclosure is onlyslightly higher than the temperature of theatmosphere surrounding the apparatus. In gene-ral, the switchgear satisfies the requirements ofthe temperature classes T5 and T6 and, there-fore, also the requirements of the classes withhigher permissible temperatures.


By comparison, motors dissipate more heat,especially with higher outputs. In order not toexceed the permissible limiting temperature, itmay be necessary to lower the rated output of aflameproof motor as compared to that of a stan-dard motor. Oil and liquids that can form explosive mixtureswith air during decomposition must not, underany circumstances, be introduced into flame-proof apparatus.

Examples for the application of type ofprotection ”d”• Motors with sliprings and commutators• Three-phase squirrel cage motors • Switchgear with N/O and N/C contacts such

as motor protection switches, circuit breakers,air-break contactors

• Control units, plugs and sockets• Fusegear• Transformers• Measuring instruments• Current and voltage transformers• Resistors• Luminaires• Communication apparatus

Ex-d distribution board.

Enclosure with type of protection ”increased

safety” and flameproof encapsuled components.

Combined types of protectionUntil now it has been common practice in Ger-many to combine a flameproof enclosure with aconnection box in the type of protection ”increa-sed safety”. Such a combination is used forluminaires and motors.

This has the advantage that the installer doesnot have to open the flameproof enclosure whencarrying out installation maintenance. In compli-ance with the degree of protection IP 54, thecable can be lead into the ”increased safety”type connection box.


Increased safety ”e”EN 50 019/VDE 0170/0171, Part 6The protection category ”increased safety” isused for electrical apparatus that, under normaloperating conditions, does not form an ignitionsource. Consequently, apapratus that producesarcs or sparks in the course of normal operationor apparatus that generates ”excessive” heatare not suitable for this type of protection. The-refore, this type of protection is not used forswitchgear, pushbuttons and slip ring motors.

In particular, this type of protection has provedeconomical and practical for electrical apparatussuch as terminal boxes, junction boxes, three-phase squirrel cage motors, luminaires, solenoidvalves and transformers.

It must not be possible for leakage currents orarcs as a result of external influences, such aswater and foreign matter, to develop. Enclosu-res that contain uninsulated live parts must fulfila minimum degree of protection IP 54. Thedegree of protection IP44 is sufficient for enclo-sures that contain insulated parts only. If rotatingelectrical machines that are installed in cleanrooms and are regularly controlled by qualifiedpersonnel, IP 20 is sufficient for group II. Therestricted range of use is stipulated on themachine. All enclosures are submitted to amechanical impact test as part of the type test.

It is possible to establish a flexible lead connec-tion by means of a trumpet-shaped cablegland. To eliminate the possibility of damageduring normal operation, all parts of the cableentry must comply with the mechanical impactrequirements. Connection terminals must besafeguarded against self-loosening and mustprovide sufficient contact pressure.

The increased safety is ensured by means of theimproved insulation of live parts and by largerclearances and creepage distances comparedto standard apparatus. With this type of protec-tion the limiting temperature also applies to allsurfaces inside the enclosure.

All insulating material is subject to naturalageing. In order to prolong the service life of theinsulating materials of windings, compared tothe windings in standard apparatus, the limitingtemperature is decreased. This reduces thedanger of damage to the windings as a result ofearth leakages or interturn short-circuits.

The following table lists the limiting temperaturesfor insulated windings in apparatus in the type ofprotection "increased safety”.

Ex-terminal box in the type of protection

”increased safety”

Limiting temperatures for Measuring Insulation classinsulated windings procedure A E B F H

All windings, except insulated R* °C 90 105 110 130 155single-layer windings in nominal operation

T* °C 80 95 100 115 135

Single-layer insulated windings R* °C 95 110 120 130 155in nominal operation

T* °C 95 110 120 130 155

Limiting temperature at the end of time tE R* °C 160 175 185 210 235

*) R = resistance measuring procedure, T = thermometer measuring procedure


Protective devices for windings shall ensure thatonly the reduced limiting temperature valuesspecified in the table are reached.

Motors are used with overcurrent protectiondevices that are released in the event of difficultstarting conditions or of a failure. After severalhours of operation at nominal rating a motor rea-ches its continuous operating temperature. If therotor stalls due to a malfunction and the supplyof voltage is not disconnected, the motor drawsan increased current, the starting current IA, thatis the rated current IN many times over. If themotor is not switched off, it reaches the limitingtemperature after the time tE. The time tEdepends on the starting current ratio IA/IN.

The overcurrent protection device must switchoff the motor before it reaches the limiting tem-perature, i. e. within the time tE. The protectiondevice fulfils the same function when the motoris stalled, irrespective of whether the motor iswarm or cold.

If the rotor and the stator take different times toheat up, the shorter time will be taken as tE. Thetype label and the certificate of approval of themotor state the time tE and the ratio of the star-ting current IA to rated current IN.

The protection devices must keep the specifiedtripping times within a tolerance of +/-20 %.

Fig. 3 shows the characteristic of a thermal relaywith an example for checking. The relay, that isset at the rated current of the motor, triggers at7.4 times the rated current within a period that isshorter than the time tE. The relay is suitable forprotecting the motor.

The protection devices must also switch off themotor in the event of the failure of one phase.Here, current-dependent thermal overcurrentrelays or circuit breakers can be used if, forexample, they are equipped with a phase failureprotection to VDE 0660.

With motors in connection the protectivedevice must fulfil the following conditions. In theseized motor and with phase failure, the trippingtime shall be tested with 0.87 times the motorstarting current, whereby the tripping time mustbe within the time tE. This test is necessary todetect the increased temperature caused by theunequal loads of the windings as it cannot beidentified by means of the mains-current con-sumption.

In general, electrical motors of the type ”increa-sed safety” may only be used in continuousoperation and for normal, seldom recurringstarts so as to prevent that the rises in tempera-ture occurring during the start exceed the per-missible limiting temperatures. In the case ofmotors in the low-voltage range, thermal motor

protection has the advantage that, due to itstemperature gauges with positive temperaturecoefficient embedded in the windings, the rise intemperature during the start-up period in swit-ching operation is monitored.

Examples for increased safety ”e”• Three-phase or single-phase rotor with cage

rotor• Transformers• Current and voltage transformers• Measuring instruments• Ballasts for luminaires• Luminaires• Resistors• Liquid starters• Accumulators• Communication apparatus• Connection boxes for any electrical apparatus

Encapsulation ”m”EN 50 028/VDE 0170/0171, Part 9With the type of protection encapsulation "m”,those parts that are capable of igniting an explo-sive atmosphere are embedded in a castingcompound with sufficient resistance to environ-mental influences. The explosive atmospherecan neither be ignited by sparking nor by hea-ting, both of which may occur within the encap-sulation.

Duromers, thermoplastics and elastomers withand without fillers and/or other additivies may beused as casting compounds. The properties ofthe casting compound must fulfil the require-ments of EN 50 028 (e.g. temperature index T1to IEC 60216-1) within the given temperaturerange.The selection of the casting compound for aspecific application depends on the function thatthe compound has to fulfil in the apparatus. Theencapsulation must ensure the efficiency of thetype of protection, even in the event of permissi-ble overloads and certain internal fault conditi-ons.

The casting compound may contain hollow spa-ces for the accommodation of componentssuch as relays, transistors etc. up to a volume of100 cm3.

If the compound in encapsulated apparatus isdirectly exposed to the surroundings, the com-pound must comply with the requirements of EN50 014 for non-metallic materials.

Examples for encapsulation ”m”• Relays, signal and control units• Transistors, sensors• Film resistors, indicators• Ballasts (conventional type)• Electronic ballasts • Subfractional horsepower motors• Solenoid valves

3 4 5 6 7 8 9 10

2

5

10

20

40

t E m

in

IA / IN

s

Fig. 1: Minimum values for the time tE

0

A

B

C

1

θ in

°C

t (1) in h t (2) in s

2

tE

3 4 5 6 7,4 8

2

5

10

20

40

t in

s

IA /IN

11

1

Fig. 2: Explanation how to calculate the time tEA max. permissible ambient temperatureB temperature in rated operationC limiting temperaturet timeθ temperature1 heating-up in rated operation2 heating-up with motor being stalled

Fig. 3: Tripping characteristic of the thermal

relay from cold

Time tE of the motor to be protected 11 s

IA/IN of the motor to be protected 7.4


Intrinsic safety “i“

EN 50 020/VDE 0170/0171, Part 7The most recent type of protection againstexplosion hazards by electrical apparatus andinstallations is called "intrinsic safety”. The mostcommon types of protection were conceived forelectrical power engineering applications. As aresult of increasing automation within hazardousareas, there has been an ever increasingdemand for explosion-protected measurementand control devices. Intrinsically safe circuitsonly have a low energy content, that is not suffi-cient to ignite an explosive mixture. Thus, forthese circuits, the creation of a type of protec-tion that makes use of this physical principle isthe obvious solution.

Technical terms

Intrinsically safe circuitUnlike all the other types of explosion protection,where the explosion protection is always relatedto the individual apparatus, the type of protec-tion “Intrinsic safety“ takes the complete circuitinto account.

Definition of an “Intrinsically safe circuit“An intrinsically safe circuit is a circuit in which nospark or thermal effect will be produced that iscapable of causing the ignition of a definedexplosive atmosphere, whereby the test conditi-ons for normal operation and defined fault con-ditions specified in the standard are to be takeninto account.

Intrinsically safe electrical apparatusDepending on the design and purpose, appara-tus in the type of protection “intrinsic safety“ issubdivided into “intrinsically safe“ and “associa-ted“ electrical apparatus.

Intrinsically safe electrical apparatusIntrinsically safe electrical apparatus is electricalapparatus in which all the circuits are intrinsicallysafe.Distinction is made between the following typesof intrinsically safe apparatus:– Active intrinsically safe apparatus– Passive intrinsically safe apparatus without

stored energy– Passive intrinsically safe apparatus with stored

energy

Associated electrical apparatusAssociated electrical apparatus is apparatus inwhich not all circuits are intrinsically safe, butwhich contains circuits that can affect the safetyof the intrinsically safe circuits to which it isconnected.Associated apparatus can be:– either electrical apparatus conforming to

another type of protection stated in the“General requirements“ of the European standard 50 014, on account of which it is suitable for use in the respective potentiallyexplosive atmospheres;

– or electrical apparatus that does not conformto any type of protection and, therefore, may not be used in potentially explosiveatmospheres.

Fundamental data

Minimum ignition energy A minimum ignition energy is required to ignitean explosive mixture. As the result of an externalignition source, for example an electric spark, ahigh temperature is generated locally in a smallvolume area of an explosive atmosphere, resul-ting in combustion. The heat produced by thespark and the ensuing combustion heats theneighbouring layers, while, at the same time,due to heat conduction, energy is dissipated tothe outside. If the dissipated heat is higher thanthe heat supplied and generated, a propagationof the combustion to neighbouring volume areasis not possible.

Only if the amount of energy supplied by theexternal ignition source is sufficient for the tem-perature of the neighbouring layers to rise abovetheir ignition temperature, the combustion isautomatically propagated and an explosionresults.

The type of protection “intrinsic safety“ makesuse of this fundamental knowledge. The electri-cal values of a circuit are limited to such adegree that the minimum ignition energy requi-red for an ignition is not reached.

Definition of the minimum ignitionenergyThe minimum ignition energy of a gas/air or avapour/air mixture is the lowest possible electrical energy occurring when a capacitor isdischarged that is still capable of igniting themost volatile ignitable mixture of gas/air orvapour/air at atmospheric pressure and20 °C.

FB remote I/O for Zone 1 under harsh operating

conditions

LB remote I/O for instrumentation and Zone 2


Fig. 1:

Ohmic circuits

Minimum ignition current

to be applied for electrical

apparatus containing cad-

mium, zinc, magnesium or

aluminium

10 V 20 V 50 V 100 V 200 V 500 V10 mA

20 mA

50 mA

100 mA

200 mA

500 mA

1 A

2 A

5 A

II C

I

II AII B

Sub-division into groupsDepending on their minimum ignition energy,inflammable substances are divided into thegroups I, IIA, IIB and IIC. The sub-division isidentical to that according to the ignition break-down capacity that is also decisive for to thetype of protection "flameproof enclosure". In thecase of intrinsically safe electrical apparatusgases and vapours are sub-divided on the basisof the ratio of their respective minimum ignitioncurrent (MIC) to the minimum ignition current oflaboratory methane.

Sub-division A ratio of the MIC > 0.8Sub-division B ratio of the MIC between

0.8 and 0.45Sub-division C ratio of the MIC < 0.45

Limiting ignition curves

The energy set free in an intrinsically safe circuitin the event of a failure must be limited to such adegree that the occurrence of an ignition isunfailingly prevented.The limiting ignition curves for the individualgroups are established with the aid of a standar-dized spark test apparatus.

