Or. Admin. R. 437-007-0335
(2) Personnel must wear hearing protection unless monitored under typical work conditions and found to be exposed to a noise level of less than an 8-hour time-weighted average (TWA) of 85 db when:
ORS 654.025(2) & 656.726(4)
ORS 654.001 - 654.295
OSHA 5-2003, f. 6-2-03, cert. ef. 12-1-03