"Tender Ear” identification—Toward an individualized permissible noise exposure limit

The U.S. has one of the least protective federally mandated occupational noise exposure limits (90 dBA time-weighted average) among comparable industrialized nations. While most developed countries use a reduced (more conservative) noise exposure limit of 85 dBA (resulting in 8% incidence of work-related hearing injury compared to the U.S.'s 25%), it is well-known that the pricetag of such a reduction is the primary roadblock between improved worker hearing safety and company profit margins. To find a middle ground, the goal of this project was to identify and individually protect potentially “tender” ears exposed to 85−89 dBA that would otherwise not require hearing protection (in the U.S.) but might still incur significant noise-induced hearing loss. Importantly, the open ear amplifies sound with as much as 15 dBA variability from person to person, due to individual differences in ear size and shape. As such, an unprotected free field noise exposure is only “equal” across workers when it's measured outside the ears, not inside. In 271 adults, we predicted individual inside-ear sound levels to identify potentially “tender” ears exhibiting high amplification, using a simple measurement—body height. Work supported by the National Institutes of Health (1R01DC020699-01A1).