Electromagnetic fields are present everywhere in our environment and the proliferation of man-made sources, such as radio waves, has become a serious concern. Imminent legislation will require employers to ensure their workforce is not exposed to potentially dangerous levels, as Howard Venning explains.
Less than two years from now, the European EMF directive will come into force. The Physical Agents (Electromagnetic Fields) Directive,1 to give it its official title, specifically applies to work activities where workers are exposed to risks from electromagnetic fields.2
The detail of the directive is expected to be finalised in the very near future, ready for adoption in April 2012. For those employers already meeting their legal responsibilities in terms of EMF, it should have little impact as the UK (along with several other countries) has already adopted the guidelines produced by the International Commission on Non-Ionising Radiation Protection (ICNIRP).
However, the new directive, once incorporated into UK law, will require a formalised approach, placing a number of explicit duties on UK employers. The key impacts are duties on the employer to conduct a risk assessment and calculate (i.e. measure) EMF strengths, and to ensure the risk of exposure is maintained below the specified ELV (Exposure Limit Values).
Radio and spectrum use
The electromagnetic spectrum can be divided, in terms of frequency, into two principal areas: ionising and non-ionising radiation. At the high-frequency end of the spectrum, ionising radiation is associated with applications such as x-rays and, ultimately, nuclear reactors and weapons, and radioactive substances. Essentially, ionising radiation can pass through the body tissues and cause damage at molecular level.
The subject of the EMF directive, however, is non-ionising radiation. This covers the spectrum from static electric and magnetic fields, through radio frequency (RF) and microwave frequencies, to infrared and ultraviolet light.3 Non-ionising radiation does not cause changes at the molecular level, but the body does absorb RF energy. There has long been concern that there may be, as yet undetected, health effects, especially over the long term. With the rapid growth in the deployment of RF technology, that concern is increasing.
Extensive studies over many years worldwide have not found any evidence of adverse health problems due to prolonged exposure,4 yet some gaps in knowledge requiring further research have persuaded the authorities to recommend a ‘precautionary approach’. Hence, the EMF directive.
Devices operating at the lower end of the spectrum are deemed to be a lower risk than high-frequency applications. All electrical appliances and most motor-driven equipment (TVs, fridges, hairdryers, power tools, etc.) emit low levels of non-ionising radiation. Moving up the spectrum, there is radio and wireless-operated equipment, microwave ovens and, especially, mobile phones. In most cases, devices rely implicitly on these RF emissions to operate. The table opposite shows frequency against the common name for each transmission type. While this does not list every radio transmission (and many frequencies are allocated for military applications) it does list those that account for the majority of EMF sources currently installed in the UK.
Today, radio (wireless) communications are becoming ubiquitous, as society moves towards an ‘always on, always connected’ lifestyle. Thanks to advanced technology, mobile phones and other portable devices are now ‘Internet-enabled’, fitted with multiple radios for Bluetooth, WiFi data, and voice communications. Wireless technology is stimulating new applications in environmental monitoring, revolutionising the health-care sector and revitalising the security industry. Consequently, the number of radio transmitters deployed in the UK is increasing dramatically, and concern is mounting about the cumulative effect of so many EMF sources in the workplace.
The band of interest
The band that has seen, and will continue to see, the greatest growth over the next few years is RF, with signals in the region 100kHz to 3GHz. Consider the devices and appliances that surround us today in our homes and places of work, such as mobile phones, DECT and cordless phones, wireless LAN routers, security devices, and industrial equipment, such as microwave ovens and microwave (diathermy) heating equipment. Consider also the radio, TV, mobile-phone and microwave transmitters, base stations, electricity sub-stations, and other major installations in the locality.
Commercial TV and radio are expanding, with DAB radio and digital TV. Mobile radio includes dedicated services such as the new police, fire and ambulance system, TETRA. Cellphone networks and wireless LANs are experiencing by far the greatest growth, especially with the increasing deployment of ‘pico’ and ‘femto’ cells. This convergence of 3G and fixed-line communications and wireless data communications is effectively bringing base stations into homes and offices. They may be lower power, but they are yet another EMF source.
Identifying the risk
The work needed to identify all possible transmitters in your location can be time-consuming. When undertaking risk assessment you should consider all sources of EMF installed in and around your premises, such as wireless LAN routers, DECT cordless telephone repeaters, and security systems. Consider also, if applicable, any industrial plant, building automation, or other systems under your control that incorporate radio transmitters and/or are known to work at radio frequencies.
You should then assess your proximity to external sources of RF transmissions, such as cellular radio base stations, radio and TV transmitters, and other communications masts. Consider your proximity to high-risk sites such as airports, military bases and industrial sites known to use radio-frequency plant. Note that in the UK, the location of mobile communications transmitters is documented and freely available.5
The next step is to conduct a survey of your premises to establish actual levels of EMFs. The directive will specify the maximum Exposure Limit Values (ELVs, which depend on frequency) to which employees can be exposed. However, some local authorities have set their own, more stringent safety levels. For example, Cambridge Council, in consultation with telecoms operators and based on figures from continuous monitoring, has stated in its Telecoms Action Plan that “[e]missions from installations on council-owned properties do not exceed 3V/m”.6 This is considerably lower than the 41V/m limit set by ICNIRP for this frequency.
Making measurements
EMF levels should be measured at various locations in and around your premises, with the results being recorded and added to the overall risk assessment report. You should concentrate on locations where most people work, and areas of potential risk, where some members of staff spend a significant part of their working day.
