Is there a reason you don't want to use drywall? USG makes a variety of gypsum fire-rated products and has recommended assemblies if you want to increase fire rating of the ceiling. I would imagine there are other commecial/industrial products as well but they might be expensive.

Thanks for asking Mike. We have an apartment above it and have numerous wires, pipes, etc. running thru the tresses. so we would like to be able to get to some of them. I doubt there is but was wondering if there was some type of dropped ceiling or other panel that was fired rated that we could use. I guess our plan will be to add a few cut outs that we can pulldown if we need to get at something. thanks for any help.

Cutting and repairing drywall is very simple.

There are not many inexpensive ways to put openings in a firewall (especially a ceiling) and preserve the fire rating.

dropped ceiling....?

Some thing that could be removed and returned without damaging or making repairs, I think of a dropped ceiling as being able to take out the panels. OK, so are there any removable panels that are fire rated.

thanks