HF Safety Awareness
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What is HF?
When you are talking to others, be aware that the abbreviation HF could stand for three
different things – ‘high frequency’, ‘hydrogen fluoride’ and ‘hydrofluoric acid’. You may meet
the former meaning in connection with welding or other electrical equipment. However most of
the time in the University context the letters HF mean ‘hydrofluoric acid’.
Hydrogen fluoride is a gas. Hydrofluoric acid is a solution of hydrogen fluoride in water.
You may also come across ‘buffered HF’. A buffered solution is designed to maintain a
reasonably constant pH against the addition of modest quantities of either hydrogen or
hydroxide ions. The way that this is normally done is to use a solution of a weak acid in
conjunction with one of its soluble salts. Thus buffered HF contains HF and a soluble fluoride.
There are therefore more fluoride ions in the solution than there are hydrogen ions and you
may decide, after reading the sections on properties and effects of exposure, that a buffered
solution may be more dangerous than an ordinary HF solution of the same pH.
HF can also be purchased in pyridine.
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The Properties of HF
Hydrogen fluoride is a colourless fuming gas which liquefies at 19oC and readily dissolves in
water. It is very toxic by inhalation, in contact with the skin, or if the liquefied gas is swallowed.
The liquefied gas causes severe painful burns on any tissue it touches. The vapour severely
irritates the eyes and respiratory system, and can also burn the skin.
Hydrofluoric acid is also a colourless liquid, both in dilute and in concentrated forms. In
concentrations above approximately 40 to 50% the acid gives off significant quantities of
corrosive fumes which have a pungent odour similar to chlorine. Unless heated, solutions at
less than 40% concentration do not give off significant vapour concentrations. The liquid is
corrosive and can dissolve glass, corrode most metals, and destroy clothing and human
tissue.
Containers of HF carry the following hazard warning symbols (black pictogram on an orange
background).
Toxic
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Corrosive
Effects of Exposure
HF burns human tissue. Burns from more concentrated solutions (> 50%) are severe and
extremely painful. The initial signs are redness, oedema and blistering.
Burns from more dilute solutions may not necessarily cause pain immediately. Nevertheless
the dilute solutions are still dangerous because they penetrate deeply into the body causing
delayed injury and symptoms due to local cellular destruction and systemic toxicity. A burn
from a solution in the range 20 – 50% may take up to eight hours to become apparent. Burns
to the fingers and nail beds may leave the overlying nail intact. Thus there could be a
significant delay in recognising that the casualty has been burned.
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The severity and rapidity of onset of signs and symptoms depends on the concentration,
duration of exposure, and the penetrability of the exposed tissue.
As users you need to be aware of this, and to seek advice if you believe that you could
have had HF solution on your skin.
HF can cause extensive damage to the eyes. It may make the cornea opaque and blindness
can result from severe or untreated exposure.
Inhalation of even quite small quantities of the vapour can cause irreversible damage, having
a serious effect on the mucous membranes. Symptoms may include coughing, choking, chest
tightness, chills, fever and cyanosis. Pulmonary oedema may occur 24 hours or so later.
Case Study
In 1996 a New York City sanitation worker died after inhaling HF fumes; a second worker
was hospitalised after coming to his aid. A plastic container with 70% HF was disposed of
improperly with regular refuse. The container burst when the waste was being compacted
by the truck.
Ingestion of HF may cause severe burns to the mouth, oesophagus and stomach. It usually
gives rise to severe systemic effects. Ingestion of even small quantities of HF has resulted in
death.
HF is unique among the acids in its ability to penetrate intact skin. It diffuses through the
tissues and disassociates into the hydrogen ion and the fluoride ion. The fluoride ion affects
tissue integrity and metabolism by liquefaction necrosis, decalcification and destruction of
bone (i.e. it starts to dissolve the calcium from the bones), and binds with calcium and
magnesium to form insoluble salts. These insoluble salts will interfere with cellular
metabolism, causing cellular necrosis and death. Loss of calcium (hypocalcemia) results from
precipitation of calcium from the blood which results in loss of calcium from the bones to try to
equilibrate the decreased serum calcium. This may be a delayed fatal event as calcium is
important for muscles, including the cardiac muscle. Without calcium many metabolic
pathways break down.