Measuring EMFs is a relatively straightforward process; however, it does require specialist equipment and knowledge on how to use it. There are three basic measurement methods available, each involving different instruments: spectrum analysers, measuring receivers and field-strength meters.
While all three are capable of measuring field strength, not all of them were originally designed with health and safety monitoring in mind. For example, equipment designed to help broadcast engineers ensure their transmitter is operating correctly over the required area might not be the most appropriate for an employer who needs to take measurements in the workplace to ensure compliance with current legislation.
The key criteria for general EMF monitoring must be ease of use, and the provision of results in line with the applicable standards. Spectrum analysis and measuring receivers require a relatively high level of knowledge of RF signals, together with detailed training on how to operate the necessary equipment.
Spectrum analysers
These concern the level of received signals versus frequency. Instruments are available from many suppliers, and range in price and complexity. Most are general-purpose units designed for use in the field, or in the laboratory and cover a wide range of radio-frequency bands. When used with a suitable antenna and properly calibrated, they can provide readings in recognisable field-strength units, e.g. V/m or µW/cm2. Data from many spectrum analysers can be uploaded to a PC or laptop and analysed with signal-processing software to give a highly-detailed analysis of the frequency spectrum.
Measurement receivers
Effectively, these are calibrated to be high-precision, laboratory-style radio receivers designed to measure the characteristics of radio signals. They may be, in some cases, more accurate and able to perform more detailed signal analysis than spectrum analysers. However, their use is typically in laboratory applications – for R&D and for product-compliance testing of specialist radio-communications equipment.
Field-strength meters
For making measurements in the field (or workplace), and to assess ambient levels of EMF signals with respect to safety standards, the most common method is to use an RF field-strength meter. Instruments are typically available with a range of antennae or probes to provide an accurate measurement of the level of EMF in that location, across a broad band of frequencies. This hand-held portable equipment can be mounted on a tripod, or other suitable stand, so that measurements can be made without being shielded by the operator, and at varying heights (as specified by the Directive). The field-strength values are displayed in V/m for easy reference, and recorded. The Directive requires that instruments measure and average over six minutes.
The latest measuring equipment is fitted with integral GPS receiver and data-logging facilities. This allows the operator to conduct surveys with just one piece of equipment, from which results can be downloaded when back in the office for further comparison, or analysis and incorporation into reports.
Longer-term strategy
Once the initial measurement survey methodology has been established, and the baseline figures recorded, long-term strategy should be considered. This will depend somewhat on the first results. Should any EMF levels be found to be above those specified, action must be taken to reduce exposure. What this action is, very much depends on the source, and how much control you have over it. Practically speaking, this is the time to call in the experts.
Where EMF levels are close to the ELVs specified by the Directive (or local plan), then a system that constantly monitors these levels is recommended. Such systems are typically fitted with alarms that can advise when reference levels are exceeded. In addition, monitoring equipment will typically log results over an extended period of time.
This sort of monitoring system is already installed in some countries in Europe. An example of how this operates effectively is where a local mobile-phone operator’s base station was measured as transmitting higher-than-permitted power levels. The base station power output was turned down and the continuous monitoring system was able to record the resulting impact. An example of these results is shown in the graph below.
If, during the initial survey, the EMF levels are well below the ELVs, then simply maintain a ‘watching brief’. Any new radio-frequency equipment installed within your premises should be noted and checked for compliance with current legislation, and that it is correctly installed and positioned to minimise employee exposure. Be aware of any new sources of EMF (e.g. radio transmitters) that are installed close to your premises. While such installations should themselves be compliant with the legislation in force, employers are responsible for ensuring their workforce is not at risk. Be aware also that old equipment can degrade, so EMF levels may change, even if the installed equipment remains the same.
Regular surveys will identify the impact of new equipment or installations, and detect any changes to malfunctioning equipment. Depending on your situation these might be conducted annually, or every two years.
In summary, for most situations, compliance with the EMF Directive is relatively simple and inexpensive. Efficient, dedicated EMF measurements systems are readily available and easy to use and, for those employers that do not have the resources to perform assessments in-house, external assessors can be engaged.
References
1 www.hse.gov.uk/radiation/nonionising/l184emf.pdf
2 www.hse.gov.uk/radiation/nonionising/ electro.htm
3 www.hse.gov.uk/radiation/nonionising/ index.htm
4 www.who.int/pehemf/about/WhatisEMF/en/ index1.html
5 www.sitefinder.ofcom.org.uk
6 www.cambridge.gov.uk/ccm/content/planning-and-building-control/development control/telecommunications.en
Howard Venning has worked in radio-frequency engineering for more than 35 years.
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Another largely pointless directive which will be as badly worded as the optical radiation regulations I would imagine.
Surely the thing to do about this is make regulation specific to the hazard (anyone who operates, installs or maintains radio transmitters in a specified frequency over a specified power) so that the rest of us who use only low power equipment can simply state “not applicable”.
I’m no expert on this but
DIRECTIVE 2004/40/EC says
1. In carrying out the obligations laid down in Articles 6(3) and 9(1)
of Directive 89/391/EEC, the employer shall assess and, if necessary,
measure and/or calculate the levels of electromagnetic fields to which
workers are exposed
Howard Vennings article doesnt mention the phrase “if necessary”. I havent heard that EU have modified the directive yet following the delayed implementation date. So its not at all clear that the duties described in this article will eventually come into UK legislation.