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Baldwin Biddeford Police Department Biddeford, Maine The use of investigative field equipment at crime scenes is an invaluable tool to investigators providing that the equipment is reliable and accurate.
At an arson scene, investigators are already at a disadvantage given the nature of the crime. In most circumstances, not only may the evidence be destroyed, but the entire scene may be compromised by smoke, fire, pressurized water and untold personnel from responding emergency agencies.
If any one specialized crime scene field investigator needed additional equipment to help locate and interpret evidence at a crime scene, one could argue that an Arson Investigator would be that one. Specialized equipment and portable resources at a fire scene is not a new philosophy.
Canines have long been specially trained and used in searching for signs of accelerants and ignitable liquid residues at fire scenes. Their usefulness and effectiveness at locating sources of ignitable liquids cannot be argued. The canines are trained to detect the vapors from minuscule amounts of remaining ignitable liquid residues that are often buried under heaps of burned debris and rubble.
Although an experienced Arson Investigator can often determine the subtle differences between signs of an arson motivated incendiary burn and the resulting burn from an accidental fire, even the most seasoned investigators will still sometimes need assistance and reassurance while determining their hypothetic conclusions.
A canine, if available, is a suitable resource to assist in the investigation. What resources does an investigator have however if a canine is not available?
What if the remaining debris from a fire does not allow for safe conditions suitable for a canine? What if the suspected ignitable liquid residue is in an area in which the canine does not have access?
If a canine is not available or it's use is otherwise not practical, a Hydrocarbon Detector may offer additional resources to the Arson Investigator. In the field of arson and fire investigations, combustible vapors or vapors resulting from accelerants and ignitable liquid residues are often referred to as "Hydrocarbons.
Although there are several derivatives of hydrocarbons, the primary categories in arson investigations are the Saturated Hydrocarbon single atomic bond, saturated with Hydrogen. These petroleum-based hydrocarbons are more easily recognized as chemical gases such as Methane and Propane, and chemical liquids such as Hexane, a common constituent of gasoline, and Benzene, a common constituent of crude oil and many solvents.
As an arson investigator, recognizing hydrocarbons used in accelerants, e. In addition to the use of canines during an investigation is the use of portable accelerant detectors.
Hydrocarbon Detectors also sometimes referred to as hydrocarbon "Sniffers" and Photoionization Detectors P. These devices are not necessarily new to the field of arson investigation, however the advanced, fast developing and changing technology has only increased the practical applications of such portable equipment when needed.
There are many types and models of both Hydrocarbon Detectors and Photoionization detectors. There uses vary from a range of employment fields including Hazardous Material teams, Plumbers, Engineers, Pipe Fitters, Miners, and any other occupation that consistently deals with petroleum products or pressurized petroleum gasses.
For the sake of this issue, I'll only be discussing the units that are practical to arson investigation. The hydrocarbon detector "Sniffer" is offered in many makes and models. Its principle is largely based on a unit-incorporated sensor that can detect minute concentrations of combustible and hazardous vapors.
The unit uses a small vacuum pump to pull vapors from your sample area into an opening. This opening, usually a narrow hose like nozzle, draws the vapors into a chemical detector that is specifically designed to detect and sometimes separate the hydrocarbon molecules from the accelerant vapors.
The electrochemical sensors contained within the units can measure the electrical currents that are produced when the target gas molecules and applied reagents react with each other. Applied catalytic bead sensors utilize a combustion chamber to burn the combustible vapors along the surface of the catalytic bead.
As a result of the combustion, a resistance level of the burnt vapors is recorded along the bead's surface. The result of resistance is then converted into a measured concentration of vapors by the unit's computer. There are various models available of the hydrocarbon detector, many of which have a practical use for Arson investigations.
This unit is a portable and battery operated electronic combustible hydrocarbon detector. A LED light bar graph displays the strength of the suspected vapors. An additional and optional audio switch allows for an alarm to sound when the vapors are detected. The alarm, a clicking sound, increases in frequency as the combustible gas vapor signal becomes stronger.
Constant adjustment of the sensitivity control knob is not always necessary if the unit is used appropriately.Practical Applications of Hydrocarbon and Photoionization Detection Units in Arson Investigations Matthew D.
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