Long-term exposure to low concentrations of anaesthetic gases is potentially hazardous. In spite of efforts to reduce the exposure of personnel by increased air conditioning, by scavenging of excess circuit gases and by improvements in anaesthetic equipment, high concentrations of gases have still been measured. Problems arise during mask induction, in paediatric anesthesia, and in certain situations with unavoidable leaks, especially in small rooms but also in recovery rooms. Experimental and preliminary clinical studies have shown that nitrous oxide pollution can be considerably reduced by using a separate close scavenging system in the area where high gas concentrations occur. The geometrical and flow dimensions of a close scavenging device used in paediatric anaesthesia are described.