A Metro employee who was seriously injured in an accident over the weekend on the busy Red Line has been released from a local hospital.

Metro spokesman Dan Stessel said in an e-mail that the man was released “late yesterday and is home resting.”

He was one of two Metro employees who were seriously injured in an accident that was triggered by a fire and explosion in a tunnel near the Union Station platform. A contractor — Harold Ingram, 41, of Blackstone, Va. — was killed in the accident.

Metro officials said they are continuing to investigate the cause of the accident. National Transportation Safety Board officials said they are unable to investigate because of the federal government furlough. The Tri-State Oversight Committee, which is charged with keeping tabs on Metro, has said it is “monitoring [Metro’s] investigation of the deadly accident.

Interviews with four people — one of whom was present at the time of the accident — indicate that the chain-reaction incident happened quickly. The people described what they knew based on interviews with those who were involved, confidential memos and briefings. They asked not to be identified because they are not authorized to speak publicly about the incident.

Shortly after midnight, in a tunnel that runs between Union Station and Judiciary Square, flames erupted and a “loud noise” boomed near a piece of equipment on the tracks, according to Metro. Some people on the tracks said it sounded like an explosion. The incident occurred about 400 feet from the Union Station platform.

Metro officials said Sunday they thought that leaking hydraulic fluid from an underground vehicle apparently was ignited by welding equipment, causing the fire and explosion. Later, in a statement posted on the agency’s Web site, officials said “the root cause of the fire/noise has not yet been determined. It is not yet known if there was a fluid leak or another mechanical issue.”

Metro spokesman Dan Stessel declined Monday to answer questions about details of the accident, because it was “an active investigation.”