Answer to Question #10180 Submitted to "Ask the Experts"

Category: Environmental and Background Radiation — Airplanes

The following question was answered by an expert in the appropriate field:


Please advise me about radiation from solar flares. I am due to travel this evening from Miami to London with two small children and wonder if I should change tickets. According to the news, today's solar flare is the worst in five to seven years.


For up-to-date information on the current solar flare, please look at the National Oceanic and Atmospheric Administration website.

The green line on this graph shows the intensity of radiation particles that have sufficient energy to impact airline passengers and crew members.

Notice that there is a horizontal dashed line running across the picture at a level of 10 (which in scientific notation is 10 to the power of 1 or 101).

I recommend that if it is not inconvenient to do so, one should consider waiting until that green line comes down below the dashed horizontal line.

It is only if the green line goes above the next line up, a value of 100 (10 to the power of 2 or 102, to us scientists) that I strongly suggest a postponement. Generally this would be a few hours at most.

For this particular flare, at the time I am writing this, the intensity of the green line (which updates on the plot every five minutes) is trending downward, so I think that if you are traveling in a few hours there should be no problem.

I recommend that you stay in touch with someone who can view this up until departure time who can let you know that there has not been a sudden upsurge in the intensity of those high-energy particles that will be evidenced by a change in the "wrong" direction (upward) of that green line.

Of course, if such a major change occurs while you are in the air, you will have to rely on the policy of the airline as to whether the crew will change the altitude or take other actions to lower the radiation dose to passengers and crew. After all, it is the airline's employees who fly all the time who are at more risk than casual travelers who might encounter something like this once in their lifetimes.

All of this is specifically addressed in detail in Appendix C of my book The Invisible Passenger: Radiation Risks for People Who Fly, 2nd Edition (Advanced Medical Publishing, Madison, WI; 2008 ISBN13 978-1-883526-13-2).  

That appendix is titled "How to Know if There Is a Solar Particle Event in Progress" and explains the above in much greater detail, as of course does the entire book.

Robert Barish, PhD, CHP, FAAPM

Answer posted on 9 March 2012. The information posted on this web page is intended as general reference information only. Specific facts and circumstances may affect the applicability of concepts, materials, and information described herein. The information provided is not a substitute for professional advice and should not be relied upon in the absence of such professional advice. To the best of our knowledge, answers are correct at the time they are posted. Be advised that over time, requirements could change, new data could be made available, and Internet links could change, affecting the correctness of the answers. Answers are the professional opinions of the expert responding to each question; they do not necessarily represent the position of the Health Physics Society.