Duct sealing and extraction during cleaning

Why duct sealing and extraction instead of cleaning alone?

A brush or compressed air nozzle loosens dirt. That is the point, but the dust has to go somewhere. Cleaning companies point out that negative pressure prevents dirt from spreading. An American cleaning specification from the University of Maryland, which refers to the NADCA vacuum test for the check afterwards, requires every section to be cleaned to be under continuous negative pressure from extraction units.

Dutch rules point in the same direction. Article 4.5 of the Working Conditions Decree (Arbobesluit), on working with hazardous substances, states that when contaminated air is removed, sufficient clean air must be supplied at the same time. And article 6.2 requires sufficient unpolluted air at the workplace. Anyone who cleans ducts in an occupied building without containment puts colleagues in the dust.

The American trade association NADCA also covers containment, negative pressure, cleaning methods and verification of cleanliness in its ACR 2025 standard. Sealing and extraction is therefore not an extra, but part of the trade.

Which duct sealing balloons and vent caps do you need?

Danduct Clean, the manufacturer of the machines Lamers supplies, has several accessories for closing off ducts and openings.

Source: Danduct Clean, accessories, checked on 6 October 2026. The sealing caps group at Lamers matches this. Which sizes and quantities you need depends on your duct diameters and the number of grilles per run.

A practical tip: keep an inventory sheet per client with the diameters and the number of grilles per run. Then you load exactly the right balloons and caps before each visit instead of finding out on site.

How fine should the extraction filter be: HEPA or not?

That depends on where the extracted air goes. The University of Maryland specification mentioned above requires a HEPA filter of 99.97% at 0.3 µm if the extraction unit exhausts inside the building. The US EPA puts it more briefly: exhaust the dust through a HEPA filter or to the outside.

Note the difference between Alimento and TNO: one source names HEPA, the other considers an M class filter sufficient for bakeries. When in doubt, choose the stricter option and consult your prevention officer. Danduct Clean has VT extraction fans with hoses and filtration. Ask Lamers which unit fits your ducts.

How to set up negative pressure and sealing step by step

1. Switch off the installation or take the run out of service, in consultation with the facilities team.
2. Define the run. Choose a stretch of duct between two logical points, for example between two openings.
3. Place the sealing balloon on the side where the clean part of the system begins.
4. Cover all grilles in the run with foam caps, so the room is not involved.
5. Connect the extraction unit to an opening at the other end and put the run under negative pressure.
6. Check the negative pressure before you start: air must flow into the duct, not out of it.
7. Clean with brush or compressed air towards the extraction.
8. Let the extraction run on, only then remove the caps and balloon and move to the next run.

A Eurovent recommendation names inspection openings at a maximum of 10 metres apart or after no more than two bends of 45 degrees or more. That also gives you a practical length per run. The full approach from inspection to handover is in the guide to cleaning ductwork professionally.

Which cleaning machine do you combine with sealing and extraction?

Sealing and extraction works with every cleaning method, but the set up differs a little.

• With a brushing machine: the DC4 duct cleaning machine cleans up to 30 metres. Make sure your extraction is at the end of that reach, so the dirt moves that way.
• With compressed air: the air nozzle with built-in camera blows a lot of air into the duct. The extraction must handle that extra air, otherwise the negative pressure disappears.
• With a drill driven cleaner: for short ducts with the compact PD4 duct cleaner the runs are short, but there too you want a cap on the grille and extraction on the opening.

Choose the brush to suit the duct material, see choosing the right duct brush. All machines and accessories together are under duct cleaning equipment.

Sealing caps and extraction per building type: what to watch out for

Food industry. The Netherlands Food and Consumer Product Safety Authority (NVWA) asks to avoid airflows from contaminated to clean rooms. Position your extraction so that you never draw air from a dirty zone into a clean zone. More under ducts in food processing plants.

Bakeries. Flour dust is the big risk. TNO states that a dust explosion is possible above 60 g/m³ of fine dust such as flour, and that ATEX certified vacuum cleaners are needed in EX zones. So choose equipment that is suitable for that zone.

Care. A guideline for operating theatres asks for an air management plan with technical management, maintenance and periodic checks. Work on ducts should fit into that plan, including agreements on containment.

Offices and schools. Here work is often done while the building is in use. Good vent caps and a quiet, well filtering extraction unit make the difference between no complaints and an office full of dust.

How do you prove the duct is really clean after extraction?

Sealing and extraction makes sure the dirt goes, but you also want to show that it has gone. The University of Maryland specification names two methods: a surface comparison and the NADCA gravimetric vacuum test. You vacuum a fixed surface area and weigh the collected dust.

In Europe, EN 15780, revised in 2025, sets cleanliness classes and the assessment of the cleaning result. According to trade publications, dust limits of 0.6, 3.0 and 4.5 g/m² apply for the classes high, medium and low. Those figures come from secondary sources, not from the standard itself. More on standards and classes under EN 15780 and VDI 6022.

Danduct Clean also has inspection cameras and dust measuring equipment. For advice on the right combination of extraction, caps and measuring tools, the fastest route is to ask for duct cleaning advice.