Laboratory Can Help Investigator Pluck Arson Evidence Out of Debris

Laboratory Can Help Investigator Pluck Arson Evidence Out of Debris

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AMERICA’S MALIGNANT CRIME

Beware arsonists! A new era has begun with the arrival of qualified, well-educated fire investigators who know where to sample and what to sample to prove their investigative findings.

The time is right for all forensic laboratories to take notes and become familiar with the laboratory needs of fire investigators. The time is right to provide the fire investigator with laboratory results quickly and accurately. It is important for all parties involved (fire investigators, laboratory personnel and legal counsel) to be aware of their interdependence. No link in the chain can be broken if the case is to be brought to a successful conclusion.

Figure 1

It is important to realize at the beginning that finding evidence of incendiarism may be analogous to finding a needle in a haystack. A trained fire investigator, however, with the help of laboratory personnel, can be directed to pick the needle right out of that haystack. A fire scene is unlike any other crime scene that a law enforcement officer will encounter. Physical evidence may either be destroyed, covered up or altered in some way, making its collection difficult, if not impossible.

Much information available

Flammable liquids, or accelerants as they are sometimes called, may appear to behave peculiarly, but once understood, a wealth of information can be acquired regarding their use in a suspicious fire. Some flammable liquids evaporate in a few hours while others will remain in fire debris for years. Table I lists the relative length of time that a given flammable liquid can be detected on fire debris.

From table I it can be seen that flammable liquids, such as fuel oil and paint thinner, are more easily discovered at fire scenes than solvents such as ether or acetone.

If left to burn, a flammable liquid will yield only gases and water vapor. For example, when a given quantity of gasoline is set afire, a time will come when all the gasoline will be converted to carbon dioxide and water. Laboratory analysis of fire debris samples relies on the assumption that traces of the original flammable liquid remain in a given piece of fire debris.

Therefore, the following guidelines will help the fire investigator secure a sample which has the greatest probability of still containing flammable liquid residues:

  1. The origin of the fire is definitely not a good place to sample. Intense heat at the origin of the fire destroys any remaining flammable liquid. The best place to sample is near the interface of severe charring and marginal burn. Figure 1 shows ideal sample selections in a situation where a flammable liquid was poured on the floor near a wall.
  2. Naturally, all rules are made to be broken and the above guideline is no exception. Depending on the intensity of the fire, the quantity of flammable liquid used and the type of floor covering used, it is possible to sample at the origin if the sample has not been exposed to intense heat. For example, if a carpet was on top of a wood floor in figure 1, the wood floor may contain flammable liquid. It is also possible that the carpet padding may contain residue of a flammable liquid.

    If a hole was burned entirely through the floor, it would be best to sample near the interface area as described earlier since much intense heat was present at the origin.

    The golden rule that all fire investigators must realize is that identification of an accelerant cannot be made from a completely charred object.

    If enough heat was present to completely carbonize a given piece of fire debris, it is impossible to isolate any residue of flammable liquid.

  3. All evidence suspected of being contaminated with an accelerant is best contained in clean, new metal cans. Clean, new mason jars can be used, but breakage is a real hazard. Plastic bags are not good long-term sample containers.
  4. Small amounts of liquid found in large containers are best transferred to small, clean glass vials in order to minimize evaporation. Containers with possible latent fingerprints are most easily transported to the laboratory suspended in a box with string or wire to minimize contact of the evidence with the sides of the box, illustrated in figure 2.
  5. It is strongly recommended that comparison samples be submitted to the laboratory along with samples to be analyzed for flammable liquid residues. For example, if it has been determined that a piece of carpet is probably contaminated with a flammable liquid, obtain a piece of identical carpet which has been protected during the fire. Such comparison saAiples may be found under pieces of furniture which were on top of the carpet at the time of the fire.
Figure 2

Similarly, if a piece of particle board is being submitted for flammable liquid identification, submit an unburned piece of particle board which has not been in contact with a flammable liquid for comparison.

Value of various samples

SOIL — Very good sample; usually no contamination. Try to submit a comparison soil sample from an area which you believe does not contain any petroleum products.

WOOD — Very good sample if a flammable liquid has been poured on the wood. Wood is porous and will soak up the liquid similar to a sponge. If the wood has been exposed to extreme heat and is completely converted to charcoal, no flammable liquid can be isolated. It is generally a good idea to secure a piece of similar wood which you believe has not been in contact with a flammable liquid. Such a comparison will allow the laboratory to evaluate any paint or varnish which may have been present on the sample at the time of the fire.

CARPET — (Fiber-backed, nonrubber pad.) Carpet can be an excellent sample, especially if it is fiber-backed and was laid over a fiber pad. Pieces of unburned carpet and pad are required to rule out decomposition products of the carpet when only traces of a flammable liquid may be present.

CARPET — (Rubber-backed, rubber pad.) Such a sample can produce erroneous results if a comparison sample is not permitted. Rubber, when burned, produces a large variety of chemicals. It is an absolute necessity that unburned rubber-backed carpet and pad be submitted as a comparison sample.

