What is being measured?
Before choosing a device, the question must be asked: is it assessing an individual’s exposure, checking dispersion from a source, studying variations during a task, or verifying a preventive measure? The same concentration measured in air may be useful for one purpose and insufficient for another. The report must explicitly state this difference.
In this context, personal sampling refers to sampling carried out in the breathing zone of the worker. Environmental sampling at fixed points keeps the sampler in a specific location. Both study air in the workplace environment, so it is important to clarify the meaning used and avoid automatically interpreting the term “environmental” as representative of all people present.
Personal sampling
The sampler accompanies the person and is positioned according to the method’s requirements to represent the air reaching their breathing zone. This allows tracking of their movements and actions, although the validity of the sample still depends on the system’s design, duration, and operation. Simply carrying a pump does not, in itself, guarantee a representative sample.
During sampling, tasks, times, products, and relevant changes are recorded. It must be verified that the device does not unnecessarily disrupt the work or create additional risk. If the sampler is moved, the pump is interrupted, or the usual procedure is modified, the incident is documented and assessed before using the results for decision-making.
Fixed-point sampling
Fixed sampling points can help study an area, compare locations, identify dispersion, or check process trends. The choice of location should reflect this objective: a sample taken by the door does not necessarily describe what is happening in front of the emission source, and a sample taken by the source does not always equate to personal exposure.
Its interpretation must consider the movement of people and air, the distance to the sources, and the status of the controls. If the data is to be related to exposure, that relationship needs technical justification. Placing the equipment wherever it is convenient and extrapolating its result to the entire building is a design flaw, even if the laboratory analysis is correct.
Duration, tasks, and benchmark values
The duration is chosen to correspond to the reference period being assessed and the conditions of the method. Assessing daily and short-term exposure requires different questions. A long average may mask a brief episode, and a short sample does not automatically reflect the entire day.
The technician must plan how to cover the relevant exposure ranges and how to address unmeasured intervals. Assigning zero concentrations to these intervals due to a lack of data is incorrect. Variable tasks, product changes, and non-routine work require additional information. Designing similar exposure groups helps in selecting conditions and individuals, provided that grouping is justified.
Sample collection method and quality
The procedure must be appropriate for the agent and the expected concentration range. The sampler, flow rate, volume, time, transport, and analysis are selected in accordance with the validated method. The INSST fact sheets provide specific information for agents or families and should be read in full before scheduling fieldwork.
Quality includes identifying samples, checking equipment, recording times and flow rates, and managing blanks when required by the method. It also includes reporting the presence of substances and potential interferences to the laboratory. An error in agent identification or preservation can invalidate a sample even if the equipment has operated for the entire expected time.
Practical example
At a packaging station, a fixed sensor is initially placed away from the container opening. The person approaches it to adjust the filling level and then moves to a table. The fixed sensor allows us to describe their location, but it doesn’t necessarily represent that sequence. A personal sampling method and a record of the operations are proposed.
As an additional objective, fixed points are used to study the spread to an adjacent area. The two data sets are identified separately. After modifying the local exhaust extraction at the workstation, a comparable check is repeated, and production, product, and conditions are documented. This allows for an explanation of what has changed and what reasonable conclusions can be drawn about the improvement.
What should the report contain?
The report must connect the objective, method, location or sampled person, time period, tasks, and result. It is necessary to express units, comparison criteria, relevant uncertainties, and any incidents. Traceability allows us to know if a measurement remains useful when equipment, formulation, or shift organization changes.
It is also important to distinguish between the analytical result and the preventive conclusion. A value below the quantification limit does not necessarily mean the absence of the agent; it must be interpreted in light of the method’s capabilities. A single data point does not, by itself, guarantee compliance on all days. Inhalation testing requires a comprehensive strategy and a technically sound decision.
Common mistakes and review
The most frequent errors consist of taking measurements without a specific target, placing the sensor outside the intended area, omitting tasks with greater exposure, and comparing incompatible time periods. Another error is using an instantaneous reading from a non-specific device as if it were the result of a selective method for a particular substance.
The review should verify whether the conditions remain representative, whether the implemented prevention measures are effective, and whether the plan needs updating. Measurements do not replace the obligation to act in the face of a clear risk. Their purpose is to provide evidence to assess and control exposure, not to delay necessary measures while accumulating data that does not answer a specific question.
