In This Issue
Nuclear Dangers
June 15, 2010 Volume 40 Issue 2

Reducing the Consequences of a Nuclear Detonation: Recent Research

Tuesday, June 15, 2010

Author: Brooke Buddemeier

Until very recently, there was no scientific consensus on measures to be taken after a nuclear detonation.

Nuclear terrorism has been an essential part of national preparedness since the formation of the U.S. Department of Homeland Security (DHS),1 but until recently little research had been done on the potential effects and mitigation strategies specific to a low-yield, ground-level nuclear detonation in a modern U.S. city. An effective response will involve large-scale measures, mass casualty management, mass evacuations, and mass decontamination. Preparedness planning for this scenario presents especially difficult challenges in time-critical decision making and the management of a large number of casualties in the hazard area. Perhaps even more challenging will be coordinating a large-scale response that involves multiple jurisdictions with limited infrastructure and limited resources.

In 2007, Congress, concerned that cities had little guidance to help them prepare their populations to react in the critical minutes after a nuclear terrorism event, directed the DHS Office of Health Affairs (OHA) to work with the National Academies Institute of Medicine, the Homeland Security Institute, the national laboratories, and state and local response organizations to address this issue (U.S. Congress, 2007). The OHA initiative is currently managed by the Federal Emergency Management Agency (FEMA) as part of a coordinated federal effort to improve response planning for a nuclear detonation.

At the start of OHA’s efforts, there appeared to be no scientific consensus on actions that should be taken after a nuclear detonation. For example, the recommendations on the DHS website,, are consistent with the recommendations of the National Academies (2005) but were criticized by the Federation of American Scientists (2006) based on conflicting recommendations in a RAND study (Davis et al., 2003; Orient, 2005).

Moreover, the existing federal guidance was focused on avoiding relatively low-level exposures to reduce the risks of cancer from an accidental release of radiation from transportation or a nuclear power plant and was not applicable for making the life-or-death decisions that would be necessary in the immediate aftermath of a nuclear detonation (DHS, 2008).

The cold war-era civil defense program can provide some insights, but many of the paradigms no longer apply. For example, community fallout shelters might have worked for people who had a few minutes warning of incoming missiles, but they would be much less effective for an attack that occurs without notice.

Through workshops with state and local stakeholders, OHA found that few, if any, communities had developed coordinated regional response plans for the aftermath of a low-yield (10 kiloton or less) nuclear detonation. The workshops revealed a general lack of understanding of the response requirements and many uncertainties about federal, state, and local roles and responsibilities. At an Institute of Medicine workshop on medical response planning for an improvised nuclear device (IND), a responder from Chicago, Joseph Newton (2006) commented, “We don’t know what perfect looks like.”

Recent Research

To resolve conflicts in the technical community and create a coordination point for research, DHS formed the IND Modeling and Analysis Coordination Working Group (MACWG), comprised of national laboratories, technical organizations, and federal agencies, to coordinate research on the effects of an IND and develop response strategies. The purpose of MACWG was: (1) to establish scientific consensus (where possible) on the effects of, and issues related to, INDs; (2) to bound uncertainties and identify unknowns; and (3) to resolve conflicts about recommended response actions.

As directed by Congress, OHA has coordinated an extensive effort to model the effects of 0.1-, 1.0-, and 10-kiloton nuclear yields in New York City, Washington, D.C., Chicago, Houston, San Francisco, and Los Angeles; sponsored workshops in state and local communities across the nation, as well as with the National Academies; conducted testing with focus groups on public messaging; and coordinated its efforts with key federal agencies, national laboratories, and technical organizations that have unique capabilities and knowledge about nuclear effects and emergency response.

Figure 1

Thermal Exposure

The results of recent modeling indicate that a modern urban environment can greatly mitigate some of the effects of a low-yield nuclear detonation. For example, thermal burns from the heat of the initial explosion, primarily a line-of-sight phenomenon, can be greatly reduced in an urban environment where structures can block the thermal radiation. Figure 1, from a model developed at Lawrence Livermore National Laboratory, shows how building shadows can protect the outdoor population from significant thermal exposure (Marrs et al., 2007).

