Safety of burning (then inhaling)Thorium Fluoride coating

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Safety of burning (then inhaling)Thorium Fluoride coating

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OpticsPerson

Posted: Wed Mar 15, 2006 5:47 pm

Guest

If I burn an AR coating of Thorium Fluoride (or burn a BIZYT fluoride
fiber laser), I am vaporizing some amount of Thorium Fluoride into the
air that I am breathing.

Does anyone know of a study addressing this issue, and if the Thorium
is oxidized and less hazardous than "free" thorium.

Reasonable precautions are always understood to be a good idea, so
please consider this in any response you might have. In other words,
I have tried to be careful.

I found some useful info at www.cerac.com/pubs/proddata/thf4.htm.

Thanks for any info.

Steve Norquist

Posted: Thu Mar 16, 2006 4:39 am

Guest

On Wed, 15 Mar 2006 16:47:12 -0600, OpticsPerson
<yes_on_purpose@yahoo.com> wrote:

[quote:075d5781b5]If I burn an AR coating of Thorium Fluoride (or burn a BIZYT fluoride
fiber laser), I am vaporizing some amount of Thorium Fluoride into the
air that I am breathing.

Does anyone know of a study addressing this issue, and if the Thorium
is oxidized and less hazardous than "free" thorium.
[/quote:075d5781b5]
Breathing? Since you're going through a bunch of these things,
you can just assay the air with a convenient polyester filter and
thus get an answer to which oxides and nitrides of Thorium (and
Fluorene) you are provening; or set up an off-axis optical path
(i.e. at least an objective lens) to assay the products of the burn
straightaway to a screen with pyrometers, cheap fluorecence etalons,
etc. in plain view of a USB camera.

From that point, you can decide which products you want to favor
during burn conditions....

--
Punchline absolutely has to be -free thorium-/what/?-

Helpful person

Posted: Thu Mar 16, 2006 7:57 am

Joined: 22 Jun 2004 Posts: 838

Thorium is highly radioactive and you should never expose youself to it
in any vapour form.

Are there really AR coatings today that use thorium?

Please visit my web site at www.richardfisher.com

OpticsPerson

Posted: Thu Mar 16, 2006 8:45 am

Guest

The optical coating question was an example. I think that there is now
a thorium-free coating available for the longer IR wavelengths. In my
case the actual source of the thorium was from the fiber laser example,
and this was several years ago. The question is the same in either
case:

"Does anyone know if the thorium become free or if it is a thorium
oxide - this can impact what might happen if it is inhaled?"

I worked for a manager who did not educate me to the hazards, and I am
now marginally anxious (this was only over a couple days and the
incidences of accidental burning were few, probably less than
micrograms of the glass. I know that we made an effort to avoid any
inhalation if a vapor appeared, holding our breath and leaving the
room! Later an elephant trunk exhaust vent was put in place.)

Still curious.....

OpticsPerson

Posted: Thu Mar 16, 2006 9:21 am

Guest

If you are convinced that I don't understand what happens to thorium -
either oxidized or other (see replies above) - you are completely
correct. I beleive if it is oxidized, there is a good chance of it
being expelled by the lungs, as some other particulates are expelled by
the body. If it is an ion somehow - ???

OpticsPerson wrote:
[quote:d830bb638e]The optical coating question was an example. I think that there is now
a thorium-free coating available for the longer IR wavelengths. In my
case the actual source of the thorium was from the fiber laser example,
and this was several years ago. The question is the same in either
case:

"Does anyone know if the thorium become free or if it is a thorium
oxide - this can impact what might happen if it is inhaled?"

I worked for a manager who did not educate me to the hazards, and I am
now marginally anxious (this was only over a couple days and the
incidences of accidental burning were few, probably less than
micrograms of the glass. I know that we made an effort to avoid any
inhalation if a vapor appeared, holding our breath and leaving the
room! Later an elephant trunk exhaust vent was put in place.)

Still curious.....[/quote:d830bb638e]

Leonard Migliore

Posted: Thu Mar 16, 2006 12:30 pm

Guest

In article <1142513873.378135.64630@e56g2000cwe.googlegroups.com>,
"Helpful person" <rrllff@yahoo.com> wrote:

[quote:9d9b6926b4]Thorium is highly radioactive and you should never expose youself to it
in any vapour form.

Are there really AR coatings today that use thorium?
[/quote:9d9b6926b4]
The standard AR coatings for the 10 micron band (CO2 lasers) use layers
of thorium flouride and zinc selenide.

danek

Posted: Thu Mar 16, 2006 12:48 pm

Guest

When I did a google search on thorium vapor a few of the summeries were
about thorium oxide causing cancer. I didn't read the actual articles
but it sounded nasty.

