Electromagnetic Fields

There are well established and understood short term adverse effects at high levels of exposure to electromagnetic fields and the University has a duty to protect staff students and others affected by the work.

The Control of Electromagnetic Fields at Work Regulations 2016 places duties on employers and sets out exposure limits. HSE guidance is available here

What Departments need to do
Trivial sources of EMF
Non-trivial sources of EMF
Risk Assessment
Summary of health effects
Individuals at particular risk
Training
Control Measures
Exposure Limit Values and Action Levels (Basic Restrictions and Reference Levels)

Further information:

Advice on specific equipment and applications:Nuclear Magnetic Resonance (NMR), Magnetic Resonance Imaging (MRI) and similar equipment, arc welding and other workshop applications, mobile phone technology, microwave ovens used for heating food, new and developing technologies.
Useful references
Warning labels/signs/symbols
Example risk assessment - NMR equipment
Example screening form - MRI
Example NMR Training Record and Safety Screening Form

What Departments need to do

First identify the electromagnetic sources for which action may be needed.

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Trivial sources of EMF

For trivial sources, no further action is needed (where following manufacturers' instructions and where equipment is not modified). This includes CE marked equipment in compliance with international standards referring to restrictions on exposure (to current guideline limits).

Some examples of sources which can be assumed to be compliant:

  • Mobile phones
  • Radiofrequency identification (RFID) tags (eg in smart cards)
  • Household/office electrical equipment including computer/IT equipment
  • Base station antennae (outside exclusion zones)
  • Wireless communication networks
  • Electricity supply networks (50 Hz) in the workplace and electricity distribution and transmission circuits passing through or over the work place

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Non-trivial sources of EMF

For sources which are considered to be safe for normal use, action is only needed if the sources are used contrary to the manufacturer's instructions. This may include modified equipment, for example, a microwave oven manufactured to heat food but adapted for laboratory work.

For these and any other sources of known or unknown risk, the DSO should keep a list of these sources, users and research supervisors should keep the DSO informed regarding this type of equipment, ensure risk assessments are carried out and that appropriate control measures have been implemented.

Examples of non-trivial applications and sources:

Some research applications:

  • Nuclear Magnetic Resonance Spectroscopy/Imaging
  • Magnetic and physical property measurement systems (MPMS and PPMS)
  • Medical and research equipment using intentional radiation with electromagnetic exposure or application of currents
  • Terahertz Imaging/Spectroscopy

Some workshop/engineering applications:

  • Electrical welding and melting
  • Induction heating
  • Dielectric heating and welding
  • Magnetisers/demagnetisers
  • Microwave heating and drying

Other applications

  • RF plasma devices
  • Diathermy
  • Radar
  • Base station antennas (installed on some University owned buildings) where there is a need to access the exclusion zone specified by the installer

Other sources:

  • Microwave Sources (Magnetron, Gyrostron, Klystron)
  • Radio Frequency sources
  • Electromagnets
  • Large permanent magnets
  • Particle accelerators and colliders
  • Terahertz sources

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Risk assessment

It is a duty of manufacturers/suppliers to design equipment so that it is safe to use, or to provide the user with information on how to use the equipment safely, any information on exposures and any precautions including access restrictions (including for cleaners, security personnel, emergency services). Note that there are limited occasions when users need to undertake or commission measurements themselves.

For trivial sources, users should simply follow manufacturers' instructions.

For non-trivial sources, risk assessments should consider:

  • Availability of alternative equipment or equipment designed to reduce the level of exposure
  • Information provided by the manufacturer
  • Comparison of exposures with exposure limit values and action levels
  • Direct and indirect effects
  • Individuals at particular risk
  • Information from health surveillance where applicable
  • Multiple sources of exposure

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Summary of health effects

Direct health effects

  • At low frequencies (300 kHz and below), effects on the nervous system and, below 1 Hz, the heart. Up to 300kHz, overexposure can cause small induced electric currents to flow in the body which can interfere with the brain and nervous system. Magnetic phosphenes are a perception of faint flickering light thought to result from interaction of induced electric currents with cells in the retina. Fields at 0-1Hz can cause cardiovascular effects and even cardiac arrhythmia, and also vertigo and nausea.
  • At high frequencies (10 MHz and above), heating effects on the body and on specific tissues. Induced currents can cause heating effects which must be limited in order to prevent whole-body heat stress and harmful localised heating of tissues in the body.
  • At intermediate frequencies (100 kHz -10 MHz) both nervous system effects and heating effects.
  • Risk of electric shock or burn from touching objects in an electromagnetic field.