As the probability of the ignition of a mixture alsodepends on the number of switchingoperations, according to EN 50020 at least1000 switching operations must be performed,whereby an ignition must not take place underany circumstances.

Depending on the design of the intrinsically safecircuit, the existence of stored energy has to betaken into account. If there are capacitances inthe intrinsically safe circuit, these are loadedonto the voltage of the circuit. The energy storedin the capacitor is 0.5 CU2 (C = capacitance, U = voltage). In the event of a short-circuit theenergy stored in the capacitor is released inaddition to the energy supplied by the associa-ted apparatus.

The same conditions apply when there are induc-tances in the circuit. If there is a flow of currentthrough an inductance, the stored energy will be0.5 LI2 (L = inductance, I = current). This energy isreleased additionally in the event of an interrup-tion.For these reasons all three borderline cases, i. e.ohmic circuits, capacitive circuits and inductivecircuits have to be taken into consideration.The European standard EN 50 020 contains limiting ignition curves for these conditions.

Categories of intrinsically safe and associated electrical apparatus

Intrinsically safe electrical apparatus and intrinsi-cally safe components of associated electricalapparatus are divided into two categories, -ia-or -ib-.

Safety level -ia-If a single fault or any combination of two faultsoccurs during normal operation, the electricalapparatus of the category -ia- must not becapable of causing an ignition. Here the following safety factors have to betaken into consideration:Safety factor 1.5 during normal

operation and with one faultSafety factor 1.0 with two faults

Explosion Limiting gap Ratio ofgroups width minimum

in mm ignitingcurrent

II A > 0.9 > 0.8

II B 0.5 upto 0,9 0.45 upto 0.8

II C < 0.5 < 0.45


Fig. 2: Capacitive circuits

Minimum igniting voltages to be applied to group

IIC electrical apparatus. The curve marked Sn is

only to be applied to electrical apparatus not con-

taining any cadmium, zinc, magnesium or alumi-

nium.

Fig. 3: Inductive circuits

Minimum igniting currents to be applied to

electrical apparatus containing cadmium, zinc,

magnesium or aluminium at E = 24 V.

1 V 3 V 10 V 30 V 100 V 300 V 1000 V

C = 40 Ω (Cd)

C = 15 Ω (Cd)C =5,6 Ω (Cd)

(Cd)

(Sn)

0,01 µF

0,03 µF

0,1 µF

0,3 µF

1,0 µF

3 µF

10 µF

30 µF

100 µF

300 µF

1000 µF

3000 µF

10.000 µF

5 mA 10 mA 20 mA 50 mA 100 mA 200 mA 500 mA 1 A100 µH

200 µH

500 µH

1 mH

2 mH

5 mH

10 mH

20 mH

50 mH

100 mH

200 mH

500 mH

1 H

I

II AII B

II C

Safety level -ib-Category -ib- electrical apparatus must not becapable of causing an ignition during normaloperation and with the occurrence of a singlefault.Here the following safety factors have to betaken into consideration:Safety factor 1.5 in normal operation and

with one fault

Constructional requirements

Any components on which the intrinsic safetydepends (with the exception of transformerswhich are subject to special conditions), mustnot be charged with more than 2/3 of their ratedcurrent, rated voltage or rated capacity, even inthe event of faults (e. g. mains voltage at theinput side of electronic circuits).

Types of limiting modules

Safety barriers with diodesSub-assemblies comprising diodes or Zenerdiodes that are protected by a fuse or a resistormay be used as safety barriers between intrinsi-cally safe circuits and a non-intrinsically safe cir-cuits. The input current of such barriers must besuch that they can be connected to a mainssupply with a maximum short-circuit current of1.5 kA.

Apparatus with galvanic isolationTransformers that, for example, are built into intrinsically safe power supplies must ensure asafe galvanic isolation between the primary andthe secondary circuit. The data that is relevantfor the intrinsically safe circuit is determined bythe output characteristic of the transformer andany external circuits (voltage limitation by diodes,current limitation by resistors or by the electro-nics).

Isolation of intrinsically safecircuits from non-intrinsicallysafe circuits

Connection piecesIn order to avoid any mistakes when connectingor bridging conductors, the connection piecesfor intrinsically safe circuits must be safely isola-ted from the connection pieces of a non-intrinsi-cally safe circuit. For this purpose the connec-tion terminals of the intrinsically safe circuit can,for example, be installed at a distance of at least50 mm from the connection pieces of each non-intrinsically safe circuit or they can be separatedby an isolating barrier or an earthed metal bar-rier. These barriers must either reach up to 1.5mm from the enclosure wall or they must ensurea minimum clearance of 50 mm between theconnection pieces.

Isolation of insulated leads of intrinsi-cally safe circuits and non-intrinsicallysafe circuitsThe distance between the conductors ofinsulated leads must satisfy specifiedrequirements. With the exception of varnishesand similar coatings, this insulation is consideredto be a solid insulation. The clearances aredetermined by the addition of the radial thickn-ess of the insulation on the wires. The minimumclearances are laid down in EN 50 020.e. g. when U =/< 60 V 3 mm

when U =/> 750 V 8 mm

The voltage U is the sum of the voltages of theintrinsically safe and the non-intrinsically safe cir-cuits. This clearance is not required, – if the leads of the intrinsically safe or the non-

intrinsically safe circuits are furnished with anearthed screen, or,

– if, with category -ib- electrical apparatus, theinsulation of the leads of the intrinsically safewires withstands an AC test voltage of 2000V. In addition to this, care must be taken thatno inductive or capacitive interferences fromthe non-intrinsically safe circuit can result inthe intrinsically safe circuit.

Apparatus for intrinsically safecircuits

As with all other types of protection, generally allassociated electrical apparatus used in the int-rinsically safe circuit and the intrinsically safeapparatus must be tested and certified. Accor-ding to EN 50014 the only exception is appara-tus where, according to the data given by themanufacturer, none of the values 1.2 V; 0.1 A;20 µJ or 25 mW is exceeded.

Intrinsically safe apparatus where the electricaldata and the thermal behaviour can be clearlydefined and that conform to the applicable con-structional requirements, do not need to betested or certified.This applies, for example, to:• switches• plugs and sockets• terminal boxes• measuring resistors• single semi-conductor components• coils (moving coil instruments)• capacitors• electric position sensors (DIN 19 234)

It is absolutely essential to comply with thegeneral requirements according to EN 50 014and for the design of enclosures and connectionboxes with regard to the surface resistance orthe choice of aluminium alloy (surface resistanceof plastic enclosures < 109 ohms).


Design of intrinsically safe circuits

When setting up an intrinsically safe circuit withonly one intrinsically safe apparatus and oneassociated apparatus, the limiting values for thepermissible external capacitance and induc-tance indicated on the type label of the associa-ted apparatus are binding for that circuit.

Based on the maximum possible feed-in energyof the associated electrical apparatus, now it isonly necessary to check the thermal behaviourof the intrinsically safe apparatus. When severalintrinsically safe circuits are interconnected (e. g.several pieces of associated apparatus act onone piece of intrinsically safe apparatus), a moredetailed check of the intrinsic safety is required.

It is necessary to determine the maximum vol-tage and current values which, due to the inter-connection, occur in a fault condition. Here thefault consideration in accordance with EN 50020 (for example, 1 fault with one intrinsicallysafe circuit or category -ib-) has to be applied tothe interconnected system.

The simplest method is based on the assump-tion that all the associated electrical apparatustakes on the sum of the maximum values of cur-rent and voltage values. If this fault considerationis not successful (inadmissibly high values), amore thorough check has to be carried outbased on the assumption of the faults possiblefor the individual categories. The check relating to the intrinsic safety of a cir-cuit is to be documented in detail.

Specification of permissible externalinductances and capacitances of sup-ply units for intrinsically safe circuitsUntil now the maximum values for La and Ca ofsupply units for intrinsically safe circuits were laiddown by some testing and certification authori-ties in such a way that the operator only had tocheck whether the connected inductances andcapacitances La and Ca (including cables andconductors) were always less than the maxi-mum values. Here it was assumed that theconnected inductances and capacitances areconnected to the supply unit simultaneously andin concentrated form, thus constituting a criticalload. These testing institutes took this simulta-neous occurrence of La and Ca into considera-tion for ia circuits and non-linear ib circuits. Asother testing institutes work on the assumptionthat either an external capacitance (with negli-gible inductance) or an external inductance (withnegligible inductance) is connected, they certi-fied the data that was more favourable for themanufacturer. Due to pressure from the market,the testing institutes that had previously workedon the basis of a simultaneous occurrence ofcapacitance and inductance when specifyingthe safety-related data now felt forced to adoptthe less restrictive approach. By way of a theo-

retical example (full utilization of the externalconnected load), it can, however, be proved thatthe safety factor 1.5 (according to the old data)can be reduced to 0.91 based on the newobservations. Therefore, in critical cases wherethere is a simultaneous occurrence of concen-trated inductances and capacitances, it isnecessary to consult a specialist (manufacturer,expert).

Intrinsically safe circuits with zenerbarriersNormally intrinsically safe circuits must be insula-ted. They may be connected to earth, if this isnecessary for functional reasons They must,however, be earthed, if this is imperative forsafety reasons. Earthing is only permitted at onepoint by connection to the potential equalizationwhich must exist in the whole area where theintrinsically safe circuit is set up.

Since, with safety barriers, there is no galvanicisolation between the intrinsically safe and thenon-intrinsically safe circuits, for safety reasonsthere must be a perfect connection to earth.

Working on and testing of int-rinsically safe circuits

As intrinsically safe circuits must be designed sothat they cannot cause an ignition, it is generallypermitted to work on them while they are live.When using measuring instruments it is, howe-ver, necessary to bear in mind the fact that suchinstruments may contain inner energy stores (e.g. the inductance of a moving coil instrument)which might neutralize the intrinsic safety.

Further informationFurther information on the subject of intrinsicsafety is available from CEAG ApparatebauHundsbach GmbH & Co. KG in the brochure:“Hazardous area protection for instrumentationand control – a practical guide“ by Dipl.-Ing.Wolfgang Gohm.


Intrinsically safe electrical systems “i“

EN 50039 / VDE 0170/0171, Part 10

Technical terms

Intrinsically safe electrical systemsAll the interconnected electrical apparatus docu-mented in a system description, where the cir-cuits that are to be used wholly or partly in apotentially explosive atmosphere are intrinsicallysafe.

Certified intrinsically safe electricalsystemsAn intrinsically safe electrical system for which acertificate has been issued confirming that thetype of that electrical system conforms to theEuropean standards.

A certificate for each individual piece of electricalapparatus in an intrinsically safe electricalsystem is not necessary, provided that the elec-trical apparatus can be clearly identified.

Non-certified intrinsically safe electrical systemsAn intrinsically safe electrical system where theintrinsic safety can be verified without a doubtbased on the knowledge of the electrical cha-racteristics of the certified intrinsically safe elec-trical apparatus, the certified associated electri-cal apparatus and of the non-certified "simpleapparatus” and based on the knowledge of theelectrical and physical characteristics of theconnecting leads.

System descriptionA document drawn up by the system designengineer in which the electrical apparatus, theirelectrical characteristics and the characteristicsof the connecting leads are described. The term“system design engineer“ designates a personwho is responsible for the intrinsic safety of thesystem.

Each part of an intrinsically safe electrical systemthat is used in a potentially explosive atmos-phere must be either classified as category ia orib. This does not mean that the whole systemhas to be assigned to one single category. Thecategories ia and ib are explained in detail in thechapter Intrinsic safety “i“.

Further information on intrinsically safe circuitscan be found in EN 60 079-14 VDE 0165, Part 1“Electrical installations in potentially explosiveatmospheres“.


Cap lamps for use inmines susceptible to firedamp

EN 50033/VDE 0170/0171Part 14

The requirements relating to the design andtesting of cap lamps for use in mines suscep-tible to firedamp (electrical apparatus for use inGroup I potentially explosive atmospheres) arelaid down in this standard

Technical terms

Cap lampAn apparatus comprising a headpiece, aconnecting cable and rechargeable secondarycell(s)/battery in a container.

Constructional requirements The cap lamp must be designed in such a waythat• the rated voltage does not exceed 6 V,• the current does not exceed 1.5 A when ope-

rated as intended,• the lamp rating is not higher than 6 W,• the circuit behaves as if it only contains active

resistances. According to the requirements ofEN 50 033, this circuit must be protected by asafety fuse, that is integrated in the apparatus.

The housing of the cap lamp headpiece mustprovide protection against the ingress of dustand water according to the minimum degree ofprotection IP 54. The headpiece housing must have a speciallocking device according to EN 50 014..

The transparent protective lens of the headpiecemust withstand the mechanical requirements inaccordance with EN 50 014. It must only bepossible to remove the protective lens and, ifavailable, the protective guard and collar afterthe locking mechanism has been released.

