Pursuant to the risk management program regulations under 40 CFR §68.115(b)(2)(iii), regulated substances in naturally occurring hydrocarbon mixtures prior to entry into a natural gas processing plant or a petroleum refining process unit do not need to be considered when determining whether more than a threshold quantity is present at a stationary source. Why did EPA only exempt regulated substances in hydrocarbon mixtures prior to entry into a natural gas processing plant or a petroleum refining process unit, but not after entry?
EPA specifically exempted from threshold determinations certain naturally occurring hydrocarbon mixtures prior to processing in order to reflect EPA’s intent to exempt mixtures that do not have a National Fire Protection Association (NFPA) rating of 4 and simplify the task of applying the judgmental criteria of NFPA-4 for these pervasive mixtures. These mixtures may have a flash point and boiling point corresponding to NFPA-4 criteria; however, they contain non-volatile components and have a low potential for vapor cloud explosions. Moreover, EPA believes that exploration and production facilities do not have the turbulent or confined conditions that lead to vapor cloud explosions.