1. a) The use of air or non-inert gases to test underground storage tanks or piping containing, or that have contained, flammable or combustible liquids is prohibited.
2. b) Approved tank or line precision testing with inert gases (nitrogen and helium) may be utilized.
3. c) Prior to the precision test, preliminary air tests may be used for tanks cleaned and vapor freed for the purposes of testing manway coverplates or gaskets.

(Source: Amended at 42 Ill. Reg. 10476, effective October 13, 2018)