Fume HoodWash-Down Systems
Perchloric Acid Wash-Down Systems
Perchloric acid wash-down systems are a specialty fume hood used to remove per-
chloric acid. A laboratory using perchloric acid, a highly corrosive inorganic com-
pound, requires a specialized fume hood. To prevent corrosion and reduce explosive
perchlorate buildup, perchloric acid fume hoods use a system of nozzles to wash
down the fume hood and exhaust system surfaces after each period of use.
oratories should follow instructions for washdown provided by the manufacturer of
the fume hood or facility health and safety guidelines, but might be able to minimize
perchloric acid wash-down system water use if shut-off valves are used to control the
flow of water.
Operation, Maintenance, and User Education
For optimum fume hood wet scrubber efficiency, consider the following:
Turn off water flow when systems are not in use.
Ensure water flow rate does not exceed manufacturer specifications.
In recirculating systems, make sure the liquid level controller and water supply
valve are functioning properly to avoid excess water overflow from the recircula-
In recirculating systems, calibrate the blowdown process so that it is sufficient
to remove entrained contaminants, without being overly excessive. In general,
constant overflows or continuous blowdown wastewater.
Consider using onsite alternative water sources to supply water for use in the
fume hood. See
Section 8: Onsite Alternative Water Sources
for more information.
For optimum perchloric acid wash-down system efficiency, use systems only when
necessary for perchloric acid handling.
There are currently no retrofit options available on the market to increase the effi-
ciency of fume hood filtration systems.
For facilities requiring a perchloric acid wash-down system, it might be feasible to
retrofit the system with shut-off valves to control the flow of water. However, facili-
ties should be sure to follow manufacturer-provided instructions for perchloric acid
wash-down systems and facility health and safety guidelines to ensure that any
changes will not affect health and safety or the performance of the system.
University of Louisville. 2012.
Laboratory Chemical Hood User’s Guide
Fume Hood Filtration and Wash-Down Systems