Hazards associated with superconducting magnet quench events: system requirements, application and consequences.

Abstract

The magnetically induced displacement force on nearby ferromagnetic objects has injured and killed people. The "quench" button dissipates the magnetic field by forcing the wire from the superconducting to the resistive state and its use in such situations should be unquestioned. Unfortunately, recent events demonstrate a reluctance to initiate a quench, perhaps because of the expense and down-time involved and the shock of confronting a rare and dire situation. Reports from various adverse incidents involving quenches also suggest a need to improve the awareness of what might happen during a quench. This review highlights relevant attributes of superconducting magnets (e.g. possible reasons for a quench, field attributes during the quench, various failure mechanisms that may occur etc.), the quench button, quench pipe, cryogen safety, and the quench sequence of events. Furthermore, it is necessary to be prepared for a rare gaseous helium release, including a nearby second safety-trained assistant, as people have been injured, incapacitated, or killed either by physical contact with a super-cooled object, hypoxia, or asphyxiation. In this regard, the development of "cryogenless" magnets demonstrates significant safety benefits. A selection of Food and Drug Administration (FDA) "Manufacturer and User Facility Device Experience" (MAUDE) incident reports illustrate these various situations, and device recalls also identify and resolve various potential, or realized, hazards, such as magnet explosions due to over-pressure and accidental cryogen release mechanisms. All users of MRI equipment must recognize when it is necessary to initiate a quench, what happens when a quench goes awry, and be prepared with quick decisions and actions. However, with small ferromagnetic objects or other non-critical situations, there may be alternative non-quench solutions. Understanding prior incidents prepares us for what might happen in a future incident and is a motivation for additional safety procedure development and training activities.