Change(s) that REQUIRE a PHA revalidation AND RMP Update

There is some language in the EPA’s Risk Management Plan program requirements that tends to cause some confusion…

The owner or operator of a stationary source shall revise and update the RMP submitted under §68.150 as follows:

(5) Within six months of a change that requires a revised PHA or hazard review

So when are we required to “revise our PHA” other than when we have to do our 5-year revalidation?