Explosion and Damage Assessment:
Computer Simulation with HExDAM
Prepared By:
Thomas G. Grosch
BREEZE SOFTWARE
12770 Merit Drive
Suite 900
Dallas, TX 75251
+1 (972) 661-8881
breeze-software.com
Modeling Software for EH&S Professionals
INTRODUCTION
Architectural and structural engineering firms, as well
as the Department of Defense, other federal agencies, and
private industry are increasingly challenged with the task
of mitigating the threats of destructive blast waves
associated with accidental or intentional explosions.
Physical security and safety requirements continue to be
reviewed and adapted to address these threats, with the
intent to prevent mass casualties and protect property.
Conventional explosives can easily be transported and
pose a severe loading condition on most commonly used
structural systems.
Structural engineers designing
government and other public buildings must often address
the overpressures resulting from events involving
conventional explosives. Simulation software that is
specially designed to predict overpressure and resulting
structural damage can help engineers to better design
structures.
The software can also help emergency
managers run “what if” scenarios for planning purposes
and for developing emergency response plans.
This article presents the results of simulation software
(BREEZE® HEXDAM) that models the effects of blast
waves from a hypothetical terrorist bombing.
Four
scenarios are modeled with HEXDAM. Since standoff
distances are important to emergency managers and
engineers, this article also uses HEXDAM to examine the
effects of varying standoff distances on blast damage to
structures and personnel; and the potential for secondary
explosions resulting from weakening of structures.
BLAST SIMULATION AND DAMAGE ASSESSMENT
The High Explosive Damage Assessment Model
(HEXDAM) is specialized explosion simulation software
that allows engineers and emergency managers to analyze
explosion scenarios and account for blast overpressures –
and more.
Recent developments have enhanced
HEXDAM’s ability to predict the effects of blast waves on
personnel and structures. The model also includes the
ability to vary the composition of a structure. HEXDAM’s
fragmentation counterpart can also model secondary
fragmentation from shattering glass and other frangible
materials.
The model’s unique ability to account for
structural shielding and secondary explosions provides
architects, engineers, and emergency managers a tool that
helps them determine structural
vulnerabilities to blast effects.
and
personnel
Figure 1 – Damage results to ships, pier, and
building from primary and secondary explosions with
standoff distance of zero. Structural subdivisions
enhance damage resolution. Red indicates severe
damage while the grey areas indicate no damage.
HEXDAM HISTORY
HEXDAM evolved from the Department of Defense’s
(DoD) development of the Nuclear Damage Assessment
Model (NDAM) in the early 1980s. NDAM was used to
assess blast damage from nuclear weapons over areas, such
as cities or military installations. In, 1986, the U.S. Army
Strategic Defense Command requested that enhancements
be made to the NDAM model, and these changes resulted
in the Enhanced Nuclear Damage Assessment Model
(ENDAM). The Huntsville Division Corps of Engineers
(CEHND) received funding through the Facility Army
System Safety (FASS) program to implement
enhancements that made the model applicable to
conventional high explosive weapons. The resulting
application was called HEXDAM. The theoretical portion
of the code as it is today is in large part due to the research
and development efforts of Dr. Frank Tatom of
Engineering Analysis, Inc. Today, the Software and Data
Services division of Trinity Consultants, Inc maintains and
continues to enhance HEXDAM.
HEXDAM was designed to predict the effects of blast
waves on a variety of structural types, with each type
having a unique vulnerability profile that varies with the
strength of the explosion.
It can be used as a
damage/injury assessment tool to determine the amount of
blast damage, or injury, to individual structures or persons.
The blasts can result from explosions at ground level or
aloft (airburst detonations). HEXDAM’s unique shielding
algorithms make the model an ideal tool for evaluating the
effectiveness of a shielding wall or blast deflector.
Additional information regarding the algorithms in
HEXDAM is given in reference 1.
THE EXPLOSION SCENARIO
Four scenarios were modeled with HEXDAM. The
scenarios involve an explosive device that is placed at a
varying distance from a ship in a harbor. See Figure 2 for a
display of the harbor. The objective of the scenarios was to
determine the minimum standoff distance from the main
ship of interest (Ship 1) required to prevent a secondary
explosion from explosive material in the vicinity of the
primary explosion; and prevent damage to the ship of
interest. The charge weights of the primary and secondary
explosives are not disclosed, as they are not critical to this
article.
A secondary explosion potential (charge weight is 7%
that of the primary explosion) comes from within a truck
parked alongside a single-story building on a pier adjacent
to the ships of primary interest (Ships 1 and 2). The
building is constructed of six-inch reinforced masonry
walls and contains a single window and a door. Nine
people are in or near the building. Other merchant ships
and smaller vessels are also included in the analysis.
