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Forensic Aspect of Arson and Explosion

Patcheappan. S

1 Jun 2022

Every fire or explosion is a unique event with its own set of circumstances, traits, and complications.


Every fire or explosion is a unique event with its own set of circumstances, traits, and complications. Crimes involving arson and explosives are the most complex to process and evaluate among the numerous types of criminal investigations and existing forensic specialties. It requires systematic approach and a deep understanding of fire science [1]. Each case necessitates the meticulous examination and documentation of physical evidence at the site, as well as the production of detailed and timely written investigative reports. Early research on fire identified three pre-requisites to starting a fire – (Fuel, Heat, Oxidiser) collectively termed as Fire Triangle. However, recently researchers point to a fourth element viz. chemical chain reaction, explained by the Fire Tetrahedron [2].

Fire is one of the most frequently occurring disasters in India, especially in the hot dry summer months. According to National Crime Records Bureau, 2018, around 83,872 fire incidents have been recorded in India during the year 2014 to 2018. The Accidental Deaths and Suicides in India (ADSI) Report of 2018 reveals that 13,099 cases of reported fire accidents caused 12,748 deaths and injuries to 777 persons.


The term "arson" is now widely used to characterise a crime involving the deliberate burning of property. It comes from an Anglo-French term that means "to burn," and the common law concept of arson was the purposeful and malicious burning of a dwelling. Arson investigators examine the physical attributes of a fire scene and identify and collect physical evidence from the scene. This evidence is then analyzed to help determine if the cause of the fire was accidental or deliberate. During the scene examination, investigators may find evidence such as accelerants, tampered utilities, and specific burn patterns, which may indicate criminal activity.


Explosion is relating to, characterized by, or operated by explosion. An explosive is a substance, may be an element, a compound or mixture, which is capable of exerting pressure on its surroundings on explosion/transformation. An explosion is defined as a violent and sudden fluid expansion, which determines a huge and rapid rise of pressure in the existing space (air or water) [3]. The main disruptive effects are caused by the movement of great air (or water) masses which provoke a rapid succession of compressive and decompressive waves [4]. Explosions can be triggered by airplane crashes, domestic gas leaks, fireworks and bombs [5]. Chemical devices (bombs) are divided into low-order and high-order explosives on the basis of the speed of detonation: the first ones include black powder and smokeless powder, while the second ones are mainly represented by dynamite, cyclonite, trinitrotoluene, cyclotrimethylene trinitramine, ammonium nitrate-fuel oil and plastic explosives [6].


The fire department's responsibility is to respond to complaints of hostile fires and take immediate action. Generally, the first officials on the scene of a fire are members of the local fire department. Several firefighting assets may arrive and engage in the activities, depending on the severity of the incident. The fire investigation officially begins at this point. They can record the timing of the fire, the fire conditions, the weather conditions, and the point of entry in order to put out the fire. Burn patterns, open doors or windows, alarms, peculiar odours, deep-seated flames, and overall behaviour and conditions should be noted as suspicious or unusual activity surrounding the fire.

A fire department's efforts at the scene can be split into three phases: (1) containment, (2) overhaul, and (3) investigation. The application of water, as previously said, removes one side of the fire "triangle" — heat. The initial purpose of the fire suppression phase is to preserve life; the second goal is to put out the fire and safeguard property. Following the extinguishment of the fire, firefighters will check for hidden flames in walls, ceiling spaces, and other hard-to-reach spots. The "overhaul" phase entails opening walls, removing ceiling materials, and removing floors, among other things, to guarantee that the fire has been entirely extinguished. By doing this, the firefighters may unintentionally change the fire scene. Unfortunately, this change in the fire scene might make the fire investigator's task more difficult. Depending on the jurisdiction, the fire scene investigation can take place concurrently with the overhaul, where the investigators on the scene to guide the overhaul and ensure evidence preservation. The final phase of fire scene activity involves the examination of the fire with the goal of discovering its origin and cause.


Witness interviews, physical examinations, and forensic or engineering analysis are the three main components of a fire scene investigation. Because each fire is unique, as are the circumstances surrounding it, the extent to which each component is involved changes from one fire to another. Firefighters can give investigators with crucial information about the fire site. The ultimate purpose of the fire scene investigation is to determine which fuels caused the fire and where the fire started. The ignition source must have the ability to ignite the suspected initial fuel. The fire investigator is responsible for examining these patterns and assigning appropriate significance to them. To do so, the investigator needs to have a thorough understanding of fire physics and chemistry, as well as heat transport modes: radiation, convection and conduction.

