Hydrofluoric acid, the water solution of hydrogen fluoride (HF), is a contact poison. Even though it is from a chemical perspective a relatively weak acid, it is far more dangerous than conventional strong mineral acids, such as nitric acid, sulfuric acid, or hydrochloric acid. Owing to its lesser chemical dissociation in water (remaining a neutral molecule), hydrogen fluoride penetrates tissue more quickly than typical acids. Poisoning can occur readily through the skin or eyes or when inhaled or swallowed. From 1984 to 1994, at least nine workers died in the United States from accidents with HF.
Once in the blood, hydrogen fluoride reacts with calcium and magnesium, resulting in electrolyte imbalances, potentially including hypocalcemia. The consequent effect on the heart (cardiac arrhythmia) may be fatal. Formation of insoluble calcium fluoride also causes severe pain. Burns with areas larger than 160 cm, about the size of a man's hand, can cause serious systemic toxicity.
Symptoms of exposure to hydrofluoric acid may not be immediately evident, with an eight-hour delay for 50% HF and up to 24 hours for lower concentrations. Hydrogen fluoride interferes with nerve function, meaning that burns may not initially be painful. If the burn has been initially noticed, then HF should be washed off with a forceful stream of water for ten to fifteen minutes to prevent its further penetration into the body. Clothing used by the person burned may also present a danger. Hydrofluoric acid exposure is often treated with calcium gluconate, a source of Ca that binds with the fluoride ions. Skin burns can be treated with a water wash and 2.5 percent calcium gluconate gel or special rinsing solutions. Because HF is absorbed, further medical treatment is necessary. Calcium gluconate may be injected or administered intravenously. Use of calcium chloride is contraindicated and may lead to severe complications. Sometimes surgical excision of tissue or amputation is required.