Procedures for Detecting the Presence of Residues of Explosives and Hydrocarbons - Essay Example

The paper aims to look at the various procedures used to detect and identify residues of both hydrocarbons and explosives. The paper identifies that there are a number of procedures used in the laboratory such as the user of sniffers, smelling, chemical tests, finger printing applications and even the use of Enzyme immunoassay and Colorimetric screening. It has also identified that the primary tool used to identify the residues is gas chromatography. Some additional information is also provided regarding their effectiveness and drawbacks. Procedures for detecting presence of residues of explosives and hydrocarbons Sniffers Sniffers are used to detect the presence of residues of hydrocarbons and explosives when there is presence of vapors or toxic dust. Sniffers are essentially portable gas detectors. However, they lack the ability to discriminate between different components of hydrocarbons and explosives. Typically, sniffers are used to measure oxygen concentration levels in the atmosphere to show the presence of flammable and toxic gasses. Their presence indicates that, the sample has residues of hydrocarbons and explosives because hydrocarbons are flammable and impact the concentration of oxygen levels in the atmosphere, by increasing carbon IV oxide levels in the atmosphere. Additional gases that are detected include ammonia, carbon II oxide and moisture (Kitts 70). For a more effective analysis, it is recommended that one employs a detector with greater sensitivity. Such devices include photo ionization and a flame ionization detector which detect hydrocarbons but not vapors of inorganic compounds. However, their shortcoming is that they fail to distinguish hydrocarbons from plastics and those from accelerants. Portable gas chromatographs When samples from a scene have been collected, they are taken to the laboratory for detection and identification. There are a number of methods used for detecting residues of hydrocarbons and explosives at the laboratory. One of them is through a portable gas chromatograph. Portable gas chromatographs are used in the analysis of accelerants. The devices are fitted with an FID detector coupled with a small separation column which is packed. The instrument has multiple purposes because it can also be used as a sniffer. As a sniffer, air is directly introduced into the detector which then acts as a chromatograph. The sample is detected into the device‘s column where separation of the various components of the sample begin. The next step involves detection of the sample once it is introduced and thereafter, a chromatogram is produced for analytical purposes. However, the method requires additional modifications in order to improve its resolving power. Chemical tests Detection of the residues is also achieved through chemical tests. There are two types of tests that are employed to detect hydrocarbon and accelerant residues- Draeger tubes and hydrocarbon field test kits. Draeger tubes, have been very instrumental in the detection of hydrocarbons in recent years. The tubes can be used to detect hydrocarbons in the air, while the hydrocarbon field test kits are used when analyzing the soil and water for the presence of hydrocarbons at a fire scene. The tests place emphasis on color change in order to detect the presence of the hydrocarbon. The hydrocarbon reacts with the emerging agent and the color change is specific to different hydrocarbons. However, the tests are mostly used for analyzing hydrocarbons on a qualitative basis and cannot be able to distinguish between hydrocarbons that are as a result of burnt plastics, or hydrocarbons from accelerants. Additionally, the methods are expensive and are used for single analysis is. Using Sense of Smell Even in the laboratory, the sense of smell can be used to detect the presence of explosive and hydrocarbon residues, as a result of the gases produced. When the hydrocarbons and explosives are burnt, they produce a specific smell that can be detected by an investigator and correctly identified. For example, hydrocarbons, which are fuels not completely burnt during combustion, emit a distinct nauseating smell such as the one from exhaust pipes of vehicles. However, the use of smelling is not a conclusive technique of detecting and should only be used to direct the analysis of the residues through other conclusive means. Additionally, it is also dangerous to smell residues of some compounds since if inhaled, they can cause serious respiratory harm and general health problems. Finger Printing Applications Another procedure used to detect residues of hydrocarbons, is through the use of finger printing applications. The applications help evaluate the type and age of the residue. The proportions of the PAH and GRO vary depending on the age and type of hydrocarbon present in the sample. The first step involves extracting and preparing the samples in solvent kits. In this stage, sediment, oil, water and soil are analyzed. The next step involves testing for the GRO. The UV-3100 analyzer is calibrated using (Site lab) GRO Calibration kit via the slot B of the optical filters. The sample is then tested and its concentration recorded. Additionally, the sample can be retested for PAH and EPH. In order to test for the PAH, the optical fibers are rotated to slot (D) and retested. However, when testing for the EPH, the optical fibers are rotated to slot (A) and recalibrated using the PAH Calibration kit. The sample is then tested and its concentration calculated. The technique is very accurate. Different hydrocarbon residues show differing fluorescence signatures and that is how an investigator differentiates different hydrocarbon residues (Gottfried 123). Colorimetric screening ad Enzyme immunoassay Enzyme immunoassay and Colorimetric screening are examples of lab procedures used to detect RDX and TNT. The procedures are reliant on detecting the residue, by using an organic solvent like acetone. The Colorimetric procedure for instance, is based on Griees and conventional Janowsky reactions.They are very useful when detecting the presence of TNT and RDX on soil samples. Procedures for identifying presence of residues of explosives and hydrocarbons Gas Chromatography The most appropriate method of detecting and identifying residues of explosives and hydrocarbons, is through gas chromatography. It is recommended when an investigator wants to identify and categorize flammable residues. It is worth noting that, many cases of arson are accomplished through the use of kerosene and gasoline. Gas chromatography is primarily used to identify residues of both hydrocarbons and explosives. The procedure separates the different constituents of the hydrocarbon. After separation, the different hydrocarbons are presented in the form of a chromatographic pattern, with each pattern corresponding to a specific type of hydrocarbon. In the case of investigators, they collect the various debris from an explosion site and then compare it to identified peaks of the gas chromatography spectrum. The gas-liquid chromatography procedure, involves the hydrocarbon or explosive residue being vaporized and then directed into the chromatographic column head. The sample then travels through the column due to the flow of the inert and gaseous phase. The column has another phase which is liquid and immobile, that is then absorbed to the surface of the inert solid. Therefore, the technique of using gas chromatography is very reliable and appropriate when identifying the various hydrocarbons present (Lucia 45). Works Cited Gottfried, J. (2007). Detection of Energetic Materials and Explosive Residues With Laser-Induced Breakdown Spectroscopy: 2: Stand-off Measurements. Ft. Belvoir: Defense Technical Information Center. Kitts, K. (2012). Evaluation of odor compounds sensed by explosives-detecting canines. Lucia, J. (2008). Tailored Ultrafast Pulses for Selective Energetic Residue Sampling. Ft. Belvoir: Defense Technical Information Center. Read More