Answer to Question #9770 Submitted to "Ask the Experts"
The following question was answered by an expert in the appropriate field:
What is considered too much radiation exposure for an infant? I have a four-month-old son, and he will be traveling with me on four domestic airplane trips within a 10-day period. There will be one connection each way, for a total of eight airplane flights (about 15 hours total in flight). I am curious if this is too much time for him to be spending at high altitudes in an airplane.
For the travel you describe, there is really no risk. As a starting point to understanding this, I suggest that you look at the web page of the US Environmental Protection Agency (EPA) where you can calculate your radiation dose.
Looking only at the external sources of natural background radiation, those that can be computed using the first three sections of this official government dose calculator, one can see that the external radiation dose can vary a great deal, depending on where you and your child reside. These natural variations are due to increased levels of cosmic radiation in cities at high altitudes compared with those at sea level, as well as to differences caused by varying concentrations of naturally occurring radioactive elements in the soil and rocks as a function of differing locations across our continent.
When setting standards for radiation safety, the organizations that are responsible for determining acceptable exposure levels for members of the public, including children, have decided that an annual exposure about equal to this natural variation, i.e., 1 millisievert (mSv), is an acceptable level that carries with it no demonstrable risk. After all, if that magnitude of exposure was truly dangerous, then whole cities such as Denver (at high altitude in the Rocky Mountains) would have to be evacuated because of the increased risk of harm from background radiation in those locales.
Looking a bit farther down the dose calculator, you can see that the EPA calculator adds 1 millirem (mrem, or 0.01 mSv) dose for every 1,000 miles (1,600 kilometers [km]) traveled by air.* Assuming a typical air speed of 800 km per hour (km h-1) and ignoring the lower doses associated with the takeoff and landing altitude changes (of which you will have several), your 15 hours in an aircraft would imply, at most, 12,000 km of air travel—producing an increased exposure of 0.075 mSv. This is only 7.5% of 1 mSv, the legal limit of radiation exposure for any member of the public (including children) that is enforced in all jurisdictions of the country, as a matter of law, for public exposures that are caused by ground-based industrial, medical, educational, or other facilities where radiation is produced.
And because it is only a small percentage of the natural-background radiation difference between many places in the country, it should be of no real concern to you. It is not a worrisome health hazard.
For flight crew members who are in the air for hundreds of hours every year, over their entire working careers, the increased risk of cancer or some other unwanted health problem may possibly be increased by a percent or two compared with the population as a whole. For casual travel of the sort you describe, there is really no risk, whether you are 4 months, 4 years, or 40 years old.
Robert J. Barish, PhD, CHP
* The radiation dose and distance are given here in mrem and miles, respectively (called traditional units) because those are the units used by the EPA. However, the Health Physics Society has adopted the International System (SI) for units and these are given in parentheses.