The opinions expressed herein are the guest's alone. If you have questions about your health, you should consult your personal physician. This event is meant for informational purposes only.

Q: The last time the nation seriously considered the threat of a nuclear explosion, the advice was to "duck and cover." Today we realize how silly that advice was, but is there anything the average person can do to prepare for the aftermath of a nuclear explosion or accident, if lucky enough to survive?

Edwin Lyman: When we look at "duck and cover" it seems silly today in the context of an all-out nuclear war between the U.S. and the Soviet Union. There was no protection in the case of such a war. But if we are talking about the possibility of a terrorist with a small number of nuclear weapons, it does make sense to ask the question, "Are there ways in which individuals can reduce their risk of injury in the event of a terrorist nuclear attack?"

The first question that is often asked is about potassium iodide -- is it something that individuals should stockpile? Potassium iodide can block the uptake of radioactive iodine, an isotope that would be released in great quantity if a nuclear power plant were to have an accident or if a nuclear bomb were to be detonated. It is my judgment that it would be useful for individuals in the vicinity of nuclear power plants to have ready access to potassium iodide in the event of an attack on a nuclear plant, however, the limitations of potassium iodide need to be explained.

The evidence now is that it would be most effective only for people under the age of twenty or for pregnant women. For adults it is less clear whether potassium iodide would be a significant factor in preventing thyroid cancer, but obviously for children it could be an important measure. This said, one has to realize that radioactive iodine is only one element of an enormous soup of different radioactive elements that would be released in a nuclear terrorism incident. And potassium iodide can provide only limited protection.

Q: Where do we obtain potassium iodide, and in what form does it come? In a pill, a shot, a liquid?

Edwin Lyman: After opposing the requirement to stockpile potassium iodide near nuclear plants, the nuclear regulatory commission has recently changed its position and has delegated the authority to state governments to make that decision. I am unaware that any state government has made that decision, but if that were the case, then people within the emergency planning zones around nuclear plants would be able to obtain it from emergency responders.

It is also being sold over the Internet and I have seen a lot of false and misleading claims about what it can do, so people should be aware that there are cons out there with potassium iodide sales.

Again, I don't think it is necessary at this point for people to obtain it unless in they are within 10 miles of a nuclear plant. The form is a tablet, I believe, and it should be noted that it does have side effects. There are some sad stories in the aftermath of the Chernobyl incident. Local governments attempted to distribute potassium iodide tablets but were short of supply, so individuals went to pharmacies and bought it in liquid form and fed it to their children and it caused injury to the children. So it should be recognized that it is a drug and it has side effects and people should not take it or give it to children in the absence of a true emergency.

Q: What long-term health effects could people expect who were exposed but didn't perish?

Edwin Lyman: The primary health effect from ionizing radiation is cancer. The type of cancer depends on the nature of the exposure. But fundamentally, ionizing radiation can damage the DNA in our cells, and this causes lesions that can affect the cell division process and ultimately lead to cancer.

Besides thyroid cancer, which we have discussed, leukemia is a very well-established consequence of radiation overexposure as well as cancer of the lungs, breast, and brain. The only cancer that is not linked to ionizing radiation exposure is one of the chronic leukemias -- CLL.

It is also interesting that the study of the victims at Hiroshima and Nagasaki is now revealing higher death rates than expected from diseases other than cancer, including cardiovascular and respiratory diseases. And, in fact, the full array and consequence of radiation exposures are still not entirely known. There are also neurological effects of radiation, especially for the developing fetus, and mental retardation has been observed in higher-than-expected rates among children who were exposed in utero in Japan.

Q: What are the first physical signs of radiation exposure? Could we see a radiation cloud, or is it invisible?

Edwin Lyman: Again, it probably makes sense to go over a few basics here. There are two distinct classes of effects of radiation exposure. There are effects in which very high doses cause acute symptoms within hours to days of exposure. These symptoms commonly include skin burns, gastrointestinal symptoms, reduced white blood cell counts, and increased susceptibility to infection, hair loss, and similar acute symptoms. There is a range in very high radiation doses where it is unlikely someone would survive, even with heroic measures.

At lower doses the acute radiation syndrome can spontaneously resolve. However, at doses below the threshold for acute effects there will be no visible symptoms although the damage to DNA that could lead to later cancers will have been done. In that case, tests may show chromosomal damage and can help to calibrate exposures.

In response to what radiation looks like -- it is well known that radiation is invisible and to detect elevated radiation levels in the environment requires instrumentation. However, that said, we can think of particular ways exposures might occur.

