Currently, OSHA policy requires only the action level to be reduced for exposures to noise during extended work shifts. The exposure limit is not required to be adjusted.
There is an OSHA formula (found in Table G-16 in Appendix A to 1910.95) to use for workers on extended shifts. Basically, the individual would be exposed to fewer decibels over a longer period of time. For instance, for a ten-hour shift, the Action Level would be reduced from 85 to 83 decibels.