Explosion Modeling and Damage Assessment Software

Environmental solutions delivered uncommonly well
Explosion Modeling and Damage Assessment
Software
Prepared By:
Thomas G. Grosch
Frank Tatom
TRINITY CONSULTANTS
12700 Park Central Drive
Suite 2100
Dallas, TX 75251
+1 (972) 661-8881
trinityconsultants.com

EXPLOSION MODELING AND
DAMAGE ASSESSMENT SOFTWARE
Thomas G. Grosch
Trinity Consultants, Inc.
12801 North Central Expressway, Suite 1200
Dallas, Texas 75243 USA
tgrosch@trinityconsultants.com
and
Dr. Frank Tatom
Engineering Analysis Inc.
715 Arcadia Circle
Huntsville, Alabama 35801
eai@mindspring.com
ABSTRACT
This article will briefly discuss the potential for industrial explosions. It will
outline the steps in using one particular type of explosion modeling software
called BREEZE®
HEXDAM and VEXDAM that is used to predict the human and
structural effects of explosions at a facility. Finally, the article will explain how to
use this information to ensure workers’ safety and minimize facility damage
resulting from explosions.
KEYWORDS:
Explosion modeling, damage assessment, software, process safety, injury,
overpressure, dynamic pressure
INTRODUCTION
Industrial facilities run like well oiled machines, keeping the pulse of the nation’s economy moving at a
steady clip. But on-site explosions slow this pulse, threatening workers’ safety and jeopardizing
production. Industry leaders know all too well the devastating effects that explosions can have on a
facility. In its 1999 Process Safety Performance Measurement report [1], the American Petroleum
Institute (API) noted that respondents reported nearly 100 industrial incidents that resulted in significant
injuries and even fatalities.
While many of these explosions may not be preventable, an industrial safety staff can predict their effects,
enabling appropriate emergency response planning. Specialized explosion modeling software allows

facilities to input potential explosion scenarios based on the types of materials they use and store as well
as the structural components of the buildings themselves, as depicted in Figure 1. These programs
model structural damage as well as potential injury to workers within the facility. Facilities can benefit
from explosion modeling in many different situations, including before constructing a new facility, when
planning renovations to a facility, when changing the amount of a certain chemical stored on site, and
before switching fuels. Equipped with this predicative tool, industrial personnel can help ensure the
safety of their employees and the soundness of the structures in which they work.
This article will briefly discuss the potential for industrial explosions. It will outline the steps in using one
particular type of explosion modeling software called BREEZE®
HEXDAM and VEXDAM that is used to
predict the human and structural effects of explosions at a facility. Finally, the article will explain how to
use this information to ensure workers’ safety and minimize facility damage resulting from explosions.
SUSCEPTIBILITY TO EXPLOSIONS
Virtually any facility that handles, stores, or processes flammable gases, liquids, or solids has an
explosion risk. Explosions can be produced either by high explosives such as TNT or dynamite, or by
vapor clouds involving hydrocarbon fuels. All structures are classified as either overpressure or dynamic
pressure sensitive. Blast waves resulting from an explosion will damage objects based on the object’s
vulnerability to either type of pressure. Overpressure is the increase in pressure that results from the
explosion, while dynamic pressure is the drag produced by the velocity of the wind behind the blast wave.
Materials such as concrete are more susceptible to overpressure, and structures like towers, telephone
poles, and bridges are affected more by dynamic pressure. In addition to overpressure or dynamic
pressure, most structures are also sensitive, to some extent, to pulse duration. The integral of the
overpressure or the dynamic pressure with respect to time, over the time interval corresponding to the
pulse duration, represents the impulse. Dynamic pressure sensitive structures are more often sensitive to
pulse duration and/or impulse than are overpressure sensitive structures.
Understanding the vulnerability of a facility’s structures is critical to predicting its ability to withstand a
blast. Explosion models use pressure/impulse (P-I) characteristics to predict a material’s ability to

