Tox Briefs

This Tox Brief looks at hydrofluoric acid

Hydrofluoric acid (HF) is a colorless acid typically found in an aqueous solution. However, HF can also be found as a gas above 19.5°C. HF is a common industrial chemical with a wide variety of uses. It is found in products used for glass and computer chip etching, porcelain and brick cleaning, metal electro polishing, petroleum processing, fluoridated hydrocarbon production, and leather tanning. Fluorinated hydrocarbons can also be found in many products like refrigerants, propellants, fire extinguishers, aluminum and chrome cleaning solutions, germicides, dyes, and rust removers. Ammonium bifluoride and ammonium fluoride found in wheel cleaner–although less caustic–can produce the same systemic toxicity as hydrofluoric acid when ingested or inhaled. HF can cause injury by ocular, dermal, respiratory and oral exposures.

HF has multiple mechanisms of injury. HF penetrates skin prior to dissociating, allowing the fluoride ions to reach deep tissues. Once dissociated, the negatively charged fluoride ions will form complexes with positively charged calcium and magnesium ions, causing both local and systemic hypocalcemia and hypomagnesemia. Hypocalcemia and hypomagnesemia results in cellular dysfunction and eventually, cell death, but also leads to depolarization of nerve, resulting in severe pain. HF poisoning can also impair function of the sodium potassium ATPase causing shifting of potassium to the extracellular space. Systemically, hypocalcemia and hypomagnesemia can result in cardiac dysrhythmias and cadiovascular collapse.

Aqueous solutions are found in different concentrations depending on its purpose. HF toxicity depends not only on the solution concentration, but also on the duration of exposure. Dilute solutions (5-8%) used in household products cause little toxicity with short exposures but can cause severe burns after prolonged exposure. Low concentration solutions (8-15%) cause little or no pain on exposure, but can cause delayed onset of severe pain and after 12-24 hours can develop signs of tissue corrosion. Intermediate concentration solutions (20-40%) cause pain after exposure and may cause deep tissue injury. High concentration solutions (50-70%) produce pain immediately after contact and result in severe tissue injury and systemic effects. The Occupational Safety and Health Administration HF workplace permissible exposure limit is 3 ppm in air, while 30 ppm concentrations are considered dangerous to life and health.

If you get aqueous HF on you remove contaminated clothes immediately (cut off clothes rather than pull them over the head), wash the exposed area with large amounts of water, and seek medical help immediately.  Exposure can be avoided by using personal protective equipment (PPE), such as nitrile, neoprene, or butyl rubber gloves and eye protection, when working with HF.  Inhalation of HF fumes can cause severe lung damage and swallowing even a small amount of HF can be fatal.

The above Tox Brief was taken from the Blue Ridge Poison Control Center’s August 2017 ToxTalks. Visit to learn more about hydrofluoric acid.