RF from Radio Towers


NEBOSH diploma questions are written to ensure that candidates don’t just have knowledge of a wide range of safety topics, but that they can also demonstrate that they can apply that knowledge. This means that they’ll often face questions about particular scenarios which they haven’t personally come across before. Students are not expected to have learnt about every possible situation or scenario that could arise, but are expected to be able to apply their knowledge to novel situations, working from first principles. They have to apply basic health and safety principles in their answer, giving enough specific detail to show that they have understood the issues associated with that particular scenario. Although hazards in a dentist’s surgery are not specifically mentioned in the syllabus, a question based on this has been used a few times. Very few of us will have actually done a risk assessment for a dentist, but as we have all sat in the chair we have some knowledge of the environment and we can apply basic principles to come up with a range of relevant health and safety issues.

There was a question set about radiofrequency (RF) radiation from telecommunications broadcast towers a couple of years ago, which caused problems for a lot of students who were put off by what seemed to be a specialist subject. RF radiation is one of the various types of non-ionising radiation in the syllabus, and so knowledge of a range of RF producers is expected. A good answer could therefore be devised by applying basic non-ionising radiation protection principles, as we have all seen radio masts and towers on top of hills – in fact they are a very common sight around the countryside.

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Applying basic principles gives us a basic list (isolation, time, distance, shielding, competence, monitoring, permits to work, signage) to which we can add scenario specific detail to get a good answer.

Isolation – anti-climbing devices on the tower, such as barriers, and lockable or removable ladders. Switch off power to work on aerials. Use of lock off systems and tags.

Time – exposure levels limited to international standards. Power reductions if working within exclusion zone of live aerials.

Distance – securely fenced site with authorised access only. Aerials located at height facing out from the tower. Feeder cables in underground duct or on overhead gantry to protect from damage.

Shielding – not commonly used apart from use of directional aerials and exclusion zones for workers.

Competence – trained, experienced, supervised workers, subject to medical surveillance (fitness for work in remote/hazardous location).

Monitoring – measurement of RF field levels at site perimeter, measurement of radiation pattern for whole site, personal field radiation alarms/monitors for workers.

Permits to work – for all work on the mast or tower.

Signage – for public at site perimeter, and on each antenna for workers.

Applying these basic principles has enabled us to produce a list of ways in which RF exposure for both workers and the general public can be controlled, but students must make sure that they give enough detail to show that they understand how they are actually applied in this specific scenario.

Of course, the enthusiastic health and safety practitioner will want to know more than the minimum information needed to answer an exam question, so here are some sources of further information:

In the UK, there is a trade association called the Mast and Towers Safety Group, which produces a number of online publications covering best practice in the industry:

http://www.matsgroup.info/index.html

Public Health England gives information about aerial positioning, radiation patterns and recommended maximum exposure levels:

https://www.gov.uk/government/publications/mobile-phone-base-stations-radio-waves-and-health/mobile-phone-base-stations-radio-waves-and-health

Exposure guidelines are based on levels set by the International Commission on Non-Ionizing Radiation Protection (ICNIRP). Reference levels are given in power densities and are set for whole body exposure, and vary according to the radiation frequency. There are different reference levels for workers and members of the public (which includes vulnerable groups). Reference levels are based mainly on short term heating effects with Specific Absorption Rates averaged over a 6 minute period:

http://www.icnirp.org/en/home/index.html


Kim Batten