How Much Cosmic Radiation Is Too Much?

Hello, and welcome to the podcast. How much cosmic radiation is too much? Cosmic radiation has been a known risk to aviation personnel for years but how much is too much radiation? How can you control your exposure? What should operators do to protect their employees?

Let’s define some terms.

• Cosmic radiation (sometimes referred to as ionizing radiation) means radiation consisting mainly of charged particles originating from galactic and solar events.
• The FAA defines ionizing radiation as subatomic particles of matter (g., neutrons, protons, and electrons) and massless particles of energy (X-rays and gamma rays), with each particle having sufficient energy so that, on interacting with a material, it can cause an atom to lose an orbital electron. Low levels of ionizing radiation are a normal part of our environment. Substances that emit ionizing radiation are present in every cell in the body.
• Effective dose means the unit equal to the equivalent dose in a tissue or organ of the human body, which is multiplied by a corresponding tissue weighting factor and summed over the tissues and organs.
• Millisievert (mSv) is the unit used by the International System of Units to express the effective dose.
• Occupational exposure means exposure caused by cosmic radiation incurred by employees working, in this case, on board aircraft.

What Are The Dose Limits?

In Canada, the Canadian Nuclear Safety Commission (CNSC) sets radiation dose limits for exposures arising from nuclear facilities or nuclear substances. The provincial and federal governments set radiation dose limits for exposures arising from X-rays.

Internationally, the International Commission on Radiological Protection (ICRP) recommends the occupational exposure limit for workers should not exceed an effective dose of 20 mSv per year averaged over 5 years, with not more than 50 mSv in any single year. However, the international body also recommends that the exposure limit for the general public should not exceed an effective dose of 1 mSv per year. So, 20 for workers and 1 for the general public, that’s interesting.

There have been many studies into the cosmic radiation effects on aviation employees and frequent flyers.

The FAA determined that ionizing radiation from natural sources is considered occupational exposure because of the high levels of galactic cosmic radiation at cruise altitudes. So, all the exposure in your life should be included in your total, not just the amount incurred at work. In 2000, the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) ranked aircrews as the fourth most exposed group of employees, with an average annual effective dose of 3 mSv. I tried to find the report to find out which occupations were higher, but I’m guessing nuclear reactor employees and medical imaging operators are high on the list.

When You Are Flying, Where Is The Radiation Level The Highest?

In general, it has been determined that the higher the altitude, latitude, and duration of the flight, the greater the aircrew exposure. Less radiation will be received on a lower-latitude flights because of the greater amount of radiation shielding provided by the Earth’s magnetic field. This shielding is greatest near the Equator and gradually decreases to zero as you travel North or South. Galactic cosmic radiation levels over the Polar regions are about double those over the Equator at the same altitudes.

In a study undertaken by the Royal Military College of Canada, the highest measured total dose equivalent was 0.052 mSv on a route from Beijing to Vancouver at an average altitude of 35,000 feet for a total airtime of 10.5 hours. So, at that rate of .052 per flight, it would only take 10 round trips to get to 1 mSv for the annual minimum amount that triggers monitoring in medical or nuclear energy workers. 1 to 6 mSv per year is the level of exposure that is received by workers who are monitored for occupational radiation exposure in Canada. Monitoring should occur if you are receiving more than 1 mSv per year.

How Much More Cosmic Radiation Are Flight Crew Exposed to Compared to People on The Ground?

The dose rates from the natural background cosmic radiation field at altitude are typically one hundred times greater than those experienced at ground level. So, for all your flight hours your radiation exposure is 100 times higher.

Therefore, Transport Canada recommends that Canadian air operators develop a plan to manage the cosmic radiation exposure of their employees based on the likelihood of exceeding an exposure of 1 mSv annually.

The Labour Code of any particular country should provide protection for employees against cosmic radiation where the responsibility is placed on the employer to monitor the exposure. Check your local rules of course. 

So, the flight I referred to earlier from Beijing to Vancouver would take 19 flights to get to 1 mSv annually, but don’t forget about the time spent on the surface where you are always exposed to cosmic radiation, as well. The FAA determined this exposure should be part of the calculated total. The recommended maximum annual does is 20 mSv. Risk principles are employed here, and cosmic exposure should be kept “as low as reasonably achievable,” known as the ALARA principle.

An intervention level is a level at which a specific protective or remedial action is taken. It is recommended that an intervention level of 6 mSv be adopted. The 6 mSv intervention level is estimated using 3/10 of the nuclear energy worker limit.

When employees approach 6 mSv, the air operator should put measures in place to adjust their working schedule so that their subsequent flights, for the remainder of the calendar year, would result in minor additional exposure.

