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Excerpts from
The Pocket Guide to Accelerant Evidence Collection

Table of Contents

I. OBJECTIVE OF THIS SECTION

II. SYMPTOMS OF ACCELERANT LIQUID USE IN AN ARSON FIRE

III. KEY PROPERTIES OF COMMON ACCELERANT LIQUIDS

IV. ACCELERANT LIQUID EVIDENCE COLLECTION TECHNIQUES

V. PACKAGING AND LABELING EVIDENCE CONTAINERS

  • Ignitable Liquid Residue samples

VI. SAMPLING PROCEDURES FOR SEVEN COMMON FLOOR TYPES

Appendix I: Glossary of Terms for the Fire/Arson Investigator

Appendix II: Twenty Common Ignitable Liquids used as Fire Accelerants


I. OBJECTIVE OF THIS SECTION

This material is an excerpt from the Pocket Guide to Accelerant Evidence Collection, 2nd Edition, (1999). The Pocket Guide was created by a unique collaboration between experienced fire/arson investigators and some of the leading forensic chemists specializing in analysis of arson debris in the United States. The objective of this effort, from the beginning, was to improve the performance of investigators by improving techniques used to recognize fires accelerated by ignitable liquids and improving the procedures used to obtain residue samples for laboratory examination.

Many of the procedures described here can be adapted for effective collection and documentation of other forms of physical evidence at fire scenes involving structures or motor vehicles.

Arson fires can also be started without the aid of ignitable liquid accelerants by using available combustibles, spontaneous ignition or electrical setups. Many common types of physical evidence such as fingerprints, footwear, tire-track impressions and tool marks are often found by skilled investigators at fire scenes. A trained evidence technician can assist in effective recovery of such evidence.

The manual describes a proven accelerant-sampling protocol, consistent with InterFIRE, that emphasizes the need to conduct certain witness interviews before attempting actual evidence collection from specific locations and materials. Interviewing those who have witnessed the early stages of fire growth can help fire investigators narrow down the area of fire origin.

These procedures take advantage of the fact that certain types of common materials in residential and industrial settings, as well as certain structural features present in most buildings, will tend to absorb and protect any ignitable liquid with which they come into contact.

Volatile ignitable liquid accelerants exposed to fire have a greater tendency to burn than most of the materials to which they are applied. This single point underlies all modern residue-sampling procedures.

In many fire scene examinations, the best potential evidence is often shoveled out a window in an effort to see if floor patterns are present. Sampling is then attempted from the floor's top surface. This can be a problem, particularly on flooring that is moisture impervious (e.g. glazed ceramic tile, sheet vinyl or linoleum, sealed cement, etc.). Material placed on the floor before the fire (e.g. newspaper stacks, clothing piles, cardboard boxes, etc.) most often will represent the best potential collection sites within the pour pattern on moisture impervious flooring.

On wood or carpeted flooring-residue sampling should be focused on areas where the ignitable liquid has seeped or has been absorbed and is protected from heat or volatilization. Generally, ignitable liquid residue sampling should be avoided where heat or hose streams were most intense during a fire.

II. SYMPTOMS OF IGNITABLE LIQUID USE IN AN ARSON FIRE

Basic rule: When volatile vapors burn above a flammable or combustible liquid-accelerant pool, they leave distinct burn/damage patterns unlike other combustible products normally found in a structure. The earlier a fire is extinguished, the more obvious these patterns will be. Except in the worst cases of destruction, there is still a chance of ignitable liquid residue recovery.

(Investigators should note that each symptom listed here could be due to a situation, cause or condition unrelated to the intentional use of a ignitable liquid as an arson fire accelerant.)

The following are possible indicators of an accelerated fire:

1. Witness observations ("an odor and gasoline," etc.).

2. A low-pressure wave ("boom" or "whomp" sound at ignition).

3. An explosion.

4. Burn injuries to the hands, face, legs or hair of a suspect/witness.

5. Unnatural fire spread (downward, unusually fast, etc.).

6. "Rolling" flames.

