Science Friday
Hosted by Flora Lichtman and Ira Flatow
Engineers take an in-depth look at why the Francis Scott Key Bridge in Baltimore collapsed and how to prevent future tragedies.
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This is Science Friday. I'm Ira Flatow. Today on the podcast, one year after the Baltimore Bridge collapse, checking on what went wrong and preventing future disasters.
These newer and larger vessels have kind of outpaced the bridges in terms of the ability to change and to be updated.
In the early morning of March 26, 2024, the container ship Dolly struck the Francis Scott Key Bridge in Baltimore. Within 30 seconds, the bridge collapsed into the river below. Six maintenance workers lost their lives. Now, almost exactly a year later, we wanted to look back on what led to this catastrophic event. And more importantly, look to the future. How to improve the safety of our nation's bridges and prevent another tragic crash. Joining me now to discuss are my guests, Dr. Abhi Agayayay, Professor of Civil Engineering at Drexel University, based in Philadelphia, and Dr. Thomas McKenney, Associate Professor of Engineering Practice,
Naval Architecture and Marine Engineering at the University of Michigan, based in Ann Arbor. Welcome to Science Friday.
Thank you.
Thank you, Ira. Happy to be here.
You're welcome. All right, let's start looking back to exactly what led to this tremendous bridge collapse. Thomas, can you give me an overview of what went wrong aboard the Dali that led it to striking the bridge?
Sure. So the basics of the incidents go roughly like this. So soon after the Dali left its terminal and entered the channel, one of its electrical breakers unexpectedly opened, which caused the first blackout. Now, although generators were running, most of the equipment lost power onboard the vessel, and that also means that the main engine automatically shut down, which stopped the propeller as well. And the crew did some additional reconnecting of breakers to restore power. However, there was another blackout that occurred, and then eventually, roughly 30 seconds after that, they did get power back, but in a last ditch effort, the pilot ordered an anchor to be dropped overboard, and then eventually that led to the elision with the bridge.
Let's get in the weeds. Tell me what actually happened.
So first of all, the cause of the incident is still under investigation. So the NTSB, however, has provided us some indications. And for me, I divide this into two main things. First of all, there was clearly some sort of electrical component fault, and that was associated with the first kind of main cause where one of those breakers was opened. Now, what this means for me at least is to put into question the condition of the vessel, the components of the electrical systems potentially might not be properly maintained. The second thing was related to the operating configuration. Now, in this case, they were operating what's called a closed bus setup, which means that it might be good for kind of efficient power distribution, but it's not so good if something goes wrong. And
so the blackout that occurred, in that case, the generators were still generating electricity, but the power wasn't able to get where it needed to go.
All right, Abi. So the ship hits the bridge. The bridge collapses quickly. Why so quickly?
Well, it turns out that this particular bridge was fracture critical, meaning that if if one tension member fails, the whole bridge comes crashing down. And so it was no surprise that it happened that way because the bridge was fracture critical. And the bridge piers were not designed for a direct strike from a ship like the Delhi.
What does it mean to be fracture critical? And and is that like an Achilles heel on a bridge?
It is an Achilles heel on a bridge. There are about seventeen thousand bridges in the United States that are fracture critical. We don't design our bridges that way anymore. We design our bridges to have redundancies, but this bridge did not have that redundancy. And the bridge piers were not protected.
So how should the bridge piers be better protected?
There are several ways you can protect bridge piers. You can have what we call dolphins. They are like huge bullets. For example, the Delaware Memorial Bridge is building about eight of those bullets, eighty feet in diameter, filled with sand or concrete. And and they stop the ship by deflecting and dissipating the energy from the ship. You can have dolphins. You can have manmade rock islands. You know, rock islands are also commonly used in some bridges like the Sunshine Skyway Bridge in Florida uses rock islands, also uses dolphins.
So those are the two main ways of stopping or preventing bridges from collapsing as a result of ship strikes.
So when you say rock islands, that means sort of the ship will run aground before it hits the bridge. Is that right?
That is correct.
Ira, can I, can I make a comment there? Because I think what we saw from the incident with the Dali here is that the ship collided with the bridge, but the ship was, I mean, from a stability perspective, the ship was fine, right? The bridge even collapsed onto the bow of the vessel. And so that confirms that we are designing ships well because we have a collision bulkhead and we have the necessary design of the vessel to withstand groundings and collisions. So if a vessel did collide with, you know, a rock island, the ship in most cases would, would survive, especially at lower speeds.
