A guest post by forensic scientist Tom Adair.
Arson is a legal characterization of fire setting that in most jurisdictions includes an intent to destroy property for malicious gain. Arson fires often include the use of accelerants (like gasoline) or combustibles (like paper or kindling) to start and spread the fire. The intensity of a fire (heat + duration) is dependant upon the available fuel including oxygen in most cases. Accelerant fires can burn several thousand degrees. Hot fires can melt aluminum (7280F), glass (12000F), and steel (27600F) and even bone (16000F). That’s pretty hot but certainly within the range of what investigators might find ay an arson scene.
I have investigated many fire deaths in my career and I have yet to see a body “turned to ashes”, even when accelerants are employed. The main reason is one of fire duration. Unless the fire scene is very remote, fire personnel will respond within minutes of the call to begin suppression efforts. This doesn’t leave a lot of time for the evidence to burn. Even if the fire is “out of control” the suppression efforts will likely reduce the heat load and temperature of the fire during the burn. Modern crematorium furnaces may take several hours to reduce a body to ashes and even then there are elements like teeth that survive.
Even a badly burned body will yield evidence...most of the time. Examination of the body at autopsy may yield DNA evidence (sexual assault), subcutaneous injuries (bruising), pettechiae (pin-point hemorrhaging in the eyes suggesting strangulation), and toxicological findings to name a few. That’s assuming the body isn’t protected from the fire in some way. As a fire burns the surrounding structure loses stability. A collapsed roof or wall may actually shield a body from the heat. Wrappings on the body may also help shield it to a degree.
Several years ago I investigated an arson fire in which the suspects poured accelerants on and in the vehicle to cover up evidence of a homicide. The vehicle was heavily damaged but after three days of sifting the debris we collected hair and fiber evidence, blood, even a fingerprint (etched into the rearview mirror). Most of the recovered evidence survived because it was protected inside wadded up towels or under the seats. The fire damaged the outside of the article but not what was protected inside.
Fire can be a very destructive force but it rarely consumes a body completely. That’s great news for homicide investigators and something that authors and readers should remember when encountering such scenes. Of course, with sufficient fuel and time a body can be reduced to ashes. More often than not though they simply run out of fuel before doing that much damage.
After 15 years as an internationally recognized forensic scientist, Tom Adair left the world of crime to become a writer. Tom has a master’s of science in entomology and is triple board certified as a bloodstain pattern analyst, footwear examiner, and senior crime scene analyst.
He has served as president of the Association for Crime Scene Reconstruction and has authored more than sixty scientific papers for peer-reviewed journals and contributed sections to several forensic text books. Tom’s first novel The Scent of Fear is planned for release in 2012. He lives in the Denver metro area of Colorado with his wife and Chocolate Labrador Sadie. Tom also writes about forensics at forensics4fiction.wordpress.com.