Hydrofluoric acid was discovered in 1771 by Swedish pharmaceutical chemist Carl Wilhelm Scheele when he was investigating the mineral called fluorite (Calcium fluoride). Hydrogen fluoride (HF) has several synonyms: Hydrofluoric acid, Fluoric acid, Hydrofluoride, Fluorine monohydride, Fluorane. Hydrofluoric (HF) acid is an extremely powerful inorganic acid and a vigorous dehydrating agent that is used in many industrial branches including production of aluminum, stainless steel and hydrofluorocarbons, glass etching, stevedoring and transportation industries, inorganic and organic chemical manufacturing, mineral processing, petroleum oil refineries, fire extinguishers manufacturing, steel mills, cleaning HVAC systems, and as the precursor to all fluorine compands in the pharmaceutical industry.  Consumer products containing hydrofluoric acid include rust removers, detergents, marble, brick and stone cleaning, toilet bowl clearners, insecticides, automobile wheel cleaners and air conditioner cleaners. 
Hydrofluoric acid is comprised of a diatomic compound of hydrogen and fluoride atoms as a gas, while in the liquid state it has strong hydrogen bonds between the chains forming a polymeric compound.  Anhydrous hydrofluoric acid and hydrofluoric acid in aqueous solutions range in appearance from colorless to slightly tinted based upon the concentration and impurities. It has a boiling point of 20 degrees celcius (68 degrees fahrenheit) at 760 mmHg, vapour density greater than air and readily dissolves in water that when diluted (exothermal reaction) is visibly indistinguishable from water. Hydrofluoric acid has a disagreeable, pungent odor at concentrations of 0.04 ppm which is way below the OSHA PEL (Permissible Exposure Limit) of 3 ppm and is extremely corrosive and has the ability to dissovle a number of materials especially oxides. 
The Major source of production of hydrofluoric acid is by treating fluorite with concentrated sulfuric acid at temperatues of 265 degrees fahrenheit to produce hydrofluic acid and calcium sulfate. Alternate production is a by-product in the production of phosphoric acid from the mineral apatite. Hydrofluoric acid is also produced by the release from industrial and welding processes and environmental activities such as volcanoes. HF production exceeds one million tons world wide by a number of manufactors and is transported and stored under high pressure as a highly concentrated liquid.  In the United States of America, the Department of Transportation Hazard Label and National Fire Protection Assocation (NFPA) 704 lists the health value of 4 (can be lethal), flammability value of 0 (will not burn under typical fire conditions), instability value of 2 (readily undergoes violent chamical changes at elevated temperatures and pressures) and special value of W with line through (reacts violently or exposevely with water). Domestic concentrations of hydrofluoric acid is typically around 0.5% with industrial concentrations approaching 100%.
Primary health consequences including dermal burns, eye injury, acute respiratory symptoms, gastrointestinal symptoms and cardiac abnormalities can occur from direct skin / eye contact, ingestion of solutions or inhalation of fumes and vapors with unintentional and intentional exposures. Unintentional exposure of hydrofluoric acid in and out of the workplace include inappropriate operations, mechanical failure of equipment, explosions of containers and tanks containing HF, during traffic incidents with leakage of HF, inadequate protective equipment and children accidentally exposed through ingestion of domestic cleaners.  Intentional cases of ingestion, with suicidal and homicidal intent, of hydrofluoric acid have been documented.
Hydrofluoric acid is highly toxic and damaging to humans due to the “double danger” properties of the corrisive nature of the hydrogen ions and toxic effect due to the ability of fluoride ions to penetrate into deep tissue causing liquefactive necrosis and release of cellular products. Hydrofluoric acid burns present with a unique concern for systemic fluoride toxicity including cardiovascular, pulmonary, renal and neuromuscular symptoms, electrolyte imbalance and enzyme inhibition which can lead to cardiac arrhythmias and death.  Chronic symptoms may occur or persist for months after HF ingestion or respiratory exposure. 
Hydrofluoric acid exposure requires immediate specific and specialized medical treatment to prevent penetration of the hydrofluoric acid into the deep tissues, decrease the dissemination of the fluoride ions through the bloodstream and subsequently reduce the toxic effects on organs or minimize the progression of damage to organ systems.  Hydrofluoric acid is technically classified as a weak acid compared to other hydrogen halide acids, but the fluoride ion can be quickly absorbed through the skin causing potential life-threatening burns and cardiac arrhythmias. With the dilute solutions, there will have delayed injury because ions will penetrate through the skin before dissociating and causing complications. A dermal injury is reported as the most common observed injury with burns to the fingers being one of the most concerning injuries for workers. 
Hydrofluoric acid exposure is a rare occurrence throughout the globe compared to other industrial injuries with an estimated 1000 cases annually, though actual incident rates are not known. 15 year study from Stuke et al showed an incident rate of 35 patients (17%) out of 204 chemical burns.  A 10-year study in China reported 690 patients with chemical burns and a little over half being involved with hydrofluoric acid and sulfuric acid. Most of the chemical burns occurred in the summer and autumn seasons.  A 20-year survey from Taiwan only had 324 identified calls of hydrofluoric acid with the majority of those incidents being dermal in nature.  Because of the nature of the occupations with the greatest potential injury from and exposure to hydrofluoric acid exposure, the majority of patients are adult males. Upper extremity location was most commonly involved. 
There are three (3) routes of entry for hydrofluoric acid into the human body - skin / eye exposure, inhalation and ingestion. Cutaneous exposure, with skin intact or damaged, is the most frequent pathway for entry with regards to aqueous solutions. Inhalation can arise from the exposure of the hydrogen fluoride gas as well as from the vapors eminating from the hydrogen fluoride liquid. 
