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Standards and certification for hazardous area instrumentation

29 January 2016

This article, written by Intrinsic Safety Consultant Chris Towle and submitted by BEKA associates, is intended to provide guidance on the certification and standards used in the design and application of instrumentation used in hazardous areas. Inevitably this subject is one of constant but usually slow change and hence the date on which this document is written – January 2016 - should be taken into account. 

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All standards are created by individuals who have a specific interest in the subject. The time involved and the costs incurred by participants are considerable. This restricts the people involved to those with an enforcement, certification or commercial interest. Consequently the major representation on international committees is from certification bodies; manufacturers have adequate representation but end-users are not adequately represented. The resultant standards are reasonable and produce adequately safe equipment, which is surprising and a testament to the integrity of the individuals involved.

1.  Standards organisations

1.1  IEC

International standards for electrical equipment are created by the International Electrotechnical Committee [IEC]. Those covering hazardous areas are created by a specific committee TC31 and its numerous sub-committees and form the IEC 60079 series. The process of creating and modifying standards is  slows. An interval of five years between editions of the standards is common. Almost all national standards-organisations are members of IEC
The format of the IEC standard number is IEC 60079-xx: yyyy. The xx being the part number of the specific section and the yyyy the year of publication.

1.2. CENELEC

The European Committee for Electrotechnical Standardisation [CENELEC] are the European standards making body for electrical equipment. Currently IEC and CENELEC hazardous area standards are voted on simultaneously and bear the same number. The CENELEC committee on intrinsic safety exists but has not  met for several years. The standards are identical in technical content but the CENELEC standard contains further information to make it more useable with the ATEX directive. The apparatus standards are ‘harmonised’ as being an acceptable interpretation of the ATEX directive. It is important to recognise that the directive is a European Union [EU] document not a CENELEC standard and hence introduces some minor differences. There is usually a time difference of several months between the publication of the IEC standard and the publication of the EN and its final ‘harmonisation’ so that it can be used for ATEX certification. This delay could lead to there being different requirements for IEC Ex and ATEX certification for a short time. However no significant problems have occurred as far as is known to the author.

The CENELEC standard number [European Norm] is the same as the IEC standard and has the form EN 60079-xx: yyyy. The date of publication may be one year later than the IEC standard.

1.3. BSI

The British Standards Institution [BSI] is the UK  member of both IEC and CENELEC. BSI publish an English language version of the CENELEC standard. The form of the standard number is BS EN 60079-xx: yyyy. The technical content of the IEC, CENELEC and BS standards are identical.

2.  IECEx

The IEC has an affiliated organisation which issues certificates of compliance with the IEC 60079 Series of standards. [There are a number of other related activities]. These certificates are based on detailed test reports created by Approved Certification Bodies [ACBs] and are granted to manufacturers with approved quality control systems. The organisation is based in Australia; it has a strong secretariat responsible to a committee controlled by the ACBs. A major advantage of IECEx certificates is that the latest version is available on the web. Anyone can use the IEC standards as a basis for ‘certification’ but cannot create an IECEx certificate, which is an ACB privilege.

The intended ideal is for IECEx certificates to be accepted universally. Some progress has been made, for example in Australia and Singapore, and there has been considerable support from the  United Nations. Numerous countries issue certificates based on the IEC test report but sometimes the acceptance is questioned in excruciating detail and other barriers to issuing the certificates erected. It can still be an irritating and expensive business.

It is disappointing that IECEx certificates are not usually acceptable in Europe and the US  In countries where the end-user decides what is acceptable then IECEx certificates are favoured. The usual practice of European manufacturers is to obtain an IECEx certificate and test report and use these to obtain an ATEX certificate. The only consolation is that the current situation is a considerable improvement on the late 1900s when everybody used different standards and their own certification body.

3.  ATEX

3.1  Introduction

There are two ATmosphere EXplosive Directives [ATEX] currently in use. The directive which covers the marketing and manufacture of equipment for use in hazardous atmospheres is 94/9/EC generally referred to as the ‘Apparatus Directive’. The other directive, 1999/92/EC is intended to ensure at least the minimum level of protection for workers in industries using hazardous materials. It is generally known as the ‘user directive’.

3.2  User Directive 1999/92/EC

This ‘worker protection’ directive requires a detailed, well documented risk analysis of the installation. Defining the acceptable risk is a very difficult task. The usual approach is to use equipment covered by appropriate Documents of Conformity, which is installed and maintained as required by the EN codes of practice [EN 60079-14, and -17]. Theoretically a risk analysis can be used to circumvent the use of certified apparatus but this would require a very detailed comprehensive knowledge of all the relevant factors which is not usually available.

Consequently this option is not often used but can be used to justify the continued use of old equipment or installations.

All European legislation has to be enacted in each country. Within the United Kingdom this Directive became law as part of the ‘Dangerous Substances and Explosive Atmospheres Regulations’ [DSEAR]. These regulations also include the requirements of the ‘Chemical Agents Directive’ [CAD], This arrangement can be slightly confusing but is  convenient since the requirements overlap.

Compliance with these regulations is the responsibility of the end-user. Some notified bodies do offer to carry out investigations and do inspections. These reports can be used to support the safety documentation but the responsibility still rests with the end-user.

