SC39 - Static magnetic fields
17 Jun 2011



Working with Static magnetic fields




PDF icon Print PDF version

BiteSize SHE BiteSize SH​E (online code summary)



Initial launch
March 2011
1.1Amendments to au​dit checklistMay 2013
Add Document Retention Policy Appendix
August 2014
Updated to comply with European Directive 2013/35/EU and HSE Consultation Document CD276 and audit findings.

November 2016 

​Minor changes to reflect the launch of SHE Assure
​October 2018
​​Update following static fields audit and Control of Electromagnetic Fields at Work Regulations 2016 by PHE and reviewed by internal STFC subject specialists.
March 2021​

NB - The changes to version 3.0 were considerable and readers should assume that significant portions of the body and Appendices have changed.

1. Purpose

Static magnetic fields are used in a range of applications across the STFC sites, for example superconducting magnets in ISIS sample environments, or the permanent magnets in particle physics experiments and accelerator wigglers or undulators. The code aims to minimise so far as is reasonably practicable, the health and safety risks to staff and other persons who may be adversely affected by strong static magnetic fields.

People can experience vertigo and other physiological effects relating to balance when an individual’s head and trunk moves within a strong static magnetic field. Moreover, very strong fields may affect the cardiovascular system. However, the main hazards to people associated with such fields comes from their influence on active medical devices and their ability to attract magnetisable objects at distance and speed, see Appendix 1.

This code sets out the arrangements adopted by STFC to achieve compliance with the Control of Electromagnetic Fields at Work Regulations 2016​.

2. Scope

This code is applicable to all staff, contractors, users and tenants working with strong static magnetic fields at STFC sites.

This code applies to all static and quasi static magnetic fields (from 0 to <1Hz) which extend into areas readily accessible to people and applies to all such fields on all STFC sites irrespective of ownership of the apparatus generating the fields. It applies to both electrically generated fields, including superconducting magnetic fields, and those produced by permanent magnets. It does not address the changes arising from a quenched/collapsing static magnetic field.

This code is not intended to cover every piece of equipment in which magnetic fields are present. For example, the code is not intended to apply to electric motors, loudspeakers and magnetrons in normal use. However, if strong magnets from such pieces of equipment were removed and made into an assembly for some new purpose generating a magnetic field extending into areas readily accessible to people then this code would apply.

This code does not address the hazards associated with time varying electro-magnetic fields, see STFC SHE Code 23: Working with time-varying EMFs.

3. Definitions

3.1 Exposure limits

Exposure limit values are specified for frequencies from 0 Hz to 1 Hz and are intended to protect employees from the direct adverse effects of exposure. It is a legal requirement to comply with the exposure limit values, subject to certain specific exceptions. Further details of exposure limit values are given in Appendix 2.

In addition, there are action levels that are intended to prevent or limit the consequences of specified indirect adverse effects. See Appendix 2 for further details of action levels. These are not legal limits, but should be used as a guide to managing risks arising from indirect effects.

4. Responsibilities

4.1 ​Directors responsible for activities employing strong sources of static magnetic fields shall:
  • 4.1.1 Appoint in writing one or more suitably qualified and experienced EMF Protection Advisers (EPA) for those areas housing equipment generating strong static magnetic fields. The letter of appointment should define the geographic and equipment scope of their responsibility and should be recorded in SHE Directory. It would be normal for the technical manager responsible for the day-to-day operation of the equipment to be appointed the EPA.
4.2 Managers responsible for sources of static magnetic fields stronger than 0.5mT (5 Gauss) whose field extends in permissible and accessible areas shall:
  • 4.2.1 Ensure that exposure assessments or surveys are carried out for equipment and activities in areas under their control. Ensure that only suitably calibrated monitoring equipment is used to measure strong static magnetic fields and to determine compliance with the exposure limit values and action levels.
  • 4.2.2 Ensure that no equipment capable of generating strong static magnetic fields is brought into their areas of responsibility, including equipment provided by visitors, facility users, contractors etc., until the advice of the EPA has been sought and the manager has approved it and suitable controls have been put in place
  • 4.2.3 Where equipment generating strong static magnetic fields is designed and constructed in house, ensure that accessible fields are considered in the context of the exposure limit values and action levels and the advice of the EPA sought.
  • 4.2.4 Ensure that documented risk assessments address the hazards from static magnetic fields, see Appendix 1, SHE code 6 Risk Management. Such risk assessments must be undertaken by individuals with sufficient expertise in such hazards (see Appendix 1), and must be based upon an assessment of the magnetic field, derived as appropriate from: field calculations; from manufacturer’s guidance; or from a site survey of the field contours using a calibrated gaussmeter. Where accessible fields exceed the action level for interference with active implanted medical devices, an EMF-specific risk assessment will be required (see Appendix 4) with the advice of the EPA. Implement the controls detailed in the risk assessment including but not limited to installing signage, barriers, floor markings etc
  • 4.2.5 Locate warning signs at all entrances to areas containing magnetic fields with strengths greater than 0.5mT (5 Gauss) where the field extends into permissible and accessible areas and able to achieve full body exposure, see Appendix 4
  • 4.2.6 The barriers, or floor marks, should define a zone outside which the magnetic field is less than 3mT (<30 Gauss) in order to delineate the boundary where magnetisable materials such as tools may be accelerated and present projectile hazards, see Appendix 1a. Specific consideration should be given to the rate of change of the field with distance above 30 Gauss
In addition for static magnetic fields, >0.1T (1000 Gauss)
  • 4.2.7 Where equipment incorporating strong permanent magnets is employed the specific risk assessment must address the movement of magnet and all such equipment constrained appropriately.
  • 4.2.8 Develop and implement documented local procedures for the safe operation of equipment generating the static magnetic fields, see Appendix 1.
  • 4.2.9 Ensure that only sufficiently competent people are authorised to operate equipment and work in the areas where strong static magnetic fields are present, and that they are aware of the hazards, risk assessments and local procedures for the safe operation of equipment generating static magnetic fields.
  • 4.2.10 ​The magnetic field hazards arising from the quenching of superconducting static magnet fields should always be subject to a risk assessment alongside related hazards such as asphyxiation from escaping cryogens, and suddenly varying forces.
4.3 EMF Protection Advisers​ (EPA) shall:
  • 4.3.1 Provide advice to management on the need to undertake specific static magnetic exposure assessments on equipment or activities for which they have been appointed. EPAs should not provide advice for equipment that they are solely responsible for and should seek the advice of another independent EPA.
  • 4.3.2 Provide advice to management responsible for sources of strong static magnetic fields on technical modifications, changes to work practices or engineering controls that could eliminate static magnetic field hazards or minimise their impact so far as reasonably practicable, including the use of signage or other warning mechanisms where appropriate.
  • 4.3.3 Where exposure or risk assessments identify the potential for hazardous exposures advise on required controls. Specific consideration should be given to undertaking field measurements following any changes that could reasonably be expected to affect the strength or spatial distribution of fields. Surveys should be documented and identify all areas above the action levels or exposure limit values.
4.4 STFC Staff, visitors, facility users, tenants and contractors shall:
  • 4.4.1 Comply with the local procedures for the safe operation of equipment which is capable of generating strong static magnetic fields.

