Shell Low Lead
Analytical Techniques in Arson Investigation
Turpentine
Amoco Kerosene
MCI No. 2 Diesel
Time (min) Figure 1. Typical chromatograms of different accelerant classes (a) Gasoline (b) Turpentine (c) Kerosene (d) Higher Fuel Oil
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Arson is the willful destruction of property by fire. In recent years this crime has received increasing public awareness. After any major fire has occurred, it is common to hear or to read the phrase "the arson squad is investigating." This article will discuss the role of the forensic laboratory in determining if arson has indeed occurred and how it was accomplished. T h e analysis of an allegedly arsonous fire begins at the scene. Any chemicals used to initiate or to spread the fire, and any mechanical or electrical device used to contain or to control these chemicals will leave some trace at the location where they were used. Even if the fire was accidental, t h e cause will still be located at the fire's origin. T h u s , the exact location where the fire started must be found. In most jurisdictions a qualified investigator bears this responsibility. T h e details of his method are not within the scope of this article. However, some basics will be given as they will affect the laboratory's results. T h e investigator will use eyewitness reports of what p a r t of the building was first on fire, descriptions of the burning characteristics from the firefighters, knowledge of the combustibility of construction materials, and educational and personal experience to locate the region of first involvement. He may also use a hydrocarbon sniffer to aid in his investigation. After finding the place of origin and reconstructing the burning sequence, the investigator has to determine if it was an accidental or an unnatural fire. Laboratory tests may be used in either case to substantiate or to disprove his theory. 0003-2700/80/0351-422A$01.00/0 © 1980 American Chemical Society
The Analytical Approach Michael J. Camp Institute of Chemical Analysis, Applications, and Forensic Science Northeastern University Boston, Mass. and Cambridge Analytical Associates, Inc. Watertown, Mass.
T h e laboratory is entirely dependent upon the investigator to provide it with proper samples—proper in both the chemical sense, i.e., t h a t they are from the fire's origin, and in the legal sense, i.e., t h a t the legal requirements have been satisfied. T h e most commonly encountered accelerants are gasoline, kerosene and home heating fuel oil. For this reason the collection, preservation and analysis of arson samples are geared toward detection of volatile materials as the first step. T h e samples of debris should be sealed at the scene in airtight containers. New, unlined metal paint cans are preferred since there is no organic matter to cause a background. Rubber-ring-sealed glass jars are also acceptable. Large items can be sealed in plastic bags at the scene and then cut up and resealed in cans as soon as possible. Paper bags and also plastic ones will slowly breathe, causing a loss of volatile vapors. Even worse, they will allow vapors to enter the sample. This is of concern since the plastic bags may be transported with or stored in areas with liquids. Cross-contamination would negate any later result. T h e main technique used for the detection of volatile materials is headspace vapor analysis. T h e goal is not to determine the brand and grade of gasoline, but to determine if any is present in the debris. Petroleum products are complex mixtures of several hundred aromatic and aliphatic compounds. T h e y are sold for specific purposes and their composition and properties vary with the end-use purpose. T h u s , they can be classed into groups by any convenient measurable property such as flash point, boiling point range or distillate fraction.
