Why don't you read the article? The source of the radiation is the person themselvees, because they happen to be at a normal temperature. They're just looking at a long wavelength region of the subjects' own black-body emmisions. \
IOWs there are no health effects and any claims that there are amounts to rubbish.
Not according to the linked article in my first comment:
But a new generation of cameras are set to appear that not only record terahertz waves but also bombard us with them. And if our exposure is set to increase, the question that urgently needs answering is what level of terahertz exposure is safe.