Sunday, October 04, 2009

The radiation dose to Formula One

Frequent business flyers, such as the team members and media representatives who fly to every Grand Prix in the Formula One World Championship, are subjected to a radiation dose which can exceed that received by workers in the nuclear industry. In fact, "estimates of potential exposures of aircrew and frequent travellers, validated by on-board measurements carried out by carriers in the United States, Canada and Europe, indicate that these groups sometimes receive exposures above the limits for the general public, and should be categorized as occupationally exposed." (Lawrence Townsend 2001, Radiation exposures of aircrew in high altitude flight, Journal of Radiological Protection, Vol. 21 pp5-8).

This dose to frequent flyers comes ultimately from galactic cosmic rays, 90% of which are high-energy protons, and 10% of which are alpha particles. These high-energy particles collide with the nuclei of atoms in the atmosphere, creating secondary particles. The dominant contribution to the radiation dose received by frequent flyers comes from the neutrons created in such reactions.

The dose varies with the 11-year solar cycle, and increases with latitude and altitude. Nevertheless, an estimate can be made of the dose to the Formula One community by taking some ballpark figures. Before launching into the calculation, it should be noted that radiation dose is estimated in units called Sieverts (Sv). The milli-sievert (mSv) is a thousandth of a Sievert, and the micro-sievert (μSv) is a millionth of a Sievert.

To estimate the average annual dose, we need to know the average dose-rate per hour, and the number of hours flown per year. Townsend reports that at typical commercial jet altitudes (30,000-40,000 ft), the dose-rate is 5-10 micro-sievert per hour. The US National Commission for Radiological Protection (NCRP) has produced a report in which this dose-rate is taken to be 20 micro-sievert per hour (NCRP Commentary No 12), but let us take 10 micro-sievert per hour as a more conservative figure.

In terms of the number of hours flown, there are 10 long-haul destinations on next year's 19-race Formula One calendar (Bahrain, Australia, Malaysia, China, Canada, Singapore, Japan, South Korea, Abu Dhabi, and Brazil). Taking round figures again, each one of these races involves a 10-hour flight each way (neglecting the fact that the Formula One community will fly direct from Singapore to Japan). That's approximately 200 flying hours to and from the long-haul races alone. Let's be conservative and neglect the additional flying hours to the European races. The total annual dose is still:

10 micro-sievert per hour * 200 = 2,000 μSv = 2 mSv.

Thus, over a 25-year career in Formula One, the cumulative dose will be 50 mSv. Now, the International Commission on Radiological Protection (ICRP) estimate that the risk of acquiring a fatal cancer from radiation exposure is per 5% per Sievert. That means that for a cumulative dose of 50 mSv = 0.05 Sv, the risk is only 0.25%. The background level of fatal cancer in the population is about 25%, so an individual pursuing a 25-year career in Formula One will experience only a one-in-a-hundred increase in the pre-existing risk of acquiring a fatal cancer.

However, there are a large number of people who fly to every Grand Prix, so we can also work out the collective dose. If we assume that there is a core of 1,000 people who fly to every race, then if the cumulative dose per person over a 25-year career is 0.05 Sv, the collective dose will be:

0.05 Sv * 1,000 = 50 Sv.

With the risk of a fatal cancer being 5% per Sievert, this entails that 2.5 people amongst the Formula One community can be expected to acquire a fatal cancer due to their exposure to cosmic radiation.


Anonymous said...

I guess the additional radiation doses and increased cancer risks could be seem as some sort of payback for the contributions made by the flights to global warning. Seems like a neat compromise.

Dan Sickles said...

Frequent fryers?

Alexander Kruel said...

Now you could look for some data on cancer and professional pilots and or flight attendants to see how your guess does match with reality...

Sean said...

Thats just blackboard numbers Gordon, I don't doubt the numbers but how they pan out in the real world is the critical issue.

For example, its more likely that before the cancer develops other cancers from greater risks might get you first?

This is a link

1% of all cancer deaths are apparently linked to Radon gases, even more on the continent, so that would present a more serious risk to worry about?>

This is the problem with trying to model stuff, you end up in no mans land.

If you want to set up a study group, I will be a willing guinea pig, just pop the flight, hotel, and race tickets in the post 2 weeks before every GP, I will pay my own food and drinks bill :0)

Gordon McCabe said...

Very droll Dan! :-)

If I recall, epidemiological studies of aircrew suffer from conflating factors, due to the 'unusual lifestyles' of aircrew...