Cryogenic Liquids - Division Of Training

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Cryogenic Liquids


Published: December 1996

Also See:

1996 North American Emergency Response Guidebook

ryogenic liquefied gases are very cold liquids. The U.S. Department of Transportation
definition of a cryogenic liquid, sometimes referred to as "refrigerated liquids", is any liquid
with a boiling point below

F. Other

sources list boiling points from

F to

F. If cryogenic liquids are

shipped above 41 psi and have no other hazard, they are
considered a compressed gas and would be placarded as a non
flammable compressed gas.
Cryogenics may carry othe
r placards such as flammable gas, poison gas, or oxidizer. If
cryogenics do not have any other placardable hazard, they are not considered a hazardous
material by the DOT. Materials listed under hazard Class 2, that are shipped as liquefied
gases, such as
cryogenics, exhibit other hazards not indicated by the placard. Cryogenics,
or refrigerated liquids, as they are sometimes called have boiling points of


zero or greater. Therefore, all cryogenic liquids are above their boiling points at ambient
temperatures. Liquid helium has a boiling point of

F below zero; it is the

material known. It is also the only material on earth that doesn'
t ever exist as a solid, only
as a cryogenic liquid and as a gas.

Unlike propane and other liquefied gases,
gases that are liquefied into cryogenics are
liquefied through a process of alternating
pressurization, cooling, and ultimate
decompression. Therefore, they do not r
pressure to keep them in the liquid state.
However, if they will be in a container for a
long period of time they are pressurized to
keep them liquefied as long as possible. Non
pressurized cryogenics are kept cold by the
temperature of the liquid a
nd the insulation
around the tanks. The cryogenic liquefaction
process begins when gases are placed into a large processing container. They are
pressurized to 1500 psi. The process of pressurizing a gas causes an increase in heat. The
molecules within a co
ntainer move faster causing more collisions with each other and the
walls of the container. As the molecules collide heat is generated. For example, the top of a
Contained Breathing Apparatus (SCBA) bottle or an oxygen bottle become hot as they
are be
ing filled. This is a result of the molecules colliding in the bottles. Once the pressure
of 1500 psi is reached, the material is cooled to 32

F by using ice water. Once cooled, the

pressure is once again increased, this time up to 2000 psi, again accompanied by an
increase in temperature. The material is then cooled to

F with liquid

ammonia. Once
the material is cooled, all of the pressur
e is released at once and the resulting heat decrease
turns the gases into cryogenic liquids. During the decompression process the heat present
within the container decreases as the pressure rapidly decreases.

Many of the gases found on the periodic table

of chemical elements are extracted from the
air and turned into cryogenic liquids. These include; neon, argon, krypton, xenon, oxygen
and nitrogen. All of the gases except oxygen are considered inert, that is to say, they are
toxic, non
flammable, and

reactive. To extract these materials from the air, the air
is first turned into a cryogenic liquid by the process mentioned previously. Then the liquid
Cryogenic Boiling Points























Nitric Ox






air is processed through a type of distillation tower where each component gas is extracted
off as
it reaches its own boiling point. Once extracted the gases are then liquefied by the
same process of alternate pressurization and decompression.

Some other common materials that are made into cryogenics include flammable methane
(LNG), hydrogen, and oxidi
zers oxygen, fluorine and nitric oxide.

Helium, He,

is a gaseous non
metallic element from the noble gas family, family eight on
the periodic table. Helium is a colorless, odorless and tasteless gas. It is non
toxic, and non
reactive. Heliu
m has a boiling point of

F. It is slightly solu
ble in
water. Even though it is an inert gas, helium can still displace oxygen and cause
asphyxiation. The vapor density is 0.1785, which is lighter than air. Helium is derived from
natural gas by liquefaction of all other component
s. Helium has a UN 4
digit identification
number of 1046 as a compressed gas and
1963 as a cryogenic liquid.

Neon, Ne,

is a gaseous non
metallic element
from the noble gas family. It is a colorless,
odorless and tasteless gas. Neon is present in
the earth's atmosphere at 0.0012% of normal
air. It is non
mable, non
toxic, and non
reactive. It does not form chemical
compounds with any other chemicals. It is
however, an asphyxiant gas and will displace
oxygen in the air. The boiling point of neon is


It is slightly soluble in water. Neon
has a vapor
density of 0.6964 which is lighter
than air. The UN 4
digit identification number
is 1065 when compressed and 1913 as a
cryogenic liquid. Its primary uses are in
luminescent electric tubes and photoelectric
bulbs. It is also used in high
, lasers (liquid) and cryogenic

Argon, Ar,

is a gaseous non
metallic element of family eight. It is present in the earth's
atmosphere to 0.94% by volume. It is a colorless, odorless, and tasteless gas. It does not
combine with any other chemical
s to form any compounds. The boiling point is

F. It
is slightly soluble in

water. The vapor density is 1.38 so it is heavier than air. The UN 4
identification number is 1006 as a compressed gas and 1951 as a cryogenic liquid. It is used
as an i
nert shield in arc welding electric and specialized light bulbs, (neon, fluorescent, and
sodium vapor), in Geiger
counter tubes, and lasers.