withstand conventional explosion or vapor cloud explosion blasts. For example, Trinity Consultants’
BREEZE VASDIP (Vulnerability Assessment of Structurally Damaging Impulses and Pressures) software
[2] generates P-I diagrams, as depicted in Figure 2, to produce vulnerability parameters, which allows
users to specify detailed properties of 24 different basic structural components and 19 human body parts.
The P-I diagram in Figure 2 pertains to a reinforced concrete beam. The vulnerability parameters
produced by VASDIP can be used as inputs to the BREEZE HEXDAM (High Explosive Damage
Assessment Model) [3-8] and/or VEXDAM (Vapor Cloud Explosion Damage Assessment Model) [9-13]
software.
MODELING AN EXPLOSION SCENARIO
The HEXDAM and VEXDAM explosion modeling software take into account the following considerations:
Pressure effects
Shielding effects
Secondary explosions
Pulse duration effects
Damage/injury levels
Subdivision of structures
The first step in modeling a potential explosion produced by a conventional high explosive is to specify a
primary explosion within or around a facility consisting of one or more structures and/or personnel. In
BREEZE HEXDAM software, the user can place an explosion within a layout diagram of the facility and
its grounds. The necessary information about the explosion includes X and Y coordinates for the
explosion’s location, the height above ground of the explosion, and the explosive yield. If the explosion is
produced by vapor clouds, in BREEZE VEXDAM the user must input the identity of the fuel, the number
and location of subclouds, the mass of fuel or volume of vapor-air mixture in each subcloud, and the
explosive strength of each subcloud.
After entering the explosion information, the user must input data about the structure or structures
potentially affected by the blast. Required data in this step includes the type of structure; the X, Y, and Z

coordinates of the structure; the dimensions of the structure including length, width and height; and the
orientation; and the number of components, or subdivisions, comprising the structure. The structure type
can be either a standard type or a special user- defined type.
Models have been pre-programmed into the HEXDAM and VEXDAM software for standard types of
structural elements such as aluminum, brick, concrete, glass, and steel, and for standard types of
composite structures, including buildings, hangars, underground structures, industrial equipment, and oil
and gas storage tanks. Specific examples of such composite structures include:
industrial building with a heavy steel frame and 25 to 50-ton crane capacity
100-pound liquid petroleum gas tank
protected 7000-pound milling machine
The models automatically define the vulnerability parameters for these standard elements. For other
(user-defined) types of elements/structures the vulnerability parameters can be generated by means of
VASDIP.
In order to get a complete picture of the damage an explosion can cause, industrial safety managers can
also use explosion models to calculate human injury resulting from a blast. Modeling software [14,15],
utilizing the HEXDAM Man concept as depicted in Figure 3, allows users to enter the description and
location of every person in a facility with respect to the blast origin. Explosion models require the X, Y,
and Z coordinates of each person, the orientation of each person in degrees from North, and the pose of
each individual. A total of 44 different poses are available. The BREEZE HEXDAM and VEXDAM
models can take into account the vulnerability to an explosion for each of twenty-eight different body
components that comprise each person.
EXPLOSION MODELING RESULTS
With the explosion, structural, and personnel data entered into the software, the model can predict the
pressures received by each structure and person in the facility based on the location of the structures and

people relative to the primary explosion. The effects of structures or people shielding one another may
also be taken into account [16]. The models then calculate the damage and injury to each structure and
person based on the magnitude of the pressure received and the ability to withstand the pressure. In
addition, the user may superpose a grid, as shown in Figure 1, over the entire facility or any portion
thereof to calculate pressures that occur at specific locations or analyze the distribution of damage or
injury among the structures and workers.
The damage to each structure, as well as the injury to each personnel can be presented graphically using
a color-coding scheme. For depicting damage, each structure can be subdivided into a number of
components with the color-coded damage level for each component displayed, as shown in Figure 4. In
this figure, structural damage is color-coded such that green corresponds to no damage, yellow to slight
damage, orange to moderate damage and red to severe damage. In the case of injury to persons, the
color-coded injury level for each of the twenty-eight body components can be depicted, as presented in
Figure 5.
HOW TO USE EXPLOSION MODELING DATA
Armed with specific information about how explosions could affect their structures and employees,
facilities can take preventative steps to ensure their safety. Engineers can consider explosion modeling
data in plans for construction or renovation, improving their ability to build structures capable of
withstanding blasts and to locate personnel in areas least at risk for sustaining explosion damage.
Managers can also give their explosion modeling information to local fire and hazard authorities so that
emergency personnel can respond appropriately if a blast occurs.
While the threat of industrial explosions may be inescapable, explosion modeling can help minimize the
damage to structures and injury to workers. Explosion modeling provides companies with a valuable tool
in their efforts to optimize productivity while maintaining the safest possible environment for their workers.

