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Civil Defense Faces New Perils

By Ralph Lapp
Bulletin of the Atomic Scientist
10: 349-5;
1954, Educational Foundation for Nuclear Science

[Abstract] Dr. Lapp assesses the radioactive hazard of "fall-out" and ana-lyzes its impact upon civil defense. His data are gathered from Japanese sources, from independent calculations, and

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from the unclassified scientific literature. He urges that the federal government release classified data on fall-out to provide guidance to civil defense organizations.

On March 1, 1954 chalk-white dust fell on twenty-three Japanese fishermen 72 miles from Bikini. It took three hours for the pulverized coral to start falling-out from the air and coat the Lucky Dragon tuna ship with a mantle of radioactive debris. However, it was not until late this summer that the Federal Civil Defense Administration felt the impact of "fall-out."

Q-cleared officials in FCDA were briefed on the nature of the fall-out. They were shown colored charts with neat elliptical contours describing the range of lethality of the residual radioactivity from superweapon explosions. Up to this point FCDA had worked and thought mostly in terms of circles - the symmetric patterns of primary damage from superbombs which the Bulletin published last month. Now superimposed upon the great circles of H-bomb blast and heat, there were zeppelin-shaped ellipses which stretched far beyond the circles of primary damage.

These ellipses stunned civil defense planners. By a major shift of policy they had replaced previous "duck-and-cover" or "stay put" planning by a policy of pre-attack evacuation which dispersed metropolitan populations beyond the inner circles of near-total and heavy blast damage. Gov. Val Peterson, as head of FCDA, made the policy switch once he took a good hard look at the blast and heat effects of our MIKE explosion of November 1, 1952. What Gov. Peterson realized very clearly was the MIKE was not the last word in superweapon development. Indeed a weapon twice its power was tested in the March-April CASTLE series of tests in the Pacific in 1954. Moreover, this weapon was a bomb, not a "device" - meaning that the United States now possesses a droppable bomb in the range of 20 megatons.

Faced with the prospect of corresponding weapons in the Soviet arsenal, Gov. Peterson recognized that too much of America's metropolitan population resided inside the 14 mile radius of the superbomb's punch. It was sheer suicide, he reasoned, to put 35 million Americans in the sitting duck category. This is the simple background for the policy of evacuation which is now being implemented.

It was at this point in the evolution of C. D. policy that "fall-out" descended upon civil defense planners.

Now radioactivity was not a new wrinkle to the planners. The Baker shot of a 20 kiloton bomb in the Bikini lagoon in July of 1946 saturated the mushroom cloud with awesome quantities of radioactivity. Millions of tons of salt water were erupted into the air and a misty radioactive steam surged across the lagoon surface. An egg-shaped ellipse about 3 miles in length constituted the lethal area of this radioactivity. This area was not comparable to that of a metropolis, so as time went by radioactivity as a menace shrunk to less formidable proportions in civil defense planning.

The dimensions of the superbomb "fall-out" greatly exceeded those for a 1946 A-bomb explosion. Unfortunately, the exact or even rough forecasting of these dimensions is subject to a number of uncertainties. These can be appreciated by describing the fall-out from a superbomb detonation. When the bomb explodes there is a flash of penetrating radiation consisting of neutrons and gamma rays. Fortunately, the area subjected to lethal bombard-ment by this primary flash is small compared with that affected by the heat and blast of the explosion. Although altitude-dependent, the area is much less than that of total destruction from the blast wave.

Once the bomb explodes and the heat-blast waves have run their course, we have to consider the fate of the bomb cloud. If the bomb is burst high in the air so that there is no significant cratering effect the bomb cloud will contain only such surface debris as is sucked up into the ascending column. In this case, the cloud radioactivity consists predominantly of split uranium or plutonium atoms (technically called fission products) which are intensely radioactive. Two factors take their toll in reducing the menace of this activity. One - the high velocity upper air winds disperse the fine (usually invisible) particles in the bomb cloud so that they are dispersed over a very large area before they finally settle out and come to earth. Two - radioactive decay sharply reduces the activity on the following time schedule:

  Time                          Radioactivity
(after burst)                 (arbitrary units)
  1 minute                        1,000,000
  1 hour                                  7,300
  I day                                      162
  I week                                     16
  I month                                     3

Assuming that there were no mass deposits of radioactive debris in the early history of the bomb cloud, then we would have to relegate the problem of cloud activity to the controversial area of global atmospheric contamination and human genetics.

