KATHLEEN DAVIS: Last week, the world watched as rescuers from across the globe searched for a tiny submersible. It had disappeared, carrying five people on a dive to the wreck of the Titanic. That search turned out sadly to be in vain. The craft is believed to have imploded, killing everyone on board.

The intersection of design, engineering, and human risk taking is a recurring theme throughout modern history. One of the finest chroniclers of those tales was Henry Petroski, who died earlier this month at the age of 81. He was a professor of engineering and history at Duke University, and he appeared on this program many times.

In 2012, Ira Flatow spoke to the late Professor Petroski about engineering failures and humanity’s follies.

IRA FLATOW: My next guest says that it’s important to look at structural failures, whether we are talking about the sinking of the Titanic, a space shuttle disaster, a smartphone malfunction– look at them in a larger context– as a system that includes people, who both maintain and use the structure. Dr. Henry Petroski is the author of To Forgive Design: Understanding Failure. He’s professor of civil engineering and history at Duke University. He joins us from Durham, North Carolina.

Welcome back to Science Friday, Henry. It’s always good to have you.

HENRY PETROSKI: Thank you, Ira. It’s always good to be here.

KATHLEEN DAVIS: You must be getting a lot of questions about the 100th anniversary of the sinking of the Titanic, about whose fault it really was.

HENRY PETROSKI: Yes. Well, that’s very difficult to pin down to one or two people. This is a system. This is a big ship, a big piece of machinery, going out into waters that are dangerous, with a lot of people on board, with insufficient lifeboats. There are so many dimensions to the Titanic story, and I think that’s one of the reasons that we keep hearing new things about it and we sometimes change our minds about what we think.

One thing seems to me to be sure. And that is that the ship was marketed as unsinkable. And as we know, that was simply not true at all. The chances of hitting an iceberg were slim. Let’s just say for the sake of argument that the chance of hitting an iceberg was 1 in a million. And everybody may have known that at least implicitly. But that doesn’t tell you when an iceberg is going to be hit. It could be hit on the first 1 in a million sailings or the last.

Things like probability are funny. They don’t give us very precise ideas about what’s going to happen or when it’s going to happen. In the case of the Titanic, the fact is that there was some overconfidence– hubris– involved on the part of the captain, who had the ship going, trying to break a speed record. Whereas, he was going through waters that were dangerous and known to be dangerous. He had been warned about icebergs.

So it was a concatenation of all these things that came together– some chance, some deliberate.

IRA FLATOW: And a lot of this seems to be the theme of your book.

HENRY PETROSKI: Yes.

IRA FLATOW: That there are a lot of things going on here. Give me some examples of other great failures that we have to understand the design and the failure.

HENRY PETROSKI: Well, you were talking with the people up in the Space Station. I talk about NASA failures with the space shuttle, and these are familiar. These are examples that are not unlike the Titanic actually.

The Challenger was not an accident that was not foreseen. The engineers warned the managers that it was a little too cold to launch that ship on that day with complete confidence that it would return. And they were proven to be right. The seals had been leaking. The engineers knew that, and they expected that they would be leaking on that day, too.

The Columbia, which came back in 2003 and disintegrated upon re-entry, there were also warnings about that– questions of foam flying off the external tank and hitting the shuttle as it took off as it launched from Earth. The engineers again said, well, some of that debris has hit the shuttle’s wing, and we really should investigate it to see whether it’s been damaged terribly or not and whether we should have to repair it. But again, basically, management overruled the engineers and had an overconfidence.

The difference between the perspective of managers and engineers with regard to safety and failure is very, very interesting. Before the shuttle missions took off, the engineers were asked, what did they think the likelihood was that there would be a failure of the kind that we now know happened? The engineers said, oh, about 1 in 100. The managers, on the other hand, predicted 1 in 100,000. Now, that’s quite a difference. And we know that the engineers were proven to be right.

IRA FLATOW: I’m Ira Flatow, and this is Science Friday, from WNYC Studios.

Tell us the Brooklyn Bridge story that I thought was also fascinating, about Roebling, who sort of built in extra stuff.

HENRY PETROSKI: That’s correct.

IRA FLATOW: He built in a safety factor into the bridge.

HENRY PETROSKI: That’s right. What responsible engineering does is it specifies the quality of the materials that go into a structure like the Brooklyn Bridge. Well, in the case of that bridge, the Roeblings owned– they ran their own wire-making factory. And they would have liked to have provided the wire for the bridge’s cables because they would have had a high level of confidence that it was high quality.

