Hi ali, you state you are an Electrical Engineer, you question is very basic in regard to your level and it also scares me that you question concerns the use of RCBO's in hazardous areas, I must recommend you call in a competent Engineer to answer your questions, at the risk you are asking this advice to do work on Hazardous area installs I am closing the Thread as you should not be asking such questions through a Forum if you are involved with such work.
-Find a local Engineer to Tehran to advise you as our regulations are British Standards and you will have your own local standards to follow.
-Strict rules and regulations apply to circuits in hazardous areas, you should have a full working knowledge of these regulations if you are involved with them and not asking such a question as above.
For these reasons I am closing the Thread ...Sorry!