How can a facility determine whether it has present an amount of an extremely hazardous substance (EHS) which equals or exceeds the threshold planning quantity (TPQ)?

To determine whether the facility has an amount of an extremely hazardous substance which equals or exceeds the TPQ, the owner or operator must determine the total amount of an extremely hazardous substance present at a facility at any one time, regardless of location, number of containers, or method of storage. This calculation must also take into account the amount of an extremely hazardous substance present in mixtures or solutions in excess of one percent and should include examination of such process components as reaction vessels, piping, etc., where formation of an EHS as a byproduct may take place.

If the EHS is a non-reactive solid in solution, first multiply the quantity of the solid on-site by 0.2 before comparing it to the lower TPQ listed for the EHS solid. If the EHS is a molten non-reactive solid, multiply the quantity of the molten solid on-site by 0.3 before comparing it to the lower TPQ listed for the EHS solid. See the frequent question regarding what is meant by "molten" and "in solution" when describing extremely hazardous substances.