D.C. lawmakers demanded fresh answers from Metro on Tuesday, peppering its board chairman with questions about the Jan. 12 smoke incident that killed one person and left dozens injured.

Most of the questions — about Metro procedures, equipment and emergency communications — went unanswered as Chairman Tom Downs said he was constrained by confidentiality rules of an ongoing federal investigation.

“I think the language from the chair of the National Transportation Safety Board is absolutely clear,” Downs said in a 40-minute public session with members of the D.C. Council. “It serves everybody’s interest that we don’t prematurely make any judgments.”

If the briefing didn’t shed any light on the tragedy, it did cause several D.C. lawmakers to become agitated over the lack of public disclosure about the still­unknown cause of and troubled response to the worst Metro calamity in six years.

With the chairman of the NTSB preparing to begin closed-door briefings for city and federal lawmakers Wednesday, several said Metro and federal investigators were providing too little information for the public to feel safe on the subway system.

The National Transportation Safety Board said Tuesday the smoke in the Metro tunnel near L'Enfant Plaza was caused by electrical arcing, which occurs when electricity escapes its prescribed path. Here's how that happens. (Jason Aldag/The Washington Post)

“We are asking people, thousands every day, almost a million in the entire system, to ride Metro. We encourage them to do that,” said council member Kenyan R. McDuffie (D-Ward 5), chairman of the public safety committee. “At the very least, we could . . . make sure they have the information that arms them to make an informed decision.”

It may take months for investigators to reach a conclusion on what caused the electrical arcing that, in turn, caused smoke to fill a disabled Yellow Line train. But more immediately, McDuffie and others said, it was time for Metro and investigators to talk openly about several safety-related questions raised by the incident: Do firefighters’ radios work in Metro tunnels? Does Metro have a system to share critical information with first responders? Can passengers self-evacuate? Do some Metro cars still require removing screws to release safety doors?

Council members took turns posing questions that have not been answered in initial reports from the NTSB and District authorities, the latter detailing the emergency response to the incident at L’Enfant Plaza.

Mary M. Cheh (D-Ward 3) asked Downs why he couldn’t discuss repairs that need to be made or are being made to address what happened during last week’s incident.

“This is of urgent concern to the public,” she said. “That, to me, should be something that is openly and immediately discussed.”

Downs replied, “Council member, I would posit that the facts are actually important before jumping to conclusions about what needs to be fixed.”

Elissa Silverman (I-At Large) asked Downs whether he could address questions raised by the city’s review of the emergency response to the disaster, including reports of radio difficulties.

“I cannot speak to it,” Downs said.

Anita D. Bonds (D-At Large) asked Downs to respond to reports that the operator of a train that had stopped in the L’Enfant Plaza Metro station had left his train at the platform, obstructing attempts to return the stranded Yellow Line train to the station.

“Given the timeline, can an employee who is operating the vehicle leave the vehicle?” Bonds asked. “I’m just trying to understand how that could be possible.”

Downs did suggest that at least some of the information disseminated publicly is inaccurate. But it was unclear whether he was referring only to the timing of people exiting the train at the platform or speaking more broadly about the entire incident. No council member asked him to clarify.

Downs said: “The timeline and the information is not accurate as it stands right now. The NTSB will produce on its own a time frame of all of the individual incident elements over time, look at each of those elements, make some findings and will release their findings of what actually occurred.”

Brianne K. Nadeau (D-Ward 1) asked Downs to respond in general terms to concerns about Metro system’s safety while the investigation is underway.

“I’ve heard from a number of constituents who are just feeling scared about whether it’s safe to ride the Metro,” said Nadeau, who said that Metro had “breached its trust” with riders.

Downs said in response that Metro is committed to acting on the NTSB’s recommendations.

“No matter what the findings are, whether it shows that Metro did something wrong in this process, we are not going to contest it,” he said. “Whatever they recommend as safety fixes, we are going to put the resources in to make those changes as quickly as they can be made.”

Downs said that Metro “lost sight” of its safety focus a decade ago and that the system is halfway through a six-year rebuilding plan.

“I ride the train every day, and I would be less than candid about not thinking about that kind of event when I’m on the train, so I know what the customer feels,” Downs said. “I think everybody on the board knows that, and everybody is interested in providing whatever the customers think they need in terms of reassurance and actual proof” that Metro is safe.

After Downs said he could with a measure “of comfort give some additional information” in a private session, the council chairman, Phil Mendelson (D), moved to close the meeting to all but council members and officers — its chief lawyer, secretary and budget director — citing a provision in city law allowing the council to close meetings to discuss open investigations.

The motion passed on a 6-5 vote.

Voting in favor were Mendelson, Bonds, McDuffie, Jack Evans (D-Ward 2), Yvette M. Alexander (D-Ward 7) and Vincent B. Orange (D-At Large). Opposed to closing the meeting were Cheh, Nadeau, Silverman, Charles Allen (D-Ward 6) and David Grosso (I-At Large).

Cheh said after the closed session that little additional information was disclosed in private. “None of the questions that we asked in the public session were ones that were answered in the private session,” she said.

Cheh and McDuffie said Metro car doors and passengers’ ability to safely self-evacuate trains were among the issues raised behind closed doors. There was also discussion, Cheh said, of scheduling a meeting between the council and NTSB officials.

McDuffie has scheduled a hearing on the incident in two weeks, for Feb. 5, and he said he would seek to pry answers from investigators by then, if not before. He said he would not hesitate to publicize facts he determines to be in the public interest.

Asked if she could confidently say Metro was safe to ride, Cheh said she has no choice but to put her faith in federal authorities.

“I have to rely on the NTSB saying that if they saw some emergency need to act, they would identify it and recommend action,” she said. “That hasn’t happened yet, but I would really like some greater confirmation.”