7. Bright yellow/orange flames accompanied by black smoke.

8. Sudden appearance of flames in an entire room followed by heavy, pushing black smoke.

9. Flames seen burning directly from the floor.

10. Intense localized rusting/warping, especially to the undersides and lower portions of metal appliances and metal objects within the suspected liquid burn-pattern area.

11. Structural damage inconsistent with fire loading.

12. Intermixed light, moderate and intense floor burn patterns in puddle or trailer shapes that correspond to the original shape of the ignitable liquid pool on tight or nonporous floors. The burn pattern appearance will vary with the type of ignitable liquid, surface texture and the amount of ventilation.

13. Localized "gapping" of wood or vinyl floor seams within the pour burn pattern, which may be caused by an ignitable liquid burning inside each joint or seam.

14. A "rainbow-colored" sheen on the surface of suppression water over the pour area.

15. Even height of smoke and heat patterns in the room of origin

16. Accelerant containers in or near the scene.

17. Increased burn damage pattern at the bottom of furniture legs. boxes, etc., on the floor in the pour pattern area

18. Burn patterns beneath doors, thresholds or floor moldings, etc.

19. "Rundown" burn patterns on floor joists beneath loose floorboards, board seams, or edge moldings.

20. Localized staining on the underside of carpet padding

21. Pool-shaped, intermixed, mottled black and brown staining on a concrete floor, together with a tendency for the mottled area to repel water - this stained area may retain the mild odor of an ignitable liquid.

22. Fire damage with no identifiable point of origin.

23. Wall burn patterns running from the floor seam up or appearing in corners.

24. Burned-out flooring beneath heavy appliances or furniture that ordinarily would be expected to "protect" the floor

25. "Ghost marks' between the seams of vinyl floor tiles in the pour area where the ignitable liquid seeped, dissolved and scorched tile adhesive, resulting in a "checkerboard" pattern on the sub-floor

26. Localized "clean burn' areas on a wall, appliance, or similar vertical surfaces above the floor pattern where intense heat burned away soot deposits

27. Sharp line of char demarcation in a cross-section of wood stud, or a sharp line of calcination (color change) in plaster or drywall, indicating a rapid (rather than smoldering) heat buildup.

28. Window glass that has melted down like "ribbon candy" and has a clean interior face (little or no soot) on the fire side.

29. Spring annealing in furniture/bedding, which may sometimes result from an ignitable liquid being poured directly onto or adjacent to upholstered furniture.

30. "Inverted cone" burn/scald patterns on vertical surfaces within the pour pattern area.

III. KEY PROPERTIES OF COMMON IGNITABLE LIQUIDS

Liquids have physical properties that cause them to behave differently from most gases or solids. Most common ignitable liquids used as fire accelerants have unique characteristics that manifest themselves in both fire development and evidence from fire scenes.

1. Liquids flow downgrade and tend to form pools or puddles in low areas.

2. Almost all hydrocarbon liquids are lighter than water, are immiscible, and may display "rainbow" coloration (sheen) floating on water. Certain other common ignitable liquids (e.g., alcohol and acetone) are water-soluble.

3. Almost all commonly used ignitable liquid accelerants tend to form flammable/explosive vapors at room temperature.

4. The vapors of most commonly used accelerants are heavier than air and tend to flow downward into stairwells, cellars, drains, crevices and cracks, etc.

5. Many ignitable liquids used as fire accelerants are readily absorbed by structural materials, and natural or man made substances.

6. Many ignitable liquids are powerful solvents, which tend to dissolve or stain many floor surfaces, finishes and adhesives.

7. Common ignitable liquids used as fire accelerants do not ignite spontaneously.

8. Ignition of a given ignitable liquid vapor requires that the vapor be within its flammable/explosive range at the point it encounters an ignition source at or above its ignition temperature.

