Crime Scene Investigations Forensic Arson Analysis

The Fire
Arson investigation starts with the fire itself. To create and sustain a fire three factors must be present. The three factors are known as the fire triangle (Peige ed., 1977). The fire triangle consists of oxygen, a fuel source, and heat. In most cases the percentage of oxygen concentration must be above 16% (Peige, ed., 1977). The fuel may be any flammable substance. The heat source needs only to match the ignition temperature of the fuel.
In a fire involving arson the arsonist will have tampered with one or more of the factors in the fire triangle. The arsonist may increase the fuel load by introducing flammable material or by adding accelerants such as kerosene, gasoline or alcohol (French, 1979) The arsonist may increase the oxygen content of a structure by opening windows or punching holes in ceilings and walls (French, 1979) Fire will follow the highest concentration of oxygen to its source. By ventilating a structure at the top and starting a fire at the bottom of the structure an arsonist can cause the fire to race upward through the structure. The fire will rapidly involve the whole structure rather than be confined to one room.
An arson fire involves the introduction of a heat source that can be as simple as a match or as complex as chemicals with very low ignition temperatures (Battle, 1978). By definition a fire is considered an arson fire when all other accidental caused have been ruled out. To say that the cause of a fire was arson and therefore deliberate, the investigator must have sufficient evidence the one of the factors in the fire triangle was tampered with.

The Fire Fighters
Arson investigations start with the observations of the fire fighters who respond to the scene. The fire fighters may not see any obvious signs of arson but may get a feeling that the fire is not behaving normally (Kennedy, 1977) (Battle , 1978) ( French , 1979).

There may be obvious signs of arson such as multiple points of origin or the presence of accelerants. What ever it is that raises the suspicions of the fire fighters at the scene it is their observations that initiate an arson investigation.
At this point the investigation deviates from the procedures used in a normal criminal investigation. In a normal criminal investigation interviewing witness is usually done after the physical evidence is processed (Osterburg & Ward, 2000). In an investigation of a fire where arson is suspected the investigator starts the interviewing of witness and fire fighters immediately (Kennedy, 1977). It is essential for the investigator to interview the fire fighters who were the first to arrive at the fire and those who fought the fire. Fire will often destroy evidence of arson. As well, the water and chemical foam used by the fire fighters may destroy evidence. The first fire fighters on the scene may have noticed evidence that may not exist by the time the fire is extinguished. The arson investigator will ask specific questions aimed at revealing suspicious conditions with in the structure and around the fire scene. The arson investigator will ask the following questions.

What was the color of the smoke? Different substances produce smoke in a variety of colors (Lane, 1992). The color of the smoke can indicate what is burning. The investigator can then determine whether a particular substance would normally be found with in the structure. For example, gasoline produces a yellow or white flame with black smoke (Lane, 1992). Wood produces a yellow or red flame and grey or brown smoke (Lane, 1992). If a burning wooden house is producing thick black smoke this could indicate the presence of gasoline. A large amount of gasoline being stored in a house is unusual and raises the suspicion that gasoline was used as an accelerant.
Were there inoperative hydrants, standpipes alarm systems or sprinkler systems? If there were the investigator will direct plumbing and other trades experts to examine the systems for signs of damage (French, 1979) (Kennedy, 1977).
What was the condition of the doors and windows? Signs of forced entry can indicate an actual break and enter or indicate a staged scene. Doors and windows propped open could indicate an attempt to ventilate the building allowing the fire to spread through out the structure. Doors and windows that have to be forced open could indicate an attempt to hinder the fire fighters. Doors and windows that have been blocked out could indicate an attempt to conceal the fire until it is fully involved (Peige, ed. 1977)
Was there anything strange about the way the fire was burning? Rapid spread of a fire can indicate the use of accelerants. Multiple points of origin, flashes and explosions can also indicate accelerants or incendiary devices (French, 1979) (Peige, ed., 1977)

Where there any familiar faces at the scene? It is possible that the fire fighters have seen the same person in the crowd at several fires. Some arsonists like to watch the fire or help the firefighters. If the fire fighters do notice the same person at several suspicious fires the investigator must try to interview this person as so as possible (Kennedy, 1977).
Did the structure contain business equipment or household items normally expected to be present?
The absence of normal household items or business equipment can indicate that they were removed before the fire started. Removal of these items can indicate that the fire was planned. Removal of sentimental items such as baby picture, school records and valuables can indicate a planned fire. Evidence of pre-planning a fire gives the investigator excellent proof of intent to commit arson.
The Witnesses
It is essential for the investigator to interview any witnesses present when the fire started. The investigator must interview the person how called in the fire immediately even before the fire is extinguished and the physical evidence is processed (Kennedy, 1977). The person that called in the fire may be able to supply the investigator with information such as the color of the smoke and the time that the fire started. The witnesses may have seen people fleeing the scene. The witnesses may have also noticed the smell of accelerants or heard explosions.
Any television stations or newspaper reporters at the scene will also be interviewed. They will be asked to provide copies of video footage or photographs of the scene ( Kennedy, 1977).

