The Environmental Protection Agency (EPA) is modifying the rule listing regulated substances and threshold quantities under section 112(r) of the Clean Air Act as amended. EPA is deleting the category of Division 1.1 explosives (as listed by DOT) from the list of regulated substances. Regulated flammable substances in gasoline used as fuel and in naturally occurring hydrocarbon mixtures prior to initial processing are exempted from threshold quantity determinations, and the provision for threshold determination of flammable substances in a mixture is clarified. The definition of stationary source is modified to clarify the exemption of transportation and storage incident to transportation and to clarify that naturally occurring hydrocarbon reservoirs are not stationary sources or parts of stationary sources. In addition, EPA is clarifying that the Chemical Accident Prevention Provisions do not apply to sources located on the Outer Continental Shelf. EPA believes these changes will better focus accident prevention activities on stationary sources with high hazard operations and reduce duplication with other similar requirements.