How does Hinton use humor during the church fire? Why does she do this?

There are a few examples of humor. At one point, Pony looks at him and Johnny "grinned at (him)...he looked like he was having the time of his life". Ponyboy also picks up the first child and he bites him. I think Hinton is using some comic relief to ease the tension of the scene.

hinton uses humor with johnny and Ponyoy

Hinton uses humor to help the readers feel less tension while the scene is going on. She does this to show how courageous the boys were not to feel scared during the fire. Hints of humor were shown when Ponyboy was bit and when the kid looked like he was having the time of his life. Also, in the dialogue Johnny jokes about how the guy was to fat to fit in providing some comic relief.