Measuring solvents and VOC in workplace air: how to select substances from safety data sheets

What VOC means and why measuring "total VOC" is not enough

The abbreviation VOC stands for volatile organic compounds. In the work environment, however, the employee is not concerned only with their total amount. Individual solvents have very different toxicological properties and also different hygiene limits.

For example, the current Czech limits for several common solvents are:

The PEL and NPK-P values are laid down in Annex 2 to Government Decree No. 361/2007 Coll..

A result such as "TVOC = 120 mg/m³" is therefore usually not sufficient in itself to assess compliance with the hygiene limits of individual substances. For job categorisation, we need to know how much acetone, toluene, xylene or another specific substance the employee inhales.

PEL and NPK-P assess different types of exposure

PEL – permissible exposure limit is the time-weighted average concentration over the whole shift. It is set for an eight-hour or shorter shift and, under basic conditions, assumes an average pulmonary ventilation of no more than 20 litres per minute.

NPK-P – maximum permissible concentration protects mainly against short-term high exposure. For comparison, a time-weighted average concentration measured over no more than 15 minutes can be used.

During an eight-hour shift, there may be no more than four fifteen-minute periods with a concentration higher than the PEL but not exceeding the NPK-P, with an interval of at least one hour between them. The whole-shift average must still not exceed the PEL.

For the same job position, it may therefore be necessary to combine whole-shift sampling with short-term sampling during the highest-risk operation.

Current safety data sheets are the basis

To select the substances to be measured, we need the safety data sheets of all chemical mixtures used at the assessed workplace. The requirements for the structure of a safety data sheet are derived from the REACH Regulation.

The following sections are the most important:

The CAS number is very useful for identifying a substance. Trade names or different translations of the same substance may differ, whereas the CAS number allows an unambiguous assignment of the hygiene limit and the analytical method.

The requirements for the content of safety data sheets are laid down by the REACH Regulation and Commission Regulation (EU) 2020/878.

A safety data sheet is not an automatic list of everything to be measured

Section 3 of the safety data sheet is the starting document, but the selection of substances must also respect the technology.

Imagine, for example, a painter who uses a primer, a top coat, a thinner and a cleaning product. Taken together, the safety data sheets may contain ten or more organic substances. Measuring all of them without further assessment is often needlessly expensive.

Conversely, it is not correct to select only the substance with the highest percentage share. A solvent present at a concentration of 5% may have a substantially lower hygiene limit than the main component of the mixture and may be more significant for the final assessment.

When selecting, we therefore assess simultaneously the content of the substance in the mixture, its volatility, hygiene limit, hazardous properties, the quantity of product used and the way of working.

Practical example: a painter uses four products

Before measurement, the safety data sheets may show, for example, the following composition:

The resulting measurement plan is not created by assigning a separate sample to each product. First, it is determined how often the product is used, in what quantity and during which operation the exposure arises.

If, for example, an employee spends most of the shift spraying a coating containing xylene and ethylbenzene but cleans the spray gun with acetone for ten minutes once per shift, whole-shift sampling of the main solvents and a separate assessment of short-term exposure during cleaning may be appropriate.

The actual work operation is decisive

The same product can lead to very different exposure depending on how it is used.

Applying adhesive with a brush to a small area, spraying the same adhesive with a spray gun and cleaning equipment with an open container are completely different exposure situations.

When designing the measurement, we therefore need to know:

• the quantity of products used, the method of application, the duration of individual operations and their frequency during the shift,
• the position of the worker relative to the source, the function of local extraction, the use of open containers and the method of cleaning equipment,
• rotation of workers, the use of PPE and the least favourable normal operating conditions.

Maintenance and cleaning are also included in the assessment if significant exposure can arise during them.

Beware of the combined effect of solvents

Employees are often exposed to several solvents at the same time. If they have the same type of effect, their additive action is assumed unless scientifically supported information to the contrary is available.

The assessment is then not carried out simply by comparing each substance separately with its PEL. The sum of the ratios of the measured concentrations to their limits is also assessed.

