Patrons were told to stay on the train and wait to get off until the next stop on the red line due to power outages at the Dupont Circle Metro station as several stations had to operate with emergency lighting on April 07, 2015. (Jabin Botsford/The Washington Post)

Disregarding its own guidelines, Metro failed to install the proper kind of protective sleeves over power cables in a number of places throughout the subway, creating a hazard that may have caused the Jan. 12 smoke incident near L’Enfant Plaza that sickened scores of train riders, one of whom died, federal safety officials said Monday.

And even after the January incident, the National Transportation Safety Board said, repairs made to the power-cable assembly at L’Enfant Plaza were done incorrectly.

In a recommendation “requiring immediate action,” the NTSB, which is investigating the January incident, called on Metro “to promptly develop and implement a program” to fix what it said is a dangerous problem in “a number” of locations “throughout . . . the Metrorail system.”

“We are vitally interested in this recommendation because it is designed to prevent accidents and save lives,” the NTSB’s acting chairman, Christopher A. Hart, said in a 10-page document delivered to Jack Requa, interim general manager of the Washington Metropolitan Area Transit Authority.

How the ventilation systems inside the tunnel affected the smoke.

Although the safety board’s final report on the smoke calamity is not due until early next year, investigators sometimes issue immediate recommendations when they find imminent safety threats.

“We are hopeful that WMATA management will act on this recommendation in a timely manner so that the hazards we have identified can be mitigated as soon as possible,” Hart said in a statement.

Metro said in a brief statement that it “will begin the process immediately” of making sure that all subway power cables are equipped with proper protective sleeves.

The NTSB has said that the Jan. 12 crisis — in which a six-car train was enveloped by noxious fumes in the Yellow Line tunnel just south of the L’Enfant station — was caused by an electrical malfunction involving track-based power cables. Electrical current escaping from the cables generated tremendous heat and smoke, officials said.

Monday’s recommendation specifically concerned protective sleeves over power-cable connections near the subway’s third rails, which carry the electricity that propels trains. The sleeves are designed to help prevent the escape of electricity.

The NTSB said it also found that throughout the subway, “some electrical connections associated with power supply to the third rail were improperly constructed and installed, which can allow moisture and contaminants to enter the components, which . . . could result in fire and smoke events.”

The power-cable connections involved in the January incident were so badly damaged that investigators “have so far not been able to determine whether the cable connector assembly was protected by sealing sleeves,” the NTSB said. But circumstantial evidence seems to suggest that improper sleeves were a culprit.

Investigators “have found a number of other power-cable connector assemblies throughout” the subway that were “constructed without sealing sleeves,” the board said.

Contrary to its own engineering specifications, “WMATA has allowed maintenance crews and contractors to use various types of . . . sealing methods,” including “heat shrink tubing and electrical tape used in place of the sealing sleeves,” the NTSB said.

After a Feb. 11 smoke incident near the Court House station in Virginia, the board said, “investigators found that the failed ­power-cable connector assembly . . . was missing its sealing sleeve.” And after the Jan. 12 incident, the NTSB said, “even the post-accident repairs made to the power-cable connector assembly at L’Enfant Plaza did not include the sealing sleeves indicated in the WMATA engineering design specifications.”

Based on the NTSB description, electricity escaping from power cables near L’Enfant station turned the tunnel’s metal walls into something like an overheating hot plate, burning almost everything around it.

“The smoke in the tunnel was generated by thermal damage to about 16 feet of electrical power cables and insulation, portions of 4 fiberglass cable-connector covers, and about 5 feet of the fiberglass third rail cover,” the safety board said.

Metro said it would “immediately” begin a program “to install the recommended weather-tight seals” over power-cable connections in the subway. “As hundreds of such connections are made throughout the system, the process will prioritize locations based on water intrusion conditions,” Metro said.

Places in tunnels that are subject to frequent water leaks are prime locations for electrical problems like the one that occurred Jan. 12, officials said.

Spokeswoman Morgan Dye said Metro engineers will publicly discuss the problem in detail at a meeting Thursday of members of Metro’s board of directors. The issue also will be the subject of testimony June 23 and 24 at NTSB public hearings on the fatal smoke incident.