Hydrofluoric Acid Handling & Lab Protocol | Safety Guide

Hydrofluoric acid is an exceptionally hazardous inorganic acid that demands rigorous engineering controls, specialised personal protective equipment, and a well-rehearsed emergency response plan before any laboratory manipulation is attempted.

CAS Number

7664-39-3

Molecular Formula

HF

Molecular Weight

20.01 g/mol

Appearance

Colourless fuming liquid (concentrated); colourless clear liquid (dilute)

Primary Hazard

Corrosive and systemic toxin; fluoride ions penetrate skin causing deep tissue destruction and potentially fatal hypocalcaemia

Antidote (topical)

Calcium gluconate gel (2.5 % w/w) applied immediately to exposed skin

Compatible Container Materials

Polyethylene (PE), polypropylene (PP), PTFE; never glass or metal

Required Equipment & Personal Protective Equipment

Before working with hydrofluoric acid, assemble all equipment and verify that an emergency eyewash station and safety shower are within 10 seconds of travel from the work area. Confirm that a telephone is immediately accessible to call emergency services.

• Gloves: Double-glove with thick neoprene or nitrile outer gloves (≥0.38 mm) over inner butyl rubber or nitrile gloves. Standard latex gloves provide inadequate protection.
• Eye/face protection: Chemical splash goggles (indirect-vent) plus a full face shield. Safety spectacles alone are insufficient.
• Body protection: Acid-resistant apron or fully encapsulating chemical suit for concentrated HF (≥48 %).
• Respiratory protection: Work inside a certified fume hood at all times. For concentrations above 3 % or volumes above 100 mL, use a full-face respirator fitted with an acid-gas/P100 combination cartridge.
• Containers: Use only HDPE, PP, or PTFE containers. Label all containers clearly with the GHS corrosion and skull-and-crossbones pictograms.
• Antidote on hand: Keep 2.5 % calcium gluconate gel (≥100 g tube) in the immediate work area before starting any procedure.

Dilution & Preparation Procedure

Always add acid to water (never water to acid) when preparing dilutions. Prepare dilutions inside a ventilated fume hood on a secondary containment tray (HDPE or PP). Allow the solution to cool to room temperature before transferring to a labelled storage container.

1. Calculate the required volumes using C₁V₁ = C₂V₂.
2. Add the calculated volume of ultra-pure or deionised water to the HDPE container first.
3. Using a calibrated HDPE or PTFE measuring cylinder, slowly pour the required volume of stock HF solution into the water with gentle stirring using a PTFE rod. Do not pipette HF with mouth-operated pipettes.
4. Cap the container loosely for 2–3 minutes to allow heat to dissipate, then seal fully.
5. Label immediately: compound name, concentration, date of preparation, preparer's initials, and hazard pictograms.
6. Store in a dedicated, ventilated acid cabinet separate from bases, oxidisers, and organic solvents.

Note: Even dilute HF (1–5 %) is capable of causing serious deep burns; do not reduce PPE requirements for dilute solutions.

Silicon & Glass Etching Protocol

Hydrofluoric acid is widely used in semiconductor fabrication and surface science to etch silicon dioxide (SiO₂) layers and to clean silicon wafer surfaces. Buffered HF (BHF), a mixture of HF and ammonium fluoride (NH₄F), is preferred for controlled oxide removal.

Procedure

1. Ensure all PPE described in Section 1 is donned before handling etchant solutions.
2. Prepare or obtain the required HF or BHF solution and pre-warm if specified in the process recipe.
3. Place the substrate (silicon wafer, glass slide, or other specimen) into a PTFE or PP etch bath using PTFE tweezers or a wafer carrier. Never use metal tools.
4. Immerse the substrate for the process-specified time. Agitation with a PTFE paddle may be used to improve uniformity.
5. Transfer the substrate to a cascade DI-water rinse bath (minimum 3 overflows) to remove residual fluoride.
6. Measure the resistivity of rinse water with a conductivity meter to confirm adequate rinsing (typically >1 MΩ·cm for semiconductor applications).
7. Dry under nitrogen stream or in a clean-room spin-dryer.

Etch rates depend on HF concentration, temperature, and substrate composition; consult your process documentation for specific parameters.

Spill, Exposure & Emergency First Aid

HF exposure is a medical emergency. Act immediately. Fluoride ions continue to penetrate tissue after apparent skin contact, and even small-area exposures can cause life-threatening systemic hypocalcaemia and hypomagnesaemia.

Skin Contact

1. Activate the emergency alarm and call emergency services (or designate a colleague to do so) immediately.
2. Remove contaminated clothing and jewellery while flushing the affected area with large volumes of running water for a minimum of 15 minutes.
3. While flushing continues (or immediately after), apply 2.5 % calcium gluconate gel liberally and massage gently into the affected skin. Reapply every 15 minutes until medical personnel arrive.
4. Do not use ice; do not apply pressure bandages without medical direction.

Eye Contact

1. Irrigate immediately with copious water or sterile saline at the eyewash station for at least 15–20 minutes, holding eyelids open.
2. Seek immediate ophthalmological evaluation.

