Since you are design phase, Ed, I'd suggest a few other changes ...

Add a wide angle passive infrared motion detector to the launch pad, so
that it refuses to commence a countdown if people are close to it.
Maybe even abort a countdown.

Since some of the system has to do with safety, I would avoid placing
those features in code in the PIC, but rather as hardware interlocks
outside the code.  See the "Risks Digest" for the past ten years for
good reasons why.  ;-)

--
James Cameron                                    (cameron@stl.dec.com)
Digital Equipment Corporation (Australia) Pty. Ltd. A.C.N. 000 446 800