Liquid Nitrogen
Liquid nitrogen, although widely used in research laboratories, represents a significant hazard to health. It is recommended that you read the University guidance notes on ‘Safe handling of liquid nitrogen’ before commencing work. This will explain the asphyxiation, combustion, burns and over-pressurisation hazards presented by liquid nitrogen. Very small rooms with poor/no ventilation should not be considered suitable when working with liquid nitrogen. Additionally, individuals should not dispense liquid nitrogen from any of the Dewars/Daleks stored in CS096 until trained to do so.
Spillage
Be aware of first aid procedures for burns, implement them and obtain immediate medical attention. Cold burns from liquid nitrogen are very penetrating and will be extremely painful. Place affected area under cold running water for at least 10 minutes and obtain medical attention.
Be aware of, and ready to implement, emergency procedures for spills.
In the event of a spill any liquid will rapidly turn to nitrogen gas due to vaporisation. If working in a well-ventilated area small volumes should not present an asphyxiation hazard.
In the event of a larger spill concentrations of oxygen in the air will fall. Evacuate the area and prevent access for a few minutes to allow the atmosphere to return to normal. Do not close the door. Open windows if safe to do so.
If equipment does not appear to be functioning correctly, report immediately.
Report all incidences/accidents to the Technical Services Manager.
Lone/out of hours working with liquid nitrogen
Staff should not handle liquid nitrogen in any confined space, when alone. All out of hours use of liquid nitrogen should be avoided if possible and, in any case, should be fully risk assessed in advance.
Transport of liquid nitrogen in lifts
Never travel in a lift with liquid nitrogen. If liquid nitrogen is to be carried in a lift, you must ensure that no unsuspecting person is able to enter the lift.
Use of liquid nitrogen at the bench
When working with liquid nitrogen it is essential that protective clothing is worn. Full face visors/safety spectacles are present at every liquid nitrogen Dewar for this purpose. Blue insulated cryo-gloves are there for your protection and should be worn when appropriate.
However, items that have been in contact with liquid nitrogen for a long time and especially metal objects will be extremely cold and will require to be handled with care and will require insulated gloves to be worn for protection.
Many procedures involving the use of liquid nitrogen can produce splashes. Splashes of liquid nitrogen to the eyes will cause serious injuries. Therefore safety spectacles or full face visors MUST BE worn when working with liquid nitrogen.
When vials previously stored in liquid nitrogen are removed, there is a strong possibility of them exploding. The wearing of safety spectacles or full-face visor is strongly recommended. Placing the vials in a lidded box immediately on removal is also strongly recommended, as this will contain exploding vials.
Dewars containing liquid nitrogen should be placed where there is no danger of them accidentally being knocked over.
Lids should always be fitted to Dewars containing liquid nitrogen to prevent the possibility of oxygen from the atmosphere condensing at the cold temperature into liquid oxygen, which could present a combustion hazard.
Uncontaminated surplus liquid nitrogen can be emptied into the liquid nitrogen storage bank after use or allowed to evaporate off in the fume hood. If leaving surplus liquid nitrogen in a Dewar to evaporate in a fume hood, display a caution notice informing other lab users of the hazardous contents.
NEVER pour unwanted liquid nitrogen down the sink.
Small splashes of liquid nitrogen on exposed skin will generally not cause serious burns as the liquid evaporates very rapidly. It is more dangerous if clothing becomes saturated and prolonged skin contact results.
Do not leave very cold items lying around if there is the possibility of other staff unwittingly handling them.
Contact your LSS if further advice is required.
Procedure for dispensing liquid nitrogen from Departmental pressurised Vessel (CS096)
To Fill The Small Pressurised Storage Vessel:
A properly fastened laboratory coat, cryogenic safe gloves and full-face visor must be worn whilst dispensing. The dispensing hose will rapidly become very cold.
The small vessel is normally kept outside.
If the brass end (sparger) is on the hose of the large vessel take it off.
Purge this hose by opening the valve (yellow handle) to allow liquid nitrogen to pass through the hose. Close yellow valve.
Connect the hose to the LIQUID FILL VALVE (INLET) on the small storage vessel, do not over tighten.
Vent small vessel by opening the TRYCOCK VALVE and the LIQUID FILL VALVE (INLET). THE OUTLET LIQUID FILL VALVE REMAINS CLOSED.
Slowly open the large storage container by turning the yellow lever handle. This will take about 5 minutes and there will be a loud noise throughout filling. You can control the speed of filling by turning the yellow handle more or less.
Fill the small vessel up to maximum 80-100%– check this by pressing the pressure button occasionally
Turn off the yellow handle on the huge container.
Turn off the LIQUID FILL VALVE on the small vessel.
Turn off the TRYCOCK VALVE on the small vessel.
Take off the hosing by CAREFULLY unscrewing it, (you may need to use a spanner if the nut has frozen). There may be some hissing.
To Fill A Small Storage Dewar Flask:
Check that the brass end (sparger) is attached to the end of the hose. It is essential that this is present in order to lessen the ferocity of discharge from the vessel.
Check sight glass to confirm that the vessel is not empty.
Place a suitable collection vessel e.g. Dewar flask on the floor and position the dispensing hose carefully into it.
Slowly open the large storage container by turning the yellow lever handle situated in line with the dispensing hose. If the valve is opened too rapidly there is a danger of splashing.
Do not overfill the Dewar. Use the measuring stick present by each of the Dewars to fill to the correct level.
Close the dispensing valve fully.
Fit a suitable lid to the Dewar flask before removing to your laboratory.
Dry Ice
Safety & Handling
Dry ice is extremely cold ( -78.5°C). Always handle Dry Ice with care and wear protective gloves whenever touching it. If touched briefly it is harmless, but prolonged contact with the skin will freeze cells and cause injury similar to a burn.
Treat dry ice burns the same way as heat burns by running under cold/tepid water for at least 10 minutes. Immediately contact a First Aider who will need to cover with sterile dressing and refer you for medical attention. See a doctor if the skin blisters or comes off. Otherwise, if only red, it will heal in time, as any other burn.
Storage
Store dry ice in polystyrene container in a designated -80°C freezer to slow down the sublimation process. Ask your LSS for advice.
Do not store dry ice in a completely airtight container. The sublimation of dry ice to carbon dioxide gas will cause any airtight container to expand or possibly explode. Keep proper air ventilation wherever dry ice is stored.
Do not store dry ice in unventilated spaces. The sublimated carbon dioxide gas, which is toxic at higher concentrations) will sink to low areas and replace oxygenated air. This could cause suffocation if breathed exclusively.
Disposal
NEVER dispose of dry ice down the sink.
If there is no room to store excess dry ice in the -80°C freezer, allow to evaporate off in the fume hood.