Indirect effects

  • Interference with active implanted medical devices such as cardiac pacemakers.
  • Projectile risk from ferromagnetic objects in static magnetic fields.
  • Initiation of electro-explosive devices (detonators).
  • Fires and explosions resulting from ignition of flammable materials by sparks caused directly or indirectly by electromagnetic fields.

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Individuals at particular risk

Individuals at particular risk must be considered as part of the risk assessment, including those wearing medical devices and prostheses, cardiac pacemakers and defibrillators, cochlear implants and other metallic implants or body-worn medical devices. Consider all students and staff, but also the risk to visitors including contractors and emergency personnel. Possible problems include electrical interference or physical movement or twisting of the implant which can give rise to safety or health effects, depending on the exposure and the implant. Disruption of cardio-pacemakers could result in serious injury or death to the individual. Other implanted ferromagnetic objects including pins, stents, shunts and also any embedded fragments such as metal splinters or shrapnel can also be adversely affected in magnetic fields.

The individual may have to check with their medical consultant as to the susceptibility of implanted material or implanted device. Access is normally restricted to magnetic flux densities of 0.5mT (5 Gauss) based on the most sensitive devices, so a further risk assessment will need to be done if the individual needs to access these areas. Please consult the Safety Office for further advice.

Pregnancy and exposure to EMF: There is no evidence of detrimental effects to the embryo or foetus within exposure limit values, but in the event of pregnancy being declared, the risk assessment must be reviewed and any concerns discussed. The main issue is excessive heating to the mother and foetus when exposed to radiofrequency fields, but this is normally very unlikely, particularly if working well within exposure limit values.

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Training

Training should include:

  • Control measures needed to comply with limits and reduce risks
  • Direct and indirect effects of overexposure
  • Results of the risk assessment
  • How to detect and report adverse effects
  • Entitlement to health surveillance
  • Safe working practices
  • Information for and regarding workers at particular risk

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Control Measures

In general control measures should include:

  • Choice of equipment and alternatives (Examples of Screening Forms can be found at the bottom of this webpage)
  • Interlocks, shielding
  • Access restrictions and setting up of controlled areas by use of warning signs, floor markings, barriers
  • Written rules for entering and working in controlled areas
  • In the case of exposure to electric fields, measures, procedures and training of workers to manage spark discharges and contact currents
  • Appropriate maintenance of equipment and systems
  • Design and layout of equipment and work areas
  • Limitation of time and intensity of exposure
  • Adequate personal protective equipment.

When considering control measures, we can consider each commonly encountered region separately:

  1. Sub-Extremely Low Frequency radiation and static magnetic fields (0-30Hz)
  2. Extremely Low Frequency radiation (ELF) (30Hz - 300Hz)
  3. Microwaves and radiofrequencies (RF) (3kHz - 300GHz)
  4. Terahertz radiation (300GHz – 3000GHz)

Sub-ELF and Static Fields (<30Hz)

Typical sources: magnetic resonance imaging equipment (MRI) used for scanning people; nuclear magnetic resonance equipment (NMR) used to investigate the properties of materials; magnetic property measurement systems (MPMS); and physical property measurement systems (PPMS). NB Additional advice is provided below on NMR and MRI which both employ RF as well as static fields, and MRI also uses fast switched gradients which are effectively pulses in the kHz range, and induced current effects can also arise.

Work with Static Magnetic Fields

Ferro-magnetic and/or electronic medical devices and medical implants can be affected at field strengths as low as 0.5mT (5 Gauss line). There is particular concern regarding disruption of cardio-pacemakers which could result in serious injury or death to the individual.

Other implanted ferro-magnetic objects including pins, stents, shunts and also any embedded fragments such as metal splinters or shrapnel can also be adversely affected in magnetic fields (at around 3mT or 30 Gauss line). These objects can move or twist in the magnetic field causing trauma to the surrounding tissues. Furthermore, ferro-magnetic objects entering strong magnetic fields ( >3mT) can pose a ‘projectile’ hazard to those in the local vicinity as they can be drawn rapidly into the magnet ‘bore’. Deaths and serious injuries have been caused by the projectile effect.

Magnetic fields can also cause damage to certain data devices such as computer hard discs and personal items such as credit cards and watches, and can interfere with electronic equipment.

