If it is not possible to avoid gases, vapours or dusts that are harmful to health by means of technological measures, such dangerous substances must be extracted, preferably at source. When wood dust or carcinogenic substances are extracted, the specific requirements stipulated by the Regulation relating to Limit Values (Grenzwerteverordnung, GKV) (see also ban on circulating of air) must be met. Check your extraction systems for their functioning at regular intervals (in addition to performing the annual functionality test), clean the systems (and all connected pipes) and replace the filters in good time. Optimum results can be achieved only if the systems used are sufficiently powerful, properly positioned and routinely maintained.