Evaluation of the bearing capacity of socket contacts within the framework of a fire investigation

Introduction. The data, provided in the article, demonstrate the relevance of the socket fire safety improvement in the course of operation. The purpose of the article is to develop a research-backed method of examining the socket contacts that feature high transient resistance or change in shape. The method can be subsequently used to identify causes of damages in a fire investigation. Materials and methods. A JSM-6390LV scanning electron microscope with a module designated for the energy dispersive microanalysis is used in the research. The subjects of research are type C (EU Type C) and type F (EU Type F) sockets. The failure surfaces of socket contacts were analyzed without preliminary sample preparation. Theoretical fundamentals (theory and calculations). A physical and mathematical model of the limit bearing capacity of socket contacts, similar to the real construction, has been developed. The model serves as the framework for a practical computational algorithm of the expert analysis of mechanical and geometrical characteristics. The solution is reduced to short calculation formulas, that can be used to evaluate the bearing capacity of so­cket contacts. The applicability of the developed mathematical model to fire investigations is proven in a specific ­example. Results and discussion. The authors analyze cases of socket fires, caused by the loss of the bearing capacity of socket contacts in the process of operation. Photos of the oxide film on the contact surface and its elemental composition are provided in the article. The experimental data have proven that the fusion of contacts and the presence of an oxide film, featuring high specific resistivity, are a significant criminalistic evidence that helps to identify causes of fire. Conclusions. The authors propose a method for the identification of the bearing capacity of socket contacts. The method can be used to determine if a subsequent fire is related to the socket ignition. The information, provided in the article, can be used by specialists in the course of an expert examination of socket contacts withdrawn from the site of the fire to identify the failure mechanisms and, ultimately, causes of fire.