Control measures: Strict control measures are required to prevent unauthorised access of individuals and equipment to magnetic field strengths of 0.5mT (5 Gauss) and above. A contour map of magnetic flux densities (both vertical and horizontal planes) should be provided by the manufacturer/supplier, and should be considered at the project design stage and confirmed during the commissioning process.

Areas where the magnetic field strength is 0.5mT (5 Gauss) and above should be totally enclosed and designated as 'controlled areas' and written "local rules" should be in place. Free access to this area should only be allowed to authorised personnel who have undergone screening protocols and appropriate training. Once sited the magnetic field position will not move unless the equipment producing the field is moved, altered or large ferromagnetic objects are introduced into the vicinity of the equipment.

Access to the controlled area (the area enclosing the 0.5mT or 5 Gauss line) should involve clearance through a strict screening process to ensure all those entering the area (users, visitors, contractors, cleaners, etc.) are safe to do so. A high level of supervision will be required to ensure unauthorised persons do not enter the controlled area (Example Training and Screening Forms can be found at the bottom of this webpage).

When routine maintenance or servicing is being carried out by staff or contractors safe working procedures should be included in the local rules. A permit to work system should be in place for service work.

ELF (30Hz- 300Hz)

Typical sources: These are associated with mains electric and power lines. Exposures can arise from arc and spot welding and induction furnaces.

Control measures: Public exposures related to power distribution will be within relevant exposure limits. For specific equipment, manufacturers' instructions must be followed. In this low frequency region, it is appropriate to consider the individual electric and magnetic field components. The electric field is easily shielded by use of metal shielding (Faraday cage). For the magnetic field component, distance is typically used to restrict exposure.

Microwaves and RF (3kHz – 300GHz)

Typical sources: Radar, microwave communications, microwave heating, RF induction heating and welding.

Specific biological and health effects: The main hazards are thermal heating, induced current burns and contact burns:

  • <10 MHz - electrical currents can be induced in tissue which can act on the central nervous system (CNS)
  • 10-100 MHz can affect CNS and cause tissue heating effects leading to a rise in body temperature
  • >100 MHz - heating affects and rise in tissue temperature
  • >10GHz – heating of surface tissues only

These radiations generally have a heating effect on the body - some parts of the eye (especially the lens) are more susceptible because they are not served by many blood vessels and therefore heat dissipation is slow. The most susceptible people to these radiations are those whose bodies have difficulty controlling internal temperature, or those suffering from a fever, or people with circulatory problems. There can also be electrical effects affecting the nervous system in RF frequencies and the possibility of shocks and burns from touching objects in an RF field.

Control measures: As noted above, control measures normally include minimising time of exposure; maximising distance and use of shielding where possible. Radiofrequency fields can be satisfactorily shielded by an appropriate metallic mesh (Faraday cage) with access prevented by interlocks if necessary (as for microwave ovens).

For open sources, consideration needs to be given to siting, restriction of access and display of warning signs. Safe distances/exclusion zones should normally be specified by the manufacturer.

The work will need to be covered by a risk assessment and users will need to be trained. Anyone who may be at particular risk from exposure to these radiations needs to be identified and additional precautions put in place as necessary.

Terahertz radiation (300GHz – 3000GHz)

Terahertz radiation lies on the boundary between microwaves and infra-red radiation. Current guideline safety limits in this region are based on extrapolation from infra-red and microwave regions. The effects on tissue are thermal.

Terahertz radiation can penetrate a wide range of non-conducting materials but can be reflected by dense materials and metals leading to the first application in security screening. There is likely to be increased research in this area developing further applications.

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Exposure Limit Values and Action Levels

Exposure limit values and action levels are set out in the Schedule of the Regulations.

Action levels are not limits but are practical in establishing compliance with the overall limits. In the regulations, action levels are given for direct effects (low action levels for sensory effects, and high action levels for health effects) and for indirect effects.

Note that workers at particular risk may not be adequately protected by action levels or exposure limits.

Before purchasing equipment, suppliers should be able to provide information on compliance with overall limits and information on how to work safely. Measurements or calculations may be needed, but these should normally be done by the manufacturer or supplier of the equipment.

The University RPO should be consulted regarding measurement or calculation of EMFs for comparison with action levels or exposure limits.

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Advice on specific equipment and applications

There is a wide range of equipment used in research establishments which generate significant electromagnetic fields and this section covers some common applications, including magnetic resonance imaging equipment (MRI), nuclear magnetic resonance equipment (NMR), magnetic property measurement systems (MPMS), and physical property measurement systems (PPMS).

