List and explain the various clues that flames and smoke can offer the investigator in an arson investigation.

Expert Answers

An illustration of the letter 'A' in a speech bubbles

Both the flame itself and the smoke associated with a fire offer important clues as to the nature of the fire. Different substances, whether wood, plastic, gasoline, kerosene, etc., burn differently, and each produces a distinctive flame and smoke. While the obvious first priority of a fire company responding to...

See
This Answer Now

Start your 48-hour free trial to unlock this answer and thousands more. Enjoy eNotes ad-free and cancel anytime.

Get 48 Hours Free Access

Both the flame itself and the smoke associated with a fire offer important clues as to the nature of the fire. Different substances, whether wood, plastic, gasoline, kerosene, etc., burn differently, and each produces a distinctive flame and smoke. While the obvious first priority of a fire company responding to an alarm is to extinguish the flames and extract any people (and animals) found within the burning structure, attention is also paid to the physical characteristics of the fire. Just as household fire extinguishers are rated for different types of fire (e.g., electrical, wood, grease and oil, etc.), so are structural fires to which fire fighters respond diverse in terms of cause and effect.

Materials used in the construction of buildings, as well as substances found in nature, all have some chemical composition that distinguishes them from each other when burning. Wood, for example, contains carbon and oxygen that burn blue, as well as sodium, which burns orange. Fires also vary in temperature, with colors emitted reflected in the spectrum—blue-violet flames the hottest and red on the cooler side of the spectrum. Because different materials, comprised of different chemical compositions, burn differently—some hotter than others, some burning out quicker than others, etc.—there is abundant evidence to be identified in what can be observed while extinguishing a fire.

When responding to a fire, fire fighters try to locate the source, which is both vital to their ability to extinguish it and to identify the cause of the fire. Skilled arsonists will usually attempt to obscure the physical evidence they know will exist, but the presence of unusual fuels in a given location as well any tools (e.g., matches or electrical wiring used to start a fire, especially a fire the initiation of which is deliberately timed to begin well after the arsonist has departed the location) can often, but not always, be identified and provide clues for a subsequent investigation.

The National Criminal Justice Reference System provides an abstract, a link to which is below, that summarizes the association of smoke color and fuel. The details in this paragraph are consistent with those found in other sources (also linked below):

Most fires involve carbonaceous fuels such as wood, paper, plastics, petroleum, or textiles. When these fuels do not burn completely because of a deficiency of oxygen, the conversion of carbon into carbon dioxide and water is impeded; and free carbon, or soot, appears as smoke. Some fuels, such as alcohols and cellulose (cotton or paper, for example), contain oxygen and tend to burn cleanly when air diffuses into the flame. Insufficient oxygen can also lead to a yellow flame because unconverted carbon particles glow yellow hot. In addition, many common materials contain some sodium or other elements that give yellow or other colors to flames. Whether a flame is light yellow, orange-yellow, or reddish depends on the temperature of the flame. The hotter the flame, the lighter the color. White or light gray smoke is usually associated with paper, straw, leaves, or wood. It is formed of pyrolysis products (gasses, liquids, and tars) that condense to form a fog of tiny droplets that bypass the flame. Other sources of white smoke include burning phosphorus, magnesium, and some other metals, but fires containing these elements in sufficient quantity are rare. Most fires will produce a mixture of black, gray, and nearly white smoke because of the variety of fuels and the variability of air supply.

Smoke is, as noted, an important clue as to the origins and stage of a fire. The longer the fire has burned, however, the more difficult it is to identify the primary materials that mark the fire’s origins. This is because the longer the fire burns, the more it spreads and the more diverse the items with which it comes into contact. Additionally, the process of extinguishing a fire can contaminate physical evidence, as chemical foams used by fire fighters can obscure chemical residues used in igniting the fire. Black smoke is usually associated with gasoline; brown smoke with wood; white often suggests the early stage of a fire which has not yet begun to consume wood, plastics, etc.; grey indicates that the temperature of the fire is dropping because the fire is being extinguished, perhaps due to a lack of oxygen but more likely to the efforts of the fire response team.

Approved by eNotes Editorial Team
An illustration of the letter 'A' in a speech bubbles

The speed in which a structure burns and the color of the smoke/flames may be an indicator of arson. Trace amounts of unconsumed flammable material around the structure may indicate that the fire was set on purpose. Also, the color of the smoke may indicate arson; for example, gasoline produces thick black smoke as it is burned. The arson investigator can interview firefighters for this information.

The direction of the smoke can also be used in an arson case, especially if it looks as though the arsonist left lots of space for oxygen to enter the building and thus fuel the flames. Smoke pouring through open windows and doors during cold weather can be suspicious. The smell of the smoke can also be considered in an arson case, as different flammable materials have different odors. Once again, it is important to interview firefighters and other witnesses in this case.

The nature of the fire itself may also be an indicator of arson. A building that goes up in flames very quickly can be considered an arson case. A building that has different origins for the fire can also be considered arson. If the flames originated away from a likely source, such as away from electricity, heaters, or kitchen appliances, then this can also be considered arson. Some of this information can be determined after the fire is over, and the investigator can piece together the timeline of the fire.

Approved by eNotes Editorial Team
An illustration of the letter 'A' in a speech bubbles

Arson is a crime in which a person purposely starts a fire with malicious intent. Investigators are charged with determining whether fires that cause damage are purposeful or accidental. In order to make these determinations, investigators use physical evidence at the scene of the fire. Physical evidence can be incendiary devices, debris patterns, and witness reports. Two other important forms of physical evidence are flame and smoke patterns.

Smoke can be evaluated by volume, velocity, density, and color. Smoke tells us about the materials that are burning and the temperature of the fire. For example, materials that are slightly wet will emit lots of smoke. Smoke can also show the direction a fire has taken, the speed it has moved, and its exit points from the building.

Flames can be evaluated by color and burn pattern. The direction and pattern of flames can indicate where a fire started and which way it spread. Flames can indicate if accelerants were used, the combustibility of source materials, and the temperature of the fire. Different colors of flames indicate different temperatures and different chemical makeups.

Approved by eNotes Editorial Team
An illustration of the letter 'A' in a speech bubbles
Flames and smoke are probably two of the main things that investigators use to judge an investigation. The color of the flames can indicate many different things like temperature and use of particular accelerants. The direction of the burn patterns left by the flames can also tell a great deal. They can indicate the point of origin, how fast the flames spread, and many other key details. The smoke patterns also indicate different aspects of a fire. Smoke might show us how fast the fire began, how long it was burning, what order the building caught fire in, etc. Investigators use the various signals to gain clues about the fire. Once they have determined the point of origin, the temperature, use of accelerants, and a few other key factors, they can usually determine if the fire was accidental or intentional (ie arson).
Approved by eNotes Editorial Team