Static Magnetic Fields Safety hints for entering magnetic field volumina Fritz Szoncso SC/GS

Static Magnetic FieldsStatic Magnetic Fields

Safety hints for entering Safety hints for entering magnetic field voluminamagnetic field volumina

Fritz Szoncso SC/GSFritz Szoncso SC/GS

What is a Static Magnetic Field?What is a Static Magnetic Field?

A magnetic field is the area around a magnet or electrical current that has a detectable magnetic force.

“Static field” indicates that the field does not change in value or polarity over a period of a few hundred seconds. Therefore no induction can occur onto still objects in the field.

Generation of Static Magnetic FieldsGeneration of Static Magnetic FieldsStatic or quasi-static magnetic fields are generated by:

Electric coils, such as magnetsPermanent magnets in loudspeakers, small motors, horse-shoe Superconducting magnets for LHC and various experiments

DC-wiringKlystrons, radio and microwave tubesElectromagnetic lifting devicesNuclear Magnetic Resonance (MRI) scanners

Properties of Static Magnetic FieldsProperties of Static Magnetic Fields

A magnetic field may be described by:

a) Magnetic flux Weber, or Wb, or Voltsecondsa) Magnetic flux Weber, or Wb, or Voltseconds

b) Magnetic flux density Tesla, or T, or b) Magnetic flux density Tesla, or T, or Voltseconds per square meter (also Gauss Voltseconds per square meter (also Gauss in old literature with 1T=10000G),in old literature with 1T=10000G),

c) Permeability µc) Permeability µoo= 4 π 10= 4 π 10-7 -7 Asec/VmAsec/Vm

Properties of Static Magnetic FieldsProperties of Static Magnetic FieldsField penetration, deviation, configuration

a) Static magnetic fields penetrate all materials, including a) Static magnetic fields penetrate all materials, including the human body.the human body.

b) Magnetic fields cannot be shielded. However, the flux can b) Magnetic fields cannot be shielded. However, the flux can be deviated and concentrated by putting higher be deviated and concentrated by putting higher permeability materials (iron, nickel alloys etc.) into the permeability materials (iron, nickel alloys etc.) into the field path. field path.

c) Stray fields can never be entirely eliminated, except by c) Stray fields can never be entirely eliminated, except by active field cancellation.active field cancellation.

d) Magnetic field lines circle around the magnetic poles but d) Magnetic field lines circle around the magnetic poles but never touch them. The lines have no beginning and no end.never touch them. The lines have no beginning and no end.Poles always appear as pairs. No magnetic monopole exists.Poles always appear as pairs. No magnetic monopole exists.

Impact of Static Magnetic FieldsImpact of Static Magnetic Fields

Static or quasi-static magnetic fields can impact the industrial environment:

a) Forces exist between the coil(s) and all a) Forces exist between the coil(s) and all surrounding ferromagnetic objectssurrounding ferromagnetic objects

b) Many things do not work any more when a b) Many things do not work any more when a magnetic field is present: Circuit breakers,magnetic field is present: Circuit breakers,microphones, fans, transformers, etc.microphones, fans, transformers, etc.

c) Magnetic fields store energy. Transferring c) Magnetic fields store energy. Transferring and storing this energy is a technical risk.and storing this energy is a technical risk.

Hazards of Static Magnetic FieldsHazards of Static Magnetic Fields

The static magnetic field can

a) Interfere with medical implants and devicesa) Interfere with medical implants and devices

b) Move, attract, accelerate, tilt ferromagnetic devices b) Move, attract, accelerate, tilt ferromagnetic devices (hammer, drill, keys, etc.)(hammer, drill, keys, etc.)

c) Cause physical symptoms like nausea and vertigoc) Cause physical symptoms like nausea and vertigo

d) Erase data on magnetic memory material (credit and d) Erase data on magnetic memory material (credit and access card)access card)

e) Induce voltages and exercise forces in apparatus moved e) Induce voltages and exercise forces in apparatus moved through the field (electronic devices, but also safety shoes)through the field (electronic devices, but also safety shoes)

Issues around Static Magnetic FieldsIssues around Static Magnetic Fields

What can I do to be safe ?What can I do to be safe ?By knowing about By knowing about the risks I can the risks I can adapt my adapt my behaviour for behaviour for maximum safety.maximum safety.

I make an effort not to I make an effort not to approach ferromagnetic approach ferromagnetic objects.objects.I know about forces that can I know about forces that can hinder the movements of hinder the movements of (normal) safety shoes.(normal) safety shoes.I have a precise field map.I have a precise field map.

Static Magnetic Field ComparisonsStatic Magnetic Field Comparisons

For comparison:For comparison:

Earth field: 0.00006 TEarth field: 0.00006 TPacemaker limit: max. 0.0005 TPacemaker limit: max. 0.0005 TLimit for General Public: max. 0.01 TLimit for General Public: max. 0.01 TExposure during 8 h workday: max. 0.2 TExposure during 8 h workday: max. 0.2 TFor comparison: LHC inside magnets 8.33 TFor comparison: LHC inside magnets 8.33 TCMS inside magnet 4 TCMS inside magnet 4 TATLAS inside strongest magnet 2 TATLAS inside strongest magnet 2 T


ALARA principleALARA principleKeep it short.Keep it short.ALARA=As Low As ALARA=As Low As Reasonably¨ AchievableReasonably¨ Achievable

Supervisors have Supervisors have the obligation to the obligation to plan work for plan work for shortest exposure shortest exposure times.times.

Nobody remains exposed to Nobody remains exposed to fields longer than absolutely fields longer than absolutely necessary.necessary.

Practical hints for ferromagn. objectsPractical hints for ferromagn. objects

Additional hazardsAdditional hazardsForces exist between Forces exist between all ferromagnetic all ferromagnetic objects.objects.

