Also, check the weighting. OSHA's recommendations are based on A-weighting with Slow Response.
As an aside, that's a horrible way to measure music's volume for the purposes of determining hearing damage, for two reasons. First, A-weighting ignores low frequencies, which make up so much of modern music. Second, while slow response may be appropriate for filtering out the odd clank from the constant whir of machinery, it ignores things like snare hits. For moderate listening levels, that may be ok, but my understanding is that the ear also has peak volume limits that you could probably exceed if you're only looking at slow response.
(I don't have a solution... I'm just pointing out that OSHA's noise limits, the only objective tool that we have, is wholly inadequate and was never designed to determine safe music listening levels.)