Date: Thu, 19 Nov 2009 17:37:54 -0500
Reply-To: tim.hawkins**At_Symbol_Here**
Sender: DCHAS-L Discussion List <DCHAS-L**At_Symbol_Here**LIST.UVM.EDU>
From: Tim Hawkins <tim.hawkins**At_Symbol_Here**SAFEFUMEHOOD.COM>
Organization: FarHawk Marketing Services
Subject: Re: Hoods
In-Reply-To: <4B056E830200002900015FD1**At_Symbol_Here**>
Hi Ed,

The regulation depends upon what safety and fire codes that you wish to be
in compliance. There are a number of them out there, the most common being
NFPA 45. Applicable portions of the NFPA code may be found on the index
(home) page of . Complete copies of the code are
available for sale at .

The question of expense to replace is a relative term. Complete retrofit
alarms/monitors are in the $300-$495 range, and can be installed by a
competent HVAC technician. Many universities use their facilities people to
replace defective alarms and monitors.

Based upon your situation, though, you may not be at the stage to replace
your alarms. Here are some thoughts and questions.

It's a good idea to annually check the face velocity displayed by your flow
gauge against a handheld thermoanemometer or some other means of verifying
actual face velocity.  That will confirm whether the flow gauges are
accurate and determine if a re-calibration is in order.

You may just need to re-calibrate the alarms. Re-calibrate a few of these
using new actual face velocities and see if they then have stable readings.

Have there been changes to a lab's HVAC system that can start to effect
monitor readings?

Are these hoods on a VAV (Variable Air Velocity) system?  If so, it would be
correct that if some number of the total sashes are up, some of the monitors
WILL begin to go into alarm.

What make/model of alarms do you have?

If you like, contact me directly, and I will arrange to have you talk to our
technical people. No charge or commitment.

Best regards,

Tim Hawkins

-----Original Message-----
From: DCHAS-L Discussion List [mailto:DCHAS-L**At_Symbol_Here**] On Behalf Of
Edward Senkbeil
Sent: Thursday, November 19, 2009 4:13 PM
To: DCHAS-L**At_Symbol_Here**LIST.UVM.EDU
Subject: [DCHAS-L] Hoods

The hoods (about 5 years old) in all our undergraduate chemistry labs are
equipped with alarms which supposedly should go off with improper air flow.
However many will continually alarm if the sash is pulled up by more than
one third the way (below where sash has a normal catch about half way up).

Is there any law / regulation which states that we must have the alarms
working if they are part of the original equipment?  All the hoods have flow
gauges on them which are functioning, but we have been unable to get all the
alarms to work properly.  We are told it would be very expensive to get them
all functioning.  They become a problem in large student labs since they
continually go off, and are distracting both faculty and students.

We have considered disarming the alarm, but are concerned about any
regulations we might be violating.
Students are beginning to not pay attention to the flow gauges, but just
automatically hit the mute button on the alarms.  We believe the flow gauges
are a more accurate reflection of any problems.

Any comments or suggestions welcome.

Ed Senkbeil, Ph.D.
Chemistry Department
Salisbury University

Previous post   |  Top of Page   |   Next post

The content of this page reflects the personal opinion(s) of the author(s) only, not the American Chemical Society, ILPI, Safety Emporium, or any other party. Use of any information on this page is at the reader's own risk. Unauthorized reproduction of these materials is prohibited. Send questions/comments about the archive to
The maintenance and hosting of the DCHAS-L archive is provided through the generous support of Safety Emporium.