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8.9.1 Hydrofluoric Acid

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Hydrofluoric Acid (HF)

Hydrofluoric acid (HF) is an extremely hazardous chemical with the potential to cause severe, life-threatening injuries from relatively small exposures. HF presents both corrosive and systemic toxicity hazards, and injuries may not be immediately painful or visible. Prompt, appropriate response following an exposure is critical.

Hydrofluoric acid is an aqueous solution of hydrogen fluoride gas. Laboratory concentrations vary widely, commonly ranging up to approximately 48% HF by weight. HF is colorless, non-flammable, and has a sharp, irritating odor. Although HF is classified as a weak acid based on dissociation, it is highly corrosive and uniquely dangerous due to its ability to penetrate tissue and bind calcium and magnesium, leading to serious local and systemic effects.

HF readily penetrates skin and can cause deep tissue damage. Fluoride ions bind calcium in blood and tissues, which can disrupt normal physiological function and result in severe injury or death if not treated promptly.

Training, planning, and authorization

Because of the significant hazards associated with HF, its use requires advance planning and additional controls.

Designated areas and engineering controls

  • HF must be used only in a designated chemical fume hood.
  • Designated HF hoods must be clearly identified using an HF designated area sign.
  • HF containers must be kept closed when not in use and handled over compatible secondary containment.

First aid and spill preparedness

  • An HF first aid kit containing 2.5% calcium gluconate gel must be readily available in areas where HF is used.
  • Calcium gluconate gel must be monitored for expiration and replaced as needed.
  • An HF spill kit containing calcium-based neutralizing agents (e.g., calcium carbonate, calcium sulfate, or calcium hydroxide) must be available.
  • Sodium bicarbonate must not be used for HF spills, as it does not bind fluoride ions and may generate hazardous aerosols.

Personal protective equipment (PPE)

PPE must be selected based on the specific task and HF concentration. At a minimum, HF work requires:

  • Acid-resistant apron and arm protection
  • Gloves:
    • Incidental contact: double nitrile gloves, changed immediately if contaminated
    • Extended handling: HF-compatible gloves (e.g., neoprene or butyl) worn over inner gloves
  • Splash goggles used in conjunction with a fume hood sash
  • Closed-toe shoes
  • Long pants and long-sleeved clothing

Safe work practices

  • Never work alone with HF; use a buddy system.
  • Use compatible secondary containment when handling HF.
  • Store HF in compatible containers within labeled secondary containment.
  • Store HF in lower cabinets to reduce spill risk.
  • Wash gloves with water before removal.
  • Ensure the Safety Data Sheet (SDS) for HF is readily accessible.

Additional technical and medical response information for HF exposure is available through recognized industrial and medical references. For questions about HF hazards, controls, or emergency response planning, contact EHS at askEHS@cornell.edu.

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