From: B.Hamilton@irl.cri.nz (Bruce Hamilton)
Newsgroups: sci.chem
Subject: Re: Trichloro ethylene?
Date: Sat, 17 Jul 1999 08:41:52 GMT

"donald haarmann" <donald-haarmann@worldnet.att.net> wrote:
>JonS999 <jons999@aol.com> wrote in message
>news:19990716084649.29666.00001103@ng-bg1.aol.com...
>> I am looking for info on this chemical. I know it is used as an industrial
>> degreaser for brass, what else is it used for? What are the handleing
>> precautions and dangers of this chemical?
>
> It was used as a non-flammable solvent/degreaser in place of carbon
> tetrachloride which was believed to be carcinogenic; in turn it also was
> believed to be carcinogenic and was replaced with 1,1,1, trichloroethane
> which probable soon be believed to be.......! Trichloroethylene was used
> as an anesthetic in child birth &c..

Trichloroethylene was replaced as a degreaser for several reasons, of which the
toxicity was only one concern. Trichloroethylene used much more energy in
vapour degreasers ( higher boiling point ), and some of the inhibitors
added to minimise hydrolysis and acid production ( eg epichlorohydrin )
were also toxic.

Trichloroethylene is very unusual amongst the chemicals used industrially
because the USSR had a occupational limit ( 2ppm (1967)) that was much
lower than all of the west ( 100ppm USA then, now reduced to 50 ppm ).
The discrepancy was the cause of much soul-searching amongst the US
occupational health community, and the carcinogenic concerns really
only appeared on the tail of the phase out in the 1970s.

The advantage of the lower boiling point of 1,1,1-trichloroethane
was not only energy saving, it meant that less thermal damage was done
to component, and it was also replaced with Freon TF, even lower
boiling point. Both 1,1,1-TCE and Freon TF were phased out under the
Montreal Protocol because of the contributions they made to pollution,
specifically Ozone Depletion.

        Bruce Hamilton