DCHAS-L Archives, Aug 02 2012 - Re: [DCHAS-L] Backup power for chemical fume hoods

Good observations, as always, Bob.

University policy requires that labs be evacuated when we lose power.

The hood receptacles will lose power so stirrer and hotplates and stills will power down. Experiments that are water cooled by domestic water will probably remain unaffected, but experiments in which chilled water is used will lose cooling capacity because the building chilled water pumps go offline.

The Metasys HVAC control system is not powered by the backup generator, and the air handlers are not, so environmental control will be lost for the duration of the power outage. If our technicians recognize a major problem, we can get a 2,000 kW diesel generator on site within 3 hours.

People with long-term experiments typically have uninterruptible power supplies that are backed up by the generator, so they see no power glitches.

Experiments run in environmental chambers have unique problems but one typical solution is to have an out-of-control cold room send text messages to its users; most quickly pack their experiments in dry ice.

Without people and active experiments, we really only need to keep an airflow sufficient to contain fumes.

--------------------------------------------------------

Scott Goode, Professor

Department of Chemistry and Biochemistry

University of South Carolina

631 Sumter Street

Columbia SC 29208

Email: Goode**At_Symbol_Here**sc.edu

Phone: 803-777-2601

Fax: 803-777-9521

From: DCHAS-L Discussion List [mailto:dchas-l**At_Symbol_Here**MED.CORNELL.EDU]On Behalf Of Robert Haugen
Sent: Thursday, August 02, 2012 7:21 AM
To: DCHAS-L**At_Symbol_Here**MED.CORNELL.EDU
Subject: Re: [DCHAS-L] Backup power for chemical fume hoods

Hello!

Narrow question first:

If labs in buildings are evacuated during this power-down situation this compromise might work. A fume hood in good working order needs less exhaust to contain fumes if there is no movement (ie. people) in the lab.

Other wider issues should, however, be equally considered. Examples follow:

1) Are power outlets to hoods also powered during outage? Hotplates with stirrers can be a problem. There is no correct answer here since failing stirrers on a still warm hotplate may become a problem. On the other hand, some automated apparatus movement inside the containment area may produce loss of containment if left on during low exhaust as described by Scott.

2) Do electronic experiment monitors fail in same scenario?

3) Is thermostatic control in labs lost when only exhaust fans operate? This situation could ruin temperature-sensitive experiments.

The answer on the partial exhaust question is clearly dependent on what is being done in the hoods and should only be answered on a case-by-case basis. It is good Scott is carefully considering this issue!

Regards,

Dr. Bob Haugen

Laboratory Design and Research International

From: "GOODE, SCOTT" <SRGOODE**At_Symbol_Here**MAILBOX.SC.EDU>
To: DCHAS-L**At_Symbol_Here**MED.CORNELL.EDU
Sent: Wednesday, August 1, 2012 11:26 PM
Subject: [DCHAS-L] Backup power for chemical fume hoods

I am seeking information on supplying backup power to fume hoods.

Our most recent buildings have generators and automatic transfer switches designed to power all exhaust fans for the duration of the outage. Our control systems fail with exhausts dampers fully open. Because the air handlers are not backed up, the building pressurization goes negative within minutes.

In a recently remodeled lab building, the negative pressure during an outage sucked in a window. I have to presume doors were quite difficult to open and likely violated building code requirements.

One engineer recently told me that his designs will place only half the exhaust fans in emergency power, which he views as a good compromise.

Hoods in unoccupied labs are allowed to function at 60% face flow rates, which lends credence to the engineer's rule of thumb. I think we can safely assume that there will be no research operations in a building without ventilation or electrical power, so a lower level of exhaust seems reasonable.

Is there any authoritative source that addresses this situation?