| |
What type of hearing protector do I need for my work environment or hobby?
You have to consider the following factors, the noise level, the exposure time, and the comfort and ease of use of the protective device. First, you have to select a hearing protector that has adequate attenuation for your work environment. Second, you have to consider how you are going to use the protector. You may for instance choose a different protector if your use is intermittent, requiring you to take on and off the protector frequently, than if you are going to work a continuous eight hour shift in a noisy environment. An earmuff may be preferable in the intermittent environment, while an earplug may be the choice in a long-term exposure. An earmuff may be preferred in a cold environment, while an earplug may be the choice in a hot and humid environment. However, there is no right or wrong choice, as long as you chose a hearing protector with adequate protection, and you use it correctly for the entire exposure time.
What are some typical noise levels of sounds and noises in our environment?
Below is a list of noise levels for sounds and equipment that you may be familiar with. Many of the examples are from the NIOSH website, but other references have also been used. It is important to keep in mind that you should really be concerned with the noise level at the ear, instead of the noise that is actually produced by the equipment. Therefore many of the examples have to be used with thought. For instance few consumers will be close to a jet engine or a fire engine siren, and their exposure is potentially more irritating than damaging. On the other hand, airport and fire engine personnel may indeed be exposed to the sound levels in the table below.
Sound or noise example |
Typical sound level |
Comments |
Weakest sound heard by average human ear |
0 dB |
This is a matter of definition |
Rustle of leaf |
20 dB |
- |
Whisper |
30 dB |
- |
Normal conversation |
60 dB |
- |
Inside passenger car at 60 MPH |
65-75 dB |
Smaller cars are usually noisier |
Ringing telephone |
80 dB |
Measured close to the phone |
Hair dryer |
85-90 dB |
Measured close to the dryer |
Lawn mower |
85-90 dB |
Measured at the ear |
Maximum exposure, 8 hours |
90 dB |
OSHA regulation |
Chain saw |
90-100 dB |
Measured at ear, sound level varies by model |
Tractor, bulldozer |
95-105 dB |
Inside cab may be less noisy. Sound level varies by model. |
Rock drill |
110-115 dB |
- |
Circular saw, table saw |
110 dB |
- |
Threshold of pain |
120 dB |
A matter of definition |
Pneumatic chipper |
120 dB |
- |
Fire engine siren |
120 dB |
- |
Jet engine at takeoff |
140 dB |
- |
12-gauge shotgun |
165 DB |
Impact sound uses a different risk criteria. |
Rocket launch |
180 dB |
- |
Loudest possible sound |
194 dB |
- |
How does exposure time affect my hearing protector requirements?
The hearing damage criteria established by the OSHA noise regulation takes into consideration the noise level and the exposure time. An exposure to 90 dB for eight hours is considered to be safe by OSHA, but it is recommended that you always use hearing protection when exposed to 100dB or more, even if the exposure is short. The exposure is doubled for every increase of 5 dB, as defined by OSHA. (Physically the sound pressure level doubles every 3 dB). The table below will explain the relationship between noise level and exposure time.
Noise level |
Maximum exposure time |
Comment |
90 dB |
8 hours |
- |
95 dB |
4 hours |
- |
100 dB |
2 hours |
- |
105 dB |
1 hour |
Always use hearing protection, any exposure |
110 dB |
30 minutes |
Always use hearing protection, any exposure |
115 dB |
15 minutes |
Always use hearing protection, any exposure |
What exposure limits are established for impact noise (such as gun fire)?
U.S. Military Standard 1474D, Requirement 4 deals with impact noise and establishes risk criteria in the way of maximum number of exposures to impact sounds at different sound levels, as well as pulse length (the duration of the impact sound, measured in milliseconds). The table below is a simplification of the military requirements, that does not take into consideration the pulse length. The table is therefore more conservative than the Military Standard.
- |
Maximum permissible number of exposures per day |
Impulse noise Limit |
No Protection |
Either Plugs or Muffs |
Both Plugs and Muffs |
140 dB |
Unlimited Exposure |
Unlimited Exposure |
Unlimited Exposure |
160 dB |
0 |
2,000 |
40,000 |
167 dB |
0 |
100 |
2,000 |
173 dB |
0 |
5 |
100 |
How do I select a hearing protector with adequate attenuation for my noise situation?
You need to know the approximate noise level of the environment you are seeking protection against. The decibel (dB) level can be measured with a sound level meter. This works fine in professional environments, but homeowners and consumers can use estimates and common sense. Most equipment and machinery used by homeowners, such as lawn mowers, chain saws, line trimmers and similar devices do not produce sounds in excess of 100dB. In addition the exposure time is usually limited to a couple of hours.
If you use a tool that produces 100 dB, and plan to use it for an hour or two, and you use an average hearing protector with a 25 dB Noise Reduction Rating, you will be more than adequately protected. Of course, if you also are exposed to noise at work, you must take this into consideration, since it is your total daily dose that matters. To calculate your exposure the EPA noise regulation advises that you deduct the NRR from the noise level.
