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A Chemical Fume Hood

The laboratory chemical fume hood

Inhalation is one of the major routes of entry for chemicals into the body.  Chemical fumes and vapors can directly enter the blood and small particles can be trapped in the respiratory system.  A chemical fume hood reduces exposure to hazardous fumes, vapors, gases and dusts.  The chemical fume hood prevents hazardous airborne material from contaminating the general laboratory space by diluting the contaminated air with a large amount of replacement air, pulling the air through an exhaust system and then expelling it through vents and air stacks located on the roof of the ISC.  Proper use of the fume-hood sash can also shield people from potential uncontrolled reactions. Chemical fume hoods at Geneseo are inspected and tested annually to assess air flow and storage standards, but it is up to you to use a chemical fume hood safely in the laboratory.

How does a chemical fume hood work?

Chemical fume hoods draw air out of the rooms in which they are installed.  There needs to be an adequate volume of air available or the chemical fume hood will not be able to draw a sufficient volume of air to function properly.  When the room is small or there are a large number of fume hoods drawing air out of a room, an additional supply of air, other than the normal room ventilation, may be required.  This additional air is known as the make-up air.  If the make-up air supply is not adequate or the make-up air is switched off then the fume-hoods may not be able to achieve the required face velocity (also known as the air flow rate, or rate of air exhausted by the hood). This can cause fumes to escape into the laboratory.  At Geneseo, all of the Chemistry academic labs use make-up air to replace the air the chemical fume hoods exhaust.  This is why after a fire alarm in the ISC, when the make up air is automatically shut off, all the doors in chemistry academic labs become extremely difficult to open due to the much lower pressure created in the labs compared to the air in the hallways of the ISC and Greene.  

 Using a chemical fume hood

Using the chemical fume hood

Working height of the chemical fume hood sash

Ensure the glass sash of the chemical fume hood is at 18 inches high or less from the working surface while working in the hood to ensure maximum air flow rate and to protect yourself from potential chemical splashes or explosions.  In Chemistry at Geneseo, this height is marked by stickers on the hood labeled "Working Height" with an arrow which marks the maximum working height.  In research situations, the sash should usually be closed when not actively working in the hood.

Work at least 6 inches into the hood from the glass sash to minimize the potential for fumes to escape. In research, if appropriate, as a useful reminder, place a strip of tape at this six-inch limit.

This may be common sense, but you should never climb inside the fume hood or stick your head inside it.