1 / 48

Commonly Used Accelerants

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 Accelerants.

nelia
Télécharger la présentation

Commonly Used Accelerants

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

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

  2. Commonly Used Accelerants 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.

  4. 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

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

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

  9. No Ignitable Liquids Were Detected An Ignitable Liquid Is 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. 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

  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.

  14. 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.

  15. 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

  16. 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

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

  18. 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

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

  20. 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

  21. 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)

  22. APPROXIMATELY MELTING TEMPERATURE OF COMMON MATERIALS (cont’d) (Source: National Fire Protection Association, NFPA 921 Guide for Fire and Explosion Investigations (Quincy, MA: NFPA, 2001), pp. 921-30.) 18-10(b)

  23. APPROXIMATELY MELTING TEMPERATURE OF COMMON MATERIALS (cont’d) (Source: National Fire Protection Association, NFPA 921 Guide for Fire and Explosion Investigations (Quincy, MA: NFPA, 2001), pp. 921-30.) 18-10(c)

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

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

  26. 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

  27. First!Search forOdd VariationsinFire Patterns Unusual “localized” wall pattern Unusual, localized damage to the bed Unusual floor burn pattern

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

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

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

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

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

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

  34. Structural damage inconsistent with fire loading

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

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

  37. Accelerant containers in or near the scene.

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

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

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

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

  42. “Inverted Cone” fire pattern

  43. Search for the soot plume!

  44. 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

  45. 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”

  46. 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)

More Related