We often read blogs, saying that to get the real effective NRR, we shall divide 2 to see if the earplugs to cancel noise is suitable for the workplace. Actually, that’s wrong. To check if the idea is correct, we finally decide to return back to OSHA for clarification.
Adequacy of earplugs to cancel noise by OSHA formula
The 50% safety factor adjusts labeled NRR values for workplace conditions and is used when considering whether engineering controls are to be implemented; However, when assessing the adequacy of the earplugs to cancel noise for hearing conservation (HC) purposes, CSHOs should only subtract 7dB from the NRR.
How to assess the adequacy of the hearing protection?
For single protection,
Determine the manufacturer’s NRR.
Subtract the NRR from the C-weighted TWA workplace noise level, as follows:
Estimated Exposure (dBA) = TWA (dBC) – NRR
If C-weighted noise level data is not available, A-weighted data can be used by subtracting a 7 dB correction factor from the NRR, as follows: Estimated Exposure (dBA) = TWA (dBA) – (NRR – 7)
Example:
let’s say TWA (the average exposure to noise) is 100dB. NRR for earplug is set to be 27dB. Then the estimated exposure shall be 100dB – (27dB-7dB) = 80dB.
For dual protection (ear muffs and plugs used simultaneously),
Determine the NRR for the higher rated protector (NRRh).
Subtract 7 dB from NRRh if using A-weighted sound level data.
Add 5 dB to the field-adjusted NRR to account for the use of the second hearing protector.
Subtract the remainder from the TWA as follows:
Estimated Exposure (dBA) = TWA (dBC) – (NRRh + 5) , or Estimated Exposure (dBA) = TWA (dBA) – [(NRRh- 7) + 5]
Example:
Let’s say TWA = 100dB, NRR for earplugs = 27dB, NRR for earmuffs = 33dB,
Then estimated exposure = 100dB – (33dB+5dB-7dB) = 69dB.
What is engineering controls?
In the context of Noise Reduction Rating (NRR), engineering controls focus on lowering the noise exposure level before workers or individuals need to rely on earplugs or earmuffs.
Key examples of engineering controls for reducing noise
Noise Barriers and Enclosures
Description: Building physical barriers or enclosures around noisy machinery or areas can help prevent sound from spreading.
Effect: Reduces noise exposure for workers in areas around the machinery.
Example: Enclosing noisy compressors, turbines, or other high-decibel machinery in soundproof rooms or barriers.
Vibration Damping and Isolation
Description: Implementing systems to isolate or dampen the vibrations from machinery that contribute to noise.
Effect: Reduces the noise generated by mechanical vibrations.
Example: Installing rubber mounts or isolators beneath equipment like pumps or engines to reduce the amount of noise transferred to the surrounding area.
Noise-Reducing Equipment and Machinery
Description: Upgrading to quieter machines or modifying existing machinery to reduce noise production.
Effect: Directly reduces the source of the noise before it reaches the worker.
Example: Using quieter motors, fans, and compressors or upgrading to equipment with lower noise emissions.
Sound Absorption Materials
Description: Adding sound-absorbing materials, such as acoustic panels or foam, to walls and ceilings.
Effect: Reduces sound reflections and reverberations within a space, helping to lower the overall noise level.
Example: Installing acoustic tiles or baffles in factory or workshop ceilings to absorb excess noise.
Acoustic Treatments in Design
Description: Incorporating noise control features in the design and layout of buildings or workplaces.
Effect: Minimizes the noise impact on workers through design elements.
Example: Designing workspaces with more enclosed spaces or directional airflow to contain noise within certain zones.
Sound Insulation
Description: Adding insulation to walls, windows, and floors to block or reduce the transmission of sound.
Effect: Helps to isolate noise from areas where workers might be exposed.
Example: Installing soundproof windows or insulated walls around loud machinery areas.
Quieting the Source
Description: Modifying or maintaining equipment to operate at lower noise levels.
Effect: Directly reduces the amount of noise generated by the equipment or machinery.
Example: Using low-noise pumps or fans, lubricating moving parts to reduce friction noise, or optimizing machinery for quieter operation.
Better Maintenance Practices
Description: Implementing regular maintenance programs to ensure that equipment and machinery are functioning properly.
Effect: Ensures that machines do not produce excessive noise due to wear and tear.
Example: Maintaining equipment like air compressors, conveyors, or ventilation systems to ensure they are operating efficiently and quietly.
Shall we divide by 2 to get the NRR for earplugs to cancel noise?
No, you should not divide by 2 to assess the adequacy when calculating the Noise Reduction Rating (NRR) for earplugs to cancel noise.
Conclusion
Only when we are implementing engineering controls, shall we divide by 2 to get the NRR for earplugs to cancel noise; if we just want to assess the adequacy of the earplugs to cancel noise, there is no need to divide by 2.
