Baffle, fume hood

Do not modify fume hoods in any way that adversely affects the hood performance. This includes adding, removing, or changing any of the fume hood components, such as baffles, sashes, airfoils, liners, and exhaust connections. 

Each chemical fume hood tested within last year Sash closed when not in active use Chemical-fume hood vents (baffles) unobstructed Chemical-fume hood used with sash in appropriate position Chemical storage limited in actively used hood Chemicals and equipment at least 6 in. firom the sash... 

Most of the chemical fume hoods considered here consist of a cabinet or enclosure set at waist level (above a table or storage cabinet) that is connected to a blower located above the hood or external to the hood through a duct system. The cabinet has an open side (or sides) to 2illow a user to perform work within. A movable transparent sash separates the user from the work. Most chemical fume hoods have a sill that functions as an airfoil at the work surface below the sash. The connection to the blower might be by use of a v-belt, or it may be direct drive. This allows provision of a smooth flow of air with minimal turbulence. In some installations, axially mounted blowers are used, especially if multiple hoods are ducted into a common blower. Baffles located in the rear of the cabinet provide control of the air flow patterns, and can usually be adjusted to provide the best air flow around the experiment or procedure being performed. Many chemical fume hoods are equipped with air flow indicators, low flow monitors and alarms, and differenti2d pressure sensors to allow the user to operate safely. The major types of chemical fume hoods include the standard/conventional, W2dk-in, bypass, variable air volume, auxiliary air, or ductless types. Additional types include snorkels and canopies that are portable. Each type must be understood to be operated most efficiently within specifications (see the section below on safe operation). 

The baffles of the chemical fume hood should be free of obstruction. 

The fume hood is perhaps the most misused item of laboratory equipment. Fume hoods are not designed for chemical storage the presence of many containers of various chemicals and other material that accumulates in hoods makes their operation inefficient and unsafe. Objects blocking baffle slots, operating the unit with the sash raised, inadequate airflow, and obstmction of the front airfoil are only some of the problems typically found in laboratory fume hoods. Satisfactory operation of the fume hood depends upon three factors proper use of the chamber and work area, correct hood location, and adequate airflow capacity. These are discussed in detail below. 

If these conditions occur in an existing installation, take steps to avoid production of crossdrafts by restricting traffic during fume hood use, baffling air ducts (but not to the point where room air balance is completely upset), closing windows or doors, or taking whatever steps may be necessary to preserve the unit s airflow characteristics. 

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