He used brake cleaner containing Tetrachloroethylene to clean rusty steel then adding welding heat in presence of oxygen made phosgene which is bad for lungs

w/o looking at the video, i can tell you bad things can happen very easily by "accident of ignorance"

Mixing Bleach and Vinegar – Here’s What Happens:

https://sciencenotes.org/mixing-bleach-and-vinegar-heres-wha...