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The Lab Analysis

excerpted from "Motive, Means, and Opportunity, A Guide to Fire Investigation."
American Re-Insurance Company, Claims Division, 1996.


Table of Contents

  • Laboratory Services for the Arson Investigator
    • Availability and Services Provided To Public Investigators
    • Lab Qualifications
  • General Fire Evidence
    • Identification of Charred or Burned Materials
    • Burned Documents
    • System Failure Analysis
    • Evaluation of Appliances and Wiring
  • Determinations Labs Can Make
    • Melting Point
    • Flashpoint
    • Mechanical Condition
    • Fire and Smoke
  • Volatile Accelerants
    • Methods of Recovering Accelerant from Solid Samples
      • Steam Distillation
      • Vacuum Distillation
      • Solvent Extraction
      • Charcoal Sampling
      • Swept Headspace
    • Volatile Accelerant Identification
      • Gas Chromatography
      • Gas Chromatography/Mass Spectrometry
      • Chemical Incendiaries
  • Non-fire Related Criminal Evidence
    • Fingerprints
    • Impression Evidence
    • Physical Matches
    • Trace Evidence
    • Blood


Modern forensic science applies the principles of analytical chemistry and physics to the identification, classification, and comparison of evidence samples collected by fire investigators. It documents and verifies the findings of field investigators. The techniques used often involve highly specialized equipment that requires the competence of dedicated field investigators and laboratory technicians working together to obtain and analyze evidence.

A. Laboratory Services for the Arson Investigator

When a fire investigator needs an analysis or interpretation of the physical evidence relating to fire causation or spread, he or she must take advantage of all the experts available to ensure that the investigation is complete and accurate. It's important to anticipate the need for such experts and determine their availability before you need them.

Laboratory specialists can perform tests beyond the capability of the investigator, but there are practical limits. A fire may burn very hot and long enough to destroy diagnostic signs. This may prevent the lab's ability to make a determination with any degree of certainty.

1. Availability and Services Provided To Public Investigators*

Most states have at least one state criminalistics laboratory and many states have a system of regional laboratories (to minimize travel time and expense) that can provide most of the analytical services a fire investigator will need. The labs generally operate under the auspices of the state's department of justice, public safety, state prosecutor, state police, or similar law enforcement authority. They usually cooperate with city or county labs to provide a wide range of services.

Services from public labs are usually available at no cost to personnel from public fire or police agencies and investigators from some semi-private agencies such as transit authorities, public utilities, and railroads.

Lab resources are limited. There are usually restrictions on which agencies a lab may serve. In addition, there may be a case priority scheme that designates fire-related evidence low-priority. Priority may be based on whether there were deaths or injuries or whether a court date has been set. To ensure the fastest service, be sure to give the lab this information when you bring the evidence in.

Nationally, the FBI and ATF labs are available.

2. Lab Qualifications

The necessary experience to provide an accurate interpretation of evidence is more important than whether a lab has the necessary equipment. To avoid critical errors in interpretation, the analyst must completely understand the effects of fire, evaporation, exposure and even sample collection and storage on physical evidence from fires. Only a qualified analyst can correctly interpret data and guide an investigator in assaying the contribution of the evidence to the case.

To avoid impropriety and fraud within laboratories, The International Association of Arson Investigators (IAAI) established a Forensic Science Committee along with guidelines on analysis and interpretation of fire-related evidence. Active membership in IAAI or a regional or national forensic science organization is considered by many as a hallmark of a professional forensic scientist.

B. General Fire Evidence

1. Identification of Charred or Burned Materials

  • Laboratory identification may consist of visual examination, re-assembly, cleaning, or complex microscopic, chemical or instrumental tests.
  • Type of exam performed depends on the nature of the material, the quantity recovered, and the extent of damage.
  • Verifying the composition of all fire remains is crucial for detecting the substitution of less valuable items or the removal of heavily insured objects like jewelry, art or clothes, often a sign of arson.
  • The lab may be able to reconstruct an ignition or time-delay device that may help to identify the perpetrator.

2. Burned Documents

  • Analysts may use visual examination under ultraviolet or infrared light, photographic techniques, or treatment with glycerin, mineral oil, or organic solvents to improve the contrast between the paper and the inks.
  • Most documents in files, stacks or books won't burn completely. Instead, they will char. If they're intact, they may be identifiable. The most critical problem is the fragility of the charred papers. Handle with great care. Every precaution should be taken against physical destruction of the remains.
  • Reconstruction is best done under controlled laboratory conditions. Don't attempt any tests in the field. Anything done to the document (coating, spraying, treating with solvent) will interfere with laboratory tests.

