From: Monona Rossol <actsnyc**At_Symbol_Here**>
Subject: Re: [DCHAS-L] Fume hoods purge buttons
Date: Tue, 13 Aug 2013 10:05:56 -0400
Reply-To: DCHAS-L <DCHAS-L**At_Symbol_Here**MED.CORNELL.EDU>
Message-ID: 8D066455D06467D-1160-22BA2**At_Symbol_Here**
In-Reply-To <7AB8F8BFE46C5446902F26C10EBF4AEA549D48F0**At_Symbol_Here**>

Ventilation for laboratories is not my area, although fume hoods and dilution ventilation systems used in art studios, printmaking acid rooms and the like are my field.  I haven't specified a purge system for an art studio, but I'm beginning to think from the conversations on this thread that that is a REALLY good idea.  
We do use a purge system on theatrical stages.  Some unions require a system that will completely clear the area behind the curtain of airborne special effects between acts in under 5 minutes. 
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 am going to consider this purge idea for some art labs and studios.  For example, I already specify special kind of displacement ventilation system for traditional solvent art painting rooms. There are two settings for air flow for these system, one during painting classes and a lower setting for night time when only the outgassing canvases in the drying rack need exhaust.  It would be so simple to have a third setting that could jack up that flow to purge the room in an emergency.   
One of these painting room displacement systems I recommend was installed in the new art building at UMass-Amherst.  The original purge question came from their EH&S person who is a friend and colleague. Hmmmm.  That's making me think even harder.  In any case, you've all given me something to think on.   Thanks.
Monona Rossol, M.S., M.F.A., Industrial Hygienist
President:  Arts, Crafts & Theater Safety, Inc.
Safety Officer: Local USA829, IATSE
181 Thompson St., #23
New York, NY 10012     212-777-0062

-----Original Message-----
From: David C. Finster <dfinster**At_Symbol_Here**WITTENBERG.EDU>
Sent: Tue, Aug 13, 2013 7:27 am
Subject: Re: [DCHAS-L] Fume hoods purge buttons

I=E2=80™m surely not a ventilation expert, and I've never heard of a "purge button" before.  However, in addition to Ralph=E2=80™s question below about the purpose of using such a device, as an volunteer firefighter for 20 years I can view this scenario of a "significant spill" as a situation that should only be handled by emergency responders.  Any situation that poses an atmosphere that is not human-friendly and/or a fire/explosion hazard should simply call for an building evacuation with appropriate power shut-downs (to eliminate ignition sources) IF POSSIBLE.   
"We found ourselves using the purge buttons a lot to exhaust the room and the hoods  in an emergency."
I=E2=80™d re-examine protocols to prevent these episodes rather than re-evaluating response options.
"This is  to allow a  safer environment for emergency personnel to enter the area and do spill clean ups, particularly when the spill happens outside of the hood. "
The firefighters who respond to this will surely be wearing SCBA and have a four-gas meter to check O2/CO/flammables/X  (where is likely H2S).  It is thoughtful of you to consider them but, frankly, they will mostly ignore you and treat any major spill as a worst-case scenario to protect themselves.  Firefighters can't afford to blindly trust information given to them by dispatch since in some instances it a wrong (even when not intended to be.)   The best thing to is to meet the officer in charge of entering crew at the door, give the best information you have, tell them if you think there is any chance that someone is still in the building, and make sure they have master keys.  They know what to do after that.
David C. Finster
Professor, Department of Chemistry
University Chemical Hygiene Officer
Wittenberg University

From: DCHAS-L Discussion List [mailto:dchas-l**At_Symbol_Here**MED.CORNELL.EDU] On Behalf Of Ralph B. Stuart
Sent: Monday, August 12, 2013 5:50 PM
Subject: Re: [DCHAS-L] Fume hoods purge buttons
> We found ourselves using the purge buttons a lot to exhaust the room and the hoods  in an emergency.
I'm not clear what hazard is being reduced by this strategy. Are you trying to prevent a fire by keeping the concentration of the spill below the LEL? Or are you trying to control levels below the IDLH? I'm not sure that general ventilation will accomplish these goals, as the spill could be a location in the lab where the ventilation system doesn't effectively clear the air. We are finding significant "dead spots" in many of our lab settings-
My personal opinion is that the ventilation system should not be considered part of the emergency response system, as its value in a specific situation is undeterminable.
- Ralph
Ralph Stuart CIH
Chemical Hygiene Officer
Department of Environmental Health and Safety
Cornell University

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