Building Fires

Building Fires

Introduction

By their very nature, fires are destructive, which often makes it difficult to find evidence of the cause of the fire. Prior to initiating a criminal arson investigation, a determination must be made that the fire was indeed arson (the intentional damaging of a building by fire) and not accidental or caused by nature (e.g., lightning). This usually requires a separate scientific inquiry called the fire investigation.

In some jurisdictions, arson investigators are trained in fire investigation; however, the more common method relegates this task to fire service personnel. Unfortunately, fire investigation, for the purpose of preventing future fires, is generally not as interesting to firefighters, who are more interested in suppression. Fire investigation, for the purpose of arson detection, was also shunned by the fire service because it was viewed as a law enforcement responsibility.

On the other hand, much of the law enforcement community viewed this function as the exclusive province of fire department personnel because of the general belief that one could not acquire the skills necessary to conduct a fire investigation without years of experience fighting fires. These problems are compounded by the volunteer nature of the fire service in many areas of the country. In such organizations, funds for fire investigation and training are scarce to nonexistent.

Another problem that has plagued arson investigations is that they are sometimes begun based on a false determination of arson. This is usually the result of a lack of scientific understanding of fire behavior and the misinterpretation of arson evidence. Unfortunately, fire/arson investigators were, in the not-toodistant past, forming opinions without a sound body of scientific knowledge.

Despite such an early beginning, the field has been slow to evolve from an art to a scientific inquiry. However, with the advent of fire research, many beliefs commonly accepted in the past have now been superseded.

As a result, many observations of fire damage formerly believed to be proof positive of a particular cause may now have more than one explanation. Ironically, it may be said, then, that our increased knowledge of fire has made determining the cause of fire more difficult, rather than easier.

Barring spontaneous combustion at high temperatures, most fires require external ignition to spark the chain reaction. Humans and lightning are the most common ignition sources, though falling rocks and volcanism also occasionally spark fires. Lightning's prevalence varies from region to region: while around 6,000 lightning discharges occur each minute across the globe, they are not uniformly distributed. Mountainous regions and places where lightning is not associated with drenching rainfall are particularly prone to lightning fire ignition. The western United States is one such place; 200-1,700 lightning fires occur each year on government forestlands in California alone.

In many places, humans ignite more fires than lightning. Humans first observed that the animals they hunted congregated on the flush of new grass after lightning-strike fires, or that useful plants grew in burned areas; archaeological evidence suggests that humans fully mastered the art of lighting and tending fires between 350,000 to 400,000 ...