Am i at risk of poisoning? ?

This fan removes the fumes from our gas boiler into a communal duct which has 10 other apartments also pumping the fumes from their boilers into it. When i stop the fan it runs backwards so dosent this mean that fumes are coming back in from the comunal duct?? Please help as managment company dont want to know. a href="http://ie.youtube.com/watch?v=KS34zZ9i9aI" rel="nofollow"http://ie.youtube.com/watch?v=KS34zZ9i9a…/a