You can view the page at [url=http://www.egpet.net/vb/content/1242-hazardous-area-classification-for-underground-valves]http://www.egpet.net/vb/content/1242-hazardous-area-classification-for-underground-valves[/url]
You can view the page at [url=http://www.egpet.net/vb/content/1242-hazardous-area-classification-for-underground-valves]http://www.egpet.net/vb/content/1242-hazardous-area-classification-for-underground-valves[/url]
check EN - ISO 60079-10-1 and requirement on ventilation available.
Thanks