In 1992, the average dose received by nuclear power workers in the United States was 300 mrem in addition to their background dose.
At low doses, such as what we receive every day from background radiation, the cells repair the damage rapidly. At higher doses (up to 100 rem), the cells might not be able to repair the damage, and the cells may either be changed permanently or die. Most cells that die are of little consequence, the body can just replace them. Cells changed permanently may go on to produce abnormal cells when they divide. In the right circumstance, these cells may become cancerous. This is the origin of our increased risk in cancer, as a result of radiation exposure.
At even higher doses, the cells cannot be replaced fast enough and tissues fail to function. An example of this would be "radiation sickness." This is a condition that results after high doses (>100 rem), where the intestinal lining is damaged to the point that it cannot perform its functions of intake of water and nutrients, and protecting the body against infection. This leads to nausea, diarrhea and general weakness. With higher doses (>300 rem), the body's immune system is damaged and cannot fight off infection and disease. At doses near 400 rem, if no medical attention is given, about 50% of the people are expected to die within 60 days of the exposure, due mostly from infections.
If someone receives doses more than 1,000 rem, they suffer vascular damage of vital blood providing systems to the nervous tissue, such as the brain. It is likely at doses this high, 100% of the people will die, from a combination of all the reasons associated with lower doses and the vascular damage.
What needs to be remembered is that very few people have ever received doses more than 200 rem. With the current safety measures in place, it is not expected that anyone will receive greater than 5 rem in one year. Radiation risk estimates, therefore, are based on the increased rates of cancer, not on death directly from the radiation.
Non-Ionizing radiation doesn't cause damage the same way that ionizing radiation does. It tends to cause chemical changes (UV) or heating (Visible light, Microwaves) and other molecular changes (EMF). Further information on EMF that may be of interest.
It is difficult to estimate risks from radiation, for most of the radiation exposures that humans receive are very close to background levels. In most cases, the effects from radiation are not distinguishable from normal levels of those same effects. With the beginning of radiation use in the early part of the century, the early researchers and users of radiation were not as careful as we are today though. The information from medical uses and from the survivors of the atomic bombs (ABS) in Japan, have given us most of what we know about radiation and its effects on humans. Risk estimates have their limitations,
Risk fro radiation exposure has been estimated by other scientific groups. The other estimates are not the exact same as the BEIR V estimates, due to differing methods of risk and assumptions used in the calculations.
To answer this, we need to make a few general statements of understanding. One is that in the US, the death rate of cancer is approximately 20 percent, so out of any group of 10,000 United States citizens, about 2,000 of them will die of cancer. Second, that contracting cancer is a random process, where given a set population, we can estimate that about 20 percent will die, but we cannot say which individuals will die. Finally, that the risk from low doses of radiation is linear with dose. That is, that the risk increases with a subsequent increase in dose. Most scientists believe that this is a conservative model of the risk.
So, now the risk estimates. If you were to take a large population, such as 10,000 people and expose them to one rem, you would expect approximately eight additional deaths (0.08%*10,000*1 rem). So, instead of 2,000 dying from cancer, you would now have 2,008. This small increase in the expected number of deaths would not be seen in this group, due to natural fluctuations in the rate of cancer.
What needs to be remembered it is not known that 8 people will die, but that there is a risk of 8 additional deaths in a group of 10,000 people if they would all receive one rem.
Risks can be looked at in many ways, but one easy way to visualize them is by looking at the number of "days lost" out of a population due to early death from separate causes, then dividing those days lost between the population to get an "Average Life expectancy lost" due to those causes. The following is a table of life expectancy lost for several causes:
| Health Risk | Est. life expectancy lost |
|---|---|
| Smoking 20 cigs a day | 6 years |
| Overweight (15%) | 2 years |
| Alcohol (US Ave) | 1 year |
| All Accidents | 207 days |
| All Natural Hazards | 7 days |
| Occupational dose (300 mrem/yr) | 15 days |
| Occupational dose (1 rem/yr) | 51 days |
You can also use the same approach to looking at risks on the job:
| Industry type | Est. life expectancy lost |
|---|---|
| All Industries | 60 days |
| Agriculture | 320 days |
| Construction | 227 days |
| Mining and quarrying | 167 days |
| Manufacturing | 40 days |
| Occupational dose (300 mrem/yr) | 15 days |
| Occupational dose (1 rem/yr) | 51 days |
These are estimates taken from the NRC Draft guide DG-8012 and were adapted from B.L Cohen and I.S. Lee, "Catalogue of Risks Extended and Updates", Health Physics, Vol. 61, September 1991.
So, in summary, we must balance the risks with the benefit. It is something we do often. We want to go somewhere in a hurry, we accept the risks of driving for that benefit. We want to eat fat foods, we accept the risks of heart disease. Radiation is another risk which we must balance with the benefit. The benefit is that we can have a source of power, or we can do scientific research, or receive medical treatments. The risks are a small increase in cancer. Risk comparisons show that radiation is a small risk, when compared to risks we take every day. We have studied radiation for nearly 100 years now. It is not a mysterious source of disease, but a well-understood phenomenon, better understood than almost any other cancer causing agent to which we are exposed.
Originally from http://www.umich.edu/~bbusby/risk.htm.