A steel beam recovered from the rubble of the World Trade Center will be driven around the country ahead of the 25th anniversary of the tragedy in part to help enlighten kids who weren't alive at the time.

A bombshell memo made public Thursday proves the city knew about the potential risks of Sept. 11, 2001 toxins weeks after the terror attacks -- as officials told New Yorkers it was safe to return to Lower Manhattan, local pols said.