Can a broken microwave leak radiation?
If the metal grid in the door is intact and the outer metal case it should be fine, one way I have seen used was to clip the leads off a neon lamp if the lamp flashes it is getting hit by microwave radiation. Or to buy a detector.  Depending on the amount of energy being released it can be a simple warming effect to burning, the eyes would be at the biggest risk of damage since they are the closest to water and are very delicate. If you have concerns it would be safer to not use it, but if the grid and case are undamaged there is no way for the energy to escape. Microwaves run at approx 2.4Ghz the length of a single wave would be under 6" and the height or amplitude is based on the power level.