I recently started adjusted the pH of my sparge water with 10% phosphoric acid.
How powerful is this stuff? I’ve been pretty careful with it, but will I get a nasty burn if I accidentally spill some on my hand?
Keep it out of your eyes and you’ll be fine. If you get some on your hand, wash it off, but it shouldn’t cause a burn since it is diluted 10:1.
Vinegar is like 5% acidity. I think acetic acid isn’t as strong as phosphoric (something about being polyprotic?). But basically, 10% phosphoric about twice as dangerous as vinegar, which is to say, not that dangerous. I always wear goggles when handling acids and bases, and I always wear gloves when handling strong bases. I got some strong solvent in my eyes once and I was blind for a couple days, so I’m pretty cautious now when it comes to my eyes.
How powerful? 10% 
I’ve gotten 75% on my hands and it started irritating them instantly, but I didn’t get a burn. I would stay on the safe side and use caution/ wear gloves if you have them.
I would disagree. Phosphoric acid is a much stronger acid than acetic. That said, if you get some on your hands nothing will happen if you wash your hands within a minute or so. Don’t believe the movies where they show acid eating away concrete and stuff within seconds. There are strong acids as well as super-acids, but they’re not something you’ll ever get your hands on in homebrewing. I’ve had concentrated sulfuric acid spill on my hand and it took about a minute to start burning my skin. And even that was slow. Feels kinda like a burn from putting pure mustard paste on your skin… then your skin flakes off. Anyway, you’re in no danger. Just don’t spill it into your eyes and wash your hands.
Yep, pretty much a standard one for any corrosive