COSMIC RADIATION
High altitude flying entails exposure to cosmic radiation.
The amount, or intensity, of cosmic radiation depends on altitude and latitude, as well as the stage of the solar cycle. The Earth's atmosphere provides considerable protection from cosmic radiation. At commercial aircraft altitudes the protective layer of the Earth's atmosphere is much thinner than it is on the ground and the intensity of cosmic radiation is approximately 100 times greater at these altitudes than it is on the ground. The Earth's magnetic field can deflect some of the cosmic radiation away from the Earth. The shielding ability of the magnetic field is most effective over the equator and least effective over the poles. The intensity of cosmic radiation at aircraft altitudes around the equator is about three times less than at the poles.
Cosmic radiation is measured in units called Sieverts (Sv). Unit 1 Sv is a rather large unit and doses of cosmic radiation are so low that are usually quoted in microsieverts (μSv) - millionth of a Sievert or milisieverts (mSv) - thousandth of a Sievert (1Sv = 1.000 mSv = 1.000.000 μSv).
In-flight exposure depends mainly on the route and altitude.
The maximum acceptable annual exposure to cosmic radiation, for crew, is considered to be 6 mSv (milli-Sievert).
The Company shall take the following measures for crew members who might be subject to cosmic radiation exposure of more than 1 mSv per year:
Crew members who are likely to be exposed to more than 6 mSv per year are considered highly exposed and individual records of exposure to cosmic radiation should be kept for each crew member concerned. Records for individuals exposed to more than 6 mSv per year must be kept for a minimum of 30 years from the last annual exposure of more than 6 mSv (even if the individual concerned is deceased) or until the individual is 75 years of age, whichever is the longer period of time.
Assessment of Cosmic Radiation
Assessment of exposure level can be made by using the values from the table below, or other method acceptable to the Authority – refer also to computer program developed at the FAA’s Civil Aeromedical Institute (CARI) and calculations at http://jag.cami.jccbi.gov./cariprofile.asp.
Doses from cosmic radiation vary greatly with altitude and also with latitude and with the phase of the solar cycle. Table below gives an estimate of the number of flying hours at various altitudes in which a dose of 1 mSv would be accumulated for flights at 60°N and at the equator. Cosmic radiation dose rates change reasonably slowly with time at altitudes used by conventional jet aircraft (i.e. up to about 49 000 ft/15 km.
Note:
The Company does not operate aircraft capable of flying at 49 000 ft/15 km). Table can be used to identify circumstances in which it is unlikely that an annual dosage level of 1 mSv would be exceeded. If flights are limited to heights of less than 27 000 ft, it is unlikely that annual doses will exceed 1 mSv. No further controls are necessary for crew members whose annual dose can be shown to be less than 1 mSv.
Note: This table is based on the CARI-3 computer program. The uncertainty on these estimates is about ± 20%. A conservative conversion factor of 0.8 has been used to convert ambient dose equivalent to effective dose.
Impact of Radiations on Health
When ionising radiation passes through the body, and energy is transmitted to the tissues, which affects atoms within individual cells and result in a variety of health effects such as development of cancer, genetic risk and risk to the health of the foetus (unborn child).
The amount, or intensity, of cosmic radiation depends on altitude and latitude, as well as the stage of the solar cycle. The Earth's atmosphere provides considerable protection from cosmic radiation. At commercial aircraft altitudes the protective layer of the Earth's atmosphere is much thinner than it is on the ground and the intensity of cosmic radiation is approximately 100 times greater at these altitudes than it is on the ground. The Earth's magnetic field can deflect some of the cosmic radiation away from the Earth. The shielding ability of the magnetic field is most effective over the equator and least effective over the poles. The intensity of cosmic radiation at aircraft altitudes around the equator is about three times less than at the poles.
Cosmic radiation is measured in units called Sieverts (Sv). Unit 1 Sv is a rather large unit and doses of cosmic radiation are so low that are usually quoted in microsieverts (μSv) - millionth of a Sievert or milisieverts (mSv) - thousandth of a Sievert (1Sv = 1.000 mSv = 1.000.000 μSv).
In-flight exposure depends mainly on the route and altitude.
The maximum acceptable annual exposure to cosmic radiation, for crew, is considered to be 6 mSv (milli-Sievert).
The Company shall take the following measures for crew members who might be subject to cosmic radiation exposure of more than 1 mSv per year:
- To assess the exposure of the crew concerned;
- To take into account the assessed exposure when organizing working schedules with a view to reducing the doses of highly exposed crew;
- To inform the workers concerned of the health risks their work involves;
- To ensure that the working schedules for female crew members, once they have notified that they are pregnant, keep the equivalent dose to the foetus as low as can reasonably be achieved and in any case ensure that the dose does not exceed 1 mSv for the remainder of the pregnancy.
Crew members who are likely to be exposed to more than 6 mSv per year are considered highly exposed and individual records of exposure to cosmic radiation should be kept for each crew member concerned. Records for individuals exposed to more than 6 mSv per year must be kept for a minimum of 30 years from the last annual exposure of more than 6 mSv (even if the individual concerned is deceased) or until the individual is 75 years of age, whichever is the longer period of time.
Assessment of Cosmic Radiation
Assessment of exposure level can be made by using the values from the table below, or other method acceptable to the Authority – refer also to computer program developed at the FAA’s Civil Aeromedical Institute (CARI) and calculations at http://jag.cami.jccbi.gov./cariprofile.asp.
Doses from cosmic radiation vary greatly with altitude and also with latitude and with the phase of the solar cycle. Table below gives an estimate of the number of flying hours at various altitudes in which a dose of 1 mSv would be accumulated for flights at 60°N and at the equator. Cosmic radiation dose rates change reasonably slowly with time at altitudes used by conventional jet aircraft (i.e. up to about 49 000 ft/15 km.
Note:
The Company does not operate aircraft capable of flying at 49 000 ft/15 km). Table can be used to identify circumstances in which it is unlikely that an annual dosage level of 1 mSv would be exceeded. If flights are limited to heights of less than 27 000 ft, it is unlikely that annual doses will exceed 1 mSv. No further controls are necessary for crew members whose annual dose can be shown to be less than 1 mSv.
Note: This table is based on the CARI-3 computer program. The uncertainty on these estimates is about ± 20%. A conservative conversion factor of 0.8 has been used to convert ambient dose equivalent to effective dose.
Impact of Radiations on Health
When ionising radiation passes through the body, and energy is transmitted to the tissues, which affects atoms within individual cells and result in a variety of health effects such as development of cancer, genetic risk and risk to the health of the foetus (unborn child).
- Development of cancer is that a cell may be altered as a result of being irradiated and subsequently become cancerous. The likelihood of this happening will depend on the dose received. It has been calculated that an accumulated dose of 5 mSv per year for 20 years increases the risk of developing cancer by 0.4%. Compared with all the other risks encountered during working life, this is very low.
- Genetic risk is that risk which may be present because one or both parents were exposed to radiation before the child was conceived, the effects of which may be passed onto future generations.
- With regard to pregnancy, risk to the health of the foetus may occur as a result of exposure to radiation between conception and birth. The risk of harm depends on the stage of development at the time of exposure as well as the amount of radiation.
COSMIC RADIATION
Reviewed by Aviation Lesson
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9:14 PM
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Reviewed by Aviation Lesson
on
9:14 PM
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