"External floating roof" means a cover over an open top storage tank consisting of a double deck or pontoon single deck which rests upon and is supported by the volatile organic liquid being contained and is equipped with a closure seal or seals to close the space between the roof edge and tank shell.
Ill. Admin. Code tit. 35, § 211.2190
Added at 17 Ill. Reg. 16504, effective September 27, 1993