Re: [CSHEMA-L] Lead bricks powdering

[daleboyce@charter.net]

Hi all,



Lead forms an oxide coating very rapidly. If you start with bricks with a

machined finish (and not all of them have that) the oxide will stay thin and

relatively "tight" not really passivated like some oxide coatings, but

fairly stable. If they are left in place in a benign environment oxide

powder is not usually a big problem.  However, if there are acid fumes

present, or the bricks come in contact with acid they will begin to oxidize

much more rapidly. Even the pH of rain will initiate the process. Seat

probably isn't very good either, so rubber gloves for handling as opposed to

work gloves.



Once they have started to form the loose oxide, cleaning them has little

effect as they will rapidly air oxidize forming the loose oxide powder

again. I once tried to decontaminate a lead brick by etching the surface

with nitric acid. We had a bunch of them with long lived contamination, and

at the time commercial decon was $6 a pound.  I learned one lesson, and

re-learned another. First the acid activated the surface such that it

oxidized as soon as it dried. Second metallic contaminants diffuse into lead

such that taking the surface off with acid did little good.  So a stiff

brush and an abrasive cleanser are probably your best bets at cleaning the

dust off prior to treatment to prevent further oxidation.



The only thing you can do once it starts is to clean them and as soon as

possible coat them with something. There are drawbacks to each solution,

especially if you wait until the problem develops before implementation.



Paint works, but will get knocked off with handling.  Duct tape helps, but

is a pain if you have many bricks to do.  There is a product out there that

is used to among other thing put a rubber coat on the handles of electrical

tools.  I've never used it myself, but am told it stands up to handling

better than most paints. Drawback is it is expensive and takes a lot of

stuff per brick.



If you are using the v-groove interlocking bricks all of the drawbacks get

amplified. Paint is probably the best choice.  Choose a hard surface paint.

Even though it may be more subject to chipping, it is better than having the

paint weld the bricks together under weight and over time. Similarly, make

sure and allow plenty of curing time before stacking with any paint.



Also, I've seen places wrap them in aluminum foil.  I don't recommend it.

You are really just disguising the problem by doing that. Something you

might try if handling isn't frequent would be to get something like Whatman

Benchcoat a stiff plastic backed paper, and glue it to the surface with

something like rubber cement.  It would work similar to duct tape, but might

be a slightly easier process.



If you buy new machined surface bricks, they usually come coated with oil to

prevent oxidation. Depending on your use you might consider leaving the oil

in place.  It makes handling a little messy, but slows the onset of heavy

oxidation. However with new bricks you have the best opportunity to get

maximum life by going ahead and getting the oil off and then painting. With

new clean bricks I've had some success with black Krylon spray paint. It can

go on fairly thin, and preserves the fit of the bricks together. Older

bricks I usually resort to a heavy coat of epoxy paint.



Oh and just because they are painted don't let people think they are safe to

handle bare handed. Gloves still should be used.



I'm sure others have tried other things. I would be interested to hear what

has worked well for you.



Dale

daleboyce@charter.net





----- Original Message ----- 

From: "Thomas J Shelley" <tjs1@CORNELL.EDU>

To: <radsafe@list.vanderbilt.edu>

Cc: <dalton@GENESEO.EDU>

Sent: Thursday, December 02, 2004 11:56 AM

Subject: Fwd: [CSHEMA-L] Lead bricks powdering





> Dear Colleagues--The following is forwarded from the mailing list of

> the Campus Safety, Health, and Environmental Management Association,

> an organization of the National Safety Council.  Could you please

> respond to our colleague's question on lead bricks and dust?  I would

> think that a standard operating procedure incorporating lead dust

> management would be in order.  Exposure monitoring and perhaps

> medical surveillance may be in order, also.  Any advice from our

> expert subscribers?  Please respond to Kim as well as to the list.

> Thanks.  Tom

>

> --- begin forwarded text

>

> Date:         Thu, 2 Dec 2004 08:56:43 -0500

> From: Kimberly Dalton Ferris <dalton@GENESEO.EDU>

> Subject: [CSHEMA-L] Lead bricks powdering

> To: CSHEMA-L@LISTS.UMN.EDU

>

> Hey all:

>

> I received a question from our Physics department and am seeking input

from

> those more knowledgeable than I on the subject.

>

> Their lead shielding bricks produce a "powder" when handled.  They are

> wearing gloves to minimize contact when having to move the bricks, but are

> wondering if there are other methods that might be more successful at

> reducing the dust - painting the bricks seems to be an option used at some

> locations - but appears to be more applicable to applications where the

> bricks are more permanently located  (here they are not, we move ours

> frequently).

>

> I'm sure some of the radiation experts out there have encountered this

> before.  Please share the knowledge...

>

> Thanks.

> Kim

>

> Kimberly Dalton Ferris

> Director, Environmental Health and Safety

> 118 Clark

> SUNY Geneseo

> (585)-245-5512

> (585)-245-5006 FAX

> dalton@geneseo.edu

>

> --- end forwarded text

>

>

> -- 

> Tom Shelley,   Laboratory Ventilation Consultant

> Department of Environmental Health and Safety

> Cornell University

> 125 Humphreys Service Building

> Ithaca, NY 14853

> 607 255-8200 (message at EH&S)

> 607 351-3233 (cell)

> tjs1@cornell.edu

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>





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