9. When an ignitable liquid is poured on a floor and ignited, two major things occur:

(a) Many types of synthetic surfaces (e.g. vinyl) or surface treatments will mollify (soften) beneath the liquid; and

(b) At the edges of the pool, burning vapors adjacent to the liquid edge will cause many floor surfaces (such as wood) to char while certain others (such as vinyl) melt then char. As the liquid pool boils off, its edge recedes. Floor surface charring (or melting and charring) follows the receding liquid edge. The floor area under the ignitable liquid is protected from the effects of burning until the liquid boils off that section.

10. Experiments indicate that the greatest temperatures in an ignitable liquid-accelerant fire occur above the center of the burning liquid pool. Scientific experiments have shown that maximum concentrations of ignitable liquid residues are more often found at the edges of the burn pattern and minimum concentrations toward the center. Some arson investigators believe this is controversial and so take samples form both the edges and the center.

11. Ignitable liquids with high vapor pressure, such as alcohol or acetone, tend to "flash and scorch" a surface, whereas ignitable liquids with higher boiling components, such as kerosene or turpentine, tend to "wick, melt and burn," leaving stronger patterns. The amount of ventilation available to the fire is a factor in burn pattern appearance.

IV. ACCELERANT EVIDENCE COLLECTION TECHNIQUES

a. The Accelerated Arson Crime Scene

Many arsonists employ similar methods when using an ignitable liquid to set a fire. Some important tips on collecting residue samples follow.

  • Accelerant container. If evidence of ignitable liquid accelerant use is identified, always search for the container. Latent fingerprints can often be developed even on scalded or sooty containers. Containers are often found at the end of a pour pattern, thrown back into the "trailer," onto the roof above the egress, into a rubbish disposal, in nearby vegetation along the escape route or may be found in the suspect's vehicle or house.
  • Plants and trailers. Many arsonists "trail" an ignitable liquid accelerant pour from a "plant" (large concentration) across a floor toward a secluded building exit or interior barrier to make ignition and escape safe, therefore:
    • Begin your search for evidence by looking for objects that do not seem to belong.
    • Concentrate the search for ignitable liquid accelerant-evidence indicators beginning where any suspected accelerant container was found, or from any possible egress concealed from view and leading back towards the areas of greatest damage.
    • Concentrate the search for remains of the ignition device (matchbook, etc.) at or near the most probable egress point or barrier.
    • The best ignitable liquid residue samples are often found around the point of origin; the best physical evidence proving a forcible entry is usually at the point of entry itself.

b. The Most Common Ignitable Liquid Residue Sampling Errors

The most common sampling errors are as follows:

  • Insufficient sample (too small).
  • Taking samples from the wrong places or materials.
  • Ineffective sample preservation techniques.
  • No comparison samples.
  • Not maintaining an evidence "chain of custody."

c. Evidence Collection Areas

The major accelerant residue evidence collection skill is knowing what to collect and what not to collect. Ignitable liquids used as accelerants burn better than most of the surfaces onto which they are poured. Expect to find better, stronger samples in protected areas and inside absorbent materials within the pour pattern.

Most Desirable
Collection Areas
Least Desirable
Collection Areas
a. Lowest areas and insulated areas within the pattern. a. Deeply charred wood.
b. Samples taken from porous plastic or manmade fibers. b. Gray ash.
c. Cloth, paper, cardboard in direct contact with the pattern. c. Edge of a hole burned through a floor.
d. Inside seams, tears, cracks. d. Samples from absolutely nonporous surfaces.
e. The edges of burn patterns. e. The center of any burn pattern.
f. Floor drains, bases of load-bearing columns or walls. f. In general, areas exposed to greatest hear, hose streams.

d. Preventing Cross-contamination

Cross-contamination is the unintentional transfer of an ignitable liquid residue from one fire scene or location contaminated with ignitable liquid residue to an evidence collection site.

There are four major potential sources of cross-contamination at a fire scene: tools, turnout gear, evidence cans and emergency equipment. Fire investigators should comply with certain "housekeeping" procedures to help prevent cross-contamination from a previous accelerated fire scene or other sources.

