Definition(s)
Barrier, Vaportight
A wall or other obstruction that will limit the passage of gas or vapor at atmospheric pressure, thus preventing the accumulation of vapor-air or gas-air mixtures in concentrations above 25 % of their lower flammable (explosive) limit, LFL (LEL).
NOTE Barrier, non-vaportight applies to any wall or other obstruction that will not meet the criteria for barrier, vaportight.
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