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6. Cryogen hazards

Cryogens should only be handled by authorised and trained cryogen suppliers.

6.1  Venting in superconducting magnets

Superconducting magnets offer a potential cryogen hazard.  Adequate attention should be paid to the provision of the venting of the cryogens, including ensuring that the external vent pipes are of the correct dimensions and in the case of a quench, able to withstand pressures above that recommended by the manufacturers as outlined in the MHRA guidelines.2  External vent pipes should also be designed and fitted so that there is no ingress of rain, or other detritus and they should have a regular maintenance and inspection schedule.

13695342-exclamation-point.jpg MRI scanner manufacturers are not usually responsible for the maintenance of quench pipes and do not routinely check them during planned preventive maintenance.2

6.2  Quench hazards in superconducting magnets

There should be no hazards from cryogens for MR scanning staff, visitors and patients, provided adequate attention has been paid to the provision of venting directly to the air outside the unit.  In the event of a quench, low temperature liquefied gases, designed to keep the magnet close to absolute zero (-273°C) expand and boil off to the outside.  In order to detect any unplanned leakage of helium into the scanner room, suitable low oxygen warning alarms should be placed in the MR room and be regularly checked and maintained.  If, for any reason, the gases should enter the room, instead of exiting to the outside, there will be the hazard of asphyxiation owing to the displacement of oxygen, hypothermia and frostbite.  There may also be over pressurisation in the room owing to the rapid expansion of the liquid gas and this may make it difficult to enter the MR room.

If the low oxygen monitor alarm sounds or a quench should occur, the MR room should be evacuated immediately.  Appropriate local emergency procedures should be in place and included in the training programme for all authorised personnel.  See also section 13.

Departments should adhere to the manufacturers’ recommendations regarding maintenance programmes and checking of equipment

Departments must also ensure that a system is in place for handover of responsibility to and from engineers during maintenance checks and system repairs

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