As a commercial airline pilot, Theresia Eberbach typically weighs several factors when deciding which trips to fly—the dates, destination and how long she’ll be away from home. Unlike most of her peers, Eberbach often has another variable to mull: How much radiation she’s willing to take.

Ionizing radiation is a permanent feature of the upper atmosphere, where the protection we take for granted on the surface is significantly thinner. At airlines’ cruising altitude, particles periodically ejected by the sun and cosmic radiation coursing through the universe are 100 times more potent than down below.

Still, the exposure for every extra-long trip across the globe is roughly equivalent to one X-ray. That is, except for two regions: The poles. The planet’s magnetic field helps to minimize radiation for most latitudes, but that shield tends to dissipate at extreme north and south.

Airline employees are already the most vulnerable to workplace radiation, but the growing number of polar and long-haul routes may make the hazard worse. A flight from Germany to Southeast Asia can be just as long as one to the western U.S., but the risks can be very different given the latter goes “over the top” of the world.

“If I go to Los Angeles or San Francisco, it’s going to be the highest dosage in our network, whereas when I go to New Delhi or Singapore, it’s about a third of those doses,” said Eberbach, an Airbus A380 first officer for Deutsche Lufthansa AG who also serves as chairman of a radiation protection working group for Vereinigung Cockpit, or VC, the German pilots’ union.

“There’s no way you can be a pilot and not get this exposure.”

Airline employees face more radiation exposure than radiology workers or nuclear power plant engineers, according to the National Council on Radiation Protection and Measurements. Such exposure is measured using the Sievert. A dose of 4 Sieverts or more at once is often fatal. A CT scan of your head is about 2 milliSieverts (mSv), or two-thousandths of a Sievert, roughly what you’d get going about your daily life for eight months. Generally, a U.S. pilot or flight attendant receives an annual exposure of as much as 5 mSv.

“In our job, we’re going to get this exposure,” said Mike Holland, an American Airlines captain and resident “radiation expert” for the Allied Pilots Association, the union that represents American’s 15,000 pilots. “There’s no way you can be a pilot and not get this exposure.”

Beyond the popularity of polar routes, airlines are also connecting more far-flung cities, with 16-18-hour hauls becoming routine thanks to modern aircraft technology. Singapore Airlines intends to resume its 19-hour nonstop service to New York this year, while Qantas Airways Ltd. has launched what it calls “Project Sunrise” to connect Sydney with London and New York nonstop by 2022.

The effort is aimed at goading Airbus SE and Boeing Co. to produce a jet able to fly more than 20 hours, fully loaded. Last month, Norwegian Air Shuttle ASA’s Argentina unit won regulatory approval to begin Boeing 787 flights from Buenos Aires to Perth, Australia, using a flight path near Antarctica.

But these lengthy legs don’t just affect airline employees. Fly frequently for long distances and you, too, may start to consider how much radiation you’re absorbing. In the most extreme examples, planes caught over the poles in a solar storm could see radiation levels spike up to 10 mSv for a single flight. But even advocates for employees say they’re having a hard time being heard by airlines focused on saving time and fuel, and thus money.

“It’s been difficult to get traction” with airlines and regulators, said Judith Anderson, an industrial hygienist for the Association of Flight Attendants-CWA, which represents 50,000 attendants. “The nature of the hazard is invisible, so it’s easier to forget about and get attention for something more pressing.”

Polar routes aren’t new, of course. The Swedish airline SAS AB completed the first trans-Arctic commercial flight in 1952, followed by a regularly scheduled “Polar shortcut” route two years later linking Copenhagen and Los Angeles. More recently, United Airlines inaugurated a Chicago-Hong Kong nonstop polar route in 2001, but only during summer months, when winds were more favorable. Today, its successor, United Continental Holdings Inc., is the U.S. carrier with the most service to Asia, with seven polar routes each day.

Airlines are keen to maximize revenue by using the most direct routes. Flights from the eastern U.S. and Canada to Asian destinations such as Hong Kong, Seoul, Shanghai and Beijing, typically traverse the North Pole—“over the top” in pilots’ parlance—to shave as many as two hours off a typical journey.

Since airlines gained access to Siberian airspace, the number of polar flights has soared, with more than 17,000 trips last year from just a few in 2001, according to data from Nav Canada, the Canadian air traffic services company. These remote regions, and areas just south of the Arctic Circle, are an important path for scores of flights each day, including many of the nonstop routes from India, the Persian Gulf states and Europe to the western U.S. and Canada.

In the far south, Qantas flies from Sydney to Johannesburg and Santiago, Chile, both routes that track below 60 degrees south, near Antarctica. Latam Airlines Group SA and Air New Zealand Ltd. also occasionally approach the region with their flights between South America and Auckland.

