When an MRI scanner has to make an emergency stop, a process called quenching is activated. In this process a sudden loss of absolute zero temperature is activated in the magnet coils. This will cease the coils to be super conducting and they become resistive instead, thus eliminating the magnetic field.
During this proces helium will escape from the cryogen bath extremely rapidly, and since helium can reach temperatures around -269 °C a special quench pipe ducting system has to be constructed to guide the gasses safely outside.