arpadveress 
…are varied. Often an area classification plan-view is provided to identify equipment ratings and installation techniques to be used for each classified plant area. The plan may contain the list of chemicals with their group and temperature rating, and elevation details shaded to indicate Class, Division or Zone and group combination.
The area classification process would require the participation of operations, maintenance, safety, electrical and instrumentation professionals, the use of process diagrams and material flows, MSDS and any pertinent documents, information and knowledge to determine the hazards and their extent and the countermeasures to be employed.
Area classification documentations are reviewed and updated to reflect process changes.
Many ask how often as minimum period of time: within 3 years if you do it, you shall be on the safe side.
Keep up good work!
Arpad
exprofessional.com
