It is a common misconception that one cannot repair IIC machines.
At one time we did teach that you could not reclaim IIC machines, but this is not what the standard says, and was incorrect.
You can reclaim IIC machines if you follow Annex C of BS EN IEC 60079-19:2011 + A1 2015, and you can normally carry out a standard repair, if reclamation is not required.
With any repair you try to get as high up Annex C: 1 to 6 sections as possible ( as demonstrated in the decision tree)
1: you have dimensions from the certificates and drawings. or
2: You have the certificate, which gives you the standard numbers to which it was certified to on the certificate, and get the flamepath dimensions from those.
3b: as above
3c: Refer to the certificate for the safety conditions that the “x” refers to. If it refers to reduced gaps then use the gaps referred to in the certificate.
4: If the gaps are badly damaged, but in other areas (say on a shaft) there is no damage and you can get the accurate measurements to which the flamepath was originally designed to from that, use these measurements,
5: or if you have the accurate measurements from when the job was in previously or another source, use those.
6: This last part is where the confusion arises. If all else fails use the gaps in the very latest IEC 60079 1 standard, but in this case you must make the reductions if using reclamation and do not know what the original dimensions were this will allow for potential pressure piling. This can only be done for IIB and IIA machines, you cannot reclaim IIC machines using the latest standard (as per note d in part 6) , but you can use methods complying with 1 to 5 for IIC machines.
It is the only reference in the standard that says you cannot reclaim (NB not cannot “repair”) IIC machines and it only refers to the part 6 method using the latest standard for reclamation.
As such the standards you should have to repair these machines are as listed on the machines' certificate ideally, or deduced from the AEMT standards date chart and name plate.