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- it says that the fume hood should be  
kept closed whenever possible.


Cat Conley
Chemical Hygiene and Safety Officer
Department of Environmental Health and Safety
Roger Williams University
1 Old Ferry Road
Bristol, RI 02809
401 254 3781


From: Paul_Poulin**At_Symbol_Here**
Date: December 10, 2008 5:04:24 PM EST (CA)
Subject: Re: Fw: [DCHAS-L] laboratory ventilation question


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  
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  
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  
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  
Constant volume hoods have there airflows set for the intended working
height of the sash as well. In either case, the maximum working height  
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  
the minimum airflow for a biology lab setting are satisfied. However,  
because the standard for ACH in a biology lab are satisfied, does not  
that fumes emitted from a source in the middle of the room (not inside  
fume hood) will not be detectable - fumes will be detectable. What is  
is that once the source of the fumes is removed from the lab, the odor  
dissipate in a reasonable amount of time.

It is probably appropriate to consider the health hazard of what the  
are as well. In this case, it's isopropanol. So:

According to a MSDS that I pulled up on 2-propanol (isopropanol), the  
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  
be exhausted back to the room through an activated carbon filter. This
sounds like a good application for this situation. As long as the  
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.



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  

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.


Robert C. Peck, MEAS, JD, CIH
Eagle's Rest Consulting Services, LLC
50 Brookhaven Ct.
Sunrise Beach, MO 65079

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