En 60079-31, introduced in 2008 is a specific standard for dust using 'Protection by Enclosure' i.e. keep the dust out.
Based on the principle, for Dust, that a good ingress protection rating, by definition, should be sufficient to prevent an explosive dust mix forming within the enclosure. The primary concern therefore is the temperature rise of the walls of that enclosure¹.

Split into 3 protection levels Ex ta, Ex tb and Ex tc for Categories 1D, 2D and 3D respectively. Ex ta is the only² Category 1 protection method other than Ex ia.

If the primary protection method is to keep the dust out then generally it does not matter what goes into the enclosure³ as long as the heat dissipation is considered. Any items going through the enclosure walls i.e. coming in contact with the dust must be suitably certified.

As of 2025 there are still equipment being sold that was certified to EN 61241-1, which was the predeccessor to EN 60079-31 and withdrawn in 2010.

Without wishing to generalise to much, most of this is equipment is category 3D self certifed and can by recognised by certification labelling such as Ex tD A22 or similar.

While the historical certification is valid and equipment in use can still be used, for recently purchased items questions should be asked regarding its provenance, as reliance on 3rd party unsupported statements of IP rating and lack of actual temperature testing was not unheard of.

One of the effects of the 2014 Atex Directive was to disallow any variations to Atex certificates based on older standard i.e. changing components.
This could cause issues with spares and component replacement as historically non certified components were often used just based on their untested (by the certifier) IP rating.

It is recommended, if using older (EN 61241-1) certified equipment to at least ensure you have a 3rd party Type certificate to verify its compliance and, if purchased since 2016, a Declaration of Conformity with standards used for certification.

Notes

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