Furse, Wilford Road, Nottingham, NG2 1EB • Tel: +44 (0)115 964 3700 • Email: enquiry@furse.com • Web: www.furse.com

Lightning protection of hazardous areas

Lightning protection ofhazardous areas to ATEX/IECEx

IECEx

Many industries, such as petrochemical, oil & gasand pharmaceutical, face the ongoing challengeof protecting people and property from the riskpresented by potentially explosive atmospheres.

These atmospheres create hazardous areas, whereflammable gases, powders, or dusts have the potentialto mix with air at a ratio which would result in anexplosion if ignited by a spark or other source ofignition (static charge, chemical reaction etc).

Clearly, lightning presents a significant threat topotentially explosive atmospheres, both through adirect strike and the risk of partial lightning currentsentering the hazardous area via incoming/outgoingmetallic services.

The employer or plant operator has responsibility forensuring safety against potentially explosiveatmospheres, and should therefore reference therelevant standards and directives - BS EN/IEC 62305 forlightning protection and ATEX (IECEx outside the EU)for protecting potentially explosive atmospheres -when establishing the requirement for lightningprotection on site.

ATEX directivesTwo ATEX directives have been published with the aimto protect employees, the public and the environmentfrom accidents owing to explosive atmospheres.

They require employers to eliminate or control risksfrom hazardous areas, to classify areas where explosiveatmospheres may occur, and to ensure productssuitable for use in those areas are applied.

From July 2006, all existing and new sites wherehazardous areas are present must be ATEX compliant.

ATEX 137, Directive 1999/92/EC

This directive covers health & safety of employees atrisk from explosive atmospheres.

It requires employers to take necessary steps to preventformation of explosive atmospheres, to avoid ignitionin explosive atmospheres where they cannot be fullyprevented, and to limit the effects of a explosionshould such an event occur.

It further classifies the places where explosiveatmospheres may occur into a number of zones (see Table 12).

ATEX Article 100A, Directive 94/9/EC

This directive covers equipment and protective systemsfor potentially explosive atmospheres and the health &safety requirements to which they must conform.

It applies both to equipment and systems used inpotentially explosive atmospheres, and those sitedoutside these atmospheres which contribute to thelevel of safety in the hazardous area.

Equipment is categorised in line with the protectionlevel offered against the risk of producing a spark orsource of ignition in a potentially explosiveatmosphere. Categories include:

l Applicable zone and equipment group forgases/vapours (II) or dusts (III)

l Protection level, per zone, according to risk fromgases/vapours (Ga; Gb; Gc) or dusts (Da; Db; Dc)

l Form of protection (flameproof enclosure - Exd;Increased Safety - Exe; Intrinsically Safe - Exi etc)

l Level of protection to gas/vapour group or dustgroup (IIA; IIB; IIC)

l Restrictions in product usage (equipment withoutrestriction; equipment with special condition - X;component - U)

l Temperature Class (T1-T6, spanning temperaturesfrom 450 ºC down to 85 ºC)

Products classified as intrinsically safe (IS) are furthercategorised according to their applicable zone (seeTable 13 below).

Products are tested to ensure compliance with therequirements of ATEX, with approved products markedaccordingly based on the classification system, andincluding their ATEX certification number.

Expectation of potentially explosive Zone Reference

atmosphere/hazard arising Gas Dust

Hazard is continuously present, for long periods orfrequently (> 1000 hours per year)

Zone 0 Zone 20

Hazard is likely to arise occasionally during normaloperation (10-1000 hours per year)

Zone 1 Zone 21

Hazard is not likely to arise during normal operation,or is of short duration only (< 10 hours per year)

Zone 2 Zone 22

No hazard is present SAFE AREA

Table 12: Zonal classification of hazardous areas

Symbol Suitable for Category Standard

Ex ia Zones 0, 1, 2, 20, 21 & 22 1 EN 50020

Ex ib Zones 1, 2, 21 & 22 2 EN 50039

Table 13: Intrinsically Safe product classification

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Lightning protection of hazardous areas

Lightning protection of hazardousareas in line with ATEX/IECExWith hazardous areas at risk from the consequences of direct and indirect lightning, a comprehensiveapproach to lightning protection in line with BS EN/IEC 62305 should be considered.

