After having revised the change schedule for organic vapour respirator cartridges in a paint plant in Iran, we established that it did not provide adequate protection against organic vapours at some workplaces and needed shortening from (48 to 72) h to 4 h. The revision also showed that relying on odour thresholds as the primary means to determine the time to change a chemical cartridge was not effective and that the National Institute for Occupational Safety and Health (NIOSH) MultiVapor service life software program could be applied to develop cartridge change schedules adjusted to specific workplaces.