From: Cat ConleyDate: 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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