Peace through practical, proved civil defence for credible war deterrence
  • Please see also post linked here, and our summary of the key points in Herman Kahn's much-abused call for credible deterrence, On Thermonuclear War, linked here.

  • Hiroshima's air raid shelters were unoccupied because Japanese Army officers were having breakfast when B29s were detected far away, says Yoshie Oka, the operator of the Hiroshima air raid sirens on 6 August 1945...

  • In 1,881 burns cases in Hiroshima, only 17 (or 0.9 percent) were due to ignited clothing and 15 (or 0.7%) were due to the firestorm flames...

  • Dr Harold L. Brode’s new book, Nuclear Weapons in ...

  • 800 war migrants drowned on 22 April by EU policy:...

  • Photographed fireball shielding by cloud cover in ...

  • Nuclear weapons effects "firestorm" and "nuclear w...

  • Proved 97.5% survival in completely demolished houses ...

    "There has never been a war yet which, if the facts had been put calmly before the ordinary folk, could not have been prevented." - British Foreign Secretary Ernest Bevin, House of Commons Debate on Foreign Affairs, Hansard, 23 November 1945, column 786 (unfortunately secret Cabinet committees called "democracy" for propaganda purposes have not been quite so successful in preventing war). Protection is needed against collateral civilian damage and contamination in conventional, chemical and nuclear attack, with credible low yield clean nuclear deterrence against conventional warfare which, in reality (not science fiction) costs far more lives. Anti scientific media, who promulgate and exploit terrorism for profit, censor (1) vital, effective civil defense knowledge and (2) effective, safe, low yield air burst clean weapons like the Mk54 and W79 which deter conventional warfare and escalation, allowing arms negotiations from a position of strength. This helped end the Cold War in the 1980s. Opposing civil defense and nuclear weapons that really deter conventional war, is complacent and dangerous.

    War and coercion dangers have not stemmed from those who openly attack mainstream mistakes, but from those who camouflage themselves as freedom fighters to ban such free criticism itself, by making the key facts seem taboo, without even a proper debate, let alone financing research into unfashionable alternatives. Research and education in non-mainstream alternatives is needed before an unprejudiced debate, to establish all the basic facts for a real debate. “Wisdom itself cannot flourish, nor even truth be determined, without the give and take of debate and criticism.” – Robert Oppenheimer (quotation from the H-bomb TV debate hosted by Eleanor Roosevelt, 12 February 1950).

    “Apologies for freedom? I can’t handle this! ... Deal from strength or get crushed every time ... Freedom demands liberty everywhere. I’m thinking, you see, it’s not so easy. But we have to stand up tall and answer freedom’s call!” – Freedom Kids

  • Sunday, August 09, 2009

    Blast Wave


    Above: Figure 2-23 on p. 2-59 of Dolan's Capabilities of Nuclear Weapons, DNA-EM-1, 1972, showing the rapid decay of the peak overpressure with increasing distance from a 1 kt nuclear surface burst:

    R (feet) - P (psi)

    25 - 300,000
    40 - 60,000
    70 - 10,000
    150 - 1,000
    400 - 70
    1,000 - 10
    20,000 - 0.1

    The curve, based on Brode's theoretical calculations with programs that include both hydrodynamic motion and radiation flow, can be represented by the simple equation:

    P (psi) = (1.7 x 1010 /R3.4) + (7.0 x 106 /R2) + (1,700 /R),

    where R is distance in feet. The R3.4 fall in pressure at the smallest distances differs from the simple theoretical R3 prediction for the fall in overpressure due to dispersal of energy over the increasing mass of engulfed ambient air (this mass is proportional to R3) because the shock front is losing energy by radiating thermal radiation at the highest overpressures, which causes an additional fall in peak overpressure with distance. Scaling to other explosion yields is done by multiplying the distances by the cube-root of the total kiloton yield.

