The SAR value is often mentioned in regard to mobile phones and exposure of users to electromagnetic fields emitted from wireless devices.
SAR stands for Specific Absorption Rate, where “specific” indicates the quantity of tissue mass, “absorption” the amount of electromagnetic energy absorbed into that mass and “rate” indicates the rate of time at which this is happening.
The use of SAR as a value to assess exposure from electromagnetic fields was first discussed in 1975 and was officially adopted in the ANSI C95.1-1982 standard.
This standard established the whole-body SAR of 4 W/kg as a threshold - which was then divided by 10 for a whole-body exposure limit for workers (0.4W/kg) and divided by a further factor of 5 to create a whole-body limit for the general public (0.08 W/kg).
These reduction factors - also commonly referred to as ‘safety margins’ - have been maintained in subsequent updates to the standard and are also reflected in the ICNIPR guidelines, which the majority of countries in the world base their exposure limits on.