Explanation W3

What is W3?

The efficiency of a filter can be measured at the level of its separation efficiency. The W classes categorize that in the field of welding smoke. The limits for respirable particles are related to the materials manufactured and the welding process used.

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

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.

W3 is the highest welding smoke class. TBH systems with this certification are particularly suitable when working with high-alloy steel. They fulfill the safety and health requirements according to DIN EN ISO 15012-1 (2005). This certifies a passed test at the internationally recognized Institute for Occupational Safety. If the compliance with the emission limit of 99% for welding smoke is well documented, the approval of the plant by the authority is smoothly possible. This is indispensable for the optimal protection of the workforce. Due to their high degree of separation, TBH filter and dust extraction systems of the dust class H and W3 can be used with hazardous substances when the discharged air is to be returned to the working area.