Definition(s)
Type 3 Open Drains
Type 3 Open Drains are open drains that can allow releases (through drain openings) of lighter-than-air flammable gases or vapors at atmospheric pressure.
API RP 500, Recommended Practice for Classification of Locations for Electrical Installations at Petroleum Facilities Classified as Class I, Division 1 and Division 2, Third Edition, December 2012, Global Standards