zone 2 normes

a report by

C EAG A pp a r a t e b a u Hund s b a c h GmbH & C o . KG

I n t r o d u c t i o n

During recent years, the importance of Zone 2-typeprocess instrumentation and lighting equipment forthe chemical, petrochemical and pharmaceuticalindustries has increased constantly.

This is primarily based on the hope that this will leadto more cost-effective installations. This articletherefore concerns itself with the basic requirementsfor this kind of apparatus for explosive atmospheres.

It is meant to give the user some practical advice onmounting and operating Category 3G equipment inZone 2 hazardous areas. It touches on importantaspects but does not claim to give a comprehensivepicture of all the rules and regulations that arerelevant in this field. For more details, we would liketo refer you to the European Directives 94/9/ECand 99/92/EC and the regulations of the usercountry as well as the European Standard EN60079–15 and EN 50021, etc.

Z on e 2 D e f i n i t i o n

Hazardous areas are divided into zones depending onthe likelihood and duration of the presence of ahazardous gas atmosphere. European standard EN60079–10 classifies Zone 2 as an area in whichexplosion hazards through flammable gases do notexist during normal operating conditions. Should anexplosive atmosphere arise, this would only happenvery rarely and for a short period of time only. Thisapplies to well-ventilated open air installations inwhich vessels containing flammable material wouldonly be opened under exceptional circumstances (seeFigure 1).

This indicates that Zone 2 is indeed a hazardous area,albeit of diminished dangers as compared with Zone1 hazardous areas.

The construction of electrical apparatus to bemounted in Zone 2 is governed by EuropeanStandards EN 50021, which specify protectivemeasures such as ‘nA’, ‘nC’, ‘nR’, ‘nL’ and ‘nP’. TheEuropean Standard EN 50021 is listed as a harmonised

European Standard referred to in Directive 94/9/EC.When harmonised standards are used, it is implied thatthe directives are indeed satisfied.

S t a n d a r d s

Standard EN 50021 applies to non-sparkingequipment and apparatus containing parts or electricalcircuits that, if left unprotected, would be capable ofigniting explosive gases in Zone 2 through arcs, sparksor hot surfaces. Their construction must ensure that afault that might lead to an ignition is most unlikely tooccur under normal operating conditions.

Zone 2 equipment is classed as explosion-protectedmaterial and therefore normally offers betterprotection than apparatus of ‘good industrial quality’,for example by ensuring minimum IP protection forenclosures, their mechanical stress resistance and theirreduced susceptibility to the build-up of electrostaticcharges. Any explosion-protected apparatusapproved for Zone 0 or Zone 1 may also be operatedin Zone 2.

It is the aim of type ‘n’ equipment and itssubdivisions to offer an economical alternative forCategory 3G equipment in Zone 2 to the superiorsafety levels of Category 2G/1G apparatus.

However, it is still necessary to carry out anddocument a safety check of interconnectedequipment in an electrical loop in Zone 2 in order toensure explosion protection.

Category 3G electrical apparatus is divided into fourgroups (protection measures). In general, thiscategory of devices bases all the protective measureson normal operating conditions, also taking care ofthe effective surface temperature and the ignitionproperties of sparks.

Fault conditions need not be taken intoconsideration. In addition, it is permitted to generateignition conditions during maintenance and repairwork as these are not classed as normal operatingconditions. However, foreseeable events that mayarise from operating conditions must be taken care of.

Exp los ion Protec t ion in Zone 2 Hazardous Areas –Elec t r i ca l Categor y 3G Apparatus

B U S I N E S S B R I E F I N G : C P I T E C H N O L O G Y 2 0 0 3

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Technology & Services

Me t h od s o f P r o t e c t i o n

Methods of protection for Zone 2 equipment toDIN EN 50021 are dealt with in brief as follows.

‘ n A ’ N o n - s p a r k i n g A p p a r a t u s

( S i m p l e , ‘ I n c r e a s e d S a f e t y ’ )

Principle of Protection

The construction ensures reliably that no unpermissiblyhigh temperatures or arcs or sparks on inner or outerparts can cause a surrounding gas atmosphere to ignite.

Applications

Plugs and sockets, low-energy apparatus (control andinstrumentation), fuses, lamps, transformers, batteriesand electrical motors, etc.

‘ n C ’ S p a r k i n g A p p a r a t u s o r

E q u i p m e n t F e a t u r i n g H o t S u r f a c e s o r

N o n - s p a r k i n g C o m p o n e n t s

( S i m p l e ‘ F l a m e - p r o o f E n c l o s u r e ’ o r

S i m p l e ‘ M o u l d e d E n c a p s u l a t i o n ’ )


Equipment is enclosed or hermetically sealed orencapsulated to ensure reliably that it will survivepossible high temperatures or arcs or sparks causingan explosion inside the enclosure and will not leadto subsequent ignition of the surrounding gasatmosphere or will avoid ignition of thesurrounding gas atmosphere reliably through their‘non-incendiveness’.

