How Many Flights From San Francisco To Washington DC Would It Take To Contaminate The Drinking Water Which The Flight Crew And

Dear Leo,

I think you might be misunderstanding the point of the airplane flight dose comparison, so I would like to repeat and extend my earlier comments about it:

First, I would urge you to read the FAQ on Total Effective Dose Equivalent and the FAQ on comparing dose from airplane flights to other doses.

The "airplane dose" comes from an increased exposure to cosmic rays at higher altitudes — cosmic rays are high-energy particles that pass happily through the hull of the aircraft and through our bodies. They give us a measurable radiation dose, and this happens continually to us even on the surface of the earth. At higher altitudes, there are slightly more cosmic rays, and the difference can actually be measured. For the most part, cosmic rays are ionizing, but they do not induce very much activity in other materials, so the elevated radiation dose is experienced only during the duration of the flight.

In the end, the idea is that doses from different sources — internal vs. external, full-body vs. single tissue, alpha vs. beta vs. gamma — can be compared after applying the appropriate weights to each. The point of comparing doses is not that exactly the same kind of radioactivity is going on, but the dose is a quantity that can be calculated from the different sources and compared.

To try and make a crude analogy here, radiation dose is something like heat. Say we have a car idling in a parking lot. There are different sources of heat on it — light from the sun, infrared radiation from the hot pavement, heat from being in contact with the air, and of course heat generated by the chemical reaction of internal combustion. If we study each component in detail, we could make a model for how much heat is added to the car from each source and compare them. Heat is the common quantity here.

Now say we have a flashlight in the car and we turn it on. How much additional heat does it add? Well, if we study how much light is produced, and how much heat is dissipated by the current flowing through the bulb, we could come up with an estimate of the added "heat dose" to the car. The flashlight is different from the other sources, but that doesn't mean that we can't compare the heat that it generates to other sources of heat. For example, we could say how many flashlights would be equivalent to the heat that the sun adds to the car, or how many flashlights would be equivalent to the heat that the engine adds to the car. The equivalence is illogical in the sense that maybe 1,000,000 flashlights would be needed to equate to one "sun dose," and you could never fit all those flashlights into a single car. But it is logical in the sense that the comparison gives the scale of the heat from the flashlight in terms of something that we might have more experience with.

So when you have a quantity that can be hard to visualize, like heat — or going back to the situation at hand, radiation dose — the question becomes how best to compare one quantity that is not well-understood with one that is. We have chosen the "airplane dose" as our dose comparison. It is not perfect, but at least it is something that many people have experience with and know is not much of a radiological risk. And it's a lot better than some other comparisons (e.g., banana equivalent dose).

If you have further issues about the dose equivalences, please bring up those specific points and we can discuss them.

Mark [BRAWM Team Member]