Application
Noise is sound waves that propagate through air or fluid at different frequencies. Noise is best reduced at the source, and it is for the employer through technical measures or adequate planning to reduce noise impact to a minimum. If noise impacts can not be reduced below 80 dB (A), work shall be performed only if there is hearing protection available. Is the noise over 85 dB (A) (over a 40 hour week), is hearing protection required. But it is recommended to use hearing protection as early as 80 dB (A) because the noise level is already here considered to be harmful. Selecting the proper hearing protection depends on the noise volume and frequency range, the needed noise reduction, and the need for combination with other safety equipment.
Relevant standards
- EN 352-1: Earmuffs
- EN 352-2: Earplugs
- EN 352-3: Earmuffs for industrial safety helmet
- EN 352-4: Level-dependent earmuffs (with amplification)
- EN 352-5: Earmuffs with active sound attenuation
Volume and frequency
Decibel (dB) is a measure of sonic power, like degrees Celsius is a measure of temperature. Roughly estimated a change in noise of 3 dB is experienced as a doubling of the volume. Therefore, even very modest changes in the noise have crucial effect. Common industrial noise is typically 100 to 110 dB, while ordinary speech is about 60 dB.
Frequency indicates the number of sound vibrations per. second and is called Hertz (Hz). One (Hz) is therefore one sound vibration per second. Slow vibrations are seen as low tones (bass around 125 Hz), while the rapid vibrations as highs (treble, like a trumpet, around 4000 Hz). Young people with good hearing can hear sounds from 20 to 20,000 Hz. Common industrial noise is typically in the range 2-8000 Hz, which is medium-and high-frequency.
Attenuation
Knowing the type of noise or the exact noise power (this measurement can be made by your local Occupational Health Center) then you can choose the proper hearing protection based on the HML-values that characterize hearing protection attenuation of High, Medium and Low frequency noise. The higher HM-values the better attenuation of high-frequency noise and higher ML values the better the attenuation low-frequency noise.
SNR value (Single Number Rating) for a hearing protection is a simplified American approach to the expression of hearing protector attenuation in the general noise. When the SNR value is subtracted from the measured noise level, then the result (noise inside the earmuff) must be less than 75 dB. Otherwise, the hearing protection is not fit for purpose.
If a hearing protection is to be effective, it must be used throughout the time you are exposed to noise. Constant use is of paramount importance, and therefore hearing protection, first and for emost, must be comfo rtable to use. If hearing protection is not used for just 1% of the time you are exposed to noise, then the effec tive noise reduction is reduced by 33%. If hearing protection is not used for 10% of the time, the effective noise reduction is reduced by 66%.
