CRYOGENIC MATERIALS Cryogenic materials have special properties that make them particularly hazardous to use in the solid, liquid or gaseous states.  Cryogenic materials are characterized by severe low temperature (-60°C to -270°C).  Most cryogenic liquids are odorless and tasteless when vaporized; however, when exposed to the atmosphere they create a highly visible dense fog that dissipates with warming.  Cryogenic temperatures are achieved by liquefaction of gases, most commonly helium, hydrogen, nitrogen, argon, oxygen or methane.

Hazards

·         The severely cold temperatures associated with cryogenic liquids can damage living tissue on contact and embrittle structural materials.

·         The release of cryogenic liquids in a confined area can result in rapid displacement of air and potential for asphyxiation by reducing or the concentration of available oxygen in the air.

·         If allowed to depressurize, cryogenic liquids will rapidly and violently expand.

·         Over-pressurization will develop in inadequately vented pressurized systems.  Relatively small quantities of cryogenic liquid can expand to high volumes.  (One liter of Nitrogen yields 696 liters of gas at STP.) 

·         Rupture of a cryogenic tank may produce shrapnel.

·         Since cryogenic gases are stored near their boiling point, they always pose a high pressure hazard.  Liquid/gas evaporation causes high pressure to build up

·         Exposure to liquid cryogens or “Boil Off” gases may result in tissue damage or skin death.  The eyes are particularly vulnerable.

·         Contact with uninsulated pipes or metal transfer containers may cause skin burns or torn flesh when an attempt is made to withdraw the skin.

·         If a leak occurs when no one is present, lab user may be entering an oxygen deficient atmosphere unprepared.  Normal air contains 19.5 - 21% oxygen.  Oxygen concentrations below 16% by volume can cause dizziness, rapid heart beat, nausea, vomiting, disorientation, mental confusion, loss of consciousness and death.  There is no warning.  Oxygen has no odor, color or means of determining concentration without direct measurement.

·         Flammable gas leaks can cause an explosion hazard in the presents of a spark or ignition source. (Oxygen above 23.5% in air creates an enriched atmosphere ripe for combustion.)

·         Liquefied inert gases, such as liquid nitrogen or liquid helium, are capable of condensing atmospheric oxygen causing oxygen entrapment and unexpected oxygen enriched atmospheres.  Condensation on cold metal surfaces can product a similar effect.

Properties

·         See the Properties of Cryogens box

Storage and Use

·         Cryogenic liquids must be kept in specially designed, high-pressure vessels that contain fittings to relieve overpressure

·         Store vessels in a dry place and periodically check for ice formation that can plug pressure release devices and pose an explosion hazard

·         Keep away from ignition sources. Cryogenic liquids present fire and explosion hazards

·         Flammable liquids will support combustion in both the liquid and gaseous states.

·         Store and work with cryogenic liquids in a well-ventilated area to prevent the accumulation of flammable, toxic or inert gases as evaporation and condensation occurs near the cryogenic tank. If allowed to depressurize, cryogenic liquids will rapidly and violently expand.

·         Vent cryogenic storage containers outdoors or into a chemical fume hood system.

·         Make sure all parts of the pressurized system are designed to accommodate the cryogen temperature.  (E.g., pressurized vessels, hoses, piping, fittings and pressure relief devices.)

·         Make sure the cryogenic system has a separate pressure relief device manufactured for the material in use for each component or segment of piping and hose that will be isolated by a valve.

·         Watch out for icing on the vessel or valves.

·         Be sure to pre-cool receiving vessels to avoid thermal shock and splashing.

·         Keep equipment and systems extremely clean.

·         Use recommended Personal Protective Equipment.

·         Use tongs to place and remove items in cryogenic liquid.

·         When discharging cryogenic liquids, purge the line slowly.  Only use transfer lines specifically designed for cryogenic liquids.

·         Rubber and plastic may become very brittle in extreme cold. Handle these items carefully when removing them from cryogenic liquid.

·         Store cryogenic liquids in double-walled, insulated containers (e.g., Dewar flasks).

·         To protect yourself from broken glass if the container breaks or implodes, tape the exposed glass on cryogenic containers.

·         Do not store cylinders of cryogenic liquids in hallways or other public areas.

Personal Protection

·         Safety glasses and face shields should be used.

·         Potholders or appropriate loose fitting thermal gloves. (Check with the glove manufacturer to assure the gloves will protect against the extreme temperatures of cryogenic material used.)