In the scenario depicted in Figure 1, involving an explosive manufacturing facility, one of four 8,000 gallon
tank cars has overturned and developed a leak, as shown in more detail in Figure 6. This car, along with
each of other three, is near-empty, containing only 480 gallons of propane, but the vapor clouds produced
by such an amount of propane, as depicted in Figure 7, represent a significant hazard. In case of a
detonation, with an explosive strength of 10, much of the facility would be exposed to overpressures in
excess of 1 psi. Such pressure levels would result in significant damage to the various structures, which
comprise the facility, as presented in Figure 8. As expected, structures nearest the vapor clouds would
be severely damaged. Most of the other structures to the north and east would be partially protected by
barricades and as a result would experience only slight or moderate damage. A plot of two-dimensional
pressure contours ranging from 1 psi to 50 psi in the horizontal plane are provided in Figure 9. Likewise,
a plot of three-dimensional pressures contours ranging from 1 psi to 50 psi are presented in Figure 10.
To further complicate the situation, secondary explosions in the building complex to the north could be
triggered by the initial vapor cloud explosions, already described. Such secondary explosions would
result in severe damage to most of the structures to the north of the rail cars, as presented in Figure 11.
Structures to the east, behind the main barricade would remain only slightly to moderately damaged. A
plot of the resulting two-dimensional pressure contours ranging from 1 psi to 50 psi in the horizontal plane
are shown in Figure 12, while a plot of three-dimensional pressure contours over the same range are
provided in Figure 13.
One of the structures to the east of the barricade, as indicated in Figure 14, is of special interest because
six personnel are located within it. This structure includes three windows facing north, as indicated in the
figure. Because of the special interest in this structure, it has been subdivided to provide greater detail
regarding damage. The positions of the six persons within the structure are shown in Figure 15.
For the case involving multiple vapor cloud explosions with secondary explosions, the damage to the
building containing personnel is shown in Figure 16. Likewise, the injury to personnel inside the building
is depicted in Figure 17. Notice should be taken that the injuries indicated in this figure are produced by

blast and do not include broken glass fragments. Such glass fragment injuries can be computed by an
associated software model, VEXFRAG that has been very recently developed.
CONCLUSION
Explosion modeling and damage assessment software has the ability to provide decision makers with
information regarding the placement and protection of animate and inanimate objects alike. 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
pressure received and the ability to withstand the pressure, coupled with shielding effects, the software
described in this article offer decision makers a cost-effective method of mitigating risk. By using simple
data entry forms and graphical displays within BREEZE HEXDAM and VEXDAM, the process of setting
up and modeling explosion scenario’s is streamlined and the presentation of the results is informative.
REFERENCES
1. Flowers, M., “1999 Process Safety Performance Measurement Report”, American Petroleum Institute
(API), April 2000.
2. Tatom, F.B., and Tatom, J.W., “Vulnerability Assessment of Structurally Damaging Impulses and
Pressures (VASDIP)”, Twenty-Fourth Department of Defense Explosive Safety Seminar, St. Louis,
Missouri, August 30, 1990.
3. Tatom, F.B., and Roberts, M.D., “Refinements to the High Explosive Damage Assessment Model
(HEXDAM)”, Twenty-Third Department of Defense Explosive Safety Seminar, Atlanta, Georgia,
August 9-11, 1988.
4. Hamilton, J.S., Jr., “High Explosive Damage Assessment Using a Microcomputer”, Twenty-Third
Department of Defense Explosive Safety Seminar, Atlanta, Georgia, August 9-11, 1988.
5. Manthey, J.P., LaHoud, P.M., and Tatom, F.B., “Structural Vulnerability to Overpressure Using a
Microcomputer”, Structures for Enhanced Safety and Physical Security Conference, Washington,
D.C., March 1989.
6. Serena, J.M., III, and LaHoud, P.M., “Validation of Airblast Damage Predictions Using a
Microcomputer Based High Explosive Damage Assessment Model (HEXDAM)”, Twenty-Fourth
Department of Defense Explosive Safety Seminar, St. Louis, Missouri, August 28-30, 1990.
7. LaHoud, P.M., “Rapid Risk Assessment from Accidental Explosions Using a Microcomputer Model”,
Tenth International System Safety Conference, Dallas, Texas, July 18-22, 1991.
8. Tatom, F.B., Roberts, M.D., Tatom, J.W., and Miller, B.A., “High Explosive Damage Assessment
Model Advanced Industrial Version (HEXDAM-D+)”, Twenty-Fifth Department of Defense Explosive
Safety Seminar, Anaheim, California, August 18-20, 1992.

