You really should talk to the chemists at Erlab. They have done loading factors for thousands of compounds. They also have a long history of developing systems for life threatening situations. I was very impressed when I met with them for a day to discuss my many concerns about using their Green Hoods. But that does not mean I would make a blanket statement approving their use.
It would be rare that I would recommend a Green Hood as the only hood in any hood intensive laboratory, even in my teaching labs. Air exchanges are required and one might as well do that through conventional fume hood. In a more undefined research lab situation, one has to be extremely careful. There are a few compounds that are not trapped, carbon monoxide being one common example. Even for any trapped compound where trace amounts would have a severe negative health impact, I would be extremely reluctant to allow its use.
Where these hoods are extremely valuable is when they are used to add an extra layer of safety to an existing situation. We are using them to significantly increase the level of safety for procedures currently done on an open lab bench. In a research environment, even doing that has issues. It requires very good labeling and training of what procedures are appropriate for the Green Hood. It also requires more follow through to make sure it is being used properly. In industry, especially in situations where the hood is used in a defined process, this is much easier to do because the command, safety, and inspection infrastructure is usually well developed. In the past when it was ok to have laboratory non-flammables in a non-flammable refrigerator, I did not allow those types of refrigerators in a laboratory because researchers would routinely put one or two small bottles of a compound dissolved in a flammable into a non-rated refrigerator. Green Hoods would be easier t!
o monitor than a refrigerator but the same issues would apply. In my current state of thinking, I would allow GreenHoods for some very well defined and easily monitored processes. If, for example, a researcher wanted some Green Hoods in a lab to place their rotovaps in, I would allow that since these rotovaps are usually located on a lab bench. Inspecting their appropriate use would be pretty easy - if a reaction is going on in that hood or they are storing chemicals in it, that would be a violation of the agreement. I might also allow them for labs that do their work on a lab bench now and have no capability to add conventional fume hoods. Fortunately, that is not an issue for our building.
We have an ~25% turnover in our researchers each year. Add to that the fact that the course of academic research can change abruptly with no notice makes me leery of using Green Hoods as a replacement for a conventional academic research hood. But I do believe they are an excellent solution in specific circumstances. I am extremely comfortable in how we have used them and I am quite happy with how they have significantly increased our safety without adding a huge environmental/energy cost while doing so.
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