For example:

C1 / PEL1 + C2 / PEL2 + C3 / PEL3 ≤ 1

If an employee is simultaneously exposed at a level corresponding to 40% of the PEL for xylene, 35% of the PEL for toluene and 30% of the PEL for ethylbenzene, no substance exceeds the PEL on its own. However, the sum is 1.05, and the resulting exposure to the mixture no longer meets the requirement.

For mixtures of solvents, it is therefore important to select a sufficient number of representative components.

Job categorisation begins at 30% of the PEL

For the chemical substances and mixtures factor, Decree No. 432/2003 Coll. sets out the criteria for classifying work into categories.

For some particularly hazardous substances, an individual approach is taken. This applies, for example, to category 1A and 1B carcinogens, mutagens, reproductive toxicants and substances or mixtures with selected H statements, including H350, H340, H360, H300, H310, H330, H370, H334 or H317.

The selection of substances to be measured therefore cannot be based solely on which component has the highest percentage in the safety data sheet.

A substance listed in the safety data sheet may not be the only risk

In some production processes, substances may be formed that are not an input component of the product.

These may be, for example, thermal decomposition products, reaction products during curing, aerosols during spraying or substances formed during welding, grinding and thermal surface treatment.

We therefore always compare the safety data sheet with the technological process. If a product is heated, sprayed, mixed with another product or reacts chemically, the substances formed during the process must also be assessed.

For an unknown or complex composition, screening analysis can in some cases be used to help identify the substances present in the workplace air. For the actual assessment against the PEL and NPK-P, however, we subsequently need a sufficiently reliable quantitative determination of the specific substances.

Personal sampling is the most valuable for employee exposure

Exposure is assessed in the employee's breathing zone. For solvents, personal sampling is therefore often used, in which the worker carries the sampling device during the shift and the sampling medium is placed near the airways.

Such sampling captures the employee's movement between individual workplaces and their actual work operations.

Stationary measurement is useful, for example, when assessing a specific work area, the effectiveness of extraction or as a supplement to personal sampling. However, measurement in the middle of a production hall alone may not correspond to the exposure of a painter who stands a few tens of centimetres from the source of vapours.

Measurement must represent a normal or least favourable shift

The protocol should describe the conditions under which the sample was taken. It is necessary to record the products used, their consumption, the duration of individual operations, the operation of ventilation and any deviations from normal production.

Measurement at minimal production or at exceptionally low solvent consumption may have limited informative value for job categorisation.

Conversely, the aim is not to create an artificially extreme operating situation that does not occur in normal work. The measurement should capture a characteristic shift and the employee's real exposure.

When measurement must be carried out by an accredited or authorised entity

If the results are used to classify work into the second, third or fourth category, or to change its classification, Section 38 of Act No. 258/2000 Coll., on the Protection of Public Health, stipulates that the measurement must be carried out by the holder of the relevant accreditation certificate or authorisation.

The result should therefore not be merely a laboratory figure. The protocol must make it possible to assess the specific job position, the work operations, the exposure time and the representativeness of the measurement.

This is particularly important if the results are to be submitted to the regional public health authority as part of job categorisation.

What to prepare before ordering a measurement

The most common complication is ordering a measurement before it is clear which chemical substances the worker actually uses.

For a measurement proposal, you can send us:

• current safety data sheets of all paints, varnishes, adhesives, thinners, degreasers, cleaning products and other chemical mixtures used at the given job position,
• a description of the work operation, its duration, the consumption of individual products per shift, the number of workers and photographs of the workplace and extraction,
• the existing job categorisation, older measurement protocols or a request from the regional public health authority.

From the safety data sheets, we will select the relevant substances, compare their hygiene limits and propose a suitable sampling method. At the same time, we will check whether it is necessary to assess short-term exposure, the combined effect of several solvents or other chemical factors arising directly in the technological process.

You can find more information on the page Work environment measurement – NATURCHEM.

Related legal regulations and sources

Government Decree No. 361/2007 Coll., laying down conditions for occupational health protection

Decree No. 432/2003 Coll., on the conditions for classifying work into categories

Act No. 258/2000 Coll., on the Protection of Public Health

Commission Regulation (EU) 2020/878 – requirements for safety data sheets