Burn pattern analysis

Definition: Analysis of the spread of a fire from its site of origin, along with the type of burn damage and extent of destruction, to determine the cause of the fire.

Significance: Burn pattern analysis helps investigators to determine whether fires were started by natural events (such as lightning strikes) or by human activity and, if the latter, whether they were caused accidentally (for example, by cooking fires or welding sparks) or intentionally. Determining the causes of fires is important to both law-enforcement and insurance investigators because arson is the most common cause of major structure fires (houses, schools, warehouses) and accounts for greater monetary losses than any other category of fires.

Every twenty seconds, a fire department somewhere in the United States responds to a fire. According to the National Fire Protection Association, in 2006 more than 1.6 million fires caused 3,245 civilian and 89 firefighter deaths and $11.3 billion in property damage. More than 31,000 structure fires and 20,500 vehicle fires were intentionally set, about half of them by juveniles. Nevertheless, despite the high rate of arson fires, few arsonists are successfully prosecuted.

In the past, much of the information investigators had about how different types of fires behave and the burn patterns they leave behind was gleaned from firefighter observation. In the twenty-first century, however, the desire to improve the rates of arson convictions has combined with advances in technology to create a movement to develop a better and more scientific understanding of how fires behave under specific conditions. Researchers at educational agencies such as the Maryland Fire and Rescue Institute at the University of Maryland use controlled experiments to demonstrate that different types of fires create different burn patterns and to validate what burn pattern analysis reveals about the origin, type of fuel, and other factors that characterize a fire.

Point of Origin and Ignition

Every fire starts somewhere. Burn pattern analysis begins with an attempt to determine the site or origin of the fire. When a fire ignites simultaneously in several locations within a building, for example, this pattern suggests that the fire was intentionally set. A single point of origin does not by itself rule out arson, however. Investigators also consider whether the fire started inside or outside the structure or vehicle, if it started in a location where one might normally expect to find an ignition source (such as in a kitchen or workshop), and what type of fuel was likely to be available. In determining the point of origin, investigators may not only examine the physical remains of the structure or vehicle but may also request a chemical analysis of the remains and interview witnesses for information about the early stages of the fire.

Spread and Intensity

Once a fire has ignited, how it behaves is determined by three factors: availability of fuel, availability of oxygen, and the heat these produce. These factors are in turn influenced by such elements as the type of fuel available, weather conditions, ventilation systems, drafts from open windows and doors, functioning of installed fire suppression equipment within a building, and firefighter intervention. Although most fires follow a characteristic pattern of development, the constellation of conditions surrounding each fire is unique, and a burn pattern analysis must consider all these factors.

Investigators know that certain materials burn in predictable ways and leave particular telltale signs. Burn pattern analysis involves putting all these signs together to explain the behavior of the fire. Examples of signs that fire investigators might look for that can become part of their burn pattern analyses include the following:

• • V-shaped charring patterns on walls, which can give clues to the intensity of fires
• • Spalling, or flaking, patterns on concrete or stone floors, which may indicate that accelerant liquids were dribbled across the floors and ignited
• • Large, shiny char blisters, which are more likely to form when accelerant liquids are present (small, dull blisters are more characteristic of slow-igniting accidental fires)
• • Atypical burn rates for specific materials, which may suggest that accelerants were used
• • Abnormal or atypical continuity of burn patterns

Because of the many factors that influence the behavior of any given fire, burn pattern analysis evidence is often successfully challenged in court. Only 2 percent of arson cases result in conviction. Since the late 1990’s, the federal Building and Fire Research Laboratory (BFRL) has conducted research to gather scientific documentation on specific burn patterns. For example, researchers have started experimental fires under precisely the same conditions but using different types of accelerants; they have also started fires in rooms that are identical except for having different types of flooring. The burn patterns and other data from these experiments are documented and made available to fire investigators. In addition, the BFRL has developed computer simulations of fire scenarios to assist in training fire investigators and to help explain the results of burn pattern analyses to jurors.

Bibliography

Almirall, José R., and Kenneth G. Furton, eds. Analysis and Interpretation of Fire Scene Evidence. Boca Raton, Fla.: CRC Press, 2004. Examines the technical aspects of fire scene investigation with emphasis on what burn patterns can tell investigators.

Faith, Nicholas. Blaze: The Forensics of Fire. New York: St. Martin’s Press, 2000. Describes how fire investigators work and the methods that forensic scientists use in examining evidence from fire scenes.

Icove, David J., and John D. DeHaan. Forensic Fire Scene Reconstruction. 2d ed. Upper Saddle River, N.J.: Pearson Prentice Hall, 2008. Shows how investigators trace the history of a fire by using physical evidence of human activity and knowledge of burn patterns.

MacDonald, Jake. “After the Inferno: Winnipeg’s Arson Squad Can Tell How a Fire Started and Often Who Started It, by Sifting Through the Ashes and Reading Scorch Marks on the Wall.” Saturday Night, May 20, 2000, 24-32. Explains how fire investigators use burn pattern analysis to determine how a fire started.

Redsicker, David R., and John J. O’Connor. Practical Fire and Arson Investigation. 2d ed. Boca Raton, Fla.: CRC Press, 1997. Provides comprehensive coverage of all aspects of fire investigations, with emphasis on fires that cause death.