I'll try to explain some of this.
For cellphone towers, the appropriate exposure limits are expressed in terms of a field intensity. Usually it's measured in watts per square metre. The Safety Code 6 limit for the general public is 10 watts per square metre.
I hope some of my other colleagues will speak up, if they know more of this technically.
Studies have shown--Industry Canada actually does measurements in the area--that the exposure limits are very much less than the safety code standard. The whole body is exposed to RF energy, and the power density is used for evaluation of exposures. Recent surveys have indicated that the exposures from cellphone towers in publicly accessible areas are normally 1,000 times below the international exposure standard or the Safety Code 6 standard: 1,000 times below.