Parameters

There are limitations to the inner volume of thesedevices depending on the type of apparatus. Also,the maximum operating temperature must be 10Kbelow the permissible temperature for theencapsulating material.

Furthermore, the application is limited to AC 690V and 16 A for enclosed switch gear or AC 254Vand 16 A for non-incendive parts. Elastic gasketsmust maintain their properties during the lifetime ofthe equipment.

Applications

Contact systems, sparking apparatus, switch gearcoils, solenoid valves, motors, electronic printedcircuit boards, etc.

‘ n R ’ E q u i p m e n t i n V a p o u r - p r o o f

E n c l o s u r e s


The construction ensures reliably that the ingress ofhazardous gases and vapours is limited.

Parameters

The power dissipation inside the enclosure must notincrease the operating temperature by more than 10K.

Housings and hot surfaces therein must satisfy thetemperature class regardless of whether they containsparking or non-sparking equipment. It must be


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Figure 1: Sufficiently Ventilated Open Air Plant – Zone 2

Exp los ion Protec t ion in Zone 2 Hazardous Areas

possible to check the vapour proofing of theenclosure after the installation has been completed.

Elastic gaskets must maintain their propertiesduring the lifetime of the equipment. Also, themaximum operating temperature must be 10Kbelow the permissible temperature for theencapsulating material.

Vapour proofing is not suitable for installations thathave to be switched frequently as this wouldindicate the likelihood that switching takes placewhen an explosive atmosphere of gas or steamsurrounds the housing.

Applications

Lighting, switch gear, measuring, monitoring andcommunication devices and their installations (seeFigure 2).

‘ n L ’ E n e r g y L i m i t e d A p p a r a t u s a n d

C i r c u i t s ( S i m p l e , ‘ I n t r i n s i c S a f e t y ’ )


Energy limited circuits and components ensurereliably that neither a spark nor a thermal effect iscapable of igniting a flammable atmosphere.

Parameters

Energy limiting components must be operated atno more than two-thirds of their nominal valuesduring normal operation.

A safety factor of one regarding sparks is consideredto be sufficient.

Minimum requirements for housings feature IP54ingress protection. Circuits must be designed forvoltages below AC 60V or DC 75V. These mustnot be exceeded by more than 40% duringtemporary faults.

Applications

Measuring, monitoring and communicationequipment and their installations, sensors and energylimited actuators, etc.

‘ n P ’ S imp l e , ‘ P r e s s u r i s e d ’ A p p a r a t u s


The construction ensures reliably that a hazardousarea inside the enclosure is avoided by generating anoverpressure compared with the surroundingatmosphere.

Parameters

Optical indication upon loss of pressure, e.g. causedby leakage. It is not necessary to switch off powerwhen opening the enclosure.

Applications

Equipment and controllers that generate sparks andarcs or hot surfaces during normal operation can beoperated safely in Zone 2 using this method.

App r o v a l s

According to EC Directive 94/9/EC, Category 1Gor 2G electrical equipment (for Zone 0 and Zone 1)must be issued with an EC-type examinationcertificate by a nominated body. Mechanicalequipment only has to fulfil these requirements forCategory 1 apparatus.

Category 3 electrical apparatus as well as Category 2and 3 mechanical apparatus has to be issued with amanufacturer’s declaration. The manufacturer ofelectrical equipment for use in Zone 2 or mechanicalapparatus for use in Zone 1 or 2 must issue an EC-type examination certificate according to Directive94/9/EC, which must be signed by a responsibleperson of that manufacturer.


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Figure 2: Explosion-proof Lighting for Zone 2

This must state that the underlying safetyrequirements in § 3 of Directive 94/9/EC are met. IfEN 50021 is fulfilled for electrical equipment, itimplies that it comforms to the EC regulations.

For mechanical equipment for use in Zone 1, themanufacturer has to deposit the underlyingdocuments on which the declaration is based with anominated authority.

Obviously, a manufacturer of Zone 2 equipment isfree to apply to a nominated body of the EC forapproval of their product in accordance with EN50021 to be issued with a statement of conformity.

We prefer the latter approach since this ensures thata recognised authorised body checks that theconditions for hazardous area apparatus are met infull independently from the manufacturer. We havechosen this route despite or perhaps because of ourmore than 30 years’ experience in the field ofexplosion protection.

As an example, CEAG have had the PTB inBrunswick issue a statement of conformity for theirZone 2 lighting and flood lights as well as the wholeof the Remote I/O product range for Zone 2mounting. The equipment carries the mark: ‘ II 3G EEx nA II T4’.

This makes use of the same electronics as theintrinsically safe approved circuits that are EEx iaIIC certified (see Figure 3).