3. System Failure Analysis

A mechanical system that has failed and caused a fire should be examined by a registered mechanical or materials engineer. This examination requires specialized knowledge of the materials or processes involved.

Many states offer a registry of qualified professional engineers for your information and reference.

4. Evaluation of Appliances and Wiring

Often, investigators themselves are able to accurately assess the condition of wiring and the contribution wiring may have made to a fire. However, many diagnostic signs require:

  • microscopic examinations
  • metallurgical tests
  • continuity and conductance tests
  • interpretation by a specialist

C. Determinations Labs Can Make

1. Melting Point

a. The Melting Point of different materials in the structure can be an indicator of some of the temperatures reached during the fire. There are many variables that affect the temperature of the fire such as fuel load, venting and nature and type of construction. Melting of metals in a fire may indicate higher heat than expected with obvious fuel load. Evidence of extreme heat at or near the floor is always a concern to the investigator. In the early stages of the fire, extreme heat at the floor level may indicate the use of some type of accelerant.

2. Flashpoint

a. Flashpoint is the temperature at which a liquid gives off sufficient vapors to form an ignitable mixture.

(Using the following apparatus, Flashpoint can be determined in the lab):

  • Tagliabue (Tag) Closed Cup (FP below 175 degrees Fahrenheit)
  • Pensky-Martens (FP above 175 degrees Fahrenheit)
  • Tag Open Cup
  • Cleveland Open Cup
  • Setaflash Tester

3. Mechanical Condition

  • Visual examination of a door lock mechanism is often enough to ascertain whether it is locked or unlocked at the time of the fire.

4. Fire and Smoke

  • A specialist laboratory can help to assess the contribution various materials have made to the fuel load.
  • Furniture coverings that remain unburned can be identified, duplicated, and tested for susceptibility to accidental ignition.
  • This type of testing, however, requires extensive experience if the results are to be used in civil litigation.
  • Some states have agencies which will test such hazards. Otherwise, the services of a private consumer or materials lab may be retained.
  • The NFPA has published standard tests for evaluating fire hazards of interior finishes.

D. Volatile Accelerants

The analysis of fire debris for suspected volatile accelerants is one of the most common services labs provide to fire investigators. Accelerant residue often remains for ready detection at a lab. However, even when investigators collect accelerant evidence immediately after the fire, and even when it is properly packaged and analyzed by the best methods, lab results are not always conclusive and a negative laboratory finding isn't necessarily proof that an accelerant wasn't used.

Key points-

  • Petroleum distillates change in their physical and chemical properties as they burn or evaporate, making their identification challenging even to experienced analysts.
  • Most liquids used by arsonists to accelerate the spread of a fire are products refined from crude oil, such as gasoline, kerosene, and diesel fuel. These products are mixtures of thousands of different organic compounds, most of which are hydrocarbons-compounds containing only carbon and hydrogen atoms.

1. Methods of Recovering Accelerant from Solid Samples

There are five commonly used methods of extracting volatile accelerants-

a. Steam Distillation is the oldest and best known technique requiring only modest equipment. The specimen is boiled with water and steam, carrying the volatiles with it and trapping them.

  • Suitable for volatiles that form an azetotropic (nonmixing) layer with water, such as petroleum distillates.
  • It cannot be used to recover acetone or alcohol.

b. Vacuum Distillation is a well-known technique requiring only modest equipment and refrigerant.

  • Suitable for recovering any volatile hydrocarbon and any debris that is susceptible to water damage, including fragile, charred documents.

c. Solvent Extraction is a test in which debris is extracted or washed with a small amount of n-pentane, n-hexane or carbon disulfide. The extract is concentrated by evaporation in a stream of warm air until a small quantity remains for tests.

This method:

  • Would be suitable for treating small, nonabsorbent specimens (glass, rock, metal);
  • Provides good recovery of hydrocarbons (except alcohols);
  • Will extract residues from partially pyrolyzed carpet or foam rubber, which often interfere with detection of low-levels of hydrocarbons.

d. Charcoal Sampling requires no manipulation of the sample or its original container. A charcoal-coated wire is inserted in the air space of a sample container and allowed to equilibrate. Then the wire is inserted in the pyrolysis unit during gas chromotography and rapidly raised to a very high temperature.

