Arson Investigation
ARSON
Understanding behavior of fire and people is a good foundation for basic
Some arson investigators have reservations about examining the circumstances surrounding a fire. This is often due to a lack of understanding the natural behavior and characteristics of a fire. But any diligent investigator can master the science of fire investigation. A working knowledge of basic investigative skills, with an understanding of fire behavior and fire science are the keys to success.
The incidence of arson has tripled in the past 10 years. It has become the most expensive property crime per incident in this country. It is estimated that an arson fire occurs 100 times an hour of every day. Before an investigator can inspect a fire-gutted building to determine the point of origin and cause, he must be familiar with the basic properties and behavior patterns of a fire.
The three ingredients of fire are heat, fuel, and oxygen. But a great deal of time in the fire investigation will be spent trying to determine the heat and fuel sources.
Heat is produced in several ways. One is chemical, or oxidation. Fire is an example of rapid oxidation. A second manner is electrical. Current flowing through a conductor may produce arcing, sparks, or electrical shorts. A third method is mechanical, or friction such as is caused by metal rubbing against metal.
In addition to determining the source of heat energy, one must determine how the heat energy was transferred from one material to another. Heat is transferred by conduction, radiation, and convection.
Conduction refers to the passage of heat through one material to another. It requires direct contact between the two materials. The amount of heat that is conducted (or transferred) depends on the thermal conductivity of the materials and the degree of heat.
Radiation is transference of heat by rays or waves. Heat rays from the sun is an example of this type of transfer. Convection is the heating of a circulating medium, usually a gas or liquid.
The second component of fire is fuel. Fuel exists in all three physical states: gas, liquid, and solid. Usually, only gas will burn. For a solid or liquid (such as gasoline) to burn, sufficient heat must be supplied to liberate and then to ignite their flammable gases.
The third component, oxygen, comprises 21% of the air around us. There is sufficient oxygen in the atmosphere to support combustion and ignition. A fire will subside if the oxygen content in the air surrounding the fire drops below 16%. A fire in a closed room, such as a closet with a tightly sealed door, will continue to smolder until it has exhausted its oxygen supply.
The movement of a fire is well documented. Fire usually burns upward and outward in a “V” or cone pattern. The base of the cone pattern is significant, as it will determine the fire’s point of origin. In a structural fire, all low points of burning must be noted, as the
If the fire is blocked by a ceiling, the fire will move laterally across the ceiling and will then roll down the opposite wall, as it was again blocked. As the fire originally spread upward along the first wall it will then spread laterally as it travels upward. But any lateral movement of the fire at the base of the “V” is cause for further investigation.
Any downward burning of a fire which is equally unnatural, should also be closely scrutinized. However, this is not to say that a fire will never burn downward. It will at times, but at a much slower rate. A common example of downward burning is a household paper match. Downward burning can be caused by several conditions. A specific draft condition may exist at the time of the fire, forcing it downward. If the fuel source above the main body of the fire becomes consumed, the fire will seek other fuel sources. The use of an accelerant also can cause the downward movement.
The range of temperatures of the fire can be determined by examining the glass and metal objects subject to the effects of heat. Pieces of fused metal and molten glass in the fire debris are heat indicators. If the type of metal is identifiable, the investigator will know how hot the fire was at a particular point, based on the metal’s melting temperature. A heat picture is drawn by examining debris from several locations within the rubble. Below are several common materials and their fusing temperatures.
The color of the flames is also used to determine the temperature of the fire. Different flame colors radiate different amounts of heat. Some common colors and their corresponding temperatures are listed below.
The investigator’s job is to arrive at the truth. He must determine the cause of the fire and decide whether or not it appears suspicious. To do this he must determine several facts by developing and evaluating various sources of information. The investigator must probe these sources and the fire scene itself quickly in order to gather as much pertinent information as possible.
The investigator must know the contents of the building and if it was used for commercial purposes. The owner or occupant of the building should be present for questioning. The amount of insurance should also be determined, as well as how recently the policy was obtained. Another important question is who called the fire department, and what connections, if any, did they have to the owner or occupants of the building. The firefighters should be questioned to determine the condition of building security when they arrived at the scene. An open or unlocked building indicates unnatural access and the possibility of arson.
It is also important to find out if the spread of the fire was normal and consistent with the construction and design of the building. Were there any unusual odors, flame colors, or smoke? Was the stock of the building usual and customary stock with this type of business? Was there an alarm and/or sprinkler system? Were they working? These questions should be answered in the course of the investigation.
The cause of the fire must eventually be resolved. There are four recognized causes: providential, incendiary, accidental, and undetermined.
