Bringing Radiation Exposure to Flight Crews and Frequent Fliers into the Spotlight

By Karen Calomino, MS

It is well known that ionizing radiation affects our health in many ways and can cause both acute and delayed symptoms such as cancer. However, although crewmembers and frequent fliers are exposed to large amounts of radiation on long-haul flights, they have been left in the dark. The US airline industry has ignored the topic for quite some time despite the fact that the International Commission on Radiological Protection classified flight crews as “radiation workers” over 20 years ago (ICRP, 1991) and the FAA agreed that, “air carrier aircrews are occupationally exposed to ionizing radiation” in 1994 (Barish, 2009). These statements justify an exposure limit up to 50 times more than the general public, and while flight crews are estimated to receive one of the highest average doses of any occupationally exposed group in the U.S. (Goldhagen, 1998) including workers at nuclear power plants (Barish, 2001), there are no regulations in place protecting them.

In addition to radiation, crewmembers and passengers are exposed to many other toxins on planes, including flame retardant chemicals, pesticides, and pathogens. Last year, through the implementation of section 829 of the FAA Modernization and Reform Act of 2012, OSHA now enforces the standards pertaining to blood-borne pathogens, hazard communications, and hearing conservation of crewmembers. The subject of radiation however is still governed by the FAA, which in its latest crewmember training Advisory Circular suggests outdated reading materials and links (FAA, 2006). As a crewmember myself, my career of flying mainly long-haul international routes across the polar region, along with recent discoveries of my health including a high amount of oxidative stress and an inflamed mucosal barrier, has brought this subject close to home and has resulted in the need to learn more about the amount we are exposed to and the detrimental effects it can have on us. I find it unacceptable that crews and passengers are neither educated nor protected from high exposure doses.

Since 2000, airlines operating in the countries of the European Union are required to limit aircrew member’s exposure to cosmic radiation (CAA, 2013). In the U.S., the Nuclear Regulatory Commission’s Code of Federal Regulations require that individuals exposed to radiation receive adequate training to protect themselves and state that these individuals have the right to know how much radiation they have been exposed to (NRC, 2013). The FAA on the other hand only recommends that airlines educate their employees about the risks involved. Since it is not a required action, airlines do not feel the need to inform them. I barely remember receiving one notice in my 25-year career explaining the effects that radiation could have when flying while pregnant. The concluding remarks stated something to the effect that it would be impossible to determine that a disease resulted from radiation exposure and that is important to keep the risks associated with flying in perspective with other risks that are related to chronic diseases. Other than that I have heard nothing. When questioning other flight attendants and pilots about this, I received similar answers. Most are aware of cosmic radiation but not the extent of it and many feel that there is nothing we can do.

Now, more than ever is awareness imperative for several reasons:

The majority of flight attendants and pilots fly until they retire at around 65, resulting in a greater cumulative effect of radiation.

Cross-polar traffic, where radiation levels are the highest, is continuously increasing. In 2011, there were 10,993 one-way crossings (Meehan, 2012).

The sun is nearing the maximum point of its 11-year cycle with solar activity expecting to peak now in 2013. This could result in huge increases in radiation during flights.

Apparently it is a U.S. legal requirement that those who are occupationally exposed to radiation knowingly and willingly accept this increased level of risk (Barish, 2001), however rather than attempting to educate flight crews and implement strategies to limit levels of radiation, airlines are expecting crews to work longer hours each month, which ultimately results in more exposure.

Everyone is exposed to ionizing “background” radiation

Energy emitted from a source is generally referred to as radiation. Ionizing radiation has enough energy to remove tightly bound electrons from an atom, causing it to become charged or ionized. It affects health when it results in changes in the cells of the human body by breaking the chemical bonds in molecules. This type of radiation can occur in waves, such as gamma radiation and x-rays that penetrate deeply into tissue, or as particles, such as alpha particles, beta particles, and neutrons.

When determining health effects of radiation, its dose is measured in “sieverts” (replaces the “rem”), or millisieverts (mSv). This measures the “effective dose”, which is a more accurate representation when exposure is limited to one or several body part(s). As an example, a typical chest x-ray involves about 0.1 mSv of radiation exposure, however since it is limited to the chest area, the “effective” dose is only about 0.02 or 0.03 mSv because only the lungs and breasts are exposed to the radiation (Blue, 2000; European Commission, 2000; FDA, 2002; Roguin & Nair, 2007; Shulman, 2008; FDA, 2009). Exposure to cosmic radiation on the other hand affects the whole body, so the “effective” dose is equivalent to the exposure amount (Blue, 2000).