Krypton, Kr,

is a gaseous non
metallic element of family eight. It is present in the earth's
atmosphere to 0.00010
8% by volume. It is a colorless, odorless gas. It is non
toxic and non
reactive. It is however, an asphyxiant gas and can displace oxygen in the
air. At cryogenic temperatures krypton exists as a white, crystalline substance with a
melting p
oint of 116


The boiling point of krypton is

F. Krypton is known to
combine with

fluorine at liquid nitrogen temperature by means of electric discharges or
ionizing radiation to make KrF2 or KrF4. These materials decompose at room temperature.
pton is slightly water soluble. The vapor density is 2.818 which is heavier than air. The
UN 4
digit identification number is 1056, as a compressed gas, and 1970 as a cryogenic





Gages and
Valves On

liquid. It is used in incandescent bulbs, fluorescent light tubes, lasers and h

Xenon, Xe,

is a gaseous, non
metallic element from family eight. It is a colorless, odorless
gas or liquid. It is a gas at standard temperatures and pressures. It is non
flammable, and
toxic, but is an asphyxiant and will displa
ce oxygen in the air. The boiling point is

F. The vapor density is

05.987 which is heavier than air. It is chemically unreactive
however it is not completely inert. The 4
digit UN identification number is 2036 for the
compressed gas and 2591 for the
cryogenic liquid. Xenon is used in luminescent tubes, flash
lamps in photography, lasers and as an anesthesia.

Xenon compounds.

Xenon combines with fluorine through a process of mixing the gases,
heating in a nickel vessel to 400

C, and cooling. The

lting compound is xenon tetra
fluoride, XeF4. The resulting product is composed of large colorless crystals. Compounds of
xenon difluoride, XeF2, and hexafluoride, XeF6, can also be formed in a similar manner. The
hexafluoride compound melts to a yellow li
quid at 122

F and boils at 168

F. Xenon and

fluorine compounds will also combine with oxygen to form oxytetrafluoride, XeOF4, which is
a volatile liquid at room temperature. These compounds with fluorine must be protected
from moisture to prevent the formation of x
enon trioxide, Xe03, which is a dangerous
explosive when dried out. The solution of xenon trioxide is a stable weak acid that is a
strong oxidizing agent.

Cryogenic Liquids have very large expansion
ratios, some as much as 900 or more to 1;
they can form massive vapor clouds. These
vapor clouds can obscure vision of the source
of the leak making the location of
the source
difficult to find. Vapor clouds from cryogenic
liquids can travel great distances and require
evacuation of the public. The visible cloud is
not the total extent of the hazard. The warmer
air on the outer edge of the vapor cloud
causes the gas t
o become invisible. It is then possible to be in an oxygen enriched
atmosphere, flammable atmosphere or in a gas that can cause asphyxiation and the gases
will not be visible. Because of the large liquid to gas expansion ratios, the other hazards of
nic liquids are magnified many times. If the cryogenic liquid is flammable or toxic
these hazards are intensified because of the potential of large gas cloud production from a
very small amount of liquid. As the size of the leak increases, so does the size

of the vapor
cloud. This means that 1 gallon of a cryogenic liquid can produce as much as 900 gallons of
a gas. Because of the large expansion ratios cryogenic liquids can turn into gases and
displace oxygen in the air which can harm responders by simple
asphyxiation. Simple
asphyxiation is not poisoning, but rather just not enough oxygen to breathe. The
atmospheric contains about 21% oxygen. When the oxygen in the lungs, and ultimately in
the blood is reduced, unoxygenated blood reaches the brain and the
brain shuts down. It
may only be a few seconds between the first breath and collapse. Response personnel
should always put SCBA on prior to entering a confined space or other area where
asphyxiant gases may be present.

Being very cold, cryogenic liquids c
an cause frostbite and solidification of body parts. When
the parts thaw out, the tissue is irreparably damaged. Touching uninsulated piping and
valves of cryogenic liquid containers can cause skin to stick to the metal, much like when
kids put their tongu
es on an ice cube tray or fence post and it gets stuck. There isn't any
protective clothing or equipment that can be worn to protect the body from the effects of
contact with a cryogenic liquid. Anything that the cryogenic liquid contacts will become
Cryogenic Expansion Ratios


981 to 1


862 to 1


841 to 1


840 to 1


754 to 1


697 to 1


637 to 1

ified and brittle. Gloves can provide protection from skin contacting piping and valves.
Body parts that have come in contact with cryogenics should be treated like frostbite. Parts
should be flushed with water that is cool to luke warm to limit additional

tissue damage.