Polar routes, while fiscally desirable, do present airlines with a few technical challenges that require additional instruction for pilots. These regions generally offer fewer diversion options for emergency landings and have a greater potential for communications glitches.

Just as airline meteorologists closely monitor storms and winds, the carriers also keep tabs on space weather. Given the sun’s potential to rapidly fry a vast array of terrestial communications, the National Oceanic and Atmospheric Administration (NOAA) monitors the sun for coronal mass ejections and other particle events that can increase ionization near Earth. It sends alerts on solar activity, with a radiation scale of 1-5.

A NOAA weather satellite launched March 1, GOES-17, is expected to increase the fidelity of space weather forecasts. A sensor developed at the University of New Hampshire is designed to monitor the level of energetic ions, the main source of radiation.

“Being able to forecast a higher radiation risk for so-called ‘polar’ planes, those that tend to fly at higher altitudes near the Earth’s poles, would allow commercial airlines to warn pilots to reroute planes to lower altitudes to decrease the risk of long-term exposure to radiation for their crews, who fly the same route over and over again,” Clifford Lopate, a UNH physics researcher and professor, said in a March 5 statement.

Few commercial aircraft carry radiation detectors, given the costs and technical limitations. NOAA monitors solar alerts and the FAA enacts altitude limits during certain events. Ultimately, pilots would like a cockpit warning system to detect severe solar flares “so I could see an alert when a storm is kicking off,” Holland said. Such a tool would provide faster notification of a large weather event that requires pilots to obtain quick clearance for a lower altitude or course deviation.

The U.S. has far less regulation than Europe when it comes to protecting flight crews from radiation.

Some airlines are quick to note they’re taking precautions. Qantas said it monitors solar flare activity before and during polar flights and “if any activity were to occur during the planning phase or during flight, we would re-route the aircraft to avoid polar regions.” United spokesman Charles Hobart said the carrier re-routes flights “several times per year,” due to solar activity.

The European Union imposed rules in May 2000 requiring that airlines calculate and catalog crews’ annual radiation dosage. Pregnant crew members typically limit their flying hours and work ground jobs or receive paid time off. A fetus should not be exposed to more than 1 mSv, according to the International Commission of Radiation Protections.

The U.S. has far less regulation, with the FAA suggesting that airlines and flight crews work to an exposure standard of “as low as reasonably achievable.” That standard is also used in other industries where workers are exposed to radiation. Airlines for America, the U.S. carriers’ trade group, referred inquiries to the FAA.

Following international standards, the FAA’s recommended limit for radiation workers is an average effective dose of 20 mSv per year over a five-year span, with no more than 50 mSv in a single year. “With regard to occupational exposure to radiation during pregnancy, the FAA recommends that a pregnant crewmember and management work together to ensure that exposure of the conceptus not exceed recommended limits,” the agency advises.

U.S. airlines aren’t required to calculate crews’ annual exposure, but the FAA operates a web site that will approximate the dosage for a particular flight if certain data such as altitude and cruise altitude period is entered. That site has been offline for at least six weeks.

“It’s always a question of radiation dose versus personal interest.”

Anderson, with the flight attendants’ union, said most flight crews are unaware of the role radiation plays in their careers and give it little thought. “To me, the bigger issue is the need for pregnancy protections,” she said.

In a January position paper, the International Federation of Air Line Pilots’ Associations said that aircraft flying above 26,000 feet in polar and near-polar regions should be equipped with a device to detect sudden increases in dose rates, as is common with a solar flare event. The Montreal-based organization also said that airlines should inform potential recruits about radiation exposure and offer “extensive educational programs” for flight crews.

“Whereas annual exposures for ground-based radiation workers have been successfully reduced, airline flight crew exposures remain at levels substantially above those of other radiation-exposed workers and are increasing with modern flight operations,” the paper stated.

Eberbach typically flies four round-trips every month. She says pilots need more training to help them consider radiation in their flight planning and altitude choices. With an annual peak of as much as 5 mSv, she has periodically eschewed some California trips to help keep her exposure lower.

“It’s always a question of radiation dose versus personal interest,” she said. “And many people say ‘Well, I don’t smell radiation, I don’t see radiation, I don’t care—I want to fly to L.A.’”

©2018 Bloomberg L.P.

This article was written by Justin Bachman from Bloomberg and was legally licensed through the NewsCred publisher network. Please direct all licensing questions to legal@newscred.com.

Photo Credit: Airlines are flying over the North Pole more often for routes, which increases exposure to cosmic radiation. The photo shows the aurora borealis, a natural electrical phenomenon characterized by the appearance of streamers of reddish or greenish light in the sky, that is not cosmic radiation but is visible, unlike radiation. Piriya / Bloomberg