Two Primary Reasons for Fire Investigation

1. to determine what caused the fire

2. to identify and collect any evidence related to that cause.

The "point of origin" is the location where a fire started in a fire investigation. This could be a specific location or a broad area. To adequately pinpoint the fire cause, the site of origin must almost always be precisely determined. When the point of origin is found, it can either confirm or refute the assertions of the owners, occupants, witnesses, and suspects. The appropriate recognition, identification, and analysis of fire patterns is one of the most critical components of any fire investigation.

Investigators perform the following tasks at the crime scene:

– Locate the origin of the fire or explosion. – In the case of fire, look for devices and containers used to ignite and/or spread the fire. – In the case of explosion, look for detonating mechanism and use dogs or a vapor detector to find residue. – Look for accidental causes as well as evidence of foul play. – Make notes, draw sketches, and take photos of the evidence. – Pack evidence in airtight containers to prevent evaporation of residues.

When the evidence has been recovered from the crime scene, work begins in the lab to reconstruct the event that produced the destruction. Arson and explosion investigators analyze residues to get information about the accelerants or explosives involved in the crime. They often perform carefully planned control experiments to try to recreate the crime, especially when they need to test different hypotheses about the events.

The arson and explosion investigator takes detailed notes during every step of the process. These notes are used to write a full report about the analysis and its conclusions. If the evidence from the analysis is used in a case that goes to trial, the arson and explosion investigator may be required to testify in court about the work. Arson and explosion investigation is an inspiring field of forensic science that will continue to provide exciting career opportunities well into the future.


Charring, oxidation, deformation, melting, colour changes, and structural collapse are all examples of fire patterns that can be seen or quantified after a fire. The borders delineating the varied amounts of heat and smoke as they influence various items at the fire scene are the lines or zones of demarcation found on vertical and horizontal surfaces following a fire.

The basic goals in understanding the origin and cause of a fire are to recognise, identify, and investigate fire patterns. The visible or measurable physical impacts that remain after a fire are known as fire patterns. Fire patterns are divided into two categories, both of which are influenced by the chemistry and physics of fire, as well as the construction process. Fire's chemistry and physics produce a variety of patterns with specific geometries or forms.

“V” Pattern

A common fire pattern shape displayed on vertical surfaces is the "V” pattern. The angled lines that produce the "V" can often be traced back toward a point of origin.

Place Where Hyderabad rape victim body was burned Hyderabad vet rape-murder, Times of India,

The larger the angle of the "V," the longer the burned material has been heated. For a comparable heat source and burn time, the angle formed on a vertical combustible surface will be wider than on a non - combustible surface. A fast-burning fire is believed to form a narrow-angle "V" pattern, whereas a slow-burning fire produces a wide-angle "V" pattern. This is incorrect, because the angles of the lines in the "V" pattern are determined by the size of the fire, its burning pace, ventilation, and the wall's combustibility. These patterns are valuable for investigation because they show the direction in which fires spread rather than what caused them.

Inverted Cone Patterns

Inverted cone patterns, also known as inverted "V" patterns, are triangular patterns that are broader at the bottom than they are at the top. Inverted cone patterns are caused by flames that are very short-lived and do not fully develop into floor-to-ceiling name plumes or flame plumes that are not constrained by ceilings. They were supposed to be caused by fast-burning fires since they frequently appeared on non-combustible surfaces. The right interpretation of such patterns is that the fire was short-lived. Inverted cone patterns have also been interpreted as evidence of a liquid accelerant fire, but they can be produced by any fuel that produces flame zones that do not become vertically confined. The flame zone and the plume of hot gases combine to create hourglass patterns. The flame zone is shaped like an inverted "V," while the plume of hot fire gases is shaped like a "V."

Scientific Protocols for Fire Investigation, 2nd Edition by John J. Lentini. Reproduced by permission of Taylor and Francis Group, LLC, a division of Informa plc.

Truncated cone patterns

Truncated cone patterns (also known as truncated plumes) are three-dimensional fire patterns that can be seen from both horizontal and vertical angles. At the intersection of two vertical surfaces, this pattern appears.