The switch for the incandescent lamp(s) must belocated on the headpiece. The battery container must provide a minimumprotection against the ingress of dust and wateraccording to IP 54 for the electrical connections.The fuse must be protected in such a mannerthat, if it ruptures, the surrounding mixture of airand gas (methane or charging gas) is not igni-ted.

The flexible cable connecting the battery contai-ner and the headpiece must features a centralcarrying pieces and must be provided with asheathing that is resistant to fatty acids and toflames.

Firedamp-protected cap lamp with nickel-cadmium

battery


Zone 0 apparatus

“Special requirements for the design, testing andmarking of electrical apparatus in apparatusgroup II, category 1G“ EN 50 284 VDE0170/0171, Part 12-1This European standard lays down detailedrequirements for apparatus in apparatus group II, category 1G. The apparatus must bedesigned in such a way that it guarantees a veryhigh degree of safety in normal service. Category 1 apparatus is intended for use inpotentially explosive atmospheres in whichexplosive mixtures of air with gases, vapours ormists occur continuously, for long periods or fre-quently. This standard also applies to apparatusthat is mounted in the barriers between differentpotentially explosive atmospheres. It also inclu-des requirements for apparatus that is installedoutside the potentially explosive atmosphere,but that is connected electrically to category 1apparatus (associated apparatus).

It supplements the standards EN 50 014 andEN 50 020 to EN 50 028 and is intended toadapt the safety level provided for by thesestandards to the extremely high risks.

In order to eliminate the ignition hazards that canemanate from the electrical circuits of the appa-ratus, the necessary measure of safety must eit-her be guaranteed, even if two faults that areindependent of each other occur, by applying asingle constructional protection measure, or, ifone constructional protection measure fails, itmust be ensured by a second, independentconstructional protection measures.Permissible individual constructional protectionmeasures are: • Apparatus and circuits in accordance with

the requirements of EN 50 020, category “ia“

• Encapsulated apparatus in accordance withthe requirements of EN 50 028 supple-mented by the additional requirements ofthis standard.

Combinations of constructional protection measuresElectrical apparatus must fulfil the requirementsof two standards of the series EN 50 014 to EN50 020 (ib) and EN 50 028 independently ofeach other. These combined standardized typeof protection must be based on different physi-cal protection principles. It must be possible totest them independently of each other. The follo-wing table illustrates the possible combinationsof barriers with the types of protection wherebarrier elements are used.

Apparatus and parts thereof for use in Zone 0must also be built in such a way that• ignition sources due to impact or friction

sparks are excluded.In the case of apparatus with parts thatmove during operation, light metals mustnot be used at the possible friction orimpact points or at other accessible points.

• no ignition hazards due to dangerous elec-trostatic charges can occur. Special conditi-ons apply for enclosures and parts of enclo-sures made of moulded plastic

Connection techniqueAs far as possible, connections for Zone 0apparatus and parts thereof should be locatedoutside the Zone 0.

Hazardousarea1)

Barrier

Less hazardous area2)

Electricalapparatus

Hazardousarea1)

Barrier3)Electricalapparatus

Gap3)

Barrier3)

Naturalventilation

(Gap3))

1) Category 1 apparatus required2) Category 2 apparatus or less required3) Flameproof joint and barrier can be swapped round

Type of construction

Requirements according to the thickness t of the barrier(i) t ≥ 3 mm, no additional measures

(ii)3 mm > t ≥ 1 mm

(iii)1 mm > t ≥ 0.2 mm

(“X“ symbol)

(iv)t < 0.2 mm

(“X“ symbol)

– standardizedtype ofprotection and

– no ignitablesparks duringoperation(e.g. no openswitchingcontacts)

Type of protectionIntrinsicSafety “ib“

Not permissible

– standardizedtype ofprotection and

– no ignitablesparks duringoperation(e.g. no openswitchingcontacts)

– standardized type of protection

– standardized type of protectionand

– flameproof joint (broken line)

– standardizedtype ofprotection

a) Barrier

b) Barrier and gap

c) Barrier and ventilation


Hazardousarea1)


Electricalapparatus


Zone 2 apparatus

Type of protection “n“EN 50 021/VDE 0170/0171 Part 16

The type of protection “n“ applies to electricalapparatus of the apparatus category 3G, that,under normal and certain abnormal operatingconditions, are not able to ignite a surroundingexplosive atmosphere. These operating conditi-ons are laid down by the manufacturer as partof the electrical and mechanical design data andit is essential that the user observe them. Theaim of this type of protection is to find an econo-mical compromise between the normal industrialstandard and the high safety requirements forthe types of protection for apparatus in the cate-gory 2G.

General requirementsAs with the already familiar types of protectionfor the apparatus category 2G, the generalrequirements for electrical apparatus (e.g. sur-face temperature, design, cables, clearancesand creepage paths, …) also apply here.

Potential ignition sourcesBasically distinction is made between non-spar-king apparatus, that does not give off anypotential ignition sparks during operation, andapparatus that gives off arc or sparks or produ-ces hot surfaces during normal operation. In thecase of this apparatus, that, on principle, fea-tures potential ignition sources, it is necessary totake additional protective measures to allow itssafe operation.

Non-sparking apparatusDepending upon the type of apparatus (e.g.electric machines, luminaires), non-sparkingapparatus must fulfil additional conditions, sothat no potential ignition sources can developduring normal operation. In addition to the appa-ratus category 3G, the apparatus is also markedwith “nA“, whereby this combination of lettersstands for “non-sparking apparatus“.

Apparatus that gives off arcs or sparksor produce hot surfaces Apparatus that gives off arcs or sparks or pro-duces hot surfaces during normal operationmust be safeguarded by additional measures insuch a way that these ignition sources cannotignite a surrounding explosive atmosphere. Themeasures that are necessary for this are model-led on the familiar types of protection for appa-ratus category 2G, whereby the safety require-ments are less stringent. Parts of apparatus can,of course, be protected by the types of protec-tion of EN 50 014. A group of additional measu-res involves the safe isolation of the potentialignition source from the explosive atmosphereby means of the technical construction, gene-rally a special enclosure, or designing the appa-ratus in such a way that flame transmissionthrough the enclosure is not possible. The “her-

metically sealed devices”, the “sealed devi-ces“ and the “encapsulated devices“ arebased on the fact that the explosive atmosphereand the potential ignition source remain safelyisolated from each other. The “enclosed swit-ching devices“ are modelled on the familiartype of protection “Flameproof enclosure“ to EN 50 018. With the “non-ignitable compo-nent“ ignition is prevented by constructionalmeasures, while, at the same time, the type ofgas is taken into consideration. The marking“nC“ is used for this group of measures, whe-reby the permissible type of gas (IIA, IIB, IIC)must also be stated. The “restricted breathingenclosure“ is another permissible explosionprotection measure with the marking with “nR“.The enclosure is designed in such a way that anexplosive atmosphere can only enter it in arestricted measure. The “simplified pressu-rization“ is modelled on the familiar type of pro-tection “Pressurization“, whereby simplifiedmeasures were approved. This apparatus ismarked with “nP“.A further explosion protection measure is the“restricted energy apparatus“ with the mar-king “nL“ and the marking for the suitable gasgroup (IIA, IIB, IIC). This is based on the type ofprotection “Intrinsic safety“, whereby the safetyfactors are less stringent.

DocumentationAs it is possible to have a combination of variousexplosion protection measures for apparatuscategory 3G, it is strongly recommended thatthe operator study the associated documenta-tion carefully, because all the safety instructionsissued by the manufacturer must be observedfor maintaining safety.

Explosion-protected plugs and sockets for zone 2 and 22




Explosiveatmosphere

Explosive atmosphere Explosive atmosphere

Hermetically sealed devices “nC“ Sealed devices “nC“ Encapsulated devices “nC“

Enclosed switching device “nC“ Non-sparking apparatus “nA“ Non-ignitable component “nC“

Retricted energy apparatus “nL“ Restricted breathing “nR“ Simplified pressurization “nP“

Inert gas

Types of protection “n“

Selection for zone 2 according to EN 60 079-14

Apparatus forzones 0,1

Apparatusdesigned for zone 2

(EN 50 021 “n“)

Recognizedindustrial standard

No IEC standardavailable => “s“

No ignitable hot surfaces

Arcs or sparks

Energy restrictionSafety factor 1 to EN 50 021

Written evaluation by a specialist

no

yes


Ignition sources

Inflammable dust can be ignited by electricalapparatus in various ways:- by apparatus surface temperatures that are

higher than the ignition or glow temperatureof the respective dust. The temperature atwhich the dust ignites is dependent on theproperties of the dust, on whether it is pre-sent in the form of a cloud or deposits, onthe thickness of the layer and on the type ofheat source;

- by sparks at electrical parts such as swit-ches, contacts, commutators, brushes orsimilar;

- by the discharge of stored electrostaticenergy;

- by radiated energy (e.g. electromagneticradiation);

- by magnetic impact or friction sparks or arise in temperature originating from theapparatus.

To avoid ignition hazards, it is necessary that:- the temperature of any surfaces on which

dust deposits can form or that can comeinto contact with a cloud of dust are keptat a temperature that is lower than the limiting temperatures laid down in EN 50028-1-2;

- all parts with electric sparks or with tempe-ratures above the ignition or glow tempera-ture of the dust are built into an enclosurethat prevents the ingress of dust in a suita-ble manner, or

- the energy of the electric circuits is limited tosuch a degree, that sparks or temperaturethat could ignite inflammable dust are avoided;

- all other ignition sources are avoided.

Electrical apparatus for use in areas with inflammable dustwith protection by the enclosure

Design and testingEN 50028-1-1 VDE 0170/0171Part 15-1-1This European standard applies to apparatuswhere protection is afforded by the enclosurewith limitation of the surface temperature. Itincludes requirements for the design, construc-tion and testing of this electrical apparatus ofapparatus group II, categories 1, 2 and 3. Thetype of protection is based on the limitation ofthe maximum surface temperature of the enclo-sure and on the limitation of the ingress of dustby the use of “dust-tight“ or “dust-protected“enclosures. The principles of this standard canalso be applied if the hazard is caused by fibresor flue dusts. The use of electrical apparatus inareas that contain both explosive gases andinflammable dusts – simultaneously or separa-tely – requires additional protective measures.

Requirements on electrical apparatusin the categories 1 and 2For the main part it is necessary to fulfil therequirements of EN 50 014:e.g. mechanical strength of enclosures, thermalstability, thermal shock tests.In addition to this, it is also necessary to takespecific requirements for dusts, that are descri-bed in the standard EN 500281-1-1, intoaccount. For example, with plugs and sockets itis necessary to ensure that no dust can fall intothe socket.This apparatus must be tested and certified byan independent testing station.

Requirements for electrical apparatusin category 3 The requirements relating to the strength hasbeen reduced to the measure required for industrial apparatus. It is, however, necessary totake into account that the TI value is decisivewhen selecting materials. It should only be possible to release locking devices that arenecessary to maintain the type of protection witha tool.

MarkingApparatus in categories 1 and 2

Name/symbol of testing stationCertification number1 or 2 to show the categoryD for dust explosion protection followed by themaximum surface temperature T as definedcoefficient, e.g. T 170 °C

Apparatus in category 3

3 to show the categoryD for dust explosion protection followed by themaximum surface temperature T as definedcoefficient, e.g. T 170 °C

The following table (page 40) lists further stan-dards or intended standards for dust explosionprotection.

Electrical apparatus foruse in areas withinflammable dusts

Explosion-protected installation and control units for

zone 1 and 21


IEC 61241 Electrical apparatus for use in the presence of combustible dust

IEC 61241-1Electrical apparatusprotected by enclosures

IEC 61241-1-1Design and testEN 50281-1-1:1998-09DIN EN 50281-1-1(VDE 0170/0171 Part 15-1-1): 1999-10

IEC 61241-1-2Selection, installation andmaintenanceEN 50281-1-2:1998-09DIN EN 50281-1-2(VDE 0165 Part 2): 1999-11

IEC 61241-2-2Method for determiningminimum ignition energyof dustDIN EN 61241-2-2(VDE 0170/0171Part 15-2-2): 1996-04

IEC 61241-2-3Methods for deter-mining the minimumignition energy ofdust/air mixturesEdition: 1994-09[under modification, workshift to CEN/TC 305]

IEC 61241-2-4Methods for determi-ning minimum ignitionenergy of dust[under modification, workshift to CEN/TC 305]

IEC 61241-2-1Method for determiningminimum ignitionenergy of dustEN 50281-2-1:1998-09DIN EN 50281-2-1 (VDE 0170/0171Part 15-2-1): 1999-11

E DIN IEC 31H/47/CDV(VDE 0170/0171 Part 1505):1995-05[Intended asVDE 0165 Part 102]

E DIN IEC 31H/67/CD(VDE 0170/0171 Part 15-4):1997-08[Intended asVDE 0170/0171 Part 15-4]

IEC 31H/84/CD[Intended asVDE 0170/0171 Part 15-5]

IEC 61241-2Methodsfor determining

IEC 61241-3Classification of areaswhere combustible dustare or may be presentEN 61241-3:199X-XX

IEC 61241-4Electrical apparatus;type of protection pressurization “p“ (pD)

IEC 61241-5Electrical apparatus –intrinsic apparatus

Notes:Documents, authoritative worked out by IEC, are guided by number 6.Documents, authoritative worked out by CENELEC, are guided by number 5.Documents in brackets are actually not published.

