In brief
Chemical exposure measurement is personal measurement made with a sampler placed in the worker's breathing zone; a fixed-point workplace measurement is not compared with personal limit values. The strategy is built according to TS EN 689: similar exposure groups are defined, representative workers are selected, and the result is calculated against 8-hour and 15-minute reference periods. The laboratory does not decide compliance; the workplace compares the result with the limit value and decides on measures.
Why is chemical exposure measured?
Art. 7/1-h of the Regulation on Health and Safety Measures in Work with Chemical Substances requires the employer to ensure regular measurement of chemicals that may pose a risk to workers' health, and to repeat the measurement when there is a change that may affect exposure. The results are evaluated against the limit values in the annexes of the Regulation; where a limit value is exceeded, the employer takes measures to remedy the situation as soon as possible (Art. 7/1-ı).
Chemical exposure measurement is therefore not a paperwork exercise but an input to the risk assessment. A poorly planned measurement can make an exposure that is actually high look low, or delay a measure that needs to be taken. We explained which workplaces need to consider measurement in our article on workplaces requiring workplace measurements; this article focuses on how measurement is planned and how the report is read.
Measurement is carried out by a laboratory holding a certificate of competence from the Directorate General of Occupational Health and Safety, which notifies ISG-KATİP (the Ministry's online OHS registration system) at least three days in advance. Bursa Sistemer does not have its own laboratory; we plan measurements with authorised laboratories, build the strategy together and enter the results into the risk assessment.
Measurement strategy: what does TS EN 689 require?
Art. 16/5 of the Regulation on Occupational Hygiene Measurements, Tests and Analyses requires the sampling and assessment strategy for inhalation exposure to be determined taking into account standard TS EN 689:2018+AC. This measurement strategy can be summarised in four steps:
- Description of the work: Which chemicals are used, in which tasks and for how long? The starting point is a current chemical inventory; for how to prepare one, see our article on preparing a chemical inventory.
- Similar exposure groups: Workers doing the same work, by the same method, for similar durations are put in one group. For example, "mixing operators" and "filling operators" are separate groups.
- Preliminary test: Three to five measurements are made on workers selected from each group, and the result is compared with the limit value.
- Statistical test and remeasurement: If the preliminary test does not give a conclusive result, a statistical assessment is made with at least six measurements; even when compliance is demonstrated, measurement is repeated at intervals.
The decision rule of the preliminary test in TS EN 689 is as follows:
| Number of measurements | For compliance, all results | Non-compliance |
|---|---|---|
| 3 | Below 10% of the limit value | Any result above the limit value |
| 4 | Below 15% of the limit value | Any result above the limit value |
| 5 | Below 20% of the limit value | Any result above the limit value |
If the results fall between these two situations, no decision can be made and the number of measurements is increased. A single measurement cannot be used to say "below the limit value, compliant"; a single measurement is only a snapshot of that day.
Personal sampling and the representative worker
Art. 4 of the Chemical Substances Regulation defines the breathing zone as the half of a sphere of 30 cm radius in front of the head, centred on the midpoint of the line joining the person's ears. Personal sampling is carried out in this zone: under Art. 16/7 of the Occupational Hygiene Regulation, the sampling device or passive sampler is placed on the worker and in the breathing zone. Usually the pump is worn on the belt and the sampler is clipped to the collar.
When choosing the representative worker, pay attention to the following:
- Choose from the group, not volunteers: The measurement must reflect the group's real working conditions. The person doing the task with the highest exposure must not be left out of the group.
- Do not skip shifts: If ventilation runs at low speed on the night shift or a different product is produced, measurement should also be made on that shift.
- A normal working day: On the day of measurement, production is not slowed down, stopped or speeded up; Art. 16/9 explicitly prohibits such manipulation.
- Inform the worker: The worker being measured should know why they are wearing the device and that they should do their work as usual.
Measurement duration: 8 hours and 15 minutes
Under Art. 16/6 of the Occupational Hygiene Regulation, the long-term reference exposure period is 8 hours for one shift, and the short-term reference period is essentially 15 minutes. The duration and number of measurements are arranged to represent the exposure during the work (Art. 16/4).
Example (with illustrative values): Suppose an operator's shift on a line using toluene is measured in three parts.
- Mixing, 2 hours: 40 ppm
- Filling, 3 hours: 20 ppm
- Meal break, 0.5 hours: no exposure (outside the area)
- Cleaning, 2.5 hours: 10 ppm
8-hour time-weighted average = (2 × 40 + 3 × 20 + 0.5 × 0 + 2.5 × 10) / 8 = 165 / 8 ≈ 20.6 ppm. In Annex 1 of the Chemical Substances Regulation, the 8-hour limit value for toluene is 50 ppm; the result is about 41% of the limit value. It is below the limit value, but according to the preliminary test rule it is not in the "clearly compliant" zone; additional measurements and measures are needed.