Right. So, so Abby, there was nothing wrong with the bridge that led to this collapse or the structure itself?
Nothing wrong with the bridge as far as we know. I mean, the bridge was, you know, was old. So, I mean, it will not be in tip-top shape like it was when it was built in 1977, but it could not, there was no way a bridge could sustain 34 to 35 million pounds of impact force that was generated when the Dali hit those bridge piers.
Hmm. As, as you just said, the Key Bridge was built in the seventies and we know back then cargo ships were not nearly as big as they are now, right? I mean, how has bridge construction changed? Are different standards now in effect?
One of the major bridge collapses that occurred in the United States occurred in 1980, the Sunshine Skyway Bridge, 35 people died. And as a result of that, the American Association of State Highway and Transportation Officials, ASHTO, came up with guidelines in 1991 to protect bridge piers that are in navigable waterways. And what happened, though, was that it only applied to new bridges. They did not mandate existing bridges or bridges that were were on that design at the time the guidelines came into being to have this protection.
So new bridges from, let's say, nineteen ninety four onwards had bridge protection. But existing bridges like the Key Bridge, like the Bay Bridge, which is not far away from the Key Bridge, do not have this protection. They don't have the pier protection and and therefore they are vulnerable. And as NTSB just reported, there are many bridges, about sixty eight bridges with unknown vulnerability that they've asked the owners, the thirty owners of these sixty eight bridges, to calculate the vulnerability and compare to the threshold
that ASHTO provides to see how vulnerable their bridges are currently.
Hmm. Who pays for for the protection? I mean, if you have a collapse of a of a bridge like this, are are the are are the ships insured enough to pay for the repairs that go on or or taxpayers or who's going to pay for that protection?
I I doubt that the the ships are insured enough. I mean, the Key Bridge is estimated to cost two billion dollars to replace. Now, you can't even put a cost on the on the loss of six lives, you know, as a result of this collapse. Then you have business disruption. That's another cost, a huge cost. So I mean, I I I think it's going to fall on the taxpayers at the end. The bulk of it, that is, I don't know that a ship isn't short enough to pay billions and billions of dollars.
Thomas, let's talk about that ship a bit. Let's go back to the issue of the power failures aboard it for a moment. Should there, could there, can there be more redundant systems aboard these huge shipping containers?
Yes, there can be, and there are vessels already out there that have redundant, more redundant propulsion systems. I designed cruise ships for over eight years. If you look at a cruise ship configuration, they have at least two, even three redundant propulsion or propellers. So think multiple shafts and propellers. And they're also all electric configurations where you have multiple engines producing electricity that provides to the propulsion and auxiliary. The reason why basic cargo vessels are single direct drive propulsion engines is because of the efficiency of them. They're very, very efficient. And what that means is that you're able to reduce your costs, right?
To transport as well as your fuel consumption and also emissions. So the kind of the configuration is driven by the efficiency of it. But there are a number of ways you can do to improve redundancy, including multiple propellers. You can also have some additional emergency systems. So if you had more like local power sources for steering and, and larger emergency generator power, you would also have the ability to do more during an emergency situation.
So we're talking money here.
It's all about the cost in the end, right? There's, there's an increase in complexity, but there's also a trade off, right? Everything is a trade off when we start looking at this. So as we move to more of these more complicated costly configurations, they're also in some cases less efficient, which means we're emitting more, more, you know, climate pollutants, air pollutants and other things as well.
Abhi?
Yeah, I'd like to jump in here too and ask Thomals about tugboats. Because I understand that the, for the Key Bridge, the dally was being escorted, but the tugboats turned back right before the, the strike, the ship strike. I was wondering if tugboats are another solution to escort these ships under these bridges? And then once they clear the bridge, the tugboats can come back rather than coming back before they cross the bridge.
So that's possible. The challenge is that if you look at how fast these vessels typically move through the channel, it's roughly six knots plus or minus a little bit. Tugboats are not that efficient at changing the kind of the trajectory or the direction of vessels that large, traveling at that speed. So of course, one solution is to go slower and to have more support. But of course, that also affects the efficiency of port operations as well.
After the break, how to protect other bridges in jeopardy of collapsing after a ship strike.
If they allow these ships to come into their port, have a responsibility to make sure that their bridge piers are protected.
