Abstract
The electrical molten marks (EMMs) are often found in the place where the fire started in. Therefore, when the fire causes are investigated, EMMs have the possibility that they become the big clue which makes the cause clear.
The following two cases were experimentally studied as a fundamental research which is necessary to establish the method of distinguishing the Primary Molten Marks (PMMs) from the Secondary Molten Marks (SMMs) ; (1)In order to research whether thermal histories affects the grain size of non-melted wire which is adjacent to EMMs or not, the grain size of copper wire exposed to various heating and cooling conditions is examined. (2)In addition, it was also researched that there were some differences of properties in external features, cavities and metallographic structures of the PMMs and SMMs made under the several different conditions.
As a result, following were obtained.
1) The grain size of the copper wire has no relationship with the cooling conditions and spontaneous heat of wires prior to the heating, but depends on the highest heating temperature only. Therefore, it is ineffective to use the grain size to distinguish PMM from SMM.
2) It is unreasonable to discriminate between the PMMs and SMMs by the external features and cavity distribution of the EMMs.
3) When the surface of the copper wire was oxidized after the exposition to the air, the oxidation structures, which reflect the effect of the oxidation before the production of EMMs, are observed from the EMMs. And oxidation structure is formed not only by oxidation of surface before short-circuit, but by oxidation during coagulation after short-circuit through absorption of ambient oxygen.
4) It is considered that the oxygen of the air is absorbed at the melting and coagulating process and then the oxidation structures could be found even when the oxygen concentration is low as in case of fire, since the oxidation structure was admitted by the ambient of oxygen concentration 2. 5%.
