Liquid Nitrogen

The lab usually receives liquid nitrogen in a 160-liter dewar. The dewar is stored by the double-door exterior entrance to the lab. The dewar should be secured to the wall backet with a chain (see photo 1). If you receive a new shipment of liquid nitrogen, make sure the dewar is properly positioned against the wall and the security chain attached. We don't want the dewar to fall over in an earthquake and become a hazard while we are trying to evacuate the building.

Transferring liquid nitrogen to a smaller dewar

Eye protection should be worn while working with liquid nitrogen to avoid potential eye injury. It is necessary to use the thermal mitten to protect your hand when opening and especially when closing values on the 160-liter dewar since these values may be well below freezing after liquid nitrogen is withdrawn from the dewar.

Liquid nitrogen in the 160-liter dewar is typically under pressure. The pressure is used to force liquid nitrogen from the dewar when the withdraw valve is opened. Never open the dewar's liquid withdraw value without first securely attaching the supply hose. The discharge end of the supply hose should be placed into one of the lab's small transfer dewars before the valve is opened. The withdraw valve should be opened slowly because the pressure in the dewar may be high and overly rapid discharge of liquid nitrogen could cause splashing and severe frostbite burns.

When liquid nitrogen is being transfered into a transfer dewar there will be rapid boil-off of the liquid nitrogen and typically a plume of fog coming out of the top of the transfer dewar. This fog is very cold - below freezing at the mouth of the transfer dewar, and has a very high concentration of nitrogen. Be careful when picking up the transfer dewar immediately after it has been filled. The handle, which is near the top of the dewar, may be very cold. Use the thermal mitten to hold the dewar handle and avoid freezing your skin to the handle.