But on the basis of a business decision, the board of directors said, no, no, you can’t use your own wire. You’re the engineer. It’s a conflict of interest. So the contract for the wire went to someone else, who Roebling warned was not a good producer of wire.

Well, everything seemed to be going fine until one day, after many deliveries of these reels of wire, it was discovered that there seemed to be some bad wire getting into the bridge’s cables. And how was that happening? Because every shipment of wire was tested before it was passed on to go ahead and be put into the bridge.

Well, it turned out that the wire supplier not only had bad workmanship, but also had bad morals. And the rejected wire was snuck into the construction site and it found its way into the bridge.

Well, Roebling– this was Washington Roebling– his decision was crucial at this point. What would he do? Would he take all the bad wire out? That would not only cost time and money, but it would also be very dangerous for the workers.

What he decided to do was estimate to the best of his knowledge how much bad wire was actually in the bridge already. And then he added additional wire beyond what was originally designed to be in the bridge of high quality and completed the project that way. To this day, that bad wire is in the bridge.

IRA FLATOW: So if you’re going to buy it, beware.

[LAUGHTER]

HENRY PETROSKI: Get a discount.

[LAUGHTER]

IRA FLATOW: Yeah. We’ve talked about the Titanic a bit, but you have a really interesting take on an aspect no one has talked about when we talk about the sinking. And that is, what would have happened if the Titanic did not sink?

HENRY PETROSKI: Yes, that’s a very interesting thought experiment, I think. If the Titanic had not sunk– and in fact, if it had reached New York and then went back and forth across the Atlantic many times– the likely result of that would have been, in my opinion, that competing steamship companies would have wanted to better the Titanic. They would have wanted to build larger ships, faster ships.

They would have wanted to build them more economically to make more profit. They would have probably used thinner and thinner steel over time. They might have put fewer rivets in. They would have maybe wanted to get rid of lifeboats altogether. Because, after all, the Titanic was unsinkable. We’re following the design of the Titanic, only we’re making it bigger and better.

Eventually, the chances are, one of those ships would have struck an iceberg or had some kind of incident in the ocean. And since it had all the inherent flaws of the Titanic, it would have sunk and probably, because it was bigger, with a greater loss of life.

This is what happens with cycles of success and failure. When we have a success– a prolonged period of success– we tend to become more complacent. We tend to become overconfident that we’re doing it right, that we’ve got it figured out finally. And then, of course, a failure occurs and wakes us up out of our dream.

The failure, the wake-up call, then causes us to look more closely at what we’ve been doing. And we discover that, in fact, we haven’t been building perfect machines or systems. We’ve been building them with inherent flaws.

IRA FLATOW: Is there one system– bridge, tunnel– anything that’s waiting to fail that you can warn us about?

HENRY PETROSKI: I think the history of bridges is very interesting. Over the past century and a half or so, there’s been a major bridge failure about every 30 years. So right now, we’re looking ahead to about the year 2025, 2030– not too much more than a decade from now– if things follow as they have proceeded in the past, we can expect some kind of big surprise.

It’ll be a bridge type that hasn’t failed before. It’ll be something that will seemingly come out of the blue. But then, in retrospect, looking at it and fitting it into the pattern, it’s something we will say, oh, we should have seen that coming.

IRA FLATOW: So it’ll be a combination of human error and design error?

HENRY PETROSKI: Yes. Generally, that’s right. You could almost say that a design error is a human error. Because, after all, it’s we humans who do the designing.

IRA FLATOW: Yeah. I recall I covered Three Mile Island, that nuclear accident, in 1979. And the investigation showed such a combination of design and human errors there.

HENRY PETROSKI: Yes, that’s fairly typical. Most systems– most machines, structures– are designed to be somewhat robust so that if some little thing goes wrong, the whole thing doesn’t fall apart all of a sudden or blow up or anything like that. But then, when humans react to this small irregularity, they sometimes make it awfully worse.

IRA FLATOW: Henry, I want to thank you very much for taking the time to be with us today. A fascinating book. It’s To Forgive Design: Understanding Failure. It talks about all kinds of engineering designs and famous failures, and Henry Petroski’s unique way of looking at them and explaining it. Thank you, Henry. And good luck with the book.

HENRY PETROSKI: Thank you, Ira. Thank you. Bye-bye.

KATHLEEN DAVIS: Ira Flatow, in 2012, talking with Henry Petroski, who died earlier this month at the age of 81. Our condolences to his friends and his family.

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