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OSHA’s New 1% Test for PSM

Posted on September 9th, 2016 by in Chemical Manufacturing Excellence

Hydrochloric acid

“OSHA requirements are set by statute, standards and regulations. Our interpretation letters explain these requirements and how they apply to particular circumstances, but they cannot create additional employer obligations.” –Statement on every OSHA letter of interpretation.

In late July, without fanfare or announcement, OSHA rescinded its 2015 memorandum on the concentrations of highly hazardous chemicals (HHCs) that count toward meeting the threshold quantities of the Process Safety Management (PSM) standard and replaced it with a new memorandum.

The 05-Jun-2015 memorandum on PSM and Covered Concentration caused a furor, not just because it rescinded the OSHA commercial grade policy, but because its explanatory notes and subsequent discussions with OSHA made it clear that OSHA would begin considering aqueous solutions of hydrochloric acid as a covered HHC.

In addition to suddenly reversing decades-old OSHA policies, the 2015 memorandum also had several technical problems.  The uproar highlights the need for the due process of the rule-making procedures: agencies sometimes make mistakes or fail to take certain concerns into account, and without public input, can fall into the trap of hearing only the echo chamber of their own offices, no matter how well-intended.

The 18-Jul-2016 memorandum addresses many of the issues with the rescinded 2015 memorandum that it replaces.

It still voids the commercial grade policy that OSHA established in 1992 during the first months, after promulgating the PSM standard and replaces it with a 1% test similar to that used by the EPA in its Risk Management Planning (RMP) rule.  But it does it in a way that is much more palatable.

The 1% test

The 1% test states that any Appendix A HHC in a process contributes to the threshold quantity (TQ) if it is in a mixture at concentrations greater than 1%, and that only the contained amount of the HHC counts toward the TQ, not the entire quantity of the mixture.  There are two important exceptions to this rule.  First, the quantity in the mixture does not count if the partial vapor pressure of the HHC is less than 10 mm Hg.  Second, the 1% rule does not apply if the HHC has a mixture concentration associated with its listing.

The Partial Pressure Exception

In the case of the exception for partial vapor pressures less than 10 mm Hg, many listed HHC will not be covered at concentrations significantly greater than 1% because of the low partial vapor pressures of the HHC.  Fortunately, the replacement memorandum corrects the error in the rescinded memorandum that indicated that partial vapor pressure is based on weight percent.  Because partial vapor pressure is based on both temperature and molar concentration, anyone exploring the partial vapor pressure exception will have to show that the partial vapor pressure of the HHC is less than 10 mm Hg in a specific mixture and a specific temperature.

The replacement memorandum acknowledges that because of partial pressure exception, aqueous mixtures of HBr will not be covered at concentration less than 63% and that mixtures of alkylaluminum at any concentration will fall within the partial pressure exemption, essentially delisting alkylaluminum.

Unfortunately, the replacement memorandum continues to illustrate the 1% test with the example of a 50% mixture of chloropicrin.  Given the vapor pressure of chloropicrin, the partial vapor pressure at 20°C will only exceed 10 mm Hg if the other components in the mixture have an average molecular weight greater than 205, e.g. C15 hydrocarbons.  At 25°C, the partial vapor pressure of a 50% mixture of chloropicrin will only exceed 10 mm Hg if the other components in the mixture have an average molecular weight greater than 124, e.g. C9 hydrocarbons.

The Listed Concentration Exception

In the case where the HHC has a mixture concentration associated with its listing, then the concentration must be above the listed concentration before the contained amount of the HHC counts toward the TQ.  So 20,000 lbs of 60% aqueous ammonia, which is above the listed concentration for aqueous ammonia of 44%, will contribute 12,000 lb of ammonia toward the TQ.  Both the rescinded memorandum and its replacement memorandum state that there are 11 chemicals to which this exception applies, without listing the chemicals.  A review of the letters of interpretation affirmed in the replacement memorandum as “currently good statements of OSHA policy” and other letters of interpretation makes it clear that these are the 11 chemicals that OSHA intends:

  • Ammonia solutions (>44% ammonia by weight)
  • Diacetyl Peroxide (Concentration >70%)
  • Ethyl Methyl Ketone Peroxide (also Methyl Ethyl Ketone Peroxide; concentration >60%)
  • Formaldehyde (Formalin) [where “formalin” means “37% by weight or greater]
  • Hydrogen Peroxide (52% by weight or greater)
  • Methyl Ethyl Ketone Peroxide (concentration >60%)
  • Nitric Acid (94.5% by weight or greater)
  • Oleum (65% to 80% by weight; also called Fuming Sulfuric Acid) [meaning 65% by weight or greater free sulfur trioxide (SO3) in H2SO4]
  • Peracetic Acid (concentration >60% Acetic Acid; also called Peroxyacetic Acid)
  • Perchloric Acid (concentration >60% by weight)
  • Peroxyacetic Acid (concentration >60% Acetic Acid; also called Peracetic Acid)

Notice that this list includes two pairs of synonyms: Ethyl Methyl Ketone Peroxide and Methyl Ethyl Ketone Peroxide, and Peracetic Acid and Peroxyacetic Acid.

