| About This Archive | | DCHAS-L 2017 Index | | DCHAS-L Yearly Index | |
Check out Safety Emporium for your N95, N99, and face shield needs.
|
Previous by Date: Subject: Re: [DCHAS-L] Fume Hood Ducting Date: Friday, October 13, 2017 at 9:50:24 AM Author: Monona Rossol <0000030664c37427-dmarc-request**At_Symbol_Here**LISTS.PRINCETON.EDU> |
Next by Date: Subject: Re: [DCHAS-L] Fume Hood Ducting Date: Fri, 13 Oct 2017 14:44:16 +0000 Author: TILAK CHANDRA |
Thanks for bringing up the fire issue which, of course, is the most important point here. It's why ventilation ducts must be planned so well that deposition cannot occur.
I have lived on the sixth floor above a restaurant since 1969. And in the early 70s, unknown to me, the grease in the hood and duct in that restaurant had smoldered all night. At 8:15 in the morning, the whole first floor of the back of the building where the kitchen is exploded blowing out the windows in the back of the building. By the time I put my cat in a pillow case and went to the fire escape that goes down the front of the building, the fire had blown out the restaurant's big front window and flames were coming up under the fire escape. I had to shelter in place and startled the hell out of the firefighter who came through the thick smoke on the stairs with his ax to smash down my door. I was the only person in our half of the building who still had a door after the fire!
So I probably have more reason than most to know that grease recondenses and deposits on surfaces --and that fire is the major issue here.
---
For more information about the DCHAS-L e-mail list, contact the Divisional secretary at secretary**At_Symbol_Here**dchas.org
Follow us on Twitter **At_Symbol_Here**acsdchas
Monona Rossol, M.S., M.F.A., Industrial Hygienist
President: Arts, Crafts & Theater Safety, Inc.
Safety Officer: Local USA829, IATSE
181 Thompson St., #23
New York, NY 10012 212-777-0062
-----Original Message-----
From: Richard Rosera <richardrosera**At_Symbol_Here**GMAIL.COM>
To: DCHAS-L <DCHAS-L**At_Symbol_Here**PRINCETON.EDU>
Sent: Fri, Oct 13, 2017 6:17 am
Subject: Re: [DCHAS-L] Fume Hood Ducting
Although my experience doesn't directly relate to lab hoods, I can relate one item concerning ducting on an aerosol production line. On this particular line, the main product contained a substantial amount of a low VOC oil (to meet CARB standards for California) that was put into the aerosol can prior to injecting the propellant. The propellant used was a mixture of LPG (propane & butane) with 1,1-difluroethane (Propellant 152a). The ductwork from the aerosol propellant filling portion of the line included a LEL detector, the calibration of which was on a quarterly PM schedule. In looking over the reports, I saw that the sensor for this detector often had to be replaced or cleaned - but no reason was given. I talked to the technician who did the checking, and he said that it was because the sensor was coated with oil & not responding properly! He also remarked about the oil coating the ductwork. I kept thinking that if a fire started, we could end up with the industrial equivalent of a "chimney fire"! Not a pleasant thought...
Richard Rosera, BS ChE, MS ChE, MBA
Rosearray EHS Services LLC
101 Beryl Street
Los Alamos, NM 87547
cell: 908-279-4463
---
For more information about the DCHAS-L e-mail list, contact the Divisional secretary at secretary**At_Symbol_Here**dchas.org
Follow us on Twitter **At_Symbol_Here**acsdchas
On Oct 12, 2017, at 5:33 PM, Monona Rossol <0000030664c37427-dmarc-request**At_Symbol_Here**LISTS.PRINCETON.EDU> wrote:
Since I plan ventilation systems, I'm going to weigh in on this even though I have never planned one of your labs. I have, however, specified fume hoods for theatrical and art purposes that are similar. And I have seen a lot of chemistry labs.
1. First big issue is that duct work should never have right angle entries into a main (should be 30 degree entries), should never make any rapid changes of direction or increase or decrease in diameter rapidly. And the diameter of a duct is never a standard dimension, it is determined by the centerline velocity that you need to achieve for the particulate.
