5. Validity of certification
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.
5.2 IECEx certificates
IECEx certificates are a statement of compliance with a particular version of the IEC standard or 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. In practice 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 recertification to the latest version of the standard. The interpretation of 'minor changes' varies between certification bodies and there is usually pressure to recertify to the latest standard.
The acceptability of an IECEx certificate [the latest version on the IECEx website] 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 Presumably if some previously unrecognised significant hazard emerged the certificate would be withdrawn or some clear warning included in the documentation.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.
5.3 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 by the European Commission]. Minor modifications are permitted in accordance with the original standard used but major changes require recertification to the current standard.
When creating the Document of Conformity [D of C] [which is necessary to comply with the CE marking and the placing of the equipment on the European market requirements], the manufacturer is permitted 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 D of C quoting a different version of the standard from that in the certificate. It is usual to add an explanatory note to the D of C.
If this procedure or an equivalent procedure is followed then the D of C confirms that apparatus certified to the older version of the CENELEC standard continues to satisfy the requirements of the ATEX apparatus directive.
This section lists the Explosive Atmosphere standards which are relevant to instrumentation. There are other standards which are partially relevant but a comprehensive list would be very long. The IEC standard is quoted in this document. The EN version has the same number as the IEC version and has identical technical requirements but with Annexes which satisfy the ATEX apparatus requirements. The English language version of the CENELEC EN standard is published by BSI as a BS EN and is usually used by UK manufacturers for both IECEx and ATEX certification.
It is important to recognise that the standards are not primers on the subject and some expertise in the subject is assumed. Similarly the requirements are additional to those required to ensure adequate safety and performance of non-hazardous equipment.
It is an unfortunate fact that standards grow and proliferate. In 1960 the subject of intrinsic safety was covered by BS 1259 [18 A5 pages] and currently requires a combination of BS EN 60079-0,-11 and -25, which comprise 303 A4 pages. This represents the advance in technology or unwarranted tedious detail depending on your viewpoint. The truth is probably somewhere in between.
IEC 60079-0 Explosive atmospheres - Part 0: Equipment - General requirements
Contains the requirements which are common to two or more methods of protection. For example requirements for the avoidance of electrostatic risk and impact test requirements are included. The individual apparatus standards state which sections are applicable to the specific method of protection, For example IEC 60079-11 the IS apparatus standard excludes several sections of 79-0.
IEC 60079-1 Explosive atmospheres - Part 1: Equipment protection by flameproof enclosures "d"
Contains requirements for 'da','db' & 'dc'. Implications being worked out.
IEC 60079-2 Explosive atmospheres - Part 2: Equipment protection by pressurized enclosure "p"
Quite complex document covering different levels of protection for different circumstances.
IEC 60079-7 Explosive atmospheres - Part 7: Equipment protection by increased safety "e"
Contains 'ec' requirements which will replace 'nA'
IEC 60079-10-1 Explosive atmospheres - Part 10-1: Classification of areas - Explosive gas atmospheres
Contains guidance on this difficult subject with some examples. Some other organisations such as the Institute of Petroleum produce documents which give useful guidance on particular situations.
IEC 60079-10-2 Explosive atmospheres - Part 10-2: Classification of areas - Combustible dust atmospheres
Dust equivalent of above
IEC 60079-11 Explosive atmospheres - Part 11: Equipment protection by intrinsic safety 'I'
Contains reference curves and tables as well as apparatus requirements. Contains the initial concept 'ic' requirements, which replaces 'nL'.
IEC 60079-14 Explosive atmospheres - Part 14: Electrical installations design, selection and erection
This standard attempts to be comprehensive so that users do not have to consult other standards. It is intended to supplement the usual good engineering practice and not replace it. There is strong interaction with IEC 60079-25, the IS system standard.
IEC 60079-15 Explosive atmospheres - Part 15: Equipment protection by type of protection 'n' electrical apparatus.
Base document. 'nL' has become 'ic' and 'nA' is migrating to 'ec', hence reference has to be made to the last appropriate edition of the standard for information on 'nL' or 'nA' equipment.
IEC 60079-17 Explosive atmospheres - Part 17: Electrical installations, inspection and maintenance.
Contains information on 'live maintenance' of IS circuits and other Zone 2 circuits. In addition has an interesting Annex C on 'Fitness-for-purpose assessment' which permits a large degree of freedom in the use of non-certified equipment.
IEC 60079-18 Explosive atmospheres - Part 18: Equipment protection by encapsulation "m"
There are three levels of protection available. Surprisingly not often used for instrumentation. Encapsulation of IS apparatus uses slightly different rules.
IEC 60079-19 Explosive atmospheres - Part 19: Equipment repair overhaul and reclamation
The majority of instrumentation is difficult if not impossible to repair but this standard gives guidance on competence and method, if this is to be attempted.
IEC 60079-20-1 Explosive atmospheres - Part 20-1: Material characteristics for gas and vapour classification - Test methods and data
Comprehensive list but inevitably does not include every explosive gas.
IEC 60079-20-2 Explosive atmospheres - Part 20-2: Characteristics of combustible dusts
This Space has been allocated but there is no supporting document. Information is available from different sources on the web. R.K.Eckhoff's book 'Dust explosions in the Process Industries' [ISBN 0 7506 32704] contains a useful list and is a good general reference on the subject.
IEC 60079-25 Explosive atmospheres - Part 25: Intrinsically safe electrical systems
Contains guidance on the safe combination of intrinsically safe apparatus. Interacts with and supplements IEC 60079-14.
IEC 60079-26 Explosive atmospheres - Part 26: Equipment with equipment protection level [EPL] "Ga"
Contains requirements for equipment used in Zone 0 or on the interface between Zone 0 and 1 not covered by 'ia','ma', 'da' and the pressurised standard. Requires detailed installation and maintenance instructions.
IEC 60079-31 Explosive atmospheres - Part 31: Equipment dust ignition protection by enclosure "t"
Lists the extensive requirements from IEC 60079-0 which are applicable.
PD CLC/TR 60079-32-1 Explosive atmospheres - Part 32-1: Electrostatic hazards, guidance
An 176 page treatise on everything you could wish to know about electrostatic problems. Only partly related to electrical apparatus.
PD IEC/TS 60079-39:2015 - Part 39: Intrinsically safe systems with electronically controlled spark duration limitation.
Permits higher power in Zone 1 by rapid switch-off
IEC 60529 Degrees of protection provided by enclosures (IP code)