> And I can see how a purge system that would keep the atmosphere in a lab somewhat under control in an emergency could be useful.  A purge system might preclude a spill getting out of hand to the point that SCBA would be necessary.  Or it could prevent a solvent spill vapor concentration from ever reaching the LEL.  

I guess my question is: What is the ventilation rate associated with "purge" mode? I can understand how some assumptions about this could be made in a specific setting such as theater stage with a limited set of emission scenarios to consider. However, in a generic laboratory with multiple potential pollutants located in a variety of places, I think that a design engineer would have a harder time specifying what higher flow rate is appropriate. It would depend on the hazard being protected against (e.g.. flammability or toxicity) as well as the geometry of the room. Of course, we have similar concerns in laboratories under normal operating conditions, as the variability in laboratory ventilation effectiveness applies to that situation as well…

- Ralph

Ralph Stuart CIH

Chemical Hygiene Officer

Department of Environmental Health and Safety

Cornell University

rstuart**At_Symbol_Here**cornell.edu