By Don Penven, Technical Support group
Introduction
The investigation of fire scenes is a very complex undertaking. Unlike most other forms of investigation, much of any possible physical evidence has been consumed by the fire.
Fire Scene Photo...Courtesy of Franklin Co. (NC) Sheriff's Dept.
The fire marshal or fire scene investigator must arrive at one of two conclusions:
1. The fire was of an accidental or unintentional nature
2. The fire was caused by the intentional acts of some individual
The purpose of this, and a subsequent post is to offer a step-by-step tutorial covering the most accepted methods for investigating a fire scene. Due to the amount material to be covered, this instruction will be offered in two parts,
Granted—no two fire scenes are identical due to the many factors that influence the spread of a blaze through a structure. For the purposes of this narrative, we will use a hypothetical, single-family, detached, two-story dwelling.
Special Note: As with any other crime, it is incumbent upon the state to prove the crime of arson. It is, therefore, the responsibility of the investigator to gather the evidence in such a manner as to conclusively and irrefutably show:
• That there was indeed a fire;
• That the fire was incendiary in nature and of human origin; and
• That the fire was willfully caused—not accidental.
This body of evidence, or corpus delicti, if conscientiously gathered, preserved and presented, will
prove the commission of the crime of arson and the culpability of the arsonist.
The Roll-Up
Approaching the Scene
For this scenario, arrival of the investigator occurs before the fire is considered to be “under control.”
The fire scene investigation begins with observing the scene from a distance as the investigator approaches the location. Make a mental note of the color of the smoke and the color and intensity of the flames. Take photos of the smoke and flames from a distance.
- Once at the scene, begin photographing any bystanders. This should be done as unobtrusively as possible as the arsonist may be a part of the gathered crowd.
- Interview bystanders: What did they see upon arrival at the scene? Did they notice any unusual odors? What color was the smoke and flames? Did they hear any sounds—like popping or explosions?
- Interview firefighters: Repeat the questions asked of bystanders. Determine if any doors and windows were open upon arrival. Were drapes, blinds or window shades drawn that may have prevented seeing the blaze from the outside?
- Determine if the property owner or tenant is at the scene. Attempt to get the details of how the fire may have started.
- A very useful investigative tool would be a pocket-sized digital voice recorder. The recorder may be concealed in states that permit recording conversations with “one party (the investigator) consent”. Clear this with your local prosecutor or district attorney.
The following are possible indicators of an accelerated fire:
1. Witness observations ("an odor of gasoline, black smoke," 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/victim.
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 subfloor
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 calcinations
(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.
Post-Fire Investigation – Step 1
Determine When it is Safe to Enter The Structure
SPECIAL NOTE! While it is very important to be in the process of examining a scene as quickly as
possible, safety concerns must be observed first. Neither the fire marshal nor the arson investigator
should enter the scene until responsible authorities have deemed it safe to do so.
Conduct a Walk-Through
- Conduct a walk-through of the structure. Visual observation should include looking for anything that seems out of place. Make written notes and/or record voice notes. Photograph any items of interest.
- Note positioning of structure contents such as rearrangement of furniture into unusual positions. Note the presence of, or the lack of items found typically in particular rooms such as TVs, home entertainment centers, etc.
- Make a preliminary determination as to the area where the most intense burning occurred.
- Photos taken should include overall views of each room that received even the slightest damage.
- Be thinking about the probable location where the fire may have started. If arson was the cause, several points of origin may be noted. Note any odors present that may indicate the presence of accelerants. The arson investigator’s search for traces of flammable liquid residues may be aided by the use of a highly sensitive portable vapor detector or “sniffer” (See Below)). This device can rapidly screen suspect materials for the presence of volatile residues by sucking in the air surrounding the questioned sample. The air is passed over a heated filament. If a combustible vapor is present, it oxidizes and immediately increases the temperature of the filament. The rise in filament temperature is then registered as a deflection on the detector’s meter. Such a device is not a conclusive test for a flammable vapor, but it does provide the investigator with an excellent screening device for checking suspect samples at the fire scene.
Hydrocarbon Detector "Sniffer"
Post-Fire Investigation – Step 2
Based upon observations and notes taken during the walk-through, begin pin-pointing the probable “low point” or origin of the fire. This will most often be the area suffering the most intense burning. See Figure No. 1.
The photographs in Fig. No. 2 depict different burn patterns on various kinds of flooring as a result of an accelerant being used.
Locating the “Low Point”
If an arsonist is intent upon destroying the entire structure, it is very unlikely that he would start a fire on the upper floors including the attic. Most humans are aware that a fire tends to move upward and laterally.
For this reason it is wise to search for the low point in and around the lower floors. But there are always exceptions to this scenario! If the arsonist’s intention was destroying certain incriminating evidence, the fire could be set in the upper part of the structure. This is especially true when the motive behind the arson is covering up a homicide.
The structural burning patterns in the above illustrations should offer some assistance in determining the low point or point of origin of the fire.
In the Arson Scene Investigation Procedure-Part B, the actual evidence collection procedure and the tools and materials needed will be covered.
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References:
National Institutes of Justice, Flammable and Combustible Liquid Spill/Burn Patterns, NIJ Report 604–00, Washington, DC, US Dept. of Justice
Inter Fire Online, “The Pocket Guide to Accelerant Evidence Collection,” http://www.interfire.org/res_file/aec.asp October 12, 2011
NFPA 921 “Guide for Fire & Explosion Investigations,” 2011 Edition, Quincy, MA
