What is Hydrogen Fluoride?

Hydrogen fluoride is a chemical compound with the formula HF. It can exist as a colourless gas or as a fuming liquid; it has a strong irritating odour and can be dissolved in water. When hydrogen fluoride is dissolved in water, it may be called hydrofluoric acid, and it can also be released when other fluoride-containing compounds, such as ammonium fluoride, are combined with water. Hydrogen fluoride boils just below room temperature, whereas the other hydrogen halides condense at much lower temperatures. Unlike the other hydrogen halides, HF is lighter than air and diffuses relatively quickly through porous substances. Hydrogen fluoride will corrode most substances except lead, wax, polyethylene, and platinum.

What is Hydrogen Fluoride Used for?

Hydrogen fluoride is used to make aluminium, chlorofluorocarbons (refrigerants), herbicides, pharmaceuticals, high-octane gasoline, plastic, electrical components, aluminium fluoride, sodium fluoride, and other fluoride salts. It is used to separate uranium isotopes. It is used to clean metals, bricks, or remove sand from metal castings. It is used to etch glass and enamel, polish glass, and galvanise iron. It is used in brewing and to cloud light bulbs.

Sources and Routes of Exposure

Sources of Exposure

• Individuals are most likely to be exposed to hydrogen fluoride by inhalation or dermal contact in the workplace. 
• Individuals may also be exposed to hydrogen fluoride and other fluorides in the ambient environment from emissions from industrial processes and coal combustion, as well as from natural sources that include volcanic activity and dust from weathering fluoride-containing rocks and soils. 
• In a natural disaster, individuals could be exposed to high levels of hydrogen fluoride when storage facilities or containers are damaged and the chemical is released. This release could occur at an industrial site or even a retail location. 
• Individuals could be exposed to hydrogen fluoride if it is used as a chemical terrorism agent. 
• Individuals may be exposed to hydrogen fluoride as part of a hobby.

Routes of Exposure

Inhalation: Inhalation hazards result not only from exposure to hydrogen fluoride gas but also from fumes arising from concentrated hydrogen fluoride liquid. Hydrogen fluoride gas is lighter than air. Even fairly low airborne concentrations of hydrogen fluoride produce rapid onset of eye, nose, and throat irritation. Hydrogen fluoride has a strong irritating odour that is discernible at concentrations of about 0.04 ppm, which is considerably less than the OSHA PEL of 3 ppm. Therefore, odour generally provides adequate warning of hazardous concentrations. Children exposed to the same levels of hydrogen fluoride as adults may receive larger doses because they have greater lung surface area: body weight ratios and increased minute volumes: weight ratios. Children may also be more vulnerable to corrosive agents than adults because of the relatively smaller diameter of their airways.

Skin/Eye Contact: Most hydrogen fluoride exposures occur by cutaneous contact with the aqueous solution. The fluoride ion, which penetrates tissues deeply, can cause both local cellular destruction and systemic toxicity and is readily absorbed through both intact and damaged skin. Hydrogen fluoride is irritating to the skin, eyes, and mucous membranes. Children are more vulnerable to toxicants absorbed through the skin because of their relatively larger surface area: body weight ratio.

Ingestion: Ingestion of even a small amount of hydrofluoric acid is likely to produce systemic effects and may be fatal.

Health Effects

Acute Effects

• Acute inhalation exposure to gaseous hydrogen fluoride can cause severe respiratory damage in humans, including severe irritation and pulmonary oedema. Irritation of the eyes, nose, and upper and lower respiratory tract, lacrimation, sore throat, cough, chest tightness, and wheezing have been reported. 
• Severe ocular irritation and dermal burns may occur following eye or skin exposure in humans. 
• Convulsions and cardiac arrhythmias and death from cardiac or respiratory failure may occur in humans from ingestion of high doses of fluorides. 
• Damage to the lungs, liver, and kidneys has been observed in animals acutely exposed to hydrogen fluoride by inhalation. 
• Acute animal tests in rats, mice, guinea pigs, and monkeys have demonstrated hydrogen fluoride to have moderate to high acute toxicity from inhalation exposure.

Chronic Effects 

• Chronic exposure to fluoride through drinking water has been observed to cause dental fluorosis or mottling (staining or pitting of teeth) in humans.  At higher intakes through oral or inhalation exposure, skeletal fluorosis (i.e., an accumulation of fluoride in the skeletal tissues associated with pathological bone formation) has been noted in humans. 
• Chronic inhalation exposure of humans to hydrogen fluoride has resulted in irritation and congestion of the nose, throat, and bronchi at low levels. 
• Increased bone density has been reported among workers chronically exposed to fluorides (including hydrogen fluoride) via inhalation. 
• Damage to the liver, kidneys, and lungs has been observed in animals chronically exposed to hydrogen fluoride by inhalation. 
• At high concentrations, chronic oral fluoride exposure has been reported to result in adverse pulmonary effects, renal injury, thyroid injury, anaemia, hypersensitivity, and dermatological reactions in humans. 
• Chronic oral exposure to fluoride at low levels has a beneficial effect on dental cavity prevention. Fluoride has also been used for the treatment of osteoporosis.
• EPA has not established a Reference Concentration (RfC) or a Reference Dose (RfD) for hydrogen fluoride.
• The California Environmental Protection Agency (CalEPA) has calculated a chronic inhalation reference exposure level (REL) of 0.03 milligrams per cubic metre (mg/m3) for hydrogen fluoride based on effects on bone density in humans.  The CalEPA reference exposure level is concentration at or below which adverse health effects are not likely to occur.  It is not a direct estimator of risk but rather a reference point to gauge the potential effects.  At lifetime exposures increasingly greater than the reference exposure level, the potential for adverse health effects increases. 

