Sound level meters and personal noise dosimeters are both used to measure occupational noise, but they answer different questions. A sound level meter is normally held or mounted at a selected position so that the assessor can examine the sound at a workplace location, around a source or during a task. A dosimeter is worn and travels with the person, integrating the changing sound reaching the microphone during the sampling period. The choice is not simply between a more basic and a more advanced instrument. Each instrument has a distinct role. A sound level meter gives the assessor direct control over location, observation and measurement timing. A dosimeter records a person's changing acoustic environment while work continues, including movement between areas that may not be practical to follow continuously with a hand-held meter. Detailed dosimetry technique and personal sampling strategy are addressed separately on /noise-dosimetry and /personal-noise-dosimetry, while this page is limited to the instruments, their specified performance and the controls needed to obtain traceable measurements.
A sound level meter places the microphone at a location selected by the assessor. It is suited to area readings, source investigation, comparison of work positions and observation of how sound changes as a machine cycles or a control is operated. The display allows immediate review, making it possible to relate a change in the reading to an observed event.
A dosimeter places the microphone on the wearer and the instrument body on the person. Its value lies in integrating sound while the employee moves, changes tasks or works where continuous observation would interfere with normal activity. The recorded result is associated with the sampled person and period rather than with one fixed point on a floor plan.
Neither instrument automatically produces a valid assessment. Correct settings, microphone position, calibration, operating observations and data review remain necessary. A technically capable instrument can still produce misleading information if it is used in the wrong place or if the sampling period does not represent the conditions being assessed.
ADOSH-SF CoP 3.0 specifies a sound level meter meeting ANSI S1.4-1983 (R2006) Type S2A or a personal noise dosimeter meeting ANSI S1.25-1991 (R2007). It specifies the A-weighting network and slow response, with integration of continuous, intermittent and impulsive levels from 80 dB(A) to 130 dB(A). These instrument-range figures come from ADOSH-SF CoP 3.0 and apply within the Emirate of Abu Dhabi.
These requirements define the minimum instrument framework stated by the Code. The assessor should be able to identify the instrument model, serial number, applicable standard and measurement settings from the field record and final report. A generic statement that a meter was calibrated is not enough to demonstrate that the device met the named specification or was configured correctly.
A-weighting adjusts measured sound to reflect the frequency response used for occupational assessment under the Code. Slow response controls how the displayed level follows short-term fluctuation. Integration allows changing sound to be accumulated rather than represented by an isolated reading.
Field calibration is a functional check of the complete measurement chain. ADOSH-SF CoP 3.0 identifies a field calibrator meeting EN/IEC 60942 (2003) Class LS and Class 1 and/or ANSI S1.40-1984. The calibrator is applied before and after measurements so that the assessor can confirm that the microphone and instrument response have remained acceptably stable during the survey period.
The pre-measurement check should be completed after the instrument has been assembled in the configuration that will be used. The microphone, preamplifier, extension lead where present and instrument settings all form part of the measurement chain. The displayed calibration result should be recorded rather than reduced to a tick box.
The post-measurement check is equally important. It may reveal microphone damage, connector movement, battery problems or instrument drift that occurred after the initial check. Where the before-and-after results do not agree within the instrument or procedure acceptance criteria, the data should be investigated and should not be accepted automatically.
The field record should identify the calibrator by model and serial number and should link it to a current laboratory calibration record. The assessor should also record any unusual condition, such as difficulty seating the calibrator or an unstable response, because such details may affect confidence in the data.
Field calibration does not replace laboratory calibration. CoP 3.0 states that laboratory calibration is to be carried out by the manufacturer or a manufacturer-approved third party. The certificate should identify the instrument or calibrator uniquely and should provide traceability for the equipment used during the survey.
An equipment register should show the current calibration status, certificate reference and any restrictions or repairs. Instruments that have been dropped, exposed to moisture, damaged or found outside field-check acceptance criteria should be quarantined until their condition is established. Continuing to use an instrument merely because its certificate has not expired can undermine the measurement record.
