Apr 21, 2015
Failure to identify and mitigate explosion hazards is a persistent cause of industrial accidents, impacting sites ranging from fertilizer storage facilities to refineries. While some explosion consequence assessments are performed to comply with regulatory requirements or industry-specific process safety standards, in many cases the potential for loss of life and property damage is overlooked until a tragedy occurs. Explosion Consequence Modeling (ECM) can provide detailed information about the possible effects of a blast, and can be used to identify and design mitigation measures. The two traditional ECM techniques have been: 1) basic phenomenological models that are very cost-effective but provide very simplistic results, and 2) computational fluid dynamics (CFD) techniques which provide great detail but are time consuming and can be prohibitively expensive. Many facilities are in need of a detailed ECM analysis to identify and mitigate explosion hazards, but require a moderate approach that can provide detailed damage and injury predictions without the high costs of CFD modeling.
For these facilities, the Explosive Damage Assessment Model (ExDAM) can provide many of the benefits of CFD modeling with a much smaller commitment of time and money. Originally developed by Dr. Frank Tatom and marketed as part of Trinity Consultants' BREEZE® Software, ExDAM expands on the basic phenomenological model concept by adding the ability to model damage and injury while accounting for the structural details of buildings as well as the shielding effect of structures and equipment on the area behind them. Thus, ExDAM provides the safety benefits of a detailed ECM study to a much wider range of facilities at risk from either conventional high explosive (HE) materials or vapor cloud explosions (VCE). Facilities around the world have used this approach to evaluate and prepare for both potential industrial explosions and potential terrorist attacks. ExDAM has been applied to a broad range of facilities, including chemical/petrochemical, military, chemical storage, oil and gas exploration, ammunition manufacturing, rocket assembly, and stadiums/public buildings.
Developed from the Nuclear Damage Assessment Model (NDAM) and the Enhanced Nuclear Damage Assessment Model (ENDAM), ExDAM currently includes two modules: HExDAM, used to model conventional high explosive materials, and VExDAM, used to model vapor cloud explosions.
These modules use the following steps to produce a detailed assessment of injury and damage:
Project development in ExDAM is relatively simple, requiring only three steps:
In formulating a modeling analysis, time constraints and user needs typically dictate one of two strategies for creating buildings and people in the model environment. For large-scale analyses or a high-level overview of a scenario, each building can simply be represented as one block or a few blocks using one of ExDAM's whole-structure material categories.
Examples of these include:
When explosions are located close to a building, such that the incident pressures/impulses of the blast wave on different parts of the structure vary significantly, or when a high level of detail is desired in the damage assessment, structures can be re-created in detail, with each of the different materials composing a structure represented separately (e.g. column, beam, wall panel, floor panel, door, window). For this type of 'micro-level' structure damage assessment, standard structure-component materials can be used such as:
Explosion consequence modeling at industrial and military facilities has historically been the most common use of ExDAM. In these scenarios, one or more explosive material storage and/or processing locations are known. By modeling worst-case explosion scenarios across the facility, worst-case peak overpressures/impulses and subsequent worst-case damage and injury levels can be estimated facility-wide. In this scenario, modeling was performed to determine the potential VCE hazard posed to existing process and office buildings, as well as a safe location for siting of a future portable building (as per API 753 ). Model execution required approximately one hour on a laptop computer for a full-facility model run. Model results predicted broken windows and minor structural damage to exposed faces of several permanent structures. Predicted injuries to personnel were slight for personnel in shielded locations, but broken bones and other injuries were predicted for personnel in poorly shielded locations such as near windows. An area for safe placement of portable buildings was defined based on areas with low modeled overpressure. The location of this area was dictated primarily by distance from explosion sources and shielding from permanent structures. A plot plan illustrating some of the shielding effects, structure damage, and occupant injury is shown in Figure 2.
Creation and execution of this modeling scenario required approximately two days of time from an experienced user. The process was expedited by features such as 3-D CAD import tools and the program's intuitive 3-D interface.
Check out our video on Petroleum Plant Siting Analysis to learn more about BREEZE ExDAM.
Another common use of the ExDAM model is to assess the potential for damage or injury in a particular structure of interest from an explosion or to reconstruct a past incident. Often, these analyses are performed in the homeland security field to model the effects of high explosives. Real-world examples performed by ExDAM's original developer, Dr. Frank Tatom, include an analysis of the 1996 Oklahoma City Bombing and a consequence analysis of a hypothetical bombing attack on a major U.S. college football stadium. Consequence analysis for a structure can also be performed for a vapor cloud scenario, as in this case.
The study scenario is a propane vapor cloud explosion in close proximity to multi-story hotel/apartment buildings. Vertical cross sections of the buildings and floor plans of each floor were imported into ExDAM and used to define the building structures (Figure 7). Tools within the program, such as the ability to create only one upper floor and then to copy/paste that to create the other levels, reduced the time required to create the structure. Building construction was primarily wood frame. Figure 3 shows the results of this modeling analysis, including predicted building damage and 3-D isosurfaces of predicted overpressure.
Check out our video on Building Structure Demonstrations to learn how BREEZE ExDAM computes damage/injury levels and simulates blast waves from an external explosion.
The model is relatively simple to use and understand in comparison to approaches such as CFD. Thus, while in no way a replacement for applications in which CFD modeling is required, ExDAM is accessible to a wider audience of safety professionals, first responders, etc. than CFD modeling. The ability of the model to correlate predicted overpressure and impulse into predictions of injury and damage adds to the potential utility of the model for these groups - impacts are translated into terms that can be readily understood by those without formal training in interpretation of overpressure and impulse data. However, some expertise is required to properly use the model, particularly when modeling vapor cloud explosions as these can be more difficult to quantify.
Originally published in the Winter 2015 issue of Environmental Quarterly.