Some specialized laboratory fume hoods require filtration or air cleaning before hood exhaust is discharged into the atmosphere. HEPA filters and air scrubber systems are available to remove most undesirable exhaust effluents; however, these added components significantly increase the pressure drop of the exhaust system and thus greatly increase the system's energy consumption. [Laboratory Control and Safety..., 1994]
Perchloric acid fume hoods present a special hazard because of the extremely corrosive vapor and explosive potential of perchlorate salts. Perchlorates typically condense in exhaust ducts downstream from the fume hood. For these reasons, a perchloric acid fume hood is normally operated as a constant air volume fume hood with an individual exhaust system. [Laboratory Control and Safety..., 1994]
Radioisotope fume hoods must also be specially constructed; charcoal and HEPA filters must be installed between the fan(s) and the fume hood. [Laboratory Control and Safety..., 1994]
