Magnet Safety

Simon Fraser University has a comprehensive Radiation Safety Program (RSP) which includes Ionizing (IR) and Non-ionizing Radiation (NIR). The use of magnetic instrumentation falls under the NIR RSP which primary objective is to facilitate and ensure safe use of magnetic devices in research, teaching and the environment.

For more information, contact: Program Manager, Ionizing Radiation, Radiation Safety Officer: ph. 778-782-3633

Exposure Control

Simon Fraser University enforces the standards with regard to safety concerning static magnetic fields established by the American Conference of Governmental Industrial Hygienists (ACGIH). Recommended limits are listed in the table (here).

Implementing administrative and engineering controls are required in order to adhere to general safety precautions and control exposure.

General Safety Precautions

  • Magnetically-sensitive equipment, such as implants and cardiac pacemakers, can be adversely affected, resulting in injury or death. All individuals with implants such as pacemakers are restricted to areas that have a magnetic field below  5 G (0.5 mT).
  • When the superconductivity of an NMR magnet is lost quenching occurs, resulting in rapid heating and the accumulation of a helium vapor cloud above the magnet which can create an oxygen deficient atmosphere. Additionally, the quench can damage the magnet, and draw in ferrous materials. Quench events can be prevented by implementing engineering controls for cryogen safety.
  • All electrical equipment should be kept off the floor in case of flooding.
  • A magnetically compatible fire extinguisher must be mounted outside of the magnet room in the event of a fire.
  • All magnet assemblies and power supplies should be restrained to prevent movement and tipping in the case of an earthquake.

Administrative Controls

Area Designation

  • As a part of area design, the static magnetic field strength should be identified and marked where pacemaker hazards (> 5 G) and kinetic energy hazards (> 30 G) will exist.
  • No work stations should be within the 5 G line, nor should the line intrude into public thoroughfares, entrances, or exit spaces. This includes locations above and below the magnet room.
  • While setting up the magnet instrumentation and prior to commencing experiments, a portable magnetometer should be used to determine the extent of the magnetic field while the device is energized, and ensure all safety precautions are adhered to.

Personal Protective Equipment

Please review the Lab Safety PPE guidelines.

  • When handling cryogens, wear insulated gloves, face shields or other splash eye/face protection, closed-toed shoes and lab coats.
  • Insulating garments and equipment should be used in areas where 60 Hz electric fields exceed 5 kV/m, as demonstrated by measurement or calculation.
  • Insulating gloves or preferably, engineered controls (e.g. enclosure or shielding of a field source) must be used to avoid contact with objects that could expose personnel to sparks associated with field strengths equal to or greater than 5 kV/m.
  • Ear protection is required for anyone inside an MRI scanner room during operation.

Shielding

If it is determined that shielding is required, an experienced consulting firm should be employed to design the magnet shielding.

Signage

Please refer to the 'Program Manuals' section for posting guidelines.

Engineering Controls

Cryogen Safety

Cryogens present a number of safety hazards. Please review the general cryogen safety guidelines. In addition, the following engineering controls are required to be in place:

  • Internal cryogen level sensors should be used to indicate low levels of helium in order to prevent a quench. If a low level is indicated, the magnet should be refilled or de-energized.
  • A liquid helium purge vent must be installed to allow excess helium gas to escape through an exhaust vent extending to the outside environment at safe height/location.
  • A visual and audible oxygen alarm must activate when levels of oxygen are below 19.5%.
  • Positive access control must be in place such as locked doors and restricted access to authorized personnel only.

Electrical Safety

  • Metallic structures that can produce contact shocks must be electrically grounded or insulated.
  • Power supplies used for NMR operation at high current (~100 A) are extremely dangerous if they come in contact with human tissue. Power supplies must be located in low traffic areas above the ground.
  • All cables, wires, or connectors should be properly insulated to prevent contact with the operating current.
  • All equipment should be powered down before any connections are broken to prevent arcing.

Interlocks

  • Areas where whole-body exposures exceed 25 kV/m or 10 G must be restricted by positive means such as locked enclosure, interlock, and safety chains.
  • Interlocked areas must be approved by EHS and registered with Facilities Services

Projectiles

The attraction between the magnet and ferromagnetic materials can produce airborne projectiles when the magnetic field is strong. To prevent a projectile hazard:

  • Magnetically permeable materials must be kept out of range of the magnetic field, or  secured and anchored.
  • Ferromagnetic tools in the area must be kept in a locked enclosure marked with the appropriate signage.

Shielding

Magnetic fields can be controlled by using permeable alloy as shielding, which confines the magnetic flux lines, diverts them and minimizes stray field lines.

  • Magnetic shielding is made of high nickel alloys called mu metal or soft iron. This type of shielding is best applied near the field source.
  • Non-permeable metals such as copper or aluminum can be used instead to produce eddy currents which cancel out the original field.