In determining the cause, the first examination should be an exterior one. This allows the investigator to inspect the burn patterns visible at the roof level and above windows and doors. Unusual burn patterns on external walls below windows should be surveyed closely. The investigator should look for the area of the heaviest damage, as this is an indication of the longest burning time. This may well be the point of origin and should be the location to begin the interior examination.
The interior inspection should start in the room or area where the damage is greatest, as this is most likely the point of origin. Some rooms, however, will appear to have a demarcation line running horizontally around the walls. The ceiling and upper walls may appear to be fire damaged, while the floors and lower walls are relatively unscathed. This is probably due to the effect of hot gases (in excess of 1,400°F) entering the room from the point of origin. In all likelihood, flame did not enter the room at all.
Bare light bulbs that have survived the fire are excellent indicators of the direction of heat flow. A light bulb subjected to high temperatures tends to expand in the direction of the heat source.
The investigator must make a visual inspection to determine what sources could have caused an accidental fire. The most likely sources are portable heating units, a furnace or boiler, any open flame (candle), fuse box, circuit panel, electrical wiring in the most damaged area, and any gas or electric appliance.
Once the investigator has determined the room of origin in his interior inspection, he must then resolve where in that room the fire began. Certain material evidence may indicate that the fire was incendiary.
The most obvious indicator will be the discovery of a “plant” or booster. A plant is used to increase the volume of fire in an area, and may consist of paper or clothing soaked in an accelerant, or matches, or other flammable material.
An unusual burn pattern may indicate the use of a trailer. A trailer is used to spread the fire from one area to another, where another plant may be located. The trailer usually consists of clothing, paper, rope, packing material, or even toilet paper.
The discovery of an electrical or mechanical time delay device should be noted. These devices are used to delay the ignition of the fire, usually to allow the arsonist to place himself at another location distant from the fire in order to establish an alibi.
Another sign of arson is multiple points of origin. This is a virtual certain arson indicator. An accidental fire does not start in several locations within a structure at the same time.
The next step in the investigation of the fire’s cause is to search for the source of the heat and fuel.
There are several possible aspects that should be noted, as they may confuse the investigator. The first is the “chimney effect.” This is the natural tendency of heat to flow upward. Fire travels upward rapidly, and in so doing may cause greater damage at a later stage of the fire than it will at the point of origin.
The second is the “puddling effect.” When a liquid accelerant is poured onto a floor, gravity causes the liquid to seek its lowest level. Thus, the liquid will run down between floorboards and possibly into a basement or under the house. When the liquid accelerant is ignited, it will burn up through the floor from underneath.
When a liquid accelerant (or any liquid) is poured onto a floor, some of it will splatter or run in “finger” patterns. When this is ignited, it will burn in this pattern. This is known as a “splatter effect.”
When high temperatures, in excess of 1,800°F, are directed against a brick or cement surface, they leave a sign referred to as “spalling.” This is caused by the high temperature breaking down the tensile strength of the mortar or brick and causing the leaded surface to become lighter in color.
Once arson has been determined as the cause of the fire, a motive should then be determined. There are as many motives as there are incendiary fires, but the following are some of the most common motives for arson.
- Probably the most common is for profit. Due to the payment of large amounts of money by insur-
- ance companies there is a probability of high profit with low risk. This motive is found in a business owner who is suffering monetary losses, or a homeowner facing financial problems. A motive can be established if the owner has a prior history of setting fires. The absence of furniture or stock in a building also can indicate that fraud or profit was a motive. If the insurance coverage was greatly increased just prior to the fire, or if it can be established that the owner had a sudden need for cash (gambling or other debts, or medical costs), that can also indicate a motive.
- Another common motive is revenge, which can be spurred by spite, jealousy, or anger. It can be established by questioning the victims of the fire and related sources of information.
- Criminals often set fire to a house or a business to conceal a crime such as burglary or murder.
- A man who is in trouble with the Internal Revenue Service may set fire to his home or business to “destroy “records that never existed.
- Juveniles often set fire to schools, vacant buildings, and garbage cans for excitement.
- A psychotic or pyromaniac has motives known only to himself for fire setting. A pattern sometimes emerges after these individuals have started several fires. In addition, the arsonist often appears at the scene, and many arrests have been made after an alert firefighter recognized a familiar face at various fire incidents. This recognition usually occurs when several fires take place within a short period of time. Photographers taking pictures of bystanders at the scene have turned up pictures of the same individual at several fires.
It is not always possible to determine the cause of a fire. Even if accidental causes are ruled out, every fire cannot be linked with a motive and suspect. The above suggestions and methods will help any investigator to effectively examine the facts at the scene. With diligence and a knowledge of the basics of fire behavior, arson can be better spotted and arsonists identified. It will take the cooperation of both fire investigators and insurance companies to combat the growing problem of arson.
