I've breached all three caverns and currently have three FBs running around in various levels. All three have Deadly Dust, so I'm hesitant to send my feeble military after them. What I'd ideally like to do is safely connect the caverns to the surface with some way of being able to block it off until a Siege shows up. Then I can pull a lever and pop open a hatch, door, something, and let the FBs out to handle the greenskins.
I've already dug a stairwell that goes from the surface outside of the fort proper, and goes just past all three caverns, but haven't breached them yet. The two problems are:
1) The FBs happen to be loitering around the area near where I've dug the stairs. So I will likely lose miners when I breach the caverns. I'd prefer to avoid this, but as I have six of them, I could afford to lose one if necessary. (My current worst option is to draft some cheesemaker into a temporary miner, burrow him outside, then close the drawbridge behind him. Then send him off to breach the caverns.)
2) I need to figure out a way to block the stairwell off until I want to release the FBs. Best would be something repeatable, so that, under perfect conditions, I'd be able to let the FBs out one at a time. If one pops out, I can pull the lever and close off the remaining two from being able to get out.
Suggestions? Ideas?