Re: Use of unsealed thorium in TIG Welding

[elw1@ix.netcom.com (Edwin Wright)]

Bill wrote: 
>
>To Radsafers:
>>Could you be specific which manufacturers and which Aluminium Oxide
>>wheels?  Are you sure the use of Thorium is intentional?
>>

Doug wrote:
>>Some manufacturers use thorium in the constuction of aluminum oxide 
>>grinding wheels. Tungsten welding TIG rods are sometimes thoriated 
also.
>

Byron wrote:
>Coincidentally, I received a call yesterday from an RSO, Mr Iain 
>Morrison, in industry who has been shown "Thoriated" welding rods, and 
>was getting 0.6 uSv/hr at the surface of the packet (gammas only.)  
>The small print on the seal of the packet said "radioactive".
>
>The rods are:
>Thermadyne (TM)  Tweco (R) Tungsten electrodes, 10 each to a packet.
>AWS Classification - EWTh-2, Ground Finish, 2% Thoriated Tungsten,
>made in USA by Osram Sylvania Inc, Chemical & Metallurgical Products,
>Towanda PA 18848.
>
>The enclosed safety information was difficult to read, but stated the
>material contained ThO-2, and then had a figure of 1 x 10*-12* uCi/ml. 
>(Is this in the rod, or in the fumes generated?).

Since no other information is given and the tips are consumed very 
slowly, I would assume that the 10^-12 value is the concentration in 
the tips. However, it would be better to contact the mfg. directly. 
Never argue about the number of teeth a horse has when you can go count 
them.

>These TIG rods are obviously deliberately thoriated.  They have been 
>used "for hard facing for many years - as long as the workshop 
>Engineer can remember - they keep them locked up in a filing cabinet 
>as they are expen$ive!!"
>
>Does anyone know why, and what would be the risk in using these in an
>unventilated area?

Thorium has very good high temperature characteristics and makes the 
tips last longer while performing TIG welding.

This, by the way, is the same purpose for using thorium in some 
grinding wheels. Many coarse and high speed wheels generate lots of 
heat, especially on contact at the surface. Most grinding materials 
"can't take the heat" and would quickly fly apart.

>I understand that fumes from TIG welding are normally removed from the
>work area by a suction line & vented outside.

This is a great idea. But my guess is that there are other constituants 
in the fumes that might be more harmful than the thorium.

An added note, thorium oxide is often used as a casting sand for high 
melting point metals. It is also sometimes used as a "plug" on steel 
melting pots.

Hope this helps.

Ed Wright, CHP
elw1@ix.netcom.com