Ductless Fume Hood Policy
Occasionally, the Department of University Safety & Assurances is asked to approve the purchase of ductless fume hoods for use in labs. The hoods are designed to remove hazardous fumes and vapors from the work area as the exhausted air passes through an absorbent, such as activated charcoal.
The system's appeal is largely economic because it does not require the expensive ductwork that traditional hoods need to exhaust fumes to the outside. However, in practice these hoods require constant attention and often do not provide adequate face velocity. In many cases, the filter is designed for specific chemicals and will not protect against the variety of chemicals used in a typical university laboratory.
Ductless fume hoods are plagued with the problems associated with "breakthrough" and with desorption of vapors from the absorbent. The user will also face expenses to replace charcoal filters and to dispose of the expended filters, which may be classified as hazardous waste. Estimated cost of filter disposal will be about $100 each. Therefore, depending upon the amount of use, annual maintenance costs to the owner could exceed several hundred dollars.
We do not believe that the hoods provide reliable protection against chemical exposure, and we think they may, in fact, give workers a false sense of security. Therefore, we strongly recommend against and, except in extremely rare circumstances, will not approve the use of ductless fume hoods. Moreover, we do not provide inspection or certification for ductless fume hoods.
If a department insists on purchasing a ductless fume hood, it should only be used with small amounts of low-toxicity chemicals, and the hood should be clearly labeled to indicate that it may not provide suitable protection from hazardous chemicals.