P l a c i n g o n t h e Ma r k e t

Zone 2 equipment has to be supplied with type tagsand labels according to Directive 94/9/EC. Thelabels have to carry the necessary information aboutthe manufacturer or the details of the manufacturer’srepresentative who is based in the EU. It also has tostate the device type and serial number, the numberof the EC-type examination certificate and detailsabout the explosion protection measures andmaximum values if applicable. Furthermore, theremust be an indication of the temperature class andthe maximum permissible ambient temperature ifthis differs from +40°C. The devices must also carry

the Epsilon ‘X’ sign enclosed by the hexagon andthe CE-mark.

Devices must also be issued with operatinginstructions for the safe installation, operation andmaintenance if applicable.

Qua l i t y A s s u r a n c e

Manufacturers of Category 3 equipment must proveto apply a quality system to ensure that the productsare manufactured in accordance with EC regulations.Normally, these producers as well as those ofCategory 1 and 2 equipment use DIN ISO 9001.

In addition, the quality system of manufacturers forCategory 1 and 2 equipment will also be monitoredby the approval body, for example PTB according tothe Directive 94/9/EC. So, manufacturers ofCategory 1 and 2 devices carry a significantresponsibility.

R e s p o n s i b l e P e r s o n

Large enterprises in the field of explosion protectionoften name a responsible person who can approveand certify equipment for use in Zone 2. The personwill be able to issue a manufacturer’s declaration ofconformity in accordance with EN 50021.

Furthermore, these responsible persons can verify thesafety integrity of the interconnection of one ormore associated pieces of apparatus with intrinsicallysafe equipment, even for Zone 1. The permission islinked to the manufacturer and will be granted basedon the long-standing experience in the field ofexplosion protection.

Ha r s h E n v i r o nmen t a l C o nd i t i o n s

Regardless of the required measures taken to ensureexplosion protection for a particular zone or area,you will have to observe the ambient conditionswhen selecting suitable equipment for a particularplant or section thereof.

Viewing these ambient conditions, it may be prudentto employ Zone 1-approved apparatus even in Zone2 to ensure the uninterrupted operation under thesecircumstances.

In Zone 2, you often meet with a harsh environmenti.e. electronic circuits exposed to a corrosiveatmosphere. This application lends itself, inparticular, to encapsulated devices. The fieldbus FBRemote I/O system may be the right answer. FBmodules are a ‘flame-proof’ yet hot-swap type ofdevice for use in Zone 1, offering intrinsically safeelectrical circuits or circuits of ‘increased safety’.


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Figure 3: Remote IO for Zone 2

Exp los ion Protec t ion in Zone 2 Hazardous Areas

As the electronics and layouts of both LB modulesfor Zone 2 and FB modules for Zone 1 are identical,an economical mix of the two systems is possible.

The housings that harbour the LB or FB modulesaccording to the declaration of conformity or theEC-type examination certificate may be openedduring operation.

Since the IP ingress protection is reduced to a lowerlevel during this maintenance operation (IP30), youshould make sure that water or rain cannot enter theenclosure at this point.

In Zone 1, the maximum permissible overtemperaturedepends on the ignition temperature of the requiredtemperature class. It must not be exceeded even underfault conditions. In contrast, Zone 2-certifiedequipment must satisfy these requirements for normaloperation within the manufacture’s specifications only.

T empe r a t u r e P r o o f i n g

Modules fitted on backplanes that are housed inenclosures intended for use in Zone 2 are subject toa temperature-proofing test in a similar way asintrinsically safe devices are for hazardous areamounting. It has to be shown that none of thesurfaces produce a temperature higher than themaximum permissible ignition temperature of thesurrounding explosive atmosphere. In Zone 2, thisapplies to normal operating conditions at themaximum permissible ambient temperature.

D i f f e r e n c e s B e tw e e n Z o n e 1 a n d Z o n e 2

CEAG imposes the same demands on electricalapparatus for Zone 1 or Zone 2 mounting during

development and production by set internal factorystandards. This concerns the safety of electricalcircuits, the choice of safety-related components andassembly in housings and their material. There is alsoa 100% factory test for all Zone 2 material. Wherepossible, Zone 2 cost reductions are realised.

The company regulations are based on thestandards for the applicable protection methods forelectrical equipment for use in Zone 1 hazardousareas. LB and FB Remote IO modules only differin the type of housing that suits the demands ofZone 1 or Zone 2.

S umma r y

The article presented here points out the demandson explosion-protected apparatus for use in Zone 2hazardous areas. It is shown that this Category 3equipment usually has to meet the samerequirements as regards intrinsically safe circuits asequipment connected to Zone 1 hazardous areas.The demands on intrinsic safety do not depend onthe mounting position but on the installation of theintrinsically safe field loops. IS circuits in Zone 2employ the same safety values as those in Zone 1,with the difference that normal operation is thebasis of the design and not a possible faultcondition. Foreseeable events that may derive from modes of operation must, however, be takeninto consideration.

This leads to the conclusion that Zone 2 designs mayoffer a certain economical advantage. On the otherhand, safety aspects should not be neglected whendeciding on the area classification. A smallcommercial advantage in the purchase of materialshould not increase the operational risk and with itthe dangers to staff and plant property values. ■


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zone 2 normes

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