FAQ

The difference is in the direction of air pressure relative to the environment. A negative pressure unit works with a lower air pressure than the environment, sucking air in. An overpressure unit, on the other hand, works with a higher air pressure, blowing air outside.

In a negative pressure unit, the fan is located behind the filter. The air is sucked through the filter, capturing dust and chips immediately. The whole unit is under slight negative pressure, so no dust can escape to the outside.

• No chance of dust leakage at seams or joints
• Safer with flammable or harmful substances
• Quiet and energy-efficient
• Less fan maintenance (operates in clean air)

In an overpressure unit, the fan is in front of the filter. Air is blown forcefully into the filter, causing the pressure inside the system to be higher than outside. This increases the chances of dust escaping outside through small openings or leaks.

No. An overpressure unit is only allowed when installed outdoors. As the system is pressurised, it should not be placed in the work area itself. This would pose risks in case of dust leakage or flammable materials. In an outdoor installation, the positive pressure unit can safely discharge the filtered air without risk to the working environment.

For safety reasons, the exhaust system is only suitable for lifting or extracting:

• Dust from dust explosion class St 1
• Wood dust and wood chips (all types of solid wood)
• Panel materials, such as:
  • laminated wood panels
  • MDF, HDF, chipboard and plywood
• Panel materials with plastic or light aluminium coatings or edges
• Woody materials such as cork, plastic, hard rubber, bone, paper and cardboard
• Woodworking machines in which ignition sparks are excluded (according to BGI 739).

Extraction of types of dust other than wood dust is only allowed after consultation with Riedex.

The extractor is not suitable for lifting or extracting:

• Explosive or similar substances according to § 1 SprenG
• Dust from dust explosion class St 2 or St 3
• Substances with low minimum ignition energy (less than 10 mJ)
• Explosive gases or gas-air mixtures
• Flammable liquids or mixtures of flammable substance and liquids
• Woodworking machines where sparks cannot be excluded (such as multi-saws)
• Sticky or volatile materials containing hydrocarbons

No. The extraction unit is not suitable for use in explosive environments.

GS stands for ‘Geprüfte Sicherheit’: an independent, legally regulated safety sign based on the German Product Safety Act (ProdSG). H3 is a test level for the residual dust content of returned air in wood dust extractors; H3 means the residual dust content is very low (typically down to 0.1 mg/m³) according to the test guideline.

It shows that safety and dust performance have been independently tested. This boosts confidence among buyers and regulators and is in line with what many market players ask for in audits or tenders. It also often helps in risk assessments by insurers, especially in international inspections.

No. The seal is voluntary, but legally regulated and only to be issued by accredited bodies. H3 is a tested performance level for dust return. Many organisations prefer it because it demonstrates compliance with strict safety requirements.

EN 16770 describes safety requirements for indoor dust extraction systems. Manufacturers build and test their systems according to this standard; H3 markings mean that the extraction system has actually been inspected by an independent party for the relevant test criteria.

All B versions and very soon also the RV versions of the XtractStart and XtractPlus carry the H3 mark. If you want to see exactly which models these are, check the product pages.

Faster acceptance of purchases and inspections and clarity towards occupational health and safety services and insurers, because the installation demonstrably meets strict safety requirements and dust performance. It is also easier to lease the installation in some cases.

Retrieved from dguv.de/pruefzeichen you will find even more information on what this seal means. 

EN 16770 is a 2019 European standard for extraction systems installed indoors. The standard allows indoor use only for systems that operate with negative pressure and keep the dust separated from the fan. Overpressure units, where dust passes through the fan, do not comply for indoor use.

The standard reduces the risk of fire or explosion and sets strict safety requirements for extraction systems located indoors. This provides clarity when selecting and setting up systems in the workplace.

No. Since 2019, positive-pressure units that move dust through the fan may no longer be used indoors.

For the self-employed, the rules can sometimes be less strict, but in shared spaces, even a self-employed worker has to consider the safety of others. This is also reflected in your Risk Inventory and Evaluation (RI&E), for instance, and insurers also pay attention to this.

Yes. Riedex supplies underpressure systems that keep the dust separate from the fan, making them suitable for indoor use according to EN 16770.

EN 12779 is a European standard for outdoor extraction systems. The standard sets out safety requirements for large extraction systems with a capacity of 8,000 m³/h or more and specifies how these installations should be built and set up.

For large exhaust systems, the risk of fire, explosion or structural damage is higher. The standard lays down strict requirements for pressure shock resistance, fire safety and reliability. This provides clarity and certainty when selecting and using outdoor installations.

No. According to European regulations, installations from 8,000 m³/h onwards cannot be installed indoors. These fall under EN 12779 and must be installed outdoors.

EN 12779 was formally drawn up for fixed extraction systems in the woodworking industry with a capacity of 8,000 m³/h and above. In practice, this standard is also often used as a guideline for similar applications in other sectors where combustible dust is released.

Yes. The MD and CDF series from Riedex are fully developed for outdoor installation and meet all the requirements of EN 12779. This ensures maximum capacity, reliability and safety according to the European standard.

Zone 22 is a safety classification set out in the ATEX Workplace Directive (2014/34/EU). It describes an environment where, under normal operating conditions, an explosive dust atmosphere is not expected, but where, if it does occur, it is only of short duration. The classification requires the employer to use only equipment in that zone that is approved for use in a potentially explosive atmosphere.