Cryogenic liquids are shipped and stored in special containers. On the highway the MC 338
tanker is used to transport cryogenic liquids. The tank is usually not pressurized but is
heavily insulated to keep the materials cold. There is a he
at exchanger underneath the belly
of the tank truck to facilitate the off loading of product as a gas. Railcars are also specially
designed to keep the cryogenic liquids cold inside the containers to minimize the boiling off
of the gas. Fixed storage conta
iners of cryogenic liquids are usually very tall, small diameter
tanks. These are insulated and resemble large vacuum bottles that keep the liquid cold.
These containers are also under pressure to keep the material liquefied. There is a heat
exchanger near

the tanks. This heat exchanger is a series of metal tubes with fins around
the outside. The liquids are passed through the tubes and the liquid is warmed above its
boiling point and turns into a gas. The gas is then used in the facility for whatever purpo
it was intended. Valves on fixed tanks have very long stems because the moisture around
the valves is frozen due to the

cold of the cryogenics. As this moisture is frozen, ice forms
on the piping and around the valves. If the valve stem were not extra long, the valve would
not be accessible because of the ice.

Other gases, such as hydrogen, are liquefied,
sometimes made into cryogenics and
placarded as flammable gases. Liquid oxygen
is placarded as an oxidizer or non
compressed gas. Oxygen
though non
toxic, is
very reactive with hydrocarbon based
materials and is an oxidizer. Liquid Oxygen in
contact with an asphalt surface such as a
parking lot or highway can create a contact
explosive. Dropping an object, driving over
the area or even walk
ing on the area can
cause an explosion to occur.

Nitrogen, N2

is a gaseous non
element, that is the 2nd most produced
industrial chemical with 68.04 billion pounds in
1995. It is a colorless, odorless, tasteless gas
that makes up 78% of the air t
hat is breathed.
The boiling point of nitrogen is

F. It i
slightly soluble in water. Nitrogen does not
burn and is non
toxic. It may, however, displace oxygen and be an asphyxiant gas. The
vapor density of nitrogen is 0.96737 which makes it slightly

lighter than air. The UN 4
identification number is 1066 as a compressed gas and 1977 as a cryogenic liquid. As a
cryogenic liquid, the NFPA 704 designation is Health
3, Flammability
0, and Reactivity
Nitrogen is used in the production of ammonia
, cyanides, and explosives, as an inert
purging agent and a component in fertilizers. It is usually shipped in insulated containers,
insulated MC 338 tank trucks, and tank cars.

Oxygen, O2,

like nitrogen, is an non
metallic elemental gas, which is the 3rd

volume industrial chemical with 53.48 billion pounds produced in 1995. Oxygen makes up
approximately 21% of the air breathed. The boiling point of oxygen is

F. It is non
flammable, but supports combustion. Oxygen can

explode when exposed to
heat or organic
materials. The vapor density of oxygen is 1.105 which makes it slightly heavier than air.
Oxygen is incompatible with: oils, grease, hydrogen, flammable liquids, solids and gases.

Tall Thin


Next to

The UN 4 digit identification number for oxygen is 1072 as a

compressed gas and 1073 as a
cryogenic liquid. The NFPA 704 designation for liquid oxygen is Health
3, Flammability
and Reactivity
0. Liquid oxygen is shipped in Dewier flasks and MC 338 tank trucks. It may
also be encountered in cryogenic rail cars.

Carbon dioxide, CO2

is the 22nd highest
volume industrial chemical with 10.89 billion
pounds produced in 1995. Carbo
n dioxide is a
colorless, odorless gas. It can also be a solid,
(dry ice), which will undergo sublimation and
turn back into carbon dioxide gas, or a
cryogenic liquid. It is miscible with water. It is
not flammable or toxic but can be an
asphyxiant gas and

displace oxygen. In 1993
two workers were killed on board a cargo ship
when a carbon dioxide fire extinguishing
system discharged. The oxygen in the area
was displaced by the carbon dioxide and the
men were asphyxiated. Carbon dioxide has a
vapor density
of 1.53 which is heavier than
air. It may be shipped as a cr
yogenic or
liquefied compressed gas. Frozen (solid) carbon dioxide gas is known as dry ice. It has a UN
digit number of 2187 as a cryogenic and 1013 as a compressed gas. The NFPA 704
designation is Health
3, Flammability
0, and Reactivity
0. It is used p
rimarily in carbonated
beverages and fire extinguishing systems.

When responding to fires involving liquefied gas tanks, firefighters often apply water to cool
the tanks. Cryogenic liquids are already colder than water at any temperature and water will
t as a super heated material causing the cryogenic to heat up and vaporize faster. This
will cause pressure to build up inside the tank and the tank may fail violently. Care should
be taken when applying water to "cool" cryogenic containers

Courtesy Robert Burke