Tools. A fire/arson squad or fire investigator should be equipped with a special tool kit to process fire scenes. These tools should be kept separate from other fire department equipment and must never be coated with any rust preventive. After a fire scene examination is completed, these tools should be rinsed clean with a strong stream of water.

It is recommended that fire investigators use steel blade tools (shovel, hoe, brick trowel, chisel, etc.) and squeegees with hard rubber blades for excavation and ignitable liquid evidence sampling. Some types of common equipment (bristle brooms) and safety gear (firefighter gloves) probably cannot be cleaned once contaminated with ignitable liquid residue. Always use latex gloves to process evidence.

It is necessary to cleanse each tool used for excavation or evidence sampling before taking it into the fire scene and, again, between evidence collection sites within the scene. Concentrated liquid dishwashing detergents effective at dissolving grease, including Ultra Dawn Concentrated Dishwashing Detergent, have also been found effective in dissolving ignitable liquid residue on steel tools when scrubbed with a clean scrub brush and flushed with clean water. Be sure to submit a sample of the liquid detergent to your forensic laboratory to ascertain its properties and ingredients.

If investigators have an accelerant detection canine or sensitive hydrocarbon detector available consider using it to double-check the tools after cleaning and prior to use.

Note that ignitable liquids derived from crude oil are generally not soluble in water alone.

Turnout gear. It is important to clean boots off before entering the area where samples are to be taken. Avoid walking through contaminated areas enroute to the collection site. Do not handle ignitable liquid residue samples with fire gloves on. Carry several pairs of sterile latex gloves in your pocket or kit. Two latex "surgical type" gloves will conveniently fit into an empty 35mm film container with a snap top. Wear latex gloves to handle potential residue evidence.

Evidence cans. It is recommended that fire investigators carry a supply of both one-quart and one-gallon "paint style" evidence cans, or their equivalent, in which to store residue samples. A good housekeeping practice is to take a new, sealed one-quart can and place it into a one-gallon can and seal that before placing it in your vehicle or kit. This saves space and prevents contamination. Open the cans just prior to physically collecting the sample at the collection site.

Portable generators and gasoline power tools. Investigators should work closely with firefighters to limit potential contamination when possible. Find out where such tools were used or fueled.

V. PACKAGING AND LABELING IGNITABLE LIQUID RESIDUE EVIDENCE CONTAINERS

Accelerant residue sampling at a fire scene can be done in a way that maximizes laboratory identification of accelerant residues. Most of the laboratory procedures involve testing "headspace" vapor in various ways. Headspace is the zone inside a sealed evidence can between the top of fire debris and the bottom of the lid. Fire/arson chemists generally recommend that evidence containers be filled to two-thirds volume with debris sample, leaving the top one-third volume as empty, air headspace.

To achieve the best laboratory results, samples suspected of containing ignitable liquid residue should always be collected and packaged into an evidence can in a way that permits volatiles to migrate and gather in the head space. Following a few basic procedures at the fire scene will facilitate this process.

Always place the evidence label on the side of the evidence container and not on the lid. Sometimes evidence can lids are removed in the laboratory and could be mixed up with another container.

VI. SAMPLING PROCEDURES FOR SEVEN COMMON FLOOR TYPES

Photograph any pour pattern before sampling it.

Gently, remove debris by layer from the floor, keeping in mind that absorbent materials laying flush on the floor within the suspected pour burn pattern, such as acoustical tile or drywall, may present outstanding sampling potential, as do other absorbent materials sitting on the floor (e.g., stacks of laundry, boxes, newspapers).

Consider the fact that floors are seldom built perfectly level. Also, human and machine traffic patterns create wear depressions over time. People tend to walk or move supplies down the center of a narrow staircase or corridor and along the right edge of a wide corridor or staircase. Any area where consistent impact occurs, such as at the base of a staircase, is also likely to become locally depressed from wear over time. Liquids tend to flow to, and pool in low areas. For best results, sampling strategies should take these things into consideration.

