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Date: Wed, 10 Dec 2008 20:26:55 -0500
Reply-To: List Moderator <ecgrants**At_Symbol_Here**UVM.EDU>
Sender: DCHAS-L Discussion List <DCHAS-L**At_Symbol_Here**LIST.UVM.EDU>
From: List Moderator <ecgrants**At_Symbol_Here**UVM.EDU>
Subject: 3 more RE: [DCHAS-L] laboratory ventilation question
From: Cat Conley
Date: December 10, 2008 4:32:50 PM EST (CA)
Subject: RE: [DCHAS-L] laboratory ventilation question
Hi Russ,
I'm looking at the 2004 version of NFPA 45 Chapter 8 "Laboratory
Ventilation Systems and Hood Requirements" and based on the language
in this section, I don't think that the solution proposed by the
design engineers is adequate.
NFPA 45-8.2.2 says "Laboratory units and laboratory hoods in which
chemicals are present shall be continuously ventilated under normal
operating conditions." Looking at Annex A-8.2.2 for a more in-depth
explanation, it says that an unoccupied laboratory requires a minimum
of 4 ACH, and an occupied one "typically operates" at 8 ACH or greater.
Based on these statements, I don't think that the "approximately 5
ACH" is appropriate. Additionally, I don't think that using fume hoods
to ventilate a lab meets the "normal operating conditions" requirement
- especially since in 45-8.8.3.1 it says that the fume hood should be
kept closed whenever possible.
Sincerely,
Cat
Cat Conley
Chemical Hygiene and Safety Officer
Department of Environmental Health and Safety
Roger Williams University
1 Old Ferry Road
Bristol, RI 02809
cconley**At_Symbol_Here**rwu.edu
401 254 3781
==
From: Paul_Poulin**At_Symbol_Here**eri.eisai.com
Date: December 10, 2008 5:04:24 PM EST (CA)
Subject: Re: Fw: [DCHAS-L] laboratory ventilation question
Bob,
The short story is that I come up with 6 air changes per hour.
I have to make a couple of assumptions to proceed with the estimate:
1) Ceiling height - I'll use 9'
2) Sash opening for the hood - I'll use 18".
More on assumption #1: A typical lab ceiling height is 10', then you
would
take a deduction for all of the solid furniture and such that takes up
space in the room. In this case, you can say that if the ceilings are
actually 10', and about 10% of the room is taken up by casework (lab
benches, cabinets, and so on), then the ceiling height of 9' has a 10%
allowance for casework built into it. If more information about the
actual
ceiling height and casework volume are known, then a better estimate
of the
room volume can be generated.
So, the exhaust CFM from the hood are calculated as area of the hood
opening times the face velocity.
18"/12"/ft (height in ft) x 6' wide (area of the opening) x 100
feet/minute or 900 CFM. That is a typical airflow for a hood of this
size,
confirming the result I have here.
Also, even variable volume hoods typically have maximum airflow volume
settings that are set based on the working height of the sash, typically
18". If that is the case here, opening the hood sash beyond the maximum
working height for the hood will not result in additional exhaust
airflow.
Constant volume hoods have there airflows set for the intended working
height of the sash as well. In either case, the maximum working height
for
the sash should be indicated on the side of the hood.
To calculate the air changes per hour (ACH), first calculate the
volume of
the room: 20' x 50' x 9' or 9,000 cubic ft.
The calculation is now:
900 cubic ft | 60 min | air change = 6 ACH
min | hr | 9,000 cubic ft
While not an expert on the required ACH, my experience tells me that the
guidelines for the minimum ACH in a biology lab is 6. So, it appears
that
the minimum airflow for a biology lab setting are satisfied. However,
just
because the standard for ACH in a biology lab are satisfied, does not
mean
that fumes emitted from a source in the middle of the room (not inside
the
fume hood) will not be detectable - fumes will be detectable. What is
true
is that once the source of the fumes is removed from the lab, the odor
will
dissipate in a reasonable amount of time.
It is probably appropriate to consider the health hazard of what the
vapors
are as well. In this case, it's isopropanol. So:
According to a MSDS that I pulled up on 2-propanol (isopropanol), the
OSHA
8 hr permissible exposure limit is 400 ppm or 980 mg/m^3. I think those
numbers gives one some concrete guidance on what should be considered
to be
an acceptable exposure level in this lab.
There are other ways of dealing with solvent fumes without increased
exhaust levels, too. There are companies that make acrylic hoods that
can
be exhausted back to the room through an activated carbon filter. This
sounds like a good application for this situation. As long as the
activated
carbon is not saturated and is effective for isopropanol, I would expect
that there would be a significant reduction in the concentration of the
alcohol vapors in the room, and the acrylic hood could possibly allow
viewing from all sides.
Regards,
Paul
===
From: "Bob Peck"
Date: December 10, 2008 6:14:40 PM EST (CA)
Subject: Re: [DCHAS-L] 5 RE: [DCHAS-L] laboratory ventilation question
I would submit that the best test for the viability of this
laboratory's design and operation might be to monitor areas and
breathing zones of staff and students to see if the OSHA standard for
formaldehyde (1910.1048(c) as monitored following Appendix A
procedures) is being met. This standard requires health monitoring
and engineering design actions if formaldehyde exposure exceeding 0.5
ppm - 8 hour TWA and 2.0 ppm for any STEL - 15 minute period. My
experience, working with rat necropsy labs in the 1980's is that the
STEL compliance might be a problem. I know that OSHA standards do not
apply to university labs in most cases. However, this is a credible
health standard that should not be ignored, given the use of the lab
and the experience in industry labs. Do not confuse ANSI standards
for indoor air quality with standards related to storage of hazardous
chemicals and the even higher standards for laboratories handling
hazardous chemicals (formaldehyde - an irritant and potential cancer
hazard).
My experience in assessing laboratory design for effective ventilation
is that there are several factors, that contribute to hood
performance, exposure control and temperature control for comfort,
that are more important than just the simple calculation of
theoretical air changes. Biology labs, that don't have open chemical
handling, frequently required additional air recirculation for
temperature control. Don't confuse this air movement as fresh air
ventilation for control against the build up of toxic materials used
and released in the lab. Indoor air quality standards for offices are
generally only intended to prevent the buildup of carbon dioxide from
the breathing of occupants and incidental releases of compounds from
surfaces or carpet.
I hope it provides more food for thought and discussion.
Bob
Robert C. Peck, MEAS, JD, CIH
Eagle's Rest Consulting Services, LLC
50 Brookhaven Ct.
Sunrise Beach, MO 65079
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