Death of Andrew Darden
In reference to the episode: "Pilot".
Darden entered the building before a successful vent could be established, resulting in a flash fire.
His death was a matter of debate in firehouse 51 during the start of Chicago Fire at firehouse 51. Kelly blamed Matt, who subsequently blamed Kelly, as they were both the Lieutenants of their squads and both believed that the other had not done their job.