An estimated 22 million workers each year are exposed to noise loud enough to cause hearing damage.¹ Additionally, 24% of all hearing difficulty among U.S. workers is due to occupational exposure.² Reducing the exposure to noise begins with understanding the issue, effects and causes.
We would like to introduce you to some of the common noises in the workplace, the necessary hearing protections, and the steps you can take to protect your workers.
A Brief Introduction to Hearing and Hearing Loss
When sound waves enter the outer ear, the vibrations impact the ear drum and are transmitted to the middle and inner ear. In the middle ear three small bones called the malleus (or hammer), the incus (or anvil), and the stapes (or stirrup) amplify and transmit the vibrations generated by the sound to the inner ear.
The inner ear contains a snail-like structure called the cochlea, which is filled with fluid and lined with cells with very fine hairs. These microscopic hairs (stereocilia) move with the vibrations and convert the sound waves into nerve impulses–the result is the sound we hear. If these hairs are damaged, this is how hearing loss occurs.
Measurement of Sound
Noise is measured in units of pressure, called decibels, named after Alexander Graham Bell, using A-weighted sound levels (dBA), which match the perception of loudness by the human ear.
How is this measured? The physics behind decibel measurement is 10 log (P2/P1) dB where the log is to base 10. To put this into context, consider this:
On the decibel scale, the smallest audible sound (near total silence) is 0 dB.
- A sound 10 times more powerful is 10 dB.
- A sound 100 times more powerful than near total silence is 20 dB.
- A sound 1,000 times more powerful than near total silence is 30 dB.
Here are some common sounds and their decibel ratings:
- Near total silence – 0 dB
- A whisper – 15 dB
- Normal conversation – 60 dB
- A lawnmower – 90 dB
- A car horn – 110 dB
- A rock concert or a jet engine – 120 dB
- A gunshot or firecracker – 140 dB
Considering the limits of the human body, 85-90 dB will result in hearing loss, 140 dB will cause immediate damage, and according to a study by Jurgen Altmann, 200 dB would cause your lungs to rupture.
For detailed information on this, please look at Optimum Safety Management Hearing Protection page.
NIOSH and OSHA Permissible Exposure Limits (PELs)
Now that you know how hearing works, and what it would take to kill a worker, what do you need to know about your own workplace? The National Institute for Occupational Safety and Health recommends that all worker exposures to noise should be controlled below a level equivalent to 85 dBA for eight hours to minimize occupational noise induced hearing loss.
Adopted by OSHA, permissible sound exposure levels are as follows (29 CFR 1910.95(b)(2)):
|TABLE G-16 – PERMISSIBLE NOISE EXPOSURES (1)|
|Duration per day, hours||Sound level dBA slow response|
The Average Sounds on the Job
What’s that sound? It could be OSHA knocking, if you aren’t protecting your workers from hazardous noise.
Here are some of the common sounds you or your workers may hear on the job. Compare them to the above table to see if you are adequately protecting your employees.
|Mitre Saw||102 dBA|
|Hand Drill||98 dBA|
|Chop Saw||106 dBA|
|Hammer Drill||114 dBA|
|Metal Shear||96 dBA|
|Hain Saw||109 dBA|
|Impact Wrench||102 dBA|
|Skill Saw||100 dBA|
|Belt Sander||93 dBA|
|Tile Saw||101 dBA|
|Circular Sander||90 dBA|
|Table Saw||92 dBA|
For information on the dB levels emitted by common power tools, check out the NIOSH PowerTools Database
Average Heavy Equipment Noise Levels
|Vibrating road roller||91-104|
|Asphalt road roller||85-103|
|Crawler crane < 35 ton (non-insulated cab)||93-101|
|Crawler crane >35 ton (non-insulated cab)
Crawler crane >35 ton (insulated cab)
|Rubber-tired crane >35 ton (non-insulated cab)
Rubber-tired crane >35 ton (insulated cab)
Average Construction Noise Levels
|Pneumatic chip hammer||103-113|
|Concrete joint cutter||99-102|
Source: CPWR – Center for Construction Research and Training
Sound Levels by Industry
|Industrial Branch||LAeq dB(A)||LCpeak dB(C)|
|Glass fibers factory||97||101|
|Copper tube factory||96||126|
See part 2, featuring hearing protection advice and insights.