Overview of Hazards

Hydrofluoric acid (HF) is an extremely corrosive liquid and vapor with a pungent, irritating odor. HF solutions are extremely hazardous and can cause serious health effects by any route of exposure. Unlike other mineral acids, they pose health hazards in addition to acid burns. The HF molecule readily penetrates the skin undissociated and can cause deep tissue damage, including destruction of the bone. Systemic effects can occur when fluoride ions bind to calcium and magnesium, forming insoluble salts. The depletion of calcium (hypocalcemia) or magnesium (hypomagnesemia) can lead to cardiac arrythemias and death. Exposing only 1% of the body surface area (approximately the palm of your hand) to 50% or stronger solutions to can be fatal. Exposure to dilute solutions (<20%) may not cause immediate pain or visible skin damage, but destruction of deeper tissues can continue and remain unnoticed for over 24 hours. Damage to the finger tips is especially painful and difficult to treat and often requires removal of the nail. It is critical to seek medical attention after any exposure, even if it seems minor and no pain is observed. Please take one of these documents with you here or here. Work with HF requires that the antidote calcium gluconate gel be readily available.

HF vapors are irritating to the eyes. Even small splashes can cause severe and irreversible eye damage. Contact lenses should not be worn when handling HF.

Safe Handling

The following safe handling instructions apply to all solutions that contain HF, including buffered oxide etch. It is crucial to avoid any exposure to HF gas or HF solutions, even at low concentrations. Solutions above 50% HF can cause significant HF evaporation.

Fume Hood

All handling of HF solutions must be done in a properly functioning fume hood compatible with acid use to prevent exposure by inhalation. If possible, carry out all work in secondary containment to minimize the likelihood and consequences of a spill. If HF is being used frequently, a work area with low foot traffic/disturbance should be dedicated to HF work. Before starting work:

• Post a warning sign on the fume hood: “HF in use in this area,”
• Remove all incompatible material from the hood,
• Verify that the fume hood is functioning properly.

Work Practices

Avoid working with HF when alone in the laboratory or outside of normal working hours. Notify others before you start using it. To minimize the chance of collisions and spills, only one person should use the HF work area at a time.

Personal Protective Equipment (PPE)

Always wear appropriate protective equipment when handling HF:

• Gloves - Thin, disposable gloves commonly used in laboratories do not provide sufficient protection against HF. A thicker glove rated to provide good protection from HF should be worn. Wearing a thinner disposable glove underneath the thicker glove is recommended. Check the glove manufacturers rating for HF resistance and breakthrough before using any glove. The table below gives ratings for gloves tested for HF. Many gloves (especially thinner gloves that offer excellent dexterity) provide only short term protection and must be changed frequently and immediately after exposure. Always check the gloves for holes or other signs of degradation before beginning work and periodically while working. 

Gloves tested by manufacturer for hydrofluoric acid solutions 48%

Rating

Poor: Provides protection against splashes only. Change frequently, and immediately after exposure.
Fair: Provides short time protection only. Change quickly after exposure.
Good: Good skin protection. Change after exposure to avoid contamination and secondary transfer. 

• Splash goggles as eye protection are a minimum. A face shield must be available and should be worn in conjunction with splash goggles whenever there is no physical barrier preventing splashes to the face, e.g., when the sash of the hood is raised. 
• An apron resistant to acids worn over a lab coat or an acid resistant smock with long sleeves is required to prevent skin contact.
• Appropriate street attire such as long pants and closed toe shoes are mandatory at all times in a laboratory.
• Acid resistant shoe covers are optional and may be required when handling large quantities of concentrated solution

When your work with HF is done, collect spent and excess solution as HF waste. Rinse used and emptied containers with a small amount of water and add the rinsing solution to the HF waste. The containers can then be rinsed thoroughly with soap and water. 

Check PPE for contamination. If no contamination is visible, wash reusable gloves with soap and water and remove. Leave disposable gloves on while removing the remaining PPE in the following order: face shield, splash goggles, apron or smock. Remove disposable gloves and wash hands with soap and water. Disposable equipment that is contaminated, and reusable equipment that is contaminated and cannot be safely decontaminated, should be discarded. Put the contaminated item into a plastic bag and label it “debris contaminated with hydrofluoric acid”. Dispose of it through the DRS chemical waste program. 

Calcium Gluconate Gel

All laboratories working with HF are required to have calcium gluconate gel available in the laboratory. Periodically check the expiration date to ensure that the gel has not expired. Once opened and used, the gel must be discarded. Calcium gluconate gel is available for purchase in the School of Chemical Sciences Storeroom or from vendors such as Fisher Scientific, Grainger, or Calgonate.

Emergency Procedures 

Immediate first aid is critical to avoid or minimize further injury. Any exposure to HF or HF solution should receive first aid treatment and medical evaluation even if no pain is felt. Delayed onset of deep tissue damage, bone damage, or systemic effects can occur up to 24 hours after exposure. 

If you are exposed to HF, have someone call 911 immediately. 

