Fine dust is what you cannot see and still breathe in
What is fine dust?
Fine dust is a collective term for dust particles small enough to stay airborne for a long time and penetrate deep into the airways. It says nothing about what the dust is: wood, flour, metal, cement or plastic can all have a fine fraction.
What counts is the size, and two classifications are used for it.
The occupational health classification looks at where the particle ends up in the body:
- Inhalable dust: everything drawn in through mouth and nose.
- The respirable fraction: the finest part, which reaches the alveoli and stays there.
The environmental classification looks at particle size itself:
- PM10: particles smaller than 10 micrometres.
- PM2.5: smaller than 2.5 micrometres.
- PM1 and ultrafine dust: smaller than 1 micrometre, fine enough to cross the lung tissue into the bloodstream.
For comparison: a human hair is roughly 70 micrometres thick. PM2.5 is therefore about thirty times thinner.
Why fine dust is harder to control than coarse dust
Coarse dust settles. It drops near the machine that produced it, you see it lying there and you clear it away. Fine dust does not.
The particles are so light that air currents carry them along. They stay airborne for hours and spread throughout the space. That has three consequences that are routinely underestimated.
- What you miss at source, you will not recover. General ventilation dilutes but does not remove. That is why capture at the point of origin weighs more heavily with fine dust than with any other fraction.
- It affects people who do not work with it. The colleague standing twenty metres away, not cutting or welding, breathes in the same fraction.
- You cannot judge it by looking at the workplace. A clean building says nothing about the concentration. Measurement in the breathing zone is the only way to know where you stand.
What fine dust does in the body
Where a particle ends up depends on how small it is. The coarser fraction is largely stopped in the nose and throat and coughed back up. The finer the particle, the further it travels: into the alveoli, and for the very finest fraction, through the lung tissue into the bloodstream.
What happens next depends on the composition. Inert dust mainly causes mechanical irritation and, over time, loss of lung function. If the dust contains silica, permanent scar tissue forms. If it contains hardwood dust or hexavalent chromium, a cancer risk is involved. And with organic dusts such as grain or coffee, an allergic component is added.
The fraction determines how far it travels; the composition determines what it does. A sound assessment needs both.
Fine dust indoors and outdoors
This is where fine dust differs from most dust questions: you are dealing with two dynamics.
Indoors, the EU Chemical Agents Directive applies, implemented in national law in each member state. It requires employers to assess exposure and reduce it as far as possible, following a fixed order of control: eliminate first, then engineering controls at source, then organisational measures, with respiratory protection last. The exposure assessment follows EN 689, with measurements in the breathing zone. Specific limit values are set nationally, so check what applies where you operate.
Outdoors, environmental law takes over. As soon as extracted air is discharged outside, emission requirements from the Industrial Emissions Directive and your environmental permit come into play. That is not about your employees' health but about the burden on the surrounding area.
Those two tracks place different demands on the same installation. A system that comfortably meets indoor requirements can still fall short on the clean-air side, and the other way round. Our engineers account for both at the design stage.
Where fine dust is released
Almost any operation that breaks down, moves or heats material produces a fine fraction. What that means for your installation depends on the material:
- Metalworking: grinding, cutting and polishing, and in welding the ultrafine fraction formed by condensation.
- Wood and plastics machining: sanding and milling, with additives and fibres as the determining factor.
- Stone, concrete and mineral raw materials: with silica as the most serious risk.
- Food and animal feed: grain, flour, sugar and coffee, where explosion risk accompanies the health risk.
- Chemicals and pharmaceuticals: powders where the active substance determines the risk.
Which approach fits therefore depends on the material and on the process. On our Processes & Dust Types page you can filter on both and find, per dust type, the risks, the applicable rules and the extraction technique that goes with them.
How do you tackle fine dust?
The order is fixed and it does not start with the filter.
- Eliminate where you can. A different process, a less dusty material or an enclosed operation achieves more than any installation.
- Capture at source. As close as possible to the point where the dust is created, before it reaches the breathing zone. With fine dust this is the decisive step.
- Separate the coarse fraction before filtering the fine. A cyclone or pre-separator removes the coarse material and considerably extends the service life of the main filter.
- High-efficiency filtration for the finest fraction. Which filter class is needed follows from the dust type and the applicable limit value. Air filters are classified under EN ISO 16890.
- Measure, and keep measuring. Not once at commissioning, but again as soon as the material, the process or the installation changes.
The techniques involved, from mobile units to central extraction and industrial dust filters, are covered under our solutions.
Kiekens: specialists in fine dust extraction
With over 100 years of experience in industrial dust extraction, we design, build, and maintain systems for virtually every sector where dust is generated. From a single extraction point at a workstation to central dust collection for an entire production facility, both within and beyond regulatory limits.
We always start by taking a look: what material is involved, what is the process, where is the employee positioned, and what is being emitted? From there, we handle the design, installation, and maintenance—all under one roof. With our Clean Air Plan, we keep your system in top condition all year round.
Want to know how much fine dust is being generated in your workplace? Request a no-obligation baseline measurement from one of our specialists.
PM10 and PM2.5 come from the environmental field and say only something about particle size: smaller than 10 and 2.5 micrometres respectively. The inhalable and respirable fractions come from occupational health and say where the particle ends up: in the airways or all the way into the alveoli. They measure the same dust for different purposes. Your risk assessment needs the occupational classification; your environmental permit needs the environmental one.
Yes, and that happens more often than you might think. The dust you see settling is the coarse fraction that has fallen out of the air. The fraction that counts toward your exposure limit does not settle but remains airborne, and that is the part you cannot see. A tidy workshop therefore says nothing about actual exposure levels. Only a measurement taken in the employee's breathing zone can provide a definitive answer.
However, it is limited. Ventilation dilutes the concentration throughout the entire room, but it does not remove the dust and only works after it has already been released. With fine dust, that is too late: once it is airborne, it spreads through the hall and reaches colleagues who are not even working with it themselves. Source extraction captures it before it reaches the breathing zone. Ventilation is a supplement, not a replacement.
That depends on the dust type and the filter efficiency. Recirculation saves considerably on heating costs, because you are not blowing warmed air outside. But for carcinogenic or sensitising substances strict requirements apply and it is often not permitted without additional measures. If you discharge outside instead, emission requirements under environmental law come into play. Have it assessed per situation.
There are three dust classes according to IEC 60335-2-69: dust class L for low-hazard dust, dust class M for medium-hazard dust and dust class H for high-hazard and carcinogenic dust.