Models developed at Applied Research Associates (ARA) and Los Alamos National Laboratory have shown similar reductions in injuries from the initial radiation produced in the first minute of a nuclear explosion. The Los Alamos graphic (Figure 2) shows the nonsymetrical nature of urban exposure. In the areas beyond the dotted line on the image, even outdoor exposures levels would be low, survivable levels from prompt gamma radiation. Like the thermal analysis, these studies indicate that the ambient radiation levels from a low-yield, ground-level nuclear detonation in an urban environment could be significantly reduced. For example, the unobstructed range for a potentially lethal radiation exposure of 400 rads (cGy)2 is about 1,200 yards. Initial results by ARA indicate that the range might be reduced by one-third or more, down to 600 to 800 yards, from the detonation point in built-up areas.

Figure 2

Blast Effects

The primary prompt effect3 of a nuclear explosion is blast damage. A 10-kiloton explosion is equivalent to ~5,000 truck bombs like the one that destroyed the Murrah building in the 1995 Oklahoma City bombing (Mlakar et al., 1998). Blast effects from such an explosion can severely damage or destroy most buildings within half a mile of the detonation point, and people in this area would probably not survive. From one-half mile to about a mile out, survival would most likely depend on the type of structure a person was in when the blast occurred. Even at a distance of one mile, the blast wave would have enough energy to overturn some cars and severely damage some light structures.

Updating our cold war understanding of blast damage in a modern city is another important area of research. The bombings of Hiroshima and Nagasaki demonstrated that the area of glass breakage is nearly 16 times greater than the area of significant structural damage (Glasstone and Dolan, 1977). Injury from broken glass has not previously been well modeled, however, because cold war planners generally considered it “not of military significance.”

Although improved building codes since the cold war may contribute to better building survival, there would be a higher likelihood of breakage and potential injury for people near windows because many modern buildings have larger windows. The American Academy of Ophthalmology has noted, “Most injuries among survivors of bombings have been shown to result from secondary effects of the blast by flying and falling glass, building material, and other debris. Despite the relative small surface area exposed, ocular injury is a frequent cause of morbidity in terrorist blast victims” (Mines et al., 2000).

Nuclear Fallout

In addition to prompt effects that radiate outward from the detonation site, a nuclear detonation can also produce nuclear “fallout,” which is generated when the dust and debris excavated by the explosion combine with radioactive fission products produced in the nuclear detonation and are drawn upward by the heat of the event. This cloud rapidly climbs through the atmosphere, and a 10 kiloton explosion could potentially rise to a height of 5 miles.4 Under ideal weather conditions, it would form a “mushroom cloud” from which highly radioactive particles would drop back to earth as the cloud cools. At Hiroshima and Nagasaki, there was no significant fallout because the detonations occurred at altitudes of 1,900 and 1,500 feet, respectively, so fission products did not have an opportunity to mix with excavated earth.

In the absence of complex, accurate weather information, fallout modeling has typically relied on the cigar-shaped Gaussian fallout pattern. Although this pattern could occur under ideal weather conditions, it is not a good planning assumption because fallout patterns would most likely be irregular or differently shaped in real-world atmospheric conditions. Even in nuclear tests at the Nevada Test Site, where the detonation could be conducted under favorable weather conditions, fallout patterns (Figure 3) were very different from the cigar-shaped Gaussian plots commonly used for response planning.

