Fire & Arson Investigation


It is the crime of intentionally setting fire to buildings, vehicles, or other property to cause damage. This also includes a set of fires to others’ property or sometimes to own property to advantaged insurance facilities.

The lightning of a fire – It is the essential element of arson, in the absence of fire lit, there is no arson.

Intention or willfulness – This does not include fire caused by natural causes or accidents.

Malice – this does not include fire i.e. intentionally set with positive intention and property.

A definition of arson must include the element of intent. People start fires intentionally for a variety of reasons, including those that are legitimate and legal.

Fire follows the well-defined principles of burning. It produces heat, flame, smoke, and gases. The byproduct in combustion processes may or may not be seen readily. The term “flame” refers to both an open flame and a smoldering glow. Smoke is made up of condensed vapors and very fine solid particles. The composition of fire gases emitted by the burning materials. These depend on the chemical makeup of the burning material, the amount of oxygen available during burning, and the temperature of the fire.

Most fire gases are highly toxic. They are the biggest cause of fire deaths. This includes carbon monoxide not because it is very toxic but due to its abundance. Carbon monoxide causes unconsciousness and, eventually, death, when breathed in quantity. At lower concentrations, it results in disorientation and confusion and may cause other health hazards to victims. Carbon dioxide is the second most dangerous gas produced by a fire. A 2% increase in carbon dioxide in the air causes a 100 percent increase in a human’s breathing rate, which is not harmful.

Fire burns up and out. On walls and vertical structures, it leaves a V-shaped char pattern. A fire that is hot and fast at the point of origin will leave a sharp V pattern. A slow fire will produce a shallow V. While burning, if fire interacts with an obstruction, for example, a ceiling then it will burn across it and look for a place to go up. Fire travels in the direction of air.

Motive of Arson

A few of the reasons for arson are given below:

• Financial gain (Insurance Claim)
• Vanity
• Revenge
• Civil Disorder
• Crime Concealment
• Delinquent Behaviour
• Excitement
• Pyromania
• Dowry Death
• Communal Purposes

Chemistry of Fire

Fire is a chemical process that occurs when fuel, heat, and oxygen are mixed in an uninhabited chain reaction. To stop the burning of fire, out of the three elements present in the fire triangle should be removed. Remove any one of the elements and the fire goes out. Because you have stopped the continuing chemical reaction. Because only gases burn, solid and liquid fuels must be heated until they become vapor before they can burn. Heat decomposes a fuel chemically into its gaseous components. This decomposition is known as pyrolysis.

For Example: When wood is heated, it pyrolyzes to form hydrogen, oxygen, ethane and methane gases, and methyl alcohol. It is these highly flammable vapors that burn. Fuel in vapor form, such as natural gas, does not need to be pyrolyzed in its natural state. The majority of fuels are carbon, hydrogen, and oxygen molecules with traces of mineral materials. Fuel in vapor form, such as natural gas, does not need to be pyrolyzed in its natural state. The majority of fuels are carbon, hydrogen, and oxygen molecules with traces of mineral materials. When the fuels burn completely and freely in the air, the carbon reacts with the oxygen, forming carbon dioxide, and the hydrogen combines with the oxygen, forming water vapor. The mineral matter remains behind as ash. As the oxygen in the fuel goes out, oxygen from the air is drawn in to continue the reaction. Mainly the fire spreads by transferring heat energy in three ways i.e. Radiation, Convection, and Conduction.

Elements of Fire


This is anything that will burn. Fuel must be available for ignition. It may be in the form of a solid, a flammable liquid, or a gaseous state. Solids may be wood, cloth, or paper. Kerosene, oil, and gasoline are examples of flammable liquids. Paint, gasoline, and other combustible compounds produce gaseous vapors. It’s critical to realize that flammable substances are surrounded by invisible, potentially dangerous fumes. Other flammable elements in a gaseous state include natural gas and propane.


This is needed for combustion. To remain in a state of combustion, fires need oxygen (burning). Smoke and toxic gases are also produced by fires.


