Hydrofluoric acid (HF) is one of the most hazardous chemicals in use on our campus. It is widely used in semiconductor work, earth sciences, for sample preparation for analytical labs and other specialized applications.
Hydrofluoric acid is very aggressive physiologically because of the fluoride ion. Both anhydrous hydrofluoric acid (hydrogen fluoride) and its solutions are clear, colorless liquids. When exposed to air, concentrated solutions and anhydrous hydrofluoric acid produce pungent vapors which are especially dangerous. Unless heated, dilute concentrations of hydrofluoric acid in water (e.g. less than 40% HF) do not produce significant vapor concentrations.
HF can cause serious, painful burns of the skin. Specialized first aid and medical treatment is required. Burns larger than 160 sq. cm may result in serious systemic toxicity. Hydrofluoric acid is highly corrosive and can severely burn eyes, skin, and mucous membranes. The vapors from anhydrous HF or its concentrated solutions can also burn these tissues. In contrast to the immediate effects of concentrated HF, the effects of contact with more dilute solutions may be delayed, and this is one of the problems with the recognition of some HF burns. Skin contact with acid concentrations in the 20% to 50% range may not produce clinical signs or symptoms for one to eight hours. With concentrations less than 20%, the latent period may be up to twenty-four hours. HF concentrations as low as 2% may cause symptoms if the skin contact time is long enough.
HF burns are usually accompanied by severe, throbbing pain which is thought to be due to irritation of nerve endings by increased levels of potassium ions entering the extracellular space to compensate for the reduced levels of calcium ions, which have been bound to the fluoride.
The usual signs of an HF burn are redness, edema, and blistering. With more concentrated acids, a blanched white area appears. The fluoride ion penetrates the upper layers of the skin. A thick granular exudate may form under blisters due to liquefaction necrosis. In rare (and untreated) cases, there may be penetration to underlying bone with decalcification.
HF burns require immediate and specialized first aid and medical treatment differing from the treatment of other chemical burns. If untreated or if improperly treated, permanent damage, disability, or death may result. If, however, the burns are promptly and properly recognized and managed, the results of treatment are generally favorable. Speed of the treatment is of the essence. Delays in the first aid care or medical treatment or improper medical treatment will likely result in greater damage or may, in some cases, result in a fatal outcome.
One of the most serious consequences of severs exposure to HF by any route is the marked lowering of serum calcium (hypocalcemia) and other metabolic changes which may result in a fatal outcome if not recognized and treated. Hypocalcemia should be considered a possible risk in all instances of inhalation or ingestion, and whenever skin burns exceed 160 square centimeters. Serum magnesium may also be lowered, and elevations in serum potassium have been reported to further complicate the metabolic imbalances which will need to be monitored and corrected. High levels of fluorides have been noted both in the blood and body organs. Hemodialysis has been reported to be effective therapy for cases of severe systemic intoxication. Treatment for shock may also be required as for other severe injuries.
Hydrofluoric acid can cause severe eye burns with destruction or opacification of the cornea. Blindness may result from severe or untreated exposures. Immediate first aid and specialized medical care is required.
Hydrofluoric acid vapors may cause laryngospasm, laryngeal edema, bronchospasm and/or acute pulmonary edema. Acute symptoms may include coughing, chest tightness, chills, fever, and cyanosis. Many reported fatalities from HF exposures have been due to severe pulmonary edema (coupled with systemic toxicity) that did not respond to medical treatment.
Burns from vapors or liquid contact to the oropharyngeal mucosa or upper airway may cause severe swelling to the point of requiring a tracheostomy. It is recommended that all patients with such exposure be hospitalized for observation and/or treatment.
Because of the strong irritant nature of hydrofluoric acid, an individual inhaling HF vapors will usually experience upper respiratory injury, with mucous membrane irritation and inflammation as well as cough. All individuals suspected of having inhaled HF should be observed for pulmonary effects. This would include those individuals with significant upper respiratory irritation, bronchoconstriction by pulmonary auscultation or spirometry, and any individual with HF exposure to the head, chest, or neck areas. It has been reported that pulmonary edema may be delayed for several hours and even up to two days. If there is no upper respiratory irritation, significant inhalation exposure can generally be ruled out.
The Permissible Exposure Limit (PEL) set by the U.S. Occupational Safety and Health Administration (OSHA) is a time weighted average exposure for 8 hours or 3ppm. The American Conference of Governmental Industrial Hygienists (ACGIH) recommends a ceiling level of 3ppm or 2.3 mg/m3. The National Institute for Occupational Safety and Health (NIOSH) has established the level that is immediately dangerous to life and health (IDLH) at 30ppm. The American Industrial Hygiene Association has published an Emergency Response Planning Guideline setting 50ppm as the maximum level below which nearly all individuals could be exposed for one hour without experiencing or developing life-threatening health effects or symptoms which would impair taking protective action and 2ppm as the maximum level below which nearly all individuals could be exposed up to one hour without experiencing other than mild, transient adverse health effects.
