It depends of what OS version you are talking about and architecture (server/Workstation or 800/700...) then of which volume group...
If its 100% full and giving you trouble its most certainly /dev/vg00/lvol3 which is / (Yes root filesystem) and main reason is someone wrote something that should not be there like a big core file, or a writing to a mispelled tape device...
get the o/.p of bdf..it should be root file system..if you have not mounted anything else then remove everything that is in the /tmp directory using rm -r
Please ignore the advice from "swap". It is not safe to blindly delete the contents of /tmp on a multi-user HP-UX system which is in use. If you don't have /tmp as a separate mountpoint and it is the cause of the disc space issue consider cleansing in single user mode.