What is noise dosimetry?
Dosimetry uses a personal device to record the noise to which a person is exposed during their activities. Its advantage is that it allows for tracking movements and variations in work. However, wearing the device for several hours does not guarantee that the day, tasks, and microphone position accurately represent the exposure being assessed.
The technique is part of the workplace noise assessment. It is not a hearing test, nor does it determine whether a person has an injury. Exposure assessment and health surveillance complement each other, but they use different information and answer different questions.
When might it be useful
This can be especially useful when tasks and locations are alternated, noise levels change in unpredictable ways, or it’s difficult to monitor all activity with a sound level meter. In other scenarios, measurements by task or workstation may be suitable. The choice depends on the job, the objective, and the technical strategy used.
Before taking measurements, a representative workday is described: operations, machines, shifts, breaks, maintenance, and exceptional situations. If there are significant differences between days or individuals, the plan must account for them. Selecting only a quiet day because it facilitates setting up the equipment may produce an accurate result for the observed day, but it is of little use for evaluating typical work.
Equipment and sampling preparation
The instrument must be suitable for the applicable parameters and requirements. Configuration, battery, memory, range, and microphone condition are checked. Royal Decree 286/2006 requires checks with an acoustic calibrator before and after each measurement or series of measurements. These field checks do not replace the corresponding maintenance and metrological control.
The person receives clear instructions on how to perform their usual work and report any incidents, avoiding hitting, covering, or tampering with the microphone. Its placement must follow the established method and technical instructions. The instrument’s identity and configuration are recorded because a percentage dose or an indicator calculated using other criteria is not automatically comparable to the Spanish framework.
What to record during the day
The task log allows you to link noise levels to specific operations. It should record times, locations, active equipment, production changes, and events that affect the measurement. It’s also advisable to note downtime, microphone issues, and any discrepancies between planned and completed work.
Unexpected spikes are investigated before their meaning is determined. A tap on the microphone may not represent actual acoustic exposure, but neither should a high spike be removed without evidence of its source. Traceability is essential: whoever reviews the report needs to distinguish between a process event, a measurement incident, and data requiring further verification.
Interpretation of the results
The assessment must express the appropriate parameters, including the daily exposure level and the peak level where applicable. An average over the measured time does not always equate to the eight-hour reference value. An explanation must be given of how unmeasured periods and day-to-day variability have been addressed.
Action values are compared without discounting hearing protection. Considering attenuation for the limit value follows specific criteria and requires knowledge of the actual use of the protection. Simply subtracting the number printed on the earplug packaging from any reading is insufficient. Uncertainty and representativeness must be considered in the technical decision.
Practical example
A person alternates between carrying loads, operating a machine, and cleaning. A sound level meter fixed in a corner does not record their movements. The assessment proposes dosimetry with a record of tasks and shifts selected for their representativeness. The time analysis identifies that a short operation contributes a significant portion of the exposure.
The company modifies that operation and reviews the equipment maintenance. Then it verifies the result under comparable conditions, keeping production and time data. Dosimetry thus allows an improvement to be linked to a specific source, instead of simply filing a daily figure without explaining what determines it.
From measurement to measures
The objective is to eliminate or reduce noise at its source and to plan technical and organizational measures. This may include studying quieter equipment, maintenance, appropriate enclosures, separation of operations, or changes in work methods. Hearing protection is incorporated according to the assessment and applicable regulations.
The report must assign actions, responsibilities, and verification procedures. Repeating a measurement without addressing a known problem does not constitute preventive improvement. Similarly, an observed reduction must be verified without automatically attributing it to an intervention if the second day had lower production or different tasks.
Common mistakes and review
Common errors include using an unvalidated application as a substitute for assessment, confusing dosage with hearing damage, and extrapolating from a sample without justification. It is also a mistake to conceal equipment malfunctions or compare results from different configurations as if they were equivalent.
The assessment is reviewed according to requirements and when equipment, tasks, shifts, or relevant conditions change. The participation of those performing the work helps to identify these changes. Properly applied dosimetry provides evidence to inform and validate measures, maintaining a clear link between person, activity, exposure, and control.
