The Earth is continuously being bombarded by high energy radiation from the sun (solar radiation) and the solar system (galactic radiation). The collective term for these forms of radiation is cosmic radiation.
Some of this cosmic radiation is absorbed by the earth’s atmosphere. The intensity and power of cosmic radiation diminishes rapidly with thickness of the atmosphere, so flying at high altitude increases exposure to cosmic radiation. The intensity of cosmic radiation is also influenced by the earth’s magnetic field, which can deflect cosmic radiation. Deflection is greatest at the equator and least at the poles where cosmic radiation can penetrate deeper into the atmosphere.
A person living at sea level receives a small radiation dose from cosmic radiation. The dose varies with latitude and altitude but the variability across Ireland is extremely small. Air crew and airline passengers receive an additional dose from cosmic radiation. For passengers and aircrew, the dose received depends on the frequency of flights and the routes flown.
Because cosmic radiation increases with altitude and latitude, air travel results in an additional radiation dose compared with staying on the ground. Higher doses are associated with long-haul and trans-polar flights, e.g. to North America and the far-east. Lower doses are associated with short-haul flights to Europe.
Air crew who fly exclusively below 8000 metres are unlikely to receive radiation doses in excess of 1 millisievert (mSv) per year – the radiation dose limit for the public as specified by the law.
Air crew who fly above 8000 metres will receive higher doses from cosmic radiation. Aircraft operating above 15,200 metres are required under Civil Aviation JAR-OPS regulations to be equipped with cosmic radiation detection and measurement equipment.
Airline operators are required by law to carry out an evaluation of the likely exposure of air crew to cosmic radiation (S.I. No. 30 of 2019). The evaluation must:
Where the evaluation shows that any air crew are liable to receive doses in excess of 1 mSv in any 12-month period, the law states the operator must:
a) assess exposures to each individual, by approved methods
b) keep appropriate records
c) apply Regulation 24 of S.I. No. 30 of 2019 for pregnant air crew
d) make their records available to crew on request
e) submit each record to the National Dose Register
f) inform crew of health risks and their individual dose
More information on the Ionising Radiation Regulations 2019 can be found here
Where air crew are liable to receive cosmic radiation doses in excess of 6 mSv in a year, this will be managed as a planned exposure situation, and the air operator shall make additional provisions:
a) apply the relevant requirements laid out in S.I. No. 30 of 2019
b) organise work schedules to reduce crew exposures
The assessment of each individual air crew dose is made by combining route dose with crew roster data. Route dose estimates can be calculated using computer programs specifically designed for that purpose. Computer programs such as EPCARD and CARI-6 are specifically designed to calculate route doses. When a pregnancy is declared by a crew member, steps must be taken to prevent that individual becoming exposed to more than 1 mSv during the remainder of the pregnancy.