The Francis Scott Key Bridge in Baltimore collapsed on March 26, 2024, after the container ship MV Dali lost all electrical power and drifted into one of the bridge’s support piers. The National Transportation Safety Board determined that the probable cause was a loose signal wire connection inside the ship’s electrical system, which triggered a total blackout and left the crew without propulsion or steering just as the vessel approached the bridge. But the wire was only the starting point. Several compounding factors, from backup generator problems to the bridge’s lack of protective barriers, turned a shipboard electrical failure into a catastrophic infrastructure collapse.
A Loose Wire Triggered a Total Blackout
The NTSB’s investigation traced the root cause to a single signal wire that wasn’t fully seated in its terminal block. The problem originated during maintenance: a small wire-label band, essentially a plastic tag used to identify wiring, had been installed in a way that prevented the wire from being pushed all the way into its connector. Over time, that improperly seated connection degraded until it failed entirely, cutting power to critical systems across the ship.
When that wire lost its connection, the Dali experienced a complete electrical blackout. The ship’s main engine shut down, its steering systems went offline, and the crew lost the ability to maneuver. The blackout happened while the vessel was still in the narrow channel of Baltimore’s outer harbor, close enough to the bridge that there was almost no time or distance to recover.
Backup Systems Failed to Compensate
Ships like the Dali carry emergency diesel generators designed to restore power within seconds of a blackout. On the night of the collapse, the backup generator did not start quickly enough to prevent the collision. The NTSB found that partially open radiator dampers on the emergency generator likely delayed or prevented it from starting automatically. Radiator dampers control airflow to the generator’s cooling system, and if they aren’t in the correct position, the engine can fail to fire when called upon.
There were also issues with how the crew managed the ship’s fuel supply systems. The NTSB recommended that the ship’s management company, Synergy Marine, develop procedures to ensure crews use fuel oil service pumps as they were designed. This suggests the fuel delivery setup aboard the Dali was not operating according to its intended configuration, which may have contributed to the difficulty in restoring power after the initial blackout. Together, these backup failures meant that a recoverable electrical problem became an unrecoverable loss of control.
The Bridge Had No Protective Barriers
Even after the Dali lost power, the collapse was not inevitable. Many major bridges over shipping channels are surrounded by protective structures, often called fenders or dolphins, that are designed to absorb or deflect a vessel strike before it reaches the bridge’s support piers. The Francis Scott Key Bridge did not have an obvious fender system around its piers.
Engineers who reviewed the collapse told The New York Times that more effective barriers might have prevented the bridge from falling. Modern pier protection systems use massive concrete islands, steel cells filled with rock, or engineered bumpers that can absorb the energy of a drifting vessel. The Key Bridge, which opened in 1977, predated many of the design standards that now call for robust ship-strike protection on bridges near major shipping lanes. The sheer size of modern container ships, which have grown dramatically since the bridge was designed, made the absence of protection even more consequential. The Dali, fully loaded, weighed roughly 100,000 tons.
The Bridge’s Design Offered No Second Chances
The Francis Scott Key Bridge was a continuous truss bridge, a design where the structural elements work together as one connected system. This makes the bridge efficient and relatively economical to build, but it also means the failure of one critical component can bring down the entire span. Engineers classify structures like this as “fracture critical,” meaning there is no backup load path. If a single key member fails, the structure collapses.
When the Dali struck the bridge’s support pier, the pier gave way, and the truss above it lost its support. Because the continuous truss had no structural redundancy, the collapse cascaded rapidly across the full length of the main span. The bridge fell into the Patapsco River within seconds. A more redundant design, such as a cable-stayed bridge with multiple independent supports, might have suffered localized damage rather than total collapse. But redundancy adds cost, and the Key Bridge was built at a time when design standards did not anticipate collisions from vessels of this size.
How These Factors Combined
No single failure caused the collapse. It was the result of a chain: an improperly installed wire label led to a loose electrical connection, which caused a full ship blackout, which could not be reversed because the emergency generator’s dampers were partially open and fuel systems were not configured correctly. The powerless ship drifted into a bridge pier that had no protective barriers, and the bridge itself was designed without structural redundancy, so a single pier failure brought down the entire span. At every link in that chain, a different outcome at just one point could have prevented the disaster. The wire could have been properly installed. The backup generator could have started. Fenders could have deflected the ship. The bridge could have been designed to survive the loss of one pier. Instead, every safeguard was either absent or failed, and the result was one of the most significant bridge collapses in modern American history.