We did not find a ductless fume hood suitable for use in our undergraduate labs until the Green Hoods came along. These hoods take filtered fume hoods to a whole new level.
They have measured the absorption capacities of thousands of chemicals and published their results. Methylene Chloride is one of the lesser trapped chemicals in the Green Hood. After 672 g have been absorbed by the filters in a 6' hood, methylene chloride will pass through the first set of filters and set off the chemical alarm. If you violate protocols and continue to use the hood, after an additional 672 g of methylene chloride have been absorbed by the second set of filters, you will get exposure in the lab. But 672 g of methylene chloride is a lot of filter exposure for an undergraduate hood, no less twice that amount. After 2 1/2 semesters of undergraduate organic lab use, we have yet to have any chemicals breakthrough the first set of filters. One has to be very careful where you use these hoods and how you design the lab but they definitely have many appropriate uses.
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