Table of EN 50 028-1-1 (VDE 0170/0171, part 15-1-1) 1999-10, S 3


Electrical installations in potentially explosiveatmospheres

Obligations of the manufacturer

The manufacturer must develop electrical appa-ratus for use in potentially explosive atmosphe-res in keeping with the latest technological developments, whereby the general and specificdesign regulations are to be taken into account.If specified in the standards, testing by an inde-pendent testing station must be arranged. Theapprovals issued by the testing station and/orthe declarations issued by the manufacturersare to be placed at the disposal of the operator.It is the duty of the manufacturer to manufactureeach piece of electrical apparatus in such a waythat it complies with the test documentation andthe test samples. Finally, he is also obligated tosubject each piece of explosion-protected appa-ratus manufactured to a routine verificationand test and, after successful completion ofthis test, to mark the apparatus accordingly. If“special conditions“ apply for the use of theapparatus, the manufacturer must provide theinstaller or the operator with this information in asuitable form together with the apparatus.

Obligations of the installer

Electrical installations in potentially explosiveatmospheres must be installed in compliancewith the statutory regulations and the latesttechnological developments. The introduction ofthe new ElexV dated December 13th, 1996means that, depending on the respective requi-rements, for a transition period (30.06.2003) theinstaller must apply either the old version ofElexV (version dated January 1994) or the newversion of ElexV in the case of apparatus accor-ding to the ATEX directive. In addition to the standard defined by the legis-lative body for the installation, VDE 0165 (1991-02) “Setting-up of electrical installations inpotentially explosive atmospheres“, the generallyrecognized rules of engineering (VDE directives)must also be taken into consideration.

Thus, the installer is obligated to install suchapparatus in accordance with VDE 0165 Regu-lations for the setting-up of electrical installati-ons in hazardous areas and VDE 0100 The set-ting-up of power plants with rated voltages upto 1000 V. Inasmuch as the provisions of VDE0101 The setting-up of power plants with ratedvoltages of more than 1 kV and/or VDE 0800Telecommunication also for the installations,these must also be observed.

If the installer is not also the operator, the instal-ler shall issue an installation certificate at theoperator’s request. This certificate confirms thatthe electrical installation conforms to the require-ments of ElexV. If such a certificate is available,additional testing by the operator prior to com-missioning is no longer necessary.

Obligations of the operator

According to § 12 of ElexV, the operator is obligated to have the electrical installations inthe hazardous areas of his plant checked by aqualified electrical engineer with regard to theirproper condition, namely• prior to commissioning (can be omitted if

an installation certificate is available) and• at regular intervals.

Here, with regard to the operational require-ments, the operator must calculate the intervalsin such a way that any faults occurring areascertained in time. The tests must, however,be carried out at least every three years. Testingat given intervals can only be omitted if theinstallations are under the constant supervisionof a responsible engineer. If requested by thecompetent authority, a test record with specifiedentries must be kept.According to §13 ElexV it is the duty of the ope-rator to keep an electrical installation in a poten-tially explosive atmosphere in a proper state, tooperate it accordingly, to monitor it constantlyand to carry out any necessary repair or mainte-nance measures immediately.

Finally, it is also the duty of the operator toensure that the electrical installation is operatedcorrectly.

The operator must report any explosion causedby the operation of the installation to the control-ling authority (§ 17 ElexV), regardless of whetheror not any damage was done. Ignitions on theinside of flameproof apparatus that are not pro-pagated to the surroundings need not be repor-ted.

The controlling authority has the right to requestthe submission of a special expert’s certificate at the expense of the opera-tor. The purpose of this expertise is to ascertainthe cause of the damage and, if applicable, todetermine any additional safety required for theinstallation.

Example of application: Explosion-protected apparatus in an oil terminal


Setting-up of electricalinstallations in potentiallyexplosive atmospheres

Before an electrical installation can be set up ina potentially explosive atmosphere, the personresponsible for the operation of the installation(company management) has to analyze andassess the explosion risks.Until now the evaluation of the explosion hazardcould be carried out by applying the “Directivefor the avoidance of hazards caused by explo-sive atmospheres with a compilation of exam-ples“, the explosion protection directive (EX-RL).Now, in addition to this directive, that until nowwas only valid in Germany, there are also theEuropean standards EN 1127-1, “Explosiveatmospheres – explosion protection,Part 1: Fundamental principles and methods“and EN 60079-10, the German translation ofwhich was published as in DIN VDE 0165, Part101, “Subdivision of potentially explosive gasatmospheres“.There will be changes when the European direc-tive (199/92/EC) “Minimum requirements for theimprovement of the health protection and safetyof employees that could be at risk due to explo-sive atmospheres“, that was passed on Decem-ber 16th, 1999, becomes national law.

The decree concerning electrical installations inpotentially explosive atmospheres (ElexV),together with the nationally valid VDE 0165/2.91and the associated series of standards VDE0170/0171 relating to the types of protection, aswell as the decree concerning inflammableliquids (VbF) with its technical rules (TRbF) mustbe observed for the technical design of theinstallation. As part of the harmonization pro-cess, the German translation of the Europeanstandard EN 60079-14 has been in existence asthe German standard DIN VDE 0165, Part 1,“Electrical installations in potentially explosiveatmospheres“ since August 1998. With regardto potentially explosive dusts atmospheres, theGerman translation of EN 500281-1-2 is availa-ble as the German standard DIN VDE 0165,Part 2, “Electrical apparatus for use in atmos-pheres with inflammable dust; Part 1.2: Electri-cal apparatus with protection by enclosure – sel-ection, installation and maintenance“, publishedin November 1999.

The national accident prevention regulations(UVV) must also be observed as a further sourceof installation requirements.

All the standards, rules and regulations for thesetting-up of electrical installations that havebeen listed until now are additional explosionprotection requirements, as it is assumed thatthe electrical installation already complies with allother laws, decrees and rules (low-voltage direc-tive, electromagnetic compatibility, VDE 0100,…). In the event of contradictions or discrepan-cies in the standards, the explosion protectionhas priority.

DIN VDE 0107 applies to locations used formedical purposes. DIN VDE 0166 applies tolocations endangered by explosive substances. DIN VDE 0105, Part 9 applies to the operationof electrical installations in potentially explosiveatmospheres. DIN VDE 0118 applies to the set-

ting-up of electrical installations in undergroundmines.In addition to this, the following must be obser-ved for all potentially explosive areas:

DIN VDE 0100DIN VDE 0101DIN VDE 0800

Safety-related data for potentiallyexplosive gas atmospheres

First it is necessary to test whether there are anyinflammable substances in the respective instal-lations and, if they exist, in what form (solid,liquid, gas, dust, …) and under what operatingconditions. If, on the basis of the process para-meters, the formation of an explosive atmos-phere is to be expected (primary explosion pro-tection not possible or applicable), the respec-tive area of the installation is divided into zonesaccording to the probability of the occurrence ofthis hazardous explosive atmosphere. EX-RL(Section B 5.2) and EN 60079-10:”Subdivsion ofpotentially explosive gas atmospheres” provideguidelines for the compilation of the necessarysafety-related data.

Division of potentially explosiveatmospheres into zones

If an installation contains inflammable liquids,depending upon the limiting temperature abovethis liquid, an inflammable gas mixture can form.This limiting temperature (Tfl) is known as theflash point and constitutes an important safetylimiting value. The limiting values of a large num-ber of substances can be found in tabular com-pilations (Nabert and Schön).

Methanol Tfl = 11 °CPhenol Tfl = 82 °CBenzine Tfl = -11 °C

If the value is not known, it can be determined ina standardized testing facility (e.g. at the FederalPhysico-Technical Institute – PTB – in Braun-schweig).

The formation of an explosive atmosphere canbe prevented (primary explosion protection), e.g.in the case of methanol in a container, by con-stantly maintaining the methanol at a tempera-ture of less than 1 – 6° C (at atmospheric pres-sure). As this maximum temperature is belowthe flash point, it can be assumed that no hazar-dous explosive atmosphere can form.

The atmospheric boundary conditions must beobserved as an essential condition, as, in gene-ral, the apparatus to be used is only approvedand certified for these conditions.

Atmospheric conditions are defined as beingpressures between 0.8 bar and 1.1 bar and mix-ture temperatures from –20°C to +60°C, inclu-ding all the usual additives found in air (e.g. moi-sture). However, in addition to the atmosphericconditions, the structure of the surface can alsoinfluence the flash point.


plan. When determining the areas, it is neces-sary to proceed cleverly to avoid a “patchwork“of various different zones. In some individualcases this can mean the allocation of more strin-gent zones for part of the area. With regard tosimple and safe maintenance, a uniform basicinstallation is also recommended.

After defining the zones, the local areas in whichthe occurrence of a hazardous explosive atmos-phere is to be expected must be clearly anddurably marked using the prohibition sign V2,“Fire, open flames and smoking prohibited“ (Fig. 1) and the warning sign, “Warning – explo-sive atmosphere“ (Fig. 2) in accordance withVBG1, VBG125 and DIN 40012, Part 3.

Temperature class – Explosion group

The temperature class and the explosion groupare values that depend on the substance (seealso: Sub-division of electrical apparatus) andthey are documented within the scope of thezone classification according to the respectivesubstances. For an appropriate zone delimita-tion it is necessary to determine the relevanttemperature class and explosion group of aninstallation, whereby the most critical parame-ters must always be selected.

Atmospheric conditions

All the previously listed directives, laws, decreesand standards are based on the assumption ofan explosive atmosphere. An explosive atmos-phere comprises an explosive mixture of gases,vapours, mists or dusts with air, including theusual additives (e.g. moisture), under atmos-pheric conditions. According to the nationaldirectives, atmospheric conditions are definedas total pressures of 0.8 bar to 1.1 bar and mix-ture temperatures from –20° C to +60° C.As a rule, all standards are based on this princi-ple, as the standardized tests of the test institu-tes also carry out tests according to the atmos-pheric conditions.In practice there are applications where thelimits of the atmospheric conditions are excee-ded, such as, for example, those found insideprocess engineering installations. Under theseconditions some safety-related parameters (flashpoint, ignition temperature) can also change.

Dependent on the local ventilation, the pressureratios, the leakage rate and a large number ofother parameters, the occurrence of an explo-sive atmosphere comprising a mixture of air,inflammable gases, vapours or mists is definedby the following zones according to the probabi-lity of its occurrence:

Zone 0 Zone 0 includes areas in which an explosiveatmosphere comprising a mixture of air withgases, vapours or mists is present constantly,for long periods or frequently.

Zone 1Zone 1 includes areas in which the occurrenceof an explosive atmosphere due to gases,vapours or mists can be expected to occuroccasionally.

Zone 2Zone 2 comprises areas in which an explosivegas atmosphere due to gases, vapours or mistsis not expected to occur; but, however, if oneoccurs, in all probability it is only seldom and fora short period.

The zones for the occurrence of explosiveatmospheres comprising air and inflammabledusts are defined as follows:

Zone 20Zone 20 comprises areas in which an explosiveatmosphere due to dust/air mixtures is presentconstantly, for long periods or frequently.

Zone 21Zone 21 comprises areas in which an explosiveatmosphere due to dust/air mixtures can beexpected to occur occasionally.

Zone 22Zone 22 comprises areas in which an explosiveatmosphere due to whirled-up dust is notexpected to occur; however, if one occurs, in allprobability it is only seldom and for a shortperiod.

For the sake of completeness, the old zone defi-nitions for dust areas, that could remain in exi-stence during the transition period (max. until2006), are listed below:

Zone 10Zone 10 comprises areas in which a hazardousexplosive atmosphere is present for a long timeor frequently.

Zone 11Zone 11 comprises areas in which the occur-rence of a hazardous explosive atmosphere as aresult of the stirring-up of dust deposits is to beexpected occasionally.

The extent of the individual zones can be deter-mined on the basis of the compilation of exam-ples in EX-RL, or of EN 60079-10 or of thedecree concerning inflammable liquids (VbF) andthe associated technical rules (TRbF)and it canbe documented relatively easily by way of a

Fig. 1: Prohibition sign V2

“Fire, open flames and smoking prohibited“

Fig. 2: Warning sign

“Warning – explosive atmosphere“


Selection of electrical apparatus

After completion of the zone classification andthe determination of the most critical tempera-ture class and the explosion group, the electricalapparatus can now be selected.

