January 3, 1997
Accident, n. inevitable occurrence due to the action of immutable natural laws.
Ambrose Bierce, 1911
After a tragic accident occurs, many people think that "they should have known better than to do that." We forget that the way that accidents are avoided is that one accident occurs and people find out that something doesn't work or is dangerous.
After a good deal of what turned out to be a lot of crap about sabotage, terrorism and crime, the National Transportation and Safety Board(NTSB) believes that the most likely explanation for the crash of the B747 (TWA flight 800) was the explosion of the center fuel tank. A combination of factors may have contributed to this. First, the plane flies better when the wing tanks are relatively full and the center tanks are relatively empty. On short flights, the center tanks are often left empty because they constitute so much dead weight. Lest you wonder why the tank was empty on TWA 800, the distance from New York to Paris is about half the distance from San Francisco to Tokyo. The air conditioners are located under the center fuel tanks and in TWA flight 800, had been running for two hours while the plane was on the ground.Air conditioners produce lots of heat which can be expected to vaporize some of the fuel, creating a potentially explosive mixture of fuel vapor and air. All that it takes is a spark to explode it, and the investigators also have a theory about where that spark might have come from. We can be pretty sure that, almost immediately, steps will be taken to prevent this from ever happening again. Eventually, aircraft design will be such that such an accident will become just about impossible.
The question is: Is it necessary to cost lives in order for accidents to be prevented? The answer is an unequivocal "YES!" If we are lucky, many of the potentially lethal problems will be discovered in test flights or when there are few passengers, but it can never eliminate all problems -just the easily found problems.
The classic engineering goof was in the design of the Tacoma Narrows suspension bridge. There is a movie of that bridge that shows the bridge twisting and contorting in the wind, vibrating in a certain frequency that resulted in the bridge tearing apart. It was such a beautiful bridge too. No engineer will ever make that mistake again.
I had a peripheral role in one of the big goofs. I was at the University of Buffalo at the time that they were developing systems for sending men into space. One thing that the engineers tried to do was to eliminate any weight that wasn't essential. A physiologist came to me and told me that they were experimenting with an atmosphere of pure oxygen at one twentieth of an atmosphere of pressure.This would eliminate the inert gas nitrogen, which was believed to be dead weight; something that was of no use whatever. He asked me what test could be performed that would test whether this atmosphere was truly physiological. I proposed that they put several pairs of mice in such an atmosphere and allow them to breed. If they bred and had and raised a normal liter, it would be a good test of whether the atmosphere was okay. They did it and it worked. I was very proud of my tiny role in the space program until that day when there was a relatively minor electrical fire in the capsule that burned out of control and killed the whole crew of the capsule while it was on the ground. Apparently the nitrogen has another role in that it buffered the combustion support of oxygen. It was something that should have been realized because everyone who has had an elementary science course has seen a demonstration where a piece of steel wool will burst into flames in an atmosphere of pure oxygen. Somehow, no one figured that it would be important. -But it was very important to three astronauts.
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