Anhydrous Chemicals

An area of significant controversy following the issuance of the rescinded memorandum was OSHA’s position that mixtures of Appendix A HHCs described as anhydrous would be covered under the 1% test, including aqueous solutions.  Fortunately, the replacement memorandum now acknowledges that the term “anhydrous” means “without water”, so that aqueous solutions of Appendix A HHCs described as anhydrous are not covered by the PSM standard.  This will be huge relief to facilities that use hydrochloric acid.  (Hydrochloric acid will still be on the RMP list at concentrations greater than 37%, but 20° Baume hydrochloric acid (31.5% by weight) and 22° Baume hydrochloric acid (35.2% by weight) will not suddenly become covered chemicals or contribute to the threshold quantity calculation for OSHA’s PSM standard.)

This acknowledgement that “anhydrous” means “without water” applies to six chemicals on the Appendix A list:

  • Ammonia, Anhydrous
  • Dimethylamine, Anhydrous
  • Hydrochloric Acid, Anhydrous
  • Hydrofluoric Acid, Anhydrous
  • Hydrogen Cyanide, Anhydrous
  • Methylamine, Anhydrous

(That said, keep in mind that aqueous solutions of >44% ammonia are listed separately.)

The replacement memorandum revised or deleted three of the five examples originally included in the rescinded memorandum.  The first example originally used 1% hydrofluoric acid, but because OSHA now acknowledges that aqueous hydrofluoric acid is not a covered chemical, the first example is now about a 10% diborane mixture.  The third example simply corrected the mistaken idea that partial vapor pressure was a function of weight percent.  The fifth example, which was about four drums of 48% aqueous HF on a pallet in a warehouse, was simply deleted.  This is most likely because the example used 48% aqueous HF, which is not covered under PSM, as the example, not because OSHA has changed its policy that collocated drums of Appendix A HHCs are a single process.

Timing for Enforcement

Finally, the replacement memorandum addressed the controversial question of timely notice.  The new 1% test is a significant departure from the long-standing commercial grade policy.  It places many facilities and processes under the PSM standard that have never been covered before, and those facilities and processes rightly felt like they needed time to comply.

The replacement memorandum includes a new section on OSHA’s interim enforcement policy.  Until the end of next March, OSHA will not cite based on this new policy, but may cite under the previous “commercial grade concentration” policy.  It is not clear whether a process that is no longer covered because of the new policy could be cited based on the previous policy.

The replacement memorandum goes on to state that beginning next April 1 and going to the end of March 2018, processes newly covered because of the new 1% test will not be cited if the employer is making a good faith effort to get in compliance.  However, OSHA also states that this forbearance will not apply in the case of a fatality or catastrophe.  So, a steady, good-faith effort to comply with this new policy by March 31, 2018 is only a defense against a citation as long as no one gets hurt in the mean time.

What does this mean for you?

For facilities that were scrambling to bring all of the elements of PSM to bear on processes that use hydrochloric acid or hydrofluoric acid, relax.  If the facility was not already covered under RMP because of exceeding 37% HCl concentrations or 50% HF concentrations, it is most likely not covered now.  That is not to say that any less care should be taken in protecting the safety of workers, the community, and the environment.  Hydrochloric acid and hydrofluoric acid are both hazardous chemicals and deserve a great deal of care.  That care is because it is the right thing to do, not because you are compelled to comply with the PSM standard.

For processes that seem likely to be covered by the new 1% test, determine the partial vapor pressure before drawing any conclusions.  If the partial vapor pressure is less than 10 mm Hg, the mixture does not count toward the TQ, and the effect may be quite dramatic.

Finally, if the new 1% test means that your process is now covered under the PSM standard, then get on with complying with the standard.  There are fourteen elements of PSM, from process safety information and RAGAGEP, to PHAs, mechanical integrity, and management of change.  Even if you have been doing all of these things, it should come as no surprise if those efforts don’t fully comply with the requirements of the standard.  OSHA has allowed about 20 months to bring your process into compliance.  You’ll need all of it.


All opinions shared in this post are the author’s own.

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