### Re: How do you scale an explosion by it's size?

Date: Mon Apr 22 01:35:09 2002
Posted By: Joseph Weeks, President
Area of science: Earth Sciences
ID: 1013984645.Es
Message:
```
Determining the size of an explosion is not an exact science because there
are a wide range of variables.  For example, the size of crater produced
by an explosion depends on a variety of factors, specifically how strong
is the material subjected to the blast, what is the distance from the
explosive to the ground, and what are the characteristics of the
explosive.  So, looking at the size of a crater isn't necessarily the best
way to determine the size of an explosion.

When an explosive detonates, it generates a pressure wave which expands
more or less spherically from the point of the explosion.  The pressure
wave decreases to the third power with distance from the source of the
blast, i.e., double the distance from a blast and the overpressure, or
pressure higher than atmospheric pressure decreases by a factor of 8.  The
http://www.fas.org/man/dod-101/sys/dumb/fae.htm presents
some simple formulas for calculating blast overpressures.  Of course,
buildings, hills, and other features can interact with the blast wave,
causing overpressures to increase or decrease.

Overpressures developed by nuclear explosives have been studied
als/amedp6/PART_I/chapter3.htm provides a description of the effects of a
nuclear blast.  Table 3-II in
that reference shows the overpressures necessary for certain types of
damage to occur.  For example, an overpressure of 3 to 7 kPa results in
glass being shattered.  So, if investigators are attempting to determine
the size of a specific blast, they can measure the distance how far away
from the blast that windows are broken and then back calculate to
determine the approximate size of the blast.

There are computer models available to predict the size of a blast and its
effect on structures which enable structural engineers to design oil
platforms and chemical processing equipment to be safer to operate.  These
models are also used to determine safe distances for storing explosives so
that in the event of an accident, an explosion doesn't propagate from one
cache of explosives to the next.

Thanks for giving me the chance to talk about explosives.  It was a blast.

```

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