In chromatographic analysis each class has a similar distribution of peaks and peak heights. Typical chromatograms are shown in Figure 1. These are fresh samples injected as liquids. Chromatograms of headspace vapor residues will be slightly different. T h e more volatile components may be completely absent and the next peaks reduced in intensity when compared to the later, less volatile materials. T h e heat of the fire will cause a differential volatility of the residue which is absorbed onto some debris material. It is, however, still possible in the majority of cases to discern the characteristic pattern. Before discussing the chromatographic techniques, the concept of class identity should be examined. Modification to the basic methods will depend upon the class of vapors present. T h e definition of a class of petroleum hydrocarbons may vary from one lab to another. It is usually based upon the patterns seen on the chromatogram (Figure 1). T h e author uses the following guidelines. All brands and grades of automotive gasolines belong to one class. All brands of kerosene and fuel oil number one belong to a second class. T h e higher fuel oils are a third class, even though it may be possible to estimate the grade. T h e centroid of the peaks shifts to longer times as the grade number increases. Distillates with a narrow boiling range are distinguished from the fuels by the compactness of the chromatogram. T h e peaks are seen over a narrower time range. This class is called a distillate material and contains thinners, charcoal lighter, patio torch fuel, turpentine (even though it is a natural product) and the various products with distillate solvents avail-
able over the counter. Very light fractions such as lighter fluids and white gas do not have the heavier, higher boiling components of the automotive gasolines. Nonpetroleum products present a problem since they contain very few components. These usually require an alternative method since the pattern is not complex enough to classify it directly. A standard reference file run under your conditions is needed for aiding in the analysis of the chromatograms. In addition to fresh samples, partially evaporated and trial burn samples with and without an accelerant should be run. Blank or control samples are a must. In some actual cases a unique class may not be determinable. In this event it is only possible to report the detection of a volatile hydrocarbon residue. Typical chromatographic conditions for a basic headspace vapor analysis of arson debris are shown in Table I. Variations are common and are usually tailored to a specific instrument and column. To obtain a sample, the sealed container is heated in an oven or on a water bath to a temperature which will desorb the volatile materials. Depending upon the amount of water present, temperatures of 6 0 110 °C for 5-20 min will be sufficient. T h e more water there is, the longer it will take to reach the final temperature and the greater the internal pressure will be. Experience is the best teacher. A chromatogram with weak peaks should be rerun after further heating before choosing a second method. T h e sample (1-5 cc of headspace vapor) is removed through a septum. Two devices are shown in Figure 2. Both are attached before heating. Ei-
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ther a gas-tight glass syringe or a dis posable plastic syringe can be used. T h e former must be cleaned thorough ly between samples; the latter intro duces a medium intensity peak in the first 2 min. No interference with the analysis has been noted when the plastic syringes were used. On some gas chromatographs the large volume of air and moisture may extinguish the flame. T h e resultant chromatogram is then compared to the standard refer ence file, to other items in the same case, or to liquid samples submitted for reference. Since analysis time for fuel oils would be over an hour, the investiga tor may a t t e m p t to characterize these materials by relying on the use of dif ferent columns ( i ) . An Apiezon L col umn would be used first. This column would detect and classify the lighter hydrocarbons u p to kerosene. If a higher material was suspected, a sec ond run would be made using a Dexsil-300 column at a higher temper ature. On this column the gasoline components are not separated; how ever, the higher boiling materials can be classified in a short time. Results are satisfactory if sufficient sample amounts are available. In most cases the headspace tech nique leads to a positive or negative conclusion, especially if there is suffi cient sample and the background does not cause problems. Occasionally a chromatogram is obtained which does not yield a definite conclusion. T h e peaks may be just larger than the base line and not well resolved. More sam ple is needed before a distinction can be made. T h e peaks may be large but too few to conform to a typical class, or they may have very short retention times. Could it be background material or a special class of accelerant? Liquid samples may be submitted when the purpose is to determine if sample A was stolen from gas station Β or gas station C to the exclusion of all other sources. And there is the instance when the suspect accelerant is a high er fuel oil whose vapor pressure may be insufficient to give an appreciable headspace concentration. It is to these questions t h a t current work is di rected. Much effort has gone into preconcentration of the headspace vapors prior to injection. Historically, steam distillation and solvent extraction methods were the first to be used. Dis tillation using water, ethylene glycol or other high boiling materials pro duces à visible layer floating on top of the distillate. This material can be injected directly into the gas chromatograph (2). In addition, instrumental methods such as infrared spectroscopy or mass spectrometry can be utilized
