Check out the video and this document
http://fromtheflightdeck.com/Stories/turbofan/
Typically there has not been a concern for tailpipe fires where there is airflow through the engine. I suppose this is due to the general abscence of persons and vehicles behind an engine that has a rare tailpipe fire.
On the other hand for the even rarer case where a tailpipe fire exists with little to no airflow (standing still and the starter is disengaged) the flames will turn upward and cook the bottom of the wing. Several severe outcomes have occured