Noise dosimetry is a measurement technique that integrates changing sound levels over time. A personal noise dosimeter records the acoustic conditions at its microphone and applies programmed measurement settings to calculate exposure quantities such as dose and time-weighted average. The technique is valuable where work does not take place at a single fixed position or where sound varies through the working period. It can capture continuous production noise, intermittent tool use, vehicle movements and impulsive events within the instrument's configured measurement range. A dosimeter result is not self-explanatory. Its validity depends on correct settings, microphone placement, calibration, representative run time and a reliable record of what occurred during the sample.
A dosimeter contains a microphone, signal-processing system, clock and data storage. The microphone responds to sound pressure close to the wearer's hearing zone. The instrument then applies the selected frequency weighting, response and exposure settings.
Many instruments retain a time history as well as an overall result. The time history shows how the recorded level changed during the sample and may assist the assessor in linking peaks or sustained periods with work activities. It is particularly useful when field observations or the wearer's activity record can be aligned with the data.
The microphone does not know whether a sound came from machinery, a nearby conversation, accidental contact or deliberate interference. Interpretation therefore depends on observations and post-sample review. A high point in the trace should not automatically be assigned to a production source without supporting information.
The instrument also cannot determine whether the sampled working period was typical. It accurately records the sound presented to it, subject to its technical performance and settings, but representativeness remains a sampling question.
The criterion level is the exposure level corresponding to the reference duration used by the dosimeter's dose calculation. Under ADOSH-SF CoP 3.0, the criterion is 85 dB(A) for an 8-hour time-weighted average.
The exchange rate defines how the allowable duration changes when the sound level changes. CoP 3.0 uses a 3 dB exchange rate. With this relationship, an increase of 3 dB halves the corresponding allowable duration, while a decrease of 3 dB doubles it.
The reference duration is calculated as T = 8 / 2^((L-85)/3) hours.
The permitted durations include 80 dB(A) for 24 hours, 85 dB(A) for 8 hours, 88 dB(A) for 4 hours, 91 dB(A) for 2 hours, 94 dB(A) for 1 hour, 97 dB(A) for 30 minutes, 100 dB(A) for 15 minutes, 103 dB(A) for 7 minutes 30 seconds, 106 dB(A) for 3 minutes 45 seconds, 110 dB(A) for 1 minute 29 seconds, 115 dB(A) for 28 seconds and 120 dB(A) for 9 seconds. These figures come from ADOSH-SF CoP 3.0 and apply within the Emirate of Abu Dhabi.
The threshold is the lower level at which sound begins to be included in the instrument's exposure integration. CoP 3.0 requires integration of continuous, intermittent and impulsive levels from 80 dB(A) to 130 dB(A). The 80 dB(A) threshold is a measurement setting and should not be interpreted as a general boundary between harmless and harmful sound. These figures come from ADOSH-SF CoP 3.0 and apply within the Emirate of Abu Dhabi.
Noise dose expresses the accumulated exposure as a fraction of the permitted exposure relationship. A dose result allows periods at different sound levels to be combined according to the criterion and exchange rate.
CoP 3.0 defines dose as D = C1/T1 + C2/T2 + ... Cn/Tn.
In this expression, C is the actual duration at a particular level and T is the permitted reference duration for that level. A value of D greater than 1 represents over-exposure under the CoP calculation. These figures and the formula come from ADOSH-SF CoP 3.0 and apply within the Emirate of Abu Dhabi.
A time-weighted average expresses the accumulated exposure as an equivalent level over the reference period. Dose and time-weighted average present the same underlying exposure relationship in different forms when the instrument has been configured consistently.
The assessor should confirm the dosimeter settings before interpreting either result. A dose based on a different criterion, exchange rate or threshold cannot be compared directly with the CoP 3.0 relationship merely because the display uses the same label.
A partial-period dose is not automatically the final daily dose. It represents only the period measured unless a justified projection or combination with other exposure periods is made.
The sample should cover enough of the work to represent the exposure question. Where a person's duties and noise levels vary through the working period, extended sampling normally gives a more direct account than a short observation.
