Frequency ranges that causes a hazard to humans
The short answer is that unless you are dealing with professional power levels in the several watts range, RF is very difficult to cause injury with.



Long answer

RF doesn't affect humans directly unless there is a tremendous amount of power.  Effects are typically thermal, when a particular chemical bond is struck just-so, it will absorb a photon, moving it slightly.  Enough heating will damage cells by denaturing or "cooking" proteins.  

Particular wavelengths (2.4 GHz) are well absorbed by water and fat, but absorption is still very diffuse so it would take a tremendous dose to cause enough heating in any one area to cause damage.  The FCC safe exposure limit is 1.6 W absorbed per kilogram (as per one source), and 4 W/kg (in following link) for the entire body.

More: 


FCC RF Safety FAQ
Specifically this question which has links to 

the Center for Devices and Radiological Health (CDRH), Food and Drug Administration.
the Environmental Protection Agency's Office of Radiation Programs
OSHA guidelines and studies



Atomic nuclei can also also respond to RF, allowing for nuclear magnetic resonance spectroscopy (or MRIs), but this is a strictly nuclear effect and has no influence on chemical bonds.

IR and light obviously can cause burns, but only at sufficient power.  IR lasers can be particularly hazardous to eyes, as it invisible it will not trigger a blink or aversion reflex, allowing a large, damaging dose to be absorbed before noticing.

Higher energy photons, UV, X-ray, and gamma, are able to ionize atoms when they strike them, causing unexpected chemical reactions to occur which can destroy, damage, or mutate cells.

These are all forms of "radiation", but the layperson couldn't tell what the implications of non-ionizing versus ionizing radiation are, which causes all sorts of unfounded fears of these invisible phantoms that carry our cell phone calls and webpages.