ABOUT RADIATION
EU Legislation:
Article 42 – Protection of air crew
Each Member State shall make arrangements for undertakings operating aircraft to take account of exposure to cosmic radiation of air crew who are liable to be subject to exposure to more than 1 mSv per year. The undertakings shall take appropriate measures …
http://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX:31996L0029
UK Legislation:
Aircrew Exposure to Cosmic Radiation – Guidance Material for the protection of aircrew from the effects of cosmic radiation
The operator should have a system of record keeping which should be detailed in the Operations Manual and which should be available for inspection by the CAA …
http://www.caa.co.uk/default.aspx?catid=49&pageid=7094
Canada’s Recommendation:
COMMERCIAL AND BUSINESS AVIATION ADVISORY CIRCULAR (CBAAC) No. 0183R
This CBAAC recommends that air operators develop a program for managing the cosmic radiation exposure of their employees who work on board aircraft …
https://www.tc.gc.ca/eng/civilaviation/standards/commerce-circulars-ac0183r-1750.htm
Australia’s Recommendation:
Statement on Occupational Exposure to Cosmic Radiation from Airflight
Employers are urged to consider implementing a process of estimating or assessing employee exposure; providing information to employees about exposures and health risks, including information for women of child bearing age about risk to the fetus; and taking exposures into account when organising rosters …
http://www.arpansa.gov.au/pubs/rhc/cosmicstat.pdf
Radiation is a form of energy that travels through the environment. Visible light is a type of radiation that we can see. Infrared and radio waves are invisible types of radiation that cannot be detected with our senses, and as we all know, these types of radiation are fairly benign.
Other types of radiation are not so benign since they can strip electrons from the atoms and cause health effects. For this reason, they are called ionizing radiation. High energy particles such as X-rays, gamma rays, and neutrons are different types of ionizing radiation.
There are many sources of ionizing radiation. Some of the sources occur naturally among us in the environment: for example the granite counter top in your kitchen is slightly radioactive. Another source of ionizing radiation is the cosmic rays from outer space. At ground level, the atmosphere shields us from most of it but as you climb in altitude, the cosmic ray levels increase.
Collectively, the ionizing radiation from these and similar sources is called background radiation. Human activities, such as medical x-rays, generating nuclear power, testing nuclear weapons in the ‘60s, and flying at high-altitude, also contribute to our exposure to ionizing radiation.
Excerpt from the Ohio State University information article, ‘What are the sources of ionizing radiation?’ by Audeen W. Fentiman, Brian K. Hajek, and Joyce E. Meredith: http://www.ag.ohio-state.edu/~rer/rerhtml/rer_22.html
Ionizing radiation is absorbed by the body and damages the tissues. The potential impact of radiation exposure to the body is called ‘radiation hazard’ and is measured with a quantity called the ‘dose’.
The ‘Effective Dose’ measures the overall cancer hazard to humans. It has units of sievert-Sv. The increase in risk of cancer is about 5% per sievert.
There are many sources of ionizing radiation. Some of the sources occur naturally among us in the environment: for example the granite counter top in your kitchen is slightly radioactive. Another source of ionizing radiation is the cosmic rays from outer space. At ground level, the atmosphere shields us from most of it but as you climb in altitude, the cosmic ray levels increase.
1 Sv is a very large dose. In real-life situations, we use sub-multiples of the Sv:
| milli | m | 10-3 | x 0.001 |
| micro | µ | 10-6 | x 0.000 001 |
| nano | n | 10-9 | x 0.000 000 001 |
The PCAIRE code calculates the doses in micro sievert (µSv).
People who get exposed to radiation as part of their occupation are designated radiation workers. Their limits have been set higher by the government regulatory agencies. In most countries, the limit is 20 000 µSv per year, while in the USA, it is 50 000 µSv per year.
In most countries, unless you are based in Europe, aircrews are not designated radiation workers. However, the government regulatory agencies have recommended that their dose be limited to less than 6 000 µSv per year. For pregnant women, the guidelines are stricter: the exposure should be kept less than 500 µSv per month.