This should cover structural lightning protection,earthing & equipotential bonding, and transientovervoltage protection.

The zonal approach to lightning protection, asestablished in BS EN/IEC 62305 (see page 272, Lightning Protection Zones), is applicable for designingan LPS suitable for hazardous areas, considering thefollowing points.

Structural lightning protection

For locations with potentially explosive atmospheres,as defined by BS EN/IEC 62305:2011 the appropriateClass of LPS required shall be dictated by the riskassessment process in BS EN/IEC 62305-2.

An isolated LPS is required since the structure includescombustible materials and/or presents a risk ofexplosion, with minimum separation distances adheredto between the LPS and structural metallic parts toremove any risk of sparking.

Additionally, catenary conductors raised high abovethe structure should be considered, where these are toprotect locations where combustibles are present, suchas gas/oil storage tanks.

Earthing & equipotential bonding

The earth termination system should meet therequirements set out in BS EN/IEC 62305-3 - a single,integrated earth termination system combininglightning protection, power and telecommunicationssystems. It should provide low electrical resistance (lessthan 10 Ohms) and be appropriately bonded to ensureno metallic part is at a different potential with respectto another.

Where incoming or outgoing services cannot bebonded directly to earth, these should be protected bya suitable SPD.

Following the zonal approach in BS EN/IEC 62305,services passing from LPZ 0 to LPZ 1 should beprotected against partial lightning currents using alightning current/equipotential bonding SPD (tested to10/350 µs waveform), as well as transient overvoltages(SPD tested to 8/20 µs waveform).

Electronic systems protection

Electrical and electronic equipment/systems need to beprotected against transient overvoltages, since damageto components could lead to risk of sparks or fire.

Equipment/systems sited in a safe area which do notcontribute to safety in a potentially explosiveatmosphere can be protected against transientovervoltages using appropriate standard SPDs, asdefined by BS EN/IEC 62305.

However, equipment/systems sited in potentiallyexplosive atmospheres (Zone 1, 2) or contributing tosafety within these atmospheres require an SPDsuitably tested and approved by ATEX.

All SPDs installed on site should form a coordinated set to ensure protection levels are maintained andeffective throughout.

Protection of intrinsically safe (IS) circuits

Intrinsic Safety (IS) is a concept for protectinghazardous areas from dangerous sparking, wherebysparks from electrical equipment and circuitry areprevented through the use of IS barriers.

These barriers limit the available electrical energy thatcould cause an explosion to below ignition threshold.

IS Barriers however are not surge protectors but arefield instruments which are themselves at risk fromtransient overvoltages. IS circuits therefore need to beprotected from transient overvoltages by a suitable(ATEX approved) SPD.

Protection should be applied at the boundary betweenthe hazardous and non-hazardous area (see Figure 23),with an isolated screen SPD installed within thehazardous area (Zone 1, 2).

For more information on protecting hazardous areainstallations from lightning, please contact us.

Inst

rum

enta

tion

InstrumentEarth

ESP SL30X/IESP SL30XControl cabinet

IP54enclosure

InstrumentEarth

SystemEarth

Fieldearth

Open end cable screen

ZON

E 0

Hazardous Area Zones 1, 2Non-Hazardous Area

Isolatedcoupling

ISBa

rrie

r

ZONE 1

ZONE 2

Figure 23: The installed SPD(here the ESP SL30X Series)provides protection for theinstrumentation as well asproviding protection forthe IS Barrier.

The isolated screen version(ESP SL30X/I) should beused in Zone 1, 2.

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