If a nuclear weapon were detonated there is a tell-tale flash followed by a shock wave blast; the bomb, if detonated near the ground, would cause a crater, and material and earth within the crater would be sucked up as fallout and then distributed over a wide area. This would be visible ash and would be extremely radioactive, so one of the first measures that could be taken for individuals surviving the initial blast would be to avoid contact with visible fallout. However, this would not ensure a lack of exposure because there are other components that would not be visible.

In the case of a nuclear power plant accident, there may be some debris, but I don't believe the radioactive plume would be visible downwind of the site; if the plant were on fire there would be smoke visible, once dissipated there would be no way to detect this visually.

Member Question: What are the levels of radiation risk at 10 miles, 100 miles, 100,000 miles from ground zero? How far can the radiation travel? Is that based solely on wind direction?

Edwin Lyman: Well, again one should distinguish between a nuclear weapon attack and an attack on a nuclear plant.

For a nuclear power plant accident, the acute effects I described -- acute radiation sickness with a high chance of death -- would be limited to within 10 miles or less of the accident. This is partly the basis for the choice of 10 miles as the size of the emergency planning for U.S. plants. However, the plume would be carried by the wind and depending on atmospheric conditions could contaminate a large area and even hundreds of miles downwind there would be some significant contamination. This was seen after the Chernobyl accident, where large sections of Northern Europe did receive significant contamination and the aftermath was detectable all around the northern hemisphere.

The range of effects from a nuclear weapon is very strongly dependent on its yield and whether it was detonated on the ground or at some height above the ground. If we take the example of a terrorist crude nuclear device, let's say one-tenth or one-fifteenth of the Hiroshima yield (which would be about a 1,000 tons of TNT equivalent), the blast affects would be fairly limited in range, probably to less than one mile.

The direct radiation effects would be felt considerably farther and fallout would travel hundreds of miles, and that would be directly related to atmospheric conditions and wind direction. So, the extent does depend on a lot of factors, but the ultimate effect could be felt tens or hundreds of miles away. However, the farther one is from the site of detonation, the more time there is to take countermeasures.

Member question: What kind of countermeasures?

Edwin Lyman: Well, this takes us back to "duck and cover." If there were a nuclear explosion of relatively small yield, such as I described above, people who are maybe tens of miles away would have something like a half an hour to shelter themselves. And such action could potentially mean the difference between life and death. Actions as simple as taking cover in a basement or reinforced concrete structure away from windows could potentially reduce radiation exposure. But fallout even at large distances would persist and people may have to remain in those locations for days or even weeks.

Does this mean that the U.S. should reactivate a system of fallout shelters? I don't know. I hope the office of Homeland Security is addressing this issue in the context that I described -- that is, in the event of a small number of terrorist weapons. I still do not believe that civil defense is an appropriate response to an all-out nuclear war, but hopefully the threat of that kind of an exchange has been greatly reduced and will continue to diminish.

Member question: How real is this threat of nuclear terrorism in our current situation?

Edwin Lyman: You cannot assess whether the threat is a real one without access to intelligence, but what one can do is point to vulnerabilities that do exist today and ask is it plausible that these vulnerabilities could be exploited?

We know that Osama bin Laden has stated he has nuclear weapons. There is skepticism on the part of the U.S. government, but not outright denial. And the fact is that there are large amounts of nuclear-weapon capable materials that are poorly secured, and inventories are not well established. This is largely the case in the former Soviet Union. So it is difficult to exclude the possibility that determined terrorists have been able to obtain nuclear material.

However, that leaves the challenges of assembling a workable nuclear device and delivering it.

It is believed that a crude nuclear device is within the capabilities of terrorists. Such a device, if it has a low yield, would be more of a threat from the radiation exposure than from the actual blast. In the case of a nuclear reactor, there are plausible ways in which a group of determined terrorists could attack a plant and cause a massive release of radiation. Nuclear plants in the U.S. are required to have security forces and other physical protection measures. But the sad truth is that the existing requirements are not likely to be adequate to prevent a determined attack by a large number of attackers. The issue of an aerial threat to a nuclear plant as we saw on Sept. 11 still remains a real possibility.

Q: Do you have any final comments for us?

Edwin Lyman: I certainly don't want people to panic. And I don't think there is any need to rush out and buy potassium iodide. But I think the public needs to be aware of the issues, especially nuclear power plant security. I would hope that people who live in the area of nuclear plants would take a critical look at the level of security that is being applied and pressure the authorities to increase that security. This can't be left up to the industry,

The opinions expressed herein are the guest's alone. If you have questions about your health, you should consult your personal physician. This event is meant for informational purposes only.