| To measure the loudness of sound, a unit of | | | | The National Institute for Occupational |
| measurement called a decibel (dB) is used. A | | | | Safety and Health (NIOSH), a branch of the U. |
| decibel is one tenth of a bel (B), or the | | | | S. Centers for Disease Control and |
| unit of measurement devised by engineers of | | | | Prevention, reports that ear injury can |
| the Bell Telephone Laboratory to quantify the | | | | develop in workers if exposed to 85 dB or |
| level of sound reduction when a tone is | | | | more over eight hours. As a result, this 85 |
| transmitted over one mile (1.6 km) of | | | | dB exposure limit for an eight-hour workday |
| standard telephone cable. Since the bel | | | | has become a standard in the mining, |
| proved to be too large for most common sound | | | | construction, oil-gas well drilling, and |
| measurements, the use of the smaller decibel | | | | agriculture industries, as well as the U.S. |
| became more popular. | | | | Air Force and Army. Loss of hearing caused by |
| | | | excessively loud or prolonged noises is |
| The decibel is used in a wide variety of | | | | called NIHL, or noise induced hearing loss. |
| scientific measurements related to acoustics | | | | |
| and and electronics. This unit of measurement | | | | Injury to the cilia cells |
| places a physical value - usually of noise or | | | | |
| light intensity - in which a doubling of | | | | Sounds of less than 80 dB do not often result |
| actual intensity causes perceived intensity | | | | in hearing loss, even after long or |
| to always increase by roughly the same | | | | repetitive exposure. It is not possible to |
| amount. Specifically, a 3 dB increase is | | | | predict how an individual will respond to |
| about equal to an approximate doubling of | | | | loud noises, since each person possesses a |
| sound. This is important to understand | | | | different hearing sensitivity. Yet, exposure |
| because when you look at the dB values given | | | | to a single loud noise or continuous noise |
| in the following charts and text, you will | | | | exposure can result in temporary hearing |
| understand a relatively small numerical | | | | loss. This temporary loss is known as |
| increase of 10 dB between the sound of | | | | temporary threshold shift, and it will |
| rainfall and a sewing machine accounts for | | | | typically resolve 16 to 48 hours after the |
| the significantly greater noise level. It | | | | end of exposure. |
| also shows that the 110dB sound of a | | | | |
| screaming child is only several times less | | | | Hearing loss can be permanent if the |
| intense than a thunderclap or a rock concert. | | | | offending sound is loud enough to damage or |
| | | | destroy the delicate inner ear cells, called |
| Sound reference chart | | | | cilia, or stereocilia, that are found in the |
| | | | cochlea of the inner ear. These cilia cells |
| 0 Rustling leaves | | | | respond to mechanical sound vibrations by |
| | | | sending an electrical signal to the auditory |
| 20 Ticking watch | | | | nerve. The mechanism of injury to cilia is |
| | | | purely physical; excessive vibration results |
| 30 Quiet whisper | | | | in microscopic tearing or breaking of the |
| | | | cilia. There are many cilia located in the |
| 40 Refrigerator hum | | | | cochlea of the ear; the more that are |
| | | | damaged, the more profound the deafness. Once |
| 50 Rainfall | | | | cilia cells are chemically or physically |
| | | | damaged or destroyed, they will not |
| 60 Sewing machine, typical conversation level | | | | regenerate or repair themselves. |
| speech | | | | |
| | | | Protect your hearing |
| 70 Washing machine | | | | |
| | | | A commonsense recommendation to avoid hearing |
| 80 Alarm clock (two feet away) | | | | loss due to excessively loud noise is to |
| | | | either wear hearing protection or remove |
| 85 Average traffic | | | | yourself from the sound source. |
| | | | |
| 90 Gas lawnmower | | | | Use either earplugs, earmuffs or other |
| | | | protection devices when exposed to sounds |
| 95 MRI testing | | | | above 85 dB. Since you cannot always be |
| | | | certain when your sound environment places |
| 100 Tractor, hair dryer, subway train | | | | you at risk, use this rule of thumb: If you |
| | | | are talking to someone three away from you |
| 105 Power mower, chainsaw | | | | and you cannot clearly hear what is being |
| | | | said, the noise level around you could be |
| 110 Screaming child | | | | damaging your hearing. |
| | | | |
| 120 Rock concert, ambulance, thunderclap | | | | Do the obvious, and simply walk away when |
| | | | sounds are too loud or turn down the volume |
| 130 Jackhammer, jet engine plane (100 feet | | | | of the sound source if possible. It is also |
| away) | | | | possible to limit the sound intensity by not |
| | | | standing directly near its source. Time spent |
| 140 Fireworks | | | | in a loud environment is important to the |
| | | | health of your hearing, so limit the time you |
| 165 12 gauge shotgun blast | | | | expose your ears to loud noises. Cover your |
| | | | ears with your hands or cross the street when |
| Noise in the workplace | | | | you hear someone operating a leaf blower or |
| | | | when you are near a jackhammer. |