Answer to Question #1764 Submitted to "Ask the Experts"

Q

For pilots flying below 6,000 feet for about 200 hours a year is there any danger from cosmic radiation? I know the annual dosage should not exceed 1 millisievert per annum (according to the UK Air Navigation Order) but what would the dosage be at or below 6,000 feet? Many thanks. Bob Bewley

A

Even at ground level, cosmic radiation is part of our normal environment. The Earth's atmosphere absorbs this radiation, so its intensity is least at ground level. The altitude of interest in this question, 6,000 feet (1,800 m), is, of course, ground level in many places. Using the CARI-6 program available from the Federal Aviation Administration, I calculated the cosmic ray dose rate at this altitude at high geographic latitude to be about 0.1 microsievert per hour. It would, therefore, require 10,000 hours of flying at this altitude to reach the 1 millisievert annual limit recommended as a maximum for members of the public exposed to ionizing radiation. It should also be noted that exposures well above this 1 mSv limit are not "dangerous." Radiation workers are allowed 20 times this level in the European Union, and that limit is not even close to a threshold of measurable harm. It is only an administrative level set so that the expected incidence of risk to any individual in the whole exposed worker population would be comparable to other work-related injuries that can occur in any occupation.

Robert J. Barish, PhD, CHP, DABR, DABMP, FAAPM