If the shift is longer than 8 hours, the calculation is still made by dividing by 8 hours. For a worker exposed to an average of 30 ppm over a 12-hour shift, the 8-hour average is 30 × 12 / 8 = 45 ppm, i.e. 90% of the limit value. A long shift directly increases exposure in the same environment.
For substances with a short-term limit value, the 15-minute operation where the highest exposure is expected, such as tank filling or opening a lid, should be measured separately. The 15-minute limit value for toluene is 100 ppm.
How is VOC measurement done in the workplace?
For volatile organic compounds (VOCs), workplace VOC measurement is usually carried out by two methods:
- Active sampling: A small pump draws air at a set flow rate through a tube containing a sorbent such as activated charcoal. The tube is analysed in the laboratory and each compound is determined separately. The pump flow rate must be verified before and after measurement.
- Passive sampler: A badge-type sampler that works by diffusion, without a pump. It is easy to use; its selection depends on the substance to be measured and the authorised method.
Direct-reading instruments (for example photoionisation detectors) are useful for finding leak points and planning measurements, but they do not distinguish individual compounds and do not replace personal exposure measurement.
In solvent mixtures, where the substances act on the same organ, the combined effect is calculated in practice: the measured value of each substance is divided by its own limit value and the ratios are added up. If the total exceeds 1, the limit is considered exceeded for the mixture. Example: If toluene is measured at 20.6 ppm (limit 50 ppm) and xylene at 18 ppm (limit 50 ppm), the total is 0.41 + 0.36 = 0.77. Toluene and xylene are marked "Skin" in Annex 1; this indicates that they can also be absorbed in significant quantities through the skin. In this case, air measurement alone is not enough; gloves and skin contact are also assessed. For the health effects of solvent vapour, see our article on solvent vapour exposure.
Comparing the result with the limit value
Art. 19/4 of the Occupational Hygiene Regulation sets two important rules: assessment of whether measurement results comply with the legislation is not carried out by the laboratory, and where there is no limit value in the legislation, a limit value published by international organisations is used, taking the measurement method into account. In other words, the "compliant" or "non-compliant" decision is made by the workplace together with the OHS specialist and physician.
In the comparison, pay attention to the following:
- The limit value is taken from Annex 1 of the Chemical Substances Regulation or, for carcinogens, from Annex 2 of the Regulation on Carcinogenic or Mutagenic Substances.
- The measurement uncertainty in the report matters for the decision, especially for results close to the limit value.
- Staying below the limit value does not remove the obligation to minimise exposure.
- If the limit value is exceeded, measures at source (substitution, closed systems, local exhaust ventilation) come first, and measurement is repeated after the measure.
Chemical measurement report: what to look for
Art. 19 of the Occupational Hygiene Regulation requires the report to state clearly the sections measured, the work done, the duration of exposure and any factors that may affect the result; for personal measurements, the person's name, title and the work they were doing must be written; and the standards used and the measurement uncertainty must be given. The data specified by the Ministry's Occupational Health and Safety Centre are also uploaded from the report to ISG-KATİP (Art. 19/5).
Once the chemical measurement report has been entered into the risk assessment, it should not just sit in the file. If the result is close to the limit value, an action plan is set; if it is well below, the date of the next measurement is set; you can track the dates with the OHS calendar. Our article on dust measurement and respirable dust explains how the same logic is applied to dust.
At chemical, paint and plastics businesses in Bursa and the surrounding provinces, we build the measurement strategy as part of our risk assessment service. Our approach to the sector is on our chemicals and plastics page.
Frequently Asked Questions
What is the difference between personal sampling and workplace (area) measurement?
In personal sampling, the sampler is on the worker and in the breathing zone; the result is compared with the personal limit value. A workplace measurement made at a fixed point does not show personal exposure and is not compared with the personal limit value.
A single measurement came out below the limit value; is that enough?
No. Under TS EN 689, the preliminary test is carried out with at least three measurements, and for compliance the results must be well below the limit value. A single measurement only shows the conditions on that day.
The measurement report does not say "compliant"; is that normal?
Yes. Under the Occupational Hygiene Regulation, the laboratory does not carry out the compliance assessment. The workplace, the OHS specialist and the physician compare the result with the limit value together and decide on measures.
How is a substance with no limit value in the legislation assessed?
Under Art. 19/4 of the Occupational Hygiene Regulation, a limit value published by international organisations is used, taking the measurement method into account. Which value has been used should be stated clearly in the report and in the risk assessment.
A risk assessment that identifies and scores hazards on site, links each measure to an owner and a date, and has a clear renewal schedule.
Bursa SİSTEMER OSGB Technical Team — written from the field experience of our OHS specialists and workplace physicians. Legal information is valid as of the publication/update date; contact us for an assessment specific to your business.