Forensic Science

T. Trimpe/B.Brooks 2006 http://sciencespot.net/

Fire Investigation Terms• Fire - Produced when a substance undergoes rapid oxidation

involving heat and light. • Fire Triangle – Shows the three elements needed to produce and

sustain a fire.• Flash Point – The lowest temperature to which a substance must

be heated in order for the substance to give off vapors which will burn when exposed to a flame or ignition source.

• Point of Origin – The location where the fire started.• Burn patterns –Noticeable patterns created by the fire as it

burns.• Accelerants – Substances, such as gasoline, paint thinner, and

alcohol, that speed up the combustion process.• Arson – A fire started deliberately.

Fuel + Oxygen + Heat = Fire

FUEL

OXYGENHEAT

The FIRE TRIANGLE represents the three elements needed for fire to occur: heat, fuel, and oxygen.

Fuel can be any combustible material in any state of matter - solid, liquid, or gas.  Most solids and liquids become a vapor or gas before they will burn. 

FUEL

OXYGENHEAT

Examples:CLOTHINGFURNITURECURTAINS

FLAMMABLE LIQUIDS

FUEL

OXYGENHEAT

The air we breathe is about 21% oxygen.  Fire requires an atmosphere with at least 16% oxygen. 

Remember: Fuel + Oxygen + Heat = Fire

FUEL

OXYGENHEAT

Heat is the energy necessary to increase the temperature of the fuel to a point where sufficient vapors are given off for ignition to occur.  Examples:

STOVESHEATING APPLIANCESFIREPLACESDAMAGED WIRING

Fire Clues• Point of Origin – Burn patterns and other damage can help determine the point of

origin, or the location where the fire started.• Char Patterns – Created by very hot fires that burn very quickly and move fast

along its path, so that there can be sharp lines between what is burned and what isn't. – A char pattern on a door would help an investigator determine which side of the

door the fire was on.– A char pattern on the floor would help investigators determine the use of an

accelerant and its path.• V-Patterns - Fire burns up, in a V-shaped pattern, so a fire that starts at an outlet

against a wall leaves a char pattern that points to the origin. – A very narrow V-shape might indicate a fire that was hotter than normal, such as

one helped along by an accelerant.– A wide V-shape might indicate a fire that was slow burning.– A U-shape could indicate that there was a "pool of origin" rather than a point of

origin, such as might be caused by, say, a puddle of gasoline.

• Heat Shadows - Occur when heavy furniture shields part of a wall; can help determine the origin point.

• Glass - Glass fragments, windows, and light bulbs can provide clues to a fire.– Light bulbs tend to melt toward the heat source, so the "direction of melt"

can indicate the direction of the fire. – The shattered or cracked glass of the windows can provide indications as to

how a fire burned. – A dark soot layer on the glass could indicate a slow, smoldering fire. – Clear glass with an abnormal pattern of cracking could imply a very hot fire,

possibly due to an accelerant. • Chimney Effect - Since fire burns upwards, there can be a "chimney effect"

where the fire ignites at a point, the superheated gases rise upward and form a fireball, which continues straight up to burn a hole in the ceiling. If the roof is not entirely burnt, and the fire investigator finds such a hole, the origin of the fire could be directly underneath.

• Color of smoke – Determine what type material was burning • Color of flames – Indicates at what temperature the fire was burning.

Fire Investigation Basics• Work from the least damaged areas to the most heavily damaged

areas.• Document with notes, photographs, and videos.• Collect evidence (accelerant samples, fire items, and other crime

scene evidence.)• Interview witnesses• Determine the point of origin.• Determine the heat source(s).• Hypothesize the reasons for the fire.

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Ignition Temperature• The amount of heat required to “push” the combustion

reaction over the energy barrier is known as the ignition temperature.

• Once the combustion starts, enough heat is created to keep the reaction going.

• For example: You need to use a match (extra heat) to light the methane gas on fire. But once that ignition occurs, the material keeps burning.