Conceptualize how the scene was constructed and what objects and materials were in the area where the ignitable liquid was poured. An interview with the person who is most familiar with the area of origin's pre-fire layout is a recommended preliminary step to prepare for an origin and cause examination along with construction of a detailed map of the suspected area of origin & showing the room shape, windows and doors and major appliances, contents or furniture.

Assemble all collection and documentation equipment into a crime scene headquarters convenient to the area of origin. Clean all tools before going into the area of origin and between evidence collection sites. Wear latex gloves when physically handling evidence. Change gloves as required between evidence sampling sites. Limit scene access to evidence collection personnel. Wear appropriate eye protection.

IGNITABLE LIQUID RESIDUE SAMPLING TECHNIQUES

1. Carpet

Carpet is a woven composition material manufactured form a variety of materials including wool, nylon, other synthetics or blends of these products. Many modern carpets and carpet padding are of petrochemical origin and, thus, share molecular similarities with many ignitable liquids. Comparison sampling is important. Most of these products have strong absorption and retention qualities, which makes them ideal for ignitable liquid residue sampling.

Suggested tools for sampling carpet include:

  • Sharp utility knife
  • Large-blade screw driver or pry bar
  • Latex gloves
  • Liquid dishwashing detergent with grease solvent, such as Dawn Dishwashing Detergent, a clean scrub brush and flushing clean water.

Lift any remaining carpet to check its underside and padding for ignitable liquid odor or staining. Document staining or localized burn damage with a photograph. If a suspect sample area is identified, cut a long strip of carpet and padding along the odor stain. Chimney-roll the carpet strip. Drain excess water. Place as much of the strip sample as possible into the bottom two-thirds of the container. Be sure to leave at least one-third volume head space below the lid. Seal the evidence can tightly, label it with its collection point, etc., and keep it in a cool place.

Most experts recommend residue sampling along the edge of a suspected accelerant burn pattern since some studies have shown the strongest ignitable liquid residues will usually be found there. This shouldn't preclude sampling from other suspect areas within the pattern when indicators are present. Place samples in evidence containers in the manner described above.

Take samples from carpet remaining beneath furniture legs, metal edge strips between room, under carpet tackboards, behind and beneath mopboards (floor moldings) and threshold boards where a suspected pour pattern intersected with these areas. The bases of the furniture legs, carpet tackboards, bottom edge of mopboards and edges of threshold boards may also present excellent sampling opportunities themselves if they are within the floor pattern area.

Many synthetic carpets and carpet pads share a petrochemical origin with ignitable liquid accelerants derived from crude oil. Seek comparison samples from protected areas on the same floor. Suitable comparison samples can be obtained from unburned carpet beneath file cabinets, dressers, or other "shield" distant from the suspected ignitable liquid burn pattern.

2. Glazed ceramic tile

Glazed ceramic tile is a product made essentially from a non-metallic mineral (clay) by firing at a high temperature. Glazing is a second step where a mixture of oxides (silica or alumina) is applied to form a moisture-impervious surface. Typically found in kitchens and bathrooms these products are nonporous and present very poor sampling potential.

Emphasize sampling grout, moldings, surface cracks, and absorbent materials found on top of the tile inside the pattern area.

Suggested tools for sampling ceramic tile include:

  • Hammer
  • Cold chisel
  • Large blade screwdriver
  • Pliers
  • Latex gloves
  • Liquid dishwashing detergent (i.e. Dawn Dishwashing Detergent), a clean scrub brush and clean water.

Emphasize sampling of any absorbent materials that may have been located on top of ceramic tile before the fire (throw rugs, piles of laundry, cardboard boxes) providing they are within the pour pattern area. Take samples of these as required.

Locate pre-fire cracks or imperfections in the tiles or grout; these may have soot deposition inside the crack or crevice. Collect from both edges and the base of the crack. Collect samples of the baseboard at the edges of the tile surface within the pattern area.

