I don't know what the face velocity listed for your specific hoods, but be very careful of the placements of each of those hoods in relation to the ventilation system's air currents and drafts. Even the best of the hoods will be negatively affected by air currents blowing into or across the faces of the hoods. Low flow hoods are at higher risk of non-capture than the standard hoods. If the hood is in a very quiet air current area, the specs for that hood may be OK. If even in the slightest doubt of the efficacy of the total intake 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 velocity allowing for contents to escape. I am speaking from experience where many 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 safe. 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 specifies face velocity rates for fume hoods. However, our newly remodeled Organic Lab has energy-efficient, low-flow hoods. What is an appropriate value of face 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. If 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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