17
•
Close the valve carefully.
•
Drain the coolant outlet.
•
Loosen the adjustment screw on the pressure regulating valve.
•
Close the valve on the receiving equipment.
•
Regulations apply to the transportation of cylinders.
•
Frames must be handled with care in the same way as cylinders.
Users of the equipment, who are fully aware of the conditions of use and thus best placed to monitor the equipment, are
solely responsible for proper use.
8.2 LN
2
backup
Precautions for liquid nitrogen use:
Strict rules must be followed when handling cryogenic fluids such as liquid nitrogen. These rules are intended to prevent
two key risks:
asphyxiation and burns
from contact or splashes. Air contains 21% oxygen and 78% nitrogen, by
volume. At atmospheric pressure, liquid nitrogen evaporates at temperatures greater than –196°C.
In a cryogenic room, natural evaporation from recipients, filling, and handling of stored samples result in continuous
evaporation of liquid nitrogen. This can increase significantly if a default occurs. If the room is not well ventilated, the
nitrogen gas generated can cause the atmosphere to be depleted in oxygen.
Properties of liquid nitrogen:
•
Does not sustain life or combustion.
•
Present in air (78%).
•
The evaporation of one litre of liquid nitrogen generates 680 litres of gas.
•
Heavier than air at low temperatures.
•
Non-flammable and colourless.
Ensuig risks:
•
Risk of
asphyxiation and loss of consciousness.
An atmosphere with less than 16% oxygen is hazardous
(nitrogen gas displaces oxygen in the air).
•
Nitrogen gas builds up in low areas.
•
Risk of frostbite.
•
Risk of corrosion of steels in the presence of humidity.
•
In closed vessels, the pressure can reach very high values (in the order of 700 bar) resulting in a risk of bursting.
Criticals precautions to be taken:
•
Areas where liquid nitrogen is stored or used must be well ventilated (extraction or ventilation at both high and
low levels in the room).
•
Areas liable to contain an unbreathable atmosphere must be indicated with an asphyxiation hazard pictogram.
•
Never enter a room that has contained liquid nitrogen without taking predefined precautionary measures.
•
Eliminate links between areas where liquid nitrogen is stored or used and low points (pits, drainage channels,
basements) where it could accumulate and render the atmosphere unbreathable.
•
Use an O
2
concentration detector to ensure that the oxygen concentration is greater than 18%.
•
Avoid uninsulated liquid nitrogen pipes in any areas.
•
Call on the services of a specialist to determine the layout of facilities.
In case of asphyxiation:
•
Check the oxygen concentration in the room and then take the victim to the open air (taking an insufflator with
you).
•
Start artificial respiration and call the emergency services.
In the event of a leak:
•
Evacuate the room.
•
Do not enter the room without breathing apparatus if the oxygen concentration is lower than 18%.
•
Close the valve on the leaking outlet.
•
Aerate the room at length, ensuring that low points are ventilated.
If liqui dnitrogen is splashed:
•
In the eyes
: rinse the eye thoroughly for at least 20 minutes.
Call a doctor
.