Whether Zone 22 applies is determined by the employer on the basis of a risk assessment and set out in an explosion safety document (EVD). This is a legal requirement for all companies that work with flammable materials, including wood.

For indoor installation of dust extraction systems that comply with NEN-EN 16770, Zone 22 is excluded for the return air. The design of the system, in particular the limitation of the dust-containing volume and the use of the outer side of the filter elements as the dust side, prevents the build-up of a hazardous dust concentration on the clean air side. This is laid down in the standard and confirmed in the type zoning of the DM series in accordance with EN 16770 and BGI-739. This exclusion applies only provided that the system is properly maintained. Failure to carry out maintenance or a filter rupture invalidates the basis on which the type classification is founded.

For dust extraction systems that comply with NEN-EN 16770 (indoor installation) or NEN-EN 12779 (outdoor installation), Zone 22 does not apply to the area around the system or to the return air, provided the system is properly maintained. The standards explicitly exclude this on the basis of the system’s construction.

Nevertheless, an employer is always obliged to draw up an explosion safety document if there is a risk of an explosive atmosphere anywhere on the premises. The assessment of this does not begin with the installation, but with the process and the area.

The practical implications of a Zone 22 classification are far-reaching. Once a Zone 22 has been designated, all equipment and tools in that zone must be approved for use in a potentially explosive atmosphere. This means that standard switchboards, standard electric hand tools and even common plant and machinery are no longer permitted unless they are specially designed. The costs and practical constraints involved are considerable.

In practice, Zone 22 is virtually non-existent in woodworking workshops with a properly functioning and well-maintained extraction system. However, this is conditional on the workshop being kept sufficiently clean. Dust accumulation on floors, machinery and structural components poses a risk that is independent of the extraction system. For this reason, the use of brooms is not recommended, as they stir up dust into the air rather than removing it. Vacuum cleaners are preferred, as they remove dust without causing it to become airborne.

In Germany, a practical approach has long been followed whereby Zone 22 is virtually never designated around dust extraction systems in woodworking workshops. This approach is based on the same reasoning as NEN-EN 16770 and NEN-EN 12779: a system designed in such a way that no hazardous dust concentration arises on the clean air side does not create an explosive atmosphere in the surrounding area.

Germany has been ahead of broader European practice in this area for many years. The BGI-739, a German guideline for woodworking companies, sets out the details of this and is also used to support the type zoning of both indoor and outdoor installations. However, this is subject to the condition that the installation has been carried out in accordance with NEN-EN 16770 or NEN-EN 12779 and has been awarded the H3 certification, the German certification for fire and explosion safety, issued by the DGUV (Deutsche Gesetzliche Unfallversicherung), the German statutory accident insurance scheme, which also acts as a recognised Notified Body for this type of certification.

The DM-120, DM-160, DM-200, DM-250, DM-300 and DM-350 from Riedex, and the XtractPlus 250, 300 and 350, are all manufactured in accordance with NEN-EN 16770. The DM-120, DM-160 and DM-200, and the XtractPlus 250, 300 and 350, also carry the DGUV’s H3 certification.

It is important to understand that this is not an exemption, but a well-founded conclusion. The employer remains responsible for the assessment via the RI&E and the EVD.

Avoiding Zone 22 does not start with the extraction system itself, but with the working environment as a whole. The key point is that no hazardous concentrations of dust must be allowed to build up in the air – not only around the extraction system, but also elsewhere in the workspace.

A properly functioning and well-maintained dust extraction system that complies with NEN-EN 16770 forms the basis for this. However, the system alone is not sufficient. Dust that settles on floors, machinery, structural components and horizontal surfaces poses a risk in its own right. If the dust is stirred up – by movement, air currents or vibrations – an explosive atmosphere can still develop, regardless of how well the extraction system is functioning.

Keep the workshop clean on an ongoing basis. Do not use brooms for this, as they send dust that has settled back into the air. Use vacuum cleaners so that dust is removed without being stirred up.

Carry out regular maintenance on the extraction system. Check the filters, cleaning and seals in accordance with the maintenance schedule. In the event of a filter failure or reduced extraction capacity, the basis for not designating Zone 22 ceases to apply.

Ensure that the extraction system has actually been installed in accordance with NEN-EN 16770. A system that does not comply with this standard does not provide grounds for excluding zone 22, regardless of how well it is maintained.

Record the assessment in the explosion safety document. The conclusion that Zone 22 does not apply must be substantiated and documented; it must not simply be assumed.

Riedex develops and manufactures dust extraction systems built in accordance with NEN-EN 16770 for indoor installation and NEN-EN 12779 for outdoor installation, the European standards that form the basis for safe wood dust extraction. The DM series, XtractPlus series and MD series are technically designed in such a way that they provide the basis for not designating a Zone 22 around the unit.

On the basis of the CE declaration and the zone classification in accordance with NEN-EN 16770, NEN-EN 12779 and BGI-739, Riedex guarantees that, provided the installation is operated and maintained correctly, there will be no Zone 22 around the unit. The technical basis for this is formally established: the unit is manufactured in accordance with the standard, certified by a recognised Notified Body where applicable, and accompanied by the documentation required for a valid Declaration of Conformity.

The broader assessment of the working environment, processes, machinery and areas outside the immediate vicinity of the installation remains the employer’s responsibility and is set out in the explosion safety document.