NFPA 45 Fire Protection for laboratories using chemicals recommends that even unoccupied laboratories (I.e. those not in use) have a minimum ventilation rate of 4 air changes/hour in A7.2.2.1. In the (unlikely) event you have 4 ACH with the hoods off then the ducts will act as stacks and suck in air from the outside. This will promote mold growth when it gets warmer and, more importantly, pull any vapors from the hoods into the laboratory. So a really, really bad idea. So close the hood doors but don't turn off the hoods.

=E2=80=8BI've received the following from a colleague at another school. 

The powers that be want to save money by shutting down the hoods in our building. That doesn't seem like a good idea to me and I have asked others and they agree, but no one can tell me why we shouldn't shut them down. Do you have any insights on this? Should I be concerned if all the hoods get shut down? If so, why?=E2=80=8B

I agree with the department, not the PTB, but would like more feedback

Joe C

--- For more information about the DCHAS-L e-mail list, contact the Divisional membership chair at membership**At_Symbol_Here**dchas.org Follow us on Twitter **At_Symbol_Here**acsdchas