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Cryogenic Purge – Quench

The cryogens used in the NMR facility are liquid nitrogen and liquid helium.

The magnet cryostats continuously expel a small quantity of gaseous He and N2 into the air. This does not present a hazard since the air is constantly changed in the NMR room by the air-conditioning system during everyday use.

During the quench helium and nitrogen suddenly evaporate and expand their volume leaving no air in the room. This is an extremely dangerous condition since exposure to atmospheres containing 8-10% or less oxygen will bring about unconsciousness without warning and so quickly that the individuals cannot help or protect them. Therefore, it is imperative that in the event of quench (which is quite obvious because of the noise of escaping gases and clouds of vapor) all lab users should instantly evacuate the area. Since Helium is less dense than air, exiting the laboratory by crawling on the floor is recommended. Doors to the laboratory should be left open to aid in the dispersal of Helium and Nitrogen gases.

The room will be safe after a few minutes.

A purge of liquid cryogens will be very fast and may only take a few seconds. A loud hissing sound will occur and gaseous nitrogen and/or helium will be observed exiting the top of the equipment. The visible cloud is condensed water vapor from humidity in the air due to the cold gasses escaping the instrument.

All lab users must leave the area immediately!

Assist any injured user to the exit. Close the door. Dial 7666 for emergency medical assistance and 7444 to inform LSS.

The emergency assembly area is outside the NMR laboratory in the L-floor hallway. All laboratory users should reassemble at that point and account for all users:

  • Make sure all lab users are present at the assembly area in the hallway outside the laboratory.
  • Do not re-enter the lab or allow anyone else to enter the laboratory until the purge has ceased and fresh air has been introduced to the lab.

Under no circumstances are users to re-enter the laboratory until the purge is complete and fresh air has been provided. The continued presence of an oxygen deficient atmosphere in the laboratory is a life-threatening condition

Please consult Cryogenic Safety section of this document for more detailed cryogenic safety information.