The firefighters pointed out that - unlike in the movies - the smoke becomes so thick so quickly that you can't run out of a burning house. You usually have to crawl. They themselves usually crawl if they really must enter a burning unit, so they can somewhat see where they're going. In some cases, even that's not possible. So they'll keep one hand on the wall and slowly make their way in. Frightening. I give firefighters a lot of credit.
http://www.youtube.com/watch?v=w4W82HIzUcc