Maximum Exposure Time (in an 8-hour working day/shift)Ĩ hours (Wearing hearing protection in the workplace is mandatory) The table below gives guidance on how long it is safe for someone to be exposed to different noise levels without wearing hearing protection. Maximum Recommended Noise Dose Exposure Levels Knowing the decibel level will help identify any noisy areas or machinery that requires hearing protection to be worn whilst in operation, as well as if anything needs sound enclosures or other noise control techniques need to be employed such as using noise-activated warning signs to zone areas. To measure decibel levels for the protection of peoples’ hearing an integrating sound level meter is required, such as the Pulsar Nova Model 44. A hearing test can tell if hearing loss is from noise or if it is from age as people who have noise-induced hearing loss have deafness at different frequencies when compared with those with age-related hearing loss. Hearing gets damaged because high noise exposure over a period of time can damage the delicate hair-like sensory cells in the ear (in the cochlea). After prolonged exposure to decibel levels above 80 dB(A) people can start to suffer from permanent hearing loss. Even a small increase in decibels has a large impact on how intense a sound is, for example – 90dB(A) is 10 times more intense than 80dB(A), where 80dB(A) is the Lower Exposure Action Value in most Health and Safety legislation. An increase of 3 dB(A) is a doubling of sound intensity, but it needs to be an increase of 10 dB in your decibel readings to be heard as double the level of noise by the ear. The decibel scale measures sound pressure level on a logarithmic scale (based on the power of 10) the human ear’s response to noise levels is also approximately logarithmic too. Most people will suffer some hearing damage at repeated exposure to levels over and above 85dB(A) or even acoustic shock (sudden hearing loss) at levels over 137dB(A). This sound is measured in units called Decibels (dB) which tell you how loud something is and if the noise is loud enough to cause damage to hearing. Noise is characterised as ‘unwanted sound’. The chart gives examples of how loud some of the common tools and objects we may see (and hear!) in our life are. Likewise our hearing does not have the same sensitivity at all frequencies.Find out decibel levels of common noises like power tools, objects and places with our decibel chart. No microphone has the same sensitivity to all frequencies and no speaker reproduces all frequencies equally well, as we will see in Chapter 18 on electronics. The above curves are very much like the frequency response curves of microphones and speakers. Medium loudness doesn't change the perceived pitch very much. Low frequencies are perceived to be slightly lower than expected if they are very loud. High frequencies are perceived to be a slightly higher pitch than normal if they are very loud. It is also the case that intensity has an effect on perceived frequency the same laboratory frequency will appear to be a slightly different frequency if the intensity is different. \( \newcommand\) is due to the tube resonance of the auditory canal (see chapter 12 for tube resonance and chapter 10 for a picture of the auditory canal).
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