Cosmic radiation is a naturally ionizing form of radiation that consists of two parts: 1) a permanent component consisting of highly charged particles ejected from the galaxy, or galactic cosmic rays (GCR) and 2) sporadic particles, or solar energetic particles (SEP), that are associated with eruptions on the sun and which varies in intensity according to the sun’s 11-year cycle. The two barriers that protect Earth (the planets magnetic field and the Earth’s atmosphere) decrease the amount of cosmic radiation that reaches the ground, however people will always be exposed to low levels of this as well as other naturally occurring sources of ionizing radiation including radon gas and radioactive elements found in the air, water, rocks, and minerals. Combined, this naturally occurring “background radiation” exposes people in the U.S. to an average effective radiation dose of about 3 millisieverts (mSv) per year. Man-made sources, including diagnostic x-rays and nuclear medicine add an additional 3 mSv per year (Bushberg, 2009). The total can of course vary from person to person depending on their location (higher altitude cities such as Denver have more cosmic radiation) and their medical imaging history.

Why is the radiation dose limit for airline crews set so high?

The National Council on Radiation Protection and Measurement (NCRP), and the International Commission on Radiological Protection (ICRP) offer recommendations for the maximum permissible dose (MPD) of radiation that people should be exposed to. These in turn are usually adopted by government regulatory agencies including the FAA, EPA, and NRC. Both the NCRP and the ICRP agree that the “general public” should not be exposed to more than 1 mSv (equivalent to an effective dose of about 50 chest x-rays) above the average background and medical radiation per year. In its’ Report No. 116, the NCRP states that the effective dose limit is 1 mSv for members of the public “who are exposed continuously or frequently”, however on an “infrequent” basis (not likely to occur often in an individual’s lifetime), the annual effective dose may go up to 5 mSv (2004). The ICRP recommendation is based on the assumption that there is no safe level of exposure, that even the smallest exposure has some probability of causing a stochastic, or long-term effect, such as cancer, and that doses rising above 1 mSv per year will justify protective actions for members of the public (Butler & Cool, 2010).

And then there are those who are occupationally exposed to radiation. The ICRP recommended limit for an occupationally exposed person is a 5-year average of 20 mSv per year with no more than 50 mSv in a single year and the NCRP recommends 50 mSv per year with a maximum permissible dose of 10 mSv times the person’s age (Friedberg & Copeland, 2011). The FAA follows the recommendation of the ICRP. If they had followed the recommendation of the NCRP, a commission chartered by the U.S. congress in 1964, crewmembers maximum permissible annual dose would be less since it is quite common that crewmembers have long careers. As an example, a flight attendant with a 40-year career who retires at age 65 would have had an average annual permissible dose of about 16 mSv (10 x 65 = 650, 650/40years = 16.25 mSv/year) Recommendations for pregnant crewmembers are much less with a dose limit of about 1 mSv for the remainder of the pregnancy or 0.5 mSv in any month (Friedberg & Copeland, 2011). With regards to frequent flying passengers or other travelers, there are no legal limits since this is considered a “voluntary” activity (HPS, 2011).

I was curious to find out why the recommended annual dose limit for crewmembers was set so much higher than the general public. I understand that the nature of the job comes with some risks, however 20 to 50 times the limit of other US citizens? After all, we are made up of the same types of cells. Perhaps they think we are super-heroes and can withstand these levels much better?

According to the NCRP, one of the goals of radiation protection is “to prevent the occurrence of clinically-significant radiation-induced deterministic effects by adhering to dose limits that are below the apparent threshold levels (2012).” Deterministic effects are usually based on acute exposures and are mostly the result of death or malformation of cells. Apparently the ICRP selected an occupational dose limit that “falls just short of unacceptable” before detrimental effects may occur (Butler & Cool, 2010).

The NCRP and ICRP have two other fundamental principles for limiting the doses received by people: justification and optimization. Justification requires that any decision that alters the radiation exposure situation should result in sufficient individual or societal benefit to justify the risks involved. Optimization is based on maintaining all exposure levels “as low as reasonably achievable” (also know as the practice of ALARA). These features are based on the linear, non-threshold (LNT) hypothesis, which assumes that any radiation exposure, no matter how small, carries with it a level of risk that is proportional to the level of exposure. So since there is no safe level and increases in exposure result in incremental increases in stochastic (or long-term low-level exposure) risks until a threshold level is reached that has been known to cause deterministic (acute) radiation symptoms, exposure should be justified and kept as low as reasonably achievable.

According to a senior Health Physics Advisor with the NRC, optimization, or the ALARA practice, is more important than setting dose limits (Sherbini, 2000). The Health Physics Society also states that this philosophy results in occupational doses that are much lower than the allowable limits and that the average annual effective dose for all occupational workers in the U.S. is less than 5 mSv (Chabot, 2012).

How much ionizing radiation are we talking about?