3.3  Apparatus Directives  94/9/EC and 2014/34/EU

The directive which covers the design, manufacture and marketing of equipment for use in hazardous areas is currently the 94/9/EC directive. It will be replaced on April 20th 2016 by the recently created directive 2014/34/EU. Fortunately  the supply and use of apparatus  which is already certified will be permitted. New equipment or equipment being significantly modified will be certified to the new directive from that date. It will be necessary to issue revised Documents of Conformity [DoC] for existing equipment from the changeover date. The new Directive does slightly tighten the requirements for Notified Bodies and it will be interesting to see if there is a flood of new certificates on the day after the Notified Bodies have their ratification renewed.

The ATEX certificate is used as evidence of compliance with the requirement of minimising the risk of an explosion and authorises the use of the distinctive hexagon Ex mark.

Usually ATEX certificates are based on the CENELEC standards [EN 60079-x Series] but theoretically can be issued based on the ‘essential safety requirements’ of the Directive, without reference to the detailed requirements of any standard. However this approach is rarely used. There are requirements for the manufacturer to have adequate quality control systems [which are subject to surveillance] so as to ensure that the product produced complies with the certification. The directive only requires Category 1 and 2 equipment [usually interpreted as equipment for use in Zone 0 and 1] to be certified by a Notified Body. Category 3 [Zone 2] equipment can be ‘certified’ by the manufacturer  but this is not always acceptable to the end-user and consequently most Notified Bodies  do issue ‘certificates’ for Category 3 equipment. There is no shortage of Notified Bodies, for example the UK has eight which contrasts with one prior to ATEX.

The ATEX certificate is evidence of compliance with minimising the explosion risk but the legal requirement and the CE marking requires compliance with all relevant directives.

This is recorded on the Document of Conformity [DoC] which lists the relevant directives and the method of compliance. The directives which are usually quoted for instrumentation are the ATEX Directive, the low voltage directive [LVD] and the radio frequency interference directive {RFID}. The RF decoupling capacitors used to ensure compliance with the RFID are usually quite small but can affect the IS certification. Late changes in value can delay final IS certification.  Other directives such as the machinery directive are applicable to some equipment. The DoC is the responsibility of the organisation placing the equipment on the market. Frequently hazardous area equipment may also be used for non-hazardous applications and the DoC should take into account this possibility.

3.4  ATEX  Countries of use

There are a large number of countries where it is a legal requirement to comply with the ATEX Directive.  The 28 states of the European Union [EU] [no longer the European Community] together with the three states which are members of the European Free Trade Area [EFTA] [Iceland, Liechtenstein and Norway] form the core of the common market. There are a variety of  agreements with other countries such as Turkey  and Switzerland.  In addition a number of territories with ex-colonial attachments are also involved, but there are some surprising exceptions such as Gibraltar and the Falkland Islands.

In these and some other countries end-users specify ATEX certified equipment as a guarantee of quality. This is common practice in the Middle East, some Asiatic countries and for some marine applications. Possibly the trend is to specify IEC Ex equipment  in preference to ATEX but the additional commitments of the DoC still influence some end-users. Offering both forms of certification is the option adopted by most European manufacturers.

4. Validity of certification

4.1  Standards

When a revised standard is issued, there is usually a period when the certification bodies can issue certificates to the previous version. Commercially there is always pressure for certificates to be issued to the latest version and consequently this relaxation is not frequently used. 

The Foreword of an IEC standard contains a list of the changes from the previous version of the standard. The changes are classified into three levels of significance:
1)  Minor and editorial changes
2)  Extensions in scope
3)  Major technical changes. The nature of these changes is also indicated in the Foreword.

If the major technical change is because of the recognition of a previously unknown significant explosion risk then corrective action to existing equipment might be considered necessary and the validity of existing certificates questioned. Fortunately no such technical change in the standards relating to instrumentation has occurred in the last fifty years. Consequently the continued use and placing on the market of equipment certified to earlier versions of the IEC/CENELEC standards is considered to be adequately safe.

4.2  IECEx certificates 

IECEx certificates are a statement of compliance with IEC standards at a specific time. There is no time limit. The standards used are the current versions with a changeover period when the standard is updated. There is always commercial pressure to use the latest version of the standard and this changeover concession is rarely used. Minor changes to the design are permitted, without modifying the certification but major changes require re-certification to the latest version of the standard. The interpretation of ‘minor changes’ varies between certification bodies and there is usually pressure to recertify.

The acceptability of an IECEx certificate remains with the end-user. Presumably if some previously unrecognised significant hazard emerged the certificate would be withdrawn or some clear warning included in the documentation. Fortunately this problem has not occurred. Certificates based on older standards are still valid but may be regarded with some suspicion by some users. In practice older equipment is adequately safe and has the additional merit of safety, proven by time and use.

4.3. ATEX certificates and Documents of Conformity

ATEX certification is based on the latest version of the harmonised version of the CENELEC standard with a transition period [1to 2 years] at the changeover. [Harmonisation is the ratification of the standard as an adequate interpretation of the ‘Essential Health and Safety Requirements’ [EHSR] of the Directive ]. Minor modifications are permitted in accordance with the original standard used but major changes require recertification to the current standard.

When creating the DoC, the manufacturer is required to quote the latest harmonised version of the standard. This is permitted provided that an analysis of the standards shows that there has been no significant change from the standard used in the original certification which detrimentally affects the EHSRs of the apparatus. This results in the DoC quoting a different version of the standard from that in the certificate. It is usual to add an explanatory note to the DoC.



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