Equipment may generate electromagnetic radiation in different frequency ranges, for example, MRI and NMR both employ RF as well as static fields, and MRI also uses fast switched gradients which are effectively pulses in the kHz range, and induced current effects can also arise. NMR equipment is normally well shielded to prevent RF exposure, but can be an issue in MRI as noted below.

MPMS and PPMS equipment can also produce significant static magnetic fields.

Although modern equipment incorporates increasingly better shielding for static fields, it is often not possible to achieve less than 0.5mT (5 Gauss) on the outside of the equipment, therefore individuals at particular risk must be considered carefully as part of the risk assessment. A screening process should be in place for new staff, students and visitors.

Applications involving radiofrequency fields include radar, microwave communications, microwave heating, RF induction heating and welding. These are not covered in detail as any safety issues depend on the design, but please refer to manufacturers’ duties and control measures for RF.

Nuclear Magnetic Resonance (NMR) and Magnetic Resonance Imaging (MRI)

RF fields associated with MR are normally shielded, but the static magnetic field (magnetic flux density) can be significant. The installer should undertake a survey to demonstrate compliance with exposure limit values and provide a field plot.

The risks will depend upon the size of the field and how it is used. There are various hazards associated with the use of NMR and MRI that should be considered, including the projectile effect of a strong magnetic field, the effect of the field on implants, burns from the heating effect of the radio frequency pulses, hazards arising from the use of cryogens, as well as the potential damage to computer hard discs and personal items such as credit cards and watches. The field may also affect monitors and other nearby electronic equipment.

Depending on the risk assessment, a controlled area may need to be set up around the 0.5 mT (5 Gauss) line to which access is restricted. Anyone with an implanted pacemaker should not enter this area. Other implanted medical devices may also be affected. See Section on 'Individuals at particular risk'.

At the 3mT (30 Gauss line), there is also a risk of ferromagnetic items being drawn towards the magnet with significant force with the potential to cause harm to people and equipment - the projectile effect. If practicable, an inner controlled area can be set up at this line in order to protect workers from the projectile effect. However, for simplicity, there is normally only one controlled area containing the 0.5mT (5 Gauss) line to protect people at particular risk, as well as the projectile effect.

For more information such as exposure limits, physical hazards associated with the equipment used in NMR spectroscopy and MRI, and advice on appropriate control measures contact the Safety Office.

Static Magnetic fields in NMR, MRI, MPMS and PPMS

Access to areas with significant static magnetic fields (such as MRI, NMR, MPMS or PPMS) should be restricted to authorised personnel who have been subjected to a basic screening process for implanted medical devices. Physical security measures such as keypad, swipe-card or traditional locking systems would be an acceptable method of preventing unauthorised access. It is preferable to locate equipment in dedicated areas, but where staff unconnected with the work need enter rooms where equipment is sited then the position of the 0.5mT (5 Gauss) line should be demarcated as a 'restricted area' and clearly indicated to permitted staffentering the room providing they have been fully trained.

Items of equipment that are intended for use in areas where magnetic fields are present must be tested and designated as MR safe/compatible as appropriate (or non-ferrous for NMR or similar systems) to prevent the likelihood of causing projectile hazards and electromagnetic interference.

If an individual (member of staff, visitor, patient or volunteer) who needs to enter the controlled area has an implanted medical device their clinical consultant should be asked for advice. A list of MR "safe" implants has been compiled (but note the disclaimer).

In addition to the potential for serious injury, MRI and similar equipment is expensive and serious financial costs can be incurred as a result of damage from projectile incidents. As a consequence of projectile incidents, a rapid 'quenching' of super-cooled magnet can occur (depending on the equipment). This results in discharge of pressurized cryogenic gases into the local environment depleting the available oxygen. 'Quench' pipes/ducting to remove rapidly expanding gas and oxygen-depletion monitoring systems are basic requirements in areas housing super-cooled equipment. The dimensions of the quench pipe must be specified by the MR manufacturer and the installer is responsible for installing the quench pipe as specified by manufacturer. The department should check that this is done.

Quenching and other incidents can be common at installation and it is important to clarify in writing that the installer is in charge of the area at this time and they must have a risk assessment for the installation.