In Germany, radiation protection regulation for air crews are based on the European Council directive 96/29 of 13 May 1996. It specifies that the employer must evaluate the dose of the aircrews that could receive dose of more than 1 000 µSv per year. Results of the dose assessment have to be made available to the aircrew within 6 months after the flight. The dose records must also be transmitted to the central radiation protection register.
German regulations also state that measures should be in place to minimize the exposure of aircrew who receive more than 6 000 µSv per year. The dose limit for aircrews is the same as for nuclear energy workers (20 000 µSv per year). The lifetime dose limit is 400 000 µSv per year. Pregnant aircrew should receive a dose less than 1 000 µSv per year for the remainder of the pregnancy.
Ionizing radiation can damage the DNA in living cells. Damaged cells can either die immediately, be repaired, or mutate into cancer cells. Very few of the cells that are damaged by radiation develop into cancer. For those that do, the time period, between the radiation exposure and the development of a cancer can extend from 3-30 years.
The International Commission on Radiological Protection and the United Nation’s Committee on the Biological Effects of Ionizing Radiation have studied large populations exposed to large doses of radiation (50 000 – 1 000 000 µSv). They concluded that the risk of health effects, such as cancer, is proportional to the dose received. In other words, the more dose you receive, the higher the risk of developing a cancer later in life.
At low doses (less than 6000 µSv per year) we don’t know with certainty if radiation makes any difference to our health. Cancer development is very complex and depends on environmental, genetic and lifestyle factors. In the interest of safety, and as precaution, international organizations and governments regulate radiation exposure as if the risk of cancer was proportional to the dose, even at very low doses. The risk factors that they adopted are shown in the table below.
| Health Effect | Risk factor % / Sv |
| Fatal Cancer | 5 |
| Non-fatal cancer | 1 |
| Severe hereditary effects | 1.3 |
| Total | 7.3 |
In summary, the risk of a fatal cancer is 5% for one sievert. For someone flying for forty years and receiving a dose of 5 000 µSv (0.005 Sv) per year, the additional risk of cancer is 1%. This is a very low risk. To put it into perspective, about 20-30% of the population dies of cancer. The increased risk of cancer from flying is very small.
Cosmic rays are high energy particles, originating from outer space, that strike the earth. An increase in altitude means an increase in radiation from cosmic rays. A move from a coastal location to the mountains increases cosmic radiation levels.
Flying on an airplane also increases the radiation levels. Although the particles responsible for cosmic radiation can affect the cells in our body, they are difficult to detect. At typical flight altitudes of 20 000 – 40 000 feet (6 – 12 km) the cosmic radiation contains a soup of neutrons, protons, electrons, photons, muons and pions. These particles will not be measured accurately with the type of simple radiation detectors that are commonly found in nuclear power stations or in army surplus stores.
Cosmic radiation levels are never constant. If you take today the same flight you took six months ago, the dose you receive will be different. The largest variations of cosmic ray intensity occur over an 11-year cycle, which is influenced by the sun’s activity (see figure below).
Galactic cosmic radiation is at a minimum during solar maximum, but during solar minimum, more of that radiation can reach the Earth. The most recent solar minimum occurred in early 1997, and solar maximum occurred ahead of schedule in May 2000. The next solar minimum will occur in late 2007 and it is already apparent that cosmic radiation levels are increasing.
PCAire updates its table of solar activity as soon as the data becomes available.
(1) Some of the information shown here is summarized from an article by Susan Baily, published in the January 2000 issue of Nuclear News.
The fetus is particularly susceptible to radiation damage between the 8th and 15th week of the pregnancy. An increased risk of childhood cancers and birth defects, particularly mental retardation of cognitive functions, can result from extended radiation exposures to pregnant women.
