Blew myself up (long story) and the damaged skin had to be abraded (scrubbed) off of my arms. It’s quite amazing how many nerve endings you have in your skin and how angry your brain gets when the skin is torn off bit by bit. Your brain is similarly unhappy when there is no skin covering your insides.
I believe they gave me fentanyl for the pain. I don’t remember exactly, except it was iirc fairly new at the time (1997), administered in microgram doses, and one nurses job during the procedure was just to ensure that I didn’t stop breathing.