Hi Monona,

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.

Ken