9. Tatom, F.B., Tatom, J.W., and Miller, B.A., “Vapor Cloud Explosion Damage Assessment Model
Second Insutrial Version (VEXDAM 5.0)”, Vapor Cloud Explosion Subcommittee Meeting, Center for
Chemical Process Safety, AICHE, January 31, 1994.
10. Dillehay, D.R., and Leande, R.C., “Cowles Dissolver Fire Involving IR Flare Mix”, Twenty-Sixth
Department of Defense Explosive Safety Seminar, Miami, Florida, August 16-18, 1994.
11. Dillehay, D.R., “VEXDAM and Pyrotechnic Safety Hazard Classificaiton”, 20th
Internaional
Pyrotechnics Seminar, 1994.
12. Iacovino, J., Jr., Miele, T., Morris, B., and Tatom, F.B., “Evaluations of Natural Gas Hazards at the
Fort St. Vrain ISFSI”, 1995 Waste managmenet Conference, Tuscon, Arizona, March 1995.
13. Dillehay, D.R., “Techniques of Incident Investigations”, 24th
International Pyrotechnics Seminar,
Monterrey, California, 1998.
14. Tatom, F.B., and Tatom, J.W., “Computer-Based Prediction of Personnel Injury Due to an
Explosion”, Twenty-Seventh Department of Defense Explosives Safety Seminar, Las Vegas,
Nevada, August 20-22, 1996.
15. Tatom, F.B., and Tatom, J.W., “Comparison of Head Injuries as Predicted by Three Different
Displacement Velocity Models”, Twenty-Eighth Department of Defense Explosives Safety Seminar,
Orlando, Florida, August 18-20, 1998.
16. Tatom, F.B., and Norman, J.S., “Comparison of Measured and predicted Peak Blast Overpressure
Behind a Shielding Wall”, SAVIAC 64th
Shock and Vibration Symposium, Ft. Walton Beach, Florida,
October 26-28, 1993.
LIST OF FIGURES
1. Undamaged Facility Example Industrial Facility
2. PI Diagram
3. HEXDAM Man
4. Color-Coded Subdivided Structure
5. Color-Coded Injured HEXDAM Man
6. Overturned Tank Car at Example Industrial Facility
7. Undamaged Facility with Vapor Clouds
8. Damaged Facility with Vapor Clouds No Secondary Explosions
9. Damaged Facility with Vapor Clouds No Secondary Explosions 2-D 1-50 psi Contours
10. Damaged Facility with Vapor Clouds No Secondary Explosions 3-D 1-50 psi Contours
11. Damaged Facility With Vapor Clouds Secondary Explosions
12. Damaged Facility with Vapor Clouds Secondary Explosions 2-D 1-50 psi Contours
13. Damaged Facility with Vapor Clouds Secondary Explosions 3-D 1-50 psi Contours
14. Undamaged Building with Personnel Inside
15. Personnel without Injuries in Undamaged Building
16. Damaged Building with Personnel Inside
17. Personnel with Injuries in Damaged Building

Figure 1. Example Industrial Facility
Figure 2. P-I Diagram For Reinforced Concrete Beam

Figure 3. HEXDAM Man
Figure 4. Subdivided Structure with Color-Coded Damage

Figure 5. HEXDAM Man with Color-Coded Injures
Figure 6. Overturned Tank Car at Example Industrial Facility

Figure 7. Undamaged Facility with Vapor Clouds
Figure 8. Damaged Facility with Vapor Clouds, No Secondary Explosions

Figure 9. 2-D Overpressure Contours, 1-50 psi, For Damaged Facility with Vapor Clouds, No Secondary
Explosions
Figure 10. 3-D Overpressure Contours, 1-50 psi, For Damaged Facility with Vapor Clouds, No Secondary
Explosions

Figure 11. Damaged Facility with Vapor Clouds and Secondary Explosions
Figure 12. 2-D Overpressure Contours, 1-50 psi, For Damaged Facility with Vapor Clouds and
Secondary Explosions

Figure 13. 3-D Overpressure Contours, 1-50 psi, For Damaged Facility with Vapor Clouds and
Secondary Explosions
Figure 14. Undamaged Subdivided Building with Personnel Inside

Figure 15. Personnel without Injuries Inside Undamaged Subdivided Building
Figure 16. Damaged Subdivided Building with Personnel Inside

Figure 17. Personnel with Injuries Inside Damaged Subdivided Building

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