Combustible materials may catch fire at ignition temperatures. Heat is needed to start a fire. The combustion temperature for many household objects is between 400 and 600 degrees Fahrenheit. Some materials are more sensitive to ignite than others.

Major Principles:

1.Fuel, heat, and oxygen are essential for combustion (burning).

2. Fuel must be ignited before it will burn.

3. Fire will not burn materials like wood, fabric, or paper until there is a reaction. Fires depend on chain reactions to develop. The fire will be altered or extinguished if the reaction is interrupted.

Combustion Comprises Three Stages:

The burning process is divided into different phases. A firefighter must be able to distinguish different phases of fire in understanding the various levels of burning fires and fight them with various instruments.
These phases are classified based on atmospheric conditions.

• Incipient/Initial Phase (Growth Stage)

This is the first phase, during which fire creates water vapor, carbon dioxide, sulfur dioxide, carbon monoxide, and other gases. The oxygen level of the air is also lowered during this period, leading to the fire. The fire may have a flame temperature of well above 1,0000 F (5370C), but the temperature in the room may have just slightly raised at this point.

• Free-Burning Phase (Fully Developed Stage)

The second phase of the fire involves all of the fire’s burning activities. In this phase, oxygen-rich air is taken into the flame, and convection carries heat to the top layers. The heated gases spread out from the top downward, resulting in a higher concentration of colder air at low levels and combustible material ignition. Firefighters are taught to stay low and utilize protective breathing equipment because of the hot air.

The lungs might be burned by just one breath of this super-heated air. The temperature in the upper regions can reach 1,3000 F at this stage (7000C). It starts to progress in the latter stages of a fire, and oxygen is continuously consumed by it until there is insufficient oxygen to react with the fuel. The fire is then reduced to a smoldering phase, needing only an oxygen supply to burn quickly or explode.

• Smoldering Phase [decay stage]

The flame may extinguish in the third phase if the confinement area is sufficiently airtight. Burning is reduced to glowing embers in this case. The chamber fills up with dense smoke and fumes, which are forced through all cracks under pressure. At a temperature of far over 1000 degrees Fahrenheit, the fire will continue to smolder, filling the room with dense smoke and combustion fumes. Lighter fuel fractions such as hydrogen and methane will have evaporated from the combustible material in the room due to the intense heat. These fuel gases will be added to those produced by the fire, creating a greater risk to firefighters. It creates the possibility of a backdraft.

Class of Fire


Any substance that contains a burning ember or leaves ash can be involved in a class “A” fire. Wood, paper, and pulp are examples of class “A” fires. The most common way for putting out a class “A” fire is to eliminate the heat. Although water is the most common agent, other agents such as foam and dry chemicals can also be used effectively.

• Class ”B” fires

A combustible liquid or gas is involved in a class “B” fire. Gasoline, oil, propane, and natural gas are all common examples. On flammable liquid fires, a range of fire extinguishing products are used, and all theories of fire extinguishment are used. The best agent to use will be determined by the circumstances. Flammable liquids do not ignite when they are in their liquid state; rather, the vapors produced by these liquids ignite. To start the combustion process, a mixture of oxygen and flammable vapors in the proper proportions simply need an ignition source.

• Class “C” fires

Live electrical equipment is involved in Class “C” fires, which require the use of an extinguishing agent and extinguisher that will not carry electricity back to the firefighter. Electricity is a source of energy and an ignition source, but it does not burn by itself. Instead, the live electrical equipment could become a source of ignition for a class A or class B fire, such as insulation or packing.

• Class “D” fires

Exotic metals such as titanium, zirconium, magnesium, and sodium are used in Class “D” flames. Special chemicals, such as dry powders, and special application techniques are required for these flames. Extinguishing agents and techniques for class “A,” “B,” or “C” fires will not work on class “D” fires, while agents and techniques for class “D” fires will not work on any other classification of fire. Many common agents, such as water, will react with burning metals and vastly increase the fire’s intensity.