Here the ruling principle says that only the elec-trical apparatus that is absolutely essentialshould be installed in the potentially explosiveatmosphere.

On principle, the apparatus must be selectedand installed in such a way that it is sufficientlyprotected against external influences that canaffect the explosion protection, e.g. chemicalinfluences (solvents), moisture (spray water, con-densation), or vibration.

Due to the validity of the ATEX directive, whenselecting apparatus it is necessary to give closeconsideration to the legal basis according towhich the apparatus is put into circulation.

Apparatus before the validity of theATEX directive (Directive 94/9/EC)This apparatus is currently still predominantlyavailable and may be put into circulation untilJune 30th, 2003. The characteristics that havechanged due to the introduction of the ATEXdirective are outlined below.

The conditions according to §8 ElexV (old) mustbe fulfilled when supplying apparatus accordingto the old law, whereby, in addition to the typeexamination certificate, the apparatus must bemarked with the symbol . Moreover, if appli-cable, the apparatus requires a special note inthe type examination certificate stating that itcan be used in zone 0 or 10. The type examina-tion certificate must be available as documenta-tion to the operator of the installation (§8 oldElexV). If the type examination certificate requi-res that special conditions be taken intoaccount, the certificate must be available “onsite“, so that the technical personnel operatingthe apparatus can take the contents of the certi-ficate into consideration at all times (§14 oldElexV).This marking is not required for the zones 2 and11. The requirements for apparatus for thezones 2 and 11 are specified in VDE 0165/02.91.An essential formal criterion for zone 2 is fulfilledif, after fulfilling the requirements, the manufactu-rer of the apparatus declares that the apparatusmay be used in zone 2. This can, for example,take the form of an entry in the catalogue. If,with this apparatus, the operating temperatureexceeds 80° C, the maximum surface tempera-ture must be stated to allow the installer to takethe temperature class into consideration.

Apparatus according to the ATEXdirective (Directive 94/9/EC)If apparatus is supplied according to the ATEXdirective, it must also be marked with the sym-bol . In addition to this, the CE mark mustalso be affixed to the apparatus. Here, it shouldbe noted that apparatus exists according to theold law with the CE marking, namely if it isalready subject to another legal area that hasalready been harmonized (e.g. EMC, machinedirective). Marking apparatus with the apparatuscategory is new. In the case of apparatus groupII (apparatus group I = underground mines,including any surface installations; apparatusgroup II = other areas) this marking is carried outin conjunction with the category number and theletter G (GAS) for gases or D (DUST) for dusts:

1G for zones 0, 1,2 1D for zones 20, 21, 222G for zones 1,2 2D for zones 21, 223G for zone 2 3D for zone 22

(2D is to be used forconductive dusts)

The documentation associated with the appara-tus is to be regarded as yet another innovation.The type examination certificate is no longer anobligatory part of the documentation.

The manufacturer or the person authorized byhim has to provide a declaration of conformityin which he declares the conformity of the appa-ratus with the valid regulations. In addition tothis, the manufacturer must draw up operatinginstructions in a community language and, ifrequired, in the language of the country of use.One aspect of the operating instructions is thedescription of the intended use. The new aspectis the description of all the necessary safetyinformation (e.g. from the type examination certi-ficate) and of all details relating to the safe use ofthe apparatus. The operator of the apparatusmust observe these operating instructions in full,otherwise the apparatus loses its approval.

Selection of apparatus according tothe temperature classesAs already described in the previous section, atemperature class (T3) is allocated to aninflammable substance (e.g. hydrogen sulphide)(TZ = 270° C). For this example only apparatuswith the temperature class T3 to T6 may beused. Thus, the maximum surface temperatureof the apparatus cannot ignite the surroundingexplosive atmosphere.


When determining the temperature class ofapparatus, one generally works on the assump-tion that the ambient temperature ranges from–20° C to +40° C. If the apparatus is to be usedin another (usually higher)ambient temperature,this apparatus must be designed for this tempe-rature, certified and marked accordingly. In thecase of certain apparatus, a temperature classrange (e.g. T3-T4) is given. Here, for example, itis necessary to consider the influence of themedium (measurement medium) on the maxi-mum surface temperature and, therefore, on thetemperature class. The connection of the mea-surement medium with the temperature class isstated in the type examination certificate or inthe operating instructions. The installer and,later, the operator are responsible for the correctselection and maintaining of the temperatureclass.

Fundamental installation requirements

On principle, the VDE regulations DIN VDE0100, 0101, ….etc. and, in additon, the regula-tion DIN VDE 0165 with the currently valid edi-tion dated February 1991 apply to the setting-upof electrical installations in potentially explosiveatmospheres. This is a purely national installa-tion standard, that is specified in ElexV (6thproclamation of the BMA dated February 18th,1998-IIIb5-35471-). In the course of the harmo-nization process, the European standard EN 60079-14 relating to the setting-up of electricalinstallations in potentially explosive gas atmos-pheres, DIN VDE 0165, Part 1, "Electrical instal-lations for potentially explosive gas atmosphe-res, Part 14: Electrical installations in potentiallyexplosive atmospheres (with the exception ofmines)” has also been available as a DIN stan-dard since August 1998. In the individual sec-tions of the following text an attempt is made tooutline the differences between the installationstandards (VDE 0165 (= VDE 0165 – 1/92) andEN 60 079 – 14 (=DIN VDE 0165, Part 1 – 8/98).

Protection against contactProtective measures against direct contact arealready required in VDE 0100. With explosionprotection, the protective aim is to prevent, asfar as possible, any formation of sparks as aresult of contact with bare active parts (with theexception on intrinsically safe parts). Similarlyworded measures relating to protection againstindirect contact are listed in VDE 0165 and EN60 079-14 for the individual network forms.

Potential equalizationAccording to VDE 0165 and EN 60 079-14,potential equalization is required for the avoi-dance of ignitable sparks within the potentiallyexplosive atmosphere. Thus, any conductiveparts, that are associated with the constructionor installation and with which a potential shift is

to be expected, must be incorporated in thepotential equalization.

Examples of potential equalization:• via compensators (non-conductive) insula-

ted pipelines• insulated seals

The following need not be incorporated:• conductive window frames• conductive door frames.

It is not necessary to additionally connect enclo-sures to the potential equalization, provided that,by means of the fixing facilities, they have relia-ble contact to parts of the installation that, inturn, are incorporated in the potential equaliza-tion.

Lightning protection installationsIn VDE 0165 reference is made to the need for afunctioning lightning protection installation (seealso EX-RL, TRbF). The individual requirementscan be found in VDE 0185, Part 2. The protec-tive aim formulated in EN 60 079-14 says thatthe effects of lightning striking must be reducedto a non-hazardous degree. Details relating tominimum values are only given for intrinsicallysafe circuits in zone 0.

Electrostatic chargesThe installation standards only formulate the fol-lowing protective aims against static charges:Electrical installations must be installed in such away that ignition hazards as a result of elec-trostatic charges are not to be expected.

Electrostatic charges are the result of separatingprocesses involving at least one chargeablesubstance. The discharging of charged particlesof non-conductive materials (e.g. plastics) isusually the result of bunch discharges that canbe ignitable. In the case of fast separating pro-cesses (e.g. pulling-off of foils from rolls, drivebelts) sliding bunch discharges are possible.These are bursting with energy and, as a result,they are capable of ignition.

In zone 0 discharges capable of ignition must beexcluded, also taking rare operational faults intoconsiderationIn zone 1 discharges capable of ignition shall notbe expected in plants that operate properly andin the event of operational faults usually to bereckoned with. Measures against discharges arenecessary in zone 2 if they occur frequently. Adischarge resistance of 106 Ω is considered tobe sufficient electrostatically.

In the case of certified apparatus it is safe toassume that an electrostatic charge is adequa-tely avoided. The installer is responsible for theinstallation of other parts of plants.


Electrical protection and monitoring devices

Overcurrent trips, safety thermal cut-outs, pres-sure switches and many more besides, that,after tripping, disconnect the part of the installa-tion in all external conductors, are considered tobe electrical protection and monitoring devices.The devices must not be able to automaticallyswitch the installation part back on again. Whenswitching on again or releasing them, it is neces-sary to ensure that the protection device is inworking order. If, as a result of the disconnec-tion, an expansion of the hazard is to be expec-ted, instead of disconnecting, it is sufficient togive a warning signal. In addition, EN 60 079-14requires the specification of measures thatafford immediate relief in this case.

Emergency shut-downAccording to VDE 0165 electrical apparatuswhose continued operation in the event of faultsleads to hazards or the spreading of fires mustbe able to be switched off from a safe locationby means of an emergency shut-down (e.g. apump motor whose pump pumps inflammableliquids into a hazardous area). The emergencyshut-down is not required for zone 2. Generalrequirements are posed according to EN 60079-14. Here, it must be possible to disconnectthe "supply of the potentially explosive atmos-phere” from a safe location, whereby electricalapparatus for the avoidance of additionalhazards must continue to be operated and, the-refore, must be supplied from separate circuits.In addition to this, it requires a disconnectiondevice to each circuit (or each group), that ismarked to show the circuit.

Cables

On principle cables must be selected in such away that withstand any mechanical, electrical,chemical and thermal stress to be expected.After clarifying the type of stress and the loca-tion, the type of cable can be selected accor-ding to the marginal conditions of VDE 0165,Chapter 5.6.1-2.

Cables that are not laid in the earth or in sand-filled ducts must be protected by flame-retardant sheaths, or proof must be furnishedthat the burning behaviour complies with DINVDE 0472, Part 804, Test Type B. Bushings forcables leading into non-hazardous areas mustbe sealed in an adequately tight way (e.g. sandcups, mortar seal).Unused openings in electrical apparatus forcable entries must be sealed in accordance withEN 50 014.

Parts of cables that are subjected to specialstress must be specially protected (e.g. conduit).However, closed conduit systems must not belaid, unless they are suited for potentially explo-sive atmospheres due to their special design(e.g. US standard).

Additional requirements

In addition to the basic requirements describedabove, there are further requirements accordingto the type of protection or apparatus.

Installations with intrinsically safe circuitsThe protection principle of the type of protectionIntrinsic Safety assumes that the energy in aninstalled circuit is always less than the ignitionenergy of an explosive atmosphere that mightsurround it. In this way, the ignition of the explo-sive atmosphere cannot occur.

An intrinsically safe circuit consists of the intrinsi-cally safe apparatus located in the potentiallyexplosive atmosphere and the associated appa-ratus for the isolation of the intrinsically safe fromthe non-intrinsically safe circuit. The associatedapparatus is installed in the non-hazardous area.Both types of apparatus are connected to eachother by cable

Selection of intrinsically safe apparatusWhen installing the intrinsically safe circuit (withjust one piece of associated apparatus), it isnecessary to ensure that, together with thecables, the maximum permissible values for thecircuit(e.g. inductance, capacitance) are notexceeded.


Type tests and marking to EN 50020 are notrequired for intrinsically safe electrical apparatusif it does not contain a voltage source and if thecharacteristics (R,L,C) and the thermal beha-viour are definitely known. This applies, forexample, to:

• switches• plugs and sockets• terminal boxes• measuring resistors• individual semi-conductor components• coil• capacitors• electric position sensors to DIN 19234

This apparatus must, however, comply with theconstructional requirements of EN 50020 andmust be clearly identifiable.

The temperature class and the explosion groupof the explosive atmosphere are further selectioncriteria that must be taken into account.

Associated apparatus with the marking ia or ibmay be used for zone 1. According to the oldElexV special confirmation in the type examina-tion certificate and an ia circuit with increasedsafety level are required for zone 0.

Special conditions in intrinsically safecircuitsBefore installing intrinsically safe circuits, it isabsolutely essential to take the special conditi-ons of the type examination certificate (X-certifi-cate) and the operating instructions intoaccount. Additional requirements relating to theinstallation and earthing are often listed here.

Cables for intrinsically safe circuitsThe following requirements apply, on principle,for cables in intrinsically safe circuits:• insulated cables only• test voltage: conductor-earth-screen min.

500V AC• fine-wire conductor ends – multicore cable

ends• conductor diameter > 0.1 mm (also for fine-

wire conductors)• protection against electro-magnetic input

couplings• wires of intrinsically safe and non-intrinsically

safe circuits must not be routed together• mechanical protection

Cables of intrinsically safe circuits must be mar-ked. If the sheathing or sleeves are to be mar-ked by colour-coding, they must be light blue.Cables marked in this way must not be used forother purposes here.

Interconnection of intrinsically safecircuitsWhen interconnecting intrinsically safe circuitswith more than one piece of associated appara-tus, the intrinsic safety must be guaranteed inthe event of a fault and must be verified by cal-culation.

