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By Joe Sesniak, IAAI-CFI, IAAI-CI, CFEI, GIFireE

Loose electrical connections at screw terminals can create an increase in resistance, which promotes development of oxide layer(s) on the affected metals and localized heating. While the oxides are conductive (meaning the circuit will still “work”) its resistance is higher than that of the original metals involved (NFPA 921, 2014)[1]. The nature of the heating results in a locally high “watt density” and creates a potentially competent ignition source for proximal fuels (DeHaan, J., Icove, D., 2012)[2]. Recent literature, including works by Benfer and Gottuk (2013)[3], Korinek and Lopez (2013) [4] and Shea (2006)[5], provide detailed explanation of the chemical and physical processes of oxidation (copper I and copper II oxides) and corrosion associated with high resistance or “glowing” electrical connections. It is the visible effects of such localized high resistance heating on the receptacle terminals, and the persistence of these effects in a post-flashover fire environment, that are the subject of this paper. INTRODUCTION In this research, glowing connections were created on multiple electrical receptacles to produce heat effects on only one line side terminal connection of each receptacle. The purpose of this experiment was not to determine how heat effects manifest themselves on the terminals of electrical receptacles and associated conductors. The focus of this study was to determine whether or not the known effects persist beyond flashover at a visually perceptible level. This information is of importance to the fire investigator in the field. The reader should note that this work is considered preliminary. Potential variables were minimized, such as having conductors terminated on all screw connections and having multiple receptacles with varying loads on the same circuit. Further testing is required to evaluate the significance of such variables. Nonetheless the results of this testing are notable. The “heat damaged” test receptacles were installed in metal junction boxes and exposed to a room and contents fire that transitioned through flashover. The compartment was not instrumented. The point of origin and fuel load arrangement was selected to expose the receptacles to varying levels and duration of heat intensity. The post-flashover persistence of the effects of a glowing connection was subsequently visually evaluated. The intent was to provide fire investigators a resource for the preliminary field evaluation of electrical receptacles as a potential ignition source.

Loose electrical connections at screw terminals can create an increase in resistance, which promotes development of oxide layer(s) on the affected metals and localized heating. While the oxides are conductive (meaning the circuit will still “work”) its resistance is higher than that of the original metals involved (NFPA 921, 2014)[1]. The nature of the heating results in a locally high “watt density” and creates a potentially competent ignition source for proximal fuels(DeHaan, J., Icove, D., 2012)[2].  Recent literature, including works by Benfer and Gottuk (2013)[3], Korinek and Lopez (2013)[4] and Shea (2006)[5], provide detailed explanation of the chemical and physical processes of oxidation (copper I and copper II oxides) and corrosion associated with high resistance or “glowing” electrical connections. It is the visible effects of such localized high resistance heating on the receptacle terminals, and the persistence of these effects in a post-flashover fire environment, that are the subject of this paper.

INTRODUCTION

In this research, glowing connections were created on multiple electrical receptacles to produce heat effects on only one line side terminal connection of each receptacle. The purpose of this experiment was not to determine how heat effects manifest themselves on the terminals of electrical receptacles and associated conductors. The focus of this study was to determine whether or not the known effects persist beyond flashover at a visually perceptible level. This information is of importance to the fire investigator in the field. The reader should note that this work is considered preliminary. Potential variables were minimized, such as having conductors terminated on all screw connections and having multiple receptacles with varying loads on the same circuit. Further testing is required to evaluate the significance of such variables. Nonetheless the results of this testing are notable.The “heat damaged” test receptacles were installed in metal junction boxes and exposed to a room and contents fire that transitioned through flashover. The compartment was not instrumented. The point of origin and fuel load arrangement was selected to expose the receptacles to varying levels and duration of heat intensity. The post-flashover persistence of the effects of a glowing connection was subsequently visually evaluated. The intent was to provide fire investigators a resource for the preliminary field evaluation of electrical receptacles as a potential ignition source.

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Courts examine the “negative corpus” amendments to NFPA 921 and process of elimination in considering the admissibility of fire experts’ opinions

 “Once you eliminate the impossible, whatever remains, no matter how improbable, must be the truth.”

Arthur Conan Doyle, The Adventures of Sherlock Holmes

For many years, it was accepted practice for a fire investigator, having eliminated accidental or natural causes of a fire, to conclude, without specific physical evidence, that the fire must have been caused by human agency, i.e., arson.  In product liability cases, investigators would conclude that an appliance must have been defective, as no other cause of fire could be identified.  Courts routinely accepted such opinion evidence in criminal and civil cases. This method of fire cause determination was referred to as “negative corpus” because it was akin to a conclusion that murder had occurred even though no body had been found.