Each of the structural components that make up the
building, ships, piers, and personnel were selected from
HEXDAM’s database of material properties containing
vulnerability parameters. Over 120 elements or structures
are contained within the database. User-defined structure
types and vulnerability parameters can be generated using
HEXDAM’s companion model, VASDIP (Vulnerability
Assessment of Structurally Damaging Impulses and
Pressures.) [2]
Each scenario modeled is identical, with the exception
of the location of the initial, primary explosion. The
primary explosion in each scenario is detonated at a height
of eight feet above water level from the bow section a 75foot long boat. The standoff distances analyzed are in
relation to the aft, port side of a 500 foot-long merchant
ship (Ship 1) and increase in distance away from the ship
and pier. The standoff distances are for Scenario 1)
directly alongside ship, Scenario 2) 163 feet, Scenario 3)
203 feet, and Scenario 4) 244 feet.
Structural Shielding
An important feature of HEXDAM is its ability to
perform analyses with or without the effects of structural
shielding. By including shielding effects, the analyst can
examine the blast deflection and shielding effects of each
structural component, including people, on other structures
and can identify specific vulnerabilities of individual
structural components or entire facilities.
Structural
damage and personnel injury are based on the magnitude
of the overpressure and the ability of a structure (or part of
a person’s body) to withstand the overpressure. In
HEXDAM’s default list of structural types, each ship was
classified as being a “Merchant Ship” while the building
and truck were created using various materials (e.g., glass,
reinforced masonry, aluminum panels).
The VASDIP model allows a user to create virtually an
unlimited number of elements or structures that can be
modeled by HEXDAM. VASDIP generates pressureimpulse diagrams, damage/injury levels for specific values
of pressure and impulse, and vulnerability parameters by
accounting for user-defined properties of 24 different basic
inanimate structural components, as well as 28 human
body components. [2]
Structural Subdivision
In each scenario, the building on the pier and adjacent
merchant ships are of special interest -- the building,
because nine people are located within and around it, and
the ships because they are high profile targets. Because of
their special interest, these structures have been
automatically subdivided by HEXDAM to provide greater
damage resolution.
Structural damage and personnel injury are graphically
presented
in
HEXDAM
using
color-coding.
Overpressures, dynamic pressures and percentage of
damage are generated as textural and graphical output for
each subdivided component. The effect of this subdivision
can be seen in Figure 1.
Secondary Explosions
HEXDAM allows the analyst to create structures,
destruction of which would pose the risk of collateral, or
sympathetic, explosions. These are called “secondary
explosions”.
If the structure containing a potential
secondary explosion is not sufficiently shielded from the
primary explosion’s blast wave, the structure could be
damaged, causing subsequent secondary explosions and
increased damage. In Figure 1, a grid was placed over the
bow of Ship 2 so that the distribution of damage from a
secondary explosion originating from the truck alongside
the building could more closely be analyzed. A threedimensional plot of blast overpressures shows
overpressures ranging from 1 to 100 pounds per square
inch (psi). Damage to Ship 2 from the secondary
explosion is apparent in the inset image of Figure 1.
Similar grids could have been placed at any location within
the modeling domain.
Personnel Damage Assessment
Blast damage to humans was also analyzed in these
scenarios.
HEXDAM allows for the creation of
individuals that can be placed in 44 different postures. For
each person modeled, the effects of the blast waves are
assessed on 28 different body components (e.g., ear drums,
larynx, lungs, feet). By default, people are modeled as
individuals standing six feet tall weighing 180 pounds with
a body height-to-width ratio of 5.4.
Figure 3 shows the position of the six people within the
building and damage to individual body components and
building subdivisions. Results are from Scenario 3 (no
secondary explosion from the adjacent truck). The person
entering the door was not shielded by the building from the
primary explosion to the extent that the other individuals
were. The person standing in front of the window was also
exposed to higher pressures. As a result, vulnerable body
components suffered more damage. In Figure 3, blue
represents essentially no damage.
Injuries are produced by the blasts and do not include
injuries from flying glass fragments of shattered windows.
An associated model, HEXFRAG, can compute glass and
other frangible material fragment injuries.
Figure 3 - Personnel damage from the primary
explosion only. Blue represents no damage; red,
severe; orange, moderate; yellow, slight.
Scenario 1
No standoff distance. Primary explosion detonates
alongside Ship 1.
Primary explosion - Causes severe damage to aft
section of Ship 1 as well as a small section of pier. Slight
to moderate damage occur along 1/3 the length of Ship 1.
The upper portion of the aft superstructure shows no
damage although this structure is closer than portions of
the main weather deck to the primary explosion.
The structural shielding effects of the aft portion of the
aft superstructure on Ship 1 prevented damage to the
forward section of the aft superstructure (see Table 1).
Figure 4 shows a cross-sectional analysis of the
overpressures (as they pass over the aft superstructure of
Ship 1). The blast wave can be seen impacting the aft
portion of the ship and rise over the superstructure while
the effects of the blast penetrate the ship below the main
deck, resulting in higher pressure levels at and below the
main deck.
