Hence the indoor ozone concentration can vary from day-to-day and room-to-room, the emissions of ozone from a laser printer have been studying in a single room of operating office equipment (personal computers, one photocopier, and two laser printer). Each test of measure was effectuated with and without the blow-down system. It has been found that the laser printers emits significant amounts of ozone, but the ozone concentration was reduced with the use of blowdown system.