so I was playing last night.. and got the Deadshot Daquiri permanent perk.. I had the Quick Revive.. but I noticed when I was in the power room after trolling the last zombie behind a door I kept replacing the boards, like for about 5 minutes... and the same green explosion popped..
Not sure what it does.
edit: So i've been playing for a while and noticed it takes zombies A LOT longer to rip off the boards of the windows so give it a try