Constant-volume ventilation systems

Fume hoods connected to a common exhaust manifold offer an advantage. The main exhaust system will rarely be shut down hence, positive ventilation is available to each hood on the system at all times. In a constant air volume (CAV) system (see section 8.C.6.3.1), "shutoff dampers to each hood can be installed, allowing passage of enough air to prevent fumes from leaking out of the fume hoods and into the laboratory when the sash is closed. It is prudent to allow 10 to 20% of the full volume of the hood flow to be drawn through the hood in the off position to prevent excessive corrosion. 

A concern associated with the commonly used alkanes, hexane and toluene, is that they have very high vapor pressures at room temperature. Because of this volatility, efforts must be made to make sure that samples dissolved in these solvents are stored in tightly sealed vials so that volumes stay constant. For LC systems that require continuous solvent sparging, fiequent replacement of the solvent or a sparging reservoir is necessary. Finally, appropriate ventilation is essential due to the extremely flammable nature of these solvents and their vapors. 

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