Results
HEXDAM was used to determine the approximate
minimum standoff distance necessary that would result in
no secondary explosion and no damage to Ship 1. The
following briefly describes the results for each scenario
while Table 1 graphically shows the damage to the ships
and surrounding structures.
Figure 4
Secondary explosion – The force from the primary
explosion is sufficient to trigger the secondary explosion
from within the truck on the pier. It causes severe damage
to the pier, while the building and personnel are
completely destroyed/killed. Ship 2 also sustains severe
damage to the hull.
Scenario 2
Standoff distance of 163 feet (49.6 meters).
Primary explosion – Causes slight damage to Ship 1
and pier. Ship 1’s hull integrity withstands the blast wave
and prevents the damage to the main weather deck that
was observed in Scenario 1. Note difference in damage
coloring to Ship 1 in Table 1 as compared to Scenario 1.
Secondary explosion – Primary explosion is sufficient
to trigger the secondary explosion from within the truck.
Results are similar to those in Scenario 1.
Scenario 3
Standoff distance of 203 feet (62.0 meters).
Primary explosion – Does not trigger secondary
explosion. Causes a small section of Ship 1 to be slightly
damaged. Portions of pier not shielded by Ship 1 are
slightly damaged. Personnel inside building sustain slight
damage to eardrums and severe damage to their feet. Foot
damage is primarily a result of the blast wave propagating
up through the floor of the building as it traveled under the
pier, coupled with the fact that feet are highly susceptible
to blast damage.
Personnel outside of building sustain severe damage to
the neck (larynx and cervical vertebrae), hands, and feet.
Moderate damage to the shoulders and chest (lungs,
thorax, and thoracic vertebrae) is observed, while slight
damage occurs to the abdomen (GI tract, pelvis, and
lumbar vertebrae). The figure in Table 1, Scenario 3
shows the building and personnel in it with resulting
damage.
Scenario 4
Standoff distance of 244 feet (74.4 meters)
Primary explosion – Does not trigger secondary
explosion and does not cause damage to any ship. Portions
of pier not shielded by Ship 1 are slightly damaged. The
truck closest to the primary explosion sustains moderate
damage to the aluminum paneling that makes up the cargo
area (see Table 1) while the truck that contains the
potential secondary explosive charge only sustains slight
damage. The metallic cab portion of each truck sustains
no damage.
The figure in Table 1, Scenario 4 shows the west facing
side of the building on the pier. A large portion of the
right half of this side sustained no damage due to the
shielding effects of the truck.
SUMMARY OF R ESULTS
Results of these scenarios show the effects that blast
waves on structures of varying composition as a function
of standoff distance. The analyses predict different levels
of damage to sub-divided building and ship components as
well as personnel. Iterative analyses indicate that a
standoff distance of approximately 200 feet prevented the
secondary explosion potential within the truck from
occurring. A distance of 244 feet resulted in no damage to
any ship. Additional analyses could have identified the
minimum standoff distance required to prevent any
damage to Ship 1. HEXDAM is undergoing additional
enhancements to incorporate the ability to perform
parametric analyses that automate the identification of
minimum standoff distances, charge weights, and
structural properties for user-defined damage thresholds.
This would allow an emergency manager or engineer to
vary one parameter in HEXDAM and quickly re-run the
model to see how the resulting damage and injuries would
change.
CONCLUSION
Explosion modeling and damage assessment software
can provide decis ion makers with information regarding
the protection of structures and people. Shielding effects
from structures or people are often an important
consideration in evaluating explosion scenarios.
By
computing the damage and injury to structural components
as a function of the magnitude of the overpressure and the
ability to withstand the overpressure, coupled with
shielding effects, HEXDAM gives decision makers a costeffective method of mitigating risk. By using simple data
entry forms and graphical displays within BREEZE
HEXDAM, the process of setting up and modeling
explosion scenarios is streamlined and the presentation of
the results is informative.
Additional information and demonstrations of versions
of HEXDAM can be obtained from the developers website
at http://www.breeze-software.com.
Thomas Grosch is an Atmospheric Scientist and
Manager, Software and Data Services for Trinity
Consultants, Inc, an environmental consulting firm in
Dallas, Tx; tgrosch@trinityconsultants.com or (972) 6618100.
Table 1 – Damage results from modeled scenarios.
Scenario 1 – No standoff distance
Scenario 2 – Standoff distance =163 ft
Scenario 3 – Standoff distance = 203 ft
Scenario 4 - Standoff distance =244 ft
Damage Legend
None - Grey
Slight - Yellow
Moderate - Orange
Severe - Red
REFERENCES
1.
2.
“BREEZE HEXDAM and VEXDAM User’s Guide, Version 7.0”, Trinity Consultants, Inc., Dallas Texas, 2003,
www.breeze-software.com
“BREEZE VASDIP User’s Guide, Version 6.0”, Trinity Consultants, Inc., Dallas Texas, 2002, www.breezesoftware.com