What is he mixing here?

No way to know for certain unfortunately as it was a short spray from condensation; this was also over a decade ago when I was in High School so I don’t have the acid bottle to check.

I was catching hydrogen in a balloon (via HCl reacting with Al). The balloon popped while I was inspecting the bottle, sending spritzing of acid onto my face/eyes, and the droplets made large holes on the polyester clothes I was wearing wherever they landed. The reaction releases a ton of heat, I think that carried acidic vapor into the balloon where it condensed and damaged the rubber. I felt there was no need for eye protection because I hadn’t anticipated droplets present if the balloon popped.

I switched sides on the PPE discussion after that. You should always wear PPE because you don’t know everything that can go wrong. In a lab setting you might be working on something safe, but your colleagues might not, or an accident happens and the situation changes making what you’re working on suddenly very unsafe. Making a decision about not wearing goggles/gloves/coat introduces the chance that your assessment is wrong. It’s easy to avoid by simply wearing them.

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