Health & Safety:
NOISE
Updated 01/06/2023
What is NOISE?
- NOISE is unwanted SOUND. OSHA considers an 8 hour time-weighted average noise exposure of 85 decibels to be the maximum noise exposure without hearing protection.
Noise Induced Hearing Loss:
- Partial or complete hearing loss in one or both ears
- Cumulative, permanent loss of hearing that develops gradually after months or years of exposure to high levels of noise
- Can arise from traumatic injury (explosions) and autoimmune diseases
- In most cases is irreversible
Decibel:
- The unit used to express the intensity of sound.
- dBA – abbreviation for decibels, “A” scale. “A” scale approximates human hearing.
What NOISE levels are safe?
- Depends upon time of exposure
- Below are the OSHA standards for noise exposure when you are wearing no hearing protection. What this means is if your noise exposure is 94 dBA, you can theoretically stay in that exposure for 1 hour and not hurt your hearing. However, it is a good idea to always wear hearing protection if you are unsure of the noise level.
- A good rule of thumb: If you have difficulty hearing someone standing 3 feet away talking at a normal level, then the noise level is too loud. You should be wearing hearing protection.
- Hearing loss is usually slow to occur so you will not notice it until it is too late!
- Glass grinders, wet belt sanders, torches, glory holes, compressors and drills are sources of significant noise exposure (often greater than 100 decibels)
The Ear
Any source of sound sends vibrations or sound waves into the air. These funnel through the ear opening, down the ear canal, and strike the eardrum, causing it to vibrate. The vibrations are passed to the small bones of the middle ear (ossicles), which transmit them to the hearing nerve in the inner ear. Here, pressure changes cause hair cells to move which become nerve impulses that go directly to the brain, which interprets the impulses as sound.
Excessive noise can permanently damage the hair cells in the inner ear causing noise induced hearing loss:
- Noise induced hearing loss can not be cured, but it can be stopped by reducing noise exposure.
- If you think you have experienced a hearing loss, go to an audiologist for a hearing test.
- Always wear hearing protection whenever you are using a noisy piece of equipment.
Hearing Protection:
Compressible Foam Ear Plugs:
- Claimed noise reductions up to 30 decibels
- Roll between your fingers and gently insert into the ear canal. Let it expand. Ensure there is a snug fit.
- Throw away when dirty.
Non-Compressible Foam Ear Plugs (reusable):
- Claimed noise reductions up to 30 decibels
- Insert gently for a sung fit
- Always wash before reuse. Throw away when damaged.
Ear Muffs:
- Claimed noise reductions up to 25 decibels
- Ensure good seal around the ears
- Make sure nothing – hair, glasses – is in the way
How effective is Hearing Protection?
- Any hearing protection sold in the USA has a NRR (Noise Reduction Rating) on the packaging.
- NRR ranges from 10 – 30 decibels. NRR is an estimate of expected noise reduction.
- These tests are conducted in a laboratory under ideal conditions and tend to over-estimate the effectiveness of hearing protection devices.
- There are several schools of thought on correcting the NRR to make it more realistic. Below are two:
7 dB correction:
- For example, there is a measured Noise Level of 100 dBA. The hearing protection you selected has a manufacturer’s claimed NRR of 26 dB.
- Actual Decibel Exposure = 100 dBA – (26 – 7) = 81 dBA
- This means that the actual noise exposure wearing this hearing protection is more like 81 dBA instead of the claimed 74 dBA.
7 dB correction + 50%:
- For example, there is a measured Noise Level of 100 dBA. The hearing protection you selected has a manufacturer’s claimed NRR: 26 dB.
- Actual Decibel Exposure = 100 dBA – [(26 dBA – 7) X 0.5] = 90.5 dBA
- This means that the actual noise exposure wearing this hearing protection is more like 90.5 dBA instead of the claimed 74 dBA.
REMEMBER! You want to keep your Time-Weighted Average noise exposure to < 85 dB!
Wear hearing protection that fits you well, is comfortable and has the highest NRR. In reality, unless you are working around high levels of noise all day, the 7 dB Safety Correction is probably adequate.