Daily noise dose

Daily noise dose (DND) The allowable noise exposure for an 8-hour workday. 

Estimating a worker s exposure and calculating the daily noise dose (DND)... 

To work out the daily noise dose for a worker you need to either fit the worker with an NDM for a day, or use a questioimaire to find out where the person typically works, what is normally done there, and how long he or she spends at each task or location. A so-called nomogram is then used to calculate the DND, based on the principle that the sound energy reaching the ear doubles for every 3 dBA increase. This allows you, for example, to work the L eq, 8 h from information like the following ... 

Add together values of f (fraction of noise dose ) received during one day to obtain total fraction of daily noise dose. 

Another important noise measurement is the daily personal exposure level of the worker, l-EP,d> which is measured over an 8-hour working day. Hence, if a person was exposed to 87dB(A) over 4 hours, this would equate to a Lep.ci of 84dB(A) since a reduction of 3 dB(A) represents one half of the noise dose. 

The changing nature of the noise intensity in agricultural aircraft makes necessary an assessment of noise dose, where the equipment performs a number of measurements of noise level and generates a projection for daily exposure. The criteria reference that supports the daily exposure corresponds to a 100% dose for an exposure time of 8 hours at the level of 85 dB(A). Furthermore, the assessment considers doubling of the dose (q = 3), in other words 88 dB(A) or 85 dB(A) -i- q is equal to the 200% of the daily exposure. 

Fig. 3.25. Drift of exposure parameters over time, (a) kV, mAs and signal-to-noise ratio of a system that was stable in terms of dose (kV, mAs) over a period of 1 year, (b) shows a system where the mAs gradually increased but the kV and mean PV remained constant. (c) Evaluation of the mAs during daily quality control. Every change in mAs indicated by an arrow is due to interventions by service engineers...

Isolation of workers in acoustically-quiet booths or control areas properly enclosed, coupled with scheduling of work periods to reduce dose. This will only be effective where there is little or no need for constant movement into or out of areas with high noise levels even a short duration exposure to high sound pressure levels will exceed the permitted daily dose. Nevertheless, improved design of vehicle and plant cabs and (for example) batch plant and lifting equipment operating positions can do much to improve the health of operators. 

The noise exposure expressed as a percentage of the allowable daily exposure. A 100% dose would equal an 8-hour exposure to a continuous 90 dBA noise a 50% dose would equal an 8-hour exposure to an 85 dBA noise or a 4-hour exposure to a 90 dBA noise. If 85 dBA is the maximum permissible level, then an 8-hour exposure to a continuous 85 dBA noise would equal a 100% dose. If a 3 dB exchange rate is used in conjunction with an 85 dBA maximum permissible level, a 50% dose would equal a 2-hour exposure to 88 dBA or an 8-hour exposure to 82 dBA. 

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