Let's Take a Peek at PEAC-WMD - by S. Bruce King
How the PEAC tool deals with explosives
This month we'll review how explosives
(by explosives we are referring to chemical formulations designed to react very rapidly
to form a "shock wave" or "blast wave" or "over pressurization") are dealt with in
the PEAC-WMD application.
There are basically two resources
provided in the PEAC-WMD application to assist the user when dealing with the possibility
of an explosive device. The first is the ATF Vehicle Bomb Tables and the second is
the Explosion Calculator.
ATF Vehicle Bomb Table
The ATF Vehicle Bomb Table is simply
a table of six (6) different sized vehicles and the estimated maximum potential destruction
that could be caused by that sized vehicle packed with explosives.
The ATF Vehicle Bomb Table has information
for the multiple categories of different sized vehicles and provides standoff distances
based on the following criteria: (1) Maximum Explosives Capacity, (2) Lethal Air Blast
Range, (3) Minimum Evacuation Distance, and (4) Falling Glass Hazard. The distances
are provided in both feet and meters and the estimated explosives capacity is provided
in both pounds and kilograms. The ATF provides the information with the following
Minimum evacuation distance is the
range at which a life-threatening injury from blast or fragment hazards is unlikely.
However, non-life-threatening injury or temporary hearing loss may occur.
Hazard ranges are based on open,
Minimum evacuation distance may
be less when explosion is confined within a structure.
Falling glass hazard range is dependent
on line-of-sight from the explosion source to windows. Hazard is from falling shards
of broken glass.
Metric equivalent values are mathematically
Explosion confined within a structure
may cause structural collapse or building debris hazards.
Additional hazards include vehicle
To access the information the user
selects ATF Vehicle Bombs from the drop-down list (it is found under the Explosives
and Bombs category) from the Lookup By field as shown in Figure 1.
The ATF Vehicle Bombs Table will
display a list of six (6) different types of vehicles as shown in Figure 2. The user
simply clicks on the desired vehicle type and the corresponding information is displayed
in the Data Display Field of the window, see Figure 2.
The reader should recognize that
the standoff distance for lethal air blast is different than the minimum evacuation
distance. This is due to the type of damage predicted for two different concerns.
The lethal air blast distance is
based on a shock or blast wave that has a peak over‑pressure of ~5 psi (pounds
per square inch). At this pressure there is a significant risk for hemorrhaging of
lungs which can lead to severe injury or even death. The minimum evacuation distance
is based on shrapnel or fragments of the vehicle being thrown a great distance and
the potential for injury and/or death from being struck by these flying fragments.
A portion of the PEAC-WMD database
is dedicated to providing the user with specific information related to explosive
materials. As shown in Figure 1, there are sublevel categories under the Explosives
and Bombs category when the drop-down menu is displayed beneath the Lookup
By field. The two sub-categories that deal with explosive materials are
the Explosives and Explosives (Long List). The only difference
between the materials displayed on one list versus the other is whether or not the
material is normally recognized by the typical user. The Explosives list
is actually a short list of common known explosive materials; versus the Explosives
(Long List) is a much longer list of sometimes relatively unknown explosive
materials. The information displayed for each is basically the same.
Associated with each entry in either
sub-category is the ability to calculate an appropriate standoff distance if there
is enough information in the PEAC‑WMD database for the specific explosive.
If the selected chemical is classified
as an explosive material and the PEAC‑WMD application has sufficient information
in its database to calculate an evacuation distance based on a user specified over‑pressurization
value, the PEAC‑WMD application will display an Explosion Calculator button
or icon  on the
screen (see Figure 3). By clicking on this button the screen for the Explosion
Calculator will appear. There are two versions of the Explosion Calculator,
the version shown in Figure 4 and the version shown in Figure 5. The difference is
whether the PEAC‑WMD database has density or specific gravity information to
calculate the mass or weight of the material based on the volume of the material.
With density information, the screen shown in Figure 4 will be displayed, otherwise
the user will see the screen in Figure 5 and there will be no option to enter the
volume of the explosive material.
Table 1 - Explosion Overpressure Damage Estimates
Minimum safe evacuation distance;
possible breakage of windows.
Some minor damage to frame houses,
typically 10% window breakage.
Significant window breakage, other
minor damage to frame houses.
Upper limit for reversible effects
on humans; window breakage and moderate damage to house structures.
Partial demolition of houses; skin
lacerations from flying glass.
Threshold for significant human
lethality from flying glass and other missiles; eardrum rupture; partial collapse
of walls and roofs of houses.
Complete demolition of frame houses.
Wooden utility poles snapped. Significant human lethality.
Probable total building collapse.
Many deaths. Lungs hemorrhage
Total destruction. 99% fatality
due to direct blast effects.