Plotted with Gnuplot 4.2.2. Isobars are based on numerically solved formulae from the internal help pages of the BLAST software, the H_opt curve is an analytical fit using the inversely plotted formula

${\displaystyle {{\mathit {GR}}_{\mathit {OP}} \over \mathrm {m} }=\left(\left(9{,}54\cdot 10^{-3}\,{H_{\mathit {OP}} \over \mathrm {m} }^{1{,}95}\right)^{4}+\left(3{,}01\,{H_{\mathit {OP}} \over \mathrm {m} }^{0{,}75}\right)^{4}\right)^{1/4}\,.}$

This function should fit both BLAST output and Figures 3.73a-c taken from Glasstone, Dolan, The Effects of Nuclear Weapons, 1977 (EoNW77) as a compromise. Both sources differ slightly. EoNW77 shows the maximum low-pressure ranges at somewhat lower altitudes whereas for high pressures >40 psi BLAST shows no optimum altitudes at all (see the innermost isobar). However, since numerical fitting of curves taken from a paper would be a Sisyphean task while BLAST already outputs plottable numbers, only isobars from the latter are plotted here.

A note on the new version on June 6 2022: The interpolation between the Mach zone and the regular reflection zone has been altered in order to steepen the "knees". This provides a better fit to the Figures 3.73a-c in EoNW77 where the relation of GR to H is actually not unique but features local minima at the onsets of the "knees" for intermediate overpressures. In addition, contours for 1.5, 7 and 15 psi have been added.

Most sources, e.g. Glasstone & Dolan (1977) or Carey Sublette's Nuclear Weapon Archive use pounds per square inch as pressure units. As a rule of the thumb, e.g. most non-reinforced buildings are destroyed for overpressures above 5 psi. However, the pressures can easily be converted into SI units, e.g. kilopascals, where 1 psi = 6.8947573 kPa or, roughly, one psi equals seven kPa.

A note on Gnuplot SVG terminal: Set size variable as "fixed" (the default in Gnuplot), not "dynamic", to ensure correct aspect ratio. This was the reason for uploading a 2nd version.

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