I wonder why this happened. I think it's unlikely the massive solar flares are part of it, as the experts at Spaceweather said ground-level effects were only at the poles and were relatively small on one day. The biggest ejection hit the planet on the 12th with big auroras visible in northern latitudes, but they are far up. Even if the experts were wrong and EPA detectors reacted, with such an obvious event it's hard to imagine any executive decisions to "hide the data to protect the public from panic". The Canadian and Danish government northern stations are gamma measuring (I don't know if they have fans or filters) but don't show a particular rise; see
https://remap.jrc.ec.europa.eu/GammaDoseRates.aspx.
Only the 2 outdoor NETC stations in Illinois show spikes on the 12th but none of the indoor detectors I looked at do. So whatever this is, it seems to be particles and not gamma rays from above. KC, your filter change on the 11th made a big difference. Are your filters typically choked with dust when they come out? The St. Charles station shows similar spikes starting earlier and it seems less affected by filter changes. Maybe those filters are less prone to clogging?
_________________http://netc.com/chart/view.php?n=1%3A77D9CCCA.5 Toronto, Ontario, Canada SBM-20 indoors