How will the list of covered toxic and reactive chemicals found in Appendix A and
their TQs be updated?
The list of HHCs can be revised through the normal OSHA rulemaking process. Other
than corrections for typographical errors, OSHA has indicated no firm plans to change
the Appendix A HHCs.
How do DOE contractors determine if a process is covered, when an Appendix A
chemical is contained in a mixture? Do you calculate the mass of the Appendix A
chemical in the mixture and then compare it to the TQ for the pure HHC listed in
The substances listed in Appendix A without specified concentration limits are intended
to be covered by the PSM Rule at commercial grade percentages purity. The commercial
grade of most of the HHCs is approximately 99% pure. Many of the HHCs, if not
actually 99% pure, are only one to two percent less than 99% pure. For example, the
commercial grades of acrolein and allyl chloride are 97% pure. However, some of the
HHCs are considerably less than 99% pure. For example, the commercial grade of
hydrogen fluoride is 70%. OSHA defines commercial grade as a typical maximum
concentration of a chemical that is commercially available, and shipped. The term
commercial grade includes reagent grades that, in some cases, differ in concentration
from the typical commercial grades. In cases where different concentrations for
commercial and reagent grades are typically shipped, the lowest (or lower) concentration
(and any concentration greater) is covered by the PSM Rule. Where covered, the total
mass of the mixture is used for comparison with the applicable TQ.
Are processes involving flammable liquids (e.g., ethyl alcohol) covered by the PSM
Processes involving flammable liquids (e.g., a distillation process) in quantities at or
above 10,000 lb. are covered. Flammable liquids in atmospheric storage tanks are
considered a part of a process if the storage tanks are interconnected with the process, or
if they are sufficiently near the process that an explosion, fire, or release could reasonably
involve the storage area.
Flammable liquids that are stored in atmospheric tanks in a tank farm where only
transferring and storage are performed are not covered by the PSM Rule. They are,
however, covered under 29 CFR 1910.106.
Two flammable chemicals in quantities below 10,000 lb are combined in a process to
form a flammable liquid in excess of 10,000 lb. Is this process covered?
Based upon this consideration alone, yes.
Are processes covered if they contain fuel used for process heating or drying only?
The PSM rule exempts processes using flammable liquids or gases solely as fuels in the
workplace. Thus, these processes are not covered unless they are covered for other