[tech] Engineers and Disasters

Jun 2, 2006

The words "engineering" and "disaster" seem to go very naturally together in the psyche of all those who aren't engineers.

This Wired Article 'showcases' some of these disasters. I have to say that I don't agree with the list... first of all for their choice of disasters and second of all for their haphazard presentation.

Some examples:


1. St. Francis Dam, 1928
Self-taught engineer William Mulholland built this LA dam on a defective foundation and ignored the geology of the surrounding canyon. He also dismissed cracks that formed as soon as the reservoir behind it was filled. Five days later, it ruptured, killing 450 people and destroying entire towns (along with Mulholland’s career).

Ok, the term 'self-taught' engineer should tell you something right there. Experience is very valuable, but you shouldn't put someone like that in charge of hugely dangerous construction projects like this! Secondly, in my opinion this is more a story about arrogance than it is about engineering blunders. There were PLENTY of geologists and engineers who could see what was happening and tried to warn people, but this Mulholland guy just wouldn't listen about it-- until it was too late.


2. Kansas City Hyatt walkways, 1981
Walkways crisscrossing the hotel’s multistory atrium collapsed, domino-style, raining debris and hundreds of people onto the packed dance contest below. The cause: grossly negligent design and use of beams that could support only 30 percent of the load.

This one was definitely an engineering mistake (or a draftsperson mistake), but this little blurb fails to mention that the "grossly negligent' design wasn't the first design that was in place. The engineer who ORIGINALLY designed the walk way designed it such that one single bolt would support the bridge through a bracket (tension force). At some point, this drawing was revised, not by the original engineer, so that instead of having one bolt support the bridge in tension, there were two bolts spaced close together. Now a lay-person would think that two bolts are better than one, but that only really works if the two bolts are increasing the same kind of force. Instead, this modification changed the stress mode from tension (pulling) to shear (ripping, like a scissor does). And that little piece of steel that was only really meant to provide some bending support was now supporting TREMENDOUS amount of shear!

The moral of this engineering tale is to always take special care reviewing your revisions, never change something without being absolutely sure it's ok (this was probably changed because the shorter bolts were cheaper), and don't sacrifice safety for cost :/ There's no question it was an engineering disaster, I just don't like that the article neglects to mention that the design WAS right in the first place. =_=


3. Vasa, 1628
Three hundred years before the Titanic, the Vasa was the biggest sailing vessel of its day. The overloaded ship ruled the seas for all of a mile before she took on water through her too-low gun ports and promptly capsized.

I don't see how you could qualify this as an engineering disaster because there weren't really engineers back then!!! The people who built this boat were shipbuilders and naval architects. The skills of these people were 100% based on experience and they had very little knowledge of fluid dynamics. I did learn about this case, however, because it illustrates a point about scale. Back then, when you wanted to make something bigger, you kept the same proportions and just scaled up. This was true for buildings, ships... everything! They knew that a ship of [x] size would sink [y] much, so they figured that a ship of [3x] would sink [3y] feet into the water. The reasoning worked out ok for awhile, but as they made their ships bigger and bigger, they came closer and closer to the point where they were forced to realize that this relationship is not linear. That point came with the Vasa put its windows too low, they loaded it up with the expected amount of cargo and it sank way more than they thought. Water poured in, goodbye Vasa. Then they learned they started working to really understand the relationship between size, weight, and sink. Even the modern science of naval architecture is 90% empirical (based on experience), so I don't see how this is a 'stupid mistake' when it was all that they knew at the time!

Unfortunately, those are the only cited instances that I am familiar with, but I'm certain that the rest of them left out some critical details to the story as well.

However, I'm baffled at how they can call these 'the worst' when they left out some of the most important engineering disasters in history, particularly the crash of the Columbia. That case was textbook-classic cost-based negligence. The engineers were under tremendous pressure to make a launch date, but it was too cold outside. The engineers KNEW that the O-rings were not rated for that temperature. They even CALLED the O-ring company and said "how cold can your o-rings withstand?" and they told them that they hadn't tested at that cold and that it was unsafe. (interestingly, after failure, it was found that the Orings failed at exactly the point that those engineers predicted by extrapolation.) The engineers kept saying "we can't launch today, we can't launch today" and the upper-eschelon people kept pressuirng "we have to, we have to." Eventually, the top dogs told the chief engineer: "I want you to take off your engineer hat and put on your manager hat and make the decision." That decision was one of the worst engineering disasters in history.

So, I am fairly displeased with this Wired article. While I think it is very educational and important to learn about these kinds of disasters, I think it is up-played far too much in the world psyche. It's no wonder nobody wants to become engineers these days. When people talk about Doctors, they always associate it with the lives they save. But doctors fix what is broken. Engineers are as important, but our role is much more subtle. You never hear about the thousands of disasters that engineers have averted.