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Laboratory Safety Manual

Reviewed May 2012  

Appendix M
Management of Exposure to Hydrofluoric Acid (HF)


Introduction and preliminary instructions

If you are a user or plan to use hydrofluoric acid (HF) in any form or use fluoride salts under acidic conditions, the following safety practices and information are applicable for OSU laboratories and work places. The major portion of this safety document was derived from a 1998 presentation by Miguel Trevino, MD, Occupational Medicine, and U.C.S.F. It includes information and instructions about self protection during use and handling of HF, decontamination on exposure, emergency treatment after decontamination, and what the user can expect to encounter during secondary decontamination and subsequent medical treatment.

Before beginning work:

  1. Familiarize yourself thoroughly with this document, the Material Safety Data Sheet (MSDS) for the specific form of HF being used, and have a written standard operating procedure (SOP) that can be incorporated into your required Chemical Hygiene Plan. 
  2. Consider your work area carefully to anticipate what can happen if a bottle is dropped, a flask cracks, a line ruptures, chemicals are spilled, or something topples.
  3. Remove all clutter from the work area and, if practical, mount your apparatus in a plastic catch pan.
  4. Have sodium bicarbonate (baking soda, saturated solution and dry solid) available for neutralization of spills and/or placement in the catch pan.
  5. Know the location of the emergency safety shower/eyewash stations and be prepared to operate both with eyes closed. 
  6. Inform your colleagues about your experiment.  If HF is being used, your supervisor must determine whether you can work alone.

Physical and chemical properties of HF  (top)

HF is a colorless gas (fumes in moist air) with an irritating and pungent odor having the following properties:

Chemical Abstracts number (CAS) [7664-39-3] bp 67 F, 19 C; dissociation K=3.5 x 10-4; freezing point -118 F, -83 C; specific gravity 0.97 at 25 F, 14 C; vapor density 3.0 at 25 C; vapor pressure at 20 C/775 mm Hg.

Exposure to HF     (top)

The extent and nature of the exposure determines the choice of decontamination procedure and the subsequent medical treatment.  If you have been exposed to HF, regardless of the source, decontamination and treatment must take place promptly because of the persistence of HF in damaging tissue.  The following sections provide information and instructions about how to proceed in the event of exposure.

Exposure to HF is a serious health and safety problem requiring prompt attention.  If the pungent and irritating odor has been detected or felt, an overexposure may have already occurred because the odor threshold is above the American Conference of Governmental and Industrial Hygienists (ACGIH) ceiling limit of 3 ppm (2.5 mg/m3).  Failure to promptly and properly treat an HF exposure can result in serious injury, disfigurement, and/or death.  In addition to being a highly corrosive acid, HF is toxic and continues to degrade tissue long after the initial exposure.  Untreated exposure results in wounds that are difficult and very slow to heal and may result in deep-seated health problems (see Section 4, Health effects and consequences of exposure to HF). 

Exposure to HF can vary in severity and the decontamination and treatment procedures also may vary with the anatomical location of the exposure.  A single approach to decontamination and treatment is not used.  Instead, exposures are divided into several categories.  These are listed below; and since all exposures require some decontamination and/or treatment, each user is expected to become thoroughly acquainted with the entire document.

There is no time, once exposure has taken place, to study procedures.  Prompt treatment is crucial.  Study this document, the relevant MSDS and your SOP thoroughly before opening a bottle of aqueous HF or turning the valve of a cylinder containing anhydrous HF.  Quiz yourself and leave nothing to chance.  HF need only contact 2% of the body area to be fatal.  Burns from strong HF (50-70% HF) are felt immediately; weaker solutions (25%) may take several minutes to be noticed; solutions of 1-20% may not be felt for several hours.  Personnel assisting the injured should also ensure they are protected by personal protective equipment.