Hazard: Loose Hazard: Loose ferromagnetic ferromagnetic objects may fly. Or objects may fly. Or turn.turn.Risk: You could be Risk: You could be in the way.in the way.

Reality: Several incidents already happened at CERN, e.g. Reality: Several incidents already happened at CERN, e.g. powertool projected into magnet aperture at high speed powertool projected into magnet aperture at high speed (ISOLDE), scaffolding flipped over (ALICE), entire test (ISOLDE), scaffolding flipped over (ALICE), entire test detector destroyed (CMS H2)detector destroyed (CMS H2)

Equipment in Static Magnetic FieldsEquipment in Static Magnetic Fields

Equipment in the fieldEquipment in the fieldAll magnetic cards (credit card, access card, All magnetic cards (credit card, access card,

etc.) are affected by the magnetic field. etc.) are affected by the magnetic field. (boxes are provided for safeguarding your valuables)(boxes are provided for safeguarding your valuables)

Equipment using conventional loudspeakers Equipment using conventional loudspeakers does not work (walkie talkie, intercom)does not work (walkie talkie, intercom)

Conventional computer screens do not work Conventional computer screens do not work any more. Even small stray fields have any more. Even small stray fields have visible effects.visible effects.

Medical requirementsMedical requirements

Medical requirementsMedical requirementsExposures beyond 10 mT are to be recorded Exposures beyond 10 mT are to be recorded

indicating values, start and end times.indicating values, start and end times.

Persons who are not physically fit, in Persons who are not physically fit, in particular persons with blood circulation particular persons with blood circulation problems, will not be allowed in.problems, will not be allowed in.

The values between 10mT and 200mT are The values between 10mT and 200mT are sufficiently far from any dangerous level.sufficiently far from any dangerous level.

Apparatus in Static Magnetic FieldsApparatus in Static Magnetic Fields

Sensitive apparatusSensitive apparatus

Sensitive equipment can be destroyed by induced Sensitive equipment can be destroyed by induced voltages.voltages.

Move equipment at lowest possible speed, do not make Move equipment at lowest possible speed, do not make jerky movements.jerky movements.

When cables are attached the surface affected by the When cables are attached the surface affected by the magnetic flux can be large - Induced voltages are then magnetic flux can be large - Induced voltages are then much higher. Equipment exposed to vibrations will be much higher. Equipment exposed to vibrations will be suffering from induction at the vibration frequency.suffering from induction at the vibration frequency.

Transient Fields and QuenchTransient Fields and Quench

Transient field (includes quench)Transient field (includes quench)In principle a In principle a field change field change induces induces voltages in the voltages in the entire field entire field volume.volume.

There is no There is no danger for danger for persons persons because the because the voltages voltages induced are induced are very small.very small.

We do not We do not foresee foresee additional additional precautions.precautions.


Forces on ferromagnetic objectsForces on ferromagnetic objectsThe forces may be surprisingly large.The forces may be surprisingly large.

No loose ferromagnetic objects are allowed in field volume.No loose ferromagnetic objects are allowed in field volume.

No unbolting is allowed inside the field volume.No unbolting is allowed inside the field volume.

Tools brought into the field volume must be compatible Tools brought into the field volume must be compatible with work in a magnetic field volume.with work in a magnetic field volume.

Power tools are forbidden inside the field volume. They Power tools are forbidden inside the field volume. They will not work anyway.will not work anyway.


Forces on ferromagnetic objectsForces on ferromagnetic objectsThe forces may provoke a torque. The forces may provoke a torque. Ferromagnetic objects want to align Ferromagnetic objects want to align themselves with the field lines.themselves with the field lines.

In case you find loose objects inside the field volume In case you find loose objects inside the field volume PLEASE DO NOT PICK THEM UP. The objects must be PLEASE DO NOT PICK THEM UP. The objects must be removed once the field is off again.removed once the field is off again.

There are non-magnetic safety shoes. This type should be There are non-magnetic safety shoes. This type should be acquired for persons entering the field volume.acquired for persons entering the field volume.


Metallic structures in the fieldMetallic structures in the fieldAll iron structures in the field will carry a larger magnetic All iron structures in the field will carry a larger magnetic flux than the surrounding air.flux than the surrounding air.

It is forbidden to be close to large ferromagnetic objects.It is forbidden to be close to large ferromagnetic objects.

The iron floors will put some force onto normal safety The iron floors will put some force onto normal safety shoes. BE CAREFUL - there is a feeling like sticking to the shoes. BE CAREFUL - there is a feeling like sticking to the surface.surface.

Metallic floor pieces (Caillebotie) must be bolted and not Metallic floor pieces (Caillebotie) must be bolted and not just lying there. just lying there.


Similar to our case: MRISimilar to our case: MRI


ConclusionConclusionTHINK prior to entering an area at risk.THINK prior to entering an area at risk.

REMOVE all items that react on magnetism.REMOVE all items that react on magnetism.

MOVE SLOWLY inside the field volume, in particular MOVE SLOWLY inside the field volume, in particular when crossing field lines.when crossing field lines.

RESPECT Code A6 - the two person rule of working, and RESPECT Code A6 - the two person rule of working, and have a corresponding person outside the field volume for have a corresponding person outside the field volume for any safety action you might require. Exercise care. any safety action you might require. Exercise care. Rescuers have difficult access and need to able to switch Rescuers have difficult access and need to able to switch off the field prior to any intervention.off the field prior to any intervention.Check on a field map to what you would be exposed at which spot.Check on a field map to what you would be exposed at which spot.

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Static Magnetic Fields Safety hints for entering magnetic field volumina Fritz Szoncso SC/GS