I'm no fireman, but I know if you have an underhood fire, and you throw the hood open, you'll feed it big-time oxygen. Maybe a pro could chime in, but I'm pretty sure you just want to peek, and then let the extinguisher blast through the "peek hole". Of course, the hood may be too hot to open.
Also, those powdered bottles make a big mess. Halon displaces the air, puts it out cleanly.
My buddy was driving our car through the pits, and people hollered to him about an underhood fire. By the time he could stop and get our halon bottle off of the roll bar, guys had opened our hood and sprayed the powder type. While the help was certainly appreciated, we learned that the bottle needs to be VERY accessible, so we could get out and use the halon. That powder made a mess.