One reported victim in western Australia spilled "about 100 mL of 70% solution of HF on his leg."  The leg was later amputated, but his blood had already been poisoned and he later died.  (Australian Institute of Occupational Hygienists Newsletter, December 1994)

Exposed skin (less than two-square inch area)

If clothing or jewelry is involved, remove these items immediately and proceed as follows:

  1. Wash the exposed area with running water (5-15 minutes).
  2. Quickly wash with saturated sodium bicarbonate solution, apply aqueous calcium carbonate paste or aqueous magnesium sulfate paste.  Have the dry materials on hand ready to be made into a paste (as described in 7C).
  3. Rinse the bicarbonate treated area with water or calcium gluconate solution.
  4. Gently dry the exposed area with clean toweling or facial tissue.
  5. Apply calcium gluconate gel.  Have this on hand and available for use.  Massage gel on and around the contaminated area with clean, preferably gloved fingers.  White specks appearing around the contaminated area indicate that the desired reaction (formation of calcium fluoride) is taking place.  Continue the massage, with repeated applications, for 15 minutes after pain has subsided or until medical treatment is available.
  6. Note the time of exposure.  Is there pain or discomfort?  Don't under estimate--seek medical help!  Phone 911 (give building and room number).

Exposed skin (exceeding two-square inch area is considered a major exposure)

Use of an emergency safety shower is warranted if the entire burn area cannot be immediately immersed or washed as described above.  Before entering shower, remove all contaminated clothing and jewelry, but do not remove safety goggles and the inner layer of gloves; modesty should not be a consideration.  After entering the shower, close eyes, face into the spray, and pull the goggles over your head.  Wash thoroughly all areas exposed to HF.  Some sources recommend limiting the shower to five minutes so that emergency decontamination procedures can be initiated.  If you are unable to read the time, count slowly to 60 for each minute.  If you are helping another person into the shower, make certain you later decontaminate yourself as well.   Phone 911 (give the building and room number) and inform the dispatcher that a hydrofluoric acid exposure has occurred.

Prior to the arrival of the emergency medical service and after the victim has been in the emergency safety shower for at least five minutes, and if time permits:

  1. Wash with sodium bicarbonate solution; apply aqueous calcium carbonate paste.  Have these on hand and ready for use.  Magnesium sulfate is unsatisfactory because the anhydrous form liberates considerable heat on exposure to water and the hydrated form is usually not available as a fine powder.
  2. Rinse the bicarbonate solution/calcium carbonate paste-treated area with water or calcium gluconate solution.
  3. Gently dry the exposed area with clean toweling or facial tissue.
  4. Apply calcium gluconate gel.  Have this on hand and ready for use.  Massage gel on and around the contaminated area with clean, preferably gloved fingers.  White specks appearing around the contaminated area indicate that the desired reaction (formation of calcium fluoride) is taking place.  Continue the massage, with repeated applications, for 15 minutes after pain has subsided or until medical treatment is available.
  5. Note the time of exposure.  Is there pain or discomfort?  Don't under estimate--seek medical help!

Exposure of eye

All eye exposures are considered severe and require medical help.  Phone 911, give building and room number and inform the dispatcher that a hydrofluoric acid eye exposure has occurred.  Decontaminate with eye wash (forcibly open the lids) or low-pressure hose for 5 minutes (count slowly to 60 for each minute), then irrigate with 500 mL of 1% calcium gluconate in saline per eye.  The calcium gluconate solution is to be kept near the eye wash.  If only one eye is involved, when rinsing make certain contaminated water does not enter the uncontaminated eye.

Exposure through inhalation

Phone 911 (give building and room), inform dispatcher that a hydrofluoric acid inhalation exposure has occurred, and oxygen (12 L/min.) as well as nebulizing (2.5% solution of calcium gluconate in saline) will be required.  Decontaminate and treat any exposed areas as described above.

Exposure through ingestion

  1. Conscious patient: Phone 911 (give building and room number).  Orally give any calcium or magnesium-based antacid; i.e. products such as Tums(r) (500 mg), Tums EX(r) (750 mg), Tums ultra(r) (1000 mg), or Alka-mints(r) (850 mg) or water only.  Do not induce vomiting.
  2. Unconscious patient: Phone 911 (give building and room number) and inform dispatcher that hydrofluoric acid is involved and the victim has ingested hydrofluoric acid.
  3. Decontaminate skin or eyes if they were exposed (fingernails not properly decontaminated can become a problem).

Health effects and consequences of exposure to HF    (top)

In addition to the corrosive effects of HF as an acid, it is toxic through binding with calcium and magnesium ions, destruction of tissue, and transport of the negatively charged fluoride anion (F-) that eventually reaches and damages the liver and kidneys.  Fluoride salts can impair blood electrolyte and cellular function at the enzyme level.  Salt (calcium and magnesium) imbalance in blood, due to presence of fluoride ion (F-), can cause heart arrhythmia.