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So how much of this disaster can we say was a result of the bridge not having enough protection versus an issue with the ship? Let me begin with you, Abi. What do you, is it 50/50, 60/40, or what?
I call it 50/50 because,
you know, one of my students did some research recently and found out that there were about 2,100 engine failures, you know, according to the Coast Guard data, within, you know, a number of years. And, you know, so engine failures will happen. But if the bridge is protected, if the bridge piers are protected, then even when those engine failures happen, what will be damaged will be the dolphins, which can be replaced. So I put it at 50/50.
Thomas?
For me, the main message here, the main takeaway is that we have this just basic difference in bridge lifetimes and ship lifetimes. So if we're talking about bridges, they're designed to last, you know, 50, 70 years, maybe, whereas ships, these basic cargo vessels, are operating 10, 20 years usually. And what that means is that these newer and larger vessels have kind of outpaced the bridges in terms of the ability to change and to be updated. I mean, so these larger vessels, while maybe there's been continuous improvement on reliability and redundancy, kind of the consequence of these larger ships impacting the bridges are higher now because of this discrepancy. So I think it's very difficult to like, place blame.
I think the most important thing is that we look at the interface between ports and ships more. You know, closer collaboration, more communication, engagement with ship owners and operators and ports going forward.
So let me jump in here regarding the apportionment of blame. We have bridges where we load rate the bridge and say that these bridges can only take this much load. And so we don't allow these, you know, heavy trucks to go on those bridges. So I, I believe, you know, the owner of these bridges, if they allow these ships to come into their port, have a responsibility to make sure that their bridge peers are protected enough to allow these, the ships, these large ships that are larger than maybe they were when the bridge was designed. If they allow these ships to come into the port, then they, they, they have the responsibility to make sure that those bridge peers are protected, to allow those, those ships coming.
So you, you say to the cities who own the bridges, it's on your head if you allow them to come in and there's an accident?
Yeah, I mean, they, they are receiving fees and monies from these ships, these large ships that come in. And, and so if you allow them to come into your port and they are maneuvering near those bridge peers that some of them, you know, totally unprotected, then you owe some responsibility to the people that are using those bridges in case that bridge goes down.
You know, Thomas, container ships have gotten so much bigger and bigger. And I'm, I'm recalling, this is not the first time that a big container ship caused some serious issues. I'm thinking of the ship that's got stuck in the Panama Canal a few years ago. I mean, could smaller ships be a solution here or is that too expensive?
I believe that the vessel was stuck in the, the Suez Canal. That was an evergreen vessel, which did cause some major disruptions. If we look at the, the kind of the growth of the, of container ships, look back into the early 2000s. The largest container ship had about eight to 10,000 20 foot equivalent units. So think about like half of the trailer that you see on the highway. Today, the largest container ship is 24,000 TEUs. Now, this gives us the economy of scale, cost per container transported, right? So larger vessels are clearly Part of this overall improvement and efficiency of maritime transportation, which is already really efficient if you look at that compared to other forms like rail,
trucking and air. So smaller vessels, of course, can be done, but you're going to lose that efficiency. You know, there's other things going on here, right? We have a climate crisis. We have to reduce greenhouse gas emissions and that would be counter to some of those other objectives.
Hmm. So has the Baltimore Bridge collapse made these projects to improve bridge safety against strikes a bigger priority?
I believe so. There are two reports that came out just in the past few days. You have the NTSB report, you know, talking about 68 bridges with unknown vulnerabilities, asking the owners, recommending to the owners to do a vulnerability assessment to know what they, you know, what risk their bridges are under. And then you have the John Hopkins University report that just came out that also talks about the probabilities of ship strikes on many bridges. And so I think there's a focus, there's a renewed focus, I believe, on our bridge peers that are in navigable waterways that need to be protected.
Well, we've run out of time. I'd like to thank both of you for letting us know more about this. Dr. Abi Agayera, Professor of Civil Engineering at Drexel University in Philadelphia. Dr. Thomas McKenney, Associate Professor of Engineering Practice, Naval Architecture, and Marine Engineering at the University of Michigan in Ann Arbor. Thank you both for taking time to be with us.
My pleasure.
That's about all the time we have for now. A lot of people helped make this show happen.
Jason Rosenberg.
George Harper.
Kathleen Davis. Shishana Buxbaum.
I'm Ira Flatow. Thanks for listening.
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