·         Make sure gloves are loose enough to be quickly removed if contaminated.  (Cryogenic liquids can damage living tissue on contact.)

·         Long sleeve shirts, long pants and substantial shoes will provide a measure of skin protection.

·         Watches, rings, or other jewelry should not be worn when personnel are working with cryogenic fluids.  Lab users should avoid wearing anything capable of trapping or holding a cryogenic fluid in close proximity to the flesh.

·         In case of frost bite, DO NOT RUB THE FROZEN FLESH.  See  the frost bite box for full explanation.

Containers

·         Cushion glassware in a protective covering to prevent injury caused by flying glass in the event of implosion/explosion.

·         Transport fragile cryogenic containers with caution -- use a hand truck if appropriate.

·         Use barrier protection when thawing cryotubes.  Cryotube Warning

Frost Bite – What is the difference between frost bite and cryogenic liquid bite?

Frost bite is a scary concept.  When we think of frost bite, images of mountain climbers come to mind.  It is important to think through the process of frost bite.  True frost bite due to the long term exposure to extreme cold is particularly damaging.  In these cases the freezing time was relatively slow.

In extreme frost bite the water in individual cells begins to freeze, beginning with those cells most distal from the central trunk of the body. The freezing process is essentially a migrating front.

Because it freezes slowly the ice crystals that form grow slowly, and they grow LARGE!  As the crystals become large they typical outgrow the cell walls themselves.  This rupturing of the cell wall is usually non-reparable by the body, or medical personnel.  The flesh is so severely damaged that amputation is necessary.

In the case of freezing via contact with Cryogenic Fluids (LN or LA) the water in the cells freezes extremely fast.  This process is essentially a quenching process, and thus cells walls do not rupture.  The trick to prevent permanent damage in the case of a LN or LA skin freeze is too NOT rub the area.  Allow the frozen area to warm up by processes that will not cause intercellular damage.

Author, Michael M. Cheatham, Syracuse University, March 1998.

Properties of Cryogens

Gas

Normal ^OC

BP ^OK

Volume of Expansion to Gas

Flammable

Toxic

Odor

Helium – 3

-269.9

3.2

757 to 1

No

No (a)

No

Helium – 4

-268.9

4.2

757 to 1

No

No (a)

No

Hydrogen

-252.7

20.4

851 to 1

Yes

No (a)

No

Deuterium

-249.5

23.6

----------

Yes

Radioactive

No

Tritium

-248.0

25.1

----------

Yes

Radioactive

No

Neon

-245.9

27.2

1438 to 1

No

No (a)

No

Nitrogen

-195.8

77.3

696 to 1

No

No (a)

No

Carbon Monoxide

-192.0

81.1

----------

Yes

Yes

No

Fluorine

-187.0

86.0

888 to 1

No

Yes

Sharp

Argon

-185.7

87.4

847 to 1

No

No (a)

No

Oxygen

-183.0

90.1

860 to 1

No

No (a)

No

Methane

-161.4

111.7

578 to 1

Yes

No (a)

No

Krypton

-151.8

121.3

700 to 1

No

No (a)

No

Tetrafluoromethane

-128.0

145.0

----------

No

Yes

No

Ozone

-111.9

161.3

----------

Yes

Yes

Open

Xenon

-109.1

164.0

573 to 1

No

No (a)

No

Ethylene

-103.8

169.3

----------

Yes

No (a)

Sweet

Boron trifluoride

-100.3

172.7

----------

No

Yes

Pungent

Nitrous oxide

-  89.5

183.6

666 to 1

No

No (a)

Sweet

Ethane

-  88.3

184.8

----------

Yes

No (a)

No

Hydrogen chloride

-  85.0

188.0

----------

No

Yes

Pungent

Acetylene

-  84.0

189.1

----------

Yes

Yes

Garlic

Fluoroform

-  84.0

189.1

----------

No

No (a)

No

1,1-Difluoroethylene

-  83.0

190.0

----------

Yes

No (a)

Ether

Chlorotrifluoromethane

-  81.4

191.6

----------

No

Yes

Mild

Carbon dioxide

-78.5 (b)

194.6

553 to 1

No

Yes (a)

Pungent

(a)     Nontoxic, but can act as an asphyxiant by displacing air needed to support life.  As with most chemicals, even harmless materials can be toxic or poisonous if taken in sufficient quantities under the right circumstances.

(b)     Sublimes

(c)      ^OK = 273.16 ^OC;  459.69^OF

(d)     Shaded rows indicate the seven most commonly used cryogenic gases