1. Flash point - The temperature at which a particular flammable liquid gives off vapors (vaporizes) and therefore can ignite.
The ignition temperature is the temperature required for a liquid to continue to emit vapors that can sustain

2. Commonly Used Accelerants
Flash Point (°C)
Ignition Temperature (°C)
Acetone
-20
465
Gasoline
-46
257
Kerosene
52-96
Mineral spirits
40-43
245
Turpentine
32-46
253
Ignition temperature and flash points are NOT related!

3. Ignition temperature. Combustion will continue until:
Fuels are consumed.
Oxidizing agent has been removed.
Fuels are cooled below their ignition temperature.
Flames are chemically retarded.
Transfer of heat. :
Conduction.
Convection.
Radiation.
Direct flame contact.
Ignition temp: The minimum temperature that will support or cause self-sustained combustion.
Combustible materials have to be heated to their ignition temperature before they burn.

4. Accelerants
Accelerants are any liquid, solid or gaseous material that will sustain or enhance flammability.
Liquid materials are commonly used because of ease of ignition and familiarity of use.
Accelerants are nearly exclusively derived from hydrocarbons.
Straight chain hydrocarbons are the backbone of the oil industry.
Hydrocarbons are molecules made up of the elements hydrogen and carbon.
Octane is a term familiar to all. It consists of a hydrocarbon having 8 carbons.

5. Accelerants Examples: Gasoline Kerosene Diesel Lighter fluids
Charcoal starters
Automobile additives
Camping fuels

6. Evidence of Accelerants
Large amounts of damage
Unusual burn patterns
High heat stress
Multiple sites of origin
“Sniffers”
Portable gas chromatographs
Chemical tests
Canines
Portable detectors
Detect change in oxygen level on a semiconductor
Guides to the best place to collect samples
Dogs can detect 0.01 mL of 50% evaporated gasoline 100% of the time.
0.01 mL is about the size of a thousandth of a drop.

7. Steps to Recover and Identify Accelerants
Evidence Containers
Steps to Recover and Identify Accelerants
The evidence container should have the following qualities:
Air tight
Highly resistant to breakage
Prevents cross-contamination
Good integrity seal
Collect samples.
Extract the fire debris and obtain a sample for instrumental analysis.
Carry out instrumental analysis.
Interpret the results.

8. Accelerant Identification : Extraction
Common methods used today:
Steam distillation
Vacuum distillation
Solvent extraction
Charcoal sampling
Swept headspace .

9. An Ignitable Liquid Is Detected
No Ignitable Liquids Were Detected
We can look at this in four different ways...
No ignitable liquids were ever used
Ignitable liquids were used to start the fire, but have been totally consumed.
Ignitable liquids are still present; however, not in the collected sample.
Ignitable liquids are still present in the collected sample; however, they are too dilute to be detected.
“Sample contains a medium petroleum distillate (MPD), some examples are paint thinners and mineral spirits”.
“Sample contains a mixture of gasoline and a heavy petroleum distillate (HPD). Some examples of a HPD are diesel fuels and heating oils.”

10. Point of Origin – Burn patterns and other damage can help determine the point of origin, or the location where the fire started.
First the point of origin is determined:
Where the fires starts
Usually contains the most damage.
Once point of origin is determined, the cause of the fire is determined.

11. Point of Origin Interior Examination.
Work backward in relation to fire travel and from least to most damage.
In accidental fires, floor damage is limited in respect to the ceiling damage.
“V” patterns may help locate
Point of Origin
Defined as where the fire originated.
Cause of fire may be near
Fire usually burns longer
If accelerants or ignition devices used, they may be present
Multiple points MAY indicate arson.
“V” patterns usually point to
Extensive ceiling damages may be present above
Origin may be either exact point or a general area.

12. EXAMPLES OF BURN INDICATORS
Alligatoring
Depth of char
Breaking of glass
Collapsed furniture springs
Spalling
Distorted light bulbs
Temperature determination
18-8

13. Fire Clues
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.

15. 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.

16. PRELIMINARY INVESTIGATION
One effective way to determine fire causes is to determine the point of origin
The investigator should check for the level of origin by examining:
the bottoms of shelves, ledges, moldings
furniture and all sides of the legs, arms, and framework of reconstructed furniture
The floor and lower areas of the room produce the most clues to the cause for the fire, because they are living area
18-2

17. WHERE AND HOW DID THE FIRE START?
Two Factors Needed to Cause Fire
During the investigation, it should be borne in mind that a fire always has two causes: a source of heat and material ignited
Accidental Fires
Once the point of origin has been discovered the next step is to determine how the fire started
Even though arson may be suspected, the investigator must first investigate and rule out all possible accidental or natural causes
18-4

18. COMMON CAUSES FOR ACCIDENTAL OR NATURAL FIRES
The electric system
Electrical appliance and equipment
Gas
Heating units
Sunlight
Matches
Smoking
18-4

19. BURN INDICATORS
Burn indicators are the effects of heat or partial burning that indicate a fire’s:
rate of development
points of origin
temperature
duration
time of occurrence
the presence of flammable liquids.
Interpretation of burn indicators is the principle means for determining the cause of a fire, especially arson
18-7

20. EXAMPLES OF BURN INDICATORS
Alligatoring
Depth of char
Breaking of glass
Collapsed furniture springs
Spalling
Distorted light bulbs
Temperature determination
18-8

21. LINE OF DEMARCATION IN A WOOD SECTION
Depth of char
is used for evaluating fire spread
is used to estimate the duration of a fire
the rate of charring of wood varies widely
(Source: Factory Mutual Engineering Corporation, Norwood, Massachusetts. Reprinted with permission.)
18-9

