While Angel seems to think it's not normal fire, he would be mistaken. The only thing abnormal about this flame is the intense heat of it. However, Dabi doesn't even flinch when the man reaches out. If the guy wanted to burn himself who was he to stop him?

"I'd be careful if I was you, they're hotter than most flames. They used to be orange when I was younger, like my old mans, then one day they just got so hot they turned this blue...been that way ever since."