arpadveress 
…normal operation with worst conditions.
iec 60079-10-1 says:
“Catastrophic failures
As far as possible, such failures should be prevented.
Reasonably unexpected catastrophic failures need not be accounted for in the hazardous area classification. For example, major accidents such as the rupture of a process vessel, or large scale failures of equipment or piping such as total breakdown of a flange or seal.
The likelihood of such failures should be reduced by appropriate inspection, design, operation and maintenance of a plant.”
That highlights the topic how many times the HAC (hazardous area classification) shall be done following the various phases of projects, and operation of Ex sites as well. If there are changes the HAC shall be updated if necessary.
Worst can happen if the one HAC during project phase – let us call the initial one – is still in place during operation.
Keep up good work!
Arpad