--- For more information about the DCHAS-L e-mail list, contact the Divisional secretary at secretary**At_Symbol_Here**dchas.org Follow us on Twitter **At_Symbol_Here**acsdchas
What I see in chemistry labs is a lot of bad practice in terms of changes in direction and right angle entries each one of which can lead to air turbulence in the duct and condensation or deposition of particulate. And I see all the ducts leading from the off-the-shelf hoods are the same diameter indicating they assume all of the ducts are transporting the same contaminants with the same particle size and characteristics. I smell the work of HVAC engineers here rather than industrial ventilation engineers. And I must say, I have a problem with using ASHRAE standards for fume hoods and ventilation systems in general.
2. The second problem is the centerline velocity of the ducts in the lab. That velocity has to be fast enough to keep what ever you are transporting moving rapidly enough not to deposit. Examples of those speeds are in table 5-1 in the ACGIH Manual of Recommended Practice for Industrial Ventilation.
Gases, vapors and smoke 1000 to 2000 feet/minute
fumes, metal smokes 2000 to 2500
fine light dusts 2500 to 3000
dry dusts and powders 3000 to 3500
grinding dusts 3500 to 4000 and etc up to 5000 cfm for heavy and sticky stuff.
Notice that there is nothing said about oil mist. This is because oil mists typically can be fume sized (0..1 to 5 microns) or much larger depending on how they are generated (I am very familiar with these due to the oil mist theatrical smoke/haze generators that can do this hot or cold and in any size needed.)
In addition, all oil mists are condensation and deposition risks. I usually recommend a centerline velocity of at least 3000 f/m if oil mist is involved.
In other words, if you are using the fume hoods for just any and all contaminants you generate, you really need to have the system designed to efficiently transport the largest of the particulates and the particulates with the worst transport issues.
So to tell you the truth, I would be surprised if you were NOT getting deposition of oil mist in ducts in the labs I've seen. And people who don't think they have this problem are just getting deposition in locations that don't drip out where you see it.
Monona Rossol, M.S., M.F.A., Industrial Hygienist
President: Arts, Crafts & Theater Safety, Inc.
Safety Officer: Local USA829, IATSE
181 Thompson St., #23
New York, NY 10012 212-777-0062
-----Original Message-----
From: Richard Van Doren <RVandoren**At_Symbol_Here**METROSOLUTIONSUSA.COM>
To: DCHAS-L <DCHAS-L**At_Symbol_Here**PRINCETON.EDU>
Sent: Thu, Oct 12, 2017 5:24 pm
Subject: Re: [DCHAS-L] Fume Hood Ducting
--- For more information about the DCHAS-L e-mail list, contact the Divisional secretary at secretary**At_Symbol_Here**dchas.org Follow us on Twitter **At_Symbol_Here**acsdchasOMG. We also experience the same thing. We are not sure what it's from. Our hood install has been only a year old and we have been using it for metals digestions using EPA 3050B. I would like to know what is causing this. I have yet to take it apart to see what the root cause of this is.
Anyone have an answer?
Richard Van Doren
Quality Assurance Manager
Metropolitan Soultions
423 Pacific Ave., Ste. 101
Bremerton, WA 98337
360-799-5699
From: ACS Division of Chemical Health and Safety [mailto:DCHAS-L**At_Symbol_Here**PRINCETON.EDU] On Behalf Of Elizabeth Brubaker
Sent: Thursday, October 12, 2017 4:14 PM
To: DCHAS-L**At_Symbol_Here**PRINCETON.EDU
Subject: [DCHAS-L] Fume Hood Ducting
Has anyone experienced accumulation of oil (perhaps mineral oil from a heated oil bath?) in fume hood duct work? Is this reasonable or even possible? Could a sufficient amount remain in the system for it to condense out in the ducts when the exhaust fans were turned off for an extended period?
--
Beth Brubaker
Laboratory/Safety/Waste Coordinator
Murray State University Department of Chemistry
2226 Jesse D. Jones Hall
Murray, KY 42071-3300
(270) 809-6390
--- For more information about the DCHAS-L e-mail list, contact the Divisional secretary atsecretary**At_Symbol_Here**dchas.org Follow us on Twitter **At_Symbol_Here**acsdchas
Previous post | Top of Page | Next post