Sorry, can't provide an actual number, but the effective pressure ratio will vary (roughly) proportionate to the square of blower (centrifugal or turbo) RPM, so really big numbers @ peak power are relatively safe at lower speeds.
Roots and screw types have much greater pressures at moderate speeds.

http://victorylibrary.com/mopar/blower/blower-choices3.htm

There are charts on line that purport to calculate blown CR from static CR and boost. They fail.
All they do is add boost pressure to ATM, divide by ATM, then multiply by static CR. What actually happens is not even close.
Better physics: http://victorylibrary.com/mopar/blower/blower-engine5.htm