Book Reviews : Fail-Succeed Paradox Plays a Role in Engineers' Design

To Engineer Is Human; The Role of Failure in Successful Design by Henry Petroski (St. Martin's: $16.95)

Failure can sire success, while success can breed failure. A Chestertonian type of paradox, that is the theme--though never stated in those exact words--of this serious, amusing, probing, sometimes frightening and always literate study.

The first element of the paradox is the easier to comprehend. When a machine fails, be it a bridge, an airplane or an electric toaster, it causes examination into just what broke and why. Then the structurally weak part can be redesigned, the quality of the manufacture or maintenance can be improved, or other action can be taken to ensure the non-repetition of the breakdown.

Thus, future machines will not have that flaw and will be successful; if the break-study-redesign process is part of the machine's total design evolution, the product will be successful from its public introduction.

But does continued use without breakdown necessarily mean success? The author turns to the old nursery tale of the Three Little Pigs and the Big Bad Wolf; if the wolf had not attacked the houses, the pigs would not have known that those of straw and twigs were unsuccessful designs--until some future pig had his house blown down around his ears by a latter-day wolf.

Probability of Wolves

The twig design was successful and the brick house was overbuilt as long as there were no wolves around. What was the probability of wolves?

A compromise between strength and such factors as cost, construction time and effort or just plan livability always must be made; we design buildings and bridges, not to withstand the greatest conceivable earthquake, but to hold up under the greatest that is reasonably likely to occur.

Such predictions are always uncertain and usually not made by the engineer. Only if the structure fails under a stress it supposedly should have survived is the engineer at fault.

But this book is not an apologia for the engineer.

Successful designs are copied. There is a natural tendency to disregard the fact that the original design was as close as was prudent to the limit imposed by the necessary safety factor and to make the copies smaller, lighter, simpler, to be cheaper and prettier. The final result can be the catastrophic 1940 destruction of the Tacoma Narrows bridge by a moderate 42-m.p.h. wind.

Further, there is what Petroski calls the cause behind the cause. Faulty engine maintenance practices are thought to have caused the 1979 Chicago crash of a DC-10, but the writer suggests that the design engineer should have foreseen and guarded against less-than-perfect maintenance.

There are also such things as inattention, such as the not-done analysis of the redesign of walkway supports that is thought to have caused 114 deaths in the 1981 collapse of those walkways in the atrium lobby of the Kansas City Hyatt Regency hotel.

Petroski's style is simple yet capable of expressing subtle and complicated notions. He can blend nursery tales or the myth of Icarus with reports of scientific societies or testimony before governmental bodies and achieve a flowing narrative.

And he has succeeded in something very difficult. He has written a book interesting and instructional to both the layman and the professional.

Neither Gods Nor Devils

The layman can learn to understand that engineers are neither gods nor devils but only human beings; for the most part smart human beings--very smart indeed, the best of them--but not omniscient. Sure-footed as they are almost all the time, they will occasionally stumble, but those stumbles can teach them how to avoid stumbling next time.

The engineer can learn to understand the same thing about himself and his fellow professionals. He can also be warned against some human tendencies that too often go unnoticed and against some dangerous trends--for instance, the growing use of computers in design by those who do not understand their limitations.

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