Microwave radiation is the same stuff being emitting from mobile phones and is completely different to radioactive radiation and is not cumulative. The only effect ever reported on the human body is one of heating.
Just as too much infra red heat can cause burning so to can high levels of microwave radiation.
Microwave equipment must be designed to comply with health and safety limits imposed by the local authorities. These levels allow radiated emissions of up to 10mW/cm2 at a distance of 50mm from the equipment. It is quite common for installations to have radiated emissions less than 1mW/cm2 .
Many installations install monitoring systems that measure the field intensity of all polarisations emitting from the machine and alarm if levels exceed a preset value.