New member here and I realise this is an old post but I have more to add to this story.
So first of all, tetrachloroethylene goes by many names. Chemically it is also known as perchloroethylene but it also goes by a number of "generic" names; dry cleaning fluid just being one. In the workshop it has many uses and is not just found in brake cleaner. Many metal degreasers contain it for instance - not just the aerosol ones either.
As to phosgene, this is produced when tetrachloroethylene is heated above 315 degrees Celcius (599 degrees Fahrenheit). Importantly, Argon is NOT required for this to happen despite what is stated in the article quoted above. Heat is all that's required. This is why you do not go cleaning hot brakes.
Now, for all the smokers out there (I'm one too) there's an additional heads-up. if you smoke while using a product containing tetrachloroethylene (or smoke in a area in which such a product has been recently used), with each inhalation you will draw tetrachloroethylene through the lit end where the heat will convert it to phosgene and deliver it straight to your lungs. Wham! Do not pass Go. Do not collect $200. You have been warned.
So, always read the label and consult the MSDS. No exceptions. Know what's in the product you're using.
Don't want to be the preachy new guy but hey, you're a long time dead!
