LECTURE 18: ARSON / ARSON INVESTIGATION / CHAPTER FIRE EXPLOSIONS

Question 1

all fires and explosions are the result of a chemical reaction known as

Answer 1

combustion

Question 2

combustion

Answer 2

the reaction of a fuel with oxygen

Question 3

exothermic

Answer 3

• A chemical reaction that releases energy as one of its products

Question 4

endothermic

Answer 4

• A reaction that requires the input of energy in order for the reaction to take place

Question 5

all combustion reactions are

Answer 5

exothermic

Question 6

Arson

Answer 6

= fires deliberately set with criminal intent.

Question 7

combustion is fast or slow?

Answer 7

slow

Question 8

fire tetrahedron

Answer 8

• the 4 elements that must be present in order to have a fire

Question 9

4 elements for fire

Answer 9

1) Source of heat or energy = necessary to elevate the fuel & oxygen molecules
o This is the activation energy
o The temperature needed to do this varies with the fuel & is called the ignition temperature
o Once this temperature is reached, a fire can continue on a self-sustaining basis.
2) Fuel
3) Source of oxygen
4) Chain reaction between the fuel & oxygen

Question 10

flash point of the feul

Answer 10

the lowest temperature that will allow a liquid to produce a flammable vapor

Question 11

smoke occurs when

Answer 11

there is incomplete combustion of fire

• If there is not enough oxygen to completely combust the molecules of fuel, then some of the combustion will be incomplete. This will yield products such as carbon particles (soot), unburnt, & partially burnt gases. Together these comprise smoke.
• A fire in a building where oxygen supply is limited & as oxygen is used up, more smoke is formed. If fire is suddenly ventilated, the increased oxygen will cause an explosive fire, a phenomenon called flashback.

Question 12

fuel must be in what form to sustain a fire

Answer 12

vapor form

Question 13

accelerants

Answer 13

fuels that are easily vaporized & support combustion, & are highly exothermic

• poured around the area to be burnt and ignited
• they provide activation energy

Question 14

common accelerants

Answer 14

gasoline, kerosene, charcoal lighters, & some paint thinners.

Question 15

3 types of fires:

Answer 15

1) Natural Fires: most caused by lightning strikes. Other types of naturally occurring fires are flammable gases that escape from the ground around an oilfield & combust.
2) Accidental Fires: difficult to distinguish from deliberate fires. Eg: a furnace malfunction. If the furnace is badly damaged in the fire, it may not be possible to tell if the malfunction was accidental or deliberate. Sometimes rag that have been used to clean up spills from fuel can heat up enough to a spontaneous combustion if they are left in a closed area for a long time.
3) Deliberate Fires: steps in determining a deliberate fire: (1) all possible natural & accidental causes of the fire must be eliminated, (2) seek to determine if the fire is arson.

Question 16

other ways of classifying fires

Answer 16

• Direct Ignition:
  • Most basic of all of the causes of fire. Involves direct application of a spark or flame source to the fuel. Eg: candles, clocks, mousetraps, exothermic chemical reactions.
  • A time delay mechanism is almost never used unless the fire is arson.
• Electrical Fires: eg: malfunctions
• Weather-related Fires:
  • Lightening striking a dead tree Possible for the sun to cause a fire. Magnifying glass.
• Mechanical Fires:
  • Machine can overheat either through misuse or incorrect placement. Eg: shaft or wheel that relies on bearings to reduce friction can overheat if the bearings become damaged or worn.
  • Overheating of an engine or catalytic converter or muffler can cause a fire if fuel leaks in the wrong place. Appliances such as toasters or clothes driers that give off heat are not given proper ventilation could overheat & cause a fire.

Question 17

Locating the Point of Origin:

Answer 17

• Characteristics present at the point of origin of a fire:
  • Low burning – fires generally start in a low area of a building
  • V patterns – if the point of origin is near a wall or corner of a room, smoke damage on the wall(s) usually occurs in a “V” shape. Burn patterns can be good evidence of the point of origin
  • Wood charring – depth of wood charring depends upon the intensity of the heat near the wood & the time of exposure. Wood near the point of origin of the fire greater depth of charring than elsewhere
  • Spalling of plaster or concrete – spalling is the destruction of a surface due to heat or other factors. In concrete, spalling may be explosive. Spalling usually occurs most where the heat is most intense.
  • Material distortion – metal & glass may melt or distort owing to high heat. Since melting points of many of these materials are well known, such destruction may indicate the approximate minimum temperature of the fire of that point.
  • Soot & smoke staining – amount of soot present in a fire may indicate the point of origin & the direction of travel of the fire

Question 18

indications of arson fire

Answer 18

• The presence of an accelerant
• Elimination of natural or accidental causes of a fire – difficult to determine at times, eg: a furnace may malfunction, leading to a fire.
• Fire trails – accomplished by pouring an accelerant along a floor in the desired direction. The result will be an uneven, intense burn along the fire trial. This would not be seen in an accidental or natural fire.
• Multiple points of origin – pouring some accelerant in each room of a building & then starting multiple fires, one in each room, is a tactic often used by arsonists. But this isn’t always the case, an example of an exception is electrical wiring – overheating of the wiring & insultation at several points in the wall.

Question 19

what is used

Answer 19

gas chromatography

Question 20

Instrumental & Other Methods of Analysis:

Answer 20

• Once an explosive residue has been isolated from bomb debris then it should be identified. Various types of chromatography & infrared spectrometry are used for this purpose:
• Thin-layer chromatography - explosives can be separated by this, includes high & low explosives.
• Griess = visualizing agent employed because they will color most nitrate-containing species bright red
• High Performance Liquid Chromatography (HPLC) - advantages over TLC - can be used for quantitative analysis. Preferred of GC
• Capillary electrophoresis (CE) - advantages over HPLC - sensitive & only needs tiny amounts.
• Infrared spectrometry - solids, liquids, mulls, & solutions. Similar compounds as TNT & DNT can be differentiated by IR.

Question 21

How to ascertain if fire was an accident or deliberate

Answer 21

• Circumstances
• Fire Scene Examination
• Analysis of fire debris
  Therefore, all fire scenes must be dealt with as crime scenes lest evidence is lost or destroyed After the efforts of Fire Fighters evidence collection is difficult enough, without careless examination destroying more

Question 22

Backwards examination

Answer 22

• Fire scene examination is often referred to as a “Backwards” examination!
• External areas  Perimeter of fire scene  Areas of least fire damage to areas of greatest fire damage
• Examine the entire scene/structure