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August 2007
[Download PDF for Printing]
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A New Capability
for the PEAC-WMD™ Explosion Calculator Tool
Explosives have two primary
hazard components; the blast effects from the over-pressure generated by the
explosive material’s rapid detonation and the shrapnel or fragmentation thrown
from the explosion with sufficient energy to cause bodily injury to persons in
the vicinity. The PEAC-WMD Explosion
Calculator has dealt with the over pressure component in the past and now
provides algorithms to estimate the fragmentation hazard.
Background
The Explosion Calculator
input requirements are the same as previously; the user selects which explosive
substance is involved with the explosive device and a specific over-pressure
value. In some cases the user may not
know what explosive material is involved and a guess may have to be made. For many of the explosive substances in the
PEAC-WMD database, a TNT equivalence factor is available, for those explosive
substances where a TNT equivalence factor is not known; a equivalence factor of
1.0 is assumed. This equivalence factor
is used in the computations for both the over-pressure or blast effects and in
the fragmentation calculations.
The over-pressure value
provided by the user allows the Explosion Calculator to compute a
distance from the center of the explosion to the concentric circle where the
over-pressure is at or below the over-pressure value provided. The basic assumption is that the explosion
is modeled as in an open-air setting and there are no major obstacles
(buildings, vehicles, or other shielding objects) between the explosion and
that distance. The user should be aware
that if there are obstacles between or adjacent to the explosion and the
calculated distance, the over-pressure value may be different (higher or lower)
depending on the arrangement or location of those obstacles. Therefore the Explosion Calculator is
a first, best estimate as to the consequences of the explosion with respect to
the blast or over-pressure effects.
AristaTek made the decision
to provide the user with the option to select the over-pressure level that was
of most interest to them. If personnel
were in the vicinity or buildings with windows vulnerable to breakage, then a
lower over-pressure level might be appropriate for developing a safe standoff
distance. If personnel are inside a
reinforced concrete building, a higher over-pressure might be selected as being
safe.
The inclusion of the
fragmentation hazard component is the recent capability that I will
discuss. Most explosive devices have
some fragmentation associated with them, if nothing more than the container,
which surrounds the explosive material.
If that is the only material involved, the fragmentation hazard maybe
minimal. But usually fragmentation from
an explosive device is much more lethal if the device has been constructed for
illegal or criminal purposes, i.e., these devices are usually constructed to
cause as many injuries as possible.
These devices are commonly referred to as IED (improvised explosive
devices) and have become the primary means of attack against coalition troops
in the Iraq and Afghanistan combat zones.
Most of the IEDs used in these combat zones appear to be modified
military munitions rigged to explode on command from remote locations when
troops or civilians are nearby or by suicide bombers that carry them in
vehicles, hence the name VBIED (vehicle borne improvised explosive devices).
These devices are extremely
lethal because they were designed with high explosives for the explosive
material and casings that are designed to fragment upon detonation into optimum
killing fragments that would have sufficient energy to damage personnel near
the detonation.
IEDs are found in other
setting, e.g., the late June 2007 London car bombs and the frequent suicide
bombers through out many parts of the world.
The shrapnel used in these IEDs can be homemade, e.g., using nails,
chains, ball bearings or any other material that will survive the explosion and
be propelled in every directions with sufficient energy to cause injury or
death to personnel in the area.
The US Navy EOD (Explosive
Ordinance Disposal) teams have developed computational tools to assist them in
evaluating and disposing of munitions or explosive devices. The tools have algorithms that compute safe
standoff distances for over-pressure blast effects and for hazardous fragments
that might be produced. Similar
algorithms have now been incorporated into the PEAC® Explosion
Calculator to provide standoff distances fro fragmentation.
Over-pressure Hazard Information
The PEAC Explosion
Calculator calculates distances for three different over-pressure values
vs. the single user specific value as with the previous version of the Explosion
Calculator. The first distance
reported and displayed on the graphic result window is the distance related to
the user specified over-pressure value.
As explained previously, the user selects this value based on the
incident and what kind of damage threshold concerns they may have related to
the incident and the surroundings.
The other two evacuation
distances calculated for over-pressure are referred to as: (1) the
Unintentional Detonation and (2) Intentional Detonation, both of which are Navy
EOD terms. The terms are defined as
follows:
- Unintentional Detonation refers to the
accidental detonation and based on a K factor of 50, which corresponds to
an over-pressure value of 0.89 psig.