P. Danek

OpticsPerson wrote:

[quote:c10f31cb10]If you are convinced that I don't understand what happens to thorium -
either oxidized or other (see replies above) - you are completely
correct. I beleive if it is oxidized, there is a good chance of it
being expelled by the lungs, as some other particulates are expelled by
the body. If it is an ion somehow - ???

OpticsPerson wrote:

The optical coating question was an example. I think that there is now
a thorium-free coating available for the longer IR wavelengths. In my
case the actual source of the thorium was from the fiber laser example,
and this was several years ago. The question is the same in either
case:

"Does anyone know if the thorium become free or if it is a thorium
oxide - this can impact what might happen if it is inhaled?"

I worked for a manager who did not educate me to the hazards, and I am
now marginally anxious (this was only over a couple days and the
incidences of accidental burning were few, probably less than
micrograms of the glass. I know that we made an effort to avoid any
inhalation if a vapor appeared, holding our breath and leaving the
room! Later an elephant trunk exhaust vent was put in place.)

Still curious.....

[/quote:c10f31cb10]

OpticsPerson

Posted: Thu Mar 16, 2006 2:20 pm

Guest

It turns out that many welding rods are 2% thorium oxide. So, inhaling
welding vapor is similarly hazardous, and far more common.

John McMillan

Posted: Thu Mar 16, 2006 2:35 pm

Guest

In article <dwhSf.986$O5.164@llslave.llan.ll.mit.edu>, danek
<danek@mmll.mit.edu> wrote:

[quote:0567d9db65]When I did a google search on thorium vapor a few of the summeries were
about thorium oxide causing cancer. I didn't read the actual articles
but it sounded nasty.

[/quote:0567d9db65]
Its pretty nasty. Both a chemical poison and an alpha emitter.
http://hazard.com/msds/tox/f/q134/q80.html
shows that the LD50 intratracheal in rats is >1140mg/kg - but thats
acute toxicity rather than long-term. There are a number of other
studies reported in the MSDS

Salmon Egg

Posted: Thu Mar 16, 2006 3:09 pm

Guest

On 3/16/06 4:57 AM, in article
1142513873.378135.64630@e56g2000cwe.googlegroups.com, "Helpful person"
<rrllff@yahoo.com> wrote:

[quote:7b19dbe856]Thorium is highly radioactive and you should never expose youself to it
in any vapour form.

Are there really AR coatings today that use thorium?

Please visit my web site at www.richardfisher.com

Thorium is NOT highly radioactive! Its problem is that it gives off alpha[/quote:7b19dbe856]
particles. External to tissue, alphas are not a big problem. Almost anything
stops them. Inside tissue, lungs, blood, etc., is what stops them. That is
what you do not want to have irradiated. Alphas, in particular, are highly
ionizing compared to other natural radiation, with the exception of
spontaneous fission fragments.

ThO2 is just about the highest melting point substance there is. It is very
unlikely that heating will cause it to evaporate and form particles. That is
one reason why ThO2 was used in Welsbach mantles. On the other hand, the
various combinations of thorium with fluorine and oxygen are much more
likely to be evaporated and form small particles.

I find it difficult to believe, but have no proof, that a thin layer of a
thorium containing film will give hazardous ionizing exposure to people
using optics coated with it.

While I am on my soap box, I also question how serious a hazard is presented
by radon. Natural Rn is found in low concentration to start. If you breath
it, almost all of it gets exhaled. It is only the small amount that
transmutes while it is in you that can give problems from its own decay and
decay of the daughter elements. Again, I have no evidence. If someone has
done a calculation, I would like to see it.

Bill
-- Ferme le Bush

Guest

Posted: Fri Mar 17, 2006 9:31 am

OpticsPerson wrote:
[quote:7b65c63b1f]If I burn an AR coating of Thorium Fluoride (or burn a BIZYT fluoride
fiber laser), I am vaporizing some amount of Thorium Fluoride into the
air that I am breathing.

Does anyone know of a study addressing this issue, and if the Thorium
is oxidized and less hazardous than "free" thorium.

Reasonable precautions are always understood to be a good idea, so
please consider this in any response you might have. In other words,
I have tried to be careful.

I found some useful info at www.cerac.com/pubs/proddata/thf4.htm.

Thanks for any info.
[/quote:7b65c63b1f]
Not yet pointed out in this thread is that optical coatings are really
thin--even for 10-micron radiation, a quarter-wave coating is only a
few microns thick. So the mass of thorium involved is truly tiny,
especially when compared to the example of a welding rod which is 2%
thorium.

