 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.
| 
