Above: Nevada nuclear tests in 1951 were photographed from the desert casino town Las Vegas, some 75 miles to the south-east of ground zero. Refraction of shock waves by the atmosphere occasionally cracked large store windows in Las Vegas, but this was purely a shock diffraction effect and of course there was no wind pressure at that distance to accelerate glass fragments into a penetrating threat. For a 1 megaton surface burst over unobstructed terrain, the range of glass fragment hazard due to blast wind acceleration is 7 miles; this should be compared to a radius of 25 miles for cracked windows! (Anti-civil defense propaganda deliberately confuses the very low blast pressures required for cracked windows with the much higher pressures that are accompanied with sufficiently strong winds to cause a flying glass fragment hazard.)
Some declassified nuclear test blast reports by Jack W. Reed, who has a site at http://www.nmia.com/~jwreed/, are now available to all online from http://stinet.dtic.mil/.
Climatology of Airblast Propagations from Nevada Test Site Nuclear Airbursts, ADA383346. SANDIA CORP ALBUQUERQUE NM. Reed, Jack W. Report Date: December 01, 1969. 122 Pages
Blast Predictions at Christmas Island, ADA349666. SANDIA NATIONAL LABS ALBUQUERQUE NM. Reed, Jack W., and Church, Hugh W. Report Date: October 25, 1963. 46 Pages
Long-Distance Blast predictions, Microbarametric Measurements, and Upper-Atmosphere Meteorological Observations for Operations Upshot-Knothole, Castle, and Teapot, AD0342207 . SANDIA CORP ALBUQUERQUE NM. Cox, E. F., and Reed, J. W. Report Date: September 20, 1957. 93 Pages.
I've given some of my calculations on close-in fireball shock waves and high pressure air blast already here and here, but Jack Reed was concerned with the harder predictions for the more distant blast broken windows by atmospheric refraction in Nevada and Pacific nuclear tests. Considering that Las Vegas was only 75 miles from the Nevada test area, that was a bigger concern than fallout prediction (which I've commented on already here). Jack Reed says at http://www.nmia.com/~jwreed/expl1.htm:
'One of the first (actually the fourth) atmospheric nuclear tests (Operation RANGER, February 1951) broke large store windows on Fremont Street in downtown Las Vegas, Nevada, over 60 miles away. A similar 8-kt (kilotons) device had been fired the week before, and a smaller, 1-kt device the day before, without being heard. Los Alamos scientists guessed that it must have been caused by a change in weather, and they were correct. A library citation search turned up a report by Dr. Everett F. Cox, who had directed long-range acoustic monitoring of the massive explosive destruction of collected Axis munitions following WW-II at Helgoland, that showed a strong weather influence. By 1951, Cox was found doing his physics at Sandia (now National Laboratories), Alburquerque, New Mexico, (a branch of Los Alamos Scientific Laboratory until 1949), where I was a meteorologist in their Field Test Department.
'I was concerned with bomb ballistics and optical refraction problems in photo-tracking bomb trajectories through desert mirages at Sandia's Salton Sea Test Base, CA. I had started at Sandia in 1948. Even as a recalled Air National Guardsman (1951-53) during the Korean War, I was kept (with my Q-clearance) at Kirtland AFB Weather Station and Sandia Lab in a "military liaison" capacity.
'We began that summer (1951) with explosions of Navy war-surplus anti-submarine depth charges, monitored at long ranges, to 200 km (125 miles), by pressure sensors borrowed from the Navy. We applied atmospheric acoustic raypath calculations, provided by Lord Rayleigh, Fujiwara, and Rothwell, and using radiosonde (raob) weather balloon reports, to try to explain results and build a prediction system.
'And this system worked quite well, as demonstrated on November 1, 1951, by 21-kt Shot Dog, when weather threatened to focus airblast by jet stream winds blowing toward Las Vegas. But the AEC Test Manager had another problem. Over 3,000 press and Civil Defense observers had been brought out to watch atomic tests. They had been there almost two weeks, had spent their travel money (or lost it in Vegas Strip casinos), and had then moved to the free Desert Rock (Army) tent city, just outside the AEC Camp Mercury, where meals were only $1.00.
