Liquid Nitrogen Liquid Nitrogen-Physical Properties Liquid nitrogen - - PowerPoint PPT Presentation

Liquid Nitrogen

Liquid Nitrogen-Physical Properties

• Liquid nitrogen (LN2) is produced industrially by

fractional distillation of air. Liquid nitrogen is a colorless clear liquid with density of 0.807 g/mL at its boiling point

• At atmospheric pressure, liquid nitrogen boils at 77 K

(−196 °C; −321 °F) and can cause rapid freezing on contact with living tissue, which may lead to severe

• frostbite. When appropriately insulated from ambient

temperatures, liquid nitrogen can be stored and transported in dewars and vacuum flasks. Here, the very low temperature is held constant at 77 K by slow boiling of the liquid, resulting in the evolution of nitrogen gas.

Hazards-Frostbite

Liquid nitrogen can cause terrible "burns." The burns are caused by death

• f living tissue caused

by the extreme cold, i.e., severe frostbite

Hazards-Oxygen Condensation?

• Liquid nitrogen will condense oxygen from the
• air. This is most alarmingly demonstrated if a

person leaves his/her vacuum pump's coldfinger in a dewar of liquid nitrogen overnight. In the morning the coldfinger will contain LIQUID OXYGEN up to the level of the nitrogen in the dewar

Hazards-Pressure Build-Up?

• LN2 will rapidly boil off and pressure will

build up.

• Can lead to explosion of containers without

venting devices

• Can pressurize at an expansion ratio of 1:700

Hazards-Air displacement

• Nitrogen is not poisonous; the air is already about

78% nitrogen (oxygen makes up about 21%, and trace gases the remaining 1%).

• If sufficient liquid nitrogen is vaporized so as to

reduce the oxygen percentage to below 19.5%, there is risk of oxygen deprivation.

• Rapid venting (spills and releases) can cause

near-total displacement of normal air, leading to a local concentration of about 100%

• nitrogen. Simple asphyxiants such as nitrogen do

not have good warning properties!

LN2 Basics

• Guard against pressure build-up by using a

pressure relief vessel or a venting lid.

• Always follow manufacturers' guidelines for

use of cryogenic vessels of any size.

• When transferring liquid nitrogen to

containers, it is possible for intense splash and spraying, so ensure that appropriate shielding and engineering controls are in place.

• Only use liquid nitrogen in well ventilated

spaces!!!

Cryovial Basics

• If at all possible, store cryovials in the vapor phase of liquid

nitrogen freezers. Most manufacturers of cryovials do not recommend liquid-phase storage.

• Do not over fill cryovials beyond the designated fill line. This will

increase the risk of cracking and possible release of contents.

• Use internally threaded caps, and do not over-tighten caps
• For cryovials currently immersed in liquid-phase storage, it is

recommended that tubes are placed in a sealed, unbreakable, plastic container immediately after removal from storage and prior to thawing.

• Tubes can also be moved from the liquid-phase to the vapor-

phase for at least 24 – 48 hours prior to removing from the storage container.

External vs Internal Threads

PPE and Engineering Controls

• Cryogenic gloves, safety glasses and face

shield

• Long sleeved clothing, long pants, and

closed toed shoes

• Work in a well ventilated area.
• Dewars must be secured in transport.

Shipping?

• You must be DOT and IATA certified to

ship LN2, as it is a dangerous goods.

• Containers must be UN rated for transport

LN2

• Use of a dry shipper allows many exemptions

to shipping LN2

The End!