HF is a systemic poison. If HF is not rapidly neutralised and the fluoride ion bound, tissue
destruction may continue for several days and result in limb loss or death. If burns are left
untreated potentially life-threatening metabolic imbalances can develop. This is true both for
burns from concentrated solutions and from burns caused by dilute solutions.
Case Study
A laboratory technician died after an incident in which it is believed that he accidentally spilt
between 100 and 230 ml of 70% HF onto his legs. He sustained burns to 9% of his body
area, despite attempting to wash the acid off. He took refuge in a swimming pool from which
he was rescued by an ambulance approximately 40 minutes later. He was hypothermic and
hypocalcaemic on admission to hospital and eventually died, after 15 days, of multiple organ
failure.
An earlier fatality in 1980 resulted from burns to only 2.5% of the body.
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Case Study
A worker who was dealing with a solution containing 5% HF had gloves that contained a
pinhole. When she consulted her doctor later for pain in her finger a non-specific burn
ointment was applied. After several days the damage had developed to the extent that when,
still in pain, she finally presented at hospital it was necessary to amputate her finger, due to
the serious and irreversible damage that the acid had done to the bone.
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Exposure Limits
Statutory exposure limits are only available in relation to exposure by inhalation. The short
term exposure limit (15 minutes) for hydrofluoric acid fumes is 2.5 mg m -3 or 3 ppm.
In view of the serious health effects that have already been described, every effort
must be made to avoid exposure to HF by either workers or First Aiders. The principal
exposure risks are by inhalation of the vapour and contact with the liquid.
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Uses of HF and Places Where it is Found in the University
Industrially, hydrogen fluoride is an important compound used for the synthesis of
chlorofluorocarbons, and in the manufacture of hydrofluoric acid.
HF in pyridine is used as a synthetic reagent.
Hydrofluoric acid (the solution in water) has widespread uses, some of which are:
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Etching silicon products in the production of semiconductors
Etching, frosting and polishing glassware and ceramics
As a rust or stain remover in laundries
On stonework surfaces
Pickling stainless steel
Electroplating operations
As a reagent in chemical reactions
Digesting rock specimens
Preparation of sediments
Hydrogen fluoride gas can be purchased in compressed gas cylinders, but these are unlikely
to be encountered in the University. It can also be made in-situ by the action of sulphuric acid
on fluorides. A risk assessment must be completed before any experiment of this nature
Clearly any experiment of this nature should be associated with a risk assessment and one of
the control measures will be confinement of the experiment to a fume cupboard. The gas
released will then be captured, diluted and exhausted by the fume cupboard. Exposure in
these cases is only likely if
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The experiment has been done on an open bench, or
The experimenter has placed his/her head in the gas stream.
It is unlikely that a First Aider will encounter such a situation.
However, hydrofluoric acid is used in a large number of Departments. The University
Departments and Institutes known to be using HF are:
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Archaeology
McDonald Institute
Chemistry
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Earth Sciences
Engineering
Geography
Materials Science
Physics
Plant Sciences
But there may be others!
Hydrofluoric acid is used in aqueous solution of varying strengths in the Departments listed
above. Usage should be confined to well-ordered laboratory areas, with well-thought out and
policed procedures, as outlined in the following section.
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Working Practices
Responsibilities of the Users
Users have obligations to themselves and others. They must have done a risk assessment
taking account of the substances that they are using, their intrinsic potential for causing harm,
the quantities, concentrations and what they are doing with them. This should have resulted in
measures to minimise the probability of anyone being harmed by the work. For HF these will
be principally measures to reduce the probability of exposure by inhalation and skin contact.
These are likely to include:
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Working in a fume cupboard,
The use of spill trays,
Visors or goggles to minimise the probability of eye contact,
Gloves that are impervious to HF,
Protective clothing, which could include aprons where concentrated solutions are
used, or where decanting is taking place,
Stressing the importance of good housekeeping, and not leaving solutions in
unmarked containers,
Stressing the importance of mopping up, so as not to leave HF on surfaces
In addition the Users should have consulted the HF trained first aider prior to commencing
work, have a contingency plan in the event of accident, to include the summoning of a First
Aider and the initial treatment (e.g. washing, use of calcium gluconate gel). They should have
a stock of calcium gluconate, in date, and provision for washing (e.g. a hose and eyewash).
They should also have a procedure for dealing with spillages, with the materials for dealing
with the release readily to hand.
