In the body, hydrofluoric acid reacts with the ubiquitous ions of calcium and magnesium and so can disable tissues and organs whose proper function depends on these metal ions. Exposure to hydrofluoric acid may not be initially painful, and symptoms may not occur until several hours later, when the acid begins to react with calcium in the bones. Under most circumstances, hydrofluoric acid exposure results in severe or even lethal damage to the heart, liver, kidneys, and nerves. Initial treatment to hydrofluoric acid exposure usually involves thorough rinsing (for up to 15 minutes) of to the exposed areas followed by the application of calcium gluconate gel. If exposure is high, or too much time has passed, a calcium gluconate solution may be injected directly into a local artery or surrounding tissues. In all cases, hydrofluoric acid exposure requires immediate professional medical attention. If coming in contact with human skin or bone the acid can severely burn and then decompose the bone, potentially necessitating amputation of the affected limbs.
The highest concentration of HF in air that can be tolerated by a human for 1 minute is 100 mg/m3.[citation needed] This causes a definite sensation of pain on the skin, a definite sour taste, and some degree of eye and respiratory irritation. If the air contains 50 mg/m3, the sour taste is apparent and there is irritation of the eyes and nose, but no pain is sensed on the skin. The concentration of 26 mg/m3 can be tolerated for several minutes, but the sour taste becomes evident after a short time, and there is mild pain in the nose and eyes. The American Conference of Governmental Industrial Hygienists has adopted 2 mg/m3 as the threshold limit for hydrogen fluoride. This comes to about 3 ppm (parts per million). Inhalational exposure to concentrated HF for as little as 5 minutes is usually fatal, producing death within 2-10 hours.[citation needed]
A concern for emergency services is the theft of drums of hydrofluoric acid, possibly after being mistaken for hydrochloric acid which has uses in the preparation of all kinds of substances, including in the clandestine production of drugs such as methamphetamines.
Hydrofluoric acid is a known hazard in car engine fires, forming when Viton o-rings and hoses are exposed to temperatures in excess of 400 °C.
