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Cal/OSHA PEL: HCl and HF Perspectives

Barbara Kanegsberg

We live in a society where numbers rule. Numbers rule in the way agencies do risk assessments. Numbers rule in the way chemicals are controlled in the workplace. It is therefore essential that worker exposure numbers properly convey hazards and in an absolute manner and in perspective to other potential hazards.

We respectfully suggest that as concerned individuals you provide constructive input to the Cal/OSHA PEL process. Cal/OSHA, a State agency that sets legally-enforceable worker exposure limits, is developing recommendations for several chemicals of interest to industry. Worker inhalation levels are under consideration for hydrogen chloride (HCl) and for hydrogen fluoride (HF).

HF is hydrogen fluoride in the gas phase or hydrofluoric acid in the liquid phase. HF is extremely toxic; exposure to HF can be lethal. HCl is hydrogen chloride (gas) or hydrochloric acid (liquid). HCl has been in common usage for centuries. While all chemicals must be managed with appropriate respect, HCl does not have anywhere near the observed problems seen with HF. Here are the levels for the two compound. The level for HF has been proposed by HEAC; the level for HCl is under discussion by the HEAC.

Chemical STEL TWA
HF (a) 1 ppm 0.4 ppm
HCl (b) 2 ppm 0.3 ppm

a. PEL project substance list as of 6/09;
b. J. Unmack, Memo to HEAC, Question of TWA for HCl, June 22, 2009

STEL is the short term exposure limit, usually 15 minutes. TWA is the Time Weighted Average, Permissible Exposure Limit (PEL). HEAC is the Health Expert Advisory Committee, a volunteer group that recommends worker exposure limits to Cal/OSHA based on risk assessment.

Please notice that the numbers for the two compounds are essentially the same, yet hazards to workers are markedly different. We are concerned that the levels under discussion, if adopted, would not reflect potential hazards in a realistic manner. Certainly, worker exposure numbers for two different compounds do not always “match up,” particularly if evaluations are performed by geographically and culturally different agencies or if one inhalation level was set in, say, 2008 and another was set decades earlier. However, it would seem reasonable for there to be internal consistency within one group or agency at a given point in time.

James Unmack, of Unmack Everett Environmental, Inc. in Torrance, CA is an Industrial Hygienist with decades of experience in worker protection. Jim has been a member of the (HEAC); for essentially two years; and in that capacity, he has been providing his expert assessment and evaluation regarding appropriate worker exposure to HCl. Jim forwarded a document expressing his concern (“Hyperplasia Not an Issue with Hydrogen Chloride”). We are pleased that Jim is also a member of the Technical Advisory Panel of SQRC and appreciate his contribution to this article.

Jim takes issue with assessment by “several members of the HEAC .” Jim indicates that these members “are concerned that the Proposed PEL for hydrogen chloride should address the issue of transient hyperplasia of the larynx.” Hyperplasia is a broad term used to describe an increased number of normal cells; hyperplasia can occur in response to many different stimuli. Jim then explains that while 20% of test animals exposed to 10 ppm HCl over a normal lifetime showed transient hyperplasia, assessments by the ACGIH TLV committee, the Air Force, and other agencies found “no issue with transient hyperplasia.”

Is a lower number more protective?
There has been concern with transient hyperplasia on the part of some HEAC committee members because even though there has been no apparent damage in animal studies and even though there are no apparent problems, in worker populations, it is impossible to prove a negative. Therefore, to be maximally protective, should not the allowed inhalation level for HCl be extrapolated directly from observations of any effect in animals?

Well, NO.

We agree with Jim Unmack’s assessment:

“Experience has not shown a need for an 8-hour time weighted average PEL of 0.3 ppm. The animal studies found normal life span, normal weight gain, and no morbidity associated with an exposure twice the current PEL.

“The HEAC has recommended an 8-hour TWA of 0.4 ppm for hydrogen fluoride. It would be absurd to recommend a lower PEL for hydrogen chloride. The consequences of exposure are vastly different. The action of hydrogen chloride is primarily in the upper respiratory tract, whereas hydrogen fluoride will penetrate into the deep lung to produce injuries to the lung and systemic hypocalcemia. The mode of action is vastly different. Hydrogen chloride becomes hydrochloric acid upon solution and its action upon living tissue is primarily that of an acid. Hydrogen fluoride introduces a toxic fluoride ion that precipitates calcium fluoride causing local and systemic hypocalcemia with totally different pharmacokinetics. The consequences of hydrogen fluoride exposure are far more severe than hydrogen chloride exposure. The consequences are not comparable and the proposed PELs should not suggest that they are.”

Basically, with HCl we have the concerns of possible risk due to transient or temporary hyperplasia. It may be that, at some point in the future, problems will be found with such transient hyperplasia relative to HCl exposure beyond a temporary hoarse voice. However, at this point, such problems have not been observed in people. In contrast, we KNOW that with HF exposure, workers have developed severe, painful, life-threatening, sometimes fatal injuries. With HF, there can be severe and painful bone decalcification.

Numbers rule

We live in a society where numbers rule. Numbers rule in the way agencies do risk assessments. Numbers rule in the way chemicals are controlled in the workplace. It is therefore essential that worker exposure numbers properly convey hazards and in an absolute manner and in perspective to other potential hazards. I communicated these concerns to the HEAC (via Jim Unmack) and to Cal/OSHA:

I have great concern that the HEAC may be inadvertently providing potentially misleading and dangerous information to the workers of California. Specifically, whether or not a TWA for HCl is proposed, the similarity in the STEL for HCl and HF conveys the erroneous message that HCl and HF pose equivalent hazards to workers.

Small business owners and inexperienced workers do not always have the advantage of advice from an on-site CIH or other safety professional. They may look at the numbers (STEL and/or TWA) as the definitive measure of a chemical’s risk, i.e. its “danger ranking”. As a long-time advisor to the manufacturing community, I am concerned that the STEL’s under consideration for HF and HCl will result in:

  1. a cavalier attitude toward HF relative to HCl
  2. adoption of HF where HCl or a more benign chemical could be used
  3. unwarranted fear regarding the hazards of HCl

    I urge that the new PEL process be approached in a more holistic, coordinated manner. Please let me know what I can do to clarify and expedite matters.


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