  • 4.4.2 Ensure, if any one of them has 
    • an active implanted medical device such as a cardiac pacemaker, implanted cardiac defibrillator, neuro stimulator, or cochlea implant; or​
    • body-worn active medical device, such as a hormone infusion pump a passive ferromagnetic implant, such as an artificial joint, surgical pin, aneurysm clip, metal surgical clip, stent, heart valve prosthesis, annuloplasty ring, contraceptive implant, active implant, or metallic dental implant.​
  • that he or she informs his or her manager or other person responsible for his or her safety before entering an area where static magnetic fields greater than 0.5 mT (5 gauss) are present in the working environment. Anyone with an implanted medical device may wish to contact Occupational Health or the SHE Group for advice on the likely sensitivity of the implanted medical device to magnetic fields.

  • 4.4.3 Report all incidents relating to strong static magnetic fields through SHE Assure following SHE Code 5 - Incident Reporting and Investigation.​
4.5 Occupational Health Advisers shall:
  • 4.5.1 Provide advice for anyone with an active implanted medical device, body-worn active medical device, or passive ferromagnetic implant.

5. References

6. Technical definitions

6.1 Exposure assessment

Like all employers/personnel, STFC has a duty under the regulations to carry out exposure assessments and record the results. It may not be necessary to measure or calculate exposure and the first approach should always be to consult any information supplied by a manufacturer or supplier. Appendix 3 provides a non-exhaustive list of some equipment that may require assessment.

In contrast, any equipment with a ‘yes’ in the first column should be subject to a specific assessment to determine if exposures comply with the exposure limit values specified in the regulations (see below).

An action plan is required if the exposure assessment does not demonstrate that exposures are below the exposure limit values. This must include some or all of the items in the first part of Appendix 5.

6.2 Risk assessment

There is a legal requirement to carry out an EMF-specific risk assessment if any of the following apply:

  • it cannot be demonstrated that the exposure limit values will not be exceeded; or
  • it cannot be demonstrated that the indirect effects action levels will not be exceeded; or
  • there are employees at particular medical risk in the workplace, see 6.3.

An EMF-specific risk assessment must address the matters listed in Appendix 4.

Any risks identified in the EMF-specific risk assessment must be either completely eliminated or reduced to an acceptable minimum.

Anyone who may be exposed to risks identified in the EMF-specific risk assessment must be provided with information and training (see second part of Appendix 6).

6.3 Employees at particular risk

Some people are at increased risk from exposure to strong static magnetic fields and may not be adequately protected by the exposure limit values. In the regulations, these people are called ‘employees at particular risk’ (see Section 4) and there is a specific requirement to consider them in the EMF-specific risk assessment. Those at particular risk from exposure to strong static magnetic fields are likely to include people reliant on an implanted or body worn active medical device, and those with passive ferromagnetic implants (see Appendix 1 for details of typical devices). It may be assumed that if exposures do not exceed the action level for interference with active implanted medical devices, then there will be no increased risk and no further action is necessary.

6.4 Medical assessment

If any person is exposed above the exposure limit value for static magnetic fields and reports experiencing a health effect as a result of the exposure, then they must be provided with a medical assessment. A record of the assessment must be retained.

Contact: Baker, Gareth (STFC,DL,COO)