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

Commonly Used AccelerantsAccelerant Flash Point (°C) Ignition

Temperature (°C)

Acetone -20 465

Gasoline -46 257

Kerosene 52-96 257

Mineral spirits 40-43 245

Turpentine 32-46 253

Ignition temperature and flash points are NOT related!

Ignition temperature.– Combustion will continue

until:1. Fuels are consumed.2. Oxidizing agent has been

removed.3. Fuels are cooled below

their ignition temperature.4. Flames are chemically

retarded.

– Transfer of heat. :• Conduction.• Convection.• Radiation.• Direct flame contact.

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.

Accelerants

• Examples:– Gasoline– Kerosene– Diesel– Lighter fluids– Charcoal starters– Automobile additives– Camping fuels

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.

Steps to Recover and Identify Accelerants

• Collect samples.• Extract the fire debris

and obtain a sample for instrumental analysis.

• Carry out instrumental analysis.

• Interpret the results.

Evidence Containers

The evidence container should have the following qualities:

Air tightHighly resistant to breakagePrevents cross-contaminationGood integrity seal

Accelerant Identification : Extraction• Common methods used today:

– Steam distillation– Vacuum distillation– Solvent extraction– Charcoal sampling– Swept headspace .

An Ignitable Liquid Is 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.”

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.

First the point of origin is determined: Where the fires starts Usually contains the most damage.

Point of Origin – Burn patterns and other damage can help determine the point of origin, or the location where the fire started.

Once point of origin is determined, the cause of the fire is determined.

• 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

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

EXAMPLES OF BURN INDICATORS

• Alligatoring• Depth of char• Breaking of glass• Collapsed furniture springs• Spalling• Distorted light bulbs• Temperature determination

18-8

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.

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.

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

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

COMMON CAUSES FOR ACCIDENTAL OR NATURAL FIRES

• The electric system• Electrical appliance and equipment • Gas• Heating units• Sunlight• Matches• Smoking

18-4

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

EXAMPLES OF BURN INDICATORS• Alligatoring

• Depth of char

• Breaking of glass

• Collapsed furniture springs

• Spalling

• Distorted light bulbs

• Temperature determination18-8

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

18-9

(Source: Factory Mutual Engineering Corporation, Norwood, Massachusetts. Reprinted with permission.)

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)

APPROXIMATELY MELTING TEMPERATURE OF COMMON MATERIALS (cont’d)

18-10(b)

Material oF oCAluminum (alloys)AluminumBrass (yellow)Brass (red)Bronze (aluminum)Cast iron (gray)Cast iron (white)ChromiumCopperFire brick (insulating)GlassGoldIronLeadMagnesium (AZ31B alloy)NickelParaffin

1,050-1,2001,2201,7101,8251,800

2,460-2,5501,920-2,010

3,3501,981

2,980-3,0001,100-2,600

1,9452,802

6211,1602,651

129

566-650660932996928

1,350-1,4001,050-1,100

1,8451,082

1,638-1,650593-1,427

1,0631,540

327627

1,45554

(Source: National Fire Protection Association, NFPA 921 Guide for Fire and Explosion Investigations (Quincy, MA: NFPA, 2001), pp. 921-30.)

APPROXIMATELY MELTING TEMPERATURE OF COMMON MATERIALS (cont’d)

18-10(c)

Material oF oCPlastics (thermo):

ABSAcrylicNylonPolyethylenePolystyrenePolyvinylchloride

PlatinumPorcelainPot metalQuartz (SiO2)SilverSolder (tin)Steel (stainless)Steel (carbon)TinWax (paraffin)White pot metalZinc

190-257194-221349-509251-275248-320167-221

3,2242,820

562-7523,060-3,090

1,760275-350

2,6002,760

449120-167562-752

707

88-12590-105

176-265122-135120-16075-105

1,7731,550

300-4001,682-1,700

960135-177

1,4271,516

23249-75

300-400375

(Source: National Fire Protection Association, NFPA 921 Guide for Fire and Explosion Investigations (Quincy, MA: NFPA, 2001), pp. 921-30.)

“One of the major objectives

of a fire scene examination

is the recognition, identification

and analysis of fire patterns.”

NFPA 921 (2004)4.1

Success in Recognizing Arson begins

with recognizing

possible Arson Fire Patterns

NFPA 921 on Fire Patterns• Holes in the floor may be caused by glowing combustion, radiation

or an ignitable liquid. 6.2.3.1

• There is no justification that the appearance of large, curved blisters is an exclusive indicator of an accelerated fire. 6.5.5

• 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. 6.6.2.3

• 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. 6.17.3.1.2

First!

Search for Odd Variations in Fire Patterns

Unusual “localized” wall pattern

Unusual floor burn pattern

Unusual, localized damage

to the bed

Symptoms of Ignitable Liquid Use (Possible indicators of an accelerated fire)

Burn injuries to the

hands, face, legs or hair of a suspect/witness.

Afternoon ProgramUnnatural Fire Spread

(downward, unusually fast, etc.)

One gallon of gasoline

was poured here!

“Unnatural” Fire Damage

Bright yellow/orange flames accompanied by black smoke.

Intense localized rusting/warping, especially to the undersides of

metal objects within the pattern

Intense localized rusting/warping,

especially to the undersides of metal objects

within the pattern

Structural damage inconsistent

with fire loading

Intermixed light, medium & heavy

burn patterns within

the overall pattern

“Rainbow-colored” sheen

on the surface of

suppression water over the

pour area.

Accelerant containers in or near the scene.

Increased burn damage

pattern at the

bottom of boxes, furniture legs, etc.

Pool shaped, intermixed, mottled black and brown

staining on concrete

together with a tendency to repel water.

“Ghost marks” between seams

of floor tiles within the pour area.

Localized “clean burn”area on a wall or appliance

above a pattern where intense heat

burned away soot deposits.

“Inverted Cone” fire pattern

Search for the soot plume!

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

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”

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)