Table I. General Chromatographic Conditions for Headspace Vapor Analysis of Arson Residues Carrier gas: Nitrogen or helium at 3 0 - 4 0 m L / m i n Injection port: 1 5 0 - 2 0 0 ° C Column: 1/8 or 1/4 in, glass or metal, 6 to 12 ft long, packed with Apiezon L, O V - 1 , O V - 1 0 1 , SE-30, or SP1200/Bentone 34 Oven: Programmable, 5 0 - 7 0 ° C initially for 0 - 5 min, heat to just below the column's maximum temperature at 5 - 2 0 ° / m i n , and hold there until no further peaks are seen. Detector: Flame ionization Sample: ^μL of liquid, 1-5 cc of headspace vapor
for a more complete analysis (3). Results are again satisfactory. However, distillation times may exceed 48 h (4), and the rate of distillation may be important. When the debris contains wood, especially pine, the chance of distilling a large amount of background material is high. Solvent extraction techniques include a soaking and rinsing or longer refluxing with a Soxhlet system. In the soaking method the volume of solvent (hexane, heptane, or petroleum ether) must be concentrated before injection. T h e process is time-consuming, and the concentration steps may cause loss of p a r t of the sample. Soxhlet extraction also takes time and leads to possible background peaks from wood or plastics. Another classical separation method which leads to a concentration of sample is vacuum distillation (5). One report describes a simple approach using a sealed can, a chunk of dry ice, and a heat lamp (6). Reported results are satisfactory for gasoline and kerosene, b u t long times are required for fuel oils. All of these classical methods will work in some cases. Most are labor- or time-intensive. In addition, the distillation and extraction methods may generate a background level of materials which could be taken as a false positive or which could interfere with the basic pattern classification procedures. T h e search for better methods has led to the adoption of concentration procedures similar to those developed for environmental air sampling and bomb detection. T h e vapors are concentrated by absorption onto a substrate and later desorbed. T h e absorbant material, process of absorption, and the process of desorption are currently being studied. Charcoal is known to be an excellent absorbant. It has a high capacity but bonds materials strongly (7, 8). Other materials such as Poropak Q, Tenax-GC, and the Amberlite XAD resins are also suitable (9). Alumina
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and silica do not absorb appreciable amounts of hydrocarbons. Absorption can be done at the scene by drawing air through a packed tube. This allows an investigator to collect air samples at specific sites. Volatile materials from a larger area will also be collected. In the laboratory, absorption is done by sweeping dry nitrogen through the sealed can and onto a packed tube. Background is limited to the actual sample material. T h e can may be placed in a water bath to increase the vapor pressure of the accelerant. Desorption is achieved by heating or by solvent stripping. For thermal desorption from charcoal, a high temperature is required. Lower temperatures can be used for the other absorbants (7). Commercial units are available which are attached directly to the injection port of the gas chromatograph. On instruments which have a moderately fast injection port heating rate, the absorbant can be packed into a spare injection port liner. Desorption can then be accomplished inside the injection port by rapidly heating from room temperature to 250 °C {10}. If charcoal is used as an absorber, elution with a suitable solvent will strip off all the volatiles. T h e solvent must be pure and have a very short retention time or be nondetectable by the flame ionization detector. A detectable solvent which tails considerably may mask the initial peaks of the accelerant. Carbon disulfide has been found to fulfill these requirements. T h e flame response is very low and elution is quantitative. (8, 9) It can not be used with Tenax-GC as it dissolves the polymer. More work is being conducted to optimize absorption/elution techniques. One major concern is the presence of background vapors. They will be concentrated at the same time as the accelerant vapors. A suitable blank sample is desirable, although it may be hard to determine what is suit-