Naturally one would want exposure to thorium to be 'as low as
reasonably achieveable', but the small mass involved in optical
coatings should be another reassurance.

D. Van Baak

jgandalf

Posted: Fri Mar 17, 2006 9:48 am

Guest

OpticsPerson wrote:
[quote:99c3a8633d]It turns out that many welding rods are 2% thorium oxide. So, inhaling
welding vapor is similarly hazardous, and far more common.
[/quote:99c3a8633d]
Are you sure about that? The thoriated welding accessories I am
familiar with are actually tungsten electrodes, not consumable welding
rods, and are used in TIG welding setups. Although they do wear, it's
usually from the tip melting a bit, requiring a resharpening - perhaps
one would do well to avoid inhaling the grinding dust, though. A safer
choice may be to use the lanthanated W electrodes.

None of the above is to imply that stick welding fumes are not harmful,
though. I only stick weld outdoors, but will do TIG wherever it's
convenient (and not critical - I'm not a very skilled welder).

Optics content: I like the electronic (LCD?) welding filters over the
older filters. <g>

Joe

OpticsPerson

Posted: Fri Mar 17, 2006 11:18 am

Guest

Joe-

Some references said the rods were 2% thorium, yet the "newer" data
said it was the electrodes. I recall one reference stating that older
rods were more of an issue for the thorium. There is data to suggest
welding outside is a safer approach, and DC is safer than AC.

http://hps.org/publicinformation/ate/q1593.html

is a good reference.

I am not much of a welder, but am thinking about getting a MIG soon. I
will educate myself a bit more along the electrode topic, but it sounds
like a TIG issue.

Optics content: uh, .....

jgandalf wrote:
[quote:3e60a724e2]OpticsPerson wrote:
It turns out that many welding rods are 2% thorium oxide. So, inhaling
welding vapor is similarly hazardous, and far more common.

Are you sure about that? The thoriated welding accessories I am
familiar with are actually tungsten electrodes, not consumable welding
rods, and are used in TIG welding setups. Although they do wear, it's
usually from the tip melting a bit, requiring a resharpening - perhaps
one would do well to avoid inhaling the grinding dust, though. A safer
choice may be to use the lanthanated W electrodes.

None of the above is to imply that stick welding fumes are not harmful,
though. I only stick weld outdoors, but will do TIG wherever it's
convenient (and not critical - I'm not a very skilled welder).

Optics content: I like the electronic (LCD?) welding filters over the
older filters. <g

Joe[/quote:3e60a724e2]

jgandalf

Posted: Fri Mar 17, 2006 1:18 pm

Guest

You provided an interesting link - thanks. Yeah, I think it's only the
electrodes that contain thorium. Experienced weldors report that the
lanthanated electrodes work every bit as well as the thoriated ones,
albeit at a higher cost. I wonder why the higher danger from AC welding
(in TIG work)? AC is usually only used with aluminum and similar
metals, but it does cause faster erosion of the electrode, due (I
think) to the much higher heat required for those metals. The issue
should not be a factor in MIG welding, which is said to be one of the
easiest to learn (and the only one I have never tried). TIG is more
like gas welding or (sorta) like soldering in its practice. If you
invest in a MIG unit, get one that uses shielding gas (Ar/CO2), and
don't mess with the flux-cored wire; it's cheaper in the long run, and
you won't have to deal with the flux fumes.

Joe

OpticsPerson wrote:
[quote:d467b1652a]Joe-

Some references said the rods were 2% thorium, yet the "newer" data
said it was the electrodes. I recall one reference stating that older
rods were more of an issue for the thorium. There is data to suggest
welding outside is a safer approach, and DC is safer than AC.

http://hps.org/publicinformation/ate/q1593.html

is a good reference.

I am not much of a welder, but am thinking about getting a MIG soon. I
will educate myself a bit more along the electrode topic, but it sounds
like a TIG issue.

Optics content: uh, .....

[/quote:d467b1652a]

OpticsPerson

Posted: Fri Mar 17, 2006 4:09 pm

Guest

I am certain that I read a reference to older tungsten welding using
thorium welding rods - again, with some reference to this being an
older technology. Regarding the TIG rods, another good link is:

http://www.orau.org/PTP/collection/consumer%20products/weldingrod.htm

The burnt thorium fluoride optics coating, or the BIZYT glass fiber
laser (when toasted by the pump laser beam), both seem like they would
produce miniscule amounts of thorium when compared to tip grinding of
TIG welding rods daily (or often). I am not advocating unsafe lab
practice, but this provides a perspective for the uncommon lab issue vs
the daily exposure to TIG welders.

The alpha emission from the coating probably does not even merit a
concern.

Thanks

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