An ambient sound level of how many dB(A) with a 6 hour exposure time requires hearing protection?

• A. 90 dB(A)
• B. 95 dB(A)
• C. 97 dB(A)
• D. 92 dB(A)

Answer: (D)

When deciding if hearing protection is needed, use how long you’re exposed to a sound at a given level. The standard reference is that 90 dB(A) can be tolerated for 8 hours, and for every 5 dB increase, the permissible time halves. So as the level goes up, the time you can be exposed without protection drops quickly.

For a 6-hour exposure, the level that just reaches the limit between 8 hours and 4 hours sits between 90 and 95 dB(A). You can find the exact threshold with the relation L = 90 + 5 log2(8/T). Plugging in T = 6 hours gives L ≈ 90 + 5 × log2(8/6) ≈ 92 dB(A). That means an ambient level of about 92 dB(A) with a 6-hour exposure requires hearing protection. Levels at 90 dB(A) would still allow up to 8 hours, and levels at 95 dB(A) would only be allowable for about 4 hours, so 92 dB(A) is the crossover point.