A refinery uses a special proprietary additive to their hydrofluoric acid (HF) alkylation process. This HF additive has shown in tests to significantly reduce aerosol forms of HF during accidental releases, and therefore reduce the distance traveled by HF releases. The additive is present at all times during the alkylation process. Can the refinery claim that this HF additive is a passive mitigation technique and use it as such in their development of their worst-case scenario numbers?

Passive mitigation systems are defined as those systems that operate without human, mechanical, or other energy input and would include building enclosures, dikes, and containment walls. In this case, the HF additive would not actually be considered passive mitigation; rather, the presence of the additive could be better reflected in the worst case and alternative release scenarios. The owner or operator could show that with the HF additive, the HF that they have on site is not a pure substance (toxic mixture criteria would apply) and in the event of an accidental release, the HF does not behave as a pure material, and the dispersion results reflect this difference. The owner or operator could highlight these differences and demonstrate how the process may be safer as a result. EPA recognizes and encourages prevention through these and other passive or inherently safer process techniques.