WATER IN BASEMENT — All common flammable liquids will float on water. Merely skim the surface of the water and enclose the sample in a clean, new can.

GLASS — No scientific evidence has been presented which shows that any useful information can be obtained from glass recovered at a fire scene unless the glass is analyzed within 24 hours of the fire.

It is good practice to keep various types of fire debris separate when submitting them to the laboratory for analysis.

Solids may be used

Arsonists can use incendiary chemicals other than flammable liquids. Aside from explosives, there are a great many flammable solids and mixtures which can ignite spontaneously, causing extreme amounts of heat and fire. The residues left by these incendiary chemicals may go undetected unless the fire investigator is alert to their possible presence. All mildly suspicious powders and solid residues should be collected and submitted to the laboratory for evaluation.

Many factors (heat, evaporation, amount of flammable liquid used, etc.) determine whether the fire investigator will be able to secure a sample which, when analyzed, will show evidence of a flammable liquid.

Modern technology has created several investigative aids to be used by the professional fire investigator. The most common aids are listed in table II.

ULTRA-VIOLET LIGHT — The ultra-violet light, or UV light, can help the fire investigator locate areas of concentrated hydrocarbon residue. The UV light will not detect trace amounts of flammable liquids or flammable liquids that are trapped inside the piece of fire debris. Many false-positives are possible, for example soaps and detergent products will cause a blue glow indicative of a petroleum product.

SNIFFERS — The hydrocarbon sniffer is also used to locate areas of possible flammable liquid residue. The device is very sensitive and easy to operate but is subject to false positive readings.

PORTABLE GAS CHROMATOGRAPH — The portable gas chromatograph offers the fire investigator the latest and most sophisticated piece of equipment that can be used at a fire scene. Extraction of the fire debris and subsequent identification of flammable liquid residues are easily accomplished at the scene.

All of the investigative aids described only help the fire investigator locate and secure reliable samples for later laboratory analysis. It is wrong to use the investigative aid as the final analysis.

Lab capability improving

Several years ago, most crime laboratories did not have sufficient equipment and manpower to even attempt the analysis of fire and explosion debris. The picture has changed and is presently improving both in the capability and speed of analysis for such evidence.

A problem, which is most evident in the development of procedures for analysis of fire debris, is the lack of communication among forensic laboratories. Organizations such as the International Association of Arson Investigators can be a good outlet for the laboratory community to exchange ideas and information. A publication called the Arson Analysis Newsletter can provide quick dissemination of information regarding the analysis of fire and explosion debris.

Flammable liquid isolation and identification is generally accomplished with the aid of a gas chromatograph. The gas chromatograph can detect flammable liquids in the part per billion range. Due to the great sensitivity of the gas chromatograph, care must be exercised by laboratory personnel in the interpretation of results generated from the instrument.

The laboratory at Systems Engineering Associates has recently instituted a secondary means of analysis for fire and explosion debris samples. Differential spectroscopy allows the laboratory to determine if a given sample contains a true flammable liquid or decomposition products from a burned carpet.

Ultraviolet light unit, in a portable package, locates concentrated flammable liquids.Portable recorder is used with the gas chromatograph shown at left.Gas chromatograph shown is portable and can be used at the scene to identify types of flammable liquids.

More data, better tacts

The more data that a scientist can gather regarding his sample, the more useful the information that can be passed to the investigator.

Modern technology has brought about automated instrumentation which is capable of analyzing fire debris samples 24 hours a day and seven days a week. Turnover time for fire debris samples should never be greater than 10 days.

It is important for the fire investigator to understand why one laboratory may find the presence of a flammable liquid and another find nothing. At the present time, there are three basic procedures of analyzing fire debris samples: (l) head space, (2) extraction and (3) steam distillation. The head space technique has been shown to be much less sensitive than either the extraction or steam distillation procedures. Many times a head space analysis shows no flammable liquid residue while the extraction or steam distillation method clearly shows the presence of a flammable liquid.

Information obtainable

The modern forensic laboratory accommodating fire and explosion debris samples generally can provide the following information for the professional fire investigator:

  1. Analyze a fire debris sample and determine if a flammable liquid is present.
  2. Determine the type of flammable liquid (gasoline, kerosine, paint thinner, etc.) present on a fire debris sample. Determine if a mixture of flammable liquids was isolated.
  3. Provide formation concerning the “freshness” of an isolated flammable liquid. For example, gasoline can be chemically changed due to heat and/or time, allowing the scientist to say that the gasoline isolated is fresh or fireaged.
  4. Lift and process latent fingerprints recovered from fire bombs.
  5. Identify suspicious residues found at the scene of the fire. Analysis may show the presence of a highly flammable solid chemical capable of producing heat and fire.

It is evident that if the laboratory is to recover any flammable liquid from a piece of fire debris, the fire investigator must be selective and use all the investigative aids at his disposal in the search for fire debris samples.

It must be realized that when a laboratory says: “No flammable liquids were detected,” two possible explanations can account for the conclusion: One, a flammable liquid was never present on the fire debris, or two, a flammable liquid was present on the fire debris at one time, but due to the extreme heat of the fire, it has been consumed.

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