Only two of those people remain hospitalized at Northwestern as of Monday afternoon. The others were treated and released.
Officials said Monday preliminary reports indicate an electrical arc sparked, igniting grease on the subway tracks. That grease is used to lubricate the tracks.
"We have two things that are unique when trains take a turn in the subway. We have a restraining rail and you have a grease machine. There is something that may have caused some arcing between the restraining rail and the running rail that caused the temperature to heat up," CTA President Richard Rodriguez.
That would "cause a very smoky situation," said CTA spokeswoman Noelle Gaffney.
Exactly what caused the electrical arc is still under investigation, as is the CTA's response to the fire. Rodriguez said communication between the operators and control center was appropriate, but there are some reports that at least one of the conductors on a stopped subway train did little to communicate with passengers, even after the emergency button to talk to him was pushed.
"The guy who was answering was like, 'Oh, well, we have a little fire.' And we're like, 'Dude, do you understand there is like black smoke coming in here? We're on the floor. Did you even comprehend this should be like a serious situation?' He didn't act like it. He wouldn't respond. We would have liked to have him at least acknowledge he heard us. Finally he said, 'Yes, I hear you,'" said Peter Kime, CTA passenger, on Sunday.
"There have been reports from some customers but we're gathering all that data, even interviewing some of those customers to get a sense of where exactly they were because we're getting mixed messages from individuals even on the same train," said Rodriguez.
Smoke filled some of the trains and came out of the subway during the fire Sunday evening. Thirty-two fire companies responded to the scene near the Clark and Division station on the Red Line. The fire was quickly extinguished, according to the CFD.
The CTA has 242 miles of elevated and subway tracks in its century-old system.
Rodriguez went on to say, that the conductors of all three trains are off-duty pending the results of their investigation, but that if the allegations are true, dismissal is certainly an option.
"...Before we start hanging anybody, let's do a thorough investigation. As of right now there doesn't appear to be anything out of the normal. Yesterday there was a lot of turmoil...There could have been an announcement and some people simply didn't hear it," said Robert Kelly, President Local 308, Amalgamated Transit Union.
On Monday, Rodriguez called on federal and local officials to approve a capital improvement plan for the CTA he said it's situations like this one that prove that rather than a piecemeal approach to solving problems what is needed is to upgrade entire substations that have now exceeded their current life expectancy.