This April, business traveler Tom Stucker has flown 18 million miles (nearly 29 million kilometers) over the past 14 years. That’s a huge amount of time in the air.
He may have eaten about 6500 meals on board, watched thousands of movies, and visited the restroom on the plane more than 10 times. He also accumulated a radiation dose equivalent to about 000 chest x-rays. But what is the health risk of such a dose of radiation?
You might think that the frequent flyer’s radiation dose comes from airport security checkpoints, full-body scanners, and hand-held x-ray machines. But you are wrong. The main source of radiation exposure from air travel is the flight itself. At higher altitudes, the air becomes thinner. The higher you fly from the surface of the Earth, the fewer gas molecules are contained in space. Thus, fewer molecules means less atmospheric shielding, and therefore more exposure to radiation from space.
Astronauts who travel outside the Earth’s atmosphere receive the highest doses of radiation. In fact, the accumulation of radiation dose is the limiting factor for the maximum length of manned space flights. Due to long stays in space, astronauts are at risk of getting cataracts, cancer and heart disease upon returning home. Irradiation is a major concern for Elon Musk’s goal of colonizing Mars. A long stay on Mars with its extremely ton atmosphere would be fatal precisely because of the high doses of radiation, despite the successful colonization of the planet by Matt Damon in the movie The Martian.
Let’s get back to the traveller. What will be the total radiation dose of Stucker and how much his health will suffer?
It all depends on how much time he spent in the air. If we take the average speed of the aircraft (550 miles per hour), then 18 million miles were flown in 32 hours, which is 727 years. The radiation dose rate at a standard altitude (3,7 feet) is about 35 millisievert per hour (a sievert is a unit of effective and equivalent dose of ionizing radiation that can be used to assess cancer risk).
By multiplying the dose rate by the hours of flight, we can see that Stucker earned himself not only many free air tickets, but also about 100 millisieverts of exposure.
The primary health risk at this dose level is an increased risk of some cancers in the future. Studies of atomic bomb victims and patients after radiation therapy have allowed scientists to estimate the risk of developing cancer for any given dose of radiation. All other things being equal, if low doses have risk levels proportional to high doses, then an overall cancer rate of 0,005% per millisievert is a reasonable and commonly used estimate. Thus, a 100 millisievert dose of Stucker increased the risk of potentially fatal cancer by about 0,5%.
Then the question arises: is this a high risk level?
Most people underestimate their personal risk of dying from cancer. Although the exact number is debatable, it is fair to say that about 25% of all men end their lives due to cancer. Stucker’s cancer risk from radiation would have to be added to his baseline risk, and thus it could be 25,5%. An increase in cancer risk of this size is too small to be measured in any scientific way, so it should remain a theoretical increase in risk.
If 200 male travelers were to fly 18 miles like Stucker, we might expect only one of them to shorten their lives due to flight time. The other 000 men were unlikely to have been harmed.
But what about ordinary people who fly several times a year?
If you want to know your personal risk of death from radiation, you need to estimate all of your miles traveled over the years. Assuming that the speed, dose and risk values and parameters given above for Stucker are also correct for you. Dividing your total miles by 3 will give you an approximate chance of getting cancer from your flights.
For example, you have flown 370 miles. When divided, this equals 000/1 chance of developing cancer (or a 10% increase in risk). Most people don’t fly 000 miles in their lifetime, which is about the same as 0,01 flights from Los Angeles to New York.
So for the average traveler, the risk is much less than 0,01%. To make your understanding of the “problem” complete, make a list of all the benefits that you have received from your flights (the possibility of business trips, vacation trips, family visits, etc.), and then look again at this 0,01%. If you think your benefits were meager compared to your increased cancer risk, then you might want to stop flying. But for many people today, flying is a necessity of life, and the tiny increase in risk is worth it.