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This may be a week too late to be of use in the discussion, but a good (and dated) reference we have used in about 2 dozen situations involving a large number of perchloric acid fume hoods is:
Perchloric Acid Contaminated Hood Decontamination Procedure Manual, 1993, Martin Marietta Energy Systems, Inc./ Oak Ridge National Laboratory/ P.O. Box 2008/ Building 3550, MS-6292/ Oak Ridge, TN 37831-6292.
Based on some site-specific experiences, NEVER believe oral histories about the use and maintenance of exhaust hood systems. Always test (we prefer an ion-specific electrode) at least every change in air flow and periodically in long horizontal runs. Facility maintenance personnel, especially plumbers and electricians, who have been around for a couple decades are probably more reliable sources of information than current laboratory personnel.
If there are auxiliary or make-up air systems, visually inspect the duct work to insure that the ventilation duct work (from the hood to the skin of the building) is physically separate from the inlet duct work (from the skin of the building to the front of the hood). We have found a number of installations were the two ducts were connected. (I guess that’s the definition of resource conservation.) Most of these “mistakes” were in relatively tall buildings where the installing contractor could save a bunch of money and effort by making only one wall penetration to the outside.
George Walton
Reactives Management Corporation
757-436-1033
From:
DCHAS-L
Discussion List [mailto:DCHAS-L**At_Symbol_Here**list.uvm.edu] On
Behalf Of Wendy Campbell
Sent: Friday, April 16,
2010 1:18
PM
To:
DCHAS-L**At_Symbol_Here**LIST.UVM.EDU
Subject: Re: [DCHAS-L]
Perchloric
Acid Fume Hood Decommissioning
Ni Nick,
You've just hit the nail straight on - at this moment there's no
evidence for
or against perchlorate contamination, so I'm taking the conservative
route and
assuming that at some point, unbeknownst to everyone else, someone fumed
perchloric in the hood. I'm not willing to rely on memories, so
we're
approaching this as if it is the most perchlorate-contaminated system
ever, until
proven otherwise.
I'm coordinating with our emergency response teams, and meeting with the
project director and contractors on Monday, armed with war stories and a
variety of publications. I'm hoping that I can impress the
potential
seriousness of the situation on the contractors, and figure out whether
to
proceed with them, or to move to someone with high-haz
capabilities.
When it's all over, I may write up a short something on how it went!
Wendy
On Fri, Apr 16, 2010 at 7:54 AM, Tsiakals, Nicholas John <tsiakals**At_Symbol_Here**illinois.edu> wrote:
Wendy, if you can share, what evidence do you have of perchlorate contamination?
Also, have you considered contracting the service – either high haz evaluation or full high haz removal? Perchlorate-contaminated ductwork presents a number of tough problems – such as removing portions of a duct run without introducing friction or vibration to a contaminated site. The approach needs to guard against metal perchlorates built-up at duct joints, at individual screws, etc. I believe there are heat-imaging field devices that help visualize pre-detonation reaction – but that’s my fuzzy memory on that. This gets very expensive – perhaps the largest problem is properly identifying work that should not proceed without the highly skilled help (and corresponding price tag).
In concept, every lab hood system can be considered perchlorate-contaminated, albeit at differing confidence levels. What I mean to say is that you frankly don’t know if some researcher ran heated perchloric up the hood a decade or two or three back, regardless of that hood bearing the label “perchloric hood”. Servicing any lab hood system in a chemical lab building should not be done lightly. To an appreciable extent, you have residual risks you don’t get to fully eliminate in the duct systems. But the more robustly you can build a case for the high haz price tag, the more likely purse strings will loosen for you in a given case.
Hope this helps,
-Nick
___________________________________
Nicholas J. Tsiakals
Division of Research Safety
Chemical Safety Section
(217) 244 - 0682
"If we don't train students in risk management and safety procedures, then we're not training them for employment in modern industry. If we want someone to turn up in a job and be productive, they can't do that if they're not safety aware."
-- Prof. Thomas Welton, Head,
Department of
Chemistry,
From: DCHAS-L Discussion List
[mailto:DCHAS-L**At_Symbol_Here**LIST.UVM.EDU] On Behalf Of Ernest Lippert
Sent: Thursday, April 15,
2010
5:09 PM
To: DCHAS-L**At_Symbol_Here**LIST.UVM.EDU
Subject: Re: [DCHAS-L]
Perchloric
Acid Fume Hood Decommissioning
Wendy,
We moved several perchloric acid hoods some years ago without incident. The city fire department was quite willing to standby at the scene. Wash down with plenty of water from the top down. Perchlorates like to build up at bends so go slow and wash well, particularly the fans. Don't rely on the old-timers, the hoods were used with perchloric acid.
Take care,
Ernie Lippert
On Thu, Apr 15, 2010 at 1:38 PM, Wendy Campbell <wendycampbell**At_Symbol_Here**boisestate.edu> wrote:
We
are in the
process of remodeling a building, which currently houses an old
perchloric acid
fume hood. I'm still tracking down how old it is, but I'm fairly
sure
it's at least 30 years of age. As part of the remodel, the perc
hood is
to be removed. There are several issues here.
1. No one remembers any hot perchloric acid work ever being
performed in
this hood (I'm still tracking down the recently retired folks to see
what they
know), and it has been either sealed shut or used as a regular chemical
fume
hood over the past 10-15 years. I'm not sure whether trusting in
people's
memories over the course of the hood's life is the best policy.
2. The duct system is plumbed above the bench of the hood so that
it
washes a six foot run of ducting and the hood itself. The plumbing
does
NOT extend any farther up the duct system, nor out onto the roof where
it
vents, which leads us to.........
3. The duct takes a turn approximately two feet above where it
emerges
from the roof, and has approximately 3-4 feet of vertical run to the
blower
assembly.
The plan under consideration at the moment is to start on the roof and
check
each section for the presence of perchlorates, then spray the heck out
of it
with water before removing just that section.
I'm hoping for some feedback regarding other people's experiences,
suggestions
for procedure / materials, and anything else the combined wisdom of
these fine
groups can give us to perform this remodel safely and in a timely
fashion. I know the contractors would like to start within the
next
couple of weeks.
Pictures of the rooftop portion of the hood's exhaust system have been
posted
to the AIHAH and Hazmat group sites on Yahoo, but I'm still working on
how to
share my Flickr account with folks - perhaps just contacting me
off-list?
Thanks in advance,
Wendy
--
Wendy Campbell,
ASP
Occupational Health and Safety Officer
Environmental Health and
Office: (208) 426-3303
Fax: (208) 426-3343
--
Wendy Campbell, ASP
Occupational Health and Safety Officer
Environmental Health and
Office: (208) 426-3303
Fax: (208) 426-3343
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