Here is a Link to the cited study.
It doesn't say how high.
I’m going to give you and all tera-hertz loving boffins a friggin big word of warning -— life on Earth did not develop in the presence of any significant level of millimeter length radiation. If you are evo that should scare you because no defense and repair mechanisms would have evolved. If you are creo or ider that will scare you even more — because the Designer is likely to have had a real good reason to ensure this green Earth had almost no radiation in that band.
Tera-hertz radiation in any significant levels is new. Very new. From the mid-nineteen-nineties. Most less than that.
YOU DO NOT KNOW THE LONG TERM EFFECT, NOR HAVE WIDE POPULATION STUDIES ON EXPOSURES TO MEASURABLE LEVELS OF THIS NEW FORM OF RADIATION.
Just how long did it take for Marie Curie to get sick? Years. She and her husband both died from what they believed to be new scientific miracle. It was. It is also dangerous, used improperly -— Radium. People bought millions of does of Radium elixirs from the 1910’s onward — the AMA insisted on a high standard dose to get it’s approval.
With the nuclear age of the late forties and fifties we finally got around to really understanding rad effects. It wasn’t until the 1960’s that personal items using radium were banned.
Use of x-rays has really improved since the 1980’s — extremely efficient detectors, highly tunable low-power emitters.
There’s no good reason to rush full public exposure to the as yet not well studied tera-hertz radiation band.