Further informationFurther information on the subject of intrinsicsafety is available from CEAG ApparatebauHundsbach GmbH & Co. KG in the brochure:“Explosion protection and instrumentation – apractical guide“ by Dipl. -Ing. Wolfgang Gohm.

Electrical machineryMost explosion-protected motors are designedin the type of protection Increased Safety.Electrical machinery must be protected againstinadmissible heating-up due to overload. Thefollowing protective devices are possible:

• Overcurrent protection devices with current-dependent delayed release

• Temperature monitoring by means of ther-mometer probes

• Other devices that provide equivalent pro-tection as required.

If the overload protection of an Ex-e machine isprovided exclusively by temperature monitoringdevices, the design of the machine must bespecially tested and certified for this. In general,current-monitored motors may only be used forcontinuous operation with easy and infrequentstarts. Variable speed electric motors must:

a) when designed in the type of protectionIncreased Safety “e“, be certified as a unittogether with the converter

b) when designed in the type of protection Fla-meproof Enclosure “d“, be operatedwith a converter if this is stipulated in thetype examination certificate.

Heating equipmentIf it is not certified as a complete unit, electricalheating equipment must be tested and appro-ved by an expert.

LuminairesOnly those lamps specified by the manufacturerin the documentation (type label) may be usedfor luminaires.


When work is carried out in potentially explosiveatmospheres, the safety of people and installati-ons depends, to a high degree, on the strictadherence to all safety regulations. Therefore,the maintenance personnel working in suchplants has a special responsibility. A detailedknowledge of the current rules and regulations isprerequisite.The following is a brief summary of the mostimportant safety measures.

Rules, regulations and decrees

The following must be observed when setting-up electrical installations in potentially explosiveatmospheres:• Decree on electrical installations in indoor

locations with a potentially explosive atmos-phere (ElexV),

• Decree concerning the putting into circulationof apparatus and protective systems for use inpotentially explosive atmospheres – explosionprotection decree (ExVO)

• Harmonization of the laws of the member sta-tes relating to apparatus and protectivesystems intended for use in potentially explo-sive atmospheres (94/)/EC)

• Minimum regulations for the improvement ofthe health protection and safety of employeesthat can be endangered by explosive atmos-pheres (1999/92/EC)

• Explosion protection rules (EX-RL) with compi-lation of examples from the Employer’s liabilityinsurance association of the chemical industry

• Directives for the prevention of ignitionhazards as a result of electrostatic chargeslaid down by the central union of the employ-ers’ liability insurance association

• Accident prevention regulations issued by theemployers’ insurance liability association“Electrical installations and apparatus“ (VBG4)

• Decree on inflammable liquids (VbF)• Technical rules for inflammable liquids (TRbF).

On principle, the following VDE specificationsapply to the setting-up of electrical installations:• VDE 0100, 0101, 0107, 0113, 0141, 0185,

0190, 0800 Part 1 - 4

In addition, the following VDE specificationsmust be observed for potentially explosiveatmospheres:• VDE 0165 (2/91), VDE 0165-1, VDE 0165-2

and VDE 0170/0171 (all parts).

The following applies for the operation andmaintenance of existing installations:• VDE 0105 Operation of power plants

– Part 1 General specifications– Part 9 Additional specifications for potentially

explosive atmospheres

Special safety measures

For all work carried out in potentially explosiveatmospheres it is necessary to ensure that neit-her sparks capable of causing an ignition norsurfaces that are too hot occur, that, in conjunc-tion with the explosive atmosphere, could leadto an explosion.

Prevention of sparkingThe types of protection of the electrical appara-tus being used ensure that sparks capable ofcausing an ignition or hot surfaces do not comeinto contact with the explosive atmosphere. Onlyexplosion-protected measuring instruments maybe used for the measurement of electric values.The question whether or not non-explosion-pro-tected measuring instruments may also be usedto test the absence of voltage in connectedapparatus is often posed. The answer to thisquestion is definitely NO, as the legislative bodyhas clearly stipulated that, on principle, explo-sion-protected apparatus only may be usedin potentially explosive atmospheres. Sparkscapable of causing an ignition can also resultwhen connecting or disconnecting cables alt-hough no voltage is connected. The reasons forthis can be possible energy stores of electricalinstallations, as well as induction or electro-magnetic fields. The electrical engineer must,at all times, be aware of whether or not sparkscapable of causing an ignition are to be expec-ted. Another hazard area, where sparks capableof causing an ignition can occur, is the dischar-ging of static charges. Electrostatic chargesresult from separating processes with at leastone conductive substance. Everyone is aware ofsuch processes, e.g. pulling foils from rolls,emptying plastic containers or conveyance ofnon-conductive liquids at high speeds. The pos-sible spark formation resulting from these char-ges must be prevented according to the respec-tive zones. The highest requirements apply tozones 0 and 20. Here it is necessary to ensurethat no discharge can occur, even in the eventof rare faults. Discharges must not occur inzones 1 and 21, even in the event of faults thatare to be expected. Measures against dischar-ges are necessary in zones 2 and 22 if theyoccur frequently. Effective measures against sta-tic discharges include making non-conductingsubstances conductive as defined for electrosta-tics. This can, for example, be achieved by intro-ducing soot particles into the non-conductingsubstance. The surface resistance achieved inthis way has electrical insulation properties of106 Ω to 108 Ω, but is, however, electrostaticallyconductive, thus preventing the formation ofsparks capable of causing an ignition. Wrongclothing of employees represents anotherpotential hazard. As a result of a high proportionof synthetic fibres in working clothes in conjunc-tion with insulting rubber soles, people canbecome so highly charged electrostatically thatsparks capable of causing an ignition can becaused as the result of discharging due tocontact with a part of the installation that is earthed.

Maintenance and repair of explosion-protectedapparatus


The possible formation of sparks must also betaken into consideration when using hand tools.Here distinction is made between two types oftools. Tools where a single spark is given offduring use, e.g. screwdrivers or spanners, andtools that give off a shower of sparks during use,e.g. cutting or grinding tools. In general, the useof tools that can give off sparks is not permittedin zones 0 and 20. According to EN 1127 onlysteel tools that can only give off a single sparkmay be used in zones 1 and 2, provided that nosubstances of the explosion group IIC are pre-sent in this area. The use of steel tools that cangive off a single spark is permitted in zones 21and 22. Tools that give off a shower of sparksmay, on principle, only be used in conjunctionwith a so-called ‘hot work permit’ if it has beenascertained that no explosive atmosphere ispresent for the duration of the work. The appro-priate safety measures must be specified in thepermit.

Hot work permit(See Annex 4 for sample)Many tasks, such as the use of tools that giveoff showers of sparks, torch cutting and wel-ding, the use of non-explosion-protected mea-suring devices or repair work with different typesof protection may only be carried out in thehazardous area if, at the same time, no explo-sive atmosphere exists. After measures (primaryexplosion protection) have been taken, toensure that no explosive atmosphere is presentin the work area, the works manager or hisrepresentative tests the effectiveness of themeasures that have been taken and takesappropriate measures to ensure that no hazar-dous explosive atmosphere can occur while thework is being carried out. As a rule, before workis commenced, the atmosphere is tested usinga gas warning device that is calibrated, explo-sion-protected and suitable for the type of gasto be detected.The works manager now issues a writtenrelease note (hot work permit) for the necessarymaintenance measures that involve the possibleformation of sparks capable of causing an igni-tion. The place, the time for the beginning ofwork, the duration and the types of protectivemeasures required are laid down in this docu-ment. Additional protective measures are alwaysnecessary if a renewed formation of an explosiveatmosphere cannot be excluded. Approachingclouds of explosive atmosphere can be detec-ted using gas warning devices, provided that thecorrect types are used for the respective type ofgas (heavier or lighter than air) and ambient con-ditions (see Permanently installed gas warningdevices for explosion protection – use and mea-suring principles – 9/95- ZH 1/8.3). The gaswarning devices must, however, be used insuch a way that, after an optical or acousticalarm warning has been given, sufficient timeremains to make possible ignition sources inef-fective.After the work has been completed and this hasbeen reported, the effectiveness of the neces-sary explosion protection measures must nowbe re-established.

CommissioningAfter an installation has been set up, before it isput into operation for the first time, the operatormust have the correct state of the installationinspected by a specialist. In Germany a specia-list for electrical engineering is required for elec-trical installations, who must, of course, alsohave a good knowledge of explosion protection.The latest technological developments must beconsidered as the basis for testing. The testscan also be carried out by a specialist from anoutside company who has the necessary know-ledge. As a rule, until now documentation is notcompulsory, but it can, however, be required bythe authorities. It is always advisable to requestwritten confirmation if the operator and thetester are not from the same company. If theplanner and the installer come from differentcompanies, they must reach an exact agree-ment regarding their respective areas of respon-sibility. In the case of intrinsically safe circuits,the planning documents that act as the basis forthe proof of the intrinsic safety must be coordi-nated with the installation, since any changesduring installation can influence the basis for theintrinsic safety.


Installation

Instructions for the installation can be found inthe chapter “Setting-up of electrical installationsin potentially explosive atmospheres” (page 42).

Maintenance

Safety measuresOn principle, work on live electrical installationsand apparatus is forbidden in potentially explo-sive atmospheres.Exceptions are work on intrinsically safe circuitsand, in special cases, on other electrical installa-tions. In this case the works management mustissue a hot work permit as written confirmationthat no explosion hazard exists at the workplacefor the duration of the work in hand.The absence of voltage may only be measuredwith explosion-protected measuring instru-ments. The special cases named above are theonly exceptions.Earthing or short-circuiting in hazardous areas isonly permitted if there is no explosion hazard.

OperationIn accordance with §13 ElexV, the responsibleoperator must observe the following importantprinciples::• Correct operation of the electrical installation• Maintaining the electrical installation in due

order• Constant monitoring of the electrical installa-

tion• Immediate execution of necessary repair

measures• Stopping operation if the event of faults that

cannot be repaired and can endanger thepersonnel

Correct operationAfter an installation has been set up correctly, itmust then also be operated correctly in keepingwith the latest technological developments. TheVDE regulations have already been cited by wayof the general administration regulation to ElexV.They were classified as being particularly rele-vant by the Federal Ministry for Labour andSocial Order. However, newer standards mustalso be taken into consideration if they containnew findings relating to safety issues. In additionto the standards and directives, compliance withthe safety-related details given by the manufac-turer in the documentation is compulsory.

Maintaining in due working orderBefore putting an installation into operation forthe first time the responsible operator must haveit inspected to ensure that the installation is indue working order. After commissioning it is alsonecessary to ensure that it remains in due order.This requires constant monitoring of the installa-tion according to §13 ElexV. Any faults ascertai-ned during monitoring must be eliminated imme-diately. Moreover, recurrent tests of the installa-tion must be carried out at least every threeyears (§12 ElexV) to verify that the installation isin due working order. These tests are not requi-red if the installation is under the constantsupervision of a responsible engineer.

Constant supervision“Constant supervision“ is defined as being thecontinuous supervision of electrical installationsby specialized personnel that is familiar with thelocality, the aim of which is the permanent main-taining of the installation in due working order,the fast recognition and immediate elimination ofany faults that may occur, and the early detec-tion of changes with the implementation of suita-ble countermeasures. In order to put this continuous supervision intopractice, the responsible operator of the installa-tion must employ specialized personnel on apermanent basis and must allow them sufficientfreedom for the supervision of the installations.Special knowledge of the installation and theparticular stresses are necessary to be ableidentify possible weak points at an early stage.In the course of his supervisory tasks, such as,for example, check patrols, inspections, servi-cing, cleaning, trouble-shooting, switchingactions, connection and disconnection ofcables, setting and adjustment work, modificati-ons and installation work, the electrical engineerdetects any faults occurring or changes at avery early stage, thus making it possible to takethe necessary repair measures in good time.


Constant supervision by theresponsible engineerAdditional tests to §12 ElexV are not required forinstallations under the constant supervision of aresponsible engineer. For the qualification of theresponsible engineer, priority is given to the fun-ction description and not the course of his trai-ning. The position requires a responsible personin a leading function and the position can, forexample, be filled by a trained technician withthe appropriate specialized knowledge. On thebasis of this knowledge, he controls the qualifi-cation of specialized staff and the execution ofthe constant supervision by specifying appro-priate operation sequences, by analyzing chan-ges in the ambient conditions, the feedbackrelating to repair work and random individualtests, in order to use the information gained toundertake the necessary measures for adaptingthe electrical installations. EN 60 079-17: DINVDE 0165, Part 10, “Testing and repair of elec-trical installations“ contains suitable measures toassist him carry out his work.