To find comparison samples, locate a protected area of ceramic tile away from the suspected pattern area. Shatter some tiles with a hammer and pry up an appropriate quantity. Collect sections of tile, grout and adhesive.

3. Concrete/cement

Concrete/cement is a hard, strong construction material composed of a mineral aggregate (sand or gravel), water and a cementing material such as Portland Cement (alumina, silica, lime, iron oxide and magnesia). (Untreated) concrete is somewhat absorbent depending on its composition.

Focus on isolating the locations of absorbent materials stored directly on the concrete floor in the pattern area. Also search for pre-fire cracks, expansion seams, floor drains, lolly columns and areas where the ignitable liquid accelerant may have spread under pallets or other objects where temperatures would probably be lower.

Suggested tools for sampling concrete include:

  • Squeegee
  • Concrete "cold" chisel.
  • 48 ounce hand sledge or carpenter's hammer.
  • A large section of clean cloth.
  • Required chemical absorbents or solvents
  • Latex gloves
  • Liquid dishwashing detergent (Dawn Dishwashing Detergent), a clean scrub brush and clean water.

Special note: common ignitable liquids poured on concrete and ignited often leave an intermixed and mottled black, brown and gray area of staining that corresponds to the shape of the original accelerant pool. This area may retain a mild odor of absorbed ignitable liquid and may repel a light coat of water. Document these characteristics. Concrete spalling from liquid accelerant fires remains a controversial topic. If spalling or any of the other characteristics are present in the suspected pour area, document them.

Investigators should take care to maintain objects (e.g., pallets, containers, stored products) in place within the pattern area to document damage and burn-pattern evidence consistent with a floor-burning ignitable liquid accelerant.

Several collection techniques are applicable to this type of surface. Which of the techniques or combination of techniques is chosen depends on the specific situation. Direct sampling from the base of absorbent objects stored on the floor within the pattern area, or from pre-fire cracks or sampling from the concrete itself may tend to yield stronger samples than the absorbent technique.

Emphasize collection of samples from the bottoms and bottom edges of any absorbent materials stored directly on the floor within the suspected pour pattern area.

Sampling from pre-fire cracks and crevices. Pre-fire cracks in the floor surface within the pour pattern area will usually display interior sooty edges after a fire caused by "wicking" and inefficient burning (sooting) of fuel vapors. Post-fire expansion or damage cracks will often have relatively cleaner crack edges. Using the cold chisel and hammer, break the edges of pre-fire cracks one-half inch on both sides. Include a sample from the base material (soil, etc.) beneath the crack. Try to identify and sample crack areas where ignitable liquid may have flowed beneath a shielding object. Pulverize the sample concrete into many small pieces. Loosely fill the evidence can to two-thirds volume and seal.

Direct surface sampling. Lay the cloth section over the outer edge (periphery) of the burn pattern. Using the hammer, sharply strike the floor at the accelerant pattern edge to fracture the concrete surface. Thin (1/2-inch thick), small, fractured concrete pieces of the floor surface may retain ignitable liquid residue. Fill the evidence container to two-thirds volume and seal.

Chemical absorbent method. The chemical absorbent method can be used if breaking up the floor's surface is impossible, or if large floor areas are to be sampled. Begin by cleaning the concrete floor where the burn pattern is located with a shovel, squeegee and water spray. Photograph and diagram suspected accelerant burn pattern evidence.

Wet down the entire burn pattern area with a mist of water. Spread a coating of finely ground agricultural lime (40/60 mesh ASTM) approximately 1/16- inch thick over the pattern area. Let stand for 30 minutes. Recover the absorbent with a shovel or squeegee, and place in an evidence can without packing down. The chemical is more absorbent than concrete and tends to soak up ignitable liquid residues. Non-self-rising flour may be used as a substitute following the same directions. Although flour absorbs as well as lime, it tends to decompose in the can and yield alcohol and carbon dioxide, which may burst the container seal or needlessly contaminate the sample. If flour is used, either have is analyzed immediately or freeze it. Agricultural lime is commonly available in lawn and garden or hardware stores, and non-self-rising flour is available in any supermarket.