  • This method is suitable for all kinds of debris and all volatile hydrocarbons.

e. Swept Headspace (Charcoal Trap) has become one of the most commonly used techniques for recovering volatile residues. This is an extremely sensitive technique. The sample container is fitted with a modified lid or septum that allows the introduction of a heated carrier gas (purified room air or nitrogen). The container is warmed while the vapors are drawn by a low vacuum through a cartridge filter containing activated charcoal or a molecular trapping agent like Tenax.

This method:

  • Requires specially built apparatus and traps;
  • Is one of the best techniques for arson analysis;
  • Is applicable to all volatiles (even fuel oils);
  • Doesn't require manipulation (if submitted in cans or jars);
  • Doesn't risk contamination of the sample;
  • Is so effective that all of the volatiles in a sample can be swept out if the time or temperature conditions are too severe for the sample size;
  • Can only be carried out once on a sample.

2. Volatile Accelerant Identification

a. Accelerant identification in the laboratory consists of three steps-

(1) Sample preparation. The process by which the liquid is isolated from fire debris.

(2) Instrumental analysis. Once isolated, a sample is analyzed using gas chromatography. This test produces a graph called a chromatogram.

(3) Data analysis. Lab analysts compare the chromatogram with chromatograms of known products in search of a match.

b. Here are some of the tests commonly used-

(1) Gas Chromatography Gas chromatography separates mixtures of volatile organic compounds. Therefore, it is well-suited for analyzing petroleum products recovered from fire debris. It's used to screen samples to determine which contain adequate volatiles for identification. It is also used for the identification itself once lab analysts isolate the volatile substance.

Types of chromatography vary in complexity but their basic principles of operation are simple. All types separate mixtures of materials by slight differences in their physical or chemical properties.

The test uses a stream of gas (nitrogen or helium) as a carrier to move a mixture of gaseous materials along a long column or tube filled with a separating compound. National standards for forensic analysis of fire debris recognize gas chromatography as the only acceptable means of identifying flammable or combustible accelerant residues.

(2) Gas Chromatography/Mass Spectrometry This test is a more selective and specific detector than gas chromatography alone. It uses computer data manipulation to identify petroleum products in evidence samples. It's also useful in identifying products that are unusual or contain only a few chemical com-pounds, which don't produce a distinctive pattern on a gas chromatograph.

(3) Chemical Incendiaries A small but significant percentage of arsonists use a chemical incendiary to start a fire. Most chemicals used in this way leave residues with distinct chemical properties. However, these residues may be nondescript physically and easily overlooked.

Whenever such an incendiary is suspected, samples of nearby materials should be collected for comparison purposes. Sometimes an elevated concentration of a particular substance compared to other background substances reveals an incendiary.

E. Non-fire Related Criminal Evidence

One of the most frequent mistakes arson investigators make is to focus so much on the fire and its origin that they miss important physical evidence. That's why it's critical to reconstruct the entire scenario.

Be alert to evidence of regular criminal activity, because arson is often used to cover other criminal activities. Some examples-

1. Fingerprints.

Many investigators and arsonists assume that fire destroys all fingerprints. It does not. New techniques permit the development of latent prints on surfaces such as leather, wood, vinyl plastics, smooth cloth, charred paper, metal, and even human skin. A fingerprint is among the most conclusive forms of proof of identity. New diagnostic techniques are always being developed, so you should never conclude that latent prints are impossible to recover before consulting a specialist in the field.

2. Impression Evidence.

Impressions of tools on windows or doors can:

  • confirm a forced entry
  • identify points of entry
  • identify the tools responsible

Marks may also be found on furnishings at the scene, confirming a burglary took place before the fire.

3. Physical Matches.

Torn, cut, or broken edges or surfaces at the scene can be compared with each other to establish a "jigsaw" fit between them. This physical comparison is among the few conclusive identifications possible with typical evidence. The evidentiary value of these positive identifications is very high. The investigator should be aware of the possibilities when searching a scene for anything that looks out of place.

4. Trace Evidence.

Paint can be transferred to the clothing or tools when an arsonist attempts a forced entry. Trace or transfer evidence such as paint, fibers, soil or glass can be used to link (or trace) a person to a crime scene.

