Quote:
You almost half way admitted it there in your answer.
The vault is better than the safe. It's better than the safe because it uses one of the best insulations available. Air. Smaller safes have to use better man made insulations, because they do not have the air volume inside.
Using the same ceramic insulation, exclusively, in a smaller safe would yield faster and higher temperature rises than the exact same test performed on the large vault. This is exactly the same when other insulations are used, and is why many of those insulations are moisture bearing. Behind air, steam is also a great natural insulator.
In a nutshell, this is why the ceramics will not pass the UL test, and is why many other dry insulations will not pass it either.
|
Well I sort of agree with you. For the three modes of heat transfer: conduction, convection and radiation, air doesn't conduct heat well so it's good at reducing that (a vacuum doesn't conduct any heat) it does not however prevent radiant heat transfer and is also an active component for moving heat in convection.
Ceramic fiber is mostly air which is good for preventing conductive heat transfer. The fiber also blocks radiant heat transfer and prevents air from moving within the insulation layer to reduce convection heating.
I don't believe you are entirely accurate with your statement that safes don't use air in their fire safe insulation. Both expanded Vermiculite and Perlite which are the aggregates most often used in concrete to give them good insulation properties are mostly air. Also, these manufacturers (safe and builders) will use an aeration process to introduce air into their concrete mixes to reduce density and improve the insulation properties.
The moisture bearing insulation is used because of the phase change that has to occur with water to change to steam. When water changes to steam at atmospheric pressure, the temperature of the water will stay at 212F until the water if fully changed to steam. Do the experiment yourself, put a pot of water on the stove with a thermometer in the water and watch what happens to the temperature when it starts to boil, it won't rise above 212F until the water is gone. Gun safe manufacturers use gypsum drywall because it is 21% water and will go through a similar process when exposed to high heat the problem is the pressure will rise in a sealed gun safe making it less effective.