Crews and passengers can be exposed to additional ionizing radiation from several sources including:

  • Galactic cosmic radiation
  • Solar radiation
  • Dark lightning
  • Radioactive cargo and security scanners

Galactic cosmic radiation

The radiation dose received from galactic cosmic rays is affected by four main factors: time spent flying, altitude, latitude, and solar activity. Since radiation is cumulative, the more you fly, the more radiation you are exposed to. In addition, exposure is more intense at higher altitudes as well as higher latitudes. This is because the thinning of the atmosphere at higher altitudes provides less protection, and electrically charged radiation particles are drawn toward the Earth’s north and south magnetic poles. A normal cruising altitude of about 39,000 feet brings the total radiation levels to about 64 times greater than at sea level (Science Daily, 2005), and the exposure rate is about four times as much at 70 degrees north or south latitude than 25 degrees (Blue, 2000). So long-haul flights over the polar routes are exposed to a lot more radiation than those flying at mid-latitudes. The final factor is solar activity. Depending on whether the sun is at a solar minimum or maximum (which varies throughout an 11-year cycle), the amount of cosmic radiation can change. At the solar minimum there is less of a shield due to few sun spots so galactic radiation can double. On the other hand, when the sun is at the solar maximum with many sun spots, this may decrease the amount of galactic radiation that gets through.

The FAA has developed a program called CARI that can either be downloaded or used directly from the Web site (jag.cami.jccbi.gov/cariprofile.asp). It calculates the effective dose of cosmic radiation received by those flying between two airports in the world, however the program does not take into account the increased radiation caused by solar flares. I utilized this program to determine radiation exposure on long-haul flights flying over the polar region at an altitude of 38,000 feet during 05/2013.

The radiation exposure for a flight from Chicago to London was estimated to be 0.055 mSv. To put this in perspective:

  • One roundtrip is equivalent to the effective dose of approximately five and a half chest x-rays
  • Five roundtrips, or a months worth of flying for full-time crewmembers, is equivalent to being exposed to the effective dose of about 27 chest x-rays.
  • A full year of flying, or about 1000 hours, exposes crews to almost 7 mSv, which is equivalent to the effective dose of approximately 350 chest x-rays.
  • The annual exposure from just galactic radiation on this flight exceeds the annual average effective dose for all occupational workers in the U.S. (Chabot, 2012).
  • Ten round trips (or two months of flying for crews) exceed the annual recommended dose limit for the general public.

Also, according to the CARI program, a one-way trip from Chicago to Shanghai is estimated to expose individuals to 0.091 mSv, which is the equivalent of about four and a half chest x-rays each direction. Crews or frequent fliers are exposed to more than the annual recommended amount for the general public after six round trips. Crews flying three trips a month or about 1000 hours per year may also reach an annual exposure amount of almost 7 mSv. A flight from Los Angeles to London is estimated at 0.071 mSv, and New York to London is estimated at 0.04 mSv.

Passengers and crews on a flight from New York to Hong Kong are exposed to about 0.1 mSv (or the effective dose of five chest x-rays each way). Five roundtrips could exceed the maximum dosage guidelines for the general public (Crampton, 2001).

Reports on pilot exposure to radiation agree that there is a high-exposed group of pilots who may exceed 7 mSv per year (Graweski et al., 2011).

Coast-to-coast flying exposes people to less cosmic radiation since they do not fly over the polar routes. A round-trip flight from San Francisco to New York is the equivalent of about two and a half chest x-rays, or 0.05 mSv. Twenty round-trips reach the limit for the general population (Drucker, 2002).

Solar radiation

Although cosmic galactic radiation may be down slightly during solar maximums, there is the possibility for solar storms, which may result in large amounts of radiation from the sun. The storms are a result of an explosive release of energy from the sun in the form of solar flares and coronal mass ejections. Solar particle events (SEP) are intense flows of radiation from the sun made up of protons and charged particles that are associated with these eruptions. They are rated on a scale from S1 (minor) to S5 (extreme) according to the amount of very energetic and fast solar particles that move through a given space in the atmosphere. Flights that rely exclusively on radio communications, such as those routed through the poles, may be re-routed during a an SEP event since it can disturb the regions through which high frequency radio communication travel (Fox, 2012). Passengers and crews may be exposed to a radiation risk during storms that are rated S2 (moderate) or higher (NOAA, 2005). These solar flares can increase the radiation exposure level by a factor of 10 or 20 and can last anywhere from a couple of hours to a couple of days. Each possible solar particle event may add an additional 1 mSv per flight to the cumulative galactic cosmic radiation effective dose (Beck et al., 2009) and could add up to a lifetime neutron dose of 46 mSv (Graweski et al., 2011). Anyone that happens to be working on one of those flights might be exposed to the equivalent of 50 chest x-rays or more. If a storm is rated as an S-5 on the center’s scale, which is the most extreme, exposure can be equivalent to 100 chest x-rays (Crampton, 2001).