2. Hazard
Describes the potential of an agent to cause
harm to persons or property. For cryogenic
liquids the main hazards are:
– Extreme cold
– Asphyxiation
– High pressures
– Fire and explosion
3. Risk
A measure of the likelihood that harm from a
particular hazard is realised the severity of
the consequences
– Risk is situation specific, i.e. depends on
application, quantity and frequency of use.
– Local risk assessment to identify risks and put
in place measures to minimise them
4. Asphyxiation
Nitrogen (helium) gas is heavier (lighter)
than air and can displace oxygen leading to
asphyxiation.
– Never accompany liquid cryogens in a lift. Use liquid
cryogens only in well ventilated places.
– If quantities are large or you are not sure about the
ventilation, fit oxygen depletion alarms set to sound at
19.5% Oxygen.
– Do not enter an enclosed area where you suspect there
has been a large spillage of liquid cryogen. Seek expert
assistance.
5. ASPHYXIATION
• oxygen
21% Normal Level
<19% Danger Level
<14% Risk of permanent effects and death
• There is no sensation of breathlessness to
warn you that you are being asphyxiated
6. 4 Stages of Breathlessness
1st Stage
– Oxygen below 20% Pulse rate increases,
breathing rate increases, clear thinking starts to
become difficult and co-ordination reduces
2nd Stage
– Oxygen below 14% Judgement becomes poor,
become bad tempered, loss of sense of pain and
has rapid fatigue.
7. 3rd Stage
– Oxygen below 10% Loses ability to perform
vigorous movements, suffers nausea and
vomiting, loss of caring, unable to stand or walk,
permanent brain damage possible even if
resuscitated
4th Stage
– Oxygen below 6% Breathing comes in gasps
with long periods between, convulsive
movements, breathing stops and then after a few
moments, the heart.
BREATHING PURE NITROGEN OR HELIUM WILL
PRODUCE IMMEDIATE LOSS OF CONSCIOUSNESS AND
ALMOST IMMEDIATE DEATH
8. Extreme cold
• Liquid nitrogen 77 K (-196 C)
• Liquid helium 4.2 K (-269 C)
– Avoid direct contact with cryogen and objects at
low temperature, e g pipes carrying the liquid
– Wear eye protection
– Wear loose fitting gloves
– Wear sensible shoes/boots (not sandals) with
trousers covering top to ensure spilt cryogens do
not run inside.
– Prevent spillage on electric cables and plastic floor
9. High Pressures
• 1 litre of liquid nitrogen (helium) expands to 0.7
(0.75) cubic metres of gas at room temperature.
• Can cause build up of high pressure if gas is
trapped, i.e. your piece of equipment becomes a
bomb! Bungs and stoppers become projectiles.
– Ensure all vents are clear and checked
regularly.
– Tie stoppers to the top of the container with
short length of string to act as a retainer.
– Use non-return and pressure relief valves.
10. Fire and Explosion
• Liquid oxygen has a higher boiling point than
liquid nitrogen. The liquid seen dripping from cold
pipes carrying liquid nitrogen is mostly liquid
oxygen.
• Liquid oxygen is a fire and explosion hazard
– Insulate pipes carrying liquid nitrogen.
– Do not allow condensate to drip onto clothing
or come into contact with grease/oil.
– Keep away from naked flames or incandescent
material.
11. Emergency Procedures
• Cold burns - Treat as a normal burn' hold under
tepid running water (not hot water!) for at least 15
minutes. If serious seek medical assistance.
• Spillage - Evacuate area in which spill has taken
place leaving doors open for ventilation.
• Overpressure in container - Evacuate area and call
emergency services.
• Asphyxiation - Seek immediate medical assistance.
