Discussion of the Physical Fire Modeling - Essay Example

Fire Modeling to Fire and Explosion Investigation Author’s Name Institutional Affiliation Introduction Fire investigation involves the analysis of fire incidents. The fire investigation is normally aimed at determining what caused the fire and the possible origin of the fire and the reconstruction measures to be undertaken. To get to know the root cause and origin of the fire, there is a need for the fire investigators to apply systematic approach and use of basic knowledge of fire. This is achieved through the use of fire modeling.There are two major categories of fire modeling which include the physical and mathematical fire modeling. In the investigation of a fire situation the appropriateness of a fire models is selected depending on the reason for the investigation, the investigation scope and the complexity of the fire as assessed by the investigators (Gregory, 2009). This paper will provide general discussion of the physical fire modeling; the main focus will be the discussion of the application of computer models for fire investigation, its potential applications and the limitations in the fire and other explosion investigations. Physical fire modeling The physical fire modeling is one of the oldest and a major form of modeling the dynamics of fire. It involves fire demonstration and testing in different scenarios and through the use of different fuels. The physical fire testing is divided into two broad categories, which includes the full scale tests, in this test a replication of the fire scenario is carried out by use of a structure that resembles the actual structure with similar geometrical measurements, the structure is then used to reproduce the fire situation . The other test is the small scale test which is also a replication of a fire tragedy by using a structure that is geometrically scaled down (Gregory, 2009). Mathematical models The study of the fire through the application of the physical model has been existence for many centuries. However, scientists shifted to using the use of mathematical fire modeling in the early 1940s.The dynamics of fire investigation since 1940s have been improving, the computer model is the current application used by fire professionals to analyse dynamics of fire (Wood, 2008). This model has greatly been influenced by the emergence of personal computers which are economical, and faster compared to the computers which were previously available. The computer fire modeling falls in the category of mathematical models. The mathematical models include mathematical equations utilised by investigators to determine how a system will behave in a given situation. This means that through the observation of the physical behaviour, scientists can attempt to come up with mathematical equations that have the thermal science basis and intended to replicate the physical behaviour that has been observed (Gregory, 2009). The equations include the simple algebraic ones that can be used to predict the basic phenomenon of fire such as flame height and the complicated equations that apply partial differentiation that can be used to predict the fire enclosure problem. The mathematical models are divided into three: Hand calculation Zone fire models Field models Hand calculation The hand calculation includes the simple algebraic equations and calculations, they calculate simple effects of fire such as predicting the height of the fire in an open. The hand calculations are often carried out into Excel spreadsheets which make them easy to manipulate (Gregory, 2009). Computer modeling The current computer modeling to fire and explosion investigations is divided into two categories, the field and the zone model, the development of these models were based on the earlier mathematical calculations (hand calculation) and the experimental correlations (Siaka, et al, 2008). Shift from the hand calculation to the current advanced application of the software models for fire modeling dates back to 1975. Zone fire models This models uses computer software to evaluate the dynamics of fire. The model involves dividing the compartments of the fire into layers, upper and lower. The two layers divided depending on fire dynamics in the compartment which include the plume of the fire, the combustion products and air entrainment. The upper layer is composed of the fire plume and the hot gas layer while the lower zone is made up of the ambient air and the entrained air (Gregory, 2009). There exists an interface between the two layers; the interface keeps on constantly changing the height due to the hot gas layer increase. The zone models are thus two disconnected control volumes, the upper layer is the control volume, it gets the mass and subsequent energy from the fire, it then loses the energy through the convection through the various opening available, this may include the radiations and conduction going to the floor, surrounding surface that are connected physically to the zone. Field models This mathematical computer model is also referred to as the computational fluid dynamics (CFD). This model separates a compartment into many small cubes which are called the calculation cells and are on the basis of the inputs of the investigator/user. Compared to the zone models, this model is more calculation intensive (Siaka, 2008). Each cell is calculated by application of higher mathematics that relate to the transfer of energy and the fluid flow to the cells. The basic laws of energy conservation, momentum and mass form the basis of the of the mathematical calculations in the specific cells which is then used to balance with all the adjacent cells. The common fire models softwares that are used include the Consolidated Model of the Fire growth and Smoke Transport (CFAST), Fire Dynamics Simulator (FDS) and the Building Research Association of New Zealand fire (BRANfire) (Gregory, 2009) Application of computer fire models for investigation There is a systematic approach that should be applied by fire investigators in the analysis of the origin of fire, its causes and subsequent responsibility or damage. This systematic approach is grounded on scientific basis of testing the hypothesis that relate to the fire. The generally accepted model for testing the hypothesis is the computer fire modeling. The computer fire modeling helps in the understanding first the fire, analysis the time of the fire, the chances of survival of the occupants, analysis of the fuels and also the analysis of the of the post fire indicators (Gregory, 2009). In order to understand the fire, the model helps in assessing the relationship of the rate of release of heat release putting into consideration the other factors which are variable e.g. the carbon dioxide production and the ignition radiant. To analyse this, the computer model makes it possible for complex scenarios that involve numerous runs to be undertaken using different ranges of ventilation, this then gives fire investigator range of results that can be used to analyse the effect. The computer model also gives the fire investigator the ability to compute the minimal energy that is necessary for a compartment