This is, not coincidentally, just under the 85 decibels or so that can, over long periods of exposure, compromise the delicate infrastructure of the human ear.

This is, not coincidentally, just under the 85 decibels or so that can, over long periods of exposure, compromise the delicate infrastructure of the human ear. There is a presumption that is commonly made in many circles (including this article) that because NIOSH noise exposure limit is 85 dBA over eight hours, that it's levels at 85 dBA or over that cause hearing damage. Hearing damage can actually start at 75 dBA for a small segment of the population and at 80 dBA for most people over the long-term (about 10 years) [0],[1]. The 85 dBA NIOSH number (and the 90-dBA OSHA number) represent a compromise between an "acceptable" (my words) amount of hearing loss and the costs for businesses to implement effective noise control measures to reduce noise. The acceptable amount of hearing loss is based around workers' ability to understand human speech, and it assumes that hearing loss above 4 kHz "must be accepted as part of the jon." Those limits also assume that workers' are only exposed to high noise levels during their work periods - if Sam works 40 hours at 84 dBA per day and then attends a rock concert on the weekend, he exceeds his allowable noise dose. I don't mean to write this to be nitpick, I just want to underscore that if you really care about your hearing, you really need to avoid levels above 80 dBA as much as possible over the long-term. However avoiding high noise levels is very difficult to do so (especially if you live in a large city) and for many of us it's way to late. For those of you in the Boston area, the Greater Boston Chapter of the Acoustical Society of America holds monthly meetings where presenters discuss and demonstrate many of the issues discussed in this article - everyone is welcome (especially students) and the meetings are usually held at Acentech's Cambridge office so you can meet some of the folks in this article. The GBC-ASA website is at http://www.gbcasa.org http://www.gbcasa.org. Unfortunately it's undergoing a takeover from national ASA so there is nothing there at the moment, but I expect content to appear again shortly. There is also the @GBC_ASA twitter account for announcements. [0] Fundamentals of Acoustics, Kinsler et al, Chapter 13 [1] Keep in mind these are A-weighted decibels, linear decibel levels will be different