What power do TETRA handsets use and how does this compare with older analogue systems?
If a TETRA radio is awaiting or receiving a call the power is very low. When it is transmitting the power levels are typically up to 1.8 Watts and this could be reduced when handsets share time-slots on a base station, and/or when they are used near a base station. Adaptive power control adjusts the power output to the lowest level needed to maintain reliable communication with the base station. These factors mean that TETRA handsets operate at considerably lower power than the professional analogue radios that preceded the TETRA system.
Do TETRA handsets pulse?
TETRA portable radios pulse at 17.65Hz. Depending on the mode of use, up to four handsets can share one base station transmitter; with four sharing each transmits for 14 milliseconds, and is then silent for 42 milliseconds before it transmits again.
The handsets operate using very low power – up to 1.8 Watts; they emit RF only while the equipment is in transmit mode, which tends to be for very brief periods; and they use a feature called adaptive power control, which means that the radio continually adjusts its power output to the lowest level needed to maintain communication with the base station.
How are SARs measured?
The exposure standard for portable and mobile devices employs a unit of measurement known as the Specific Absorption Rate (SAR) which is measured in Watts per kilogram. The ICNIRP guidelines set a localised exposure limit for occupational use of 10 Watts per kilogram, averaged over 10 grams of body tissue. SAR measurements are generally calculated in a laboratory using a ‘phantom’ head or body which contains material of a similar density to that which would be found within the human body, and using probes to measure the level and distance that the heat penetrates.
Whilst there may be differences between the SAR levels of various devices, and variations depending on the way they are used and how they are carried or worn, all the products supplied by members of the TETRA Health Group comply with the ICNIRP guidelines for radio frequency exposure.
If TETRA radios are used in cars or on motorbikes is the user exposed to a higher level of RF?
Measurements have shown that if multiple occupants in vehicles all have TETRA handsets people experience the greatest exposure from their own handset because the power drops very rapidly with distance. It is advisable not to stand within a few centimetres of a vehicle mounted aerial for a period of time as in this circumstance exposure limits could be exceeded.
Measurements done on motorcycles using a 3 Watt antenna showed that if the antenna is more than 10cm away from the rider’s body, which is usually the arrangement, the exposure is not an issue. When the antenna was moved to within a few centimetres of the rider’s back during the study, measurements of around 0.5 Watt per Kg over 10g of body tissue were obtained. This is well within the exposure guidelines.
For more information on vehicle SAR measurements, look at Dr Phil Chadwick’s research (opens in a new window).
What effect does wearing a ear-piece have?
The exposure to RF from a TETRA handset is below guidelines in all points of the head when a handset is used, and less than that if an earpiece is used. There is a possibility that is a cable from an earpiece runs along a cheek the exposure can be greater than with a handset alone, but again, always within the limits set by the guidelines.
What if a TETRA handset is worn on a lapel or on a belt?
SAR measures were conducted by Dr Phil Chadwick using ‘phantoms’ with the TETRA handset worn on belts and lapels, with and without anti-stab vests. The localised results were 0.4 Watt per Kg when worn on a belt, and 0.2 Watt per Kg when worn on the lapel, both well within the exposure guidelines. The wearing of anti-stab vests reduced the exposure slightly when the radio was worn at the belt, probably as they move the antenna of the handset slightly away from the body, but did not affect the SAR when worn at the lapel.
Can there be audio problems or ‘spiking’ from TETRA handsets?
Some people experience a well known phenomenon called ‘microwave hearing’ at high intensities. In the early days of TETRA handsets there were adjustment issues and unpleasant spikes of noise were heard by some users. This must have been annoying but unlikely to cause a health effect.
Should covert users, who wear concealed devices on their bodies next to their skin, and sometimes transmit continuously for longer periods, be concerned about RF exposure?
No, laboratory testing has been carried out using various configurations of body-worn equipment using a body phantom. The results have demonstrated that exposure remains within occupational ICNIRP guidelines wherever the equipment is worn. There is no cumulative RF exposure effect from longer transmissions.
Will the use of ElectroDOT on TETRA terminals help mitigate the impact of radio frequency emissions on users?
From time to time a number of different products come onto the market making various claims about providing protection against radio-frequency or electrical emissions.
All the terminals and equipment manufactured and supplied by members of the TETRA Health Group comply with international guidelines that are fully supported by robust and rigorous scientific research and endorsed by the World Health Organisation (WHO). The members of the group do not therefore endorse the use of ElectroDOT or similar products.
ElectroDOT claims to combat ‘electro-pollution’ by adjusting the ‘vibes’ or emissions from electrical equipment. To the best of our knowledge there has been no independent scientific or health study to review these claims. Expert advice suggests that the alleged health effects that the product seeks to negate are not recognised by science and that the way the device operates does not seem to be based on the laws of physics.
What are the risks when using TETRA terminals at petrol stations?
- The risk is very low, but unless operationally vital it is good practice to switch off equipment, as is suggested for mobile phone users, or to put it into transmit inhibit mode before entering the petrol station (or other potentially explosive environment).
- It is the responsibility of site owners (petrol companies) and employers (of those using TETRA terminals) to make a risk assessment and establish a policy.
- For a vehicle-mounted terminal it should be possible to perform a risk assessment based on the position of the antenna mounting; for hand-held terminals the position is more variable.
- If an organisation undertakes regular operations within a petrol station environment or similar, consideration could be given to the use of intrinsically safe terminal equipment.
Are there any issues arising from using copy or cloned batteries?
Safety and operational issues have been identified with some batteries that have been copied (cloned) from those supplied by radio manufacturers. Users need to be aware of these issues so that they can make informed decisions. Examples of specific issues found by manufacturers when evaluating copy/cloned batteries include incorrect charge data, inadequate internal fusing, drop test failure and a reduced number of charging cycles resulting in reduced battery life. More information may be found in the associated pdf note – click here.
An article in the Irish Times on Tuesday 31 March 2015 suggested that the Association of Garda Sergeants and Inspectors, and individual Garda staff, had questioned the safety of TETRA hand-held terminals, in particular, is there an additive effect when used inside a vehicle or within a police station?
There is a wealth of peer-reviewed research concerning the radio-frequency emissions from handsets and whether this poses any health risk, and about whether using a handset or multiple handsets within a vehicle increases the exposure and hence the risk. Examples of the research available include studies which measure the radio-frequency emissions from handsets and compare them with international guidelines which measure the emissions from aerials used on cars and motor-cycles, and those from using multiple handsets within a vehicle.
The results of all these studies suggest that there is very little cause for concern. No additive effects have been found.
Dr Phil Chadwick has researched the effects of using TETRA terminals in vehicles and his full report can be found here (opens in new window). A presentation given by Dr Chadwick at a THG seminar in 2007 can be found here (opens in a new window).
What are the implications of the Control of Electromagnetic Fields at Work Regulations 2016 (“the CEMFAW Regulations”)?
Employers have a duty to take reasonable steps to prevent harm in the workplace and this duty includes considering any risks arising from exposure to electromagnetic fields (EMFs).
Employers’ duties under the CEMFAW Regulations, which came into force on 1st July 2016, are explained in a guide issued by the Health and Safety Executive (HSG281). This guide may be viewed here and the Regulations themselves, Statutory Instrument 2016 No. 588, may be viewed here.