An official website of the United States government.

This is not the current EPA website. To navigate to the current EPA website, please go to This website is historical material reflecting the EPA website as it existed on January 19, 2021. This website is no longer updated and links to external websites and some internal pages may not work. More information »

Aggregating a substance located in multiple processes

Under 40 CFR Part 68, if multiple processes at a stationary source contain the same regulated substance, must the amounts of the substance in the individual processes be aggregated to determine whether a threshold is exceeded?

No. Applicability of the risk management program requirements is based upon the presence of more than a threshold quantity of a regulated substance in a process at a stationary source (40 CFR §68.10(a)). The quantity present is evaluated on a process-by-process basis. It is important to note, however, that multiple, separate vessels located such that both could potentially be involved at one time in an accidental release are considered to be a single process (40 CFR §68.3). The owner or operator of a stationary source will need to make a reasonable determination as to whether two or more vessels may be involved in the same accident. The owner or operator should be able to document the decision that the individual vessels do or do not constitute a single process. If the threshold is not met for a process and thus not subject to part 68, the process is still subject to Section 112(r)(1), the general duty clause.