In article , peterv666
@nospam.adelphia.com (PVR) says...
I'm finishing my basement. Before starting, the joists supporting the first
floor were very visible. I want to put in a ceiling in part of the basement
and I can use either drywall or a drop ceiling. I understand that if I use
drywall I must use 5/8" type for fire resistance purposes. If I install a
drop ceiling this will be the kind where the 2' x 2' tiles are supported by
plastic extrusions (CeilingMax/GridMax system) which are attached directly
to the joists. This gives a drop which is only 1.5" below the joists. I have
two questions.

1). If the joists are currently unprotected why is it necessary to use 5/8"
drywall for the ceilings in the finished areas?

I don't understand why a fire separation is necessary. Are you parking
cars in the basement? Fire separations between occupancy ratings are
required, like in the case of a garage and living quarters. If your
local jurisdiction requires a firewall between single family residential
stories, perhaps you could let us know what country you are in? In the
USA, such a separation is not required, unless each story is a separate
dwelling unit, like an apartment.

That said, there is 5/8" sheetrock that is not type X. It may be that
1/2" rock is not rigid enough for your application.

2). If I use ceiling tiles supported by plastic extrusions, the plastic
would melt in a fire. How can the drop ceiling be a satisfactory alternative
to a 5/8" drywall ceiling?

There may be drop ceilings that are fire rated, but not with plastic
components.

I prefer the drop ceiling because there are several electrical junction
boxes attached to the joists and I assume reasonable access to these should
be provided.

Yes. If you use gyp board, you will need to move the junction boxes
into the face of the board and install the appropriate cover plates.

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