02.03.10. Quench process
Measures are put in place to ensure the safety of patients and staff in the event of a quench
Risks associated with magnet quench
- A quench is an event that occurs when a superconducting magnet (such as those used in MRI) loses its superconductivity and undergoes a rapid increase in the resistivity of the magnet coil1.
- The quench process once set off cannot be reversed and takes approximately two minutes2
- The quench generates heat that results in the rapid evaporation, or boil-off, of the magnet coolant (liquid helium)1
- There are two situations in which a quench may occur1:
- Spontaneously: due to some force or disruption to the magnet system (these events are rare)
- Intentionally: when the “Magnet Stop” button is depressed in response to an emergency situation
- Evaporated helium created by a quench poses an immediate hazard to those in the vicinity of the magnet and the quench exhaust vent:
- The coolant is extremely cold and can cause cold burn and frostbite within seconds for those that come into contact with it
- The rapidly released gas can enter the MRI scanning room (if there is a problem with the venting) and displace the oxygen, posing a risk for asphyxiation
- A quench can also cause damage to the MRI equipment and disruption to the function of a department:
- A quench can potentially damage the MRI magnet itself
- Regardless of the damage done, a quench will result in at least several days of system down-time, and recovery to operation is expensive
Intentional quench
- Intentional quench is an emergency measure to be initiated in cases where no other alternative will suffice1:
- Fire that cannot be controlled by the non-magnetic fire extinguisher
- An individual pinned against the magnet, trapped or in a potentially life-threatening situation by a non-removable ferrous object
- In case of an intentional quench:
- The MRI department is evacuated
- The exhaust fan is activated
- The door to the scan room is fixed open – a build-up of pressure in the scan room could make an inward opening door difficult to open3
- Following the quench, the MRI department should remain evacuated until a suitably qualified person (e.g., a representative of the supplier) has inspected the system and confirmed it is safe.
Precautions for a quench emergency
- MRTs should be aware of any and all local or provincial guidelines that relate to quench in their facility.
- An accidental quench requires immediate evacuation of the vicinity.
- Procedures are put in place to establish evacuation routes and responsibilities
- Evacuation procedures are reviewed by all staff on a regular basis
- Safety measures are implemented to allow exit from the scan room in case of a quench emergency. These may include:
- A reconfiguration of the door so it opens outwards
- Installation of sliding doors that can be opened in an emergency
- Installation of emergency escape/ventilation panels on the door or in a suitable wall
- Provision of emergency equipment to allow MRTs to break a window in the event of door malfunction
- Police and fire response personnel are restricted from entering the MR scan room with their equipment until it can be confirmed that the magnetic field has been successfully dissipated4.
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References
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Queen’s University. Centre for Neuroscience Studies. Standard Operating Procedures: Emergency Shutdown and Quench Procedures. Available from: http://neuroscience.queensu.ca/MRI-facility/operation-procedures/shutdown. [Accessed 28 May 2018]
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Louisiana State University Health Shreveport Radiology Department. MRI Quenching the magnet. Available at: http://www.sh.lsuhsc.edu/raddept/pdf/sec14/Rad%20Proc%2014.13.pdf. [Accessed 3 Nov 2014]
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Medicines and Healthcare products Regulatory Agency (MHRA). Device Bulletin: Safety Guidelines for Magnetic Resonance Imaging Equipment in Clinical Use. Available at: http://www.mhra.gov.uk/home/groups/dts-iac/documents/publication/con2033065.pdf. [Accessed 3 Nov 2014]
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Kanal E, Barkovich J, Bell C, et al. ACR Guidance Document on MR Safe Practices: 2013. J Magn Reson Imaging 2013;37:501-530.