Scientific Protocols for Fire Investigation, 2nd Edition by John J. Lentini. Reproduced by permission of Taylor and Francis Group, LLC, a division of Informa plc.

The cone-shaped pattern is caused by the fire plume's natural expansion as it rises, as well as the horizontal distribution of heat energy when it collides with a horizontal surface, such as a ceiling. Round patterns are prominent at fire scenes, and they usually depict areas that were shielded from the flames by circular items like wastebaskets or the bottoms of furniture. Patterns on floors and floor coverings that were irregular, curved, or pool-shaped used to be regarded proof of the presence or usage of a liquid accelerant. While such patterns can be caused by an accelerant, visual observation alone does not necessarily provide a reliable answer. These patterns are highly common in post-flashover flames, fires that take a long time to extinguish, and structure collapse. Radiant heat, blazing and smouldering trash, melting plastics, and ignitable liquids can all cause them. Supporting evidence, such as the use of a flammable gas indicator and/or chemical analysis of debris for residues, or the presence of liquid containers, should be sought if the presence of ignitable liquids is suspected. When employing flammable gas indicators, be in mind that many plastics emit hydrocarbon smells when they pyrolize or burn. When no ignitable liquids have been utilised, these gases may have an odour similar to petroleum products and can be identified by a combustible gas detector.

“Hourglass” Pattern

M. Mangione F. Bontempi C. Crosti, “Structural Fire Investigation and Forensic Engineering”,

Patterns can also be in the shape of an hourglass, particularly when a pool of liquid fuel burns adjacent to a vertical surface, as shown in Figure.


Major complications in fire investigations are:

1. A fire can be a complex event whose origin and cause are not obvious. Investigators may have to expend considerable time and effort before the cause can be identified. Without gathering data, the investigator can only guess at what might have caused the fire, based on circumstances alone. The training and preparation of qualified investigators are often costly and time-consuming, requiring dedication to the profession over many years.

2. The destructive power of the fire itself compromises evidence from the outset. The larger a fire becomes and the longer it burns, the less evidence of causation will remain. In some fires, sufficient data to establish the origin and cause (i.e., evidence) do not survive, no matter how diligent the search or well prepared the searcher.

3. The complexity of the threat a major fire presents to the health and welfare of the community. The presence of so many people, in addition to members of the press and the public who were attracted by the sights and sounds of a major fire, offers yet more chances for scene security to be compromised and critical evidence to be contaminated, moved, or destroyed.

4. A lack of commitment to conduct fire investigations exists on the part of some law enforcement. These are the major impediments of investigations in case of fire.


The chemical analysis of fire debris is usually the extent of laboratory-based arson inquiry, which is used to assist field investigators in determining whether a fire is intentionally set (arson) or accidentally set (accident). The scientists and engineers who do laboratory experiments to verify the field investigators' hypotheses have a gap between them and the field investigators, most of whom have practical experience but a limited comprehension of scientific principles. However, the gap is progressively narrowing.


[1] Jose R. Almiral & Kenneth G. Furton, ‘Analysis and Interpretation of Fire Scene Evidence, 1st Edition, CRC Press:2004.

[2] “Bandyopadhyay, C., & Manna, M. (2020). Fires in India: Learning Lessons for Urban Safety. New Delhi - 110001: National Institute of Disaster Management (NIDM); Ministry of Home

[3] Wolf SJ, Bebarta VS, Bonnett CJ, Pons PT, Cantrill SV. Blast injuries. Lancet. 2009; 374:405–415.

[4] Arnold JL, Halpern P, Tsai MC, Smithline H. Mass casualty terrorist bombings: a comparison of outcomes by bombing type. Ann Emerg Med. 2004; 43:263–273.

[5] Arnold JL, Halpern P, Tsai MC, Smithline H. Mass casualty terrorist bombings: a comparison of outcomes by bombing type. Ann Emerg Med. 2004;43:263–273.

[6] Galante, N., Franceschetti, L., Del Sordo, S., Casali, M. B., & Genovese, U. (2021). Explosion-related deaths: An overview on forensic evaluation and implications. Forensic science, medicine, and pathology, 17(3), 437–448.

Author S. PATCHEAPPAN is Assistant Public Prosecutor (APP), Puducherry

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