Hydrofluoric Acid

Classification

Acute toxicity (oral), Category 2; Acute toxicity (dermal), Category 1; Acute toxicity (inhalation), Category 2; Skin corrosion, Category 1A; Serious eye damage, Category 1 (per the Sigma-Aldrich SDS for 30–50% hydrofluoric acid). Dilute solutions are still dangerous; check your supplier's safety data sheet.

Hazard statements

• H300+H310+H330 Fatal if swallowed, in contact with skin or if inhaled.
• H314 Causes severe skin burns and eye damage.

Key precautionary statements

• P260 Do not breathe mist or vapors.
• P262 Do not get in eyes, on skin, or on clothing.
• P271 Use only outdoors or in a well-ventilated area.
• P280 Wear protective gloves, protective clothing, eye protection and face protection.
• P284 Wear respiratory protection.
• P303+P361+P353 IF ON SKIN (or hair): Take off immediately all contaminated clothing. Rinse skin with water.
• P304+P340+P310 IF INHALED: Remove person to fresh air and keep comfortable for breathing. Immediately call a POISON CENTER or doctor.
• P305+P351+P338+P310 IF IN EYES: Rinse cautiously with water for several minutes. Remove contact lenses, if present and easy to do. Continue rinsing. Immediately call a POISON CENTER or doctor.
• P405 Store locked up.

The federal OSHA PEL is 3 ppm as an 8-hour TWA (29 CFR 1910.1000 Table Z-2). NIOSH recommends 3 ppm TWA with a 6 ppm ceiling over 15 minutes. ACGIH is much lower at 0.5 ppm TWA and a 2 ppm ceiling, with a skin notation and a biological exposure index for fluoride. Cal/OSHA sets 0.4 ppm TWA and 1 ppm STEL with a skin notation. The NIOSH IDLH is 30 ppm. Skin contact can cause serious poisoning even when air levels are low. State OSHA plans may set different limits.

• Appearance: Colorless, fuming liquid (solution); anhydrous hydrogen fluoride is a colorless gas or liquid
• Odor: Strong, irritating
• Molecular weight: 20.0
• Boiling point: 67°F (19.5°C) anhydrous; about 152°F (67°C) for a 70% solution
• Freezing point: -118°F (-83°C) anhydrous
• Flash point: Not flammable
• Explosive limits: Not applicable
• Vapor pressure: 783 mmHg anhydrous; 150 mmHg for a 70% solution at 77°F
• Specific gravity: About 1.16 (48% solution) to 1.23 (70% solution)
• Water solubility: Miscible

Inhalation

Irritates and burns the nose, throat and lungs. Higher exposures can cause fluid in the lungs (pulmonary edema), which may be delayed, and fluoride poisoning.

Skin

Hydrofluoric acid passes through the skin and destroys deeper tissue and bone. With dilute solutions, pain and visible damage may not show up for several hours, up to about 24 hours. Fluoride absorbed through even a modest burn can lower blood calcium and cause dangerous heart rhythm problems and death. See burn injury.

Eyes

Causes severe burns and can cause permanent damage or blindness.

Ingestion

Can be fatal, even in small amounts. Get emergency medical help immediately.

Target organs

Eyes, skin, respiratory system, bones; high exposures also affect the heart, liver and kidneys

Long-term effects

Repeated high exposure can cause fluorosis, with fluoride deposits in the bones and teeth.

Gloves

For full contact, the Sigma-Aldrich SDS lists Viton gloves at least 0.70 mm thick (breakthrough over 480 minutes); for splash contact, chloroprene at least 0.65 mm. Thin disposable nitrile gloves are not enough on their own. See hand protection.

Eyes and face

Non-vented chemical splash goggles plus a full face shield. Do not wear contact lenses. Provide an eyewash station and safety shower close to the work area.