It is suggested that you, as First Aiders, familiarise yourselves with the areas where HF is
used and you are likely to be called, and ask questions. While First Aiders have no safety
management role, you can ask reasonable questions aimed at discovering the extent of the
dangers that you might face. Speak to the Department DSO if there are any unresolved
concerns that you have. The users have a specific duty of care to you, the First Aider.
8.2
Immediate Decision-Making Process
Medical help is required urgently if:
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The casualty is collapsed or has been unconscious due to inhalation of HF fumes
The casualty has ingested HF
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The fire brigade will be required if a person has collapsed in an HF atmosphere, and you have
been unable to ventilate the atmosphere and make it safe.
If either of these is the case, send someone to make a 1-999 call immediately, before
deciding on your next action. Make sure that the following information is passed on:
 The direct dial number of a telephone close to you, so that the emergency
services can call you back
 The exact location of the incident, including the department name and the room
number
 An indication of the seriousness of the incident, and that it is HF exposure.
 The number of casualties involved.
Ensure so far as you can that someone is sent to meet the ambulance and guide them to the
casualty. In other, less urgent cases, transport to hospital may be arranged by car.
8.3.1
RPE
If the HF is at approximately 40% dilution or less and it is at room temperature, RPE is not
required.
If the HF is greater than 40% or has been heated AND has been spilt outside the fume
cupboard, then your first priority is to get the casualty to leave the room where it happened. If
the casualty is unable to do this, they will need rescue. Normally this will require assistance
from the Fie Brigade, since it will need more than one person with RPE.
8.3.2
Hand/body protection
Two pairs of gloves are recommended in all cases.
 Inner (surgical) gloves
 Outer gloves, acid resistant which give at least one hour breakthrough time.
An apron will protect the body, and is highly recommended. Aprons can be made from
polyethylene or rubber.
Examples of suitable gloves (others are available):
Natural Suregrip code G04Y – splash protection for 480 minutes (to 36% aqueous solutions),
170 minutes to 48% solutions.
Marigold medical protection code S340 – splash protection for 120 minutes.
Neoprene lined and unlined:
Unlined
10” wrist
BP110
Unlined
16” wrist
DP112
Lined
10” wrist
D4 201
8.3.3
Eye protection
The First Aider should wear eye protection – goggles are preferred.
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8.4
Dressing Procedure
The sequence should be
Apron
Eye protection
Inner gloves
Outer gloves
And the removal sequence:
Apron
Outer gloves
Eye protection
Inner gloves.
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First Aid Treatment
This information is summarised in Appendix B
9.1
Preliminaries
In all cases, the First Aider should wear gloves and eye protection. If the casualty is not fully
responsive, assess his/her level of responsiveness:
Note the time of response to the following:
Eyes
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Are they open?
Do they open on command?
Do they open in response to pain?
Do they remain closed?
Movement
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Does the casualty move on command?
Does the casualty move in response to pain?
Does the casualty make no response?
Speech
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9.2
Is the response to question and conversation normal?
Is the casualty confused?
Does the casualty use inappropriate words?
Does the casualty make incomprehensible noises?
Does the casualty make no response?
Inhalation
The casualty should be taken to fresh air as quickly as possible. This should have already
been done by the time the First Aider arrives, but if not then the First Aider should ensure that
it is done. An ambulance should be called if the casualty is overcome and becomes
unconscious at any time after HF exposure, otherwise arrange for transport to hospital by
other transport (e.g. taxi). After exposure to HF fumes, surveillance will be required for
approximately 24 hours to rule out the possibility of pulmonary oedema developing.
Assess the casualty – lungs, throat, eyes and skin.
If the casualty is conscious, treat any burns to the eyes or skin by flushing with water,
removing any contaminated clothing and applying calcium gluconate gel to any burnt skin.
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Keep the victim warm, quiet and comfortable.
If the casualty is unconscious, maintain the airway. If breathing stops, apply artificial
ventilation using the Ambu-bag. If trained, administer oxygen. Be prepared to administer full
CPR if necessary. Details of the administration of oxygen and the checks that need to be
carried out on the equipment are in the Appendix.
9.3
Eye Contact
Flush the eye with water for at least 15 minutes. Hold the eyelids open and away from the eye
surface if possible. If the casualty has contact lenses these should be removed if possible, but
not at the expense of flushing the eye.