22. APPROXIMATELY MELTING TEMPERATURE OF COMMON MATERIALS
Arson investigators use charts such as the one on the next two slides to determine the approximate melting temperature of a material
Arson investigators try to estimate the temperature to which melted material was subjected
this helps to evaluate the intensity and duration of heating
18-10(a)

23. APPROXIMATELY MELTING TEMPERATURE OF COMMON MATERIALS (cont’d)oC
Aluminum (alloys)
Aluminum
Brass (yellow)
Brass (red)
Bronze (aluminum)
Cast iron (gray)
Cast iron (white)
Chromium
Copper
Fire brick (insulating)
Glass
Gold
Iron
Lead
Magnesium (AZ31B alloy)
Nickel
Paraffin
1,050-1,200
1,220
1,710
1,825
1,800
2,460-2,550
1,920-2,010
3,350
1,981
2,980-3,000
1,100-2,600
1,945
2,802
621
1,160
2,651
129
660
932
996
928
1,350-1,400
1,050-1,100
1,845
1,082
1,638-1,650
593-1,427
1,063
1,540
327
627
1,455 54
(Source: National Fire Protection Association, NFPA 921 Guide for Fire and Explosion Investigations (Quincy, MA: NFPA, 2001), pp )
18-10(b)

24. APPROXIMATELY MELTING TEMPERATURE OF COMMON MATERIALS (cont’d)oC
Plastics (thermo):
ABS
Acrylic
Nylon
Polyethylene
Polystyrene
Polyvinylchloride
Platinum
Porcelain
Pot metal
Quartz (SiO2)
Silver
Solder (tin)
Steel (stainless) Steel (carbon)
Tin
Wax (paraffin)
White pot metal
Zinc
3,224
2,820
3,060-3,090
1,760
2,600
2,760
449
707
88-125
90-105
75-105
1,773
1,550
1,682-1,700
960
1,427
1,516
232
49-75
375
(Source: National Fire Protection Association, NFPA 921 Guide for Fire and Explosion Investigations (Quincy, MA: NFPA, 2001), pp )
18-10(c)

25. of a fire scene examination is the recognition, identification
“One of the major objectives
of a fire scene examination
is the recognition, identification
and analysis of fire patterns.”
NFPA 921 (2004)
4.1

26. Success in Recognizing Arson begins with recognizing possible Arson Fire Patterns

27. NFPA 921 on Fire Patterns
Holes in the floor may be caused by glowing combustion, radiation or an ignitable liquid
There is no justification that the appearance of large, curved blisters is an exclusive indicator of an accelerated fire
The presence or absence of spalling should not, in and of itself, be construed as an indicator of the presence or absence of a liquid fuel accelerant
The collapse of springs cannot be used to indicate exposure to a specific type of heat source or ignition such as smoldering ignition or the presence of an ignitable liquid. 6.14
Inverted cone patterns have been interpreted as proof of flammable liquid fires, but any fuel source that produced flame zones that do not become vertically restricted can produce inverted cone patterns

28. First! Search for Odd Variations in Fire Patterns
Unusual “localized”
wall pattern
Unusual,
localized
damage
to the bed
Unusual floor
burn pattern

29. or hair of a suspect/witness.
Symptoms of Ignitable Liquid Use (Possible indicators of an accelerated fire)
Burn injuries
to the
hands, face, legs
or hair of a suspect/witness.

30. (downward, unusually fast, etc.)
Unnatural Fire Spread
(downward, unusually fast, etc.)
Afternoon Program

31. “Unnatural” Fire Damage
One gallon of gasoline
was poured here!

32. Bright yellow/orange flames accompanied by black smoke.

33. Intense localized rusting/warping, especially to the undersides of
metal objects within the pattern

34. especially to the undersides of
Intense localized
rusting/warping,
especially to the undersides of
metal objects
within the pattern

35. Structural damage
inconsistent
with fire loading

36. Intermixed light,
medium & heavy
burn patterns
within
the overall pattern

37. sheen on the surface of suppression water over the pour area.
“Rainbow-colored”
sheen
on the surface of
suppression water
over the
pour area.

38. Accelerant containers
in or near the scene.

39. bottom of boxes, furniture legs, etc.
Increased
burn damage pattern
at the
bottom of boxes, furniture legs, etc.

40. Pool shaped, intermixed, mottled black and brown staining on concrete
together with a tendency
to repel water.

41. “Ghost marks”
between seams
of floor tiles
within the pour area.

42. Localized “clean burn”area
on a wall or appliance
above a pattern
where intense heat
burned away
soot deposits.

44. “Inverted Cone”
fire pattern

45. Search for the soot plume!

46. Key Properties of Common Ignitable Liquids
Behave like any liquid before ignition.
Most float on water, are immiscible, rainbow
Form explosive vapors at room temperatures
Vapors are heavier than air
Readily absorbed
Powerful solvents
Don’t spontaneously ignite
Explosive Limits/Ignition Temperature
Sampling the accelerant fire pattern

47. Related Physical Evidence
The Accelerant Container
Other instrumentalities (i.e. ignition device)
Changing the arrangement of combustibles to increase fire loading
Propping open doors & windows
The ignition device
Explosion/Deflagration?
Burn patterns and the burned “perp”

48. INTERVIEWS IN AN ARSON INVESTIGATION
Possible Witnesses
Prospective witnesses include tenants, businesspeople and customers from the burnt building and surrounding buildings
Passers-by, including bus drivers, taxi drivers, delivery people, garbage collectors, police patrols, and people waiting for busses and taxis
Questions to Ask. Did you observe the fire? At what time did you first observe the fire? are examples of questions asked in an interview
18-19(a)