Superbombs which burst close to the surface present quite another problem. In this case, the 3 1/4 mile wide fire-ball of a 10-megaton bomb introduces a radically new factor into the fall-out equation. Much of the substratum below the exploding bomb is dislodged and volatilized into particles impregnated with radioactivity. In addition, some of the elements in the substratum may become radioactive by the primary penetrating radiation from the bomb. Sodium in sea water, for example, is easily activated (made radioactive) and can become a hazard. The pulverized substratum is funneled upward much in the manner of a cyclone. In this way, the coral and sand of a low-lying Bikini atoll island were sucked up into the bomb cloud.

As is well known the cauliflower cloud mushrooms upward to a height of over 10 miles in about 12 minutes. The characteristic 40 to 60 knot winds of the stratosphere then distort the mushroom in a downwind direction. At this point the difference between a high air burst and a low one becomes significant. The subsurface particles tend to all out from the bomb cloud early in its history because of their massiveness. Fall-out of up to 50 per cent of the radioactive debris occurs in the first 24 hours with the maximum activity being deposited in the 1 to 3 hour period.

Estimation of the area of serious-to-lethal fall-out involves many unknowns. First, there is the power of the bomb. Second, the architecture of the weapon, involving principally the contribution of fission to the energy release in the bomb. Third, there is the height of the bomb burst. Fourth, one is confronted with the nature of the substratum - both as a carrier of the radioactivity and also as a producer of radioactivity. (In general, it would seem that induced activities cannot compete with the radioactivity produced in the bomb itself. However, a bomb burst close to sea water would produce vast quantities of radiosodium and radiochlorine. For example, a bomb burst in the Pacific Ocean off the coast of Los Angeles would probably cloak the city in a lethal fog even though no blast shook the city.) Finally, the meteorology at the time of the burst would determine the location and extent of the fall-out.

It is like seeking the Holy Grail to quest for hard data on the fall-out as applied to an American city. The unknowns enumerated above make pre-diction of the fall-out a highly tentative business. About all one can hope to do is to define what might happen. Assuming a 15 megaton superbomb burst close to the ground the author has made the following estimates for the fall-out ellipses:

Time                        Area                         Intensity
(after  burst)                                         (gamma radiation)

1 hr                          250 sq. mi.                 2500 roentgen/hr
3 hr                        1200 sq. mi.                   200 roentgen/hr
6 hr                        4000 sq. mi.                     30 roentgen/hr

It must be remembered that his fall-out will occur downwind. Upwind for 15 miles and sideways for 20 miles the fall-out should not be lethal. Integration of the dosage rate for the 4,000 square mile area leads to the conclusion that people will receive a serious to lethal dose in the first day. The area and hazard represents a conservative calculation. The radioactive hazard is truly immense. The explosion of 50 superbombs could blanket the entire N. E. USA in a serious to lethal radioactive fog.

A schedule for the effects of external radiation upon a man in the open is as follows:

                                                        Roentgen Dose                Effect on Man
                                                        50 to 100 r                Few per cent casualities
                                                        150 to 200 r              50 percent casualities
                                                        200 to 300 r              100% casualities plus some mortality
                                                        400 to 500 r               50% mortality
                                                        700 r                          close to 100% mortality

Applying the 500 roentgen criterion to the fall-out pattern at 1 hour after the bomb burst it is clear that an individual within the 2500 r/hr area would accumulate this dose in 12 minutes. At 3 hours a person much farther down-wind might be exposed to a very serious dose. Here we must consider the relation between the intensity of the radioactivity and the time of exposure. Fortunately, the process of radioactive decay reduces the intensity quite sharply as time goes by. However, one must seek shelter as a protection against the radiation if caught in a near-lethal area. That is, unless some means is provided to direct downwind populations out of the path of the fall out.

Just what kind of shelter protection is required? The answer depends upon how close to ground zero one locates the shelter since blast then becomes the criterion. Assuming, however, that the shelter is located beyond the range of primary blast, the radiation shielding requirements are as follows:

Reduction Factor                       10                 50                     100                     1000
Inches of concrete                        6                 11                       13                         19
or Inches of packed soil               11                18                       21                         30

The relatively small thicknesses of concrete or earth shielding needed to reduce the incident radiation to one-hundredth of its topside value may surprise the layman. Exponential absorption of gamma radiation accounts for the fact that a foot and a half of hard packed soil can reduce an intensity of 2500 r/hr to 50 r/hr. Thirty inches of soil cuts this intensity down to 2.5 r/hr which can be regarded as acceptable for survival in a shelter.

In addition to the external radiation hazard there is the enigma of in-gested or inhaled radioactive debris. judging from the brief reports issued by the Atomic Energy Commission on the medical histories of the Marshall Islanders exposed to fall-out, the internal radiation hazard may be less serious than generally believed. However, data on the Japanese survivors does not make for complacency on the significance of radioactive material taken into the body.

