I appears the EPA numbers came from their 1978 EPA Report No. 550/9-79-100. A quick skim of the report (available on the EPA site) shows that it 1) is very old, 2) is concerned more with public nuisance / protection rather than the individual creating the noise.
It also appears that their numbers came from a much more conservative unlimited exposure of 70db, rather than 75db (actually they admit is is overly conservative because the report says 71.4 db should be the starting point... They rounded down for additional margin). The exposure durations are then cut in half for every 3 db gain.
LFR1100 Actives,QS10HPx2,QS8x2,EP800,M3x4,M3x2 (Wood),M5HPx2 (Wood),AxiomAir,ADA1500-8,ADA1500-7
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