API Bubbles

Not sure about your part of the world but the information on zone determination is generally found in a purchased standard (for example for us it would be IEC 60079.10 - Classification of Areas - Explosive Gas Atmospheres) and zone areas specified by the applicable project contractors (NOT the equipment supplier).

If you are just an equipment supplier then this is not your job and you should be contacting the customer or their consultant to provide this information for you.

Have you tried a search of the standards websites? Due to the specialist nature of zone determination you will likely need to buy the applicable standard(s) to assist in guiding you through the process (I doubt it will just give you a distance value) if you are the one who is contracted to designate the zoning on site.

Zone selection is a bit of an application and equipment specific risk management art form.

Try API RP500, RP505, and possibly 14F.

I believe that's 10 ft...

http://petrowiki.org/Hazardous_area_classification_for_electrical_systems#cite_ref-r2_2-0

https://global.ihs.com/doc_detail.cfm?&item_s_key=00122786&item_key_date=020131&input_doc_number=&input_doc_title=#abstract

It depends upon the nature, the quantity and the frequency of the release.

If in doubt, consult an appropriately-qualified Chemical Engineer locally.

Are you a licensed electrical contractor in the USA?

If so, you should be able to find this in the NEC.

If you are not a licensed electrical contractor,you should not be doing this type of work.

There are many caveats involved with hazardous locations that you should be aware

of,including the sealing of conduits entering the hazardous area from a non

hazardous area,disconnecting of ALL conductors entering the area(including neutral)

at the panel,etc.,etc.

Sounds like you are in over your head.

Consult a local inspector,or a qualified electrical contractor for information.

If you know it is Class I Div.2, who determined that? Usually the determination of an area classification also includes the boundary points as well. Ask the person responsible for the classification determination where the hazard rating ends.

If you determined that yourself, I think you may be attempting something beyond your capabilities. I am sure your insurance company will have some thoughts on this.