Arson Scene Investigation Procedure-
Part B
By: Don Penven, Technical Support Group
Introduction
According to statistics published by the National Fire Incident Reporting System (NFIRS), an average of 267,000 fires per year are the result of arson. Annual property losses amount to more than $1 Billion and the number of arson-caused deaths are nearly 500 each year.
The public perception of arson is that it is most often a “paper” crime—a fraud perpetrated against insurance companies. But arsonists also manage to kill and injure civilians and firefighters as well. So regardless of the motivation—monetary gain, revenge or a childish prank—the investigation of every fire requires a serious approach to determine the actual cause.
Was it accidental or intentional?
This post is based upon the latest information published from the National Fire Protection Association (NFPA) 921 – Guide for Fire and Explosion Investigations (2011 edition), and interFire’s Pocket Guide to Accelerant Evidence Collection.
In Part A of this series, the reader was introduced to the basic steps recommended for the fire investigator when responding to the fire scene:
1. The Roll Up—approaching the scene
2. Interviewing bystanders and firefighters
3. Post fire investigation: Enter the structure when it has been ruled safe to do so
4. Conduct a walk-though of the structure taking written and recorded notes and photographs
5. Locate the “low-point” of the fire.
Here in Part B we will continue with the investigative procedure covering the following topics
- Tools required
- Evidence collection and packaging equipment
- Evidence collection and preservation procedures
The Fire Scene Investigator’s Basic Toolkit
While individual investigators will, over time, assemble a comprehensive collection of evidence-gathering tools, this basic kit is a recommended starting point.
Heavy-Duty Sledge-Type Mallet
9” (22.9cm) Tongs
Hammerhead/Hatchet
Collapsible Folding Steel Shovel
Heavy-Duty Rubber Gloves, Pair
Pair of Safety Goggles
Disposable Jumpsuits
5” (12.7cm) Wire Cutter Pliers
8” (20.3cm) Scraper/Putty Knife
11” (27.9cm) Screwdriver
7” (17.8cm) Screwdriver
8” (20.3cm) Phillips Screwdriver
All-Purpose Hack Saw w/Spare Blades
Keyhole Saw
Heavy Duty Tin Snips/Scissors
Box Cutter Knife
Claw Hammer
3/8” (9.525mm) Electric Drill, Rechargeable
5/16” (8mm) Masonry Drill Bit
3/8” (9.525mm) Masonry Drill Bit
1/2” (12mm) Masonry Drill Bit
Assorted Drill Bits
1” (25mm) Heavy-Duty Masonry Chisel
1.25” (31mm) Wood Chisel
6” (15.2cm) Regular Pliers
Mason’s Trowel
Metal Tool Box-Type Carrying Case
Debris-Sifting Shovel
Debris Sifting Screens
Evidence Collection and Packaging Equipment & Supplies
Magnifier, 2.5X, 2.5” dia. (6.3cm)
Solid Material Evidence Containers, Metal, 1 qt. (946ml)
Solid Material Evidence Containers, Metal, 1 gal. (3.9L)
Glass Jars w/Polypropylene Cap, Assorted Sizes
Pair of Scissors, 5” (12.7cm)
Spatula, Steel Blade, 7” (17.8cm)
Spoon, 12” (30.5cm)
Scalpels, Disposable, 5” (12.7cm)
Plastic Tweezers, 4.75” (12.1cm)
10cc Syringes w/Needles, Disposable
Spatula, Stainless, Micro
Prober w/Blade, Chrome Steel, 6” (15.2cm)
Latex or Nitrile gloves
Zip-Top Evidence Bags, 4” x 6” x .004” (10.2cm x 15.2cm x 4 mil)
Zip-Top Evidence Bags, 9” x 12” x .004” (22.9cm x 30.5cm x 4 mil)
Zip-Top Evidence Bags, 13” x 18” x .004” (33cm x 45.7cm x 4 mil)
Liquid Collection Hand Pump
Liquid Collection Bottles with valve heads
8 oz. (250ml) Nalgene Liquid Sample Bottles with screw-on-caps
Funnel, Transfer
Tubing, Teflon®, 10’ (305cm)
Cutter, Tubing, 5” (12.7cm)
Vials: 40mL 28x95mm clear flint screw thread 24-400 with Teflon lined cap
Test Tube and Filter Closures
Test Tubes, Polypropylene, Vacuum Filtration
Strips, Accelerant Test Paper
Strips, pH Paper, Acid/Base, Litmus
Syringe w/Needle, Disposable, 10cc
Assorted Evidence Tags, Tape, Labels and Integrity Seals
Locating The Point of Origin (Low-Point)
The obvious place to begin narrowing the search for the low-point is the room or area suffering the most extensive damage. The problem with this is, however, that the entire structure may have burned to the ground. This is often the case with fires in rural structures when the fire may not be noticed until it had engulfed the entire structure. And distance from the scene to the responding fire service is also a problem.