If hydrofluoric acid is ingested, severe burns to the mouth, esophagus and stomach may occur. Severe systemic effects usually also occur. Ingestion of even small amounts of dilute HF have resulted in death.
First Aid Treatment for Hydrofluoric Acid Burns
A. Skin Contact
- Move victim immediately under safety shower or other water source and flush affected area thoroughly with large amounts of cool running water. Speed in washing off the acid is of primary importance.
- Remove all contaminated clothing while flushing with water.
- Rinse with large amounts of cool running water. If 0.13% benzalkonium chloride solution or 2.5% calcium gluconate are available, the rinsing may be limited to 5 minutes, with the soaks of gel applied as soon as the rinsing is stopped. If benzalkonium chloride or calcium gluconate gel is not available, rinsing must continue until medical treatment is rendered.
- While the victim is being rinsed with water, someone should alert first aid or medical personnel and arrange for subsequent treatment.
- Immediately after thorough washing, use one of the measures below:
a. Begin soaking the affected areas in iced 0.13% benzalkonium chloride solution
Use ice cubes, not shaved ice, in order to prevent frostbite.
If immersion is not practical, towels should be soaked in iced 0.13% benzalkonium chloride solution and used as compresses for the burned area.
Compresses should be changed every two to four minutes.
Do not use benzalkonium chloride solution for burns of the eyes. Exercise caution when using benzalkonium chloride solution near the eyes as it is an eye irritant.
Benzalkonium chloride soaks or compresses should be continued until pain is relieved or until more definitive medical treatment is provided.
b. Start massaging 2.5% calcium gluconate gel into the burn site.
Apply gel every 15 minutes and massage continuously until pain and/or redness disappear or until more definitive medical care is given.
It is advisable for the individual applying the calcium gluconate gel to wear gloves to prevent a possible secondary HF burn.
6. After treatment of burned areas is begun, the victim should be examined to ensure there are no other burn sites which have been overlooked.
7. Arrange to have the victim seen by a physician. During transportation to a medical facility or while waiting for a physician to see the victim, continue the benzalkonium chloride soaks or compresses or continue massaging calcium gluconate gel.
8. The physician may advise continued treatment with benzalkonium chloride or calcium gluconate gel.
B. Eye Contact
- Immediately flush the eyes for at least 15 minutes with large amounts of gently flowing water. Hold the eyelids open and away from the eye during irrigation to allow thorough flushing of the eyes. Do not use the benzalkonium chloride solutions described for skin treatment. If sterile 1% calcium gluconate solution is available, washing may be limited to 5 minutes, after which the 1% calcium gluconate solution should be used repeatedly to irrigate the eye using a syringe.
- Take the victim to a doctor, preferably an eye specialist, as soon as possible. Ice water compresses may be applied to the eyes while transporting the victim to the doctor.
- If a physician is not immediately available, apply one or two drops of 0.5% tetracaine hydrochloride solution or other aqueous, topical ophthalmic anesthetic and continue irrigation. Use no other medication unless instructed to do so by a physician. Rubbing of the eyes is to be avoided.
C. Inhalation of Vapors
a. Immediately move victim to fresh air and get medical attention.
b. Keep victim warm, quiet, and comfortable.
c. If breathing has stopped, start artificial respiration at once. Make sure mouth and throat are free of foreign material and airway is open.
d. Oxygen should be administered as soon as possible by a trained individual. Continue oxygen while awaiting medical attention unless instructed otherwise by a physician.
e. A nebulized solution of 2.5% calcium gluconate may be administered with oxygen by inhalation.
f. Do not give stimulants unless instructed to do so by a physician.
g. The victim should be examined by a physician and held under observation for at least a 24 hour period.
h. Vapor exposures can cause skin and mucous membrane burns as well as damage to pulmonary tissue. Vapor burns to the skin are treated the same as liquid HF burns.
1. Have the victim drink large amounts of water as quickly as possible to dilute the acid. Do not induce vomiting. Do not give emetics or baking soda. Never give anything by mouth to an unconscious person.
2. Give several glasses of milk or several ounces of milk of magnesia, Mylanta, Maalox, etc. The calcium or magnesium in these compounds may act as an antidote.
3. Get immediate medical attention.
The OHSA Lab Standard requirement falls under Section (e)(3)(viii), “Provisions for additional employee protection for work with particularly hazardous substances.” The following instructions will facilitate the establishment of an HF use area in your lab.
