Few places release fine dust as fast, or in such concentration, as tunnels and construction sites. Diesel machinery, grinders, drills, saws and wind-blown soil all add to it. These sources sit close to the people working there, and to the people living next door. At the same time, the limits keep getting stricter. Clients, contractors and tunnel operators are asked more and more often to prove they have the risk under control. Measuring is no longer a luxury. It is the proof.
Why fine dust matters
Fine dust (PM, particulate matter) is classified by particle size:
- PM10 covers all particles smaller than 10 micrometres.
- PM2.5 covers all particles smaller than 2.5 micrometres.
- Ultrafine particles (PM0.1) are smaller still.
Black carbon, or soot, is a separate fraction and typical of diesel engines. The smaller the particle, the deeper it gets into the body and the more damage it can do.
The Flanders Environment Agency (VMM) says there is no safe threshold: even low exposure carries a health risk. Short peaks are linked to more hospital admissions for heart and lung problems and to asthma attacks. Long-term exposure is linked to several types of cancer and to premature death.
The authorities take construction sites seriously. Besides its permanent monitoring network, the VMM runs extra fine dust measurements around the Oosterweel works in Antwerp. Large infrastructure projects are under the microscope.
What do the regulations say?
Three frameworks come together here:
- European limits for ambient air.
- Belgian law on the well-being of workers.
- A specific limit for silica dust.
| Framework | What it covers | Key figure |
|---|---|---|
| EU Air Quality Directive 2008/50/EC (current) | Ambient air, annual mean | PM10 40 µg/m³, PM2.5 25 µg/m³ |
| EU Directive 2024/2881 (from 2030) | Ambient air, annual mean | PM10 20 µg/m³, PM2.5 10 µg/m³ |
| WHO guideline (2021) | Ambient air, health-based only | PM2.5 5 µg/m³ |
| Belgian Code on Well-being at Work, Book III Title 1 | Indoor air in workplaces | CO₂ normally < 900 ppm or ≥ 40 m³/h fresh air per person |
| Belgian Code on Well-being at Work, Annex VI.1-1 | Silica dust (respirable crystalline silica) | 0.05 mg/m³ over 8 hours, since 1 September 2025 |
Ambient air limits are being halved. By 2030, the new European directive cuts the annual limits for PM10 and PM2.5 in half. It also puts more weight on monitoring with harmonised measurement methods. Tunnels and major sites often run for years, so the limit can tighten halfway through a project.
The indoor air rules don't apply to the site itself. The Belgian Code transposes European Directive 89/654/EEC on workplaces. It requires employers to carry out a risk assessment of indoor air quality and sets CO₂ targets. But Article III.1-1 explicitly excludes temporary or mobile construction sites and the extractive industries.
The rules do apply to the contractor's permanent offices and workshops. In the tunnel or out on the site, the employer relies on their own risk assessment and on the specific rules for chemical agents. Without measurement data there, that assessment rests on assumptions.
Silica dust carries the strictest limit on site. Crystalline silica is released when cutting, drilling, grinding, milling or blasting concrete, brick and natural stone, and even when sweeping. Since 1 September 2025, Belgium has applied a limit of 0.05 mg/m³, stricter than the European 0.1 mg/m³. According to Buildwise, the Belgian construction research centre, employers must assess the risk at least once a year for every activity that can cause exposure.
The practical guideline from the Belgian Federal Public Service Employment focuses on tracking down sources rather than just meeting limit values. Under that guideline, measurements are generally only required when there is uncertainty or dispute. The guideline is written for indoor workplaces, but the logic carries over: on a site with neighbours, unions and inspectors, there is almost always a dispute.
What to measure, and where?
No single instrument does it all. The right strategy depends on the goal: protecting workers, protecting neighbours, or controlling ventilation.
| Situation | What to measure | Why | Examples from our range |
|---|---|---|---|
| Site boundary, neighbours | Real-time PM10 and PM2.5, with wind direction and speed | Prove or disprove nuisance, alarm on peaks, identify the source | Met One ES-642, Acoem Met One OPX 1025, weather station |
| Workers cutting, drilling, grinding | Respirable dust (PM4) and silica via personal sampling | Check against the 0.05 mg/m³ limit | BGI cyclones (PM4) with filter analysis |
| Tunnel under construction | Diesel particulate matter (DPM), black carbon, ultrafine particles, PM | Machine exhaust in a confined space | BGI SCC0.695 (DPM), Magee Aethalometer AE36, AVL CPC |
| Tunnel in operation | Visibility (opacity), CO, NO₂, PM | Control ventilation and protect maintenance staff | Tunnel sensors, Met One |
| Long-running projects | Reference-equivalent PM10/PM2.5 | Results that hold up before authorities and courts | Met One BAM-1020 |
Three lessons from the field:
- Combine dust with weather and noise data. A dust peak without wind direction is a number without a story. Measure noise as well, and one monitoring station answers two kinds of complaints.
- Use real-time for control, gravimetric for proof. Optical monitors raise an alarm straight away. Filter measurements and beta attenuation deliver the figures for the file.
- Think about the data, not just the sensor. Text or email alerts, an online dashboard and automatic reporting make the difference between measuring and managing.
Built for dust, water and the pressure washer
An instrument that gives in to dust or water produces no data. In tunnels and on sites, the enclosure matters as much as the sensor.
The IP code tells you how well an enclosure seals. The code is defined in the international standard IEC 60529. The first digit (0 to 6) rates protection against solid particles and dust. The second digit (0 to 9) rates protection against water.
| IP code | Meaning | Typical location |
|---|---|---|
| IP54 | Dust-protected, splash-proof | Sheltered site cabinet |
| IP65 | Dust-tight, protected against water jets | Outdoor installation on site |
| IP69K | Dust-tight, protected against powerful water jets | Direct cleaning with a pressure washer |
| IP67 | Dust-tight, protected against temporary immersion up to 1 m for 30 min | Low points, risk of flooding |
An "X" in the code (for example IPX7) doesn't mean there is no protection. It means that property wasn't tested.
The electrical connection counts too. The Belgian Code requires electrical installations to take voltage and external influences into account, so they create no risk of fire, explosion or electric shock (Art. III.1-5). In Belgium, the AREI (General Regulation on Electrical Installations) is the reference framework for this. A monitoring station on a site cabinet or in a tunnel niche must be connected and protected to match.
Note: Belgian law explicitly lists tunnel construction among the activities that expose workers to carcinogenic silica dust.
From measurement question to monitoring network: why AAVOS
AAVOS is the Benelux distributor of the instruments in this article and supplies them as turnkey solutions. We choose the right technology for your question without being tied to one brand. We combine instruments from Met One and Acoem, BGI/Mesa Labs, Magee Scientific, AVL, Tunnelsensors, among others.
In practice, we take care of:
- Measurement plan: which fractions, which locations and which period, matched to your permit, risk assessment or complaint.
- Installation: a rugged enclosure with the right IP rating, power supply, data communication and weather station.
- Data: a real-time dashboard, alarms when limits are exceeded, and reports you can present to your prevention advisor, the authorities or local residents.
- Service: calibration, maintenance and support from a VCA*-certified team.
Is a tunnel or construction project on your agenda? Or do you want to know whether your current measurements will stand up to the 2030 limits? Get in touch for a no-obligation conversation.