Fire Investigation Methodology Essay, Research Paper
A fire investigation is a difficult task. The devastation, charred debris, collapsed structures, water soaked ashes, along with the smoke and stench, make an investigation uninviting and seemingly impossible.
There are different types of fires; in homes, factories, brush, and in the forest. The best way to investigate a fire would be to use a trained team of personal. Fire marshals and private investigators with their experience of fires along with police officers skills for determining motives make a great team. An electrical engineer or electrician may be used to investigate electrical systems. The knowledge of a scientist may also play a valuable role. A scientist should understand the properties of fuels and building materials, and have an understanding of the combustion process. A scientist should also be able to identify in the lab materials found at the fire scene, even if they are only present as trace amounts.
At the fire scene the investigator has two major tasks. First to determine the origin of the fire and second to closely examine the point of origin to try and determine what it was that caused a fire to start at or around that location. An examination would typically begin by trying to gain an overall impression from the point of origin. From this one might proceed to an examination of the materials present, the fuel load, and the state of debris at various places. The search for the fire?s point of origin should be based on elementary rules such as:
? Fire tends to burn upwards and outwards (look for the V-pattern).
? The presence of combustible materials will increase the intensity and extent of the fire. The fire will rise faster as it gets hotter (look for different temperature conditions).
? The fire needs fuel and oxygen to continue.
? A fire?s spread will be influenced by the factors such as air currents, walls, and stairways. Falling burning debris and the effects of the fire-fighters will also have an influence.
The color of materials and the state that there in may be used to help determine the temperature of the fire where those materials were located. An examination of structural deformations, char depths, and smoke patters should also be carried out. It is important to try and discover if the fire started at the floor level or at an elevated level.
These procedures are designed to locate the point of origin of the fire. Multiple points of origin suggest a deliberately set fire. Assuming that the point of origin has been found, a thorough examination of the debris in the area is necessary. All the electrical appliances in the area should be examined. The presence of any flammable liquids, trails, spalling of concrete, or intense burn-marks in the floor should be checked. No fire can exist without an ignition source. Be on the lookout for matches, lighters, sources of sparks, hot objects, chemicals, gas and electrical lines, cigarettes, fireplaces and chimneys.
Provided the investigation has been patiently and scientifically carried out, when combined with the evidence of witnesses or fire fighters, it may be possible at this stage to draw a conclusion about the fire. Typical causes of accidental fires are cooking accidents, overheated or short circuited electrical connections, spontaneous combustion of oils, welding sparks, burst gas lines, sparks from fireplaces, lightning, cigarette butts, left-on appliances, reacting chemicals. The list of all the possible causes is very long.
If a fire is not the result of an accident, it must have been deliberately lit (arson). The motives to commit arson include vandalism, fraud, revenge, sabotage and pyromania. A major objective in any suspected arson case would be to search for, locate, sample and analyze residual accelerants. Most but not all incendiary fires involve the use of an accelerant to speed the ignition and rate of spread of fire. A rapid, intense fire inconsistent with the natural fuel of the fire is indicative of an accelerated fire. Such a fire is likely to be started at ground level, possibly in a number of sites and may produce trail marks, burn-throughs and/or spalling.
The accelerants most commonly used, on account of their flammability and availability are petrol, kerosene, mineral turpentine, and diesel. Accelerants such as alcohols, acetone, and industrial solvents are less commonly used. It might be thought that after an intense fire there will be little amounts of the accelerant remaining. This is not true. The amount of accelerant remaining after a fire will depend on factors such as the quantity and type of accelerant used, the nature of the material it is poured on, the elapsed time since the fire, and the severity of the fire.
Detection of trace quantities of materials requires careful sampling techniques and analysis. The most frequently sampled material is flooring such as wood, carpet, soil, and linoleum. There may be a need to take control samples away from the area where the accelerant is suspected, preferably of the same material.
Some investigators may use ?sniffers? at the fire scene. These portable detectors usually note changes in the oxygen level. They respond to a variety of vapors and need to be used with caution. They can be used as a guide as to the best place from which to collect samples.
The materials found to give the most positive analyses for accelerants are usually porous samples; carpet and underlay, cardboard, paper, felt, cloth and soil. Because of the sensitivity of the analysis care must be taken to avoid contamination at all stages of sampling.
The methods of extraction most commonly used for fire debris samples are distillation, solvent extraction, and headspace analysis. The distillation techniques used have included steam distillation, ethylene glycol distillation, ethanol distillation, and vacuum distillation. Steam distillation has been the most widely used, and is still used, particularly where reasonably large quantities of an accelerant are present. Solvent extraction is not used except in special cases. Both static and dynamic headspace analysis are now in common use.
Detection and Identification
Ultraviolet, infrared, and nuclear magnetic resonance spectroscopy have all been used for identifying accelerant components, but by far the most widely used technique is gas liquid chromatography. It is able to separate and detect trace amounts of volatile hydrocarbons in complex mixtures.
The four most commonly found accelerants (petrol, kerosene, mineral turpentine, and most diesel) are all highly complex mixtures of many components, in very different ratios. Most forensic laboratories feel confident in identifying these compounds on the basis of their gas chromatograms alone, even if the sample are evaporated and contaminated.
In order to make a positive identification it is necessary to identify a large number of the components present, and to note that their ratios are very similar to that of a standard. The use of evaporated and burnt standards may aid this comparison. To make absolutely sure of the identity of any component you can usually rely on gas chromatography.
Fires present a major social an economic problem. A thorough investigation of any large-scale fire, be it accidental or deliberate, is necessary. Scientists have expertise that can be used in the investigation, which may help find the origin of the fire if it is not found otherwise.
Redsicker,D.R.,& O?Connor,J.J,(1997).Practical Fire and Arson Investigation(2nd ed.).Boca Raton,FL:CRC Press