The Investigation
Motives for arson can range from attempts to collect insurance money to revenge or intimidation, attempts to cover up a crime, destruction of questionable business records, Pyromania and occasionally suicide (Battle, 1978)(French 1979)(Lane, 1992)
The most common type of Arson is a fire set in an attempt to collect insurance money (Lane, 1992) (French, 1979).
For the purpose of this discussion of an arson investigation I will discuss the steps taken in an investigation where insurance fraud is suspected.
As well as interviewing the firefighters and other witnesses the investigator will conduct a complete investigation into the insurance policy holder’s background and finances (Kennedy, 1977). The investigator will usually start with the insurance agent who wrote the policy. The investigator is looking for evidence of over insured property or recent changes to the policy. The insurance agent may also recall recent questions about the policy the assured may have asked (Kennedy, 1977).
The investigator may choose to hire a forensic accountant to study bank records, business records and tax returns. A certified document examiner may be used to examine business records and documents that may have been altered (Kennedy, 1977).
Records of merchandise received and shipped to the site of the fire will also be examined. The debris from the fire will be compared to the records of the quantity and type of merchandise assumed to have been destroyed in the fire. The intent is to determine whether a loss of merchandise or household items of value actually occurred (Kennedy 1977) (Battle, 1978).

Records of the history of late or delinquent mortgage payments will be obtained. The ownership of the property in question will be established through the mortgage records. As well, liens and caveats against the property will be established through mortgage records (Kennedy, 1977)
A background check of the owner of the property will be conducted. The investigator is looking for signs possible hidden debt that would indicate motive. Possible signs of hidden debt include a history of gambling, alcohol abuse and recent divorces. In Alberta a search for court ordered child maintenance payments should be made as well. In Canada a credit bureau report can be requested. Multiple requests for credit checks will show that the person in question may have been shopping around for credit.
Real estate listings for the area as well as classified ads and real estate sites on the Internet should be examined to see if the property was for sale recently (Kennedy, 1977)
Physical Evidence
Once the investigator has obtained information regarding the evidence that the fire fighters observed and a check of the financial records is complete the investigator will examine the results of the physical evidence found once the fire was extinguished. When examining the physical evidence the investigator must be able to rule out accidental causes of the fire in order to establish that the fire was deliberate (Battle, 1978).
Some of the most common causes of accidental fires are faulty gas or electrical equipment improperly stored material, children, pets, smoking, stoves left on and lightning. Plumbers, Electricians and Gasfitters may be asked to examine these systems for signs that they were faulty (Lane, 1992) These types of fires usually show one obvious point of origin as opposed to multiple points of origin or no detectable point of origin as with an arson fire (Lane, 1992)

Several things are looked for when examining the scene for signs of accelerant use. The first and most obvious sign is the presence of containers in areas where accelerants would not normally be found (French, 1979) ( Kennedy , 1977). A hydrocarbon vapor detector can be used to do the initial examination of the area in question. Once the presence of hydrocarbons has been detected further sampling must be done and sent to the lab for analysis (French, 1979)(Saferstein, 2004).
Liquid when poured on a carpet will soak into the carpet creating a concentrated char pattern on the sub-floor below. Investigators will pull up carpeting and examine the surfaces below the carpet. Samples of the carpet and the floor below will be sent to the lab for analysis (French, 1979) (Kennedy, 1977). Liquid poured on hard surfaces tend to flow. The underlying sub-floor should be examined for charring showing flow patterns. The baseboards and walls should be examined for char patterns indicating liquid was splashed on them. The baseboards and underlying sub-floor should be examined for sign of seepage. Floors below the suspect area should be examined and sample taken. Samples should also be taken of the soil under the foundation (French, 1977)
When samples are taken they are placed in airtight containers. An older method of testing was to withdraw a sample of the air in the headspace’ of the container and test is using gas chromatography (Saferstein 2004). A newer method is to place a strip of activated charcoal in the container. The container is heated to allow the vaporization of any hydrocarbon residue. The vaporized residue is trapped in the charcoal. This method allows the analyst to test much smaller concentrations of residue since it is being concentrated with in the charcoal (Saferstein, 2004)
Incendiary devices can be as simple as a lit match and as complex as a timed system utilizing and electric current imaginable. Common timed devices are candles or lit cigarettes attached to a book of matches (Kennedy, 1977) Cell phones, computers and thermostats can all be rigged to set of ignition of a fire when activated. The key to these devices is for the investigator to determine if they were likely to cause a fire and is the location reasonable. Candle residue in a hallway or closet is not reasonable and raises suspicion. The point of origin must match the ignition source and the ignition source must be in a place in which it would not normally occur to prove an arson has been committed (Battle, 1978).

Arson investigation occurs in a different order than the usual criminal investigation. However the same steps are covered and it is the job of the investigator to analyze all of the information and come to a conclusion. The arson investigator most act swiftly in conducting interviews because fire may destroy physical evidence making witnesses all that much more important. A combination of interviews, background information and physical evidence is used to determine whether a fire is the result of arson or not.