NBC has tacked another hour on to the freshman season of drama Chicago Fire, bringing its order to 24 episodes. The network first ordered one extra episode last week, followed by another episode pickup yesterday. After a slow start, Chicago Fire has found its groove, enjoying a ratings surge in January when its three originals posted the series’ three biggest overall audiences to date and three of its four highest adult 18-49 ratings. The show has now topped its premiere 1.9 demo rating four times and its premiere viewership (6.6 million) six times, including with the Jan. 2 show which posted Live+Same Day series highs of a 2.4/7 in 18-49 and 8.5 million viewers overall. The order upgrades for Chicago Fire come amidst disappointing premiere ratings for NBC’s new midseason drama Do No Harm (0.9 in 18-49) and the second season of Smash (1.2). Chicago Fire is exec produced by Dick Wolf, Danielle Gelber, Michael Brandt, Derek Haas, Matt Olmstead and Peter Jankowski.