Respiratory

Handle in a fume hood or with local exhaust ventilation. Up to 30 ppm, NIOSH lists cartridge respirators with cartridges approved for hydrogen fluoride, powered air-purifying respirators, gas masks, supplied-air respirators or SCBA. Above 30 ppm or at unknown levels, use a pressure-demand full-facepiece SCBA. See respiratory protection.

Clothing

Acid-resistant apron, sleeves and closed shoes; NJDOH lists Tychem Responder and TK and Trellchem HPS for full suits. Keep calcium gluconate gel on hand wherever hydrofluoric acid is used.

Store in tightly closed polyethylene, fluoropolymer or other compatible containers, never glass, in a cool, well-ventilated area with secondary containment. Hydrofluoric acid etches glass, concrete and ceramics. Vent metal containers regularly, because reaction with metal can build up hydrogen gas.

Only trained workers should handle hydrofluoric acid. Never work alone with it, and keep unexpired calcium gluconate gel and a written first aid plan in the work area.

Keep away from

• Strong bases such as sodium hydroxide and potassium hydroxide
• Metals such as iron and steel (form flammable hydrogen)
• Glass, concrete and silica-containing materials
• Oxidizers and other strong acids such as sulfuric acid
• Water and steam (anhydrous HF reacts violently)
• Cyanide salts (release hydrogen cyanide)

• Evacuate and isolate the area. Only trained responders in acid-gas respiratory protection or SCBA and full acid-resistant gear should respond.
• Do not touch spilled material; even small splashes can cause serious injury.
• Neutralize and absorb with a hydrofluoric-acid spill kit, calcium carbonate, or sodium carbonate mixed with slaked lime. Do not use sand or other silica-based absorbents, which react to form toxic silicon tetrafluoride gas.
• Collect in polyethylene containers and dispose of as hazardous waste.
• Keep out of drains and waterways.
• Follow ERG Guide 157 for solutions (UN1790) or ERG Guide 125 for anhydrous hydrogen fluoride (UN1052).

Suitable extinguishing media

• Hydrofluoric acid does not burn; use media suited to the surrounding fire
• Water spray to cool exposed containers and absorb vapors

Special hazards

Heat releases toxic, corrosive hydrogen fluoride gas. Contact with metals can produce flammable hydrogen gas, and containers may burst. Firefighters need positive-pressure SCBA and full acid-resistant protective gear; regular turnout gear does not protect against HF.

• OSHA Hazard Communication (29 CFR 1910.1200): Hazardous chemical; SDS, labels and training required.
• OSHA Air Contaminants (29 CFR 1910.1000 Table Z-2): Hydrogen fluoride, 3 ppm TWA.
• OSHA Process Safety Management (29 CFR 1910.119 Appendix A): Hydrogen fluoride and anhydrous hydrofluoric acid, threshold quantity 1,000 lb.
• CERCLA (40 CFR 302.4): Hazardous substance, reportable quantity 100 lb (RCRA waste U134).
• EPCRA Section 302 (40 CFR 355 Appendix A): Extremely hazardous substance, threshold planning quantity 100 lb, reportable quantity 100 lb.
• Clean Air Act 112(r) (40 CFR 68.130): Hydrogen fluoride/hydrofluoric acid at 50% or greater, threshold quantity 1,000 lb. Also a listed hazardous air pollutant.
• DOT (49 CFR 172.101): UN1790, Hydrofluoric acid, Class 8 with a 6.1 poison label; PG II for 30–50% solutions per supplier SDS. Anhydrous hydrogen fluoride ships as UN1052.

• NIOSH Pocket Guide: Hydrogen fluoride
• OSHA Occupational Chemical Database: Hydrogen fluoride
• Sigma-Aldrich SDS: Hydrofluoric acid 48% (product 339261)
• NJ Department of Health Hazardous Substance Fact Sheet: Hydrogen Fluoride
• CAMEO Chemicals: Hydrofluoric acid, solution
• 40 CFR 302.4, CERCLA hazardous substances
• 40 CFR 355 Appendix A, EPCRA extremely hazardous substances