Why the Towers Fell - Embedded.com

Why the Towers Fell

They didn't all die. Thousands of them escaped the inferno; thousands of families were not shattered. Structures designed merely as office spaces absorbed planes, burned, and stood for a time as their denizens made their way to safety. An engineer's work, so boring to most people, saved so many lives.

This week we'll remember the horrific events of a year ago. The nation and the world will celebrate the rescue workers' bravery and mourn the dead. Like so many others I watched the towers burn, aghast. During that hour never in the deepest recesses of my mind did I imagine they would collapse. Yet raging fires ignited by cruelly deployed jet fuel softened steel and snapped connections till the structures could stand no longer.

Sales of the Koran and books about Islam jumped as the nation sought understanding rather than ethnic condemnation. I felt proud to be an American as we groped for insight rather than lashing out in revenge.

And I felt proud again this week, watching a NOVA program, Why The Towers Fell , broadcast on PBS channels. The show described the investigation into the engineering of the buildings. It showed clearly the steps leading to their collapse, without a hint of accusation or blame. No scapegoats were sought, no malfeasance exposed other than that of the sick perpetrators.

As engineers we're trained to examine problems dispassionately, yet this show was hardly dispassionate. Poignant, painful images again seared the soul, tempered with interviews with the designers and forensic engineers.

The central character: Leslie Robertson, the World Trade Center's structural engineer, the man who designed the buildings over 30 years ago. The haunted look in his eyes shouted a tale of personal agony more clearly than words. The producers treated Robertson gently, maybe even heroically, showing how his design saved many lives. If the buildings had been knocked over, whole swaths of Manhattan would have been leveled; instead, they pancaked straight down despite the awesome sideways force imparted by the impacting aircraft. The buildings stood, absorbing the fires, until many thousands evacuated.

A horrible failure, certainly, but one tinged with elements of success.

But a failure nonetheless. Everything can fail. There is no way to design a structure or an embedded system that's immune from any imaginable or unimaginable insult. America often deals poorly with failures. I remember the hysteria surrounding Challenger's explosion, another awful event that now seems like a shadow of happier times. Reporters asked NASA officials how they could ensure such a calamity would never reoccur. What a dumb question! Anything flung into space atop 6 million pounds of explosives is a disaster held at bay by perfect engineering, unstinting QA and perpetually enlightened management. Though the unethical behavior of Thiokol's program managers was the proximate cause of the explosion, things fail, for both technical and human reasons. Perfection is too high of a standard for mere humans to attain.

Build it, and it will break. Challenger was a total failure consuming her entire crew, as was the Apollo 1 fire so many years earlier. The World Trade Center was a total failure, too, but one mediated by a design that gave a bit of desperately needed time to the occupants.

I salute Leslie Robertson. Though the program showed a man who appeared riddled with guilt, tormented by the imperfections in his creation, his work saved thousands. That's the legacy of heroes.

Jack G. Ganssle is a lecturer and consultant on embedded development issues. He conducts seminars on embedded systems and helps companies with their embedded challenges. He founded two companies specializing in embedded systems. Contact him at . His website is .

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Reader Feedback

Good Article — suggest some embedded systems Gems like:

1) Don't takeoff and do design without a safety analysis (www.safeware.com)(At least a hundred good ideashere)

2) Have a good reset scheme that does an orderly startup and shut down for your processors.

3) Have a good watchdog timer scheme so that if the code does go in the weeds something sets it back on track.

4) check over the data before writing it to your flash/eeprom memory. (buffer and CRC/Checksum) Also a good idea to check it when you get it back out of the flash or eeprom.

5) Keep backup data on your design/system off site so that it can be rebuilt
a) if the customer site is lost
b) if your site is lost

Bill Murray


I work on Long Island now, but for a few years I used to work in the city, traveling through the Towers to the Amex building across the West side Hwy. The immensity of the towers always filled me with a sense of awe – that people could concieve, construct and operate such an endeavour.

I originally worked on the Space coast, and watched Apollo 16, 17, ASTP, Skylab and the first two shuttle missions from the visitors center. I also got to take an impressive tour of the VAB as Apollo 17 was being assembled. Again, the impression of a vast organization working towards an incredible goal stays with me to this day.

Many will castigate either the designers of the towers, the engineers involved with Apollo 1, Challenger, and any future disasters – yes there will be future disasters as sure as the sun rises. In some cases there may be criminal resposibility – those that knew better decided to ignore problems, banking on statistics to bail them out. But most will be repsonsible people, doing their best.

Anyone who has read the chain of events behind the Apollo 13 explosion, or who has read NTSB reports on civil aviation accidents will understand that the most improbable chain of events can form and lead to a catastrophic accident.

Certainly, the lessons learned from the Towers collapse will be taught to engineers in the future. Buildings will be safer. People will be more aware of the dangers involved in spaceflight – and yes I share your disdain for anyone who doesn't understand that sitting your tail on a few million pounds of hi explosive isn't dangerous.

But the destruction of the Towers only affirms and old adage – in the battle between warhead and armor, warheads always win. No matter how great a job future engineers do in the future, a concerted effort to destroy will almost always succeed.

Yet as Americans, we can stand confident in knowing that no matter how much adversity we will face, we won't collapse. America was attacked because it stands for things – freedom, justice and the rights we cherish and safeguard and have fought for for over 200 years.

The Bin Ladens, the Husseins, Hitlers and all the other little men who have made such misery in this world will eventually be a footnote – referenced only as persons who sought to deny the truth and freedom to others – and remembered as having been defeated by the free people they challenged.

Tom Mazowiesky
Global Payment Technologies, Inc.

JACK REPLIES: As I recall Jules Verne wrote, in From the Earth to the Moon, about the battle between the canon makers and the armour makers. The armour folks always played catch-up, and were incensed when Verne's protagonists planned a canon large enough to shoot people to the moon.

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