Depending on the location of the hydrofluoric acid exposure and the percentage of the acid, patients can present immediately with severe caustic burns to the body and severe pain, with pain out of proportion as the hallmark finding. Solutions greater than 14.5% will produce immediate symptoms, 12% solutions can take up to an hour, and solutions less than 7% can take hours before symptoms occur. The concern exists for ocular and respiratory injury when any chemical is splashed / sprayed in the face.
History should include any exposure to hydrofluoric acid through workplace or domestic type exposures to include potential products containing hydrofluoric acid such as rust removers or cleaning agents within the past 24 hours. One should ascertain the concentration of the solution, exposure time of HF, use of protective agents or any other chemicalsthat was contained in the solution. Additional information inclucdes any treatment that has been given thus far to the individual.
Physical assessment should include immediate evaluation for life-threatening emergencies including airway compromise, respiratory distress, and cardiac arrhythmias. Additionally, one can assess for pulmonary edema, ocular injuries, and symptoms of hypocalcemia including Chvostek and Trousseau signs and tetany.
Electrolyte imbalance is one of the hallmark concerns for systemic poisoning from hydrofluoric acid exposure through all routes of entry. Immediate electrolyte assessment at minimum includes calcium, potassium, and magnesium levels to ascertain hypocalcemia, hypomagnesia and hyperkalemia. Even though the concern is with systemic poisoning, patients with simple exposures can develop hypocalcemia, hypomagnesia, and hyperkalemia.
Cardiac monitoring and electrocardiography (EKG / ECG) are important to assess for clinically significant electrolyte imbalance to include QT prolongation from hypocalcemia (Figure 1), peaked T waves/arrhythmias from hyperkalemia, and polymorphic ventricular tachycardia (specifically Torsades de Pointes) from hypomagnesia.
Chest x-rays should be performed on all patients with respiratory exposure to evaluate for pulmonary edema or pneumonitis. Inclusion of EtCO2 monitoring can be considered for individuals with inhalation type exposures. Urinalysis with evaluation for hematuria and proteinuria will indicate renal dysfunction, insufficiency and renal cortical necrosis.
Primary concern with the high corrosiveness and toxicity of hydrofluoric acid should be through the prevention of exposure. All individuals that use HF should be aware of the toxic properties of the agent which include information and procedures for safe handling of the acid, appropirate means of transporting and storage, management of waste containing HF, gross and fine decontaminiation procedures and medical treatment for exposure and intoxication. Hydrofluoric acid should be exclusively used in industrial settings and laboratories that are appropriately equipped to handle the chemical, have appropriate exposure control plans in place which includes having appropriate treatment modalities on site to initiate therapy prior to transport of the exposed individual to the hospital. Likewise, household and cleaning agents should be stored out of the reach of children.
Personal and general protectice equipment and measures should be implemented and adhered to at all times with equipment including:
Initial treatment for HF acid includes quick assessment, removal of contaminated clothing, as well as jewellery that could trap HF, should be immediately removed and double-bagged to prevent secondary exposure. Decontamination with copious amounts of water, saline or solution of soap and water along with neutralization using calcium gluconate, benzalkonium chloride polyethelene glycol, magnesium oxide or Hexafluorine.  Assessment and management life-threating conditions such as airway compromise or cardiac arrythmias.
The decontaminzation and neutralzing process for hydrofluoric acid exposure is primarily through the mechanical rinsing and diluting effect of water, as a hypotonic solution. Likewise it has no active ability to bind or chelate any chemical substance with the concerning hydrofluoric acid exposure and thefore neutralizing agents with their mechanism of actions can help reduce the necrosis from the fluoride ion. Calcium gluconate is the primary neutralizing agent and is capable of chelating the free fluoride ions, forming insoluble salts. Calcium gluconate should be applied multiple times to mitigate the damage from the fluoride ions. 
Hexafluorine solution developed by PREVOR laboratories was designed for active washing of hydrofluoric acid splashes. The solution has a triple effect in that it has the same rinsing and diluting properties as water, can neutralize the hydrogen ions and chelate the fluoride ions thus reducing the corrosive and cytotoxic effects of hydrofluoric acid. Though in an experimental study by Hulten et al, there was little difference in reducing the electrolyte disturbances caused from dermal exposure of hydrofluoric acid when compared to water rinsing.  
Burns with concentrated HF are usually very serious, with the potential for significant complications due to fluoride toxicity. Concentrated HF liquid or vapor may cause severe burns, metabolic imbalances, pulmonary edema, and life-threatening cardiac arrhythmias. Even moderate exposures to concentrated HF may rapidly progress to fatality if left untreated. Burns larger than 25 square inches (160 square cm) may result in serious systemic toxicity. Relief of pain is the only indication of the effectiveness of treatment. Therefore, the use of any analgesic agents is not advisable. 
A person who has HF burns greater than four square inches should be admitted immediately to an intensive care unit and carefully monitored for 24 to 48 hours. Anyone who has been exposed to gaseous HF and experiences respiratory irritation also should be admitted to and monitored in an intensive care unit. Blood sampling should be taken to monitor fluoride, potassium, and calcium levels. In some cases, hemodialysis is necessary for fluoride removal and correction of hyperkalemia and recurrent hypocalcemia.
Isolation and Evacuation
Hydrofluoric acid is a common chemical that is utilized in several domestic and industrial products and treatments for producing other manufactured products. Though the literature for treatment of hydrofluoric acid is based upon animal studies and some case reports / small case series, the mainstay treatment has not changed since the mid 1970's. Prehospital and emergency medicine physicians should be familiar with the initial and ongoing management and treatment with potential life threatening arrhythmias from the sequestration of calcium, magnesium and release of potassium. Easy transfer to burn centers should be in place for continued monitoring and treatment for patients with profound hydrofluroic acid burns.
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