    Dolan gives also a free air burst curve in Figure 2-2 on p. 2-7, which can be obtained by scaling the surface burst peak overpressure curve to a yield of about 0.565 kt, implying that surface bursts have an effective yield (due to reflection of blast wave energy into a hemispherical region) of 1.77 times the free air burst yield. Hence, the distance for any given pressure in a surface burst extends about 1.771/3 = 1.21 times as far as in a free air burst in sea level air. For a perfectly rigid surface, an effective yield increase factor of 2 would be expected since the same amount of blast energy for any radius would be concentrated in a hemisphere with only half the volume of the sphere for that distance. A reflection factor of 1.77 therefore implies that only 100(1 - 1.77/2) = 11.5% of the blast energy in a surface burst is permanently absorbed by the ground in the cratering, ground shock, and soil heating (fallout formation) processes. If the initial blast energy is 50% of the total yield in a free air burst, then in a surface burst it will be reduced to 44%. A discussion of blast theory and some test data is given in an earlier post linked here.

    PRECURSOR EFFECTS

    The history of the precursor is discussed in earlier blog post about Glasstone and Dolan. The billowing of thermally-raised smoke and dust in the blast wave of the TRINITY test (100 feet over dark desert soil) in 1945 should have been the suggested a modification of the blast by dust loading of the air in that region, but the first film of the precursor shock wave was obtained on the DOG shot of TUMBLER-SNAPPER in the Nevada in 1952. Dark coloured (brown) desert sand, consisting of crystals of silica, was exploded or 'popcorned' into hot dust by thermal radiation exposures of 11-19 cal/cm2 for yields of 35 kt to 1.4 Mt; a similar effect on lighter coloured (grey-white) coral sand required 15-27 cal/cm2. This formed a cloud of hot dust-laden air several metres high over the ground, which caused the blast wave to speed up and change in characteristics. The density of the dust added to the air increased the blast wind or dynamic pressure (which is directly proportional to the density), while the added momentum increased the duration of the blast winds, greatly increasing damage to structures and vehicles by the 'sandstorm effect' of the air-blasted dust cloud. The peak overpressure is somewhat reduced by the upward refraction of energy due to the temperature-height profile in the precursor region.

    In 1953, the precursor effect was demonstrated by a comparison of damage from the ENCORE and GRABLE shots. The second test was at lower altitude so the thermal radiation was able to popcorn the desert effectively, creating far greater dynamic pressure effects than ENCORE at the same overpressures for drag effects on jeeps, trucks, and other dynamic-pressure sensitive targets. At subsequent tests in Nevada, selected areas around ground zero were flooded to form shallow lakes, while other areas were coated with asphalt, concrete, grass and other surfaces to investigate precursor development as a function of the reflective and physical nature of the surface. Precursors were noted at higher overpressures over coral sand, including surface bursts of over 30 kt yield (so that the fireball at thermal maximum is high enough to irradiate the ground with sufficient thermal energy to cause popcorning). Dolan's Capabilities of Nuclear Weapons, DNA-EM-1, 1972, p. 2-81, states that dust blast precursors will occur over dark city asphalt for burst altitudes below 800W1/3 feet, for W kilotons total yield, and for bursts over dark desert sand precursors will occur for burst altitudes below 650W1/3 feet. These formulae are valid for yields of 1-50 kt where observations are available (for other yields consideration must be given as to whether there is sufficient thermal exposure in the time before blast arrival for a dust layer to be produced).



    Above: some typical qualitative precursor blast waveforms for overpressure and dynamic pressure, taken from Dolan's DNA-EM-1, 1972, which on pages 2-81 to 2-89 includes a detailed predictive system to indicate the shape of the precursor waveforms as a function of yield, height of burst and distance from ground zero. This was later developed into a quantitative precursor waveform prediction system in the late 1990s. At very high overpressures, the blast arrival is so soon after that detonation that very little of the thermal radiation has been emitted by the fireball, so there has been little development of a precursor in the available time. Therefore, the precursor develops gradually as the shock travels outward into areas which have been irradiated for longer times after burst, where enough thermal radiation has been emitted to cause a hot dust layer ahead of the shock wave. At long distances, the blast wave runs out of the dust layer because it encounters a region where the thermal radiation exposure has simply not been strong enough to 'popcorn' the sand or to 'smoke' the asphalt or grass. When this happens, the precursor encounters cooler air which makes it slow down, allowing the main blast wave (still travelling through air warmed by the precursor) to catch up and merge with the precursor, forming an ideal shaped blast wave once again.

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