Inhalation

1. Move the casualty to fresh air immediately.
2. If breathing is laboured, administer 100 % oxygen if available and trained to do so.
3. Transport to hospital for monitoring of pulmonary oedema.

Small Spill (<10 mL)

1. Alert colleagues to evacuate the immediate area.
2. Neutralise spill with calcium carbonate (CaCO₃) or sodium bicarbonate powder (not sodium hydroxide, which generates heat).
3. Absorb neutralised material with dry vermiculite or specialised HF spill pillows; place in a sealed HDPE waste container.
4. Dispose according to local hazardous waste regulations.

For large spills (≥10 mL concentrated HF), evacuate the area and call the hazardous materials (HAZMAT) response team.

Waste Disposal & Storage

Hydrofluoric acid waste and fluoride-containing solutions must be managed as hazardous chemical waste. Never dispose of HF or fluoride solutions down the drain without prior neutralisation and confirmation that local regulations permit it.

Neutralisation before disposal

Add excess calcium hydroxide (Ca(OH)₂) slurry to the HF waste to precipitate calcium fluoride (CaF₂). Allow solids to settle, decant supernatant, and verify pH 6–8 before any drain disposal. Confirm fluoride ion concentration meets local discharge limits (commonly <10–20 mg/L) using an ion-selective electrode or test strips.

Solid waste

Collect CaF₂ precipitate, spent absorbents, contaminated PPE (gloves, apron), and wipe materials in a sealed, labelled HDPE container. Submit to a licensed hazardous waste contractor.

Storage

• Store in a dedicated, ventilated, locked acid cabinet away from direct sunlight and heat sources.
• Segregate from bases (e.g. ammonia, NaOH), oxidisers, and organic solvents.
• Keep in original or HDPE/PP/PTFE containers; never store in glass.
• Maintain a chemical inventory and record opening dates; concentrated HF should be used within 12 months of opening.

Frequently asked questions

Why is hydrofluoric acid more dangerous than other mineral acids at the same concentration?

Unlike strong mineral acids that cause immediate, localised corrosive burns, hydrofluoric acid is a weak acid that penetrates skin and tissue rapidly with little initial pain, allowing deep fluoride ion distribution before the victim realises the severity of exposure. Fluoride ions then chelate calcium and magnesium ions in tissue and blood, potentially causing fatal cardiac arrhythmia and hypocalcaemia even from relatively small skin exposures (as little as 160 cm² of skin contact with concentrated HF has been reported as fatal).

Can I use glass beakers or glass volumetric flasks when working with hydrofluoric acid?

No. Hydrofluoric acid reacts with silicon dioxide in glass to form silicon tetrafluoride (SiF₄) and water, rapidly etching and weakening the vessel. This can cause unexpected container failure, release of HF vapour, and inaccurate concentrations. Always use containers made of polyethylene (PE), polypropylene (PP), or PTFE when handling any concentration of HF.

What concentration of hydrofluoric acid does Aladdin Scientific supply, and what is the SKU?

Aladdin Scientific supplies hydrofluoric acid under SKU H485836. Please refer to the product page or contact our technical support team for the exact concentration grade, purity specification, and available pack sizes, as these details may be updated.

Is calcium gluconate gel always sufficient as first aid for HF skin exposure?

Calcium gluconate gel (2.5 %) is the recommended immediate first-aid measure for dermal HF exposure and must be applied without delay while emergency services are contacted. However, it is not a substitute for medical evaluation. For exposures involving concentrated HF, large surface areas, fingertip exposures (where subcutaneous calcium gluconate injection may be required), or any systemic symptoms (tetany, chest pain, arrhythmia), immediate hospitalisation and management by medical professionals is essential.

How should I dispose of HF-contaminated PTFE labware?

Rinse contaminated PTFE labware thoroughly with copious deionised water in the fume hood, collecting all rinse water as fluoride-containing hazardous waste. If the item cannot be adequately decontaminated (e.g., cracked or deeply stained), place it in a sealed, labelled HDPE container and submit it to your institution's hazardous waste programme. Never dispose of HF-contaminated items in general laboratory waste.

References

1. Occupational Safety and Health Administration (OSHA). Hydrofluoric Acid. OSHA Safety and Health Topics. U.S. Department of Labor.
2. National Institute for Occupational Safety and Health (NIOSH). Pocket Guide to Chemical Hazards: Hydrogen Fluoride. CDC/NIOSH.
3. Kirkpatrick JJR, Enion DS, Burd DAR. Hydrofluoric acid burns: a review. Burns. 1995;21(7):483–493.
4. Siegel DC, Heard JM. Intra-arterial calcium infusion for hydrofluoric acid burns. Aviation, Space, and Environmental Medicine. 1992;63(3):206–211.
5. European Chemicals Agency (ECHA). Hydrogen Fluoride (HF) — Substance Infocard. ECHA.

Products are supplied for research and development use only. Not for use in humans, animals, diagnosis, or therapy.