Process Of Fire Investigation

It’s nearly tough to preserve proof of arson. Any potential proof of arson will almost certainly be destroyed by the fire itself, and if that isn’t enough, the water and chemical foam used to put out the fire can also eliminate evidence.

In order to detect and perhaps identify ignitable liquid residues (ILRs) on seized evidence (such as jerry cans or clothing) and fire debris samples, forensic investigators must use cutting-edge analytical techniques. Determining the presence, absence, and likely source of ILRs on burned material, mainly in wildland and bush fires, is extremely difficult.

The principal witnesses, the firefighters who arrive first at the scene, are an important source of evidence in these situations. A fire investigator will make a mental note to inquire about the colour of the smoke, the state of the windows and doors, any damaged sprinkler systems, and whether the flames are somehow different.

The following are some crucial points to remember:
• Wind conditions;
• Color of smoke;
• Rapidity of spread;
• Initial observations of people at the scene;
• Means of entry;
• Mumber of areas of fire;
• Intensity of heat;
• Unusual odors);
• Condition and contents of the building (furniture, closets, holes in floor, sprinkler system operation, fire doors);
• Possible ignition devices;
• Trailers; and
• Condition of appliances and electrical system.

Finding the location of origin and any obvious physical evidence will be the most important aspects during the inquiry. Arson can be proven with the use of scientific methods.
A five-step process that law enforcement agencies must follow in the case of arson is following:

1.Arrival at the Location

“As first responders approach a fire scene, they should observe and mentally note the following conditions and activities, and finally start permanent documentation of the information.”

2. Assessing the Situation

Investigators should meet with first responders after the situation has been secured and covered to analyse previous events and the present status of the fire scene, make introductions, identify critical persons, and determine scene safety and integrity issues.

3. Photographing the Scene

The scene must be documented after the lead investigator has reviewed it. This enables for the permanent storage of the scene’s original state in the event of tampering or moving evidence around. Later in the investigation, photos and videos can be used to search for clues and evidence that the investigator may have missed on the scene.

4. Analyze the Information

Investigators must locate, gather, and preserve evidence, as well as protect it from contamination, package and transport it, and establish and maintain the chain of custody. Investigators must physically comb through the scene and collect any materials they feel pertinent to the inquiry in order to identify, collect, and preserve the evidence.

5. Completing The Investigation

Investigators are required with performing the final steps in their investigation once the scene has been secured, documented, and cleansed of all pertinent evidence. Investigators must ensure that they have collected all feasible evidence, appropriately recorded the scene, and removed any objects or things used in the investigation before they can release the scene.


Hammett, Theodore M. and Kimberly A. Wylie (l987a). Issues and Practices: Toward Comprehensive Arson Control Programs.

Hammett, Theodore M. (1984). Arson Investigation and Prosecution: A Study of Four Major American Cities. Ku, Richard,

Theodore M. Hammett, et al., 1980. Arson Control: A Synthesis of Issues and Strategies Based on the Arson Control Assistance Program.

Factory Mutual System, A Pocket Guide to Arson Investi ation (2nd edition: Norwood, MA, 1979. Available from Factory Mutual Engineering and Research, 1151 Boston-Providence Turnpike, Norwood, Massachusetts 02062.

Gaensslen, R.E. and Henry C. Lee, Physical Evidence and Forensic Science, (2nd ed.: American Insurance Association, 1986).

Gelband, Barbara (I980). “The Prosecutors Role in Fire rnvestiga tion.” Presented at National College of District Attorneys Seminar on Arson Investigation and Prosecution

Pisani, Angelo (1982). IIIdentifying Arson Motives,” Fire and Arson Investigator 2l(June 1982), pp 18-24.

U.S. Department of the Treasury, Bureau of Alcohol, Tobacco and Firearms, Arson Case Briefs (Washington, November 1985). Available from BATF Explosives Division, Arson Enforcement Branch, 1200 Pennsylvania Ave., N.W., Washington, D.C. 20226).

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