The more complete story is that a massive maintenance project had begun by crews disconnecting the towers from the concrete supports, for replacement. The crew needed to abandon their work because of bad weather, then the tornado came that night and the bridge supports were twisted away.
Was it a confluence of risk factors?
You'll hear this phrase in industry and business: a confluence of risk. It is about seemingly isolated risks combining to create a higher level of risk. FMEA is a bottom-up approach, meaning that we analyze single points of risks. FMEA is weak with multi-point failures. To analyze combined risks, we use tools like tree diagrams, fault tree analysis, and top-down approaches like hazards analysis - tools that help us model interactions. When creating risk files, I would use both a fault tree analysis and FMEA together. I use the swiss-cheese model of accident causation, too.
Back to the bridge:
- Risk of tornado: Given the time of year and location, there was a risk of high winds and tornados. Crosswinds at that location were notoriously high and the bridge was designed to address that even with a train crossing it. The bridge existed for over 100 years. Still, the risk of a tornado within the maintenance window was probably relatively small.
- Risk of maintenance: There is risk in maintenance and how it is performed. Remove bolts from a tower and risks increase: not supporting the bridge (or relying on the bridge to support it), extra stress on neighboring towers, more susceptible to twisting...Multiply that out with multiple towers being released at once and the probability of things going wrong increases.
I wasn't part of this project and am only looking at it from a perspective of knowing what happened. What a generous position to be in! What I want to do is to avoid the same kind of mistake.
There are two takeaways for me:
- The environment in which our product is used affects risks. It not only includes things like weather and other common causes of failures from the environment (like temperature and humidity). It also includes who is using it, where, how and with what other things.
- It may be more efficient to do things a certain way, but is it introducing risks?
To understand both of these for product design, we need to understand the user and use environment. No matter how much I would research on my own, it just didn't compare with the knowledge pool of my cross-functional team. They always provided extra twists and information that I would have never considered. That's because they were looking at it from a different viewpoint and had different experiences - usually more direct experiences.
These are reasons why I encourage you to work out ideas with your team. You're going to learn things that affect your design decisions.
After the fall of the Kinzua Viaduct, the state preserved what was left and turned it into a sky walk. It's a scenic tourist stop in northern PA. I took my family there this summer.
If you're in the area, visit it. You won't forget it!