5. Blood.

Today, bloodstains have more evidentiary value than ever before because great strides have been made in determining subtle variations in the proteins and enzymes of human blood. Bloodstains can be subjected to DNA typing.

a. Blood Evidence

Here are some methods of identifying blood samples-

( 1) Screening Tests: Tests are based on the reaction of a portion of hemoglobin with chemical reagents, such as o-tolidine, phenolphthalein, luminol, tetramethylbenzidine, or leucommalachite green.

(2) Confirmatory Tests: Not as sensitive as screening tests, but necessary to prove that the suspect stain is blood.

  • Miscrocrystal tests: Chemical reagents react with components of the blood and produce characteristic crystals
  • Immunological test: Anti-human hemoglobin is used. The test also confirms that the blood is human.

(3) Species Tests: Determine the human or other animal origin of a bloodstain. In the immunological precipitin test, anti-serum for a particular species, such as anti-human serum, gives a visible reaction with human serum proteins.

Blood Typing in Dried Bloodstains Various blood group antigens and antibodies can be identified in dried bloodstain evidence. Age and condition of the stain may affect testing.

b. Collection and Preservation of Evidence For DNA Analysis***

Evidence that can be subjected to DNA analysis is limited to biological specimens. Biological evidence such as tears, perspiration, serum and other body fluids aren't amenable to DNA analysis.

DNA has been successfully isolated and analyzed in-

(1) blood and bloodstains

(2) semen and seminal stains

(3) tissues and cells

(4) bones and organs

(5) hairs with follicles

(6) urine and saliva (with nucleated cells)

Key points-

  • Biological evidence is generally transferred either directly or secondarily.
  • Blood, semen, tissue, bones, hair, urine and saliva can be transferred to an individuals body or clothing, or to an object or crime scene directly.
  • Once liquid biological specimens have been deposited, they become stains and adhere to the surface or the substratum.
  • Direct deposit and transfer can result from:
    • Suspect's DNA deposited on victim
    • Suspect's DNA deposited on an object
    • Suspect's DNA deposited at a location
    • Victim's DNA deposited on suspect
    • Victim's DNA deposited on an object
    • Victim's DNA deposited at a location
    • Witness' DNA deposited on victim or suspect
    • Witness' DNA deposited on an object
    • Witness' DNA deposited at a location
  • Secondary transfer occurs when biological evidence is transferred through an intermediate medium (a person, object or location).
  • The ability to successfully perform DNA analysis on biological evidence recovered from a crime scene depends on the kinds of specimens were collected and how they were preserved. Critical:
    • The technique used to collect and document evidence.
    • The quantity and type of evidence collected.
    • The way the evidence is handled and packaged.
    • How the evidence is preserved.
    • If the evidence is improperly documented, collected, packaged and preserved, it may not meet the legal and scientific requirements for admissibility in court.
    • If DNA evidence isn't properly collected, its biological activity may be lost.
    • If DNA evidence is improperly packaged, cross contamination might occur.
    • If DNA evidence isn't properly preserved, decomposition and deterioration may occur.

c. Examining Trace Evidence

Trace evidence is examined to either identify the material or its source, or associate it with another sample. A wide variety of techniques are used to analyze trace evidence. Most techniques involve careful, detailed examination. Special equipment may be used to enhance the analyst's visual capabilities and produce permanent records or images of the observations made.

The most popular instruments used to analyze trace evidence are the magnifying glass and stereo microscope. Scanning electronic microscopes, metallurgical, x-ray diffraction, infrared, ultraviolet and other techniques are also often used.

Latent fingerprint examiners identify, classify and analyze fingerprint evidence.

Scientists chemically analyze serological samples to:

  • identify blood type;
  • perform DNA fingerprinting;
  • determine specimen morphology for comparison with samples from suspects.


*This section is based upon and contains excerpts and quotes from "Kirk's Fire Investigation" (Brady Fire Science Series, Third Edition), Prentice-Hall, Inc. 1991 by John DeHaan. It is used with the permission of the author and publisher.

***This section is based upon and contains excerpts and quotations from "Physical Evidence in Criminal Investigation" that is published by the Narcotic Enforcement Officers Association in 1991. It was written by Henry C. Lee, Ph. D.; R.E. Gaensslen; Elaine Pagliaro, M.S.; Robert J. Mills, M.S. and Kenneth B. Zercie, M.S. and is used with permission.

Reprinted with permission.

 
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