Foundry specific, device and geometry specific, node-
to-node specific (BVdss != BVox, and so on). BJTs
different than CMOS. The foundry probably has simple
rules, sandbagged for long term reliability, that are well
tighter than true breakdown of any feature. You would
be ill advised to design anything up to the breakdown
limit, aside from avalanche photodiodes or zener voltage
references.