SEPS Guidance Note

(GN-CHEM11/2018)

Hydrofluoric Acid
Properties of Hydrofluoric Acid
Hydrofluoric acid (commonly referred to as HF) is formed when anhydrous hydrogen fluoride dissolves in water to
form a weak acid. Hydrofluoric acid is an extremely dangerous substance and can cause severe tissue damage and
toxic effects via inhalation, ingestion or skin / eye contact. Both anhydrous hydrogen fluoride and concentrated
hydrofluoric acid are clear, colourless, fuming liquids that produce a strong smelling, pungent fumes that are
extremely hazardous.
Hydrofluoric acid reacts strongly with several substances including silica, glass, ceramics, leather, concrete and metal
oxides but reacts poorly with metals. It is commonly used to etch glass and ceramics and to remove metal oxides
from the surface of metals without harming the metal underneath and is therefore in common use in several areas
across the university of Glasgow.
Hydrofluoric acid (and hydrogen fluoride) pass readily across the skin into the bloodstream and will cause severe
tissue damage to both skin and eyes. Direct contact with a concentrated solution will causes severe, painful burns
with a characteristic white or grey colour that may take a long time to heal and can lead to gangrene and loss of
tissue. Exposure to more dilute solutions can lead to a delayed reaction meaning that exposures may not be noticed
for several hours (in the case of solutions with a concentration <20% the effects may not be observed for up to 24
hours). The ability of hydrofluoric acid to pass through the skin means that burns can be very deep and damage may
continue for some time after the initial exposure has occurred.

Hydrofluoric Acid Burns and Toxicity

Hydrofluoric acid (and hydrogen fluoride) pass readily across the skin into the bloodstream and will cause severe
tissue damage to both skin and eyes. Direct contact with a concentrated solution will causes severe, painful burns
with a characteristic white or grey colour that may take a long time to heal and can lead to gangrene and loss of
tissue. Exposure to more dilute solutions can lead to a delayed reaction meaning that exposures may not be noticed
for several hours (in the case of solutions with a concentration <20% the effects may not be observed for up to 24
hours). The ability of hydrofluoric acid to pass through the skin means that burns can be very deep and damage may
continue for some time after the initial exposure has occurred.
Hydrofluoric acid will cause very severe damage to the eyes potentially resulting in blindness due to destruction of
the cornea if the exposure is prolonged or severe. Eye splashes should always be treated as quickly as possible using
an eye wash and/or suitable “antidote”.
Inhalation of hydrogen fluoride vapour should be avoided as the vapour is extremely harmful and can dissolve in
body moisture forming hydrofluoric acid, in cases of severe exposure pulmonary oedema could develop due to the
destruction of lung tissue. Symptoms of exposure include coughing, choking, tightness of the chest, chills, fever and
cyanosis of the skin (blue colouration). The HSE document EH40 sets out the short and long-term exposure limits for
HF as follows:
15 STEL 3ppm
8h TWA 1.8ppm
The level of HF vapour in the air can be monitored using Draeger colorimetric tubes to give an indication of the level
of risk and effectiveness of control measures.

University of Glasgow Safety and Environmental Protection Service

Telephone: 0141 3302799 E-Mail: safety@glasgow.ac.uk
In addition to causing burns, hydrofluoric acid is highly toxic reacting strongly with calcium in the body to cause
hypocalcemia. Large areas of skin contact (around the size of your palm) can cause a risk of hypocalcemia whereas
exposure of just 2% of the body’s surface to concentrated HF can be fatal.
First Aid Requirements
Due to the potential severity of the injuries caused by hydrofluoric acid it is unsurprising that very specific first aid
requirements apply. In the event a person is suspected or confirmed to have been exposed then the following steps
should be taken.
• The site should be flushed with copious quantities of water for a few minutes using a sink or emergency
shower to remove any hydrofluoric acid residue from the surface of the skin. If an HF “antidote” is not
available (or is not suitable for use) this time should be increased to around 15-20min.
• Contaminated clothing and jewellery should be removed while flushing with water and placed in a safe area
for disposal, remember to avoid spreading contamination from affected clothing and wear appropriate PPE
when assisting someone to remove contaminated clothing.
• If an “antidote” is available then it should be applied following the manufacturer’s instructions, remember to
avoid coming into contact with contaminated skin or clothing. Note that some “antidotes” are applied
immediately instead of flushing first with water, always follow the instructions from the manufccturer /
supplier.
• Medical attention should always be sought following an exposure to hydrofluoric acid.
Exposure to hydrofluoric acid can be mitigated by application of neutralising agents such as calcium gluconate gel or
a commercial product known as Hexafluorine. These agents are commonly referred to as “antidotes” or
“neutralising agents” and while this is not strictly the case they do help to mitigate the effects of exposure to HF.
Calcium Gluconate
Calcium gluconate gel is the most common Hf “antidote” in use in the UK. It consists of a small tube of gel
containing 2.5% calcium gluconate. Calcium gluconate reacts with hydrofluoric acid producing calcium fluoride
which is non-corrosive, insoluble and non-toxic (causing the gel to turn white). Once an exposure has occurred
calcium gluconate gel should be applied liberally to the affected area and massaged into the skin using a gloved
hand. This should be repeated every 15min until medical attention has arrived or the affected person has been
transferred to hospital. Medical attention should be sought as quickly as possible. Calcium gluconate must not be
applied to the eyes and is therefore not suitable for eye splashes involving HF.
Hexafluorine
Hexafluorine is a commercial HF “antidote” which is supplied as either an eye wash style bottle or in a spray
cannister intended for use on larger areas. It is recommended that it is used without a prior wash with water and
should be applied directly to the affected site. Unlike calcium gluconate hexafluorine can be applied to the eyes and
can also be used to rinse out the mouth following ingestion of HF (although it should not be swallowed).
Note: in the event that a person is exposed to hydrofluoric acid by ingestion or direct contact (or inhales HF
vapour) they should always be referred to hospital for further treatment even if they have used an HF
“antidote”. Remember that in some cases exposure may not be immediately obvious.
Note: Before beginning work involving the use of hydrofluoric acid the appropriate first aid materials should be
located and placed within easy reach. Calcium gluconate gels or other neutralising agents should be
checked to ensure they have not expired.

