Arson Investigations

by William A. Tobin

ARSON INVESTIGATIONS

By

William A. Tobin
Special Agent
FBI Laboratory
Washington, DC

Collapsed furniture springs, which have been subjected to fire, have been used by arson investigators for many years, both as an indicator of arson and/or of a slow, smoldering source, such as a cigarette. However, FBI Laboratory research has revealed that collapsed springs are not a valid indicator of the presence of an accelerant or of a smoldering source.

A review of the literature reveals that there are contradictory conclusions regarding the condition of springs subjected to fire. Some sources maintain that collapsed springs are, indeed, an indication of a slow, smoldering origin because of the consistent heat required to collapse them. Others argue that collapsed springs are positive proof of the presence of an accelerant because the temperature required to collapse the springs cannot be reached by the burning of normal building materials alone. The contradictory nature of these conclusions, therefore, suggests that a detailed metallurgical investigation was necessary to determine which theory was valid.

When metals are subjected to elevated temperatures, many metallurgical parameters and considerations can come into play. Metallurgists have long known, for example, that in order for a metal to be of equal strength, it must be heated to a certain temperature in a certain amount of time. This can be accomplished by applying twice the heat in half the time, or half the heat in twice the time. The FBI Laboratory's investigation examined not only the interactions of time and temperature but also of chemical composition, fabrication history, and other metallurgical conditions.

Part of the FBI's investigation involved actual test burnings of mattresses of varying inner-spring construction. The mattresses were placed in a room full of furniture at the FBI's Test Burn Facility in Quantico, VA. To simulate an accelerant-based fire, gasoline was poured on the mattresses and ignited. To simulate a cigarette or other slow, smoldering type of fire, 10 ml of propanol was placed on the mattresses and ignited. After the resulting fires were allowed to burn for varying amounts of time, they were extinguished and data, including photographs, were collected. The most notable conclusion was that within the same mattress, there were both collapsed and uncollapsed springs. Therefore, consistent with metallurgical expectations, controlled testing revealed that the collapsed, partially collapsed or uncollapsed condition of furniture springs is of no value as an indicator of arson or of a slow, smoldering fire.