Installation of Liquid Nitrogen. Despatch 924E, 925E, 926E

b. Shut off the valve at the cylinder. c. Crack the hose fitting slightly, and allow the residual CO

2

pressure in the hose to bleed off before disconnecting the hose. d. Connect hose to new cylinder. e. Open cylinder valve. f. "Crack" the fitting at the bulkhead to bleed off gas and moisture. g. Turn chamber on.

Installation of Liquid Nitrogen

Some models of test chambers use pressurized liquid nitrogen (LN

2

) so that lower test temperatures may be reached. Line pressure should be between 55 kPa (8 PSI) and

310 kPa (45 PSI).



The following precautions should be observed in handling LN

2

:



Liquid nitrogen is extremely cold (-196



C or -320



F) at atmospheric pressure and can damage skin or eyes on contact.



Insulated gloves and safety goggles or face plates should always be used in handling LN

2

.



Clean cotton clothes or lab coats should be worn where LN

2

spillage or prolonged contact with its vapors is a factor.



Smoking should be prohibited in the immediate area were LN

2

is being handled.

WARNING: Nitrogen and carbon dioxide gases can cause asphyxiation and death



All handling equipment such as funnels, dewars, piping and tubing must be clean, dry and free of grease.

if used in confined, poorly-ventilated areas.

Nitrogen and carbon dioxide as liquid or cold gases can cause freeze burns of

the eyes and skin.



All transfer tubes, valves and other equipment which reach liquid nitrogen temperatures should be properly insulated with a non-absorbent insulation which is properly contained within a vapor seal.



Liquid nitrogen is not in itself explosive or combustible; however, its low temperature will cause condensation of the water vapor in the air and all the

14

gaseous constituents of the air which liquefy above -196



C (-320



F), including oxygen. Therefore, supply lines, clothes and equipment which are subject to this temperature can absorb or liquefy oxygen, which will cause a severe fire if ignited and which can become explosive when in contact with grease.



LN

2

should not be left in sealed containers or hoses. When the LN

2

turns to nitrogen gas, it will build up very high pressure. Unless LN

2

is being actively used in test chamber operations, care should be taken that an adequate vent is provided and that excessive pressure is bled off.



The concentration of liquid oxygen suspended in the LN

2

builds up as the LN

2 is used. Consequently, nearly empty LN

2

containers should be handled as if they were liquid oxygen containers. The presence of liquid oxygen in LN

2

can be determined by the milky appearance of the liquid. LN

2

is normally clear.



If parts of the body are frozen by contact with these cold liquids, first-aid treatment for frostbite should be given, with slow thawing of the frozen parts.

Severe cases should be referred to a physician for treatment.

15