In our previous blog post on changes to IEC 60079.14, we noted that the EEMUA had expressed some serious misgivings about the new criteria for determining whether a compound barrier gland was required on Ex d cable entries. And it seems that they are not alone – the UK Health and Safety Executive (HSE) has recently chimed in on the subject by posting a Safety Alert that echoes the EEMUA’s concerns, and states that there is evidence that the new gland selection process creates a fire and explosion risk. The HSE has initiated a process to request a change to the IEC standard through the UK standards committee (presumably with the support of the EEMUA) and recommends users continue to use the Ex d gland selection flowchart found in the previous edition of the standard until such time as a change to IEC 60079.14 Ed 5.0 is agreed.
So there seems to be widespread concern about the changes, at least in the UK. But we found it interesting that neither the EEMUA position paper, or the UK HSE Safety Alert make any mention of cable construction, as we have always regarded it as the key issue in the debate – clearly a cable that is loosely constructed is more likely to allow flame propagation than one that is compact, but there has never been universally agreed criteria for determining what is compact enough. IEC 60079.14 Ed 5.0 appeared to try to clarify this by introducing a pressure test for cables in Annex E, and while we applauded the attempt we had our own criticism about the way this new test was referenced – the intent seems to be that cables passing the test are deemed “filled” and do not require barrier glands as long as they are longer than 3 m, but it’s not entirely clear in the current wording. The safety alert makes no mention of the pressure test, only the 3 m length criteria, so perhaps their interpretation of the clause is different from ours? But in any case the alert questions whether there is sufficient evidence to be sure that this new approach is in fact safe.
So what to do then? Well, it seems to us that it would be wise to heed an official warning from a UK government body (even if they have no jurisdiction in our part of the world), and apply the new cable test with caution, and in conjunction with the flow chart from the previous edition – i.e. cables passing the test are considered filled, but glands should be selected according to the flow chart rather than solely based on cable length. And we should note that the new IEC version has not yet been adopted as an AS/NZS standard, so the AS/NZS committee may take the UK comments on board during the adoption process.
In the longer term we think there is still a bit of work to be done to make this issue simpler – the flow chart and particularly the requirements for cables are complicated and open to different interpretations. As we have noted previously, the IEC offshore standard for hazardous area installations (IEC 61892.7) simplifies things by requiring compound glands on all Ex d cable entries. While simple, we think this is slightly over the top. But we wonder if requiring compound glands on all Ex d entries except enclosures containing only terminals might be a simple path forward? With no ignition source in the enclosure the risk of an internal explosion is very low, and the Ex d enclosure itself provides very good mechanical protection. Obviously we defer to the standards committees, but in our opinion this would be simple, easy to follow, and safe.