Originally Posted by bobhope2505
He said it swells when exposed directly to flame to maintain the seal instead of converting to ash and reducing in volume.
No he didn't.
Intumescent sealants swell to close gaps and openings. The usual ingredient is vermiculite, and required "swell temperature" is about 600F. There are also other ingredients in use. 3M FireBarrier 2000 appears to be intumescent. In addition, many products form a char on their surface, which is an insulator, and thus desirable. Some firestop products depend entirely on char-based protection. Char alone is a poor protection for an airplane firewall. The chars are fragile, and firewalls vibrate while being blasted by cooling air at high velocity.
Proseal is a polysulfide sealant. It was not included in the burn test earlier in this thread. I'm sure it would be a fine gas sealant when enclosed between the fay surfaces of a sheet metal joint, but I would not allow any to be exposed inside the cabin, as outgas, flame, and smoke results are unknown.