to change in a flashover (Siaka, 2008). The computer modeling can also be applied by the investigator to evaluate if the fuels were sufficient for the flashover and the relation to the damage that happened after the fire as a result of heat flux from an object that could have been burning during the fire (Gregory, 2009). Therefore, through the computer model, fire investigators have a better understanding of the fire which can help them to have links for follow of the possible causes of the fire. The computer fire modes also utilize the time factor in the analysis of fire. This is through the computer fire model timeline analysis (Gregory, 2009). Through the time analysis, the model makes it easy for the investigator to have an insight on the timing issues that are crucial for further understanding the different accounts of the eyewitnesses. In addition, the timeline analysis of the models helps in comprehending the fire progression in relation to inherent variable factors, the occupants’ survivability, comparison in the developments of the fire and the injuries and the interaction of the fire protection agents putting into consideration the activation of the protection elements. Through the use of the computer fire model timeline analysis, the analysis of the fire becomes more objective and more directional. The computer models also incorporate the survivability analysis. It is worth to note that in case of a fire break out people experience adverse effects from the various by-products of the tragic fire. The by-products include temperature, toxic gases, heat, the flame and the reduction of visibility. The by-products usually have tenability limits that the computer model can analyse. The investigators can apply the tenability limits calculated using the computer model to help in analysing the escape issues and the egress in relation to the fire situation (Gregory, 2009). The computer models can also be used in the analysis of the post fire indicators. Computer fire models make it easy for the investigators to compare the damage of the fire. The computer models have the capability to give insight into how the heat was transferred and the emerging effects of the heat transfer on the different materials (Gregory, 2009). The post fire indicators assist the investigators to draw conclusions on some issues that may relate to the fire. In the investigation of the fire, it is always good for investigators to visualize the fire. Most of the computer fire models have special features that can transmit the mathematical output and change it into a 3D dimensional graphics in the computer (Wood, 2008). This is through a visualization phenomenon of the models. For instance CFAST has companion software that provides animation of the fire situation. This gives the investigator ability to visualise the fire and draw inferences on the same. Scientific investigations are depended on testing of the hypothesis. The computer fire models give a grounded multiple hypothesis testing which allows the investigator to test his hypotheses or hypotheses by other investigation group. Through the multiple hypotheses testing, a hypothesis regarding the fire can be refuted or validated (Gregory, 2009). Use of the models by investigation Through the applications discussed, it means that the computer models can serve as an investigation tool. For instance, the investigating team could draw a theory of where the fire started and how it developed. Through the computer modeling application, the fire can be modeled which help the investigation team to decide whether their theory was correct. The applications of the models depend on appropriately choosing the model and application of the model within its specified limits and assumptions. Computer fire modeling is a tool that helps the investigators in the evaluation and fire analysis. Modeling of fire using computers is normally used to supplement the other possible information and to validate or refute a hypothesis. The other possible information could be from eyewitness, evidence of forensic experts and reports released by the departments of fire and police. This implies that the computer models should provide range of variables that are applied to evaluate the sensitivity and to make sure that variables that may are unknown are accounted for (Wood, 2008). The investigator using the computer models need to input the various variables that relate to the situation of the fire, include the data that was collected and the possible hypothesis. The variation of the input is necessary as it affects the outcome of the model and gives the investigator a range that can be used in the analysis of the fire. For instance, if the amount of data collected and the possible hypotheses are many, the outcome will be too huge to provide significant help for the fire analysis (Gregory, 2009). Limitations of the computer models Since the inception of the computer modeling, it has undergone significant improvement and many investigators have relied on the computer fire modeling to supplement the other information that may be from the fire scene. However, the computer model has some limitations despite of the improvements which may make it unfavorable fire investigation tool. One of the limitations of the computer fire model is in its inability to factor in many parameters related to the fire and the accuracy of the parameters. According to Gregory (2009) if the data collected and the possible hypothesis are too great, the output will subsequently be too huge. This makes it hard for the investigators to analyse the fire. The computer fire models are used only as supplementary tool to the investigation, this means that they have to put into consideration information from other sources. Limitation also crops in the input of the data. During the process of the scene investigation, the fire investigators sometimes can forget to remember that the computer fire model will be used to assist in the investigation at a later point. This means that for every investigation on the scene, it calls for the investigators to collect data that will be used for the computer fire modeling; investigators sometimes forget this which leads to inadequate data for the computer fire modeling. Conclusion The use of computer fire modeling has been on the increase, investigators use the models to test their hypothesis, understand the fire, occupants’ survivability, and do timeline analysis and validation or refutation of a hypothesis. The causation of the fire cannot be proved by the computer models and they serve as a tool to supplement other investigation. Therefore it is through the combination of other scene investigations that a detailed analysis can be drawn Work cited Gregory E. G. Computer fire models for fire investigation and reconstruction, Eastern Kentucky University, 2009. Siaka, D., Ricardo, R., Jennifer, W., Paul, W., and Stuart, D. Simulation of Glazing Behavior in Fires using Computational Fluids Dynamics and Spectral Radiation Modeling. International Association for Fire Safety Science, 2008. Wood, E. Applying Fire Models to Fire Protection Engineering Problems and Fire Investigations. Quincy, MA: NFPA.2008. Read More