In hazardous area classification, which standard should I refer to get the extent to which a zone extends?

IEC 60079-10-1 is applied where there may be an ignition hazard due to the presence of flammable gas or presence of flammable gas or vapor, mixed with air under normal , mixed with air under normal atmospheric atmospheric

IEC 60079 series apply to mines (gas group I), processing and manufacturing of explosives, areas where a hazard may arise due to the presence of combustible dusts or fibers (refer to IEC 61241-10 / IEC 60079-10-2), catastrophic failures which are beyond the concept of abnormality dealt with in this failures which are beyond the concept of abnormality dealt with in this standard, rooms used for medical purposes, domestic premises.

There are different standards including National & International Standards those can be used to classify the Hazardous area and zoning of the Hazardous areas depending upon the level of hazard and area application. Some are as under:

International - IEC 60079 series

European - CENELEC 60079 series

USA - ANSI/API RP 505 (zone system)

Russia - Gost R 51330-X-99 series