Module 3 - Arson and Explosives

Obviously not all fires are caused by arson. In fact, most fires are accidental. The single, most common human cause of fires is careless smoking. Certain telltale signs indicate that an arson fire has occurred.

Fire investigators look for these signs when they first arrive upon a fire scene:

• Multiple points of origin
• Point of origin near a good supply of oxygen (such as an open window)
• Evidence that fire burned quickly and for a relatively long time
• Empty fuel cans or other evidence of the use of accelerants
• Unusual odours caused by the use of accelerants

To ensure fire safety, all building products, materials, and furnishings in North America must be tested for fire resistance, combustibility, and flammability before they can be used in construction. The same applies to upholstery, carpeting, and plastics used inside vehicles.

Four Areas of an Arson Investigation

To prove that arson was the cause of a fire, investigators look for evidence in the following four areas:

1. Proof of Incendiarism:  Fire investigators classify the cause of a fire as natural, accidental, unknown, or incendiary. An incendiary fire is one deliberately set by an arsonist. To classify a fire, investigators first try to locate the origin of the fire. To do this, photographs and diagrams of burn patterns are made and physical evidence is collected and analyzed at the fire scene. The origin of the fire along with other physical evidence can help determine the cause and the approximate time the fire was ignited.
   
   
2. Proof of Opportunity:  To identify suspects in arson investigation, fire investigators consider everyone who had opportunity to set the fire. They examine building security. Everyone with access to the site before the fire is asked to provide an alibi for the period of the fire. If all alibis are confirmed, investigators conclude that the arsonist must have gained access to the site illegally; consequently, other evidence must be used to identify the suspects(s).
   
   
3. Proof of Motive:  Arsonists set fires for several reasons, such as financial gain, revenge, crime concealment, or vandalism. An owner may become a suspect if he or she gained financially from properties destroyed by fire in the past or if he or she is having financial difficulties and stands to gain from an insurance claim for the property under investigation. Investigators examine the owner’s current insurance policies, insurance history, and current financial situation.
   
   
4. Circumstantial Evidence:  Because the evidence related to arson is often circumstantial, investigators collect as many different types of evidence as possible to support their case. Following is a list of several types of evidence that investigators may use to support their case:
   • On-site fire or burglar detection systems are inspected for evidence of malfunction or tampering.
   • If the fire was reported, the identity of the caller is determined and a background check is completed.
   • The license plates of automobiles in the area surrounding the fire may be checked.
   • Previous police activity conducted in the area is reviewed, as well as any reports of vandalism.
   • Hospitals in the local area may be asked if any patients with fire-related injuries were treated soon after the fire was set.
   • If an accelerant is identified, investigators may question local gas stations or hardware stores to see if a similar accelerant (such as gasoline or paint thinner) was purchased locally.

Indoor Fire Scene Investigation Tasks

After a fire has been extinguished and arson investigators can safely enter the site, access to the fire scene is controlled by police and fire department personnel to avoid scene contamination.

Arson investigators create an evidence collection area near the fire scene where they store any physical evidence found. Furniture, appliances, and other materials are often placed back in their pre-fire positions using the maps drawn by the occupants. This helps investigators examine and document every potential accidental ignition source or origin of arson in the rooms. In general, fire will burn longer at or near the point of origin. Therefore, damage will generally be more severe at the point of origin. Often physical evidence of the cause of the fire is found at or near the point of origin.

When the origin of the fire has been determined, a detailed diagram of the site is drawn. Windows, walls, floors, doors, ceiling composition, and the locations of key items are noted. All the entrance and exit points with lock types and conditions are identified. Sometimes, investigators call in experts to inspect and examine electrical wiring, appliances, or furnaces.