4. Floor tiles

Floor tiles may be made from vinyl, ordinary ceramic or other substances. Asbestos and other substances were sometimes added to increase durability. This product may offer good residue collection possibilities because of the abundance of seams into which accelerant liquids may seep or be absorbed. Adhesives used with these products, and some of the products themselves (vinyl), may have a petrochemical basis. Comparison sampling is necessary.

Suggested tools for sampling floor tiles include:

  • Cold chisel
  • 48 ounce or heavy carpenter's hammer
  • Large-blade screwdriver or putty knife
  • Utility knife
  • Pliers
  • Latex gloves
  • Liquid dishwashing detergent (i.e. Dawn Dishwashing Detergent), a clean scrub brush & clean water.

To start, gently clear and then clean the surface of the tiles with a gentle water rinse and a squeegee until any remaining burn pattern can be photographed. Include photographs of objects within the floor pattern that display damage patterns consistent with burning ignitable liquid accelerants such as wall or appliance surfaces.

Photograph "ghost patterns," where ignitable liquid seeped into tile edges and either dissolved or seared the adhesive, leaving a checkerboard-like appearance. Photograph areas on the same floor outside the pattern where ghost marks are not present.

Lift the edges of many tiles within the pattern area with a screwdriver or putty knife, and break them off about 1/2-inch from the edge of each seam. Fill the evidence can two-third full and seal.

Comparison sampling of floor tile is important. Certain categories of floor tiles (i.e., vinyl) and many types of tile adhesives share a common petrochemical origin with common ignitable liquids. If an adequate comparison sample is not available, always take the residue sample. Seek comparative tile samples from protected areas outside the pattern area beneath appliances and floor storage.

5. Linoleum/vinyl sheet floor coverings

These thin-layer composition products are manufactured from a base of burlap, canvas, or similar material covered by a mixture of linseed oil, gum, cork dust and /or wood flour (linoleum flooring), or thermoplastic polymers of vinyl compounds (vinyl flooring). Sheet flooring may also contain substances like asbestos, which increases durability. Many are top-coated with a tough, nonabsorbent coating, which inhibits absorption into the product. They are often glued to subsurfaces using epoxy or glues containing hydrocarbon-based adhesives. Comparison sampling is important.

Pouring common ignitable liquid accelerants on linoleum/vinyl flooring will usually have two effects: (1) the surface will often mollify (soften) and begin to dissolve; (2) once ignited, the edge of the accelerant pool will begin to melt, burn and char. As the pool recedes during the fire, the burning and melting will recede with it, resulting in a burn pattern.

As with any type of ignitable liquid accelerant pattern, the center of the pattern is ordinarily exposed to the greatest heat and is less likely to produce a valuable sample.

Tools for sampling linoleum/vinyl floor coverings include:

  • Utility knife
  • Large-blade screwdriver
  • Wood or cold chisel (as appropriate)
  • 48 ounce hand sledge or heavy carpenter's hammer
  • Latex gloves
  • Liquid dishwashing detergent (i.e. Dawn Dishwashing Detergent), a clean scrub brush & clean water.

With this type of flooring focus on first sampling from absorbent materials (paper/cloth, storage boxes, throw rugs, collapsed ceiling materials, etc.) and lower portions and joints of any construction materials (floor moldings, door casings, threshold boards) within the pattern area using the appropriate tools.

Look for pre-fire tears, rips or cracks within the pattern, especially near heavy appliances or items that may have been dragged across the floor. Using the utility knife and screwdriver, cut out the remaining surface and underlayment.

Linoleum/vinyl is usually installed in six- or twelve-foot-wide sheets. Locate a seam between two sheets and trace it into the pattern area. Sample from between and beneath the two adjoining sheets in the pattern area.

