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Previous by Date: Subject: JCHAS on the web Date: Thu, 18 Dec 2003 20:08:53 -0500 Author: "Ralph Stuart, University of Vermont" |
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>We've traditionally said 5% is a de minimis hazardous concentration.
>Does anybody know what this might be - a concentration of HF below
>which it becomes relatively "non-hazardous"?
>
>Gordon Miller
>Lawrence Livermore National Laboratory
>P.O. Box 808 (L-379)
>Livermore, California 94550
>(925) 423-8036
>Fax (925) 422-5176
>miller22**At_Symbol_Here**llnl.gov
We did some work with DuPont CR&D on their HF training program a
couple years ago. According to the MSDS we used:
Skin contact with dilute solutions may cause latent skin burns with
necrosis even at concentrations of 2%. In concentrations greater than
50%, the burn is felt immediately and tissue destruction is rapidly
apparent; in concentrations of 20% to 50%, the burn becomes apparent
1-8 hours following the exposure; and in concentrations of less than
20%, the pain and erythema can be latent for as long as 24 hours
after exposure. Hydrogen fluoride can permeate the skin and cause
systemic toxicity. There are no reports of human sensitization.
Eye contact may cause eye irritation with discomfort, tearing, or
blurred vision.
Inhalation may cause irritation of the upper respiratory passages; or
calcium deficiency in the blood (hypocalcemia).
Ingestion may cause severe burns of the mouth and tissues of the
upper gastrointestinal tract with severe pain, bleeding, vomiting,
diarrhea and collapse of blood pressure; or calcium deficiency in the
blood (hypocalcemia).
Higher exposures may lead to eye corrosion with corneal or
conjunctival ulceration; severe and extremely painful skin burns, or
a deep-seated ulceration; prolonged exposure can cause fluorosis
which is characterized by weight loss, brittleness of bones, anemia,
weakness, general ill health, stiffness of joints and discoloration
of the teeth when exposure occurs during tooth formation; temporary
alteration of the heart's electrical activity with irregular pulse,
palpitations, or inadequate circulation; temporary lung irritation
effects on inhalation with cough, discomfort, difficulty breathing,
or shortness of breath; may cause pulmonary edema (body fluid in the
lungs) with cough, wheezing, abnormal lung sounds, possibly
progressing to severe shortness of breath and bluish discoloration of
the skin. Symptoms may be delayed. Prompt medical attention is
required. Fatalities have occurred from gross overexposure.
DuPont is probably the single largest user of HF around. They take
the threat posed by HF very seriously and (from the comprehensive
materials that I've seen) do not treat any exposure level as "safe"
or de minimus. The smallest possible exposures (and even near
misses) are immediately given first aid and medical
treatment/examination and post-incident analyses are performed to
identify what factors lead to the incident.
One needs to consider many factors in an aqueous HF exposure - the
size of the affected area is absolutely critical. Even a "dilute"
concentration can be dangerous if the victim receives a splash that
covers a large part of the body. (A 2 % body burn from 70 %
hydrofluoric acid may cause death; an untreated major skin exposure
can cause death within 2 hours from hypocalcemia). An area covering
under 2 square inches is generally considered "minor", anything more
than that is "major".
Likewise, one has to consider ingestion and inhalation as accidental
entry routes. For example, someone using a 5% solution may
concentrate it or release fumes upon heating.
Overall, I would personally discourage any and all HF whenever
possible. There are safer acceptable alternatives for many of the
processes that use it.
Dr. Rob Toreki
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