My assumption that the basement document safe had an effective door seal turned out to be wrong, so I replaced the bagged desiccant with a tray of granules, sealed the door with masking tape, and tried again:
The jagged black curve shows the Basement Laboratory temperature trending toward the usual mid-50s winter level. The dead-flat horizontal blue line at 15% RH shows the tray of desiccant can keep up with whatever air leakage might occur around the tape and through the floor bolts.
I cannot find the table (that I once had and know exists somewhere) which lists various desiccants and their terminal humidity levels in a sealed container. I’m pretty sure the low humidity means it’s one of the clay-based desiccants, not silica gel.
The Smell of Molten Projects in the Morning 
Comments
5 responses to “Basement Safe Humidity: Sealing the Door”
For the capacity of various desiccants, how about the charts that are found here:
http://www.sorbentsystems.com/desiccants_charts.html
I must be mis-remembering that chart, because the stabilized humidity would obviously depend on the amount of water in the air and the amount of desiccant in the box.
Knowing the volume of the safe and the starting RH would give the amount of water, then it seems you could inject that into Figure 2 and work backwards to the RH. I think so, anyway…
[…] desiccant in the basement safe: Desiccant in […]
[…] the door sealed, that tray of desiccant ran out of capacity after holding 14%RH for four months. The humidity rose to 24% at the end of […]
[…] gel (or whatever those granules might be) holds the humidity firmly at 14 to 15 %, at least with a simple masking tape seal around the door opening that dates back to early 2012. Less water vapor gets through the door during the winter, due to the […]