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From Out of the Abyss...

This week’s article from the past is titled Incendiary Fires Can Be Spotted and was written by Benjamin Horton, CPCU, who was President of the National Adjuster Traing School in Louisville, Kentucky..  It is taken from the Decembe 1968 Vol. XVI No.5 issue.

Incendiary Fires Can Be Spotted 

In the new issue of NFPA Journal®, President Jim Shannon said the Association will focus on the leading causes of home fires, including cooking. "We also need to continue to push hard for home fire sprinklers. That's still a large priority for NFPA, and we plan to work very aggressively in 2014 on our residential sprinkler initiative," he said.

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NFPA 921, Guide for Fire and Explosion Investigations plays a fundamental role in fire and explosion investigations. A new edition of NFPA 921 is scheduled to be published in 2014. For years, this document has played a critical role in the training, education and job performance of fire and explosion investigators. It also serves as one of the primary references used by the National Fire Academy to support its fire/arson-related training and education programs. It is imperative that investigators understand the scope, purpose and application of this document, especially since it will be used to judge the quality and thoroughness of their investigations.

NFPA 921, Guide for Fire and Explosion Investigations plays a fundamental role in fire and explosion investigations. A new edition of NFPA 921 is scheduled to be published in 2014. For years, this document has played a critical role in the training, education and job performance of fire and explosion investigators. It also serves as one of the primary references used by the National Fire Academy to support its fire/arson-related training and education programs. It is imperative that investigators understand the scope, purpose and application of this document, especially since it will be used to judge the quality and thoroughness of their investigations.

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SAN DIEGO - A Team 10 and Scripps News investigation found arson fires are not investigated properly in many American cities -- including San Diego -- due to a chaotic patchwork of reporting systems and standards.

Many deliberately set building fires are not reported to the federal government.

Nationally, just 5 percent of all residential building fires are intentionally set, according to the National Fire Incident Reporting System, which is part of the Department of Homeland Security.  Data collected by Scripps News suggests the national arson rate to be significantly higher.

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February 25-28, 2019  &  September 23-26, 2019

Flashover Fires in Small Residential Units with an Open Kitchen

ABSTRACT
The open kitchen design in small residential units where fire load density and occupant
load are very high introduces additional fire risk. One big concern is that whether
flash-over can occur which may trigger a big post flashover fire, resulting in severe
casualties and big property damage. It is important to understand and predict the
critical conditions for flashover in this kind of units. Based on a two-layer zone model,
the probability of flashover is investigated by a nonlinear dynamical model. The
temperature of the smoke layer is taken as the only state variable and the evolution
equation is developed in the form of a simplified energy balance equation for the hot
smoke layer. Flashover is considered to occur at bifurcation points. Then the influence
of the floor dimensions and the radiation feedback coefficient on flashover conditions
is examined. When the dimensions of the floor vary, the resulting changes in internal
surface area or size of floor area both have effect on the flashover conditions. When the
radiation feedback coefficient is of small value, there is no possibility of flashover.
With the increase of the radiation feedback coefficient, at first it significantly affects
the conditions for flashover and then moderately when it reaches a larger value. It is
proved that the flashover phenomenon can be demonstrated well by nonlinear
dynamical system and it helps to understand the effect of various control parameters.

Abstract

The open kitchen design in small residential units where fire load density and occupant load are very high introduces additional fire risk. One big concern is that whether flash-over can occur which may trigger a big post flashover fire, resulting in severe casualties and big property damage. It is important to understand and predict the critical conditions for flashover in this kind of units. Based on a two-layer zone model, the probability of flashover is investigated by a nonlinear dynamical model. The temperature of the smoke layer is taken as the only state variable and the evolution equation is developed in the form of a simplified energy balance equation for the hot smoke layer. Flashover is considered to occur at bifurcation points. Then the influence of the floor dimensions and the radiation feedback coefficient on flashover conditions is examined. When the dimensions of the floor vary, the resulting changes in internal surface area or size of floor area both have effect on the flashover conditions. When the radiation feedback coefficient is of small value, there is no possibility of flashover.  With the increase of the radiation feedback coefficient, at first it significantly affects the conditions for flashover and then moderately when it reaches a larger value. It is proved that the flashover phenomenon can be demonstrated well by nonlinear dynamical system and it helps to understand the effect of various control parameters.

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