Captain Joyce May, a commercial airline pilot, says, "By the time you're at normal jet cruising altitude of, say, 39,000 feet, the total radiation is about 64 times greater than what it is at sea level."
"People who work in the nuclear power industry on an average basis are getting 1.6. There are people who fly in airplanes who are getting 2 or 3 or 4 milliSieverts per year. So they are truly radiation workers."
http://www.sciencedaily.com/videos/2...ation_risk.htm