I have a tank with 1,000,000 pounds of toluene diisocyanate (TDI), which is covered under the RMP rule, but not under OSHA PSM. Considered by itself, the TDI would be Program 2 for EPA. The tank, however, is close to equipment that has chlorine above the applicable threshold and is subject to OSHA PSM and Program 3. Should the TDI tank be considered part of the same process as the equipment containing the chlorine? How does this affect the program level?

If a release event involving one regulated substance, such as a fire, explosion, collapse or collision, could also involve the release of another regulated substance or interfere with mitigation of such a release, then both substances, and their associated vessels and equipment are considered part of a single process. When you do your PHA for the process, you must evaluate whether a release event involving the TDI tank could have such effects on the chlorine, or whether a release event involving the chlorine could affect the TDI tank. If a single release event could involve both the TDI and chlorine, then both are subject to both OSHA PSM and Program 3.