Experts say protective structures may have saved the Baltimore bridge from collapse, but they could also have completely shut down the waterway.
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The 984-foot container ship that caused the Francis Scott Key Bridge to collapse has raised questions about whether the structure could have been saved.
The Key Bridge, Baltimore's biggest bridge and a critical piece of infrastructure for the city, finished construction in 1977.
It was destroyed on Tuesday when the Singapore-flagged vessel Dali slammed into one of its support pillars.
Six of eight construction workers who were on the bridge at the time are presumed dead. There are also fears that the bridge's collapse will severely impact the regional economy, with the nearby Port of Baltimore closed to ships until further notice.
As the city grapples with the fallout, discussions have started to grow around the bridge collapse. Some say it's possible protective structures could have been introduced to protect it.
Others, however, say protecting the bridge from the impact of a massive cargo ship would be unrealistic.
The issue is likely to be at the center of investigations and raise questions about the fitness of America's infrastructure.
Since the bridge fell, protective structures called dolphins have been hailed by some officials and experts as potential bridge saviors.
Dolphins, in this case, don't refer to aquatic mammals but rather structures built up and down stream designed to shield important naval structures from incoming objects.
Jacksonville Mayor Donna Deegan sought to assure her constituents that the Dame Point Bridge in Florida was protected by large dolphins with sensors.
A bridge engineering expert also pointed them out to the Sydney Morning Herald in an article discussing whether a similar bridge collapse could happen in Australia.
The collapse harks back to another painful event — the 1980 Sunshine Skyway Bridge disaster, a similar incident when a 600-foot freighter struck a support pillar and caused the span of the bridge to collapse.
When it was rebuilt, the Sunshine Skyway Bridge was fitted with quarter-mile dolphins to guard against a repeat tragedy, and a federal memo from 1983 recommended that bridges be built with structures to shield them from collisions.
That's not possible everywhere though, the federal memo noted.
It "may be extremely difficult to retrofit some existing bridge piers" with protective systems, it said.
Key Bridge, built in 1977, was finished before the reform was published. Still, footage suggests it had some protection in place.
Small dolphins were placed about 320 feet upstream and downstream of the piers, Colin Caprani, associate professor of civil engineering, said in a post in The Conversation.
The bridge also had concrete "fenders," timber and concrete structures placed around the piers, Caprani added.
In 1980, a container ship called the Blue Nagoya ran into the bridge at a speed of 12 knots. One fender was damaged badly enough that it had to be replaced.
Still, faced with a ship of the size of the Dali, they would likely not have been fit for purpose, Mimi Gao, a naval architect with the Singapore Chamber of Maritime Arbitration, told Business Insider.
Ships as large as the Dali weren't plying the Port of Baltimore when the Key Bridge was built in 1977, she said.
Donald O. Dusenberry, a consulting engineer, told The New York Times that "maybe it would stop a ferry or something like that. Not a massive, oceangoing cargo ship."
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The Dali was moving at a speed of about eight knots, per local authorities. Its crew attempted to slow the ship by dropping its anchors, but to no avail, the Maritime and Port Authority of Singapore said.
Maryland Gov. Wes Moore told reporters at a news conference on Tuesday that the bridge was "fully up to code."
"This is a unique circumstance. I do not know of a bridge that has been constructed to withstand a direct impact from a vessel of this size," Transport Secretary Pete Buttigieg told reporters.
Gao said that more robust protections "could have potentially prevented the bridge collapse." But with any changes to a structure's strength comes a payoff. The more solid the protection, the bigger the structure.
With huge vessels becoming the norm for container shipping, Gao said there comes a point when designing a dolphin to stop them becomes ridiculous.
"There's a possibility that the required size could become impractically large, potentially interfering with river traffic or rendering construction impractical," she said.
Tim Broyd, a professor at University College London and a former president of the UK's Institution of Civil Engineers, agreed.
"I think you're looking here about a low probability but high consequence event and you get to a point where you have to accept there is some small residual risk that you can't mitigate," he told BI Wednesday.
To illustrate his point, Broyd pointed to planes flying above crowded cities every day. There is always a small risk that one could crash.
"You look to reduce the probability of it happening, but you can never take that down to zero," he said.
Still, there may be ways to further reduce the risk.
Tugs could be used to move larger ships under bridges, and regulators could impose speed limits on vessels passing through the area, Gao said.
Engineers looking to rebuild the bridge could also consider spacing its support structures well out of the way of the transit route or moving it upstream of the shipping port, Broyd said. They could even consider replacing the bridge with a tunnel to abrogate the risk of a collision completely, he said.
Still, no engineering structure will ever be 100% safe, said Broyd. It's all about balancing out risk and probability.
"Any politician who, after this sort of thing, stands up and says: 'I'm going to make sure that this can never ever happen again' just doesn't know what he or she's talking about," Broyd added.