The final report should state the laboratory calibration status relevant to the date of measurement. Attaching a certificate can be helpful, but the report should still identify which certificate belongs to which item so that a reviewer does not have to infer the link.
A windshield reduces the influence of air movement across the microphone. It is generally appropriate where ventilation currents, outdoor air movement or movement of the wearer could produce turbulence at the microphone. The windshield should be compatible with the microphone and should be clean, dry and undamaged.
A windshield does not make every condition suitable for measurement. Strong airflow, contact with clothing, rain, contamination or mechanical vibration can still distort the result. The assessor should observe the microphone and surroundings and should note conditions that may affect data quality.
For a hand-held meter, the assessor should avoid standing in a position that shields or reflects sound towards the microphone. The instrument should be held or supported so that the body, clipboard and nearby surfaces do not become unintended acoustic obstacles.
Microphone position should represent the sound relevant to the question being assessed. For an area or workstation reading, the position should correspond to the occupied location while avoiding placement that is unrepresentatively close to a reflecting surface or source unless that close position is the subject of the investigation.
For a worn instrument, the microphone should remain near the person's hearing zone and should be fixed securely. It should not be placed beneath clothing, pressed against a collar or located where tools, straps or equipment repeatedly strike it. The assessor should observe the arrangement after fitting and should check it again when practical during the sample.
Position should be documented in clear terms. Photographs or diagrams may assist where permitted by workplace controls, but written notes remain necessary. A report that states only that a dosimeter was worn does not show whether the microphone was exposed correctly or whether the arrangement changed during the shift.
The instrument should also be protected from tampering. Employees should understand the purpose of the device and should be told not to cover, remove or relocate the microphone. Any event that may have affected the measurement should be recorded and considered during data review.
A sound level meter is generally suitable where the assessor needs direct observation, spatial comparison, source investigation or a controlled measurement at a known position. A dosimeter is generally suitable where movement, changing tasks or variable sound makes a fixed position unlikely to represent the person's experience.
ADOSH-SF CoP 3.0 states that representative personal sampling must be used where high mobility, significant level variation or a significant impulse component makes area monitoring inappropriate, unless area sampling is shown to give equivalent results. Instrument selection should therefore follow the work pattern rather than convenience.
The decision should be recorded. A defensible explanation may refer to employee movement, source variability, access constraints and the purpose of the assessment. Using the same instrument for every workplace without considering these factors can leave a gap between the data collected and the conclusion reached.
ADOSH-SF CoP 3.0 Occupational Noise, Version 4.0, dated 15 July 2024, sits in the mandatory Codes of Practice layer and applies to all employers within the Emirate of Abu Dhabi. For instrumentation, the Code names the required sound level meter, dosimeter and field-calibrator standards, requires field calibration before and after measurement and specifies laboratory calibration by the manufacturer or a manufacturer-approved third party. It also requires representative personal sampling where area monitoring is inappropriate because of high mobility, significant variation or a significant impulse component, unless equivalent area results can be demonstrated.
It should not be treated as a substitute for an instrument meeting the standards named by CoP 3.0. A phone application may be useful for informal awareness, but its microphone, dynamic range, settings, calibration control and traceability may not support a compliance assessment.
Yes. Field calibration checks the assembled measurement chain at the time of use. Newness does not confirm correct settings, microphone connection or stability across the measurement period.
The assessor should investigate the difference against the instrument procedure and acceptance criteria. The affected data should not be accepted automatically, and the report should explain any exclusion, repetition or qualification.
It can be used where it is compatible with each microphone and meets the required standard. Each use should remain traceable, and any adaptor should be suitable for the microphone arrangement.
Rubbing, impact or partial covering can create non-acoustic signals or alter the sound reaching the microphone. Secure fitting and observation help distinguish workplace noise from artefacts caused by the mounting arrangement.