The casualty should be transported to hospital as soon as possible for assessment. If flushing
can be maintained during the journey this is of advantage to the casualty.
9.4
Skin Contact
The affected area should be washed thoroughly as soon as possible. Speed and
thoroughness of washing are extremely important. Begin flushing before removing
contaminated clothing, but remove it as quickly as possible during the flushing process.
Emergency dump showers are a mixed blessing, since the volume of cold water can lead to
hypothermia and slips on the floor, and the water is coming from above and may not fall on
the affected areas.
If a dump shower has been used, the First Aider should be vigilant for the signs of
hypothermia in the casualty, since this can be fatal.
After about 5 to 10 minutes, if calcium gluconate gel is to hand, flushing can be stopped and
the gel applied to the area. If the casualty is able to do this, it is preferred. Apply the gel in all
cases, whether the burn is painful or not, and continue until at least 15 minutes after the pain
has been relieved.
Arrange for transport to hospital. This can be by car, unless the casualty has extensive burns
or has other associated conditions, such as shock or hypothermia.
9.5
Ingestion
Never attempt to induce vomiting. If the casualty is conscious, rinse out the mouth with water.
This could be a life-threatening emergency; call an ambulance and send the casualty to
Hospital.
Be prepared to resuscitate the casualty
9.6
Information to Accompany the Casualty to Hospital
If possible the First Aider should accompany the casualty to hospital.
The hospital will need to know:
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That the exposure was to HF
The concentration of the HF
The approximate quantity
The route of exposure -.e.g. inhalation, skin contact
When this took place
The immediate signs and symptoms. This will include the level of responsiveness and
any changes.
Any treatment given.
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Any associated injuries
Pulse rate and any changes
Any blood loss sustained
Any unusual behaviour of the casualty
Making The Area Safe
It is the responsibility of the Users to ensure that the area is made safe – e.g. the room
ventilated, and spills neutralised and mopped up.
If the incident has been serious, requiring the transport of the casualty to hospital in an
ambulance, only the minimum clearing up should be done – confined to making the area safe.
A formal investigation may be required.
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The Immediate Aftermath and Reporting the Incident
A normal accident report form should be completed. In addition, the DSO must be informed
as quickly as possible, in addition to the person who has supervisory responsibility for the
area concerned.
Informing the next of kin is the responsibility of the Departmental Administrator, who should
be called without delay.
Any personal possessions of the casualty should either accompany them to hospital or be
given to the Administrator or their Supervisor for safe keeping.
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Maintaining the First Aid Equipment
Goggles/safety spectacles should be washed in warm water and dried.
Ensure that the outer gloves are tested for pinholes by filling with water, and are washed and
dried. The inner gloves should be discarded.
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Appendix B
Summary of First Aid Treatments
First assess the situation to decide on the protective measures necessary for yourself. These will include gloves, eye protection and
an apron. They may also include Respiratory Protective Equipment (RPE) if you need to go into a room where there is HF vapour in
the air.
SKIN
EYES
INHALATION
INGESTION
Remove or cut off contaminated
clothing. Wear neoprene gloves
and protective clothing.
Immediately flush the eye with
water or eyewash and continue
for at least 15 minutes.
(Unlikely unless exposed to HF at
40-50% or greater)
Never attempt to induce vomiting.
Flush the burn with water for at
least 5-10 minutes, then apply
calcium gluconate gel, gently
massaging it into the burn.
This can be done while the
casualty is being transported to
hospital.
Continue for at least 15 minutes
AFTER pain is relieved. The
person applying the gel should
wear gloves.
Remove the casualty from the
contaminated area immediately
and place in fresh air.
If the casualty is conscious, rinse
out the mouth with water.
Call an ambulance and send the
casualty to Hospital.
If necessary, resuscitate.
Transport to hospital should be
arranged immediately.
Call an ambulance. Send the
casualty to Hospital.
This could be a life-threatening
emergency.
Be prepared to resuscitate the
casualty.
Transport to hospital (this can be
started as soon as washing is
finished).
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Further Information
For further advice and information please contact:
Mr John Hulme, University Safety Adviser, Chemical and Physical hazards, Health and Safety
Division
Dr Margaret Glendenning, Departmental Safety Officer, Department of Chemistry
Mr Will Hudson, Deputy Director of Health and Safety Division and Secretary of First Aid SubCommittee, Health and Safety Division.
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