Explanation W3

What is W3?

A filter's efficiency can be measured by the level of its separation degree. Welding fumes are categorized in the so-called W classes. For effective welding fume extraction, attention must be paid to welding smoke classes, as the particles produced during welding are extremely hazardous to health. The limit values ​​for respirable particles depend on the welding process as well as the used materials.

Welding smoke refers to health-hazardous particles that arise during welding processes. These pollutants are smaller than 1 µm. From a size of less than 10 μm, particles are respirable, below 0.1 μm they are ultrafine and therefore nanoparticles. According to the Technical Rules of the Hazardous Substances Ordinance (German “Technische Regeln zur Gefahrstoffverordnung”), the concentration of pollutants generated in welding processes are carcinogenic and thus extremely harmful to health. When inhaled, the natural human filters, such as the cilia or nose hairs, are unable to retain the smallest pollutants. A W3 certification from the IFA (Institute for Occupational Safety of the German Social Accident Insurance) is needed for safe extraction of welding fumes. Only these filters can remove smoke and dust from high-alloy steels reliably, with a separation efficiency of 99%. Air that has been filtered by certified equipment can then be returned to the room. In order to protect the employees, installations must be checked at least once a year for their filter effectiveness.

Ventilation measurements in the room are not sufficient in welding processes. As the air molecules spin around, warm air rises, cools off at the ceiling and slides down the walls. These air currents cause turbulences of hazardous pollutants, which can settle in the room and people might inhale it. A filter and extraction system draws in these particles from the process air completely, separates them reliably and removes the cleaned air to the outside or back to the working area.

The Hazardous Substances Ordinance generally prohibits the air return to the working area after filtering so-called CMR (AGW in German) substances. There is an exception when the air recirculation is submitted to the authorities as an individual approval, when it is carried out in accordance with an accepted, tested procedure or the plant is certified in accordance with DIN EN ISO 15012-1 Class W3. In any of these cases, the air return is possible even with carcinogenic pollutants, or if smoke or dusts of the filtered air contained chrome or nickel.


Separation efficiency

Usable for


> 95 %

Unalloyed or low alloy steel


> 98 %

Alloy steel with 5 – 30 % nickel and chrome parts


> 99 %

High-alloy steel with > 30 % nickel and chrome parts

A directive takes into account certain rules and safety aspects and ensures that nothing dangerous can happen with certified equipment. The DIN EN ISO 15012 "Health and safety in welding and related processes" is used for the evaluation according to TRGS560 and TRGS528 not only for classical welding, but also for all thermal processes in which high-alloy steels are machined. These are, for example, laser welding, cutting, and marking.

The test at the internationally recognized Institute for Occupational Safety confirms the degree of separation and thus the safety / performance of the welding smoke separator. TBH systems that passed this test, protect the health of employees effectively and are marked with W3. The test according to DIN EN 15012-4 additionally assesses among other things the general structure and filter change. After both tests, the systems also receive the "DGUV tested" marking and are listed as a type-approved device in the IFA positive list.

The limit value of alveolar dusts, up to a particle size of 100μm, determines the required filter performance. If the limit value of 10 milligrams per cubic meter is exceeded, the maximum value is 1.25 mg / m³, based on a size of 10 μm. Its degree of separation indicates the filter efficiency. The DIN EN ISO 15012 classifies welding smoke in three separation classes, the W classes. Which of these is required in each individual case depends on the materials to be welded. Furthermore, the procedures and resulting hazardous substances must be observed.

Due to their high degree of separation, TBH filter and extraction systems of the H class and with W3 labeling of hazardous substances can be used if the discharged air is to be returned to the working area. We will be pleased to answer further questions you may have on welding fume extraction. Call us at +49 (0) 7082/ 9473-0 or write us