Is postgres 7.2.1 safe if there is a power fail.

Is postgres 7.2.1 safe if there is a power fail.
The system is running 24/7/365 and I have had occassional problems with
duplicate records including oids. This happened in two different tables at
the same time, it seems to have appeared immediately after a power (and ups)
fail. Is it a known problem with power fail or is this just a coincidence. I
have tried to scour the maillists and docs but cannot find a definitive
answer to this.

Regards
Steve