If not promptly treated, painful lesions can result that are difficult to heal.  The question of pain needs emphasis.  The initial exposure may not be painful for lower concentrations of HF and consequently the user may be lulled into not properly decontaminating and treating the exposure and/or seeking medical aid.

Calcium gluconate and calcium carbonate aqueous paste--why?    (top)

Exposure of tissue to HF causes a corrosive reaction as HF dissociates on contact with moisture in tissue to form the fluoride ion (F-).  This ion associates with soluble counter ions (sodium, potassium, etc.) as well as insoluble counter ions (magnesium and calcium).  The soluble counter ions (K, Na) more readily transport the fluoride ion to sensitive organs (liver, kidney, heart) whereas the less soluble calcium and magnesium fluorides are localized and their formation is beneficial by trapping the fluoride ion, thus limiting transport.  Calcium gluconate (non-toxic) is a better choice than calcium acetate since use of the latter results in release of acetic acid on reaction with HF in exposed tissue.  Check the HF kit to make certain the necessary sources of calcium or magnesium ions (calcium gluconate solution, calcium gluconate gel, antacid) and neutralizing agents (bicarbonate, calcium carbonate paste) are on hand before beginning use of HF.

Protective equipment    (top)

HF is more hazardous than most users realize (see Sections 3, Exposure to HF, and 4, Health effects and consequences of exposure to HF).  The following alphabetized list of protective equipment should be carefully considered and the necessary items acquired before using HF.  Materials listed below may be obtained from the Chemistry Storeroom (4-7211), University Health Center pharmacy (4-7025), Stillwater Milling Agri-Center (372-2766), or safety equipment suppliers.

  1. Absorbents:  Calcium carbonate (CaCO3, limestone), magnesium carbonate [(CaMg(CO3)2, dolomitic limestone], calcium sulfate (CaSO4, gypsum).  Do not use kitty litter or any material containing silicates as SiF4 (toxic and corrosive gas) may be formed.
  2. Apron:  rubber or approved plastic. (Neoprene has a 60 min. breakthrough time.)
  3. Decontamination supplies:  locate and check HF kit before working.
  4. Eye wash:  locate and know how it is used.
  5. Face protection:  face shield is very important.  Splash-proof goggles and face shield are recommended.  Use of contact lenses is prohibited.
  6. Glasses, safety:  safety goggles are better.  See Face protection.
  7. Gloves:  two layers recommended--inner layer of latex or nitrile, outer layer of Neoprene, nitrile, or buna.  Inner gloves should be new; all gloves should be checked for leaks.  Have spare gloves in reserve.
  8. Goggles:  splash-proof; see Face protection.
  9. HF kit:  check contents (see below for list).
  10. Hood:  make certain it is working.  Is verification current? (Never use HF outside of the hood).
  11. Phone:  locate and decide in advance what kind of emergency help should be sought--see emergency section.   Remember 911 (give building and room number).   Emergency phone numbers, name of building, building number, and room numbers should be posted by the phone.
  12. Safety shower:  locate and know how it is used.
  13. Sleeve protectors:  or gloves that pass the elbow.

Emergency HF kit and a supply of other items wherever HF is used   (top)

  1. Aluminized plastic sheet. One or more (comes with 911?)
  2. Antacids (calcium and magnesium-based).
  3. Calcium carbonate for preparation of aqueous paste.   Magnesium sulfate paste may be substituted.   However, the anhydrous magnesium sulfate powder evolves much heat on exposure to water and the heptahydrate (Epsom salt) is a hard, needle-shaped crystal.  The latter can be ground in a mortar to a fine powder.  In either case, practice preparing a paste by drop wise addition of water, with stirring, to the powdered, solid calcium carbonate or magnesium sulfate heptahydrate (when tried, calcium carbonate gave the better paste).
  4. Calcium gluconate, gel, two or more 30-gram tubes.
  5. Calcium gluconate, solid.
  6. Eye wash.  Include two 500-mL eye irrigation bottles filled with 1% calcium gluconate solution.
  7. Gloves, (inner and outer), two or more pairs.
  8. Shower.
  9. Sodium bicarbonate (solid) and sodium bicarbonate (saturated solution).

