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Destructive Effects of Nuclear Weapons. The generation of a mechanical shock through sudden increase of pressure causes mechanical damages The generation of a heat wave expanding with the shock causes incineration The distribution of radiation through
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Destructive Effects of Nuclear Weapons • The generation of a mechanical shock • through sudden increase of pressure • causes mechanical damages • The generation of a heat wave • expanding with the shock causes • incineration • The distribution of radiation through • Short range and atmospheric fallout • causes short term and long term • radiation sickness effects • Electromagnetic shock leads to • break-down of communication systems Blast damage Thermal damage Radiation damage EM-pulse
0.10 ms The mechanical shock 0.24 ms shock velocity: vs sound speed: cs specific heat: =1.4 peak pressure: p air pressure: p0=15 psi wind velocity: vw dynamic pressure: q 0.38 ms 0.52 ms pressure 0.66 ms 0.80 ms 0.94 ms
Example Depending on the peak pressure (atmospheric pressure 15 psi) and the speed of sound (cs=330 m/s in atmospheric gas) you receive the following values for shock and wind velocity and dynamic pressure
for large dynamic pressure for small dynamic pressure Shock characteristics Shock on flat surface causes reflection which is expressed by reflected overpressure pr!
example 250 kT blast Nevada 1953 effect on houses in different distance from center of blast 2.65 miles 5.3 miles
Shock expansion Shock expands radially from explosion center. Amplitude decreases, but after time t5 the pressure behind shock front falls below atmospheric pressure, Under-pressure which causes the air to be sucked in.
Pressure conditions with transversing shock • Shock hits • generates strong wind • Shock decreases • Underpressure • Wind direction changes • Normal air pressure • Wind calms down
Distance Effects Scaling for blast intensities 100 kT e.g. the effect which occurs for a 1 kT blast at distance D1 occurs for a 100kT blast at distance D. D1=10,000ft D=24,662ft 1 kT Peak over pressure as function of distance for a 1kT blast
Scaling laws for blast effects Shock/blast expands over volume ~d3,the following scaling law can be applied for estimating distance effects between different blast strengths Normalized to a standard 1kT blast the following expression can be applied:
Distance effects of airburst damage comparison for a 1000 kT and a 500 kT bomb using the scaling law with respect to 200 kT bomb
Scaling in Altitude often scaled to W1 = 1 kT Similar scaling relation for altitude dependence of blast effects. For altitudes less than 5000 ft (1700 m) normal atmospheric Conditions can be assumed. For higher altitude effects changes altitude dependence of air pressure and sound speed need to be taken into account.
Peak overpressure in height & distance Suppose you have 80 kT bomb at 860 ft height, what is the distance to which 1000psi overpressure extends? Normalization: W1=1kT Corresponding height for 1kT burst (or scaled height) Distance of 1000 psi overpressure
Surface burst versus airburst Suppose you have 500 kT bomb at 1.1 mile height, what is the distance to which 2 psi overpressure extends and compare with ground zero detonation. Scaled height for 1 kT bomb; h1 = h/W1/3 = 0.14 miles ≈ 765 ft. This corresponds to d1 = 3800 ft = 0.69 miles. The distance for the 2 psi overpressure on the ground from the 500 kT blast would be d = d1·W1/3 = 0.69·5001/3 = 5.5 miles. Surface burst: d1=2500 ft=0.45 miles, d = d1·W1/3 = 0.45·5001/3 = 3.6 miles.
Thermal 35% Blast 50% Fallout Initial 10% Radiation 5% Thermal effects Approximately 35 percent of the energy from a nuclear explosion is an intense burst of thermal radiation, i.e., heat. Thermal effects are mainly due to originated heat from blast which expands with wind velocity and incinerates everything within expansion radius. The thermal radiation from a nuclear explosion can directly ignite kindling materials. Ignitable materials outside the house, such as leaves, are not surrounded by enough combustible material to generate a self-sustaining fire. Fires more likely to spread are those caused by thermal radiation passing through windows to ignite beds and overstuffed furniture inside houses.
Thermal Energy Release For a fireball with radius r the heat emitting surface is: Total energy emitted per cm2 and second is described by the Stefan Boltzmann law Total thermal energy emission from fireball is therefore: With radius r in units m and temperature T in Kelvin
The thermal power of the fireball changes with time. Thermal energy release should be expressed in terms of maximum power Pmax (scaled power) and in terms of scaled time tmax which corresponds of time of the maximum thermal energy release from the fireball.
For air bursts below 15,000 ft altitude the maximum power Pmax & the maximum time tmaxare related to the bomb yield W (in kT) e.g. for a 500 kT burst in 5000 ft altitude: The total amount of thermal energy emitted at t=1sec is:
Hiroshima firestorm Fires can result from combustion of dry, flammable debris set loose by the blast or from electrical short circuits, broken gas lines, etc. These fires can combine to form as terrible firestorm similar to those accompanying large forest fires. The intense heat of the fire causes a strong updraft, producing strong inward drawn winds in which fan the flame, take away oxygen so it is difficult to breath, and destroy everything in their path.
The expansion of firestorms Different scaling laws apply for calculating the heat and incinerating effects from bomb yield. Fire advances by wind driven heat propagation. In a uniform atmosphere without turbulent or convective processes the expansion would follow an exponential law with the radiation absorption parameter . The heat exposure at distance d would be: For turbulent firestorms empirical approximations are used to describe transmittance of heat in terms of the transmittance factor (empirical factor for visibility) and f the thermal heat fraction of total energy release (f ≈ 0.35-0.42 depending on altitude).
1000 10 combustibles heat release cal/cm2 0.1 0.001 10 100 1000 10000 Distance [m] Ignition of combustibles 10 kT Threshold ignition for combustibles
Fire expansion Fire expansion is driven by shock driven winds which develop rapidly turbulences due to temperature Differences. Fire spreads with rapid Speed, leaving no chance to escape.
Eyewitnesses A bright flash and explosion at the same time; I could not see an inch ahead Is it smoke or dust? It all happened in a moment Hiroshima was engulfed in a sea of flames. Those who got burns were fleeting here and there, crying in pain “Help!" With screams, a wave of people come rushing toward me. Kojin-machi,
Burn wounds Peeled skin was dangling like seaweed from their armsRed flesh exposedPeople were staggering with vacant eyesExtending their arms forwardLike ghostsSuddenly they fell, stumbling over somethingNever to get up again
