Investigating the oxidation behavior of carbon steel in fire scene: a new method for fire investigations

Abstract

A major component of fire investigation is tracking the cause of fire, finding of which help to strengthen the physical evidence, especially in case of arson with accelerants. When metallic substances are exposed to fire at high temperature, they undergo oxidation. Accelerants at the fire scene impart some oxidative characteristics on metallic materials. For instance oxides and substrates found on metal surfaces provide valuable information for determining the characteristics of fire, such as exposure temperature, duration and involvement of a liquid accelerant. In this study, we investigated the oxidation behavior of carbon steel at high temperature in a simulated flame environment using ethanol combustion. After oxidation, the morphological and microstructural features of the samples were characterized by observation, scanning probe microscope, X-ray diffractions and scanning electron microscopy with energy-dispersive spectroscopy analysis. The results showed that elemental carbon was deposited on the samples surface, which were ascribed to the incomplete combustion of ethanol. An oxide with a mesh-like pattern appeared on the samples, which was ascribed to the complex oxidation conditions of the fire scene. The properties of the oxides were strongly dependent on the oxidation duration, temperature and atmosphere. These results provide reference information for determining the presence of combustion accelerants at the fire scene.

Effect of kerosene combustion atmosphere on the mild steel oxide layer

“…The carbon content deposited by kerosene combustion was higher than the carbon content deposited on the metal surface by ethanol combustion. This was attributed to the different lengths of the carbon chain of the accelerants 13 . Additionally, carbides with high carbon content were found on the surface of the sample after an oxidation time of 20 min (Fig.…”

“…The amount of the deposited carbon may be related to the length of the carbon chain of accelerants. The longer the carbon chain, the higher the carbon content deposited on the sample surface 13 . Deposition of carbon occurred inside the oxide layer through an "oxide–carbon" symbiosis model and does not enter the crystal lattice of substrate metals.…”

“…Herein, the oxidation behavior of metallic materials present in the combustion atmosphere was used to judge the presence of the accelerants in a fire scene based on this theory. Previous studies demonstrated that the oxidation characteristics of carbon, steel, copper, aluminum alloys, and stainless steel materials may be closely related to the oxide properties alerted by the combustion byproducts in combustion environments 13 – 17 . Carbon produced during the combustion of accelerants can have a range of effects on formation of the oxide layer on metal surfaces and facilitates the inference of the type of accelerant present in the combustion environment.…”