This is not to say the situation is hopeless—it just presents a great deal more difficulty at the scene.
Common Liquid Accelerants
The physical properties of liquids differ greatly from solids and gases. The accelerants most often used at the scene of a fire possess very unique characteristics. As indicated in earlier posts, liquids and solids in and of themselves do not burn. In the case of liquids, the vapor given off by the substance burns when mixed with oxygen and its temperature reaches its flash point. Solids, like wood, cloth, paper, etc. give off flammable gases as they are heated (pyrolization). When these gasses mix with oxygen and their flash point is reached, these gasses will burn.
Characteristics of Liquid Accelerants
1. Liquid flows downgrade and will form pools in low areas.
2. Most hydrocarbons are lighter than water and are insoluble. As they float on the water’s surface they display a rainbow-like “sheen.” Certain other liquid accelerants like alcohol and acetone are water soluble.
3. The vapors given off by flammable liquids are heavier than air and will travel to low points such as stairwells, basements cracks and crevices.
4. Many of the flammable liquids used as accelerants are easily absorbed by materials such as wood, sheetrock, carpet, rags, etc.
5. Some flammable liquids begin producing vapors at or below room temperature—such as gasoline.
6. The common accelerants, most often used by an arsonist, do not ignite spontaneously and require a flame or spark to begin the burning process.
7. Some flammable liquids tend to partially stain and/or dissolve some finishes on floor surfaces.
8. When poured onto some synthetic surfaces such as vinyl tile, the surface will mollify or soften.
9. As a pool of accelerant burns, the edges of the pool will cause tile to melt and wood to char. The center of the pool receives less damage until the liquid burns off of that section.
10. Flammable accelerant residues are more often found around the edges of the pool, but it is always advisable to take samples from all areas of the burn area.
11. Flammable liquids like alcohol and acetone have a high vapor pressure and they tend to flash or scorch the surface. Hydrocarbons, on the other hand leave much stronger burn patterns.
12. In any case—regardless of the accelerant—the most important factor influencing the burn pattern is the ventilation present.
Collection of Accelerant Evidence
- One of the most important pieces of physical evidence is the accelerant container and every effort should be made to locate it. On occasion it may be discarded within the fire scene, but do not overlook a search of the outside areas such as bushes, shrubs and other nearby vegetation. The container can tell the criminalist with greater certainty the exact chemical content of the accelerant and the possibility of finding latent fingerprints must also be considered. Even when burned or scorched, the container may yield latent prints that have been baked onto the surface.
- Locate plants and trailers. The arsonist may set a plant like a pile of rags, crumpled paper or cardboard boxes that are soaked in accelerant, and he will pour a trail of accelerant in the direction of his escape route.
- Look for objects that do not seem to belong in the scene or are found in unusual configurations..
- Begin your search for accelerant evidence from the possible exit points that may lead to the area revealing the greatest damage.
- Search for ignition devices such as burned matches, matchbook, etc. near the possible exits.
- The best samples of possible accelerant evidence are most often found at the “low point” or point of origin of the fire.
Common Sampling Errors
1. Collecting insufficient samples
2. Sampling the wrong materials or locations
3. Improper evidence preservation
4. A lack of taking comparison samples
5. Failing to properly identify and label all collected evidence
6. Failing to maintain the evidence chain of custody
Other Evidence Collection Criteria
The most beneficial evidence collection areas are as follows:
1. Low points with heaviest burning
2. Collect samples from porous materials like plastic or manmade fibers
3. Collect any paper, cloth or cardboard that may have been in contact with the accelerant burn pattern
4. Inside cracks and seams in wood or tile flooring
5. The edges and center of burn pattern areas
6. Along baseboards, door sills, floor drains, and bases of load-bearing columns
The least beneficial areas for evidence collection are as follows:
1. Deeply alligatored or charred wood
2. Gray ash
3. Edges of a floor burn-through
4. Non-porous surfaces like ceramic tile
5. Areas exposed to the greatest amount of heat and fire suppression water streams
Eliminate the Possibility of Cross-Contamination
Ignitable liquid residue is highly volatile and fragile and every effort must be made to prevent various collected samples from contamination by other samples from the collection site or from other fire sites.
The principle sources of contamination are:
- Tools used during the evidence collection procedure
- Turnout gear
- Evidence containers
- Portable generators and other gasoline-operated motors and tools
References
National Fire Protection Association, NFPA 921: Guide for Fire and Explosion Investigations, NFPA, Quincy, MA, 2011
Inter Fire Online, “The Pocket Guide to Accelerant Evidence Collection,” <http://www.interfire.org/res_file/aec.asp> February 24, 2011
