EXPLOSION MODELING

Using Software to Develop a Risk-Based Approach

An explosive, when heated, intentionally or unintentionally (e.g. fire), can produce a thermal explosion or even a detonation, producing a great deal of damage. Thermal explosions are complex events which typically include many chemical and physical processes such as heating, expansion, phase transition, chemical reactions, heat, and finally heat and momentum transfer.   Evaluation of an explosion can involve a description of the initial material physical and chemical states, rate of heating, rate of decomposition kinetics, the changes in the explosive chemical and mechanical properties, rate of burning, transfer of explosive energy into thermal and mechanical energy (hydrodynamics), and, finally, amount of damage (violence).

Evaluation of Explosions by Modeling

Two main methodologies exist for modeling the explosion resulting from a vapor cloud explosion:

• TNT Equivalency methods
• Methods based on the fuel-air charge blast

The explosion models include the following widely accepted approaches:

U.S. Army TNT Equivalency was based on the work of the U.S. Army. This model uses a proportional relationship between the flammable mass in the cloud and an equivalent weight of TNT and assumes that the entire flammable mass is involved in the explosion and that the explosion is centered at a single location. The model uses one of two blast curves, depending upon whether the explosion being modeled is a surface burst or a free-air burst.

U.K. HSE TNT Equivalency was based on the work of the U.K. Health and Safety Executive (HSE). This model uses a proportional relationship between the flammable mass in the cloud and an equivalent weight of TNT. It assumes that the entire flammable.

High Explosives:  High Explosive Damage Assessment modeling has been conducted to evaluate the damage caused to structures within a facility as a result of a primary explosion and any accompanying secondary explosions.  High explosive damage assessment models can also predict injury to an unlimited number of personnel in a facility. The principal use of such software is for site analysis of explosive storage and manufacturing facilities; however, the software can also be used to evaluate terrorism and sabotage threats to an industrial or military facility. 

Explosion Modeling Software

Geologic Resources is a reseller of Breeze air dispersion, hazardous gas dispersion, explosion, and fire modeling software.   We also provide links to a number of sources of geologic, scientific, and environmental software on our internet software links page.   Some Breeze software that can assist with compliance, explosion prevention, explosion evaluation, and security are listed below:

• BREEZE Fire/Explosion models are ideal for real-world applications, such as control-room siting at a natural gas refinery, or meeting governmental regulations, such as the US EPA's Risk Management Plan (RMP) ruling.
• BREEZE HEXDAM:  The High Explosive Damage Assessment Model (HEXDAM) is designed to evaluate the damage caused to structures within a facility as a result of a primary explosion and any accompanying secondary explosions.   The application can also predict injury to an unlimited number of personnel in the facility. The principal use of HEXDAM software is for site analysis of explosive storage and manufacturing facilities; however, the software can also be used to evaluate terrorism and sabotage threats to an industrial or military facility. 
• BREEZE VEXDAM (Vapor-cloud Explosion Damage Assessment Model), is designed to evaluate the damage caused to structures as a result of a primary explosion and accompanying secondary explosions from vapor clouds at any elevation.  VEXDAM can be used to access damage to a multitude of structure types, including bridges, buildings, hangars, magazines, shelters, underground structures, industrial equipment, gas or oil storage tanks, and user-defined structures. Structures can be constructed of various building elements such as aluminum, asbestos, brick, concrete, glass, steel, and wood.
• BREEZE VASDIP (Vulnerability Assessment of Structurally Damaging Impulses and Pressures), calculates explosive safety and physical security parameters for use in predicting possible damage to buildings and humans resulting from an external explosion.
• BREEZE DEGADIS software is ideal for determining toxic endpoint distances and distances to lower flammability limits (LFLs) for certain toxic and flammable chemicals in accordance with EPA’s Risk Management Program (RMP) requirements.
• BREEZE SLAB softare is ideal for determining toxic endpoint distances and distances to lower flammability limits (LFLs) for certain toxic and flammable chemicals in accordance with EPA’s Risk Management Program (RMP) requirements.
• BREEZE HAZ EXPERT:  The algorithms contained in HAZ EXPERT are based primarily on EPA’s document, “Guidance on the Application of Refined Dispersion Models to Hazardous/Toxic Air Pollutant Releases.