Working with Hydrofluoric Acid

Due to the hazards presented by hydrofluoric acid we strongly recommend that it is only used by experienced,
competent staff and students who have been instructed in safety procedures and handling techniques. The use of
hydrofluoric acid should always be supported by a robust CoSHH assessment and Standard operating Procedures
(SOPs) should be implemented to help ensure that a safe system of work is implemented. Consider the following
precautions:

University of Glasgow Safety and Environmental Protection Service

Telephone: 0141 3302799 E-Mail: safety@glasgow.ac.uk
 • Where a viable alternative exists hydrofluoric acid should not be used unless there is a specific reason for
doing so, this eliminates the hazard entirely.
• A suitable and sufficient CoSHH assessment should be prepared before any work with hydrofluoric acid (or
hydrogen fluoride) is started. We strongly recommend that users are asked to sign the assessment
confirming their understanding of the risks and agreeing to adhere to the specified precautions prior to
commencing any procedures involving this substance.
• Where possible Standard operating procedures should be in place for routine processes involving the use of
HF. These should be regularly reviewed and include key safety information.
• Only staff and students who have received appropriate training should be permitted to work with
hydrofluoric acid. This can take the form of “on the job” training under the supervision of an experienced
user.
• Hydrofluoric acid should only be used in a controlled area where spillages and leaks can be contained. It is
good practice to ensure areas where HF is in use are clearly marked to alert other users and visitors to the
potential risk. If HF is used regularly then where possible specific work areas should be designated for HF
use and not used for any other purpose.
• Hydrofluoric acid should only be used in a well ventilated area with a suitable extraction system present to
remove any vapours. The ideal solution is to use a suitable LEV system such as a fume cupboard. Note that
in many applications (e.g. electronics) a laminar air flow cabinet is used to prevent dust contamination f the
working area. While these may provide some containment for liquid spills and help to dilute any vapours
released they do not fully extract and harmful gases released and in fact may blow them into the working
area.
• Where a risk of vapour release is present atmospheric monitoring should be considered to ensure hydrogen
fluoride levels are within acceptable limits in working areas.
• Suitable PPE should always be worn when handling hydrofluoric acid even when working in a fume cabinet.
As a minimum this should include acid resistant gloves, safety glasses and a suitable lab-coat along with
normal laboratory attire which covers exposed skin. It is strongly recommended that double gloving is
considered along with the use of an acid resistant apron.
• Lone working should not be permitted when using hydrofluoric acid or hydrogen fluoride gas.
• Glass containers should never be used for the storage or transport of hydrofluoric acid (including dilute
solutions) as the acid will react with the glass leading to weakening of the structure and potential failure of
containment.
• Disposal procedures should be established before the procedure begins, in general acid waste should be
collected for disposal using an appropriate container (see above). Waste should be clearly labelled, stored in
an appropriately ventilated area and disposed of as quickly as possible. Neutralisation of HF waste is not
recommended due to the formation of reactive intermediates that can re-release HF vapour.
• Emergency procedures / first aid protocols including the use of “antidotes” such as calcium gluconate gel
must be established before the process begins. Antidotes, spill kits and washing stations should be located
nearby and expiry dates checked to ensure that they are in date. Anyone involved in the process should be
clearly briefed on the protocols to be implemented in the event of an exposure.
• In the event of a leak or spillage the area should be evacuated, you should only attempt to clear up small
spills if trained to do so, using an HF specific spill kit only. HF will react with sand and some other absorbents
and the risk may be increased if attempts are made to neutralise it using inappropriate methods (see above).

University of Glasgow Safety and Environmental Protection Service

Telephone: 0141 3302799 E-Mail: safety@glasgow.ac.uk
Further Information
Hydrofluoric acid is a potentially lethal chemical and should be treated with caution. However, like most hazardous
substance sit can be used safely if appropriate precautions are taken. Further information can be obtained by
contacting Safety and Environmental Protection Services
General Office: 0141 3305532
Chemical Safety Adviser: 0141 3302799

University of Glasgow Safety and Environmental Protection Service

Telephone: 0141 3302799 E-Mail: safety@glasgow.ac.uk