Acid spray from prae or boilers will put out fires on the ground/xenos. Acid traps can do the same thing, even putting out the fire from an OB if destroyed.
Boiler gas can be removed with grenades and other explosives
Oh Shit. You're right
If you press E and start putting on armor on, throw it away or drop it - It will instantly stick to your character
Fatty gives about 1-2 seconds of warning noise to xenos before it hits like a truck. Always use fatty.