MaintenanceMaintenance includes all measures (inspection,servicing and repairs) for maintaining and resto-ring the nominal state, as well as for the determi-nation and evaluation of the actual state. Inspec-tions and supervision help prepare servicingwork and outline trends indicating possibledamages. The inspection in the form of a visualcheck shows the experienced specialist, e.g. bydrips at the switch box, whether more intensivechecks are necessary. Based on this experi-ence, maintenance work must be carried outdependent on the type of protection being used.In the case of apparatus that is manufacturedand approved according to the ATEX directive94/9/EC, the necessary maintenance measurescan be found in the operating instructions.Some possible maintenance tasks are listedbelow.Since, due to the specified joint, the protectionagainst water of flameproof enclosures and ofEEx-e enclosures is only limited (IP 44 and IP54), special attention must be paid to any accu-mulation of water in the enclosure. Slightly rusty joints must not be cleaned with anabrasive or wire brushes, but with chemicalagents such as non-resinous and non-acidreducing oils. Afterwards, the joint surfaces mustbe carefully preserved.Particular attention must be paid to ensure thatany covers that were removed are put back ontheir associated enclosure base and screweddown well. Covers of the same type must not beinterchanged.The gasket on EEx-e enclosures must bechecked for damages and, if necessary, repla-ced.Terminals, in particular in an EEx-e enclosure,are to be tightened. Any discoloration indicatesa rise in temperature.Cable glands, blanking plugs and flanges are tobe checked for tightness and close fit.

When replacing incandescent lamps, it is neces-sary to ensure that only lamps have been certi-fied for the luminaire may be used. Overcurrent protection devices and the suitabi-lity of fuses, motor operating currents and tEtimes must be checked. Windings and bearingsof motors must – as far as possible – bechecked for damages (running noises) andchanges (rise in temperature). Sand fillings in cable ducts and wall bushingsmust be checked. Cable trenches and ductsmust be checked for water. Cable sheaths mustbe checked for perfect condition and cable traysfor mechanical and chemical damage.

Repairs

Repair measures should be planned and, as arule, be carried out during a scheduled shut-down.

Replacement of apparatusWork on electrical apparatus and installations inexplosive atmospheres may only be carried outif a work permit stating the necessary safety pre-cautions has been issued by the works managerand if these measures have already been carriedout.When replacing electrical apparatus, attentionmust be paid to the intended application , i.e. tothe temperature class, explosion class and(Ex)zone or apparatus category. Moreover, thecertificate of conformity, PTB test certificatesand design approvals must be available. Themanufacturer’s declaration of conformity and theassociated operating instructions must be avai-lable for apparatus according to the ATEX direc-tive 94/9/ECIn the case of EEx- e type motors, the time tEmust be observed. Lamps in stationary light fittings may only bereplaced if• in zone 0 the external and neutral conductor

are switched off, • in zone 1 at least the external conductor(s)

is/are switched off.

Lamps in portable lights may only be replacedoutside of hazardous areas.Lamps may only be replaced by lamps whoserating and type correspond to the data on theluminaire.In the case of luminaires in the type of protection"Increased Safety” only general-purpose lampsaccording to DIN EN 16064 and EM 432 maybe used. In the case of special lamps only lampswhose identification number is given on therating plate of the luminaire may be used.


When replacing incandescent lamps in portableor vessel light fittings, only incandescent lampsfor voltages up to 42 V are to be used, or, if hig-her voltages are required, only incandescentlamps that are marked as being impact resi-stant.In areas containing substances in the explosiongroup IIC, an ignition hazard in the event of abroken lamp already exists when no voltage isapplied. For this reason, fluorescent lamps mayonly be replaced if it is ensured that no explo-sion hazard exists during the relamping of thelight fitting or transport of the lamps.

After completion of the work, • the cable ducts must be refilled with sand or

well ventilated and drained,• the bushing openings of cables to non-

hazardous areas must be sealed tightly,• unused cable entries on electrical apparatus

must be closed reliably and captive-lockedagainst self-loosening,

• the glands of cables must be tight.

Repair of apparatusAfter apparatus parts upon which the explosionprotection depends have been repaired, thisapparatus must be inspected by a recognizedexpert (§ 9 ElexV). If the result of the appraisal ispositive, he will issue an expert’s certificate. Onlythen may the apparatus be put back into opera-tion. Inspection by an expert is not required ifthe repair of the apparatus was carried out bythe manufacturer and the apparatus was sub-mitted to a renewed routine test. If , for example, only the bearing is replaced in amotor, no expert’s certificate is required.If a special apparatus design was installed for aparticular application, this must also be testedand certified by a recognized expert (§10 ElexV:no longer possible from 01.07.2003).Instructions regarding the required inspectionsafter repairs can be found in the publication byDreier and Krovoza (Work protection No.3/1968, page 79).

Modifications to apparatusIf parts of electrical apparatus on which theexplosion protection depends are converted ormodified (e.g. new bushings), it is regarded asbeing a special design. The apparatus may onlybe put back into operation after inspection by arecognized expert (§ 10 ElexV) who must thenissue a certificate. This also applies to electricalapparatus that does not have a type examina-tion certificate. It does not apply to the replace-ment of original apapratus and modifications tothe wiring in flameproof compartments. As partof the latest amendment of ElexV, §10 was dele-ted, so that special models may only be issuedwith a certificate by an expert until June 30th,2003.


Definition of potentially explosive atmospheres andrequirements for explosion-protected apparatus on theworld market

Summary of the explosion protection measures,standards, categories and classifications thatare applicable worldwide.

On the world market potentially explosiveatmospheres are divided into areas with variousdegrees of hazard according to the IEC publica-tion IEC 60079-10 (EN 60079-10 in Europe) orthe NEC (National Electrical Code).

The following is a brief overview of the NECrequirements and a comparison of the require-ments/specifications to IEC (EN) and NEC.More detailed information can be found in theCrouse-Hinds Code Digest. This publication canbe ordered on the Crouse-Hinds web site“www.crouse-hinds.com“.

NEC:

Classification according to the explosive medium

Class I Mixtures of gas or vapour with airClass II Mixture of dust with airClass III Mixture of fibres with air

Subdivision of potentially explosiveatmospheres:

Division 1 Areas in which inflammable gasesor vapours can be present:– under normal operating

conditions– frequently in the case of repair

and maintenance work– in the event of operating

troubles or faulty functioning ofapparatus or in the process flowif, at the same time, faults toelectrical apparatus can becaused

In class III areas in which fibres orfloating substances can be pre-sent in such quantities that, if theyare whirled-up, they can form anignitable mixture with air belong todivision 1.

Division 2 Areas in which inflammable gases,vapours or easily vaporized liquidsin closed systems or suitable con-tainers are to be found; areas inwhich, under normal operatingconditions, the formation of ignita-ble mixtures is prevented by a for-ced ventilation; areas that borderonto division 1, so that clouds ofthe explosive atmosphere canoccasionally enter it.

In class III areas in which easilyinflammable fibres are stored orprocesses belong to division 2.

Division of explosive mixtures intoexplosion groups:

Group A Acetylene

Group B Hydrogen

Group C Ethylene

Group D Propane

Group E Metal dust

Group F Coal dust

Group G Flour dust

Division into temperature classes:

T1 max. 450°CT2 300°CT2A 280°CT2B 260°CT2C 230°CT2D 215°CT3 200°CT3A 180°CT3B 165°CT3C 160°CT4 135°CT4A 120°CT5 100°CT6 85°C

Table of comparison NEC IEC/EN

Hazard categories/gas groups

Examples NEC 500-503 NEC 505

IEC 60079-0

EN 50014

Class I Gases and vapoursAcetylene Group A Group IICHydrogen Group B Group IICEthylene Group C Group IIBPropane Group D Group A

Class II DustsMetal dust Group ECoal dust Group FGrain dust Group G

Class III FibresWood, paper No subdivision

for material processing


Classification of potentially explosive atmospheres

Long-term or Occasional hazard Hazard only in event of frequent hazard fault and short-term

North America NEC 500-503 Division 1 Division 1 Division 2

North America NEC 505 Zone 0 (gas) Zone 1 (gas) Zone 2 (gas)IEC / EN Zone 20 (dust) Zone 21 (dust) Zone 22 (dust)

Apparatus categories to G1 (gas) G2 (gas) G3 (gas)directive 94/9/EN D1 (dust) D2 (dust) D3 (dust)

Division into temperature classes

Maximum permissible surface temperature NEC IEC 60079-0Table 500-3(d) EN 50014

450°C T1 T1300°C T2 T2280°C T2A260°C T2B230°C T2C215°C T2D200°C T3 T3180°C T3A165°C T3B160°C T3C135°C T4 T4120°C T4A100°C T5 T585°C T6 T6

Overview of the types of protection and their permissible use in potentiallyexplosive atmospheres

Type of protection Symbol IEC EN For use in For use in standard standard division zone

General IEC 60079-0 EN 50014requirements

Oil immersion o IEC 60079-6 EN 50015 1 and 2 1 and 2

Pressurization p IEC 60079-2 EN 50016 1 and 2 1 and 2

Sand filling q IEC 60079-5 EN 50017 2 1 and 2

Flameproof enclosure d IEC 60079-1 EN 50018 1 and 2

Increased safety e IEC 60079-7 EN 50019 2 1 and 2

Intrinsic safety i IEC 60079-11 EN 50020 1 and 2 0*,1 and 2

Electrical apparatus n IEC 60079-15 EN 50021 2 2in type of protection “n“

Encapsulation m IEC 60079-18 EN 50028 1 and 2

Table of comparison NEMA classification and IP degree of protection

NEMA IP

3 IP 543R IP 543S IP 544 and 4X IP 565 IP 526 and 6P IP 6712 and 12 K IP 52

Degrees of protection against water designated by the second code No.

Second Degree of protectioncodeNo. Brief description Definition

0 No special protection –

1 Protected against Vertically falling drops must not have a harmful effect.dripping water

2 Protected against Drops falling vertically must not have a harmful effect dripping water when the enclosure is inclined at an angle up to 15°when the enclosure on either side of the vertical. is inclined up to 15°

3 Protected against Water being sprayed at an angle of up to 60° on spray water either side of the vertical must not have a harmful effect.

4 Protected against Water being splashed against the enclosure from any splash-water direction must have no harmful effect.

5 Protected against Jet water from a nozzle turned on the enclosure from jet water any direction must have no harmful effect.

6 Protected against There must be no harmful effect from powerful water powerful water jets jets being turned on the enclosure from any direction.

7 Protected against Water must not enter in harmful quantities when the water when the enclosure is immersed in water at specified conditionsenclosure is of pressure and time. immersed in water for a specified time

8 Protected against Water must no enter in such a quantity as might have awater when the harmful effect when the enclosure is continuously sub-enclosure is conti- merged in water at conditions which are to be agreednuously submerged upon between the manufacturer and the user. Conditions

must, however, be more stringent than those for code No. 7.

Degrees of protection against foreign matter designated by the first code No.

First Degree of protectioncodeNo. Brief description Definition

0 No special protection –

1 Protected against solid The object probe, a ball of 50 mm dia.foreign bodies 50 mm dia. must not fully penetrate *)and bigger

2 Protected against solid The object probe, a ball of 12.5 mm dia.foreign bodies 12.5 mm dia. must not fully penetrate *)and bigger

3 Protected against solid The object probe of 2.5 mm dia.foreign bodies 2.5 mm dia. must not penetrate at all *)and bigger

4 Protected against solid The object probe of 1 mm dia.foreign bodies 1 mm dia. must not penetrate at all*)and bigger

5 Dust protected Ingress of dust is not totally prevented, but the dust must not enter in such an amount as to interfere with satisfactory operation or with the safety of the apparatus.

6 Dusttight No ingress of dust

*) Note: The full diameter of the object probe must not pass through any opening of the enclosure.


The IP degrees of protection havebeen defined in accordance with EN60529 (protection against accidentalcontact, foreign matter and water):

IP degrees of protection


Table 1 – Procedure for theassessment of the zone classification according to ElexV, directives on explosionprotection (EX-RL) and VDE 0165

1. Are there explosive substances being used?

Yes / No

2. If yes:Do electrical

installations/apparatushave to be taken into

operation ina hazardous area?

If yes, then:

3. Determination of the zone acc. to ElexV, EX-RL

and VDE 0165,whether

zone 0zone 1zone 2zone 20zone 21zone 22

3.1

Clarify:Whichsubtanceswill be used?

1. Flash point

2. Volumepercent orweight per-cent

3. Density

4. Glowtemperature

5. Ignitiontemperature

6. Explosion

group3.2

Apply dataacc. to 3.1 of EX-RLCheckwhether thepractical caseis in confor-mity with theexample inthe EX-RL;adopt thezone andextent of zone.

3.3

Where appro-priate, refer to otherstandards forzone classifi-cation e. g.VbF/TRbF orothers.