Storage and use of HF    (top)

Since aqueous HF is highly corrosive and highly toxic, it must be stored in a well-ventilated cabinet or hood.  With each use, the bottle should be tightly recapped and rinsed with water to remove any acid from the cap area or the outside of the container.  Aqueous HF (about 50% max. conc.) attacks silica-containing glass, so HF is supplied in wax or plastic bottles (keep this in mind should you prepare solutions containing HF).

Anhydrous HF is a gas at room temperature (bp 67 F, 19 C) and is supplied in steel cylinders.  A vented (to exterior of building) toxic gas enclosure is required.  HF can be withdrawn from a cylinder, as a gas, through copper or Teflon(r) tubing and then recondensed to a liquid by chilling the tubing.  Because the vapor pressure of anhydrous HF is 775 mm Hg at 20 C, it must not be resealed in bottles.  Anhydrous HF is the most dangerous form.  Do not use any form of HF without thorough prior training and preparation.  There is a specific MSDS for each form of HF.

Potential uses of HF    (top)

  1. Acid catalysis in organic chemistry.
  2. Brightening aluminum or other metals.
  3. Cleaning brick and stone.
  4. Cleaning components used in production of particle beams.
  5. Cleaning surfaces of electronic components and circuit boards (RCA process).
  6. Cleaners, low concentration in many cleaners.
  7. Cleaving synthetic peptides from resins.
  8. Digesting samples prior to metal analysis.
  9. Digesting soil and rock samples for pollen analysis.
  10. Dissolving steel samples.
  11. Excimer laser (fluoride mixes).
  12. Opening rock samples for analysis.
  13. Processing plant/animal fossils.
  14. Wire stripping (HF in methylene chloride).

What to expect at a Medical Facility    (top)

Secondary examination and decontamination

  1. Orifices including ear canals, mouth, nose, anus, and vagina.
  2. Skin folds of neck, auxiliary regions, sub-mammillary, groin, behind knees, inter-digital.
  3. Under nails, hands, feet.
  4. Areas covered with hair; scalp, pubis.

Secondary medical treatment

  1. For exposed area under two inches, with pain persisting 20-30 minutes beyond exposure, initiate 2.5% calcium gluconate infiltrations using long and small caliber needles (preferably steel).
  2. For exposure area exceeding two inches, administer intravenously at a slow rate 1000 mL of Hartman or saline solution plus 2 ampoules (10 mL of 10% calcium gluconate).
  3. Possible studies: EKG, serum calcium, magnesium, and electrolytes, renal function, neurological function, blood chemistry, arterial gases and chest x-ray if there is respiratory involvement.
  4. Hemodialysis to provide adequate elimination of fluorinated compounds in serum.

Eye exposure

  1. Subsequent to initial irrigation (see 3c) use 1% calcium gluconate eye drops as required and ophthalmic Dexamethasone or prednisone solution as required by the ophthalmologist.
  2. Monitor ocular pressures.  Rise in eye pressure may indicate HF penetration.

Inhalation exposure

  1. Maintain airways open.
  2. Intubate or use tracheostomy procedure.
  3. Initiate intermittent positive pressure ventilation (volumetric respirator).
  4. Nebulize or ultra-nebulize calcium gluconate (2.5% in saline) until the resolution of the upper or pulmonary edema.
  5. Include positive and expiratory pressure (PEEP), which is vital to the minimization of pulmonary fibrosis and edema resolution.
  6. Monitor: EKG, serum calcium and electrolytes, arterial gases, chest X-rays, hepatic functions, renal functions, neurological functions, blood chemistry.

Ingestion exposure

  1. Access the esophagus and gastric cavities to neutralize or dilute HF.
  2. Monitor the patient and systemic effects.
  3. Titrate calcium, magnesium, and other electrolytes in serum.

Emergency help and evacuation     (top)

Exposure to HF is considered an emergency; dial 911 (give building and room) for prompt evacuation to the Stillwater Medical Center Emergency Room for treatment.  A copy of this document [Management of Exposure to Hydrofluoric Acid (HF)] has been sent to the Director of the Stillwater Medical Center Emergency Room (405)-372-1480.

 


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