I was curious about how much we could rely on that safety, and it turns out there are threshold limit values (see the sixth slide) for UV-C. Between 200 and 220 nm the TLVs are .02 to .08 J/cm^2 (200 to 800 J/m^2), according to the American Conference of Governmental Industrial Hygienists. At 5W/m^2 (your suggested irradiation) that gives you 40 to 160 seconds of reasonably safe human exposure.
I was curious about how much we could rely on that safety, and it turns out there are threshold limit values (see the sixth slide) for UV-C. Between 200 and 220 nm the TLVs are .02 to .08 J/cm^2 (200 to 800 J/m^2), according to the American Conference of Governmental Industrial Hygienists. At 5W/m^2 (your suggested irradiation) that gives you 40 to 160 seconds of reasonably safe human exposure.
Apparently those slides contradict the studies cited in my article.
I don’t know which to believe. The rational action is to urgently run more experiments to assess the risk from 200nm-220nm band.
It would be really great if those slides had a references section.