- Example, the tool and hearing protector discussed above: 100 dB - 25dB = 75 dB at the ear.
- For professional applications, OSHA advises that the NRR be reduced by 7 dB:
- Example: 100dB - (25 - 7)dB = 82dB at the ear.
- OSHA may also require a 50% reduction of the NRR after the above reduction:
- Example: 100dB - (25 - 7) x 0.5 = 91dB at the ear.
What are the advantages of earmuffs over earplugs and vice versa?
Earmuffs are easier to use correctly, and therefore provide attenuation that is much closer to the laboratory derived NRR. Earplugs are hard or sometimes very hard to insert correctly, and therefore often do not provide the same attenuation in the field, as they do in the laboratory. This is the reason that NIOSH recommends different de-ratings for earplugs and earmuffs. You can read more about this subject by clicking on this link.
An earmuff may be preferable in the intermittent environment, while an earplug may be the choice in a long-term exposure. An earmuff may be preferred in a cold environment, while an earplug may be the choice in a hot and humid environment.
Most importantly, you should chose a protector that is comfortable and you should use it during the entire noise exposure.
How is the attenuation for hearing protectors measured?
In order to establish the effectiveness of a hearing protector, the following method (with certain modifications) is used by all current standards. Each subject is exposed to sounds at different frequencies (tones) and the lowest sound level that can be heard is established. Thereafter each subject uses a hearing protector, and the procedure is repeated. The difference between the hearing threshold with and without hearing protector is the attenuation (noise reduction) achieved by a particular hearing protector. The average for all subjects become the mean attenuation, and the variance establishes the standard deviation.
What does the NRR (Noise Reduction Rating) mean?
You can read an article about the NRR and other simplified methods at the following link.
www.elvex.com/facts03.htm
What factors, other than the noise level, combine to create a hearing damage?
Hearing damage can be created for many different reasons and sources. Industrial noise is certainly the most common and serious cause of hearing damage. Many leisure time activities also contribute, such as target shooting and hunting, noisy hobbies such as woodworking, as well playing in an orchestra or simply listening to music at excessive noise levels.
Another factor that contributes is heredity, and a certain level of hearing damage simply occurs from aging. Certain medications have also been demonstrated to contribute to hearing damage.
As discussed above, exposure time is a major factor in determining the total daily noise dose.
Can I still hear the machinery and warning signals, when I use a hearing protector?
Extensive studies show that individuals with normal hearing, will hear warning signals slightly better when using a hearing protector. Individuals with an existing hearing damage will not hear the warning signals as well while using a hearing protector. Read more about this subject at EarLogs by Aearo Corporation.
Can electronic hearing protectors help improve the ability to hear and communicate in a noisy environment?
Most likely you have heard about active headsets and noise canceling earmuffs. In theory the noise cancellation technology works by creating a negative sound wave for every noise (a series of sound waves), and thereby successfully cancel all noise for a perfectly quiet environment. Unfortunately this scenario is much more wishful thinking than reality. In order to be able to make the computations instantly, as we walk around in a changing noise environment, we would need a computer on a cart.
Today’s active or electronic headsets therefore are compromises that either are designed for specific noise environments, such as an airplane cockpit, or use some sort of filtering technique. The latter technique seeks to eliminate much more of the noise environment than of the speech, in order to improve the speech to noise relationship.
Electronic earmuffs can successfully eliminate impact noise, such as gunfire, and significantly contribute towards the ability to hear and communicate while on the shooting range or on a hunting team. This is done with an impact filter, which simply closes the electronics after sensing the sound wave from the noise impact. The filter reacts in microseconds and opens the electronics again after milliseconds (when the sound peak has passes).
Read about Elvex new DeTune electronic hearing protector.
Is it safe to listen to FM Radio earmuffs when you work?
OSHA has issued a letter of principal acceptance of this type of protection, on the condition that the noise level produced by the FM radio does not exceed 85 dB. Read the OSHA letter.
Who pays for my hearing protection at work?
OSHA has ruled that the employer pays for all necessary hearing protectors, including replacements. The employer decides what types of hearing protectors to offer, and has to make sure that they are adequate for the noise environment. The employer is required to offer a reasonable choice in order to maximize compliance.
How do I know if I have a hearing damage?
Your hearing threshold can be measured by an audiologist, and the instrument used to measure the hearing is called an audiometer. If you work in a noisy environment, and work for a larger company you have most likely already had your hearing tested.
What can I do if I already have an existing hearing damage?
Hearing damage is irreversible! If you already have a hearing damage, it becomes even more important that you make every effort to preserve your remaining hearing level. This means that you should avoid noisy environments whenever possible, and when you cannot avoid them, use an effective and comfortable hearing protector 100% of the exposure time.
If your hearing is already severely damaged, you should consult with an audiologist or specialist, in order to determine if a hearing aid may be able to improve your situation.
Return to top of page!
|
|
