Comments on: Ex d – a non solution to a hot problem http://mtlinst.wordpress.com/2006/11/24/ex-d-%e2%80%93-a-non-solution-to-a-hot-problem/ Thoughts and Comments on what is happening in the Ex field Fri, 03 Jul 2009 11:09:33 +0000 http://wordpress.com/ hourly 1 By: mtlinst http://mtlinst.wordpress.com/2006/11/24/ex-d-%e2%80%93-a-non-solution-to-a-hot-problem/#comment-1705 mtlinst Fri, 03 Jul 2009 11:09:33 +0000 http://mtlinst.wordpress.com/2006/11/24/ex-d-%e2%80%93-a-non-solution-to-a-hot-problem/#comment-1705 It comes from the German "Druckfeste" It comes from the German “Druckfeste”

]]> By: Somasekhar.K http://mtlinst.wordpress.com/2006/11/24/ex-d-%e2%80%93-a-non-solution-to-a-hot-problem/#comment-1704 Somasekhar.K Thu, 02 Jul 2009 11:49:30 +0000 http://mtlinst.wordpress.com/2006/11/24/ex-d-%e2%80%93-a-non-solution-to-a-hot-problem/#comment-1704 In"Ex-d",What is d In”Ex-d”,What is d

]]> By: mtlinst http://mtlinst.wordpress.com/2006/11/24/ex-d-%e2%80%93-a-non-solution-to-a-hot-problem/#comment-68 mtlinst Tue, 23 Jan 2007 09:59:11 +0000 http://mtlinst.wordpress.com/2006/11/24/ex-d-%e2%80%93-a-non-solution-to-a-hot-problem/#comment-68 It is interesting and commendable that at least one other supplier has considered the problem. There remains the fundamental problem that area classification of a location which contains a flammable gas at temperatures above atmospheric is not covered by the IEC or CENELEC standards and hence a risk analysis is the only appropriate technique. It is reasonable to argue that gases at a high temperature are easier to ignite than those at ambient temperature and hence a higher than normal level of protection is required. I would argue that the only method of protection that meets this requirement is the enhanced 'ia' which was previously discussed and that this needs to be used even where the gas/ air mixture being monitored is not always within the flammable range. Personally I would not consider a thermocouple assessed only against the Exe standard to be adequately safe. It may be that whoever certified the device took into consideration other factors not included in the Exe standard and thus ensured that it is adequately safe. If this is so then the test report and installation manual will list the additional factors considered and would make interesting reading if it can be published. On a more provocative note: It is possible that the IEC standard that suggests that a combination of Exd and Exe has got it wrong when considering thermal ignition. Exd apparatus is temperature tested in normal operation and this is accepted as being adequate in Zone 1 because the electrical protection will remove the fault in a relatively short time. If the Exe equipment inside an Exd enclosure within a Zone 0 develops a fault it seems questionable that the electrical protection will operate fast enough to prevent a possible explosion. The minimum requirement is that the electrical protection should be clearly specified. It is interesting and commendable that at least one other supplier has considered the problem. There remains the fundamental problem that area classification of a location which contains a flammable gas at temperatures above atmospheric is not covered by the IEC or CENELEC standards and hence a risk analysis is the only appropriate technique. It is reasonable to argue that gases at a high temperature are easier to ignite than those at ambient temperature and hence a higher than normal level of protection is required. I would argue that the only method of protection that meets this requirement is the enhanced ‘ia’ which was previously discussed and that this needs to be used even where the gas/ air mixture being monitored is not always within the flammable range. Personally I would not consider a thermocouple assessed only against the Exe standard to be adequately safe. It may be that whoever certified the device took into consideration other factors not included in the Exe standard and thus ensured that it is adequately safe. If this is so then the test report and installation manual will list the additional factors considered and would make interesting reading if it can be published.

On a more provocative note: It is possible that the IEC standard that suggests that a combination of Exd and Exe has got it wrong when considering thermal ignition. Exd apparatus is temperature tested in normal operation and this is accepted as being adequate in Zone 1 because the electrical protection will remove the fault in a relatively short time. If the Exe equipment inside an Exd enclosure within a Zone 0 develops a fault it seems questionable that the electrical protection will operate fast enough to prevent a possible explosion. The minimum requirement is that the electrical protection should be clearly specified.

]]> By: Chris Chant http://mtlinst.wordpress.com/2006/11/24/ex-d-%e2%80%93-a-non-solution-to-a-hot-problem/#comment-66 Chris Chant Mon, 22 Jan 2007 20:54:31 +0000 http://mtlinst.wordpress.com/2006/11/24/ex-d-%e2%80%93-a-non-solution-to-a-hot-problem/#comment-66 I agree that most suppliers do not take into account the Thermocouple or RTD when they have their terminal heads certified we Okazaki have taken this into account an dhave considered all fault conditions an dhave had our range of temperature senors certified EExde which takes into account the two fault conditions EExd for the enclosure and E increased safty fo the senor so we can issue a cert without any thermowell I agree that most suppliers do not take into account the Thermocouple or RTD when they have their terminal heads certified we Okazaki have taken this into account an dhave considered all fault conditions an dhave had our range of temperature senors certified EExde which takes into account the two fault conditions EExd for the enclosure and E increased safty fo the senor so we can issue a cert without any thermowell

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