non-ionising radiation -- uk health and safety for rf and non-ionising radiation

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January 1, 2012

RF safety BY JULIA CLARK

Britain’s powerful terrestrial broadcast transmitters, such as London's iconic CrystalPalace tower, deliver television and radio signals to millions of homes across the country.

Arqiva owns, operates and maintains these landmarks of British broadcasting, with ahistory that can be traced back to the early years of the BBC. Although the company wasconceived more than 50 years ago, the service-level agreements with the broadcasters -and the expectations of the general public - now require these towers to broadcast 99.99percent of the time, and to 99 percent of the British population.

The company's experience and expertise in broadcast engineering enable it to maintainsuch stringent service levels, but with high power comes great responsibility to ensure

the well-being of its field operatives. Although they do not pose a threat to the generalpublic, at close range these broadcast transmitters emit significantly high levels ofnonionizing radiation, meaning Arqiva engineers are exposed to power levels that areextremely close to safety guidelines.

The mobile phone masts dotted around the country require the same precautions, but ingeneral, these are no major issue. They operate at a relatively low power of 60W to120W - a small fraction of what is actually permitted. Compare this to the Sutton Coldfieldtransmitter, which has for many years been operating at 1000kW for analog televisionand 250kW for FM radio. The radio frequencies used for broadcast TV and radio sharethe thermal range of the electromagnetic spectrum with microwaves, and the humanbody absorbs this energy more readily than any other part of the spectrum. With thatsaid, I need hardly spell out the dangers of climbing a broadcast mast with an antenna

operating at full power.

National service

In order to meet its stringent service agreements, Arqiva needs to operate at full poweras much as possible. It uses a simple hierarchy of control to manage health and safety,with each successive control growing weaker. The most stringent control, of course, is todesign the antenna to be safe to climb through on full power, which the communicationscompany has done with the new antennas it has switched over to digital. The majority ofits older masts were not designed this way, however. The second control would be toturn off a transmitter while working near its antenna. Unfortunately, that simply is notsomething the company's service agreements usually allow, so the next stage is toimplement engineering controls. The most important of these is to reduce the antenna's

power, rather than turning it off. Major work in close proximity to the antenna requires amore significant decrease in power. To change a structure's mast lights, for example, thecompany would need to drop the power significantly, as the task requires engineers toclimb right through and past the high-power antennas.

Even then, the engineers must be suitably prepared. Engineering controls may alsoinclude surveying and adding permanent or temporary screening to the mast. Arqiva'sexperience has enabled it to take the lead in devising a safe and fact-based set ofguidelines for its workers; despite the dangers, the United Kingdom currently has nolegislation for managing RF. Everything falls back on the Health and Safety at Work Act



1974 and general management regulations that require risk assessments to becompleted. From the point of view of a health and safety executive (HSE), as long ascompanies follow the guidelines set by the International Commission for Non-IonizingRadiation Protection (ICNIRP), they are doing the right thing.

Measuring the immeasurable

ICNIRP is a body that publishes world-standard safety guidelines for radio frequencies aspart of its guidance for the whole nonionizing radiation spectrum. A few countries dosomething different, but most countries base their safety guidelines on ICNIRP. Everyfrequency range has a basic restriction, but this is usually in a form that is impossible tomeasure technically in a working situation. One example is SAR, which stands forSpecific Absorption Rate and is quoted in terms of watts per kilogram of human tissue.

Mobile phone users may have seen "SAR" referred to in their phone's manual. Simplyput, this is based on how much heat a device emits into a human head. However, there isno current way to measure this using the human body in real time - so devices such asmobile phones are SAR tested in a lab using a "phantom." This is a head-shaped mouldcontaining liquid that is used to simulate human tissue. A sensitive probe is thenrobotically moved around within the phantom with readings taken in different places. This

might be a reasonable test for mobile phone manufacturers in carefully controlledconditions, but it is difficult to translate this testing method to human beings working on abroadcast tower.

