Why the Baltimore Bridge Collapsed So Quickly

Steel structures aren’t as strong as you might think—and the immense power of a container ship shouldn’t be underestimated.

Just shy of half past 1 in the morning, the MV Dali, a giant container ship, was sailing gently out of the port of Baltimore when something went terribly wrong. Suddenly, lights all over the 300-meter-long vessel went out. They flicked on again a moment later, but the ship then began to veer to the right, toward one of the massive pylon-like supports on the Francis Scott Key truss bridge—a huge mass of steel and concrete that spans the Patapsco River.

The Dali’s lights went out a second time. Then the impact came. The ship plowed into the support, with large sections of the bridge’s main truss section instantly snapping apart and falling into the river. It took just 20 seconds or so for the structure to come down.

Now, a major US port is in disarray, and several people who were working on the bridge at the time of its collapse are missing. A rescue operation is underway. President Biden has called the disaster a “terrible accident.” Ship traffic is currently stuck on either side of the crash site, and a major roadway through Baltimore has been cut off.

“It’s a dreadful tragedy and something you hope never to see,” says David Knight, a bridge expert and specialist adviser to the UK’s Institution of Civil Engineers. But commenting on footage of the bridge collapse, he says he is not surprised by the manner in which it crumpled.

Large steel structures may seem invulnerable, but steel, explains Knight, is relatively lightweight for its size. As soon as it is pushed or pulled the wrong way with enough force, it can fold like paper. In this case, the Francis Scott Key Bridge was a “continuous,” or unjointed, bridge that had a 366-meter-long central truss section. (Truss bridges use steel beams, arranged in triangular shapes, to support their load.) The central truss was made up of three horizontal stretches, known as spans, with two sets of supports holding these above the water. It was the third-largest structure of its kind in the world.

“When you take a support away, there is very little in the way of robustness,” says Knight. “It will drag down, as we saw, all three spans.” The separate approach spans remain standing. There is nothing in Knight’s view that immediately suggests any structural problem with the bridge. An engineering firm, Hardesty & Hanover, confirmed to WIRED that it performed an inspection of the bridge in 2019, and that other inspections have been carried out since, but did not provide any additional details on the state of the structure. WIRED has approached H&H for further comment. In June last year, the US Federal Highway Administration rated the condition of the bridge as satisfactory.

The immense force of the container ship impact should not be underestimated, adds Knight. Such vessels require a lot of power and time—perhaps many minutes—to come to a complete stop. The Francis Scott Key Bridge was completed in 1977. In more recent decades, bridge engineers have commonly incorporated defenses to reduce the potential damage by ship strikes when bridges are erected in similar locations, Knight says. These include hydraulic barriers and additional concrete around the base of bridge supports, for instance. However, even with such fortifications in place, heavy strikes can still cause devastating damage.

It is not clear why lights turned off and on again on the Dali, a Singapore-flagged ship built in 2015. “That is an indication of a massive problem,” says Salvatore Mercogliano, a maritime historian at Campbell University in North Carolina and a YouTuber who has analyzed the crash.

At the time of the accident, two pilots—mariners who board a ship to help it navigate particular stretches of water, including in and out of ports—from Baltimore were on board. The Dali was broadcasting its position publicly via the automatic identification system (AIS) and was traveling at a speed of over 8.5 knots. It then slowed to around 6 knots in the moments before the crash, according to AIS data.

Both pilots and all crew members on the Dali are accounted for. There are no reports of injuries, the ship’s management company, Synergy Group, said in a statement on March 26.

ABC News reports that the crew of the vessel made a desperate mayday call in an attempt to warn transport officials that the crash was about to occur. A report from the Cybersecurity and Infrastructure Security Agency, seen by ABC, says the Dali “lost propulsion” and that the crew were aware they had “lost control” of the ship. Maryland governor Wes Moore told reporters that, thanks to the mayday call, officials were able to stem the flow of traffic over the bridge, an intervention that he says “saved lives.”

Mercogliano says it is very difficult for ships of this size to make rapid adjustments to their trajectories. Video footage shows a sudden outpouring of smoke from the vessel’s stack, indicating a change in engine activity of some kind. What is particularly disturbing is that, in this case, the vessel ends up plowing straight into one of the key supports for the bridge, clearly off course. No information as to why this happened has become public.

Photographs of the aftermath show the bow of the ship pinned beneath fallen sections of the bridge. The anchor chain is visible, meaning that at some point the anchor was dropped, though it is not certain whether this happened before or after impact. The chain appears to be at an angle, however, which Mercogliano says could be a sign that it was dropped shortly before the crash and dragged for a brief time.

Lawyer James Turner of Quadrant Chambers in London specializes in, among other things, ship collisions. He says that there would have been no automated systems on board a merchant ship of this kind able to prevent the impact. Information from radar, AIS, and visual observations would have been available to the crew, however.

But data-collecting systems may now reveal exactly what happened. As on airplanes, commercial ships have data and audio recorders on the bridge, which are often a key source of information for investigators post-incident. “The master will hit a button and that ensures that the last two hours of audio recording are preserved, as well as all the data from the various parts of the ship, like the engine and steering and so on,” explains Turner. “That can be downloaded and queried.”

He adds that estimates of the ship’s speed at the time of the incident as recorded by AIS are likely “99.99 percent accurate.”

For now, the focus of responders will be on locating survivors from the fallen bridge. Two people have been rescued, one of whom is in the hospital. Six construction workers remain missing.

The disaster has come at a difficult time for shipping, with drought afflicting the Panama Canal and Houthi attacks striking multiple vessels in the Red Sea in recent months. Somali piracy is on the rise again, also. The grounding of the Ever Given in the Suez Canal is very much still within recent memory—it occurred a mere three years ago.

The Port of Baltimore insists in a statement that it has not been shut down—road vehicles are still operating within the port—however, all ship traffic in and out is suspended until further notice. AIS data reveals around a dozen commercial vessels at anchor outside the port, their entry now blocked by the stricken bridge and the Dali. It will take some time for the US Army Corps of Engineers to remove the steel pieces of the bridge, which present a significant threat to passing vessels, from the river.

“Whatever ships are in the port are now stuck,” says Mercogliano, who notes that Baltimore is an important port in terms of car deliveries and coal exports.

Overall, he argues, maritime operations are extremely safe today, though the volume and velocity of trade mean that when things go wrong it can be especially serious.

“We move goods a lot faster than ever before, and there’s very little margin for error,” he says. “When there is a mistake, the mistakes tend to be very large.”

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