Figure 3

Basing community or regional response plans on the expectation of a Gaussian fallout pattern would create a false impression that fallout would be limited to a symmetrical, easily defined area that could be quickly and easily traversed and that the population in the fallout area would have perfect situational awareness of which areas had been contaminated. These false expectations may have contributed to “evacuate immediately” guidance, which can actually result in higher exposures because it would put people outdoors and in harm’s way when the radiation levels would be highest (Davis et al., 2003; Federation of American Scientists, 2006).
Figure 4 

An artist’s rendition of the combined prompt effects and fallout (Figure 4) provides an example of a complex fallout pattern. The image also shows thermal exposure ranges for someone with an unobstructed view of the fireball; the circles should be considered the likely maximum range, although actual effects could be significantly attenuated by intervening buildings. The fallout pattern in this figure (the shaded areas northeast and east of ground zero), is just one possible ground contamination pattern and potential exposure pattern. Actual exposures would depend on how long an individual spends in the fallout area and on the quality of the shelter.

Unlike prompt effects, which occur too rapidly to avoid,5 health effects from fallout can be mitigated by leaving the area before the fallout arrives or by taking shelter from it. Although some fraction of ionizing radiation can penetrate buildings, shielding by walls and distance from outdoor fallout particles can easily reduce exposures by a factor of 10 or more, even in common urban buildings.

The quality of shelter is defined by a protection factor (PF), which is equal to the ratio of outside dose rate divided by inside dose rate. Like sunscreen SPF, the higher the PF value, the lower the exposure compared to the exposure of an unsheltered person in the same area. Figure 5 shows sample PF estimates based on evaluations conducted circa 1960 for typical structures during that era.

Figure 5  

Figure 6

Efforts are under way at several national laboratories and at ARA to use advanced modeling capabilities to update our understanding of the level of protection modern buildings could provide. Figure 6 shows an analysis of a modern, three-story office building (left), in which most of the first floor locations had PFs of 10 (shown as light colored areas near the border of the building [right]); PF 10 is considered adequate according to federal Planning Guidance for Response to a Nuclear Detonation (Homeland Security Council, 2009). Most other areas in the building provided even better protection with PFs higher than 100 (darkest areas inside the building) (Johnson et al., 2010).

Studies by Sandia National Laboratories evaluated the effectiveness of various shelter/evacuation strategies (Brandt, 2009; Brandt and Yoshimura, 2009a,b). In the Los Angeles scenario, even a moderate shelter with a PF of 10 reduced the number of people who received significant exposures of 100 rem or more from ~285,000 to ~45,000. Higher PF shelters, which are common in the urban environment, can reduce the number of significant exposures even further.

Evacuation Strategies

The Sandia studies also analyzed various evacuation strategies (Figure 7). The exposure dose received by an evacuee leaving reference point #1 would depend on the evacuation route. The heights of the path in the image represent radiation levels (or dose rates) to which the evacuee would be exposed during the journey.
Figure 7

Unfortunately, unless evacuees had information on where the hazard zones are, they would not know which route would have the lowest exposure. Within a few miles of the detonation, dust and debris created by the blast wave would probably cloud the air and limit visibility. Once the dust settled and the fallout cloud had passed downwind, there would be little visual evidence to indicate fallout hazard areas when sheltered populations emerged.

The hazard from fallout is not from breathing in the particles, but from exposure to the ionizing radiation given off after particles have settled on the ground and on the roofs of buildings (Crocker et al., 1966; Lacy and Stangler, 1962; Levanon and Pernick, 1988; Mamuro et al., 1967; Peterson and Shapiro, 1992). Radiation levels from these particles drop off quickly, however, with most (~55 percent) of the potential exposure occurring within the first hour after detonation and ~80 percent occurring within the first day.

Figure 8 

The graph in Figure 8 shows the rapid decay of outdoor radiation levels at one point downwind of a 10-kiloton explosion (Buddemeier and Dillon, 2009). Depending on weather conditions, the most dangerous concentrations of fallout particles (i.e., potentially fatal to people outside) occur within 20 miles downwind of the event and are expected to be clearly visible as they fall, possibly as particles resembling sand, table salt, ash, or rain (Lessard et al., 1954; NCRP, 1982).

