This is in followup to your response "Plating Tank Exhaust Systems" in the March 2001 issue. I think your reference to the ACGIH (American Conference of Governmental Industrial Hygienists) reference was an excellent response. The comment regarding a push-pull system, however, raises a flag of caution. Research has revealed that many industries exacerbate the breathing environments of their employees by attempting to "muscle" the fumes with lots of air movement. In so-doing, they tend to disperse the fumes within a room and increase the concentrations in the breathing zones of workers. This research found that even the pedistal-mounted fans, positioned to blow across the operator toward the source of fumes that are so popular, actually increased concentrations in the breathing zones of the operators they were intended to help. An improperly positioned "push-pull" system could similarly be harmful to the ultimate objective–move the fumes from the tank to the exhaust with minimum mixing within the area.
Key parameters to engineering a coaxing system are the proximity of the exhaust intake to the source of the fumes, exhaust intake in relation to the relative density of the fume-containing air, and the locations of the air makeup units. These locations must be selected so that they cause the incoming air to gently sweep past the operators' stations to the exhaust. Coincidentally, such a system would likely require the lowest energy consumption. I hope you find this information useful. J.B.
Thank you for your valuable input.
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