From the foregoing description it can be readily appreciated that fall-out presents civil defense with potentially greater perils than those of heat and blast. Blast can be readily felt as can heat and they both come in a flash. Radioactivity, on the other hand, cannot be felt and possesses all the terror of the unknown. It is something which evokes revulsion and helplessness - like a bubonic plague.

Having been already weighted down by the incubus of the immense primary effects of the superbomb, civil defense planners may well feel that they are condemned to a labor of a Sisyphus. Unless the challenge of the fall-out is met head-on, the very burden may kill civil defense in this country. Those who oppose the FCDA policy of evacuation may use fall-out as the excuse for rejecting the recommendation. They can (and with partial justification) point out that the mass removal of metropolitan population to the suburbs or open country may be like jumping from the frying pan into the fire.

Civil defense must reckon with the hazards of fall-out, but it would be utterly disastrous if it abandoned its policy of evacuation at this time. No one is going to come up with a perfect civil defense plan. As long as we have such huge agglomerations of people on a few bits of territory there can be no perfect civil defense. There will always have to be the element of the calculated risk to civil defense just as there is for the soldier at the front line. What civil defense must do is to acknowledge certain risks in its planning.

First things must come first in any good C. D. plan. This means that one must deal with certain primary effects of superweapons. The great circles of heat and blast effects for weapons in the 10 to 40 megaton range are simply too large to neglect. They are predictable whereas fall-out is not. Further-more, it makes no sense whatsoever to plan for a secondary hazard if you fail to survive the primary effects of the bomb.

The Federal Civil Defense Administration has assessed the true signifi-cance of the circles of damage from H-bombs and has boldly put forth an evacuation policy to deploy urbanites to the suburbs beyond the 12 to 14 mile radius of the city. This policy has yet to be implemented but cities are going ahead with their plans. Milwaukee, Washington, Seattle, and Detroit are a few that have reached an advanced state of planning.

Consideration of the fall-out ellipses must be made and the C. D. plan of each city modified accordingly. One thing is perfectly clear-evacuation even on present plans does provide a. large measure of protection for people since distance is still the best defense against the bomb. Those who are de-ployed upwind or laterally will escape the lethal fall-out. In general, viewed as a problem in geometry, it is the area of the evacuation circle which is intersected by the fall-out ellipse which requires special planning. It will be argued that since we have so many unknowns it is futile to plan. For ex-ample, the wind may be in a contrary direction. However, local data on upper air winds often show a pattern of prevailing winds which may indicate preferential evacuation in upwind directions. Moreover, when an alert comes civil defense directors can make an immediate prognostication of the probable fallout area based on current weather data.

The alert is the great and vexing problem in evacuation. It is often pointed out that there may be no warning whatsoever. This is possible but it certainly does not apply to all cities. Moreover, it flies in the face of probability. There may, in fact, be a long period of alert - a strategical alert of days, weeks, or even months.

Dr. Vannevar Bush, in his testimony before the Riehlman subcommittee, pointed out that conventional warfare might precede nuclear warfare due to the initial respect which each nation might have for the other's nuclear capability. Such a period of tension would make possible gradual decentralization of urban populations in anticipation of a nuclear attack. Time would also be given, plus the incentive of imminent attack, to prepare peripheral shelters to accommodate evacuees.

Besides the strategical alert period accompanying Dr. Bush's concept, there is a shorter term alert which would be concomitant with Soviet aggression into zones to which we guaranteed military support. Should the Soviets strike in such an area they might well limit themselves to conventional weapons, and it would then be up to the President to issue the fateful ultimatum for "retaliation in advance." Any such ultimatum would be, if sanity prevailed, accompanied by a nation-wide evacuation order.

The announcement that a Distant Early Warning line of radar posts is to be established in the far north provides hope that before long a 4 hour tactical alert will be assured for continental cities. Four hours is sufficient for most cities to deploy their populations to relatively safe sites provided evacuation plans are perfected and test drills are inaugurated.

Progress is being made in civil defense despite the vertiginous, almost exponential, rise in the hazards faced. The year 1954 may well mark the turning point in our C. D. activities. One very favorable index is that more and more top advisors in the government are becoming serious about civil defense. More and more, it is becoming clear that the security of the home base is of paramount importance. In this security, civil defense must assume a high priority.

The Federal Civil Defense Administration must be permitted access to classified data about fall-out. Furthermore, the agency must be able to translate these data or "sanitize" them so that a realistic picture of the radioactive hazard can be given to the American people. Local communities should not be left to plan in the dark nor should they be put in the position of planning on the basis of newspaper reports.

In the final analysis the solution to civil defense problems will not come from Washington. it is in the local communities that they will find a solution. The federal government can help with solid planning data, with technical assistance, and with financial support. But the real burden of the work must be shouldered by the people who reside in the cities. However, the new peril from radioactive fall-out is more than just a threat to civil defense-it is a peril to humanity.