Whose health is at risk from EMF radiation?

To a degree, everyone who is exposed to EM radiation bears an increased health risk.

In fact it appears there is no safe level of electromagnetic radiation, either for low frequency (ELF & VLF) or Radio/Microwave fields. 

For example, biological effects have been observed with low-frequency EMF (50/60 Hz) at levels as low as 0.2 mG, which is far lower than a typical urban dweller's average exposure level. 

But that doesn't mean that we are all doomed to get sick. It means that we need to understand and manage our risk. The good news is that

Whatever your present EMF health risk category, reducing your electromagnetic radiation exposure will reduce your risk of becoming sick.

EMF Health damage - High risk group #1

Given the same EMF exposure, some people are more likely to suffer EMF health effects than others, because of their own biology:

Children are particularly at risk for several reasons. They are biologically more vulnerable - their skulls are thinner, their tissues - including their brains - are not fully developed. 
Children will accumulate higher lifetime levels of radiation than older people because they have entered the world at a time when electromagnetic pollution levels are much higher than was the case when their parents were young.
Children are also at risk because they may not be able to control how much they use cell phones, how long they play on computers or watch TV and how close they sit to the screen.
Pregnant women should be especially conservative when evaluating their risk from electromagnetic fields because any cellular damage in a developing embryo may have magnified consequences for the child. They should avoid electromagnetic exposure as far as possible, by keeping away from high EMF sources and by minimising the duration of any electromagnetic exposure.
It has been demonstrated that pregnant women are at risk of miscarriage if they are subjected to high intensity EMFs during pregnancy. Miscarriage is an extreme (and tragic) response to a high level of EM radiation exposure. Lesser EMF levels may still damage the foetus while not causing an actual miscarriage.
Nutritionally Compromised Persons. As with all biological stresses, EMF-induced stress does not occur in isolation. The cumulative effect of electromagnetic stress combines with other biological stresses and lifestyle factors.
Nutritional status almost certainly has an effect, either for good or otherwise, on the amount of cellular damage caused by electromagnetic radiation and on the extent to which the body can repair it.
People who are already suffering from chronic degenerative conditions. If you are sick then your body is already using all its available energy to heal itself. It is unlikely to have much energy to spare for repairing the damage done by electromagnetic radiation. 
Also consider that electromagnetic pollution may have been a contributing factor to your illness. If so, you may be dealing with an actual cause of your illness, not just its symptoms, when you reduce your exposure to electromagnetic pollution.

EMF Health damage - High risk group #2

These people are more likely to suffer EMF health effects than others, because of their heavy EMF exposure:

Workers are at risk if they work in close proximity to electrical machinery (e.g. computers including laptops, electric ovens, sewing machines). 
People who work with very strong electromagnetic fields like welders, power line technicians, subway workers, cell phone network operating equipment technicians, electric train drivers and others like them, may be strongly at risk and should carefully follow all sound guidelines and safety procedures to reduce their electromagnetic exposure. Even so, they might incur less risk if they were able to change their trade. 
Appliance Users. People who spend more than a few (ten?) minutes a day talking on a cell phone (pressed to their ear), or standing next to a microwave oven or other high-EMF electrical appliance (see EMF Table), especially if they do this every day for years.
People who live in a high-EMF Neighbourhood. Anyone who lives within range of electric power lines or cell phone towers for several (five?) years or more (and especially children). The range depends on the electromagnetic field strength and distribution pattern. Generally 400 metres or more seems to be a safe distance for most power lines. An EMF meter (gauss meter) can determine the effective EMF strength at different times of the day. (There is no authoritative safe level, but I would not want to live so close to an electromagnetic source that I was subjected to a constant electromagnetic field of 0.3 milligauss or more).

It's worth noting that when the body is overwhelmed by too much electromagnetic radiation, health effects can occur many years later. For instance, exposure to power line EMF in childhood can predispose a person to certain types of cancer later in adult life, according to one study.