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Main Menu > 5: Learning About Risks > What Are The Odds? 
What are the odds?

Would you bet a month's spending money on a spin of the roulette wheel? Would your lucky number be the winner? The odds against your winning are 35 to 1. Not interested? Maybe you'd rather go skydiving. You won't win (or lose) any money, and the chances you'll become a fatal statistic are only 1 in 57,000, a safer bet. And if you prepare everything exactly as you should, jumping out of a plane and hurtling 12,000 feet toward the ground at 120 miles per hour should be a snap.


Making all those precious preparations is called "risk management." It's based on the premise that even if we can't control the outcome of certain actions or events, we can at least plan ahead as carefully as possible to avoid potential pitfalls. The residual risk that remains after all known associated hazards have been assessed and accepted is called "acceptable risk."


Some people take more than their share of risks every day. According to the Bureau of Labor Statistics, the group that holds down the most dangerous occupation in the U.S. are fishermen (and women!), who are 21.3 times more likely to have a fatal accident on the job than the average worker. The next most dangerous job is timber cutter (at 20.6) followed by airplane pilots (19.9).

This graph shows the index of relative risk in relation to occupations in the U.S. (Click for larger image.)

An occupation that doesn’t even make the list of dangerous jobs, but which some people consider the riskiest job of all, is astronaut. Besides the obvious dangers inherent in being shot into space, there are quite a few minor health risks that astronauts incur while on the job:

  • Living at zero gravity can cause muscles to atrophy, disrupt blood circulation, and make bones porous (which can also lead to tooth loss).
  • Because astronauts take in less fluid than the average person, they have a higher risk of developing kidney stones.
  • Then there's space junk, the 10,000 or so large objects—everything from old satellites to discarded fuel tanks—that pose the threat of possible collisions with spacecraft—and spacewalkers. This is not to mention all the tiny objects out there, which can be just as dangerous.


But perhaps the greatest health danger an astronaut faces comes from the Sun. Astronauts working outside a spacecraft—on the Moon, for example—during a major solar particle event could receive a dose of 6 sieverts (Sv) of radiation to the skin, equal to 600 rem, short for "roentgen equivalent men." Rem are defined as the dosage of any ionizing radiation that will cause the same amount of biological injury to human tissue as one roentgen of x-ray or gamma-ray dosage. That same solar event would cause a bone marrow dose of close to 0.9 Sv (90 rem), something like 500 to 1,000 times higher than the dose one receives from a chest x-ray.

While the experts point out that such a high dose isn’t life-threatening, they mention a variety of long- and short-term consequences. A skin exposure of 6 Sv will, in about 50% of cases, cause visible reddening, and an increased risk of skin cancer in later years because of damage to the skin. It's also likely that the astronaut would temporarily lose all of his or her hair. Male astronauts would likely experience temporary sterility (for 10-20 months). And it's generally accepted that there is an increased risk of cancer as a result of a whole-body radiation exposure of this intensity.


For all you non-astronauts who think you can hide from radiation by staying home, be advised that all of us, indoors or out, receive about 300 mrem a year in natural background radiation.

Related to chapter 5 in the print guide.
Related Materials

Learn how astronauts and scientists study harmful radiation in orbit with in the Phantom Torso article.

Hear from the astronauts themselves in Interview With Astronauts movie.

Glossary Terms

Click for the definitions of the following words that are used on this page: (Definitions appear in a pop-up window.)


View the full, printable version of the glossary.

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