Skin Contact

Rinse off affected skin immediately with copious amounts of water for 5 minutes; if necessary, use the safety shower. Remove contaminated clothes under running water. Apply calcium gluconate gel to the affected area while wearing a disposable glove. Repeat the application every 15 minutes until medical assistance arrives.

Eye Contact

Use the eye wash to rinse the eye thoroughly for at least 15 minutes, occasionally lifting the upper and lower eyelids and rolling the eyeballs. If sterile 1% calcium gluconate eye wash solution is available, use the eye wash for a first thorough rinse and then use the solution to repeatedly irrigate the eye.

Inhalation

Move into fresh air immediately.

Ingestion

Do not induce vomiting. Do not take activated charcoal. Drink water or milk. 

Provide the medical team with the Safety Data Sheet (SDS) for HF.

Spills

Verify that a spill kit is readily available before working with HF. 

The use of solid calcium carbonate is recommended to absorb spills. Calcium will form an insoluble salt with fluoride and prevent fluoride absorption through the skin. Do not use sand, as HF reacts with it forming toxic tetrafluorosilane. The spill kit should also contain:

• A plastic container with lid or heavy duty plastic bag to collect any contaminated material,
• Gloves resistant to HF,
• Dust pan and broom.

Commercial spill kits are also available. They must be rated for HF use, not just acid use. 

Spills inside the fume hood should be neutralized immediately and the area cleaned up thoroughly after neutralization. Ask for assistance if you do not feel confident that you can perform the clean-up adequately.

In the case of a spill outside the fume hood, that cannot be neutralized safely, evacuate the area immediately and alert others. If possible, close the door to prevent vapors from spreading to other spaces and call 911 immediately. 

In the case of splashes on clothes, gloves, or shoes with no contact to skin, remove the item carefully, avoiding contact to skin. Put the items into a heavy-duty plastic bag, seal and label the bag. Wash the affected skin area with soap and water even if no skin contact is evident.

Storage

Store HF solutions and all HF waste in polyethylene or fluorocarbon plastic containers. NEVER store HF solutions in glass or metal containers.

Store HF solutions in a cool, dry, and well ventilated place away from incompatible materials. Use secondary containment. An acid neutralizer such as calcium carbonate can be added to the secondary containment to absorb spilled product.

Designate a storage area for HF and label it clearly with “Hydrofluoric Acid, extremely corrosive and toxic” (not just “HF”) on the outside of the cabinet.

HF is incompatible with

• Glass
• metals
• strong bases
• alkalis
• silica
• cyanides
• carbonates
• reducers
• ceramics

Disposal

Aqueous HF waste solutions should be collected in polyethylene containers and labeled accordingly. Dispose of all waste through the DRS chemical waste program. The following UI#s are established to request a waste pick-up:

573:      Hydrofluoric acid (unused)

15292:  Hydrofluoric acid (used)

14737:  Buffered Oxide Etch

Any HF-contaminated items should be collected separately in plastic bags and disposed of as HF-contaminated debris. Contact DRS if you are unsure of proper waste disposal procedures.

Responsibilities

All personnel working in a laboratory where HF is being used, even those not using HF, should be familiar with the hazards and receive training in first aid measures.

PI/Supervisor

• Be familiar with hazards related to HF and how to use it safely.
• Know how to respond to emergency situations and first aid measures.
• Provide personal protective equipment. 
• Train all personnel before they start work with HF in:

1. the safe handling of HF,
2. the location of the SDS for HF and this fact sheet,
3. the location of the spill kit,
4. the location of calcium gluconate gel.

• Maintain training records.
• Have calcium gluconate gel available in the HF use area. Note that the gel has an expiration date and must be periodically checked or replaced.
• Have a spill kit for HF available in the HF use area.

Student/Laboratory Personnel

• Read the SDS and this fact sheet carefully.
• Follow all safety instructions.
• Work with HF only under the buddy system and never when alone in the laboratory. 
• Make sure the hood is working properly before starting work.
• Make sure a spill kit and calcium gluconate gel are available and not expired before starting work.
• Know the location of the safety shower/eye wash.

References 

Centers for Disease Control and Prevention (CDC):
https://www.cdc.gov/niosh/npg/npgd0334.html 

American Chemistry Council HF Emergency Preparedness Guide:
https://www.americanchemistry.com/ProductsTechnology/Hydrogen-Fluoride-2/Emergency-Response-Guidelines-for-AHF.pdf 

Agency for Toxic Substances and Disease Registry (ATSDR) Medical Management Guidelines:
http://www.atsdr.cdc.gov/mhmi/mmg11.pdf

First aid for a unique acid, HF: A sequel, Chemical Health & Safety, January/February 2000:
http://depts.washington.edu/cosmolab/chem/hfsafety.pdf

Fact sheets from other universities that were helpful in compiling this Safety Guide:

Harvard University
https://chemistry.harvard.edu/files/chemistry/files/safe_use_of_hf_0.pdf

Columbia University, New York City
http://ehs.columbia.edu/hfPolicy.html

Stanford University and National Accelerator Laboratory:
https://www-group.slac.stanford.edu/esh/eshmanual/references/chemsafetyGuideHydrofluoricAcid.pdf