Noise Levels and Exposure Guidelines
To fully understand your audiogram and hearing aid specifications, you need to relate various sounds to the sound pressure level (SPL) in db (decibles) and the danger of loud noises to your hearing. This is why when wearing a hearing aid for the first time, always start with a low volume setting and then increase it gradually. Also the hearing aid should not output a sound greater than 130dB regardless of the input sound level.
Normal conversation is at around 50dB and this is normally used as reference input signal. A very loud sound is at 90dB and beyond, and 90dB input sound is used to test the output at the upper limit.
According to 2002 recommendation from CDC and NIOSH, continuous exposure to loud noises can cause permanent damages to your ear. The following is the accepted standards for recommended permissible exposure time for continuous time weighted average noise. For every 3 dBs over 85dB, the permissible exposure time before possible damage can occur is cut in half.
|Noise Level (dB)||Common Sounds||Hearing Sensation||Permissible Exposure Time|
|0||Hearing threshold||Not quite audible||No limit|
|10||Rustling leaves||Just audible||No limit|
|20-30||Quiet whisper at a distance, library, very quiet PC||Subdued sound||No limit|
|35-40||Quiet office, normal PC, bedroom, sound of a mosquito, refrigerator hum||Subdued sound||No limit|
|50||Light auto traffic (100 feet), normal conversation||Clearly audible||No limit|
|60||Restaurant, air-conditioning, slightly elevated conversation||Slightly intrusive||No limit|
|70||Noisy restaurant, freeway traffic, busy office||Noisy, hard to use a phone||No limit|
|80||Vacuum cleaner, alarm clock, hair dryer||Very noisy, annoying||No limit|
|85||Average factory, electric shaver||Increasing annoying||8 hours|
|90||Heavy truck, busy city street, lawn mower, screaming child||Very loud, very annoying||~2 hours|
|100||Jet takeoff @ 500m, train horn @ 30m, jackhammer||Very loud||~15 minutes|
|110||Rock concert, chainsaw, snowmobile||Very loud||~1.6 minutes|
|120||Car horn, air-raid siren, propeller aircraft||Extremely loud||~7 seconds|
|130||Military jet, shotgun, hydraulic press||Almost intolerable||None|
|140||Gunshot, jet engine taking off||Pain threshold, intolerable||None|
|180||Rocket launching||Instant eardrum perforation||None|