Tag Archives: NAFI

Total Station Surveying Technology for Forensic Mapping

Total Station Surveying Technology for Forensic Mapping of Fire and Explosion Incident Scenes

Brian C. Dunagan, CSP, CFEI, CFII
IFO Group, Inc. – Incident Free Operations, Inc., USA
Christopher F. Schemel, Ph.D.
IFO Group, Inc. – Delta Q Consultants, Inc., USA

Total stations (electronic surveying equipment) are frequently used in traffic accident investigations to collect data for reconstruction specialists. For more than 20 years these devices have dramatically reduced the time and labor required to document and map vehicle accident scenes. The data collected by a total station can be easily imported into modeling and sophisticated mapping software. This technology can be deployed in other forensic applications and can be readily used to assist investigators in systematically and accurately mapping fire and explosion incident scenes. This paper summarizes the role a total station plays in forensic mapping. First, an overview of forensic mapping using total stations and associated equipment such as prisms and data collectors is presented. Second, the constraints and the legal considerations of the technology are discussed. Third, a case study using forensic mapping of an explosion scene is presented. Finally, it will be demonstrated that the use of these techniques can assist the savvy investigator in building a compelling case narrative that builds on and complements other evidence collected while satisfying the ever increasing standards for reliable and accurate documentation of scenes.

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Explosion Severity: Propane Versus Natural Gas

Alfonso Ibarreta, Ph.D., PE, CFEI, Timothy Myers, Ph.D., PE, CFEI, CFI, James Bucher, Ph.D., CFEI and Kevin Marr, Ph.D., CFEI Exponent, USA

Presented at International Symposium on Fire Investigation, 2012

Natural gas, composed mainly of methane, is in some ways similar to propane gas. Both fuels have similar energy densities per unit mass, and similar laminar premixed flame burning velocities. However, propane explosions have been shown to produce higher overpressures in unconfined explosion tests when compared to methane. In vapor cloud explosion modeling, methane is considered to be a “low” reactivity fuel, while propane is listed as a “medium” reactivity fuel. In closed vessel explosion testing, the maximum rate of pressure rise for propane is almost twice than that for methane (based on KG  values reported in NFPA 68 (2007) Standard for Explosion Protection by Deflagration Venting , table E.1).

This study provides a direct comparison of the explosion severity between commercial propane and natural gas. Empirical correlations available for vented vessel explosions and unconfined Vapor Cloud Explosions (VCEs) are used to predict the difference in overpressure expected for a commercial propane explosion versus natural gas explosion. Although the maximum laminar burning velocity associated with propane is only about 15% higher than that associated with methane, commercial propane explosions are expected to result in overpressures that are about 40% higher than that of a natural gas explosion under identical conditions with a perfectly-mixed nearstoichiometric fuel-air mixture, based on empirical correlations.

In addition to the laminar burning velocity, other fundamental differences in the fuels may also play an important role in the explosion severity. Propane has a slightly higher expansion ratio than methane when undergoing combustion. The mass diffusivity of propane and methane are also quite different, making the premixed propane flame more prone to wrinkling under turbulent conditions. Future testing in the 20-L explosion chamber is suggested.

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Project Arson: Uncovering the True Arson Rate in the United States

Project Arson: Uncovering the True Arson Rate in the United States
David J. Icove, The University of Tennessee
Thomas K. Hargrove, Scripps News Washington Bureau

Presented at International Symposium of Fire Investigation, 2014

Many forensic investigators and practitioners in the field of arson suppression sense that the true arson rate in the United States is far higher than is commonly reported. This paper reports on efforts to uncover the true arson rate in the United States through a nationwide audit conducted by a national news service in partnership with a major university. Using traditional social science research methods and constructing pattern-recognition algorithms, the project focused on an examination of building and vehicle fire statistics for the 2006-2011 time period recorded by the National Fire Incident Reporting System (NFIRS) and the application of geographic, socioeconomic, and mortgage foreclosure data to those statistics.

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