Tag Archives: fire investigation

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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Joel Liebesfeld, PI, MA, MAS, CES
James F. Valentine & Associates, Inc.

Presented at International Symposium of Fire Investigation, 2014

Making use of the scientific method means testing hypotheses until one final hypothesis survives that is durable enough to be sufficiently conclusive to meet the threshold of the standard of a reasonable degree of professional, scientific or engineering certainty. This paper is meant to elaborate on some common exemplar mathematical formulae and related information that, when applicable, can complement the expert reporting in subrogation losses. Proper insertion and reflection upon mathematically applicable formulae can add to the certainty of a report’s conclusion and the outcome in a subrogation proceeding.

The objective of the paper will be to turn the symbolism of mathematics into a language or a resource that can be used or extrapolated for testimony or reporting. The selected topics are those primarily seen or discussed in NFPA 921 and other fire and water related losses. In some instances the topical material presented will directly reflect on how the concepts are derived for applicable use in fire science/hydraulics. The topical material deploys mathematical notions derived from physics and chemistry that are the underlying sciences for most of the captioned losses.

Topics will include, but not be limited to, for example; detailed discussions about Heat Release Rates, Conduction, Heat Transfer, Air Flow and Ventilation, Water Flow, et al.

This paper is not intended to be a course in mathematics but rather intended to convey how specific mathematical values may be applicable, vary or can be affected by changing data related to certain nuances, such as ambient factors. These notions will be applied to selected mathematical principles that may be present in such situations as compartment or open fires, the treatment of fires, hydraulics, et al. Discussion may be extended to reflect on why certain constants are used and what they represent. Additionally, where appropriate, discussion will be reinforced by mathematical modeling. I have successfully used similar techniques when teaching adults in a university setting.

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