In: Physics
TO know.A worker is exposed to 100 dBA for an 8-hour TWA. Earplugs with a 28 NRR and ear muffs with a 25 NRR are available. What attenuation level can you achieve with (8a) only earplugs and (8b) only ear muffs? Is this good enough? Show your work.
In order to calculate the attenuated level, we must follow following steps
1. find the NRR
2. If the noise is given in dBA , subtract the NRR by 7 to convert it to dBA.
3. divide (NRR-7) by 2-----derating
4. subreact the noise level with the result we obtained in 3.
now, lets calculate this for ear plugs :
NRR = 28
NRR - 7 = 21
NRR-7 /2 = 10.5
attenuated level = 100 - 10.5dBA
attenuated level for ear plugs =89.5 dBA--------------------answer for 8a
For ear muffs, follow the same procedure
NRR = 25
NRR-7 / 2 = 9
attenuated level = 100 - 9
attenuated level for ear muffs=91
According to industry ergonomics, the attenuated level should be below 90dBA for 8 hour TWA
hence, ear muffs are not good enough (91dBA)
but earplugs can be used to reach the level within the specified limit (89.5 dBA)