Identify the edge of the accelerant pool. Cut long, narrow strips of flooring along this periphery zone. "Chimney-roll" and arrange the samples vertically in the evidence can, allowing for one-third volume headspace.

Seek comparison samples outside the pattern areas on the same floor in a protected area. Good comparison samples can usually be found beneath heavy appliances, storage or furniture, which sit flush on the floor. Sample both the flooring and adhesive.

6. Sand/soil floors or building aprons

Ignitable liquid accelerants draining onto or poured across dug cellars and crawl spaces, or exterior ignitions or a liquid-accelerant trailer running out of building to adjoining soil aprons are frequently encountered. Soil generally provides an excellent sampling opportunity because of its high surface-to-weight ratio and the fact it often remains moist and cool during an abutting fire, inhibiting ignitable liquid volatilization.

  • Suggested tools for sampling sand/soil floors include:
  • Mason's trowel
  • Large-blade screwdriver
  • A gardener's hand shovel
  • Latex gloves
  • Liquid dishwashing detergent (Dawn Dishwashing Detergent), a clean scrub brush & clean water.

Determine the dimensions of the sampling area by lifting the top two inches of soil, or by pulling tufts of grass of other vegetation with root systems to check for odor. Sample the top four to six inches of topsoil from within the trailer or pour area. Include vegetation roots if they are the dense, surface types.

Fill the evidence can to two-thirds volume. Do not pack down the sample. Clean the evidence container's V-groove and seal tightly.

When soil evidence is believed to contain ignitable liquid residue, either transport it to the laboratory promptly, or make arrangements to refrigerate or freeze the soil samples. Naturally occurring bacteria present in soil degrades many common ignitable liquids derived from crude oil and will quickly break down the remaining residue unless precautions are taken.

Take a comparison sample away from the pour/drain pattern area. If you sample the top four inches of trailer soil, then do the same when sampling for comparison purposes.

7. Wood flooring

Wood is used in a vast number of residential and commercial construction and cosmetic applications. The most important uses for fire investigators seeking ignitable liquid residue evidence would be in the use of wood for flooring, floor moldings, threshold boards, door casings, furniture joints and staircases. Most arsonists pour ignitable liquids on a floor or staircase and ignite it.

Ignitable liquid residue sampling techniques with wood surfaces should concentrate on seams and joints.

Investigators should also search within the pour pattern for places where wood grain is vertically aligned, such as in furniture legs or wooden door casings. Ignitable liquids reaching such areas are often absorbed into the vertical fibers of the wood boards in much the same way water is absorbed in a tree.

Suggested tools for taking samples of wood surfaces include:

  • 1" or 3/4" inch steel wood chisel
  • 48 ounce hand sledge or heavy carpenter's hammer
  • Pry bar
  • Wood or keyhole saw
  • Latex gloves
  • Liquid dishwashing detergent (Dawn Dishwashing Detergent), a clean scrub brush & clean water.

For tongue and groove or barnboard wood flooring, use the wood chisel and hand sledge to cut thin slivers from both sides of many adjoining board seams within the suspected accelerant burn pattern. Place splintered seams vertically in the evidence can until two-thirds of the volume is filled. Since ignitable liquids will not be absorbed very far into wood fibers, try to collect as many narrow cut seam edges as possible. Try to fill the evidence can to two-thirds volume for best results. If sufficient "hot" splinters cannot be found to properly load an evidence container to 2/3rd volume then use a smaller evidence can.

When collecting evidence from wooden staircases, use a chisel to cut into the seam between the tread and riser within the accelerant burn pattern on the various steps.

Appendix I: Glossary of Terms for the Fire/Arson Investigator

Appendix II: Twenty Common Ignitable Liquids used as Fire Accelerants

Excerpted from A Pocket Guide to Accelerant Evidence Collection, 2nd Edition, (1999).

Courtesy Massachusetts Chapter, IAAI. Reprinted with permission.

 
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