Reproductive/Developmental Effects

• Fluoride has been observed to cross the placenta in humans. Dental fluorosis can occur in a child's teeth when the mother receives high levels of fluoride during pregnancy. 
• In some animal studies, oral exposure to fluoride has caused impaired reproduction and malformation of foetal bones and teeth. 
• Inhalation of hydrogen fluoride resulted in degenerative testicular changes in male dogs. 
• Menstrual irregularities have been observed in women occupationally exposed to fluoride; no differences were found in the numbers of pregnancies, miscarriages, or births. 

Carcinogenicity

• Epidemiological studies have not demonstrated an association between fluoride in drinking water and an increased risk of cancer. 
• Increased rates of cancer have been observed in workers involving possible fluoride exposure; however, these situations involved mixed exposures to several chemicals, and fluoride could not be specifically implicated as the cause of the cancers. 
• EPA has not classified hydrogen fluoride with respect to potential carcinogenicity.

Hydrogen Fluoride Safety

First Aid Measures

• Eye Contact: Check for and remove any contact lenses. In case of contact, immediately flush eyes with plenty of water for at least 15-30 minutes. Cold water may be used. Keep the eyelids apart and away from the eyeballs during irrigation. Do not use oily drops, ointment, or HF skin burn treatments on the eyes. Get medical attention immediately, preferably from an eye specialist. If a physician is not immediately available, apply one or two drops of ophthalmic anaesthetic (e.g., 0.5% Pontocaine Hydrochloride solution). Place an ice pack on eyes until reaching the emergency room.
• Skin Contact: In case of contact, immediately flush skin with plenty of water for at least 15 minutes while removing contaminated clothing and shoes. Cover the irritated skin with an emollient. Cold water may be used. Wash clothing before reuse. Thoroughly clean shoes before reuse. Get medical attention immediately. While waiting for medical attention, it has been shown that flushing the affected area with water for one minute and then massaging HF Antidote Gel into the wound until there is a cessation of pain is a most effective first aid treatment. HF Antidote Gel contains Calcium Gluconate, which combines with HF for insoluble Calcium Fluoride, thus preventing the extraction of calcium from the body tissue and bones. Another alternative first aid treatment, after thorough washing of the burnt area, is to immerse the burnt area in a solution of 0.2% iced aqueous Hyamine 1622 or 0.13% iced aqueous Zephiran Chloride. If immersion is impractical, towels should be soaked with one of the above solutions and used as compresses for the burn area. Hyamine 1622 is a trade name for Tetracaine Benzethonium Chloride. Zephiran is a trade name for Benzalkonium Chloride. Again, seek medical attention as soon as possible for all burns, regardless of how minor they may appear initially.
• Serious Skin Contact: Wash with a disinfectant soap and cover the contaminated skin with an antibacterial cream. Seek immediate medical attention.
• Inhalation: If inhaled, remove to fresh air. If not breathing, give artificial respiration. If breathing is difficult, give oxygen. Get medical attention immediately.
• Serious Inhalation: Evacuate the victim to a safe area as soon as possible. Loosen tight clothing such as a collar, tie, belt, or waistband. If breathing is difficult, administer oxygen. If the victim is not breathing, perform mouth-to-mouth resuscitation. Warning: It may be hazardous to the person providing aid to give mouth-to-mouth resuscitation when the inhaled material is toxic, infectious, or corrosive. Seek immediate medical attention.
• Ingestion: If swallowed, do not induce vomiting unless directed to do so by medical personnel. Never give anything by mouth to an unconscious person. Loosen tight clothing such as a collar, tie, belt, or waistband. Get medical attention immediately.
• Serious Ingestion: Not available.

Exposure Controls & Personal Protection

Engineering Controls

• Provide exhaust ventilation or other engineering controls to keep the airborne concentrations of vapours below their respective threshold limit values. 
• Ensure that eyewash stations and safety showers are proximal to the workstation location.

Personal Protective Equipment

The personal protective equipment recommended when handling hydrogen fluoride is as follows: 

• Face shield
• Synthetic (impervious) apron or full suit. A full impervious suit is recommended if exposure is possible to a large portion of the body
• Vapour respirator (be sure to use an approved/certified respirator or equivalent);
• Gloves (impervious—neoprene, nitrile)
• Impervious Boots.

Personal Protection in Case of a Large Spill:

• Splash goggles
• Full suit (impervious)
• Vapour respirator
• Impervious Boots
• Gloves (impervious)
• A self-contained breathing apparatus should be used to avoid inhalation of the product. 
• Suggested protective clothing might not be sufficient; consult a specialist BEFORE handling this product.

Regulation

United States

^* Osteosclerosis or increased bone density due to excessive absorption and retention of fluorides.

Agency for Toxic Substances and Disease Registry (ATSDR) Inhalation Minimal Risk Level (MRL): 0.02 ppm (acute)

NIOSH Immediately Dangerous To Life or Health Concentration (IDLH): 30 ppm

Australia

Safe Work Australia has established an eight-hour time weighted average (TWA) exposure limit for hydrogen fluoride of 2.6 mg/m³. Safe Work Australia reports this product causes severe burns and is toxic by inhalation.