Although the lowest possible exposure can be achieved through delayed departure, the delay also means that individuals would be receiving exposure from fallout while waiting in their shelters. To evaluate the total radiation exposure for various shelter/evacuation strategies, the cumulative dose received within the shelter was added to the dose received during evacuation for a continuum of shelter departure times. Figure 9 is a graph showing total exposures (shelter dose + evacuation dose) for various shelter departure times for a given shelter located a little more than a mile downwind and a shelter PF of 100, which can be found in the core of most office buildings.
Figure 9

In this example, departure after one hour results in a cumulative shelter dose of 8 rem and an evacuation dose of 62 rem, with a total exposure of 70 rem. Notice that the longer the sheltering time, the lower the total dose. A 24-hour departure can result in a total dose of 17 rem, significantly lower than the one-hour departure dose.

This analysis reveals the hazards of early or immediate evacuation, when initial fallout radiation levels are extremely high. More detail on the methodology of this analysis can be found in Key Response Planning Factors for the Aftermath of Nuclear Terrorism (Buddemeier and Dillon, 2009).

Community Outreach

If a nuclear detonation were to occur in a modern U.S. city, the best way to reduce casualties6 during the response phase (post detonation) would be by reducing exposure to fallout radiation. This can be accomplished through early, adequate sheltering followed by informed, delayed evacuation.7 However, the most critical decisions must be made in the first few minutes. Unfortunately, many people incorrectly believe that response efforts are futile. Thus responses to a nuclear detonation must include public information, planning, and rapid response. Because a successful response will require extensive coordination by a large number of organizations supplemented by appropriate responses by local responders and the general population in the hazard zones, regional planning will also be essential.

By the nature of their work, response organizations are distributed throughout a community, and the vast majority of them would survive. However, unless there has been a basic level of large-scale emergency planning, response organizations will not know how to apply their skills safely and effectively. Although there are considerable federal capabilities, it is unlikely that comprehensive assets would arrive in the first few days, and they could be further delayed by actions taken nationally to prevent or mitigate further attacks.

The convergence of detailed, three-dimensional prompt and atmospheric modeling capabilities, day and night time population distribution information, and building type and distribution information in the DHS HAZUS8 database provides an unprecedented basis for community-specific, science-informed response planning. FEMA is working on integrating this information to support community response planning.

The results of initial DHS modeling and analyses were presented to federal, state, and local working groups in New York City, the national capital region, Charlotte, Houston, Portland, and Los Angeles to obtain broad-based reviews and feedback on strategies and messaging. In addition to some of the technical information pre-sented above, advanced modeling, animation, and graphics were used to illustrate how a nuclear detonation event in the city of the community of interest might unfold. Emergency responders, emergency managers, and public health officials were shown animations of cloud movements (from the perspective of a person on the ground), visualizations of rapidly changing affected areas as fallout accumulates and then decays (Figure 8), and the efficacy of various shelter/evacuation strategies.

The updated information and methods of communication were well received by the response-planning community and have helped correct misunderstandings about the crucial importance of local response planning. Regional planning for response to nuclear terrorism are also being initiated in several communities.

National Guidance

Until recently, there was no scientific consensus on the correct actions to take, and response planners had no federal guidance. The Federal Register Notice published by DHS (2005), which clarified how existing guidance for protective action applies to response to radiological or nuclear terrorism, did not specifically address guidance for dealing with the acute effects of a nuclear explosion (MacKinney, 2006).

Now, in addition to the technical reports cited above, a number of federal agencies have worked together to develop National Planning Guidance for Response to a Nuclear Detonation (Homeland Security Council, 2009; a 2010 update is currently under review). In addition, the National Council on Radiation Protection and Measurements will soon publish Responding to Radiological and Nuclear Terrorism: A Guide for Decision Makers.

