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Noise Dose
This is more commonly known as Dose and is expressed as a percentage.
The Noise Dose represents the total noise received by an employee over the
working day and is therefore not only a function of the noise level but also of the
time the employee is exposed to it.
Dose is similar to Lep,d but as dose is represented as a percentage the daily
total dose can be calculated from partial dose values by simply adding them
together or using the Exposure Calculator in dBdataPro.
Dose in general however is measured for the complete shift using a dose meter
which the employee wears for the entire shift resulting in a total daily dose
figure.
Alternatively if required you may measure individual partial tasks the employee
undertakes throughout the shift for shorter periods and adjust the Exposure
Time on the instrument. Exposure Time on your Sonus instrument is displayed
as ET, if an ET is not entered then the Measurement Time MT is used instead.
Remember that the longer the noise level is recorded over then the more
accurate the result will be although it is possible to take valid Dose readings
from short recordings of as little as 5 minutes assuming all the variations in the
noise emissions are captured.
Also be aware that low noise levels with Exposure Times over a longer period
may give the same Dose as noises with higher levels with Exposure Times over a
shorter period.
Noise Dose is also governed by the settings of Criterion, Threshold and
Exchange Rate.
In the UK a Criterion of 85dB with a 3dB Exchange Rate is used for Noise at
Work assessments. 85dBA Lep,d is also the UK Upper Action Value as stated
in the Noise at Work Regulations 2005.
The Criterion is the sound level that if continually applied for the working shift
(typically 8 hours) will produce a Dose value of 100%.
Therefore in the UK if an employee is subject to a noise level of 85dB continually
for 8 hours then they will be subject to 100% Dose. This is the maximum
allowable dose percentage an employee can be subject to before action must be
taken.
The Exchange Rate is the amount by which the permitted noise level increases
when the exposure time is halved or vice versa, therefore in the UK this value is
3dB.
As an example, if 8 hours is the maximum period for a continuous noise level of
85dB then 4 hours is the maximum time period an employee maybe subject to a
continuous noise level of 88dB.
