Lewis K.H.,Case Forensics Corporation |
Scheiff S.,Case Forensics Corporation |
Challman T.,Case Forensics Corporation |
Murphy D.,Case Forensics Corporation |
Thoresen A.,Oracle Inc.
Fire Technology | Year: 2015
Over the last several years, the forensic community has experienced an increase in the number of fires which have been attributed to ventilation fans. These failures have been anecdotally observed in Jakel motors, specifically model numbers J239-050-5138 and J238-050-5494, manufactured between 2000 and 2003. While there have been a number of variations to motors within exhaust fans over the preceding decades, including different winding size, winding metal, and thermal cut-off (TCO) manufacturers, two design implementations have led to the higher incidents of failure. The first design change is the implementation of 27 American Wire Gauge aluminum winding (magnet) wire. The second, and most important, is the implementation of the Tamura Thermal Device Corporation (TAM) TCO to replace the Elmwood Sensor/Honeywell (Elsen) TCO. Through investigations and testing, the Tamura TCO has been found to be unreliable at opening the circuit within the motor when exposed to temperatures above its specified cut-off temperature (136°C). Thermal testing of a Tamura TCO showed that even when exposed to temperatures as high as 260°C, the flux of the fusible thermal link is incapable of breaking down the oxides created by the metal alloy. The hypothesized failure mechanism for the Tamura TCO include increased exposure to high temperatures during fan operation and/or air infiltration from cracks in the epoxy sealant due to improper installation, along with the corrosive effects of the chlorinated flux. This work presents case studies, experimentation, and analysis of the failure mechanisms related to fires associated with the aforementioned motors. © 2014, Springer Science+Business Media New York.
Henriksen T.L.,CASE Forensics Corporation |
Warren C.,CASE Forensics Corporation |
Lewis K.H.,CASE Forensics Corporation
Fire and Materials 2015 - 14th International Conference and Exhibition, Proceedings | Year: 2015
With the size and number of wildland fires in the U.S. this year, it is important to identify the types of ignition sources capable of igniting forest floor debris, and the conditions necessary for ignition to occur. Often, cigarettes are discounted for their ability to ignite nearby fuels based on weather conditions. While environmental factors will continue to be important in assessing wildland fuel ignition achievement, the values of relative humidity which have been used by investigators to discount cigarettes as competent ignition sources have been historically underestimated in the literature. It has been suggested in the literature and in training materials provided to fire investigators that cigarettes cannot ignite wildland fuels when relative humidity is above 25%.1,2 Recognizing that ignition achievement is dependent upon several variables, including weather conditions; it was desired to assess the ability of a cigarette to act as an ignition source when the relative humidity was above 25%. © Interscience Communications Limited, 2015.