Exposure to radio frequency (RF) fields from mobile devices is measured using the specific absorption rate (SAR) – the amount of energy from an RF field absorbed by the human body, expressed as watts per kilogram (W/kg).
SAR is the accepted international measure of exposure to electromagnetic fields, and the SAR value determined under standardised test conditions for a particular mobile is provided in the product safety information when it is bought. Many manufacturers also make this information available on their own website or the Mobile Manufacturers Forum website http://www.mmfai.org/public/sar.cfm.
The International Commission for Non-Ionizing Radiation Protection (ICNIRP) guidelines http://www.icnirp.org/documents/emfgdl.pdf recommend a maximum SAR value of 2W/kg for a mobile. All mobiles operating below this level are considered safe to use. Some countries such as Canada, South Korea and the United States have adopted slightly lower SAR limits of 1.6W/kg for the head and the trunk. Mobiles are tested to ensure compliance with the SAR limit for the countries where they are sold.
The United States' Federal Communications Commission (FCC) explains what SAR values mean in its consumer factsheet. http://transition.fcc.gov/cgb/consumerfacts/sar.html . This factsheet states that:
“While SAR values are an important tool in judging the maximum possible exposure to RF energy from a particular model of cell phone, a single SAR value does not provide sufficient information about the amount of RF exposure under typical usage conditions to reliably compare individual cell phone models.”
The level of exposure depends on the distance between the person and the mobile and the amount of RF power the mobile transmits. Mobiles always use the minimum amount of energy to provide a service, so actual exposure varies continually depending on a range of factors:
• The distance between the person and the mobile device
RF fields are much weaker even a short distance from a mobile. Keeping the mobile away from the body by using an earpiece or loudspeaker function will significantly reduce exposure.
• The distance from the base station
The signal from a base station becomes weaker the further away the mobile is, meaning the RF field strength from the mobile must increase so it can still communicate with the base station.
• The landscape between the user and the base station
If there is a building, hill or other obstruction between the mobile and the base station, the signal from the base station may also be weaker.
• The service being used
Making a voice call from a mobile leads to greater exposure to RF fields than texts, emails, pictures, web, TV and downloads. This is because voice calls are generally made with the mobile next to the head, while it is held away from the body when sending texts and emails and watching TV. Calls also take longer than sending texts and emails, again increasing exposure.
Vodafone continues to require manufacturers to test the amount of energy from a radio frequency (RF) field absorbed by the human body – the specific absorption rate (SAR) of mobile devices – when used against the ear or near the body.
The International Electrotechnical Commission http://www.iec.ch/index.htm (IEC) standard for testing mobile device use close to the body was published in April 2010, but has not yet been incorporated into EU Regulations. We have been actively advocating its adoption at a European level. Until this happens, we will continue to require testing using the FCC methodology.