ADDITIONAL ALTITUDE CONCERNS


Solar Radiation


In 1994, the Federal Aviation Administration (FAA), formally recognized that (commercial) aircrews are occupationally exposed to ionizing radiation and recommended that they be informed about their radiation exposure and associated health risks; and that they be assisted in making informed decisions with regard to their work environment. (see Advisory Circular 120-61A, In-flight Radiation Exposure)


Our planet is surrounded with a protective layer of ozone. This layer lessens the harmful effects of cosmic/ solar radiation. The average American living at sea level receives the equivalent of nine chest X-rays annually. Conversely, if you live in Denver, the “mile high city”, that dosage is increased by a factor of two.


Solar radiation doubles with approximately every 6,000- foot increase in altitude. As an example, at FL390 your exposure is nearly 60 times greater that of sea level. Currently, several corporate aircraft are capable of operating at or above FL 500. Flights at those altitudes increases your dosage nearly 200 times.


The earth’s magnetic fields play a role in determining where that cosmic radiation is concentrated. (Ever wonder why you see those beautiful light shows near the higher latitudes?) Exposure rates at 70 degrees North or South latitude is approximately four times greater than that at 25 degrees latitude. In addition, during the suns solar storms, the risk increases by a factor of 10!


The average person does not spend enough time aloft to be at risk; however, if you regularly operate at altitudes above FL350, there is some evidence that you may be at risk. How much risk, no one really knows.


Here are a few things to bear in mind as you are donning your lead-lined suit in preparation for your next flight. If you are flying in the vicinity of 1000 hours annually and, a “major portion” of your flights are in the higher latitudes/altitudes, there is some cause for concern.


If you fall into this category you are to encouraged to increase vigilance regarding this issue. At least tracking your exposure time. And, as a minimum, pregnant crewmembers should exercise increased caution prior to committing to flights into known or forecasted high solar/cosmic radiation areas. The FAA recommended limit for a crewmember is a 5-year average dose of 20 millisieverts per year, with no more than 50 millisieverts in a single year. For a pregnant aircrew member starting when she reports her pregnancy, the recommended limit is an equivalent dose of 1 millisievert, with no more than 0.5 millisieverts in any one month. For more information on how to calculate exposure. (see Advisory Circular 120-61A, In-flight Radiation Exposure)


Ozone


Pure ozone is an unstable, faintly bluish gas, with a characteristic fresh, penetrating odor. The earth’s ozone layer is formed in the stratosphere by the interaction of solar ultraviolet light on oxygen. This ozone layer is our protection against both solar and cosmic radiation; however, at lower altitudes high concentrations of ozone, primarily created by pollution and daylight UV rays at the earths surface, can be particularly irritating.


Evidence shows that high concentrations of ozone can harm lung function or, at minimum, irritate the respiratory system. Symptoms include coughing, irritation of the throat, chest discomfort, and difficulty in breathing as well as eye discomfort. Symptoms, usually short term, normally do not persist beyond four hours of exposure. However, asthma sufferers may be more vulnerable.


Current regulations, requiring ozone removal/scrubbing equipment, pertain only to commercial aircraft. Your particular aircraft may also have this scrubbing equipment installed, which obviously remedies the issue. For those operating equipment without ozone scrubbers, there is also abundant evidence that suggest that the aircraft’s pressurization equipment does a fairly good job in keeping the ozone level in check. It was also


High Altitude Awareness Training 20


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