Stupid question of the week

How do they clear ice off the field? After halftime (Chicago game) they showed grounds crew clearing ice off the filed. They removed all that shit in like 15 minutes! How the hell do they do it? Are they using steam or some kind of heat source, or is it more likely a chemical? I know chemical ice removers exist (though in So Cal I've managed never to see one) but I would expect it to be toxic.

Okay, so enlighten me...someone please lol.

Bump for the stupid question...I really want to know lol