Air purification method The concentration of anesthetic gas in the air collected from the anesthetist's breathing zone (ppm) Without air conditioning unit N2O: 1000-3000 Halogenated anesthetics: 10-35 With air conditioning unit N2O: 200-500 Halogenated anesthetics: 2-5 With air-suction device, without air conditioning unit N2O: 100-300 Halogenated anesthetics: 1-4 With both air suctioning and conditioning devices N2O :10-35 Halogenated anesthetics: 0.2 to 0.5

Table 1: Relationship between how well equipped the operating rooms are and anesthetic gas exposure. (ppm=parts per million).