This is part of the Navy EOD safety protocol when dealing with
ordinance that may be unintentionally detonated and a safety zone around
the area must be established in case there is a detonation.
- Intentional Detonation refers to the anticipated
detonation and based on a K factor of 328, which corresponds to an
over-pressure value of 0.07 psig.
This is part of the Navy EOD safety protocol when dealing with ordinance
that will be intentionally detonated and a safety zone around the area
must be established for this detonation.
Fragmentation Hazard Information
The PEAC Explosion
Calculator automatically generates two different types of fragmentation
information that are provided in the Explosion Calculator Results Report. These values are computed without the user
having to select a Level of Concern since they are a function of the equivalent
amount of TNT involved in the device.
The first value computed is
the Hazardous Fragments distance, which corresponds to a distance based on one
hazardous piece per 600 square feet with an impact energy of 58 ft-lb. This value is reported and displayed on the
graphic.
The second value computed is
the Maximum Fragment Throw distance, which is the maximum distance any fragment
will be thrown.
Running the Explosion Calculator
To demonstrate the new Explosion
Calculator I’ll run through a fictitious scenario that involves a large
suspicious suitcase found setting outside a downtown hotel in Denver, CO. The estimated volume of the suitcase is
5,000 in3, and there is no idea what the contents might be. The assumption is that it might be an
explosive device and a quick estimate needs to be developed on how far to move
people back till the bomb squad arrives and make a determination.
Since there is no evidence
of what might be in the suitcase, the assumption will be to use TNT as the
explosive, which is selected from the list of explosives in the PEAC database
(Figure 1)
If the user has a GPS
installed in the platform they are using or they have available a handheld GPS,
the next screen displayed will allow them to specify the geographical location
(latitude and longitude) of their position plus an offset (direction and distance)
to the specific incident, in this case the suitcase. For simplicity, we have left that screen out and just provided a
general location (latitude and longitude) of Denver and not used the GPS
options. This will still plot the stand
off distances on a street map, and we can modify where the shapefile is
positioned for the final location.
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Figure 1 –
Selecting TNT as the explosive from the PEAC database
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As shown in Figure 1, the Explosion
Calculator icon [
 ] can
be clicked on to start the Explosion Calculator. The first screen to appear is the warning
screen that describes the limitations and basic assumptions made when running
the calculator (Figure 2). The user
simply clicks on [Yes] to proceed. This
window is only displayed the first time the calculator is used during a
session.
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Figure 2
– The Explosion Calculator warning screen.
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Figure 3
– Providing either the mass or volume of the package
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The next window displayed is
the input window for mass of explosive involved or volume. Since the PEAC database has density for TNT,
we can provide the estimated volume of 5,000 in3 and the window will
fill in the corresponding mass of TNT (Figure 3).
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Figure 4 – Specifying the over-pressure level and
results displayed
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The last input window is for
provision of the over-pressure level associated with certain damage threshold
for which the user is primarily concerned.
In our scenario, I’ll specify a 0.74 psi over-pressure level that
corresponds to the minimum safe building distance for protection against flying
glass from an outdoor explosion (Figure 4).
In addition to this results
window being displayed, a PEAC Map Tool window is displayed which displays the
graphic to scale on a local street map (Figure 5).
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Figure 5 – Standoff distance plotted to scale on a street map
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When the user is finished
and exits the Explosion Calculator window (Figure 4) by clicking on the
[X] in the upper right corner, an Explosion Calculator Results Report is
automatically generated and displayed (Figure 6 and 7).
The first part of the report
recaptures the input and computations made along with the map embedded in the
report (Figure 6). The last portion
(Figure 7) provides a table of distances to other types of infrastructure
damage that may of use to the user. At
the end of the report is the warning statement provided on the first screen
when the application was started. The
report can be printed, reviewed or recalled for later access.
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Figure 6 – Top portion of the Explosion Calculator Results Report
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Figure 7 – The table of distances to other blast effects
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If a reader needs more
information on the Explosion Calculator or other computational tools or
data contained in the PEAC tool, please give our staff a call at 877-912-2200
or email support@aristatek.com.
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