Typical fume hood scrubber schematic

Contaminated air from the fume hood enters the unit and passes through the packed hed, hquid spray section, and mist eliminator, and then into the exhaust system for release up the stack. The air and the scrubbing liquor pass in a 

An undesirable characteristic of these t) pes of scrubbers is that if bigh concentrations of organics or hydrocarbons are carried into the bed, as would occur if a liquid were spilled inside the hood, a large exotham will occur in the reaction zone of the bed. This exotherm may cause a fire in the scrubbo. These devices and other downstream devices such as particulate filters should be located to minimize tbe effects of a fire, should one occur. Fires can start in these devices at surprisingly low temperatures due to the catalytic action of the adsorbent matrix. TbCTefore, such devices should be used and operated with care. 

The bag-in, bag-out method of replacing filtaa is a popular way to prevent worker exposure. This method separates the contaminated filter and housing from the 

Thermal oxidizers and incinerators are extremely expensive to purchase, install, operate, and maintain. However, they are one of the most effective methods of handling toxic and etiologic agents. The operational aspects of these devices are beyond the scope of this book. Also, their application to fume hoods has historically been rare. When considering this method of pollution control, an expert should be called to assist. 

Whether the emission source is a vacuum-pump discharge vent, a gas chromatograph exit port, or the top of a fractional distillation column, the local exhaust requirements are similar. The total airflow should be high enough to transport the volume of gases or vapors being emitted, and the capture velocity should be sufficient to collect the gases or vapors. 

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A fume hood scrubber is a laboratory-scale version of a typical packed-bed hquid scmbba- used for industrial air pollution control. Figure 8.7 shows a schematic of a typical fume hood scrahher. 

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