Based on yesterdays FC troubles I went back and had a look at some of my alogs regarding humidity in chamber.
By looking at the various pics I posted of particle counts in links:
https://alog.ligo-wa.caltech.edu/aLOG/index.php?callRep=12874
https://alog.ligo-wa.caltech.edu/aLOG/index.php?callRep=12873
https://alog.ligo-wa.caltech.edu/aLOG/index.php?callRep=12866
https://alog.ligo-wa.caltech.edu/aLOG/index.php?callRep=12859
You can see the humidity in chambers varies from 13%-33%. I was surprised at this, and I have to take back what I had said to Kate and Calum yesterday at how I said I had noticed that the humidity levels usually stayed pretty constant in chamber here at LHO
No surprise,
According to the weather station at PASCO airport (KPSC) the relative humidity on Sunday ranged from 71% at 5am to 21% at 6pm.
The indoor humidity is influenced by the outdoor humidity and temperature.
Inside a chamber the air near a door is a mixture of purge air and LVEA air. The purge air is nominally 0% RH but the LVEA has been ranging between 20 and 40 recently. In addition those water molecules are moving way faster than the purge air and are very happy to move upstream.