Precision Reads & Reviews: Applying Engineering Failure To Metrology

Applying Engineering Failure to Metrology:  To Engineer is Human

Engineering failure is measured in two ways: human death toll and materials lost. This is just one of many insights from Henry Petroski’s book To Engineer is Human: The Role of Failure in Successful Design.  As the president of a force calibration laboratory that has seen over 120 years of success in the industry, I found the content of this book to be both fascinating and indispensable. Petroski analyzes case studies and describes tragic yet avoidable failures in engineering; thus, he proves that with better practices, lives need not have been lost.

Engineering Failure

The book opens by mentioning an engineering failure caused by a simple design error that, on July 17, 1981, caused a walkway collapse at the Hyatt Regency Hotel in Kansas City, Missouri. This collapse resulted in the death of 114 people and injured another 216.  The disaster, a product of a corporate culture of profound neglect, subsequently became a case study in engineering ethics.

Petroski discusses what happened in detail and how the cause of the eventual failure was determined.  Put, the constructed walkway created double the amount of force on a nut than originally intended in the design. How and why did this egregious error occur?  From the first chapter onward, I considered how these details relate to Metrology. More specifically, how does this example relate to Measurement Risk?

Did the manufacturing company know the proper requirements? Did they have the right equipment to measure force? Did they follow the correct documented processes? What caused this engineering failure? Further investigation would reveal the answers to these questions.

The above questions could be posed about other illuminating case studies that Petroski explores. Petroski's examples captivated my attention from beginning to end, from buttons wearing out on Texas Instruments Speak & Spell toy to the cause of the 1979 DC-10 crash in Chicago to how an oversized waterlily inspired the Crystal Palace. I could not help but draw parallels between the DC-10 crash and more recent airplane failures, and I found myself asking, “Why have we not learned from previous failures?”

Petroski addresses this issue by stating, "Failures appear to be inevitable in the wake of prolonged success, which encourages lower margins of safety. Engineers and the companies who employ them tend to get complacent when things are good; they worry less and may not take the right preventative actions." Petroski's claim about complacency might merely describe human nature or point to the old but well-known motto, "If it ain't broke, don't fix it."

This motto has haunted our society in various ways long after Petroski first published To Engineer is Human. Consider the BP Texas City Refinery explosion, where the root cause was a combination of cost-cutting, production pressures, lack of preventative maintenance, procedural workarounds to compensate for deteriorating equipment, and collapsing cranes due to premature removal of the pins.

Unfortunately, this attitude, which leads to negligence, may be present in our Metrology community today.  Some companies might be using outdated equipment, or, like the BP Texas City Refinery, they may have established procedural workarounds to compensate for not having the right equipment.  In applications of force, some companies use equipment beyond its lifecycle. That situation is purely one of engineering failure to know the use cycles. They could be avoiding upgrades to the proper equipment or using the wrong adapters, another common and unethical practice.

Such adapters could range from being unsafe to improperly machined, allowing the user to fixture the force-measuring device in the frame to apply forces and record output at those forces. Many do not realize that failing to use proper adapters to calibrate load cells, truck scales, aircraft scales, tension links, dynamometers, and other force-measuring devices can produce significant measurement errors that pose serious safety hazards. Another pitfall is that some purchase an adapter based on a copied design, assuming that it can work for a similar one because it worked for one application.

Petroski’s book enriched my appreciation for specific design elements and the importance of design safety factors while enhancing my awareness of what aspects of a design may fail. Petroski cites studies where a successful design was copied and failed because the engineer may not have understood concepts such as resonance. For instance, a successful bridge design in a certain area accustomed to low winds may fail under high winds. This information is even more relevant today since our climate produces more severe storms, higher winds, and the destruction of structures that may have been built to withstand only weather conditions that were once typical for their location.

To Engineer is Human discusses why understanding failure is essential to understanding and achieving success. Those who achieve success do so because they recognize how failure can occur and design accordingly. Because today's designs are pushed to the limit in terms of complexity, thorough knowledge of failure is imperative. A crewed mission to Mars would be an example of a highly complex project with a higher probability of failure. In a world of ever-increasing complexity, knowledge truly is power.

Essentially, Petroski highlights just how successful engineers can be when they choose to learn from failure. His book is one of my top ten all-time favorites because it remains as important today as it was over 35 years ago. I encourage everyone in the Metrology community to read it.

-Henry Zumbrun, Morehouse Instrument Company

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Companies around the globe rely on Morehouse for accuracy and speed.

Our measurement uncertainties are 10-50 times lower than the competition.

We turn around your equipment in 7-10 business days so you can return to work quickly, saving you money.

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