NTSB: Single Loose Wire Caused Dali Bridge Strike

The immediate cause of the incident in Baltimore, Md., on March 26, 2024, in which the container ship Dali struck a support pier of the Francis Scott Key Bridge, causing a total collapse of the bridge into the Patapsco River, was a single loose wire. When it disconnected, it led to a cascade of events that caused the vessel to lose power twice and ultimately strike the bridge, causing six fatalities when bridge workers plunged into the water.

That was among the final findings of the National Transportation Safety Board (NTSB), which held a public livestreamed meeting November 18. However, the NTSB found a host of technical conditions and safety shortcomings that—while perhaps not contributing directly to the bridge strike—could have shortened response times and possibly saved lives if corrected.

“This tragedy should have never occurred,” NTSB board chair Jennifer Homendy said. “Lives should never have been lost. As with all accidents we investigate, this was preventable.”

In all, the NTSB issued 24 specific recommendations to various agencies, including HD Hyundai Heavy Industries (the vessel builder), Synergy (the company responsible for installing the electrical system), the vessel owners, the Corps of Engineers and Coast Guard, and owners of 68 bridges in 19 states.

The loose wire was part of a breaker known as HR1. When it opened, the ship lost power and the main engine shut off. The engineering crew quickly closed the HR1 breaker, but the fuel pump remained offline and had to be restarted manually.

After months of investigation, the team found that a part of the wire tip known as a ferrule was improperly fastened because of a wrongly placed label. That caused the ferrule to be loosely placed in its terminal block. The NTSB team concluded that the crew would have been unaware of the wire glitch, which led to off-and-on connection issues.

Those wires are regularly inspected visually, but the NTSB team found the operations manual didn’t specify in enough detail how that inspection was to take place. Visual inspection is impractical and risky. One investigator compared it to looking for a single loose bolt in the Eiffel Tower. The team recommended the use of hand-held infra-red thermal imaging cameras, which can spot heat discrepancies in wires and terminals invisible to the naked eye.

The crew was able to get the power back on after the first blackout, but a second blackout shortly after the first was caused by a lack of fuel because the fuel flushing pump used to supply the generators. The fuel flushing pump in question didn’t restart automatically. Rather, it had to be restarted manually by a crew member leaving the engineroom and heading down two decks in complete darkness to access it.

One reason why the crew was using a flushing pump had to do with recently enacted emissions regulations. Two of the Dali’s four generators were allowed to use heavier fuels, but two could use only lighter low-sulphur fuels. The main pump system aboard the Dali had been isolated for months because it handled denser, higher-sulfur fuel. The crew suspected fuel contamination in that system and instead used the flush pump, which had no automatic restart capabilities. Homendy returned several times to the issue of emissions regulations causing unintended safety issues.

The NTSB repeated prior recommendations for 30 owners of 68 bridges across 19 states that traverse waterways or rivers to conduct a vulnerability assessment to determine the risk of bridge collapse from a vessel collision.