In addition to guidance specific to nuclear terrorism, DHS has undertaken extensive preparedness activities, including providing billions of dollars in preparedness grants to states and urban areas. DHS preparedness programs and strategies favor a capability-development approach that stresses mitigating the effects of adverse events. Thus preparedness for a low-yield nuclear detonation would create important capabilities that would also be crucial in responding to other catastrophic events that require coordinated regional response, time-critical decision making, caring for mass casualties, crisis communication, and the prioritization of resources.

Because many, many lives depend on actions taken by citizens and responders in the first few hours after a catastrophe, the capability of making those decisions and disseminating information and guidance quickly is essential during rapidly unfolding catastrophic events.


Recent research indicates than many potentially lethal effects of a nuclear detonation can be greatly mitigated by the urban environment. Urban shadowing and shielding can significantly reduce the range of prompt thermal and ionizing radiation, and, although fallout continues to be a significant issue, adequate shelter can easily be found in the urban environment.

If a nuclear detonation were to occur in a modern U.S. city, the greatest reduction in the number of casualties would be achieved through rapid actions taken by citizens supported by accurate, timely information and prompt actions by state and local officials. Unfortunately, most response organizations (and the general public) currently lack a fundamental awareness and have not developed plans to make informed decisions in the event of a nuclear explosion.

Given the daytime population density of a large modern city, the number of people who could be hurt by prompt effects or threatened by fallout could easily be in the hundreds of thousands. Fortunately, the number of casualties could be significantly reduced by taking appropriate action and by community pre-event planning at the local level.

Reducing exposure to fallout radiation, which can be accomplished through early, adequate sheltering followed by informed, delayed evacuation, would result in the largest potential reduction in casualties. A well organized response would enable sheltered populations to make informed evacuations and support timely medical interventions, which would greatly improve the prognosis for the injured (Einav et al., 2004; Ellidokuz et al., 2005; Macleod et al., 2007; Noland and Quddus, 2004; Sampalis et al., 1993; Teague, 2004; Trunkey, 1983; Wightman and Gladish, 2001; Wyatt et al., 1995).

Recent advances in scientific understanding, federal guidance, and preparedness tools have provided a foundation for state and local planning. Resources are now available for state, local, and regional response planning that can help bring a region together to address a number of difficult challenges presented by the nuclear terrorism scenario. The capabilities gained through response planning can also facilitate effective responses to a variety of natural and other man-made catastrophic events that require large-scale coordination to handle mass casualties and mass evacuations.


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1 Scenario #1 of the 15 Department of Homeland Security national planning scenarios is an improvised nuclear detonation in the national capital region.

2 Rad (radiation absorbed dose): a unit of measurement of the absorbed dose of ionizing radiation, corresponding to an energy transfer of 100 ergs per gram of any absorbing material. cGy (centigray): a unit of absorbed radiation dose equal to one hundredth (10–2) of a gray, or 1 rad. Gray (Gy): The SI special name for the unit of absorbed dose. 1 Gy = 1 J kg–1.

3 Prompt effects are effects that radiate outward from the detonation location, referred to as ground zero. These effects include blast effects, electromagnetic pulse, light, thermal radiation, and the ionizing radiation produced in the first minute.

4 The estimated cloud height is based on an extrapolation from nuclear test data for desert detonations, but more research will be necessary to determine how an urban environment would affect cloud rise.

5 Note that the Civil Defense program “Duck and Cover” strategy can provide protection from prompt effects of flying glass and the thermal pulse; however it requires reacting properly to the bright flash within the first few seconds.

6 Casualties are defined in this document as both injuries and fatalities.

7 This article focuses primarily on protection from fallout. Other issues, including planning actions that would reduce injuries/fatalities arising from prompt effects (e.g., “duck and cover” to reduce injuries from broken glass) are discussed only briefly.

8 HAZUS (abbreviation for HAZards United States) is a geographic information system-based natural hazard loss estimation software package developed and freely distributed by FEMA.



About the Author:Brooke Buddemeier is a health physicist, Radiological and Nuclear Countermeasures Division, Lawrence Livermore National Laboratory.