1966 ranch house in Denver Metro, Colorado. (I am not the original
owner.)
The attached garage does have a firewall (5/8 drywall) that separates
it from the house.
Two issues:

1. About 8-9 ft above garage floor is a hatch in the firewall; the
hatch allows access from the garage to the attic above the house.

See http://picasaweb.google.com/bubbabub...39865428189714

The hatch is, essentially, a 2ftx2ft opening in the drywall/firewall.
The 2'x2' piece of drywall is not even attched with any hinges, it's
just put in place to cover the opening and is fastened with four
nails. Naturally, there is a little bit of space inbetween, so I would
like to seal that space - basically, seal off that whole hatch. The
idea is to ensure a good fire-resistant seal between the garage and
the attic. (Going forward, I won't use the hatch; there is another
hatch in the hallway inside the house for attic access.)

My question: what kind of sealant should I use to seal the spaces
between the hatch "square" and the firewall. Would any kind of fire
resistant caulk do the job? Or is there some kind of tape I'm
supposed to use?

2. The firewall/drywall doesn't go all the way down to the garage
floor. Rather, it ends about 3 inches above the garage floor.

See http://picasaweb.google.com/bubbabub...40119956909026

Also, the drywall protrudes by about 3-4 inches from the wall on which
it is mounted - you can see how the bottom edge of the drywall is a
few inches away from the bottom concrete part of the wall. The space
behind the drywall is hollow (some 2-by-4s, I guess), so I would like
to seal off the bottom in order to create a fireproof seal, but also
to prevent moisture/insect/debris intrusion. But that area is a bit
awkward to work around.

My question: what is the best way to seal off that space? Can I use
the expanding foam sealant that somes in an aerosol can?

Thanks
Bubba