NEN-EN 689 explained: assessing workplace exposure

NEN-EN 689 is the European standard describing how to assess workers' inhalation exposure to hazardous substances and test it against the occupational exposure limit. In the Netherlands it forms the basis for a defensible exposure assessment under the Working Conditions Decree.

Why a standard for exposure?

Many hazardous substances have a statutory or in-house exposure limit. The question is not only whether you stay below that limit, but whether you can reliably demonstrate it. NEN-EN 689 provides a structured testing strategy for this, so that a favourable snapshot does not wrongly lead to a 'safe' conclusion.

The steps of an assessment

1. Basic characterisation. Map which substances are released, in which tasks, in what quantities and under what conditions. The information in Section 8 of the SDS (exposure limits and exposure controls) connects directly to this.

2. Define the exposure group. Group workers who perform similar tasks and therefore have similar exposure (a Similar Exposure Group). The assessment then applies to the whole group.

3. Test against the limit. NEN-EN 689 uses a statistical test: based on a number of measurements, it judges whether the probability of exceeding the limit is small enough. One measurement below the limit is not the same as 'compliant'.

4. Reassess periodically. Do the substances, quantities, ventilation or working method change? Then the earlier conclusion lapses and a new assessment is needed.

Qualitative assessment as a first step

Not every situation calls for measurements straight away. A qualitative (Tier 1) assessment — based on hazard classification, physical state, quantity and exposure duration — often already shows where the risk is controlled and where a further, quantitative assessment is needed. NEN-EN 689 and a Tier 1 approach complement each other: you deploy measurement capacity where it yields the most.

Common mistakes

The most common pitfall is drawing a conclusion from too few measurements, or from a measurement that is not representative of a 'bad day'. A lack of clear exposure grouping also makes an assessment hard to defend in an inspection.

How Chemspark helps

Chemspark records each product's hazard classification, physical properties and exposure limits from the SDS and runs a qualitative risk assessment per component. That shows you immediately which exposures are likely controlled and which deserve a further assessment under NEN-EN 689 — substantiated and traceable.