'This food supply was about to run out; under this pressure, the the Test Manager decided to shoot. Again, windows were smashed along Fremont Street; Sears' large show-windows fell out on the sidewalk. In those days, however, this was in a commercial section, with no pedestrians so early in the morning. After that, blast predictions were taken very seriously, and only one more broken window was reported (but no claim made) in Las Vegas from any further nuclear airblasts through 1968.
'That one incident came during Operation TEAPOT, from 20-kt Shot Bee, 3/22/55, by an MB-recorded 200 Pa (pascals) overpressure, 290.4 Pa amplitude airblast wave. This observation, plus two other reports, of single windows broken, in St. George, Utah, 200 km east of NTS, during TEAPOT from similar recorded pressures, provided a basis for an estimated threshold for airblast window damage. This 200 Pa (2 mb - millibar, 0.03 psi) overpressure threshold still appeared valid in 1988, when only one damage claim out of more than 17,000, came from a lower estimated overpressure (160 Pa) from the large PEPCON accidental explosion in Henderson, Nevada. ... Near the end of HARDTACK I, rocket-delivered megaton-class Shots Teak and Orange were fired over Johnston Island, giving a host of observations that took years to explain.'
Left: large window shattered outward in Fremont Street, Las Vegas, Nevada; Sears' large show-windows fell out on the sidewalk, due to the 21 kt Dog test at the Nevada test site. This was due to the suction phase of the blast which had been focussed on Las Vegas by jet stream winds. The man responsible for predicting this damage, Jack Reed, blamed the test manager for firing the nuclear bomb under adverse conditions because the food had run out for 3,000 press and civil defense observers (see quotation from Reed's site, above). A big window is more likely to fail than a small one. 0.03 psi is small compared to normal pressure (14.7 psi), but the force exerted on a big window is appreciable, for example a window 6 feet high and 10 feet wide subject to 0.03 psi gets 6 x 10 x 144 x 0.03 = 259.2 pounds of force (1153 Newtons). At great distances, the window often survives the inward push in the compression phase but then shatters when the low-pressure (rarefaction) phase occurs, pulling the window the other way suddenly. There is no significant flying glass hazard (except from vertically falling glass right beside the window), because the blast winds are too weak to accelerate fragments into high velocity missiles. Near the explosion there is a greater risk of this, but clothing or 'duck and cover' action offers good protection (see Glass Fragment Hazard from Windows Broken by Airblast, ADA105824; Operation PLUMBBOB: Secondary Missiles Generated by Nuclear-Produced Blast Waves, ADA397401; ADA383465; ADA394861; Operation TEAPOT: Distribution and Density of Missiles from Nuclear Explosions, ADA395151 - the 'open shot' with the community of different types of American houses built about a mile from ground zero in Nevada, for which the data is given in this last report is of course Apple-2.).'Shock waves go out in all directions from the detonation. Some strike the earth and are dissipated. Some bounce back to earth from various atmospheric layers. If they reach earth at an inhabited point they may be felt or heard.
'Waves curved back to earth by the ionosphere, which is an atmospheric layer over 50 miles above the earth, have been recorded on very sensitive instruments 100 or more miles from the target area. There is no evidence that they have been heard at that distance or have caused any damage.
'The ozonosphere, a layer 20 to 35 miles above the earth, bends waves back at distances from 60 to 150 miles. Usual ozonosphere wind directions cause these waves to reach St. George and Cedar City, Utah, in winter and Bishop, Calif., in summer. Every shot fired in Nevada has been heard either in St. George or Bishop, or both.
'Past Experience With Blast
'Light damage to structures and broken windows have resulted up to 100 miles, most of this having been in the first series on a line from the test site through Las Vegas and Henderson. Only very light damage has been reported within 100 to 200 miles. Blast has been heard but has not caused damage at greater distances, including Los Angeles, Calif., and Albuquerque, N. Mex.' - ATOMIC TEST EFFECTS IN THE NEVADA TEST SITE REGION, UNITED STATES ATOMIC ENERGY COMMISSION, JANUARY 1955.
Further vital reports on low overpressure air blast focussing by refraction etc can be found online here (Jack Reed's report ADA279735 on the DANNY BOY cratering nuclear test) and a report by John Slater here.
There is also an interesting discussion of air blast and ground shock problems with the efforts in the 1960s to excavate a new Panama canal using relative clean (REDWING-NAVAJO, 5% fission test, type) nuclear explosives in a book: Emperors in the jungle By John Lindsay-Poland.
