Injecting air into a vein or artery w/ a standard syringe could cause an air embolism, but anywhere into the human body, other than a vein/artery, will do zero. It’ll simply be absorbed and dissipated, without any damage to the injected person.
Using an air hose would be a problem...
https://www.youtube.com/watch?v=uRpt4a6H99c
Maybe maybe not. Had a guy that worked for me that blew sawdust off his hand with a high pressure air hose. Had a small cut in the web between his thumb and finger. Blew up like a balloon. Company doctor made a few slices to let the air out. No problem.