From: Allen Niemi <anniemi**At_Symbol_Here**MTU.EDU>
Subject: Re: [DCHAS-L] Fume hoods purge buttons
Date: Tue, 13 Aug 2013 16:27:42 -0400
Reply-To: DCHAS-L <DCHAS-L**At_Symbol_Here**MED.CORNELL.EDU>
Message-ID: CAN0bzO6LohptSWSrfOcAs8K1rN-poZOTq6-aZZ4ngY_gVti+dQ**At_Symbol_Here**
In-Reply-To <7AB8F8BFE46C5446902F26C10EBF4AEA549D4A83**At_Symbol_Here**>

As pointed out by many the space must be made safe (ventilated, in some cases) before it can be safely reentered. The purge mode (we have one for the entire Chemical Sciences Building) helps expedite the ventilation process. How do you know when it's safe to reenter the space? With or without a fume hood purge, the process is the same -- air monitoring. Students and employees are supposed to be trained how to respond in an emergency. Training should include the evacuation and reentry process. If there has been no training, I can assure you from experience that it is unlikely there will be an emergency call made or even an evacuation, with or without a fume hood purge. In the absence of training most faculty and students use similar logic. If there's no fire, you're good. If there are no bodies, you're good. If you can smell something, it must be bad and probably causes cancer. If the air doesn't smell, it must be OK.

We use our purge system to reduce the time before we can get back to business. There are classes to teach and research to get done. We can wait for the hazmat team to arrive (a minimum of four hours away) or start the ventilation process while we wait. For less serious cases, we might not even need to call hazmat -- just air out the building.


On Tue, Aug 13, 2013 at 9:44 AM, David C. Finster <dfinster**At_Symbol_Here**> wrote:


Thanks for the info about purge systems. If they are designed to function as you describe I would not disable or override them. However, my concern is that an unsafe situation (hazardous atmosphere) may exist/persist and local personnel might assume that the purge system will render this "safe" before the atmosphere is actually safe and then find themselves in an unsafe atmosphere. The scariest situation is that you walk by a lab and observe a victim on the floor and rush in to help. This is a natural response but emergency responders (firefighters and EMTs) are always taught to first assess scene safety. If someone appears to be unconscious on the floor, it could be medical (= heart attack), trauma (fell and bonked their head), or asphyxiation due to simple (N2) or chemical (CO) asphyxiant. Without proper scene assessment, the Good Samaritan might become the second victim. So, back to the purge system: How quickly does this work? My concern is that local personnel might assume the purge system "has worked" before it has worked effectively. Noses are sometimes crudely reliable but without a gas meter to assess the atmosphere, it may be difficult to assess the safety of the atmosphere.

If I were responding to a major spill as a FF, I'd be happy to learn that a purge system was functioning since one of the top tactical priorities would be to ventilate..


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 Rielly, David
Sent: Tuesday, August 13, 2013 8:42 AM
Subject: Re: [DCHAS-L] Fume hoods purge buttons

Interesting commentary David as you have real world experience as a voluntary firefighter. Most fume hoods, in particular VAV hoods, have some form of fume hood monitor/flow alarm on the hood with an "emergency" purge button of sorts to allow the operator to force the hood to max flow, and thus increase the ventilation at the hood and room. There are now also systems that actively monitor the room environment (eg. Aircuity) and also increase the ventilation in the room in the advent of a spill. Essentially what you are recommending is that you don't enable these purge systems, but allow the responders to assess the situation and respond as they see appropriate?

David A. Rielly, CEM, LEED GA

Global Energy Manager

Novartis Institutes for BioMedical

Research, Inc.


From: DCHAS-L Discussion List [mailto:dchas-l**At_Symbol_Here**MED.CORNELL.EDU] On Behalf Of David C. Finster
Sent: Monday, August 12, 2013 9:07 PM
Subject: Re: [DCHAS-L] Fume hoods purge buttons

I'm surely not a ventilation expert, and I've never heard of a "purge button" before. However, in addition to Ralph'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'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


Allen Niemi, PhD
Occupational Safety and Health Services
Room 322 Lakeshore Center
Michigan Technological University
Phone: 906-487-2118
Fax: 906-487-3048

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