Definition¶
Quenching is a term referring to the events that occur when the cryogenic liquids used to cool the magnetic coils rapidly boil, resulting in a very rapid escape of helium from the cryogen bath.
This means that the superconducting coils cease to be superconducting and return to a resistive state. A ‘Quench’ will generally be accompanied by a loud detonation similar to a thunderclap, a hissing sound, or an abrupt sound with the expulsion of cold gas.
The STOP button¶
A Quench can be triggered by the user in a controlled manner by activating the Magnet Stop button. This button de-energizes the superconducting magnet.
Press this button in case of emergency in the magnetic field and notify the Siemens service immediately.
Only superconducting magnets have a magnet stop switch - permanent magnets cannot be turned off.
Quench and magnetic field¶
Note that initiating a Quench does not result in the complete removal of the magnetic field, and a danger may still exist. Some magnets only partially quench and the magnetic field is therefore not completely eliminated. In such cases, appropriate safety measures must still be taken when handling ferromagnetic objects near the magnet.
One of our magnet manuals suggests that the field intensity is likely to be reduced to ~ 20 mT approximately 20 seconds after the initiation of a Quench (Kanal, MR Safety, translation of the English version).
Emergency procedure¶
In the event of a Quench in the MRI unit, MRI staff must evacuate the magnet room if possible, and the UNF department.
If someone is in the MRI room (in the magnet) or in the MRI room during the QUENCH, the person/people must be taken out of the MRI room, then assist the individual(s) using first responder first aid principles.
Call 5555 for all emergencies; identify:
What the emergency situation is: There is a Magnet Quench in MRI room C-0674
Where you are: Functional Neuroimaging Unit
Who you are: Your name
Once everyone is out of the magnet room, the door must be locked.
If the emergency response team is present, ensure that they are aware of the existence of a residual magnetic field.
Inform the Functional Neuroimaging Unit staff of the events.
UNF staff will inform management, Siemens Uptime service, etc.
Siemens Uptime Service 1-800-359-6709 Site #8010
A written summary of the incident (incident report) will also need to be made.
Reference¶
Siemens Healthcare_ Safety_Guide_AE_4c.pdf p.15