1) A standard operating procedure (SOP) for the use of HF in your lab should be in place. The written SOP (preferably laminated) should be posted next to the area where the HF is used as well as a copy kept in the Chemical Hygiene Plan in the section where all individual laboratory SOPs are kept. Everyone who will be using HF is required to read and understand the SDS as well as the contents of this protocol before they are allowed to handle this chemical.
2) HF may only be used in a properly working chemical hood. All benchtop use of HF is disallowed. A “danger” sign must be posted in a prominent position on the front of the hood where HF is used and also on the cabinet where HF is stored. In addition, the following points must be observed:
a) The area in the hood where HF is used should be taped-off with a good grade of permanent tape to designate the use area.
b) The area of the floor immediately in front of the HF use area should be taped-off. This means a rectangle, with the HF use area of the hood as one side of the rectangle, extending at least three feet from the hood must be defined with a highly visible tape which will stay stuck to the floor with normal use and maintenance. Only those individuals meeting the requirements for HF use may enter the taped-off area when HF is in active use.
c) A sturdy plastic tray with at least a 1inch lip must be used for all operations with HF to serve as containment in the event of an HF spill.
d) Containers of HF should never be left open. They should be open even in the hood only when necessary. HF will etch the glass of the hood sash causing it to cloud over. If a hood is used heavily or continuously for processes involving HF, it may be necessary to replace the glass sash with polycarbonate plastic.
e) Sodium carbonate or bicarbonate should never be used to clean up HF spills. They will form aerosols with HF that make the cleanup process very dangerous. Powdered or finely granular calcium sulfate (commercial gypsum), calcium carbonate, or calcium hydroxide are the best materials for neutralizing HF spills. HF combines with the Ca++ ion and is rendered insoluble as CaF2. You should have one or more of these materials in your lab at all times in case of HF spill. See Chemical Hygiene Plan (Appendix C) for more complete information on Spill Cleanup Procedures.
f) All containers of chemicals must be properly labeled. When making dilutions of HF in a container other than the original container, the new container label must include the complete chemical name, hazards, and date of preparation at a minimum.
g) No one may work alone when using HF. A buddy system must be in place, even if the “buddy” is in an adjacent room. This is critical in the event of a spill or exposure.
h) Personal Protective Equipment (PPE) required for use of HF is as follows:
a) All work with HF must be done in a properly working chemical hood. The sash must be kept as low as possible, preferably 6-10 inches from the hood deck. If you have any doubts about the functionality of the hood, please contact RS.
b) Thicker (10-20 mil) PVC or neoprene gloves provide resistance to HF but do not provide the necessary dexterity for many lab procedures. For better dexterity, use an 8 mil nitrile glove over the thicker PVC or neoprene gloves. Silvershield gloves can be worn for added protection as they offer very good chemical protection. However, they do not have good cut/puncture resistant properties, so they should be worn under thicker PVC or neoprene gloves.
c) Splash goggles must be worn at all times HF is in use.
d) If work cannot be completed with the hood sash at the 6-10 inch height, a face shield is required.
e) A lab coat, a neoprene rubber apron and sleeve protectors should also be worn.
f) As with all laboratory operations involving chemicals, long pants and substantial shoes that cover the entire foot (no sandals, cloth or canvas shoes) must be worn.
g) No eating or drinking is allowed in any Clemson University lab at any time.
h) Exercise caution with PPE and lab clothing used for HF work. In the event that PPE becomes contaminated, it should be effectively decontaminated disposed of properly.
i) First aid knowledge is very important with HF use. No one is allowed to use HF without having studied the SDS and required first aid response to exposure to HF. The Allied Signal publication and the SDS give excellent first aid information.
j) Calcium gluconate gel (other recommended treatment such as benzalkonium chloride may be provided in addition to calcium gluconate) must be available in every lab/area where HF is used. Benzalkonium chloride should not be used in or near the eyes. First aid supplies must be kept in designated location known to all employees. Calcium gluconate (or other treatment) must be replaced as necessary (before expiration date) to ensure its effectiveness.
k) Anyone experiencing an HF burn/exposure must report to Redfern Health Center (or Clemson Health Center, Oconee Hospital Emergency Room, or Anderson Hospital for additional treatment/monitoring.
Emergency Room during after hours for Redfern) where the exposed individual will be given immediate medical attention.
There are now some alternative procedures to etch silicon that don’t use concentrated HF. For example, there is an ammonium bifluoride preparation that may be used to etch silicon in some situations. Perhaps the literature of your discipline may have examples of other alternatives to the use of HF.
AlliedSignal Chemicals “Recommended Medical Treatment for Hydrofluoric Acid Exposure”
Honeywell “Recommended Medical Treatment for Hydrofluoric Acid Exposure”