We Are Exposed To Radiation All The Time


Radiation reaches us from outer space and from radioactive substances in the ground, in the sea and in the air. We are also exposed to artificial radiation which comes from X-rays, from medical treatments, and from certain types of measuring equipment in industry. Apart from the very narrow spectrum of visible light, radiation cannot be seen, touched or tasted, but can only be measured by scientific instruments.

We measure the amount of received radiation in millisieverts (mSv) and call it the radiation dose. The radiation comes from natural radioactive sources, which includes cosmic rays, the geology and the building materials, is called “background radiation”. It varies from place to place but in Hong Kong, we are typically exposed to 3 millisieverts of radiation each year. We would receive a higher dose in our way of life such as the food we consume, the medical treatment we receive, the air travel or smoking we take.


From natural 85%

From medicine 14%

From nuclear < 1%

Radiation can have an impact on the living tissues. Our bodies are usually capable of repairing this minor damage or even making use of the changes without any apparent ill effects. However, the affected cells are radically altered or may die in strong radiation. It is a common understanding that no harmful effect or only a small consequence can be observed in low radiation dose. However, the early effects may appear just a few days after exposed to a high dose of radiation and the late effects may take several years to appear after exposed to a dosage much above natural levels.


"Radiation sickness may appear when the dosage is above 1,000 millisieverts. People may suffer early effects with the symptoms of hair loss, nausea and skin burns. The severity of the symptoms will increase with the dose. Fatality becomes more frequent at higher doses and at above 10,000 millisieverts, a person will die within a few weeks. The late effects of having exposed to the radiation dose below 1,000 millisieverts are a higher risk of developing cancer at a higher dose. For example, someone living in an area with a high level of background radiation of 100 millisieverts may have an extra risk of 1 in 80,000 of getting cancer. However, there is one location in Iran where the natural background radiation is reportedly above 100 millisieverts, but this apparently has no ill effects on the local inhabitants . In practice, it is very difficult to say at precisely what level will radiation pose no risk to human beings, since it is not practically possible to isolate the effect of low radiation doses from other possible causes of cancer, including tobacco smoke, ultra violet lights, asbestos, some chemical dyes, fungal toxins and viruses."


Radiation Dose and Effects

Dose Comments and Effects
0.25 mSV/year PRC Regulatory limit for the collective effect of nuclear installations at a site onto its nearby general public
0.3 - 0.6 mSV/year Typical range of doses from artificial sources of radiation, mostly medical
2 mSV/year Minimum natural radiation worldwide
2.4 mSV/year Typical additional dose to US nuclear workers
3 mSV/year Typical radiational dose in Hong Kong
Up to 5 mSV/year Typical additional dose to aircrew in middle latitudes
15 mSV/year Typical natural radiation dose in Kerala and Madras, India
20 mSV/year Internal limit from work for Daya Bay nuclear workers. Average regulatory limit from work for PRC nuclear workers
50 mSV/year Highest Regulatory limit from work for PRC nuclear workers. Natural radiation doses for several places in Iran, India and Europe without apparent harm to the local population
100 mSV/year Lowest level at which cancer is clearly evident. Above this level, the risk of cancer increases with the dose.
260 mSV/year Maximum natural radiation dose known on earth (Ramsar in Iran)
350 mSV/lifetime Criterion for relocating people after the Chernobyl accident.
1000 mSV/cumulative Probably causing fatal cancer many years after the exposure for 5 out of 100people.
1000 mSV/event Radiation sickness. Above this level, severity increases with dose.
5000 mSV/event Fatality for about half of those receiving it within a month.
10000 mSV/event Fatality within several weeks.

The public is protected from artificial radiation by the careful design and operation of equipment that contains or emits radiation, so as to keep radiation within confined areas in a confined location, and through the enforcement of the statutory regulations designed to safeguard the public. Through prompt and appropriate action, the risk of radiation is kept very low.

To protect individuals from sources of radiation:



The intensity of radiation will decrease away from its source. Keeping away from a radiation source will reduce the radiation dose and the resulting risk. So, workers are kept away from the radiation-controlled area in a nuclear power station unless work is necessary.


Time of exposure

Limiting the time of exposure to a radiation source will reduce the dose and therefore the risk. Work in the radiation-controlled zone is carefully planned for workers to reduce their time of exposure.


Physical shielding

Having a layer of protective material, such as lead, concrete or water will reduce the intensity of the radiation reaching the people. Radioactive materials are often stored or handled under water, or in rooms with thick concrete walls.



Radioactive materials are kept in closed containers away from the environment. Nuclear reactors are operated in closed systems with several barriers to keep the radioactivity inside.

Safety Regulations


The operation of a nuclear power station is closely monitored by national regulators, to ensure that the safety regulations developed in line with international practice are being followed, in order to keep radiation away from the public and the environment.

The Radiation Hazard Symbols





Risks to individuals

Accidents Annual Risk of Death
Heart Disease 1 in 300
Cancer 1 in 400
Flu 1 in 4000
Accidents Annual Risk of Death
All Accidents 1 in 3000
Road Accidents 1 in 7000
Lightning 1 in 6million (UK)
Diseases Annual Risk of Death
Natural Background 1 in 40,000 (UK)
Nuclear Industry 1 in 40 million (UK)