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Topic Title: ATEX hazardous area classification
Topic Summary: T class allocation
Created On: 15 August 2012 05:40 PM
Status: Read Only
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 15 August 2012 05:40 PM
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SeanElec

Posts: 16
Joined: 01 February 2006

When preparing a specification for equipment in a hazardous area the engineer needs to know the gas which might be ignited. My query is about the T class, where the auto-ignition temperature of the gas must be above the maximum equipment surface temperature in fault conditions. For example auto-ignition of heptane can occur at 215 DegC. A T3 equipment can reach 200 DegC in fault conditions. Is a 15 DegC allowance acceptable or is it too small ??
What is the accepted practise ??

Thanks.
 17 August 2012 11:33 PM
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neilparsons

Posts: 31
Joined: 29 October 2002

A safety margin of 25degC is normally applied to the T Class. You should really look at equipment with a rating of T4.

Also bear in mind that the T Class ratings for most kit is based on a max ambient temperature of 40degC. Any higher and you will need to consult the manufacturer regarding further de-rating.
 23 August 2012 11:03 AM
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SeanElec

Posts: 16
Joined: 01 February 2006

Neil,
Thank you for that. 25 DegC seems reasonable to me also. I afterwards discovered that the manufacturer has to allocate a safety margin also when he declares the T class of his equipment.
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