What Are Some Control Measures?

Control measures available to operators include managing the time of exposure, the altitude flown, and the latitude. So low flight time, and low altitude, and low latitude or close to the Equator are best.

Also, something to consider with future supersonic high-altitude flying business jets is that the exposure risk above 50,000 feet is significant. This is due to the possibility of sporadic exposure from solar flares during solar cycle maximum conditions.

This is when an overexposure could occur during a solar flare. Aircraft operating at high altitudes, particularly in the upper 40s, are more susceptible to solar flare exposure. Preparation is important, but sometimes solar flares occur without warning. If you are notified of a solar flare while inflight, then descend if you can.

Early warning notices are available on most government websites, including the U.S. Space Environment Center and Government of Canada websites.

How Do Employers or Their Radiation Contractors Predict Employee Doses?

Dose rate meters for the aircraft itself are a great idea to monitor exposure; however, research shows that radiation affects the aircraft uniformly so everyone on the flight is receiving the same amount.

The most popular method is the route dose data method, where a route is assigned a certain amount of radiation exposure which is then applied to the employee who operates it. There are different codes used to predict the correct dose for a route. There are measured codes and theoretical codes. Transport Canada developed route dose data many years ago, whereas the U.S. and Europe use theoretically developed codes. If you find out this has changed, then let me know.

In Canada, air operators should send the dose record of their employees to the National Dose Registry, which is a database containing dose records of all workers who are monitored for ionizing radiation exposure in Canada. The data is used by regulators for monitoring compliance with existing regulations and by Health Canada for publishing reports on occupational radiation exposures and epidemiological research.

When predicting employee doses, don’t forget about non-operating, deadheading, or commuting flights. All this exposure time should be considered. A larger consideration is pregnancy. It is recommended the foetus does not receive exposure exceeding 1 mSv. In Canada, a pregnant employee who is concerned about the health of the foetus may cease to perform her job until such time as a medical practitioner has determined whether or not there is a risk. If there is a risk, the employee may then be re-assigned to other duties. 

Bottom line: it is the responsibility of the operator to ensure that employees are informed of the potential risks of cosmic radiation exposure and the measures taken to ensure that these risks are minimized. The workplace health and safety committee should take this on.

The Canadian company PCAire Inc provides measurement-based code to estimate crew exposure. Their website is also informative.

So, summing up some important numbers:

• You should be monitored if your exposure level is expected to exceed 1 mSv annually.
• The United Nations determined that aircrew absorb an average of 3 mSv annually.
• 6 mSv is the intervention level amount so other flying or duties should be considered.
• Most regulatory bodies recommend that an average annual maximum dose does not exceed 20 mSv over a five-year period, with a maximum one-year exposure of 50 mSv.
• During pregnancy, the recommended maximum exposure should be less than 1 mSv.
• Short-duration flights have lower exposure.
• North/South flights have less exposure than long flights on northerly routings.
• If you are on a northerly route, flying lower will reduce your exposure.
• You can monitor solar flare activity on government websites.

In The News: Making Aircraft Fuel from Sunlight and Air

Let’s change gears for a moment. In The News is a section of the podcast where I talk about other happenings in aviation.

The fello’fly demonstration program was started in 2019 by Airbus but performed its first actual flight of November of 2021. The program is based on geese and birds flying in a V formation to save energy. In this case, the goals are reduced fuel burn and emissions. Two Airbus 350s flew in formation where the trailing aircraft was 3 kilometres behind and was able to reduce thrust resulting in a 5% savings in fuel burn.

Over 6 tons of CO₂ emissions were saved on the trip. For context, a typical passenger vehicle emits about 4.6 metric tons of CO₂ per year. There are about 1,300 flights per day in the North Atlantic so the program could reduce daily emissions equivalent to 850 cars operating for a year if aircraft were flying in pairs.

Airbus says the next step is to gain the support of the regulators.

Thanks for listening. Have a great day!

References

AbsoluteAstronomy.com. Space Environment Center.

Bryan, V. (2021, November 10). Can flying in formation save fuel? Airbus trials concept on transatlantic flight. AeroTime Hub.

PCAire Inc. Cosmic Radiation Monitoring.

Royal Military College of Canada. (March 2000). Cosmic Radiation Exposure of Aircrew Project Report, Volumes 1 and 2.

Royal Military College of Canada and Defence Research Establishment Ottawa. (March 1998). Canadian Aircrew Radiation Environment Study (CARES) Report, Volumes 1, 2 and 3. 

Transport Canada. Commercial and Business Aviation Advisory Circular (CBAAC) No. 0183R.

– Brent Fishlock, Technical Advisor Team Lead, TrainingPort.net