Arson or accident ? How do fire investigators decide?

Arson or accident? Arson is defined as intentionally setting fire to any property, either personally owned or belonging to someone else.

Arson or accident ? How do fire investigators decide?It is the job of a fire investigator to decide whether a fire was due to accidental causes or deliberately set, which is a criminal offence. Investigating a fire, however, is a quite complicated task due to certain factors.

Firstly, fires are destructive by nature so most of the evidence is usually destroyed especially if detecting the fire and extinguishing it were delayed. Moreover, extinguishing a fire requires large amounts of water being used through pressure hoses to extinguish the fire and this further disturbs the crime scene.

Correctly concluding arson is even more difficult due to the faulty science which has plagued this field for a long time. Hundreds of people all over the world have been wrongfully convicted due to the myths regarding the signs of arson, and these myths have only recently started getting debunked.

Now a days, more accurate protocols for fire investigations exist but even then, it is important for the investigator to analyze individual cases in depth from every angle and not just accept the easiest explanations.

The aim of examining the scene and collecting physical evidence in a case of suspected arson has three aspects. Firstly, it is important to determine where exactly the fire started. Secondly, it should be established whether the fire was intentionally set or not.

Finally, if the fire is determined to have been set deliberately, the arsonist has to be connected to the crime scene. In determining whether the fire was accidental or intentional, some evidence of the cause will usually be found at its source.

The most common accidental causes include faulty cooking and heating systems, malfunctioning electrical equipment and appliances, careless smoking, children playing with matches or lighters. A fire can also result due to natural heat sources, such as lightning, spontaneous combustion, convex lens effect on sunlight.

The absence of a natural cause, or an accidental cause leads to the assumption of arson. One of the first things that an investigator has to do in a fire investigation is to locate the point of origin of the fire. Only when the origin is known can possible causes be analyzed accordingly and eliminated.

When all relevant sources of information (fire patterns, witnesses and other relevant people, heat distortion) on the fire have been exploited, the fire’s point of origin can be found. Multiple low points, which signify possibility of multiple origins, are very suspicious. They signal an intentionally set fire.

Questionable sites include: attic, a closet, bathroom, crawl space, the area under the stairs. This is because accidental fires in such locations are not common. Things like fire patterns and heat distortion can be used to discover point of origin.

Fire normally shoots upward and fans out, often showing as a “V” pattern left after the fire is put out. When the “V” or a cone pattern is distinctly located, the bottom of the cone sometimes points to where exactly the fire started, or to where the fuel was burning. An ignition or fuel source may be found at the base of a “V” pattern.

However, obstructions to the spread of fire can prevent a fire from spreading in a normal pattern. For example, strong drafts from windows and elevator shafts can distort the shape of the “V”; and, as a result, the configuration of its fire pattern is altered.

Direct flames or build-up of atmospheric heat can alter objects, thereby showing telltale signs on materials (such as plastic) that partially melt, fuse, or crack when exposed to intense heat. Thus, the direction of fire travel can be established through the deformation of some objects by heat.

For example, the glass cover of a light bulb can be partially melted, and the distorted form that results will point in the direction of the fire.

The best indication that the fire was intentional is the presence of accelerant residues at the crime scene, Accelerants can usually be detected at the scene of a crime by visual inspection, by odour, or by means of instrumental devices. Gasoline, is the most common accelerant, and has a very clear odour.

Other fuels like turpentine and kerosene are also readily identified by their distinctive odours. The sense of smell, however, can be easily dulled and it is not always accurate. A more accurate method is the use of scientific instruments. There are many instruments available for the detection of accelerants.

The catalytic combustion device is the most common instrument employed to detect flammable vapors and is commonly called a sniffer. Pour patterns can also indicate use of accelerants. Pour patterns are a kind of fire pattern that results from pouring an accelerant onto the floor of a room and are particularly important as evidence of use of accelerants.

Fire investigations also involve interviewing witnesses and first responders. Firefighters in particular are able to pinpoint the origin of fires most of the time. Based on past experiences, they also happen to be the first to suspect arson and quick to recognize the unusual.

Giving voice to their suspicions, they will note: flame height; how rapidly the fire expanded; smoke density, and any odd color of the smoke; odor redolent of organic accelerants; fire doors that are open but should be shut; and boxed merchandise blocking passageways and doors.

They will recall having responded previously to alarms from the same location, and whether a fire benefited the owner. A failed fire alarm or sprinkler system certainly will give firefighters pause (later, the investigator should have such equipment checked to see whether it was tampered with).

Analyzing possible motives why someone would set fire to that particular property is another aspect of fire investigations. The motives for committing arson are many, but they can be summed up as follows: spite, profit, revenge, pyromania, and vandalism.

Usually, the motive is quite personal. When the motive is identified, it prompts the investigator to search records, bank statements, surveillance videos etc.

All of the above elements of fire investigation, if carried out properly, can help the investigator decide whether the fire was an accident or a case of arson.

Authors; Wajeeha Naeem from Kinnaird College for Women.

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