Liquid and Solid Fuels

• So far we discussed methane – a gas. Its molecules mix with the molecules of oxygen when the ignition temperature is reached.

Question: What about liquids and solid fuels? How do oxygen molecules combine freely with them if they are not in the gaseous state?

Answer• Both liquids and solids must first be converted into gas

molecules, so that oxygen molecules can combine with them to produce fire.

• Liquid fuels have to turn to vapor or gas first. The lowest temperature at which this happens is called the Flash PointFlash Point of the liquid.

• Once the Flash Point is reached, a light or spark can cause the gas/vapor to reach the ignition point and combustion to occur.

Photos provided by Brock Brooks & the Havana Fire Department

Havana – Laurel StreetPractice Burn Photographs

What clues might a fire investigator gain from

this photograph?

Photos provided by Brock Brooks & the Havana Fire Department

Havana – Laurel StreetPractice Burn Photographs

A fire started in the kitchen area does not take long before it is a ball of flame reaching quickly to the ceiling.

Fires can easily double in size every 60 seconds, meaning there is little time to extinguish a fire before escape should be your primary goal if trapped.

Fire fighters look on as the fire spreads across a room.

The house is nearly completely consumed. Source: http://www.ci.east-grand-forks.mn.us/fire/gallery/burn/burn.htm

Practice Burn Photographs

Accident or Arson?• Accidental Nature

– Heating System – Electrical appliances – Lightning– Children playing with matches– Smoking

• Non-Accident – Odors – Gas, kerosene, or other accelerants– Furnishing – Removal of personal objects and valuables– Clothing – Check debris for buttons, zippers, etc– Locked windows, blocked doors– Two or more points of origin– Look for inverted v-patterns (can be a sign that an accelerant was used)– Floors charred –Can indicate use of an accelerant– Trailers that lead the fire from one place to another

Image: Havana Rural Fire Department

Solid Fuels• Wood for example, cannot generate a vapor easily.

• It has to first be exposed to enough heat to breakdown some of the solid organic material into gases that are combustible.

• The chemical breakdown of solids into gas is known as pyrolysis.

Glowing Combustion

• If there is not enough heat to pyrolyze the solid fuel If there is not enough heat to pyrolyze the solid fuel to produce flames, the solid fuel does not combust to produce flames, the solid fuel does not combust through-and-through, only on the surface.through-and-through, only on the surface.

• This produces a glowing effect – Examples: This produces a glowing effect – Examples: embers, burning cigarette, etc.embers, burning cigarette, etc.

Hydrocarbon Detector or Sniffer

Gas Chromatography, Mass Spectroscopy

• Analysis of materials collected at a suspected arson site is done using GC-MS.

• The chromatogram is compared to known petroleum standards.

• One such standard is called the “gasoline standard”• But first, the debris has to be prepped.

Headspace vapor

• The debris is placed in an airtight container and the container is heated.

• If the debris contains any volatiles or hydrocarbons (from accelerants), the vapors will rise to the top of the container.

• This risen vapor or headspace is removed with a syringe and injected into a GC.

This is a Gasoline Standard Gas Chromatograph

This is a Gas Chromatograph from suspicious fire debris

6) How do we control fire ? The conditions necessary for producing fire are :- i) Fuel ii) Air (to supply oxygen)iii) Heat (to raise the temperature of the fuel beyond its ignition temperature). Fire can be controlled by removing any one or more of these conditions. A fire extinguisher cuts off the supply of air or brings down the temperature of the fuel or both and controls the fire.

Methods of controlling fire :- i) By using water :- Water is the most common fire extinguisher. It can be used only when materials like wood , paper etc. are on fire. Water cannot be used if electrical equipments are on fire because water conducts electricity and can harm those trying to put out the fire. Water cannot be used to put out oil and petrol fires because they float on water and continue to burn.ii) By using carbon dioxide:- Carbon dioxide is the best fire extinguisher to put out fire caused by inflammable materials like oil and petrol and electrical equipments. Carbon dioxide is heavier than air and it covers the fire and cuts off the supply of oxygen and puts out the fire. Carbon dioxide is stored at high pressure as liquid in cylinders. Chemicals like sodium bicarbonate (baking soda), potassium bicarbonate produce carbon dioxide near the fire.

