From this study, and others, estimates of the risk associated with radiation exposure have been made. The current estimate of the risk of developing a fatal cancer as a result of exposure to radiation is about one in 80 000 per millisievert. However, at their meeting in Como, Italy, in September 1987 the International Commission on Radiological Protection noted a technical report of the Radiation Effects Research Foundation (ref 42) which suggests that radiation risks as estimated from studies on atomic bomb survivors are about a factor of two higher than previous estimates. Other authoritative studies are currently in progress. All these studies have been carried out on groups of people exposed to relatively high doses of radiation, typically a few hundreds of millisieverts. Studies of populations exposed occupationally to low doses of radiation, typically a few tens of millisieverts have been unable to confirm or disprove that there is any significant risk at such low doses, nevertheless it has been prudently assumed that the same risk per millisievert exists at low doses as at high doses.
3.7 Summary
Early Effects (non-stochastic)
Doses in excess of 10 000 mSv will cause death.
Doses of 3 000-10 000 mSv will cause injury and may cause death.
Doses of 1 000-3 000 mSv may cause injury but are unlikely to cause death. Doses of 300-1 000 mSv will cause temporary physiological changes. Doses below 300 mSv are unlikely to cause any noticeable health effects.
Late Effects (stochastic)
All doses of ionising radiation are assumed to be associated with a risk of developing a fatal cancer, after
a latent period of about 10-30 years, of about one in 80 000 per millisievert. This is demonstrable at high doses and also prudently assumed at lower doses.
The average natural background dose received by the population of Hong Kong is about 2 mSv per year.
17