The answer, most of the time, is zero.
- Radio waves are not 'ionising radiation' which could be dangerous at fairly low power levels.
- Radio waves in general pass through living things, with only a very small percentage of the energy being absorbed. The few transmitters which are powerful enough to be dangerous are surrounded by security fences to keep people at a safe dictance.
- There is a frequency in the low microwave region (just above 2GHz) which is strongly absorbed by molecules of water. This frequency can be produced in dangerous quantities by specially built magnetrons, and anything containing water can be boiled after a fairly brief exposure to the output from one of these. There are lots of these about, all safely shut up inside microwave ovens.
