Liquid Nitrogen Safety
Environmental Health and Safety
Environmental Health & Safety
What is Liquid Nitrogen?
• Liquefied form of nitrogen (N2) gas.
• When in the gaseous phase, it is a mostly
inert gas, that is colorless, odorless, and
tasteless.
• In the liquid phase, it’s very cold (BP=195.8°C), which makes it ideal to transport
cold materials.
– This however, can cause severe frostbite
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Why Take Precautions?
• The gas isn’t technically toxic, but it can easily
start to replace oxygen in the air so your body
can’t breathe in enough oxygen. This can cause
affixation very quickly.
• Oxygen becomes a liquid at a higher
temperature than nitrogen, so liquid oxygen can
become encased in liquid nitrogen. These
oxygen enriched environments can cause
materials to burn rapidly.
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Why Continued
• It’s very cold!
– Since it’s so cold, any
exposure to your skin
can cause severe
frostbite.
– It will be very painful.
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Lab Safety Do #1
• Wear Safety Gear!
– Lab coats can save your body
parts from freezing during an
accidental spill!
– Safety goggles are required but
a full face shield is
recommended.
– Gloves are also required –
preferably cryogenic but leather
will work for smaller scale
applications.
– Long pants and close toed
shoes are also required.
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Don’t Forget To
• Always follow general
lab safety procedures.
– (especially the do not
drink the chemicals
one).
• Take your time and be
careful!
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Lab Safety Don’ts
• Don’t completely seal off the container.
– At room temperature, nitrogen is going to create
a gas.
– This requires exhaust, or the container could
potentially explode.
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More Lab Safety Don’ts
• Funnel the liquid nitrogen
– This could potentially cause spills and splashes
that could come into contact with skin.
• Dip a hollow tube into the container
– Could potentially splatter.
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Nitrogen Containers
• Three types of containers
– Dewar, Cryogenic Liquid Cylinder, and Cryogenic
Storage Tank
• Storage varies from a few liters to thousands.
• Vaporization is always continuous.
– This is because heat leaks are always present.
• Know your specific container and proper
handling procedures.
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Container’s -Dewar
• Non pressurized container.
• Typical capacity is a liter.
• Product may be removed
to smaller containers by
pouring, but larger sizes
require a transfer tube.
• A loose fitting dust cap over
the outlet prevents
moisture from plugging the
vent, allowing gas to
escape.
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Container’s – Cryogenic Liquid
• Insulated, vacuum jacketed
pressure vessels.
• Operate up to 350 psi and have
capacities between 80-450 L.
• Product may be withdrawn as a
gas by passing through an
internal vaporizer.
– Or as a liquid under its own
vapor pressure.
• Come equipped with safety relief
valves and rupture discs.
– This protects from pressure
build up.
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Container’s – Cryogenic Storage
• Typically includes a
tank, a vaporizer, and a
pressure control
manifold.
• May be spherical or
cylindrical in shape.
• Sizes range from 500420,000 gallons
• Powder and vacuum
insulated.
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Transfer Lines
• Transfer lines are used
to remove liquid from
Dewar or cryogenic
liquid storage
containers.
• Cryogenic lines are
always connected to
the cylinder’s liquid
withdrawal valve.
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Transfer Lines – Part II
• A typical Dewar
transfer line is
connected to a
bayonet.
– This provides a means
to remove product by
pressure build up.
• Use only transfer lines
designed for cryogenic
equipment.
*Bayonet for vacuum transfer line
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Transport
• Find a cart
– Don’t try to carry or roll
the container.
• Keep upright
• Don’t try to pull the
container, always push.
• Avoid mechanical or
thermal shock.
– Sudden environmental
change could potentially
change the pressure.
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Handling
• Use cryogenic gloves when
operating any valve or any place
of a possible air leak.
– Leather gloves can also be
used, but for larger scale
operations use cryogenic.
• Be aware of the weight and
design of your specific container.
– This can help prevent laboratory
accidents.
– The figure on the right is a
diagram of a liquid nitrogen
storage tank.
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Gas Withdrawal
1. Connect a control regulator to the gas
withdrawal valve and the outlet of the valve
to the system receiving gas.
2. Open withdrawal and pressure building
valves until the container reaches desire
pressure.
3. You may begin withdrawing gas.
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Liquid Withdrawal
1. Always wear a face mask for liquid withdrawal.
2. Connect a transfer line from the liquid valve to
the system being filled.
3. Open valve to desired rate of flow, close when
finished.
4. To prevent back contamination, all valves
should be closed when the container has been
emptied.
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Storage Part I
• Keep in a well ventilated room
– The room shouldn’t be a confined area to help
exhaust any nitrogen gas off-gassing from the
container.
– A non ventilated room could very quickly become
oxygen deficient.
– It is also recommended that the building that the
nitrogen is stored in has an exhaust ventilation
system to outside the building. All lab buildings
have this system.
• Do not leave Dewar containers uncovered,
but make sure to have an exhaust system
– If the container is completely covered, the
pressure could increase to dangerous levels, so
exhaust is required. If left completely uncovered,
the liquid nitrogen will evaporate much faster.
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Storage Part II
• Store in a controlled environment
– Away from weather change. This will help the
nitrogen from undergoing drastic changes in
temperature or pressure.
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In Case of Emergency
• If your skin comes into contact with liquid nitrogen
– Thaw slowly with warm water
– Always seek medical attention though 911
• In case of a lack of oxygen, move immediately to a
well ventilated area, or outside and acquire a
respirator.
– Reentry may only occur by trained personnel with air
supplying respirators.
• If an emergency happens, contact 911 then your lab
coordinator and EHS ((740-593-1666).
– Also, contact your lab coordinator if anything seems out of
the ordinary.
• If there is a fire call 911.
– This is due to the possible asphyxiation hazard.
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Other Resources
• http://www.airproducts.com/responsibility/ehs
/productsafety/productsafetyinformation/safet
ygrams.htm
• http://engineering.dartmouth.edu/microengin
eering/ln2.html
• http://www.physics.unc.edu/about/safety/cont
ent/N2operationSW_2.pdf
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