The 1990 changes adopted by WorkSafe Australia and the National Health and Medical Research Council recommended stricter controls on radiation levels for people, such as flight attendants and technical crews, who are exposed to radiation when at work. As a result, the Australian recommendations for pregnant air crew are now the lowest in the world.
Radiation is measured in Sieverts(Sv) and the exposure levels for workers are measured in millisieverts (mSv), which are one-thousandth of a Sievert. Air crew have been defined as "occupational exposed workers", and the dose limit for ionizing radiation recommended for such operations is set as 2OmSv per year, averaged over five years. However, the new exposure limit for pregnant- workers is one millisievert per year.
The International Commission on Radiation Protection ( ICRP ), in 1990, revised the 1976 exposure limits for both Occupational Workers and the General Public. Air crew are considered to be occupation exposed
ICRP 26 (1976) limits:
ICRP 60 (1990):
In Australia, the NH&MRC and WorkSafe have unilaterally further reduced the pregnant worker exposure limit
NH & MRC & WorkSafe limits:
All humans are exposed to ionizing radiation and the risk of ill effects from cosmic radiation is considered to be extremely low for air crew operating under normal conditions.
However, the new, lower standards set a limit to radiation exposure which is 50% lower than the international standards for pregnant workers. This is because of a concern that levels which might be harmless to air crew could, however, affect the human fetus.
Two extensive monitoring surveys by the Australian Radiation Laboratories to measure radiation exposure of cabin and technical crews show Australian technical crews on domestic routes are exposed to, on average, to 1. 1 mSv/year for flight engineers and 1.8 mSv/year for pilots, making it possible to exceed the 1 mSv dose during a full nine month pregnancy. Until the exposures are reworked using the latest FAA software it should be considered possible within the current 30 week pregnancy licensing cut off to reach the new 1 mSv exposure maximum.
Cosmic radiation means any radiation transmitted through space and matter in the form of packets of energy (photons) or as subatomic particles. The term Ionizing Radiation is used where photons or subatomic particles, on colliding with any material, removes one or more electrons from an atom This results in a positive ion (the remaining nucleus) and a free electron. Ionization is the principle means by which radiation exposure leads to harmful biological effects.
Ionizing radiation results from exposure to gamma rays, X-rays and subatomic particles. Ionizing effects do not occur with ultraviolet, infrared, radio and microwave radiation. We are continually exposed to Ionizing Radiation from Cosmic Radiation from Space, Terrestrial Radiation from our Earth, inhaled Radon, naturally occurring Nucleotides (such as radioactive potassium in our diet) and man-made sources from medical X-rays and nuclear power plants.
This is produced from radioactive materials in the soil and rocks. By far the largest source is Radon Gas produced from Radium present in the soil. The United States Surgeon General has estimated that 20,000 cases of lung cancer a year are caused by radon gas exposure in peoples house building materials and the soil beneath
A certain amount of radioactive material as radioactive carbon is retained in our bodies from the plants and animals we eat.
1. Cosmic Galactic radiation
This radiation originated from outside our Solar system as high energy subatomic particles which collide with and disrupt constituent atoms of the atmosphere producing additional subatomic particles.
2. Cosmic Solar radiation
This is emitted continually by our Sun and is usually too low in energy to contribute a hazard. However the infrequent and unpredictable 'solar flare events' can substantially increase our dose rate.
All air crew are exposed to cosmic radiation levels that are higher than those levels encountered on the ground. An additional very low hazard exposure source comes from onboard Radioactive Material shipments. Internationally, in nuclear armed and nuclear powered countries, this may amount to 10% of the Cosmic exposure dose.
Radiation Sources
A number of factors affect the amount of radiation exposure a crew member receives on any particular flight
The Tech. Crew can receive on average 10% more radiation than Cabin Crew. For International operations the average exposure dose is said to be 3.8 mSv per year.
Epidemiological studies have shown that, for the general public, the % risk of dying of Cancer is about 23%. The most recent radiation risk models indicate that a crew member flying long haul routes for 20 years would increase this risk from 23% to 23.3%.
For example in the US the likelihood of dying of cancer from all causes is 220 in 1,000 ( i.e. for every 1,000 persons 220 would be expected to die of cancer). The radiation exposure on air crew from international flying (all routes average) over 20 years may increase this risk to 225 in 1,000. Domestic routes in Australia would carry a lower risk.
The minimum estimated added risk to air carrier crew members of developing fatal cancers from Cosmic Radiation (for 30 years of flying at 900 hours per year) is 1 in 3,700, the median risk is 1 in 170 and the maximum risk is 1 in 100.
No studies have ever confirmed the maximum risk figures. In fact, studies in Japan, Canada and Europe concluded that radiation associated cancers e.g. leukemia, are less common in air crew than in the general population.
For the unborn child the risk of harm depends on several factors
The estimated risk to a child of a serious health defect from prenatal exposure to Cosmic Radiation (flying for 7 months at 100 hours per month, with an exposure of 0.58mSv/100 block hours - say continual work on the Athens - New York route) is 1 in 1,100.
A live born child conceived after radiation exposure of one or both parents is considered to be at risk of inheriting one or more radiation-induced genetic defects.
Worse case scenario: where both parents have been exposed (Risk is additive) is 171 in 1 million (or 2 in 10,000) which is 0.002% , 1 /100th of the general population risk
Note:
These are additional risk factors to the general population rate
of serious anatomic abnormalities in offspring which, in the West,
is 200 - 300 in 10,000 or 2% to 3%
Written by Dr Dai Lewis, Medical Director, Occupational
Medicine Department, Ansett Australia
Using the following references:
- FAA Circular (AC 120-52)
- Health Physics May 1994 Vol. 66 No. 5
- Australian Radiation Laboratories Radiation Survey, Ansett (Domestic) 1991