As shown in the table below, which is adapted from the 1990 recommendations of the International Commission on Radiological Protection, radiation damage to the fetus is likely at doses in excess of 0.1 Sv (100 000 µSv). At lower doses, like those that a pregnant crewmember might receive, the damage to the fetus is unlikely and the risk is low.
| Week after conception | Delayed health effect | Acute health effect |
| Less than 3 |
Unlikely |
Unlikely |
| 3 – 7 | Probability of cancer of 5% / Sv | Deterministic organ malformation with a threshold of 0.1 Sv |
| 8 – 15 | Severe mental retardation with a probability of 40% / Sv and a threshold of 0.1 Sv |
Deterministic mental retardation of 30 IQ / Sv with a threshold of 0.1 Sv |
| 16 – 25 | As above, but less likely | As above, but less severe |
| More than 25 | Probability of cancer of 5% / Sv | Unlikely |
The risk is low, but exactly what is it?
The most recent risk estimates published by the US Federal Aviation Authority, in 1992, appeared in “Radiation Exposure of Air Carrier Crewmembers II.” This document states that “once a pregnancy is known . . . the dose to the unborn child from occupational exposure should not be more than 500 µSv in any month. For radiation protection purposes, the dose to a fetus is considered to be the same as that received by the mother.
In the US, the FAA recommends that women pilots and flight attendants who are pregnant read the report “Galactic Cosmic Radiation Exposure of Pregnant Aircrew Members II”
Flight attendants at British Airways, are ‘grounded’ immediately after declaring pregnancy, and are given other tasks until they take maternity leave. The British government has published a report, “Protection of air crew from cosmic radiation: Guidance material” , that explains the risks to the fetus.
In Germany, pregnant crewmembers are limited to a dose of 1 000 µSv for the remainder of the pregnancy. In practice, this means that they are grounded.
(1) Some of the information shown here is summarized from an article by Susan Baily, published in the January 2000 issue of Nuclear News.
Most of the cosmic radiation that can affect crewmembers and frequent flyers comes from galactic cosmic rays, originating outside our solar system. The activity of the sun can reduce or increase this flux of particles from space, but the sun itself is a weak source of cosmic radiation.
Only very rarely does a solar flare accelerate particles to energies sufficient to penetrate the Earth’s magnetic field defenses and cause the radiation levels to increase by more than a factor of 10. Only 7 such events have occurred in the last 50 years of the 20th century.
- 23 February 1956
- 17 July 1959
- 13 November 1960
- 09 August 1972
- 20 October 1989
- 24 March 1991
- 20 January 2005
While it is not possible to predict solar flares, several observatories, such as the NOAA’s Space Weather Prediction Center , or Space Weather , sites can give early warning of an imminent solar storm. If such an event occurs, PCAire will add an estimate of the exposure you received from a solar event to your dose records.
If exposure to cosmic rays is potentially harmful, why aren’t we better protected? The answer is that galactic cosmic rays are very penetrating. It takes a very thick radiation shield to completely stop the type of cosmic rays that are encountered at high altitude. Shielding the whole airplane would add too much weight to an aircraft.
Flying at a lower altitude is not an option. The fuel consumption of an airplane would be prohibitive at lower altitude.
Even measuring the dose is not easy. Traditional radiation badges are not sensitive to the type of particles found at high altitude. The best instrument to measure galactic cosmic rays is the size of a suitcase and requires hours of analysis to extract the dose.
Our research scientists flew a large radiation detector, sensitive to cosmic rays, on hundreds of flights, all over the world. The radiation field was recorded every minute along each of these flights. Analysis of this data led to the development of mathematical functions that matched the measurements for any flight, at any altitude and anywhere in the world.
The PCAire code uses these mathematical functions to calculate the dose to a person on a given flight. For each flight that is entered, the code takes into account the date, time, and flight path and recomputes the radiation field during that flight. The results are summed and recorded in your dose profile.
It is possible to enter a flight in the future and get an estimate of the dose that you would get. However, the cosmic radiation intensity in the atmosphere changes continuously, and the dose you would eventually receive could be quite different from the estimate.
PCAire takes into account the variations of the cosmic radiation caused by the solar cycle. At the end of each month, we obtain the latest measurements of the solar activity and update our database. It is almost impossible to accurately predict what the solar activity will be six months from now. For this reason, any estimate of the dose received on a future flight may be inaccurate. The best results are obtained when you wait one month before entering a flight into PCAire.
