So most of the time, you would be exposed to very little of that power. That's why people spend big bucks for the big antennae, to get the power sent where it is needed.
Just don't spend too much time in the direct line between them and whatever they are aimed at.
I used to do that. I trained at Little Black Mtn. in Ranco Penesquitas west of San Diego. Had a massive comm tower. The idea was to take a thermal over the top of the towers which I did on a number of occassions.