umns will resolve gasoline into 200+ peaks (14). When coupled with steam distillation, capillary columns have been used on test burns. Identification is based on the use of Kovats indices as well as visual comparison (4). This brings up the last topic in arson analysis. T h e final decision is currently made by visual examination of a complex chromatogram. How reliable is this step? For most instances it is quite good. Could it be better? T h e use of computer-based pattern recognition has been applied to many forensic topics. Paper, glass and whiskey adulteration are just a few of these areas. A preliminary report suggests t h a t these methods may well be applicable to arson analysis (15). T h e application of new methods to arson analysis is a rapidly growing field. It will become easier for the laboratory to detect trace levels of accelerant with more confidence. T h e goal of identification of brand or grade of gasoline may be attained in the near future. This may have an impact in a related criminal area if the theft of fuels becomes a major problem. References Figure 2. Two headspace sampling devices (a) An apparatus which pierces a paint can lid and screws tight via an o-ring. The top has a septum under a Swagelok nut. (courtesy of the Wisconsin State Crime Lab) (b) Simple device to hold a septum in place with a tension bar. Bar has a hole in it which must mate with hole in can lid. (courtesy of Demers Laboratory, Springvale, Maine)
able at the scene. Test burns of Various materials without the use of an accelerant can be concentrated and used to form a reference library. If any doubt arises in a specific case, the use of mass spectrometry is recommended. A GC/MS combination has several useful applications in arson analysis (11, 12). By monitoring selective ions, one can determine the presence and distribution of materials, such as the polycylic aromatics, which are common to petroleum products. T h e mass spectrometer's sensitivity is greater t h a n the flame ionization detector, enabling very weak samples to be analyzed. Bones from bodies which may have been burned have been successfully studied (11). In this instance it was necessary to add some water to the bone before appreciable vapor was detected. T h e mass spectrometer is currently the best method for determining if observed peaks may be a commercial solvent or may have originated from the background. In those cases where a nonpetroleum accelerant is used there are too few peaks to yield any classification. Mass spectral identification is required. Similarly the decomposition of wood and plastic will yield a number of peaks but their pattern is not consistent with known accelerants ex426 A ·
cept for turpentine. Identification of these materials will assist the analyst in deciding t h a t no accelerant was present. It is not known whether GC/IR will be of assistance in this area. A preliminary study reports the use of the ratios of the lead alkyls (Me x Et4- x Pb) as determined by G C / M S (13). Another area of possible G C / M S involvement would be to determine the proprietary additives used by each manufacturer. Detection of these additives may lead to the longsought goal of brand and/or grade identification. When liquid samples are submitted, the class is usually known and more specific identification on direct comparison of samples is required. There is more information in a liquid than in the vapor and not being sample limited is a definite advantage. Traditional classification by flash point or the percent of the sample which distills in a given temperature range can be determined. T h e dyes can be examined and compared by thin layer chromatography, and the lead and bromine content can be quantitated. Beyond these basic steps one wants to determine the relative amounts of each component. This requires much greater resolution than the packed column can provide. Capillary col-
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(1) H. Evans, Unpublished Master's Paper, Northeastern University, 1979. (2) R. W. Clodfelter and E. E. Hueske, J. Forensic Sci., 22(1), 116 (1977). (3) I. C. Stone, J. N. Lomote, L. A. Fletcher, and W. T. Lowry, J. Forensic Sci., 23(1), 78 (1978). (4) A. T. Armstrong and R. S. Wittkower, J. Forensic Sci, 23(4), 662 (1978). (5) R. Hrynchuk, R. Cameron, and P. G. Rodgers, Can. Soc. Forens. Sci. J., 10(2), 41 (1977). (6) H. G. Linde, Crime Laboratory Digest, 79-6,3(1979). (7) F. J. Conrad, T. A. Burrows and W. D. Williams, Sandia Laboratories Report SAND78-1246, August, 1979. (8) D. V. Canfield and S. J. Irwin, private communication. (9) W. Graziano, Unpublished Master's Paper, Northeastern University, 1980. (10) H. Evans and P. Demers, private communication. (11) H. Harris, "Identification of Accelerant Peaks by Gas Chromatography —Mass Spectroscopy," presented at the 5th Annual Meeting, Northeastern Association of Forensic Scientists, Albany, N.Y., October; 1979. (12). M. H. Mach, J. Forensic Sci., 22(2), 348 (1977). (13) L. T. Lytle, L. C. Ford and P. T. Williamson, "GC-Mass Spectroscopy: Its Use in Determining Gasoline Lead Alkyl Ratios and Their Use in Forensic Examinations," presented at the 31st Annual Meeting of the American Academy of Forensic Sciences, Atlanta, Ga., February, 1979. (14) K. A. Oakes, "The Use of Glass Capillary Columns in Arson Analysis," presented at the 31st Annual Meeting of the American Academy of Forensic Sciences, Atalnta, Ga., February, 1979. (15) B. R. Kowalski and W. R. Gresham, "Use of'Pattern Recognition' in Arson Cases: a Progress Report," presented at the 31st Annual Meeting of the American Academy of Forensic Sciences, Atlanta, Ga., February, 1979.
