A. Hazards – Overview

Hydrofluoric acid (HF) differs from other acids because it readily penetrates the skin and dissociates into fluoride ions, causing destruction of deep tissue layers, including bone. The fluoride ion affects tissue integrity and metabolism by liquefaction necrosis, decalcification and destruction of bone, and production of insoluble salts. Loss of calcium (hypocalcemia) results from precipitation of calcium from the blood as CaF2. This results in calcium loss from the bones to equilibrate the decreased serum calcium. The development of hypocalcemia can be rapidly fatal because calcium is important for muscles, including the cardiac muscle (heart), to function properly. Fluoride ions might also bind to potassium and magnesium ions, leading to myocardial irritability and arrhythmia. Death from metabolic acidosis, hypocalcemia, or ventricular arrhythmias can occur several hours after exposure.

Pain associated with skin exposure to HF may not occur for 1-24 hours. Unless you can rapidly neutralize the HF and bind the fluoride ions, tissue destruction may continue for days and result in limb loss or death. HF is similar to other acids in that the initial extent of burn depends on the concentration, temperature, and duration of contact with the acid. Eye exposure to concentrations of HF greater than 0.5% can result in severe ocular damage, with delayed signs and symptoms.

Hydrofluoric acid vapors are also hazardous. Ocular irritation and injury can occur from working with HF outside a vented enclosure (laboratory hood). Inhalation can cause severe throat irritation, cough, dyspnea, cyanosis, lung injury and pulmonary edema. In severe exposure cases, these can result in death.

B. Dermal Exposure Case Studies

  • An adult patient who developed 25% total body surface area second degree burns after exposure to a 70% hydrofluoric acid preparation died in cardiac arrest. Ionized serum calcium level was 1.7 milligrams per deciliter (mg/dL) immediately premortem. The normal range is 4 to 4.8 mg/dL.
  • A dermal exposure to 70% hydrofluoric acid over a 2.5% total body surface area resulted in death. The serum calcium level was 2.2 mg/dL.
  • Two workers died following a splash exposure of 70% hydrofluoric acid to the face, chest, arms and legs. Both workers were promptly removed from site of exposure. Clothing was removed and burns were initially treated at the workplace with a cold shower and alcohol applied to burn areas. No suitable protective clothing was worn at the workplace.
  • A woman died from severe chemical burns of the skin and lungs, with intense pulmonary hemorrhagic edema after having acid thrown onto her face during an attack.
  • A patient with HF burns over 8% of his body died from intractable cardiac arrhythmia secondary to the depletion of ionized calcium.

C. Handling and Personal Protective Equipment

  • Familiarize yourself with the hazards specific to HF before handling. Consult this Chapter, the SDS, the EHS HF webpage and label information.
  • Always handle HF in a properly functioning laboratory hood, and in an area equipped with an eyewash and safety shower.
  • Do not work alone when using HF and alert colleagues when using the material.
  • Ensure that calcium gluconate antidote is on hand before handling HF.
  • Required Personal Protective Equipment:
    • Goggles
    • Face shield (plastic)
    • Gloves: Thin disposable gloves (such as 4, 6, or 8 mil blue nitrile gloves) used in laboratory operations provide a contact barrier only and should be disposed immediately when contamination is suspected. Thicker (10-20 mil) PVC or neoprene gloves provide better resistance to HF but do not provide the necessary dexterity for many lab procedures. Thinner PVC or poly gloves can provide some resistance to HF, but require immediate changing at the first sign of contamination. Do not wear disposable gloves without double gloving because of the potential for exposure through pinholes
    • Acid resistant apron
    • Long pants and sleeves (note that these are required when working with all corrosive materials, including HF)
    • Closed toe shoes (required for ALL laboratory work)

D. Post-Exposure Treatment

This manual (Chapter 3, Section VIII) contains a recommendation that upon skin or eye exposure to hazardous materials, flush the affected area for at least 15 minutes with an eyewash or safety shower. This general guidance is appropriate for almost every lab chemical, including corrosive acids and bases. However, HF has more specific treatment requirements, outlined below.

In the event of a skin or eye exposure to HF:

  • Have someone call 911 immediately, to facilitate arrival of medical assistance.
  • Remove all exposed clothing and immediately wash all exposed areas with copious amounts of water from the safety shower or eyewash. Flush exposed eyes for at least 15 minutes, but flush exposed skin for only five minutes, followed by treatment with a calcium source.
  • For skin exposures, after flushing for five minutes, apply a gel or slurry of calcium gluconate (preferred) or calcium carbonate directly to the exposed area. Use concentrations between 2.5% and 33%.
  • For severe exposure cases, consider subcutaneous infiltration with calcium gluconate. Infiltrate each square centimeter of affected dermis and subcutaneous tissue with about 0.5 mL of 10% calcium gluconate, using a 30-gauge needle. Repeat as needed to control pain. Split or remove nails to treat nail bed burns. The earlier this is administered, the more rapidly symptoms resolve.
  • CAUTION: Avoid administering large volumes of subcutaneous calcium gluconate, as this will result in decreased tissue perfusion and potential necrosis.

Note that calcium gluconate gel has an expiration date. Make sure that you always have access to a non-expired supply if you are working with HF.

DO NOT USE CALCIUM CHLORIDE – Calcium chloride is irritating to the tissues and may cause injury.

Figure 6.3
Tube of calcium gluconate gel. Make sure you have one or more non-expired tube of this present in your lab when working with HF.

E. Incompatibilities and Storage

Store HF and HF waste in a cool, dry place away from incompatible materials. Storage areas should be clearly marked as containing HF. HF reacts with many materials; therefore, avoid contact with glass, concrete, metals, water, other acids, oxidizers, reducers, alkalis, combustibles, organics and ceramics. Store in containers made of polyethylene or fluorocarbon plastic, lead, or platinum. Place storage bottles in polyethylene secondary containment trays.

Never store HF, or HF waste, in glass containers.

Figure 6.4
Hydrofluoric acid. Note that the storage bottles are plastic. Make sure to store all forms of HF, including dilutions and waste, in compatible containers that are not glass.

F. Spills

Ensure all areas where HF is used are equipped with proper spill response equipment. You can neutralize small spills (100 mL or less) by covering with magnesium sulfate (dry) and absorbing with spill control pads or other absorbent materials. Add sodium bicarbonate or magnesium oxide to any absorbent and place in a plastic container for disposal. Wash the spill site with a sodium bicarbonate solution.

Use 3M’s Universal Sorbent or similar, as it does not react with HF. Do not use spill sorbents that contain silicon, such as vermiculite or sand, as this can produce silicon tetrafluoride, an odorless toxic gas.

If the spill is large, in a confined space, or in an area where there is not adequate ventilation, evacuate the room and immediately report the spill to 911. Contact EHS at 919-962-5507 if you have questions about spill response, or if you do not feel comfortable trying to clean up the spill yourself.