Types of combustion :- There are three main types of combustion. They are :- i) Rapid combustion ii) Spontaneous combustion iii) Explosion Rapid combustion:- is combustion in which a substance burns rapidly and produces heat and light with the help of external heat. Eg:- burning of LPG Spontaneous combustion:- is combustion in which a substance burns spontaneously and produces heat and light without the help of external heat. https://www.youtube.com/watch?v=LSYLUat03A4 Eg:- phosphorus burns spontaneously at room temperature Explosion:- is a combustion in which a substance burns suddenly and produces heat, light and sound with the help of heat or pressure. Eg:- explosion of fireworks on applying heat or pressure.

Types of combustionRapid combustion

Spontaneous combustion

Explosion

9) Flame :- Flame :- is the zone of combustion of a combustible substance. Substances which vapourise during burning produce flames. Eg:- kerosene, wax etc. Substances which do not vapourise during burning do not produce flames. Eg:- coal, charcoal etc. kerosene wax coal charcoal

Structure of a candle flame

Outer zone (blue)

Middle zone (yellow)

Inner zone (black)

(Complete combustion)

(Partial combustion)

Unburnt wax vapours

Hottest part

Moderately hot

Least hot

Luminous zone

Non luminous zone

10) Structure of a candle flame :- A candle flame has three main zones. They are:- i) Outer zone ii) Middle zone iii) Inner zone In the outer zone complete combustion of the fuel takes place and the colour of the flame is blue and is the hottest part of the flame. It is the non luminous part of the flame. In the middle zone partial combustion of the fuel takes place and the colour of the flame is yellow and is moderately hot part of the flame. It is the luminous part of the flame. In the inner zone there are unburnt vapours of the fuel and the colour is black and is least hot part.

11) Types of fuels :- Fuels are of three main types. They are :- i) Solid fuels :- Eg:- wood, coal, charcoal etc. ii) Liquid fuels :- Eg:- kerosene, petrol, diesel etc.iii) Gaseous fuels :- Eg:- CNG, LPG, biogas, hydrogen etc. Solid fuels Liquid fuels Gaseous fuels

According to the FBI Crime Index, juvenile and adult arson cause an annual average of 560,000 fires, 750 deaths, 3,700 injuries, and $1.5 billion in property loss. 55% of all arson arrests in the US are children under 18.

Arson Facts in America

Source: http://www.state.il.us/osfm/Arson/ArsonIsAFelonyCrime.htm

• Crime concealment: To conceal another crime such as murder, burglary, or vehicle.

• Revenge or spite: To get back at someone for a perceived injustice.

• Monetary Gain: Arson-for-Profit fires are set to burn a building, vehicle, or some other object in order to gain profit from the fire. The profit may come in several forms; from insurance coverage on the property, or from putting a competitor out of business.

• Malicious Vandalism: Fire set to someone’s property, just to destroy it. Malicious vandalism fires account for the largest percentage of arson fires. These fires are frequently set by juveniles.

• Mentally Disturbed: Some persons have been found to have an irresistible impulse to set fires.

What are Common Motives for Arson?

Florida Division of State Fire MarshalBureau of Fire and Arson Investigations

Mission Statement“To effectively prevent, discourage, investigate and prosecute arson and

arson-related crimes for the protection of Florida citizens and their property.”

Conducts about 4,000 investigations each yearUses accelerant detection canines

Report suspicious persons and activities that may result in arson.

If you have a friend or classmates that has set fires in the past or plans to set a fire, tell an adult – parent, teacher, counselor, police officer, or a fireman.

Start or participate in a community watch program with your parents.

Install and properly maintain fire alarms in your home and encourage friends and relatives to do the same. Your family should also have a fire escape plan for your home.

What can you do to help prevent arson or arson damage?