on what ken stated. check it through various times of day. in my lab, the warming of the building from the sun actually changes the air flow. I don't know if it affects our hoods but it can definitely be seen on a high precision balance. On Mon, Oct 5, 2009 at 7:05 PM, Jean & Ken Smithwrote: > I don't know what the face velocity listed for your specific hoods, but b e > very careful of the placements of each of those hoods in relation to the > ventilation system's air currents and drafts. =A0Even the best of the hoo ds > will be negatively affected by air currents blowing into or across the fa ces > of the hoods. =A0Low flow hoods are at higher risk of non-capture than th e > standard hoods. > > If the hood is in a very quiet air current area, the specs for that hood may > be OK. =A0If even in the slightest doubt of the efficacy of the total int ake > capture velocity at the hood face for whatever hood sash height is used, a > smoke test should always be used in addition to the average velocity > measured. > > It takes only a very small draft of air blowing across the face to reach in > and negate one area of the open sash to reduce or negate the inflow veloc ity > allowing for contents to escape. =A0I am speaking from experience where m any > hoods in our labs were badly placed and were negatively influenced by > drafting air. > > Use a smoke test at the open face of the hood to determine the trajectory of > the air capture (or non-capture) across the opening of the sash to be saf e. > Ken Smith > CIH, Retired > > -----Original Message----- > From: DCHAS-L Discussion List [mailto:DCHAS-L**At_Symbol_Here**list.uvm.edu] On Behalf Of > Barbara Mowery > Sent: Monday, October 05, 2009 1:42 PM > To: DCHAS-L**At_Symbol_Here**LIST.UVM.EDU > Subject: [DCHAS-L] Low-flow hoods > > Dear Colleagues, > > I am doing the annual update of our Chemical Hygiene Plan, which specifie s > face velocity rates for fume hoods. However, our newly remodeled Organic Lab > has energy-efficient, low-flow hoods. What is an appropriate value of fac e > velocity to specify for such hoods? > > Barbara Mowery > General Chemistry Laboratory Coordinator > Physical Sciences Department > York College of Pennsylvania > 441 Country Club Road > York PA 17403-3651 > 717-815-6480 > Fax 717-849-1653 > > > This information is intended solely for the use of the individual to whom > it is addressed. Any review, disclosure, copying, distribution or use of > this e-mail communication by others is strictly prohibited. =A0If you are > not the intended recipient, please notify us immediately by returning > this message to the sender and delete all copies. >
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