It will not catch on fire, but it does burn it. Using flat irons too often is extremely bad for the hair. Temper your iron down first by using a damp towel, then use it on your hair. Also make sure your hair is completely dry before straightening it. Make sure the ends are kept trimmed and use a hot oil or deep moisturizing treatment once a week.
It's not gonna catch on fire. Try using heat protector on your hair put it on before you straighten it ... It should help a little not a lot and you can use moisturizer conditioner and hair products sold like at target or beauty saloons