Destructive Effects of Nuclear Weapons Blast damage Thermal damage Radiation damage EM-pulse  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

The mechanical shock 0.10 ms 0.24 ms 0.38 ms 0.66 ms 0.52 ms 0.80 ms 0.94 ms pressure shock velocity: v s sound speed: c s specific heat:  =1.4 peak pressure: p air pressure: p 0 =15 psi wind velocity: v w dynamic pressure:q

Example Depending on the peak pressure (atmospheric pressure 15 psi) and the speed of sound (c s =330 m/s in atmospheric gas) you receive the following values for shock and wind velocity and dynamic pressure

Shock characteristics Shock on flat surface causes reflection which is expressed by reflected overpressure p r! for large dynamic pressure for small dynamic pressure

Example shock front against house

example 250 kT blast Nevada 1953 effect on houses in different distance from center of blast 2.65 miles 5.3 miles

The American Home

Shock expansion Shock expands radially from explosion center. Amplitude decreases, but after time t 5 the pressure behind shock front falls below atmospheric pressure, Under-pressure which causes the air to be sucked in.

Pressure conditions with transversing shock 1.Shock hits 2.generates strong wind 3.Shock decreases 4.Underpressure 5.Wind direction changes 6.Normal air pressure 7.Wind calms down

Pressure induced wind effects

Peak over pressure as function of distance for a 1kT blast Distance Effects Scaling for blast intensities e.g. the effect which occurs for a 1 kT blast at distance D 1 occurs for a 100kT blast at distance D. D 1 =10,000ft  D=24,662ft 100 kT 1 kT

Scaling laws for blast effects Shock/blast expands over volume ~d 3, 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 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. often scaled to W 1 = 1 kT

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: W 1 =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; h 1 = h/W 1/3 = 0.14 miles ≈ 765 ft. This corresponds to d 1 = 3800 ft = 0.69 miles. The distance for the 2 psi overpressure on the ground from the 500 kT blast would be d = d 1 ·W 1/3 = 0.69·500 1/3 = 5.5 miles. Surface burst: d 1 =2500 ft=0.45 miles, d = d 1 ·W 1/3 = 0.45·500 1/3 = 3.6 miles.

Blast effects on humans

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. Fallout 10% Blast 50% Thermal 35% Initial Radiation 5%

Thermal Energy Release For a fireball with radius r the heat emitting surface is: Total energy emitted per cm 2 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 P max (scaled power) and in terms of scaled time t max which corresponds of time of the maximum thermal energy release from the fireball.

For air bursts below 15,000 ft altitude the maximum power P max & the maximum time t max are 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 ≈ depending on altitude).

Transmittance

Ignition of combustibles combustibles Distance [m] heat release cal/cm 2 Threshold ignition for combustibles 10 kT

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.

Hiroshima

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 arms Red flesh exposed People were staggering with vacant eyes Extending their arms forward Like ghosts Suddenly they fell, stumbling over something Never to get up again

People burning

Victims