There is currently a key difference between the current IEC 60079-14: 2013 Standard and previous versions of BS EN 60079 -14:2008 IEC 60079- 14: 2007 for use of electrical equipment in potentially explosive atmospheres in that the IEC Standard currently allows the Duty Holder to use a ‘standard’ Ex certified flameproof gland as opposed to a Ex certified ‘barrier gland’ without the requirement to apply the previous flowchart used in the British Standard which identified glanding requirements based on gas group / zone / enclosure size. There is evidence that this approach creates a fire and explosion risk and this Notice provides Duty Holders with information on what action to take.
The current International Standard, IEC 60079-14: 2013 Standard allows Duty Holders to use a ‘standard’ Ex certified flameproof gland as opposed to a Ex certified ‘barrier gland’ without the requirement to apply the previous flowchart used in the British Standard which identified the glanding requirements based on gas group / zone / enclosure size, provided that the Duty Holder uses:
IEC 60079-14: 2013, Clause 10.6.2
b) Cables and glands meeting all of the following:
- Cable glands complying with IEC 60079-1
- Cables used to comply with (Clause) 9.3.2 (a)
- The connected cable is at least 3m in length.
There is credible independent evidence that this approach poses a risk of fire propagation through the cable sheath (after multiple ignitions) and therefore such a scenario may pose an ignition risk if the new IEC Standard is applied by Duty Holders, i.e. no barrier gland is used.
The 2014 version of BS EN 60079-14 does mirror the IEC Standard in respect of the above clause and requirements in the ‘Normative’ body of the Standard, however this version also contains a National Annex (NA) (see p138 onwards) that acknowledges the British Standards Institution’s (BSI) concerns over the application of the IEC Standard to the use of barrier glands (see below). Reference to this National Annex is also clearly stated in the ‘National foreword’ of the British Standard:
NA.4 UK committee concerns
- The UK Committee is not aware of any issues (either unsafe or over-engineered situations) relating to the use of the selection chart since its adoption in the UK in 1989 and subsequent international adoption in 1996.
- The UK Committee have not seen documented evidence of any tests carried out to justify either the removal of the selection chart or its replacement by the new selection procedure.
- Verbal descriptions of recent tests seem to suggest that tests only relate to ignitions through the cable. The original ERA research project highlighted that severe thermal damage can be inflicted on the core insulation and bedding by the heat generated by multiple explosions within the enclosure. This could result in subsequent catastrophic failure of the cable leading to ignition of the surrounding atmosphere.
- The selection chart only applied to flameproof enclosures which contained a source of ignition in normal operation, but the new procedure applies to all flameproof enclosures. Previously all junction boxes and indirect entry terminal boxes did not require barrier glands; however, under the new edition, unless the cable is at least 3m in length, a barrier gland will be required. The UK committee is unclear as to the justification for this change given that potential failures only arise after multiple ignitions.
Note 1 The new edition seeks to clarify the requirement for the cable to be at least 3m in length by referencing the new Annex E of the Standard. Annex E is titled “Restrictive breathing test for cables” and prescribes pressure drop tests with the cable connected to an enclosure. However, as this annex is informative, it is not clear whether cables will require testing to avoid the need for a barrier gland. The UK committee is of the opinion that such testing is not reasonably practicable.
NA.5 Recommendation by the UK committee for users of this Standard and notice of future intent
- Given the serious concerns expressed by the UK committee in relation to IEC 60079-14: 2013 (Edition 5), Clause 10.6.2 (b) throughout the whole revision process, they intend to submit a proposal to IEC to amend Edition 5.
- Until such time as the situation is resolved, the UK committee recommend that users continue to consult the selection chart, reproduced as figure 1 in this Annex, to compliment the Standard.
At the moment this issue is being escalated by the BSI Technical Committee and the British Standard is also clear (although this National Annex section is ‘Informative’) that Duty Holders should continue to consult the existing flowchart (i.e. the selection chart – included in the NA annex Figure 1) to determine if a flameproof ‘barrier’ gland should be used.
HSE recognises the risks identified by the BSI Technical Committee and also has further independent 3rd party evidence that supports the BSI’s conclusions.
In order to ensure that this risk is suitably controlled, the HSE
has defined the ‘Informative’ National Annex of BS EN 60079-14: 2014 as an ‘Established Standard’ (see http://www.hse.gov.uk/enforce/emm.pdf ) as it is considered to be a “published or commonly known standard of performance interpreted by HSE as a level of performance needed to meet a general or qualified duty under health and safety“.
Duty Holders should therefore apply the Informative National Annex of BS EN 60079-14: 2014 as Relevant Good Practice when assessing the requirements for fitting a barrier gland to electrical equipment in potentially explosive atmospheres.
Control of Major Accident Hazards Regulations (COMAH) 2015
Dangerous Substances and Explosive Atmospheres Regulations 2002
BS EN 60079 -14: 2014 (National Annex)
Contact the HSE’s CEMHD Electrical, Control and Instrumentation team for further information on the subject or visit http://www.hse.gov.uk/eci/index.htm
This Safety Notice should be circulated to all relevant Duty Holders / Employees that are involved in the design, selection, installation, inspection and maintenance of electrical equipment in potentially explosive atmospheres.
Article source: http://www.hse.gov.uk/safetybulletins/use-of-barrier-glands.htm