Acoustic Glossary


 

Noise Dose : Definitions, Terms, Units and Measurements.

Noise Dose is the measured Sound Exposure Level normalized to an 8-hour working day.


% Dose is the Noise Exposure expressed as a percentage (%) of an 8-hour working day. In the UK the 100% level is 85 dBA using the 3 dB Exchange Rate. Dose% varies according to National Standards.


Daily Exposure Level - LEX,8h is the Sound Exposure averaged over 8 hours.

The Noise at Work Directive 2003/10/EC : defines the following limit and action values:

Exposure Limit Values - ELV : the LEX,8h = 87 dB(A) and LCpeak = 200 Pa respectively.

Upper Exposure Action Values : the LEX,8h = 85 dB(A) and LCpeak = 140 Pa respectively.

Lower Exposure Action Values : the LEX,8h = 80 dB(A) and LCpeak = 112 Pa respectively.

LCpeak is the maximum value of the C-weighted, instantaneous noise pressure.

see also Daily Personal Noise Exposure - LEP,d below.

LEX,8h is the Leq - Equivalent Continuous Sound Level corrected for the length of the working shift, in this case 8 hours.


Daily Personal Noise Exposure : LEP,d is the averaged A-weighted noise exposure level for a nominal 8-hour working day and is for assessing the noise exposure of a employee during a working day. It is also known as LEX,8h.

LEP,d is calculated from the measured Sound Exposure, the Exposure Time and a Reference Time of 8 h.

If the Leq is measured over 8 hours then Leq and LEP,d and LEX,8h would all be the same.

The European Directive recommends LEX,8h is adopted from 2006 onward.

see also Leq - Equivalent Continuous Sound Level

Damage Risk Criteria : recommended maximum noise levels for given exposure periods. See Exposure Action Value (EAV) and Exposure Limit Value (ELV)


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DOHR : Dose per hour - shows the dose profile for each hour.

Dose% is the amount of noise expressed as a percentage of the normal allowable daily collected during a measurement on a worker with a noise dosimeter.

Dose% varies according to National Standards

Dose Badge : small device worn by operator to store fluctuating noise levels during working day. Similar to a Dosimeter.


Dose per Hour : DOHR : shows the dose exposure over each hour.

Dosimeter : a pocket sized instrument designed to be worn during all or part of the day as a personal monitor in order to check an operator's personal exposure to workplace - Noise Dose.

see also : Sound Exposure Meter.

EAL : Exposure Action Level
ELV : Exposure Limit Value

Estimated Dose : the exposure received if the measured level had existed for the specified Criterion Time.


Exposure Time : the time a person is exposed to noise during a workday - used for calculation of LEP,d - Daily Personal Noise Exposure.


Noise Dose : D : the Sound Exposure expressed as a percentage (%) of a fixed level for the working day.

If the noise limit is 85 dBA and a person is exposed to a constant or Equivalent Sound Pressure Level of 85 dBA for eight hours, then the result is a 100% noise dose.

ISO use an energy-based average for noise dose calculation, based on the 3 dB Exchange Rate. This means a noise level of 88 dBA has twice as much energy as a level of 85 dBA.

So if 85 dBA = 100%Dose = 8 hours exposure, then 88 dBA = 200% exposure so only a maximum of 4 hours is allowed per shift

The 3 dB exchange rate is also used in the UK, and the 8 hour average level is known as the Daily Personal Noise Exposure LEP,d or LEX,8h.

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The Sound Exposure (in physical units) for the whole measurement duration of Dose is known as E (Pa².h)

Leq = 10 lg(Dose/100 x 8/T) + 85 dBA : where T = measurement time in hours.

LEX = 10 lg(Dose/100) + 85 dBA : where T = measurement time in hours.

The Noise Dose examples above assume the UK and EU default Criterion Time of 8 hours and Exchange Rate : Q = 3.

see also : Projected Dose and Threshold Level

Noise Dose Meter : Sound Exposure Meter also known as Noise Dosemeter and Noise Dosimeter.


Noise Dose per Hour : DOHR - shows the dose exposure over each hour.


Noise Dosimeter : a pocket sized instrument designed to be worn during all or part of the day as a personal monitor in order to check an operator's personal exposure to workplace noise - see Sound Exposure meter.


NProjDose : Projected Dose : uses the current Noise Dose value, logged during the present measurement, to be projected forward to give the predicted 8 hour period, assuming the sound levels for the remaining time stays the same.


Threshold Level : most regulations specify that for the measurement of noise at work, the sound levels below a certain limit (the threshold) should be disregarded. A Noise Dose Meter, therefore only sums up the contributions from the levels above the threshold and uses these values to calculate the Noise Dose parameters.


See also : Sound Exposure l PSEM Personal Sound Exposure Meter