12 . Limit values for controlling emissions of sulphur dioxide from stationary sources in the following stationary source categories , and the sources to which they apply , are specified in the following documents : ( a ) Electric Utility Steam Generating Units -- 40 Code of Federal Regulations ( C.F.R . ) Part 60 , Subpart D , and Subpart Da ; ( b ) Industrial-Commercial-Institutional Steam Generating Units -- 40 C.F.R . Part 60 , Subpart Db , and Subpart Dc ;