Yes, travel at the typical altitudes of commercial aircraft involves a measurable increase in exposure to natural ionizing radiation. This occurs at elevations of 30,000 to 40,000 feet, where the Earth’s atmosphere provides less protection than it does at ground level. This increased radiation dose affects all passengers and crew, regardless of the flight’s duration or destination.
Cosmic Rays The Source of Aviation Radiation
The radiation encountered during flight originates primarily from cosmic rays, which are high-energy particles traveling through space. These particles are composed mostly of protons and atomic nuclei, originating either from outside the solar system (galactic cosmic rays) or from the sun (solar particle events). The Earth’s magnetic field and atmosphere act as two layers of defense, significantly shielding the planet’s surface from this constant bombardment.
At cruising altitudes, the aircraft is above most of the atmospheric shielding, causing the radiation exposure rate to increase significantly compared to sea level. When primary cosmic rays strike air atoms in the upper atmosphere, they trigger a cascade of nuclear reactions that create a shower of secondary radiation. This secondary radiation field consists of various subatomic particles, with neutrons being a major contributor to the radiation dose received inside the cabin.
The magnitude of this exposure is not uniform and depends on several factors related to the flight path. Radiation exposure increases with altitude because less atmosphere remains above the aircraft to attenuate the cosmic rays. Exposure also increases at higher latitudes, particularly on polar routes, because the Earth’s magnetic field directs more cosmic radiation toward the poles and away from the equator. Furthermore, intense, though infrequent, solar particle events can cause short-lived but significant spikes in the radiation dose.
Quantifying Radiation Dose During Flight
The amount of radiation absorbed is measured using the unit of effective dose, the sievert (Sv). This is commonly expressed in smaller units, the millisievert (mSv) or the microsievert (µSv). The dose received during a single flight is generally quite small, but it varies depending on the flight’s duration, altitude, and latitude.
For example, a round-trip transatlantic flight between Frankfurt and New York typically results in an effective dose of about 100 µSv. A long cross-country flight within the United States, such as from the East Coast to the West Coast, exposes a passenger to approximately 35 µSv. These single-flight doses are often compared to other common radiation sources.
A ten-hour flight results in an exposure roughly equivalent to that from a standard chest X-ray, which delivers about 0.1 mSv. The average person receives an annual dose from natural background radiation on Earth of approximately 2.1 to 3.0 mSv. The 100 µSv from a transatlantic round trip adds about five percent to the average person’s annual natural radiation exposure.
The radiation dose rate at typical cruising altitudes of 10,000 meters is approximately 15 times greater than the average dose rate at the Earth’s surface. However, the exposure from a flight is a transient event, whereas natural background radiation is a constant exposure over a full year. The accumulated dose from a year of constant exposure to natural background radiation is equivalent to about 600 hours of continuous flying at altitude.
Health Considerations for Frequent Flyers
While the occasional passenger receives a negligible dose, the concern shifts to individuals whose occupation requires frequent flying, such as pilots and flight attendants. Aircrew are considered occupationally exposed to ionizing radiation due to their cumulative time at high altitudes. Regulatory bodies, such as the ICRP, recommend an occupational dose limit of 20 mSv per year, averaged over five years.
The average annual cosmic radiation dose for aircrew is well below this occupational limit, typically ranging from 2 mSv to 6 mSv per year, depending on their routes and flight hours. Those who fly long-haul routes, particularly over the poles, are at the higher end of this range. The ICRP recommends that airlines implement a dose reference level, often in the 5 to 10 mSv per year range, to manage the exposure of their most frequently flying personnel.
Pregnant flight crew members are a specific concern due to the sensitivity of the developing fetus to radiation exposure. International guidelines recommend that the dose to the fetus, from the time pregnancy is declared, should not exceed 1 mSv. For pregnant aircrew, this often means adjusting flight schedules to reduce exposure for the remainder of the pregnancy. Research has suggested that exposure above 0.36 mSv in the first trimester may be linked to an increased risk of miscarriage.
Frequent business travelers, whose flight time may approach that of aircrew, are also advised to assess their personal cumulative exposure. These individuals may choose to adjust their travel frequency or routes to minimize their lifetime dose. For all frequent flyers, the cumulative dose over a career or lifetime is the primary metric used in assessing potential long-term health risks.