This is why so many welders are sick and disabled.
Check labels and when you see 'chlor' as part of a chemical name, beware!
This guy made several mistakes from my reading his account.
1. Inadequate ventilation
2. Lack of Personal Protective Equipment, PPE-something as simple as a half face respirator suitable for the type of welding being utilized
3. Not using compressed air at a minimum to blow the area to be worked clean of contaminants in this case brake cleaner
4. Not wire brushing the area as as part of the surface prep at the same time with other compatible surface prep methods to reveal previously unnoticed pitting and/or other defects and prepare the surface for work
5. Not being fully versed in the Hazards of the product being used
6. The list could go on...
Safety First - Look, Think, Ask