According to Prudent Practices for the Laboratory , the air in a science laboratory should be changed a minimum of six times per hour. As with room ventilation, a minimum of six air changes per hour are recommended. Fume Hoods Fume hoods are the most important equipment used to protect teachers and students from exposure to hazardous chemicals and agents used in the laboratory. Rules for Using Fume Hoods Do not store reagent chemicals in a fume hood. Fume hoods must be inspected for proper use.
Devices are available to measure face velocity.
Keep the sash at its most efficient level. Work as far inside the hood as possible, but keep your head outside the hood. A minimum working distance of 6 inches from the front of the hood is recommended. If possible, the hood should be located away from windows, doors, and areas of heavy traffic to avoid drafts.