Hydrofluoric Acid: What You Need to Know

Hydrofluoric acid has unique properties that make it extremely dangerous to emergency personnel and others

Incidents involving hydrogen fluoride, or hydrofluoric acid, are not common, but the consequences of exposure to this compound by any means can be devastating. This little-known acid has unique properties that make it extremely dangerous to emergency personnel and others. Frequently mistaken for or confused with hydrochloric acid, hydrofluoric acid should be referred to as HF.

I became interested in HF while working in an oil refinery that uses it as a catalyst to make high-octane gasoline. As a paramedic, I found the effects of HF on the human body fascinating. I learned what I could about it and began teaching HF safety to my coworkers.

Then, in 2001, I was involved in an HF incident in which I was seriously exposed. I had been sprayed with anhydrous HF at approximately 150 pounds of pressure when a ¾" pipe broke at an ell as I was preparing to remove a plug. The HF had eaten the threads inside the ell and the weight of my pipe wrench caused the damaged pipe to give way, spraying both my legs just below my groin, and my right forearm. That exposure began a battle for my life that continues today.

Luckily, our local EMS and emergency facility had been trained on the dangers of this acid and proper treatment. Many EMS and ER personnel have probably never heard of this dangerous compound, but all emergency services, fire or law enforcement personnel who operate near and may be called to respond to any facility that uses or manufactures a form of HF should receive yearly training on treatment for HF exposure. This information should be available from your county LEPC.

Anhydrous hydrogen fluoride (HF) is an inorganic, corrosive compound with many industrial and commercial uses. It is manufactured by heating purified fluorspar (calcium fluoride) with concentrated sulfuric acid to produce the gas, which is then condensed by cooling or dissolving in water. It can also be refined as a by-product of the production of phosphoric acid, which is derived from the mineral apatite. Apatite sources typically contain a small amount of fluorite. The acid hydrolysis of fluorite-containing minerals generates an impure gas stream consisting of sulfur dioxide, water and HF. Separating gases from solids and treating them with sulfuric acid and oleum produces anhydrous HF. HF can also be released when other fluoride-containing compounds, such as ammonium fluoride, are combined with water or when certain plastics are exposed to fire conditions, creating carbonyl fluoride (the fluorine analog of phosgene).


Hydrogen fluoride is available commercially either in an anhydrous (water-free) state or in water solutions of various concentrations. At higher concentrations, HF is a colorless gas or a fuming liquid. HF may be known as Hydrogen fluoride (UN 1052), hydrofluoric acid (UN 1790) or fluorohydric acid. Identification numbers are CAS number 7664-39-3, UN: 1052 or RTECS: MW7875000. Main Manufacturers/main importers are DuPont (US), Allied (US) and Honeywell (US).

Its physical properties are:

  • Molecular weight: 10
  • Boiling point: Gas at temperatures above 19°C
  • Auto-ignition: Not relevant
  • Vapor pressure: 150mm (70% solution at 26.7°C); 70mm (70% solution at 20.0°C)
  • Solubility: Aqueous solutions to 70%
  • Explosive limits: Not applicable--non-flammable (BLEVE hazard if container subjected to fire conditions)
  • Shipping name: Hydrogen fluoride, anhydrous (1052), hydrofluoric acid, with not more than 60% strength (1790)
  • Identification number: 1052 (hydrogen fluoride, anhydrous) (Guide 125), 1790 (hydrofluoric acid) (Guide 157)
  • Hazardous class or division: 8 (1052)
  • Subsidiary hazardous class or division: 6.1, Inhalation hazard (1790)
  • Label: Corrosive, Poison (toxic) (1052), Corrosive, Poison (Toxic), Inhalation Hazard (1790)
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