How should you dilute concentrated acid?
The best advice I can give you:
I am not making a joke.
The order of addition is important. A small drop of water in conc. acid will heat rapidly as the bulk acid hydrates, and it may spit. On the other hand, when conc. acid is added to water, the BULK of the water heats up; it will still heat up, but it will do so gradually.
Here is another piece of juvenile doggerel:
I can't stress how important this is. You get a drop of hot nitric acid in your eye, that's your eye gone. So don't spit in the acid!
It goes without saying, that when you do such operations, you MUST wear safety spectacles, and a laboratory coat to protect your clothing.