Answer of this basic question defers person to person. Some users say that sash of the fume hood should not be open more than 450mm vertically from the work surface when others say that it should not be opened more than 300mm. The fact is, height of the person working at fume hood varies. So logically safe opening height of the sash also varies. The thumb rule is: SAFE OPENING HEIGHT (vertically) of the fume hood front fascia should be below breathing zone of the user. The hood user should never allow his head inside the running hood as this will cause contaminated air to pass through the breathing zone. Raise the sash to fully open position for set-up purpose only.

• Always work at least six inches away the plane of the sash. It is better to work keeping ourselves as much away as we can.
• Keep the apparatus as deep as possible inside the hood.
• Avoid rapid withdrawal from the hood.
• Always keep the sash in close condition when hood is running.
• Close horizontal panels on combination sashes before opening the sash vertically.
• Elevate contaminants and equipment above the working surface of the hood to enabling the flow beneath and around the obstructions.
• Do not store any equipment that restricts the closing of the sash or blocks the bottom slot of the baffle directly in front of the user.
• Minimize the movement in front of the hood to avoid air turbulence.
• Keep motion in the lab minimum while working in the hood. Traffic past the hood can generate considerable cross draft.
• Ensure head and upper body part remains outside the plane of hood opening at all times.
• Open and close the sash slowly.