Permissible noise exposure limit depend on equivalent Noise Exposure factor
If any employees are exposed to sound levels exceeding those listed in below Table (as per OSHA 1926.52 standard), feasible engineering and administrative or controls shall be utilized. If it is not possible to utilize effective engineering or administration controls, personal protective equipment according to OSHA standard must be in place.
Maximum Duration Per Day (Hours) – Sound Level (dBA) – Slow Response
8 90 dBA
6 92 dBA
4 95 dBA
3 97 dBA
2 100 dBA
1.5 102 dBA
1 105 dBA
½ 110 dBA
¼ or Less 115 dBA
PPE requirement for Hearing protection: Definitely our first target is reducing noise levels by engineering control, If not feasible, need to provide hearing protection. Hearing protection devices inserted in the ear must be fitted. For using hearing protection, all employees must have to get training by a Competent Person and its employer responsibility to ensure training for all employees. Cotton wadding is NOT acceptable hearing protection!
Combined Noise Exposure Impact: When the daily noise exposure is composed of two or more periods of noise exposure of different levels, their combined effect should be considered, rather than the individual effect of each.
Determining Combined Noise Exposure Impact:
- F(e) = The equivalent noise exposure factor.
- T = The period of noise exposure at any essentially constant level.
- L = The duration of the permissible noise exposure at the constant level
The permissible level for personnel exposure by noise depends on the equivalent noise exposure factor. The equation for Determining Combined Noise Exposure Impact is-
F(e)= T(1)/L(1)+ T(2)/L(2)+ T(n)/L(n)
If the value of F(e) exceeds unity (1) the exposure exceeds permissible levels. For example, a noise exposure scenario is given below, lets calculate the value of the equivalent noise exposure factor-
- 110 dB A 1/4 hour.
- 100 dB A 1/2 hour.
- 90 dB A 1 1/2 hours.
For, 110 dB A 1/4 hour: T=1/4 and L=1/2 as per table.
For, 100 dB A 1/2 hour: T=1/2 and L=2 as per table.
For, 90 dB A 1 1/2 hours: T=1½ and L=8 as per table.
The equivalent noise exposure factor, F(e) = ( ¼ ÷ ½) + (½ ÷ 2) + (1½ ÷ 8)
Or, F(e) = 0.500 + 0.25 + 0.188
So, F(e) = 0.938
Since the value of F(e) does not exceed unity (1), the exposure is within permissible limits
Noise Exposure: Some example of exposure-
- Decibel Level 90-Truck traffic, lawn mower
- Decibel Level 100-Chain saw, pneumatic drill, excavator
- Decibel Level 120-Close thunder, rock concert
- Decibel Level 140-Jet plane, gunshot blast