From: "Norwood, Brad"
Date: Wed, 10 Dec 2008 15:28:18 -0500 Subject: RE: [DCHAS-L] laboratory ventilation question Russ, My back-of-the-envelope calculation gives me 9000 cubic feet in the room (assuming 9' ceiling) For a 6' hood with 3' opening **At_Symbol_Here** 100 ft/min linear velocity, I get approximately 900 cu. Ft./ min. (not atypical for a hood). That would give you six air changes in an hour (so my calculation isn't far off from theirs). That being said, the air brought in to the room to make up for what the hoo= d takes out typically comes in AT the hood. This will do NO good for the students at the other end of the room. In fact, IMO this does no good for any students not working IN the hood. So, again in my opinion, this is NOT adequate for the protection of the students or the faculty. Brad Bradley K. Norwood, PhD Laboratory Director Arista Laboratories 1941 Reymet Road Richmond, VA 23237 (804) 271-5572 ext. 307 (804) 641-4641 (cell) brad.norwood**At_Symbol_Here**aristalabs.com == From: "Bell,Martin" Russ, To determine the number of air changes you divide the total room exhaust volume (cfm) by the room volume. This will give you the air changes per minute. Convert that to air changes per hour by multiplying by 60. For example let's use you numbers and some assumption to determine the number of air changes per hour in this lab: Room volume - 50'x20'x10' = 10,000 cf - assuming the ceiling height is 10 feet. Room Exhaust Volume - I assuming the hood is the only exhaust in the room so if you have a hood that is 6' with an 1.5' (18 inches) opening and a face velocity of 100 feet per minute - 6'x1.5'x100 fpm = 900 cfm Air change per minute = room exhaust volume/room volume = 900/10000 = = 0.09 air changes/minute x 60 = 5.4 air changes per hour. Martin W. Bell, CHMM Drexel University Department of Environmental Health and Safety Environmental Health and Safety Manager Telephone : 215-895-5892 Cell Number: 215-778-4278 Fax Number: 215-895-5926 == Subject: RE: [DCHAS-L] laboratory ventilation question Date: Wed, 10 Dec 2008 15:38:07 -0500 From: "Wawzyniecki Jr, Stefan" Russ- Here's a quick calculation: Assuming 18" sash opening (1.5') 6' X 1.5' X 100 FPM = 900 CFM Assuming 10' ceiling 50' X 20' X 10' = 10,000 ft^3 Dividing 10,000 ft^3 by 900 cfm = 11.1 min, the time it would take for one air change. ....or, roughly 5 ACH So, theoretically, that's how they calculated it. BUT- The best mgmt practice would be to provide local exhaust. Someone else can poke holes in my math skills or in my reasoning. -Stefan Wawzyniecki == From: "Debbie M. Decker" Date: December 10, 2008 3:43:49 PM EST (CA) To: chas list Subject: RE: [DCHAS-L] laboratory ventilation question The University of California Laboratory Design Guide (http://ucih.ucdavis.edu/docs/labdesignguideSept2007.pdf ) recommends at least 6 air changes per hour or 1 cmf per square foot of (gross) lab space. This recommendation is based on ANSI Z9.5 and long years of arguing with design engineers over acceptable ventilation in a lab space . For 1000 sq ft lab, the fume hood would need to exhaust at least 1000 CFM. With a 6 foot fume hood at 100 fpm with a wide open sash, you might be close. But it's a lazy engineering solution, IMHO. What if the noise from the fume hood makes it difficult for the instructor to teach? You said that the hood is in the corner of the room. There will not be good mixing of make up air nor will there be good sweep of contaminated air from the entire space. Contaminated air will pool and eddy, conditioned supply air won't be sufficiently mixed and hot/ cold spots will develop - occupant comfort will be compromised and occupant safety may be compromised as well. Relying on a fume hood for all of the ventilation into and out of a space is risky and a really poor engineering solution. At the very least, there should be a minimum of 4-6 ach all the time out of the lab, through a general laboratory exhaust. Operating a fume hood at a full open sash height and at a (relatively) high face velocity wastes energy and doesn't necessarily increase safety. Debbie M. Decker, Campus Chemical Safety Officer Environmental Health and Safety University of California, Davis 1 Shields Ave. Davis, CA 95616 (530)754-7964/(530)752-4527 (FAX) dmdecker**At_Symbol_Here**ucdavis.edu Co-Conspirator to Make the World A Better Place -- Visit www.HeroicStories.com and join the conspiracy == From: "Lazarski, Peter M." Date: December 10, 2008 3:52:22 PM EST (CA) Subject: RE: [DCHAS-L] laboratory ventilation question Looking at ANSI/ASHRAE 62-1989, Ventilation for Acceptable Indoor Air Quality. Table 2 shows for a laboratory with an estimated maximum occupancy of 30/1000 sq. ft., 20 cfm/person as a requirement for outdoor air ventilation. If these criteria are met, indoor air quality can be considered acceptable. I would think local exhaust ventilation in the form of 'snorkels' would have been more appropriate for this area. Out of curiosity, was this space designed specifically to be a dissection laboratory or was the use decided after the building plans were finalized and well under construction? Two suggestion: 1st - calculate the room height to see whether the 5 air changes/hr meets the total occupants x 20 cf/m requirement. 2nd - set off a smoke candle in the hood to determine whether its working at all. The information contained in this e-mail message and any attachments may be confidential. 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