Time to COVER UP

UV Radiation and the Risks Pilots Face

Ultraviolet radiation is an electromagnetic wave that occupies a portion of the spectrum between X-rays and visible violet light. This corresponds to wavelengths of between approximately 400 nanometers on the visible light side to about 10 nanometers on the X-ray side. This spectrum is subdivided into several sub regions.

Physicists and biologists look at ultraviolet (UV) radiation differently, and while physicists concern themselves with the entire UV spectrum, biologists and physicians are primarily concerned with ultraviolet light which has a wavelength of over 100 nanometers. Ultraviolet A (UVA) consists of light with a wavelength of 315-400 nanometers; Ultraviolet B (UVB) with a wavelength of 280-315 nanometers; and Ultravio­let C (UVC) which has a wavelength of between 100 and 280 nanometers.

In terms of biological effects, the danger of UV is inversely proportional to the wavelength – the longer wavelength (UVA) is less dangerous than the shorter wavelength of UVC, which is potentially highly toxic to living organisms.

The sun produces UV rays over the entire spectrum and is the source of ultraviolet radiation. The earth’s atmosphere, primarily the ozone layer, absorbs all of the UVC so it is of no biological concern to those of us who remain in the earth’s atmosphere. Most UVB is also absorbed prior to reaching earth, but with the thinning of the ozone layer, more is getting through. Furthermore, the higher you go, the more UVB you will be exposed to. UVA easily reaches the earth’s surface and accounts for about 99 percent of the UV at the surface.

Both UVA and UVB are unable to penetrate deeply into the body, unlike X-rays, but they do penetrate the surface of the skin and can affect the cells of the superficial layers of skin. Because UV rays are a form of energy, they have the ability to cause burns of the skin, and they can initiate changes in the cells of the skin that may result in the formation of skin cancers. There is also evidence that UV radiation can play a role in the development of cataracts.

Because UV is absorbed by the atmosphere, as you go to higher elevations, you will be exposed to more ultraviolet radiation because there is less atmosphere between you and the sun to absorb it. Remember, the atmosphere is only half as thick at 18,000 feet as at sea level, so you would expect significantly more UV at altitude, and measurements confirm this. In fact, for every 1,000 feet of elevation, the total amount of UV increases by about five percent.

Due to the increased amount of UV radiation at altitude, pilots are exposed to more UV radiation than the average land-bound person and therefore would be expected to have a higher incidence of skin cancers than a random population – and that seems to be the case. Several epidemiological studies have shown that flight crews have nearly two-times the chance of developing melanoma, the most serious form of skin cancer, than a random population. The incidence of basal and squamous cell tumors in pilots is also about double of what would be expected. While there are problems with these studies, and they are not universally accepted, it still seems prudent for pilots to take active measures to minimize UV exposure while in flight.

Many pilots think they are protected by the windscreen, but that is not necessarily the case. A recent FAA study measured the ability of aircraft windscreens to block UV radiation. The good news is that UVB is almost completely absorbed by the laminate glass used for the windscreens of the tested aircraft. UVA, however, was poorly absorbed leading to potentially higher UVA exposure in flight crews. Interestingly, acrylic windscreens used in light GA aircraft (the Bonanza and C-182 were the specific ones tested) block almost 100 percent of UVA below a wavelength of 380 nanometers. Glass was only effective blocking UVA with a wavelength less than 340 nanometers; and remember, the shorter the wavelength, the potentially more hazardous the radiation can be. Crews of jet aircraft therefore are at greater risk because 1) their glass windows do a poorer job of blocking UVA than the acrylics used in light aircraft and 2) because they fly at higher altitudes where there is more UVA.

It is worthwhile for pilots to take protective measures. This includes the use of sunscreens, long sleeved clothing and sunglasses that block UV radiation. There is really no downside to using these protective measures and remember, an ounce of prevention is superior to a pound of care.