On 11 Jan, 19:45, "Ed Huntress" wrote:

No, Kaowool is an insulator, but only an insulator. The lining in a
firesafe contains a significant quantity of water too, bound up as
hydrated lime compounds in this "drywall".

So the material they line the safes with is lime, rather than gypsum?

Milner's original fireproof patent was for about 4" of sawdust, kept
wet!

"Lime" in en_GB speak is generally hydrated lime, not CaO. That's
termed "quicklime". It's crucial to the fireproofing that this would
be "slaked" lime (i.e. hydrated), not quicklime.

The stuff used is safes has varied. As was typical for Victorian
innovations, much of the "innovation" was driven by trying to dodge
around other peoples' patents, so much as choosing materials for their
own sake. Both lime (carbonate) and gypsum (sulphate) compounds have
been used, also alum (aluminium / potassium sulphate, rather than
calcium sulphate).