The Lake Washington Ham Club of Kirkland, WA has posted a great tool you can use to determine safe limits of RF exposure given various parameters including operating power, mode, transmit time, antenna gain, and operating frequency. Check out the tool here.
The Javascript contained on this page was derived from a public domain BASIC program written by Wayne Overbeck N6NB and published in the January, 1997 issue of CQ VHF, p. 33.