Full-period sampling can capture changes in location, task sequence, breaks, intermittent equipment and production stages. It may, however, include periods outside the intended scope if the instrument remains running during activities unrelated to the assessed work. Start and finish times therefore need to be documented.
A shorter run may be suitable for a stable task or a defined operating cycle, provided that the task duration and frequency are known. The result can then support a broader calculation, but it should not be labelled as a complete working-period exposure without the necessary combination or extrapolation.
The assessor should consider whether the sampled period includes foreseeable higher-exposure work. A technically sound sample collected during unusually quiet production may underestimate the exposure pattern intended to be represented.
Likewise, a sample dominated by an unusual breakdown or abnormal event may not describe routine exposure. The event may still be important and should be reported separately rather than silently removed or treated as normal.
CoP 3.0 specifies that employee noise exposure is to be determined using a sound level meter meeting ANSI S1.4-1983 (R2006) Type S2A or a personal noise dosimeter meeting ANSI S1.25-1991 (R2007). The measurement device is to use the A-weighting network with slow response.
A field calibrator complying with EN/IEC 60942 (2003) Class LS and Class 1 and/or ANSI S1.40-1984 is to be used before and after measurements. Sound level meters and dosimeters are also to be calibrated by the manufacturer or a manufacturer-approved third party in accordance with the manufacturer's specifications. These requirements come from ADOSH-SF CoP 3.0 and apply within the Emirate of Abu Dhabi.
The pre-use calibration check confirms that the instrument and microphone respond appropriately before deployment. The post-use check helps identify a change that may have occurred during the sample. A satisfactory display at the end does not correct an unsuitable microphone position or an unrepresentative sampling period, so technical checks and sampling quality must both be considered.
The instrument clock should be checked against the field record. An incorrect clock can make it difficult to associate events with the time history and may lead to mistaken interpretation.
A sample may be invalid where the calibration checks indicate unacceptable performance, the instrument develops a fault, the microphone is disconnected, the battery fails or the data record is incomplete.
Microphone obstruction can also compromise the result. Clothing, protective-equipment straps, hair or other objects may cover or repeatedly strike the microphone. Wind, water ingress and accidental impact can create artefacts unrelated to ordinary exposure.
Removal of the instrument during part of the intended sampling period creates a data gap. The assessor must determine whether the missing period can be reconstructed reliably or whether further sampling is needed.
Deliberate shouting into the microphone, tapping the microphone, blowing across it or positioning it beside an unrelated sound source can create artificial events. These may be identifiable from the trace and field information, but the assessor should not remove data without a documented technical basis.
A sample may also be unsuitable even where the instrument operated correctly. Examples include sampling the wrong work group, measuring an atypical shift, omitting a material task, using inappropriate settings or extrapolating a brief and variable period beyond what the evidence supports.
The neighbouring page /personal-noise-dosimetry addresses selection and management of the person wearing the instrument, while /noise-exposure-assessment addresses the subsequent calculation and comparison strategy.
Abu Dhabi's ADOSH-SF requires the CoP 3.0 measurement relationship to be used for relevant occupational-noise exposure assessment within the Emirate. This includes an 85 dB(A) 8-hour criterion, a 3 dB exchange rate, integration from 80 dB(A) to 130 dB(A), A-weighting and slow response. The instrument and calibration provisions stated above also come from CoP 3.0 and apply within the Emirate of Abu Dhabi. Exposure is calculated without allowing for hearing-protector attenuation.
No. It records sound reaching the microphone from all nearby sources. Field observations are needed to determine which sources and activities contributed to the result.
No. The criterion, exchange rate, threshold, weighting and response must be confirmed. A result calculated using different settings may not be comparable with the applicable assessment relationship.
No. The highest level describes a particular part of the sample, while daily exposure depends on the combined level and duration of all relevant periods.
Only where there is a documented technical basis for identifying them as artefacts. Removal should be transparent, and the effect on the overall interpretation should be stated.
The missing period must be evaluated. Where its exposure cannot be reconstructed reliably, the sample may be incomplete and further measurement may be necessary.