Because of this, ICNIRP also publishes "reference levels," known as "action values" inthe EU directive. These are levels stated in terms of quantities that can be measured, forexample, using professional survey meters to measure electric and magnetic fields orpower density. If the company meets that level, it is guaranteed to be compliant with thebasic restrictions. If it knows, for example, that it needs to be operating at less than61V/m and it receives a reading of 50V/m, then it knows it can proceed safely. However,that doesn't mean that if levels of 70V/m are reached, the company has endangered itsworkforce. It simply means that the organization has to do more work to demonstrate thatthis higher level still results in compliance with the safety standard. This can be done by

referencing published dosimetry information carried out by organizations such as theradiation protection division of the Health Protection Agency.

Tools of the trade

Test equipment has improved dramatically over the last fewyears. The company previously used devices without isotropicprobes - meaning that readings were highly directional. Engineersalso would need to contort their wrists in every angle possible inorder to get a maximum reading for the area from a probe, whichwas far from ideal - as was reading that maximum from a needleon a gauge rather than from a digital readout.

The company now employs two pieces of high-tech measuringequipment: the Nardalert XT RF personal monitor and the NardaNBM-550 broadband field meter. The latter is equipped with amultidirectional isotropic probe, which provides a reasonablyaccurate numerical measure of RF levels measured in V/m (for

the electric field) or A/m (for the magnetic field) in order to establish safe zones andmeasure field strengths to comply with ICNIRP guidelines. It is a reliable and importanttool but, due to its size and visual requirement, engineers are protected only while theyare staring at its screen. Because of this, all company engineers are required to wear aNardalert XT RF personal monitor. About the size of a cigarette packet, this clips to a



climbing harness, providing an audible alert and vibration when the engineer reaches 50percent of the reference level and a different audible alert at 90 percent. The company'sspecialist RF surveyors take careful note of the readings, and their RF survey reports aremade available to others who need to plan work on the structure.

Arqiva has invested money and time into the study of RF emissions, and its researchdemonstrates that, generally, its engineers can safely work above reference levels and

still meet basic restrictions. It only does this occasionally, and only if it has explored allother possible avenues such as power reductions; working within reference levels makesfor a simpler working regime.

As head of RF safety at Arqiva, I, or my deputy, have to approve every request tooperate above reference levels. In this sort of situation, the company safety team willoften employ further personal protective equipment such as RF protective suits. Theseare not widely used in the United Kingdom because they limit movement, but they areemployed by the communications company when it is faced with a situation in which allother avenues of control have been explored and the safety team still feels a greaterfactor of safety is needed. For these projects - and the previous example of changing themast lights comes into this category - I will always send one of my team to be solelyresponsible for overseeing RF safety throughout a job of this kind, leaving the other

engineers to focus on their primary task, such as re-engineering the lights while thesafety team checks and records the RF levels to which everyone is exposed.

Arqiva's ongoing research into RF has enabled it to lend significant insight into theEuropean Commission's proposal to revamp rules protecting EU workers from harmfulelectromagnetic fields. This directive covered the entire nonionizing electromagneticspectrum, including much lower frequency such as that employed in MagneticResonance Imaging (MRI) as well as the higher frequency used in broadcasting. Firstpublished in 2004, the directive should have been implemented in 2008 but wasdismissed due to its unnecessarily stringent regulation at lower frequencies. Thecompany assisted in the revision of the current version, working closely with the U.K.HSE and the EU to demonstrate that many of the proposed restrictions had no scientificfoundation and to ensure that the resulting regulation was practical to implement.

Training for safety

The final, yet most important, control is simply training, assessment and information. Anywork the company performs is meticulously planned, and it ensures that any contractors,as well as its own engineers, are trained to an extremely high level of RF awareness. Itmakes clear what the risks are and how to avoid them with sensible use of RF personalmonitors. It is my belief that Arqiva's exemplary safety record is not attributable to thehardware it uses nor the levels and restrictions it abides by, but rather, it is in thecompany's dedication to training its staff to react knowledgeably and safely to any givensituation.

Julia Clark is head of RF safety at Arqiva.

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