Ive been wondering this for a while now...
Can you barrel bejind the door another barrel behind the door?

no, barrel does not inflict damage, so a second barrel cannot be chained to it.

thanx for clearing that up for me... it makes sinse now

"Barrel Behind the Door" can only be activated against DAMAGE. It cannot be activated against costs like "Imperial Order" or "Wall of Revealing Light". It cannot be activated against effects that cause you to lose Life Points like "The Immortal of Thunder". It cannot be activated against effects that switch damage, like another "Barrel Behind the Door", because they do not inflict damage, they simply transfer it.