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 Smith
 wrote:
> 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
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>

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