4. Decisionbased on TABLE 2

4.1 Is a type sampletest certificate required?

4.2 Type ofinstallation according

to zone


Table 2 Explosion protection at aglance

Electrical installations in potentially gas atmospheres in the Federal Republic of Germany: Overview in accordance with 94/9/EC, 199/92/EC, ExVO, ElexV; EX-RL; VDE 0165, 0170/0171

Zone Explosive Inflammable Apparatus Electrical installationatmosphere media/substances category

0 Constantly, Gases, vapours, mists 1G to VDE 0165 (2/91)for long periods to VDE 0165 Part 1 (8/98)

to VDE 0170/0171 Part 1,12

1 Occasionally Gases, vapours, mists 2G to VDE 0165 (2/91)to VDE 0165 Part 1 (8/98)to VDE 0170/0171 Part 1-11

2 Not to be expected, Gases, vapours, mists 3G to VDE 0165 (2/91)for short periods to VDE 0165 Part 1 (8/98)

to VDE 0170/0171 Part 1,16

20 Constantly, Dusts 1D to VDE 0165 (2/91)for long periods to VDE 0165 Part 2 (11/99)

to VDE 0170/0171

21 Occasionally Dusts 2D to VDE 0165 (2/91)to VDE 0165 Part 2 (11/99)to VDE 0170/0171

22 Not to be expected, Dusts 3D to VDE 0165 (2/91)for short periods (2D)* to VDE 0165 Part 2 (11/99)

to VDE 0170/0171

* For conductive dusts


Appendix 1 – Sample ofan expert’s certificateaccording to § 10 ElexV

Expert's certificate according to § 9 ElexV

The electrical apparatus altered - repaired by Messrs.

(detailed description of the electrical apparatus)

with the following marks and details

was tested by me. It does not conform to the requirements of the decree on electricalinstallations in hazardous areas dated Febr. 27, 1990 (BGBI.I page 173)in the following details: (Delete what is not applicable)

The approved expert:

(Place) (Date) (Signature)

(Date, reference and certifying authority)


Appendix 2 – Sample ofan expert’s certificateaccording to § 10 ElexV

Expert's certificate according to § 10 ElexV

Based on § 10 of the “decree on electrical installations in hazardous locations” dated

February 27, 1980 (BGBI.page 173) the following special make of an apparatus was tested

with regard to its type of protection against explosion

in acc. with VDE section tested.

Test documents:

Assessment: The special make conforms to

The special make does not conform to the requirements of Elex V with regard to the

following details

Marks:(will have to be affixed onto the apparatus)

An exception in acc. with § 5 cl. 1 ElexV is considered to be necessary/is notconsidered to be necessary.

The approved expert:

(Place) (Date) (Signature)

(Date, reference and certifying authority)


Installation certificate

in compliance with § 12 cl. 1 of the decree on electrical installations in hazardous locations (ElexV)

The installation

set up/altered on the premises of Messrs.:

(details of type and location of the installation)

complies with the decree on electrical installations in hazardous locations (ElexV) dated December 13, 1996 (BGBI.page 214) as well as with the rule for prevention ofaccidents “Electrical installations and apparatus” (VBG 4).

In particular, the VDE regulations 0100, 0101, 0165, 0800 were observed. Protective measures against shock-hazard voltages have been taken in accordancewith VDE 0100 and been tested in respect of their efficacy.

The electrical apparatus installed by us in hazardous areas of the plant conform to VDE 0171. As far as gases, vapours and dusts are concerned, they meet the requirements of:

Temperature class: Explosive dust class:

(abbr. of dept.) (Place/ Inital)

(Place) (Date) (Signature of the signing clerk and firm stamp)

Appendix 3 – Sample ofan installation certificate

Hot work permit for hazardous areasTick off where applicable. Delete what is not applicable in lines ticked off.

Permit for welding, burning and other hot work, for drilling, grinding, impact and calking work, for the use of non-explosionprotected apparatus.

A 1. Contractor: Building: Tel.: Foreman:2. Place and kind of work

3. Hot work permit from o’clock to o’clock, for the time4. For workshop/Messrs Building Foreman:

B Dangerous places in the environmentof the workplace, buildings, equipment etc. Person responsible Building Tel.

1.

2.

3.

4.

C Security precautions To be executed by: Settled 1. Checking the tightness of pipes, equipment in the environment of the workplace 2. Fire fighting and other security precautions a. Placing in readiness at the workplace of water for fire fighting and fire extinguishers b. Connecting the fire hose c. Placing look-out man

craftsman staff member supervisor fireman d. Removal of inflammable substances, vapours, gases or dust deposits e. f.

3. Signposting of the workplace (road, railroad tracks etc.) a. By means of red flags (20 m on either side of the workplace) b. By means of signs (e.g. hot work on pipe bridge) c. Blockage, diversion for tank lorries, blockage for rail cars

4. Protection of the environment from welding sparks a. Covering of the adjacent conduits b. Setting up of a protective wall, protection of the roof surface, possibly keeping wet c. Stopping of hot work with running of trains d. Keeping a min.distance of m from tank wagons, tank farms etc. with fire hazard e. Covering and sealing of pipe openings, gratings, light wells and gully holes f.

5. In case of hot work in and on containers, apparatus, pits, pipework, dismantled parts of installations, in confined rooms etc. Additional measures such as:

a. Travelling permit No. dated b. Work permit No. dated c. Test certificate for electrical apparatus No. dated d.

6. a. Before starting to work, daily report to B 1, 2, 3, 4. b. Report end of the work daily to B 1, 2, 3, 4.

7. a. Check of the security precautions ticked off by (name) b. Check of the workplace after ending the work by (name)

C Consent of responsibilities Starting time reportedfor the dangerous places on: to:For B 1 measures C figureFor B 2 measures C figureFor B 3 measures C figureFor B 4 measures C figure

Date Signatures

Hot work permit issuedDate Signature of the works supervisor or his mandatary

Look-out man (name)


Appendix 4 –Sample of a hot workpermit


Annex 5Bibliography

Title Author Obtainable from

Explosion protection of electrical installations Jeiter W. and Nöthlichs, M. Erich Schmidt Verlag GmbH, Berlinin hazardous areas(commentary and text compilation)

Decree on electrical installations Steyer H., Birkhahn, W. Carl Heymanns Verlag KG, in hazardous areas (ElexV) and Isselhard, K. Cologne, Berlin, Bonn, Munich

Decree on electrical installations in Gazette I, No. 8 of March Bundesanzeiger Verlags mbHhazardous areas dated February 27, 1980 1, 1980, page 214

General administrative rule related to the Gazetter No. 43 of Bundesanzeiger Verlags mbHdecree on electrical installations in hazardous areas March 1, 1980, page 5

Directives for the prevention of ignition hazard on account Employers’ insurance Printing house Winter, of an explosive atmosphere with compilation of examples liability association of the P.O.Box 106140, Heidelberg 1Directives on explosion protection (EX-RL) 1985 chemical industry

Decree on inflammable liquids (VbF) and Carl Heymanns Verlag KG, Technical rules for inflammable liquids (TRbF) Cologne, Berlin, Bonn, Munich

Decree on facilities for the storage, filling and Gazette I No. 8 of Bundesanzeiger Verlags mbHtransport of inflammable liquids on land (VbF) March 1, 1980, page 229of February 27, 1980

General administrative rule related to the decree Gazette No. 43 of Bundesanzeiger Verlags mbHon inflammable liquids of February 27, 1980 March 1, 1980, page. 5

Mining decree on the general certification Gazette No. 54, Part 1 Bundesanzeiger Verlags mbHof firedamp-protected electrical apparatus (1983)(mining decree on the approval of electrical apparatus – ElZulBergV)

The new equipment safety law (1980) Jeiter, W. Verlag C. H. Beck, Munich

Safety coefficients of inflammable gases and vapours; Narbert, K. and Schön, G. Deutscher Eichverlag 2nd edition (1963), 5th supplement 1980 Berlin W 30

Directives for the prevention of ignition hazards Central union of the employers’ Carl Heymanns Verlag KG, as a result of electrostatic charges – insurance liability association, , Cologne, Berlin, Bonn, MunichDirectives "Static electricity” – (1980) central office for industrial medicine,

Bonn

Notice “B“ of the Federal Physico- Technical Institute, , PTB PTBGroup 3.5; 1985

New procedure for the testing and certification Dreier H. and Hofer D. PTB notices No. 4 (1980)of explosion-protected electrical apparatus


EN 1127-1:1997 CEN VDE-Verlag GmbHExplosive atmospheres – Explosion protection – 10625 BerlinPart 1: Fundamental principles and methods

EN 50014: 1997 CENELEC VDE-Verlag GmbHElectrical apparatus for potentially explosive atmospheres - 10625 BerlinGeneral RequirementsAmendment A2:1999 to EN 50014:1997Amendment A1: 1999 to EN 50014:1997

EN 50015: 1998 CENELEC VDE-Verlag GmbHElectrical apparatus for potentially explosive atmospheres - 10625 BerlinOil immersion “o“

EN 50017: 1998 CENELEC VDE-Verlag GmbHElectrical apparatus for potentially explosive atmospheres – 10625 BerlinSand filling “q“

EN 50021: 1999 CENELEC VDE-Verlag GmbHElectrical apparatus for potentially explosive atmospheres – 10625 BerlinType of protection “n“

EN 50054: 1998 CENELEC VDE-Verlag GmbHElectrical apparatus for the detection and measurement of 10625 Berlininflammable gases – General requirements and testing methods

EN 50055: 1998 CENELEC VDE-Verlag GmbHElectrical apparatus for the detection and measurement of 10625 Berlininflammable gases – Requirements relating to the operationalbehaviour of group I apparatus with a measuringrange up to 5% (V/V) methane in air

EN 50056: 1998 CENELEC VDE- Verlag GmbHElectrical apparatus for the detection and measurement of 10625 Berlinbrennbarer Gase – inflammable gases – Requirements relating tothe operational behaviour of group I apparatus with ameasuring range up to 100% (V/V) methane in air

EN 50057: 1998 CENELEC VDE-Verlag GmbHElectrical apparatus for the detection and measurement of 10625 Berlininflammable gases – Requirements relating to the operationalbehaviour of group II apparatus with a measuring rangeup to 100% of the lower explosion limit

EN 50058: 1998 CENELEC VDE-Verlag GmbHElectrical apparatus for the detection and measurement of 10625 Berlininflammable gases – Requirements relating to the operationalbehaviour of group II apparatus with a measuring rangeup to 100% (V/V) gas

EN 50104: 1998 CENELEC VDE-Verlag GmbHElectrical apparatus for the detection and measurement of 10625 Berlinoxygen – Requirements relating to the operational behaviourand test methods

EN 50241-1: 1999 CENELEC VDE-Verlag GmbHRequirements relating to apparatus with an open measuring path 10625 Berlinfor the detection of inflammable or toxic gases and vapours, Part 1: General requirements and test procedures


Annex 6Harmonized standards todirective 94/9/EC



EN 50241-2: 1999 CENELEC VDE-Verlag GmbHRequirements relating to apparatus with an open measuring path 10625 Berlinfor the detection of inflammable or toxic gases and vapours –Part 2: Requirements relating to the operational behaviourof apparatus for the detection of inflammable gases

EN 50281-1-1: 1998 CENELEC VDE-Verlag GmbHElectrical apparatus for use in areas with inflammable dust – 10625 BerlinPart 1: Electrical apparatus protected by the enclosure –Design and testing

EN 50281-1-2: 1998 CENELEC VDE-Verlag GmbHElectrical apparatus for use in areas with inflammable dust – 10625 BerlinPart 1-2: Electrical apparatus protected by the enclosure –Selection, installation and maintenance and corrigendum of December 1999 to EN 50281-1-2: 1998

EN 50281-2-1: 1998 CENELEC VDE-Verlag GmbHElectrical apparatus for use in areas with inflammable dust – 10625 BerlinPart 2-1: Examination method – Method for determining the minimum ignition temperature of dust

EN 50284: 1999 CENELEC VDE-Verlag GmbHSpecial requirements relating to the construction, 10625 Berlintesting and marking of electrical apparatus in apparatus group II,category 1G

All rights reserved, in particular the right to reproduce and circulate, as well as theright to translate.

The data was compiled and verified with due care in keeping with the latest standardsand regulations. The prevailing technological and statutory rules are binding.

No liability will be assumed for any damages that may arise from the use of this data.

© 2000 CEAG Sicherheitstechnik GmbHSenator-Schwartz-Ring 26D-59494 Soest/Germany

Setting: Scholz-Druck, DortmundPrinting: Scholz-Druck, Dortmund

Publication No.1213/8/02.01/SDPrinted in the Federal Republic of Germany

CEAG Sicherheitstechnik GmbHSenator-Schwartz-Ring 26 Neuer Weg – Nord 49D-59494 Soest D-69412 EberbachPhone 02921/69-0 Phone 06271/81-500Fax 02921/69-636 Fax 06271/81-476Internet http://www.ceag.dee-mail [email protected]

1213

/8/0

2.01

/SD

Tech

nica

l det

ails

sub

ject

to a

ltera

tion