Time-Varying Magnetic Field Gradients in MRI

The biological effects from time-varying magnetic field gradients can interfere with normal function of nerve cells and muscle fibres, while more serious effects can cause ventricular fibrillation. In such cases frequencies >1MHz are regarded as significant with those >30MHz wavelength influencing the electric field and current distribution in conductive tissues. Peripheral nerve stimulation in patients undergoing MRI scans has been observed. In gradient fields no movement is necessary to induce currents, unlike in static fields.

Time-varying magnetic field gradients produce acoustic noise (sound waves) when alternating between low frequency currents. Noise levels can reach dangerous levels and therefore appropriate measures (eg hearing protection) should be implemented to prevent noise-associated injury where necessary (contact the Safety Office for noise measurements).

Radiofrequency Fields in MRI

Induced current burns result from people coming into contact with conductive loops that may become hot during operation (generally in MRI). This can be avoided through equipment design and from the positioning of subjects in the MRI equipment. Contact burns can result from metallic objects in close proximity to the subject becoming heated when the radiofrequency induces currents in conductors such as metal in objects of clothing or probes attached to subjects.

Assurance should be sought from the manufacturer/supplier of the equipment that action levels cannot be exceeded during normal operation.

Other Associated Hazards (MR and similar equipment)

Below are some hazards that will also need to be addressed by a risk assessment, and always refer to manufacturer's instructions. General health and safety issues such as the positioning of the equipment and supply cables should be considered during the planning and installation stages.

Manual Handling: The excess heat produced by strong magnets will require a liquid cryogen to act as a coolant. This may involve the manual handling of Dewars and other heavy equipment in the refilling procedure

Cryogenic Gases: The potential hazards associated with handling cryogenic liquids include cold-burns and oxygen depletion due to accidental escape of cryogenic gas. Equipment involving use of cryogens must always be situated in areas with adequate ventilation, and where quench pipes are used, these must be installed as specified by the equipment manufacturer. Oxygen depletion monitors must be appropriately sited, used and maintained. HSD053C Reduced Oxygen Atmospheres Resulting From the Use of Cryogens or Compressed Gases in the Work Place

Electrical: As with all equipment using the electricity supply the likelihood of electric shock and fire etc should be considered in any risk assessment. Care should be taken if handling flammable and other liquids around this equipment and only competent service engineers should gain access to electrical workings

Noise: (for example from switched gradients used in MRI). There are action levels for noise exposure and the employer is required to take reasonably practicable measures to reduce noise exposure

Arc welding and other workshop applications

The welding cable can lie close to the operator, leading to relatively high exposures normally mainly when the arc is struck but also in maintaining the arc. If the manufacturers’ instructions are followed, exposure should not normally exceed exposure limit values but if there any concerns, please refer to the manufacturer for advice. The Section on 'Individuals at particular risk' must be considered carefully as part of the risk assessment.

Mobile phone technology

Mobile phone telephony continues to attract more interest from the public than other sources of radiofrequency (RF) fields. Controversy has centered on whether long term low-level exposure below guideline limits can cause adverse health effects, and this has been the subject of many of the health-related studies carried out in recent years.

Evidence suggests that exposures within international guideline limits do not cause adverse health effects but research is continuing.

Microwave ovens used for heating food

For microwave ovens which are used in accordance with manufacturers'instructions, there is no need to carry out routine leak tests.

You should routinely check that:

  • the oven housing is undamaged
  • door seals are in good condition
  • interlocks are working.

Also ensure that the oven is cleaned regularly to prevent build-up of food which might affect the seals.

New and developing technologies

In 2008 ICNIRP published a statement on emf-emitting new technologies - which includes information on a wide range of mobile communication and wireless technologies, and non-communication uses such as ground penetrating radar, medical MRI and wireless transport of electrical energy.

For in-house built equipment, measurements may be needed in order to ensure compliance with the Section on 'Exposure Limit Values and Action Levels' and the Section on 'Individuals at particular risk'. These must be considered carefully as part of the risk assessment.

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Useful references

Health Protection Agency

Health and Safety Executive (including links to the Regulations, guidance and exposure limits)

Safety Guidelines for Magnetic Resonance Imaging Equipment in Clinical Use

International Commission for Non-Ionising Radiation (including current guideline limits)

A list of MR "implants" (note the disclaimer)

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Warning Labels/Signs/Symbols

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Example Risk Assessment - NMR Equipment

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Example Screening Form - MRI

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Example NMR Training Record and Safety Screening Form

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