FIPP PPT Ch 4 Fire Patterns

12/20/201344FirePatternsKnowledge Objectives Identify fire effects and understand theircauses. Recognize fire patterns. Identify the cause of fire patterns. Analyze fire patterns to produce a hypothesis.44IntroductionSkills Objectives Interpret fire patterns to determine the pointof origin. Recognition, identification, and analysis of fireeffects and fire patterns Knowledge of fire dynamics is important tounderstand fire patterns.44Fire Effects and Fire Patterns (1 of 2)Fire Effects and Fire Patterns (2 of 2) Fire effects observable or measurablechanges in material resulting from fire Fire pattern visible or measurable changesor shapes formed by fire effects Fire investigator attempts to recreate firedevelopment history and origin Primary physical evidence of a fire:– Burned materials– By‐products of burning Pattern interpretation changes over time.1

12/20/201344Fire EffectsMass Loss Knowledge of fire effects is necessary toidentify and interpret fire patterns. Melting can help determine temperature in agiven area. Temperatures at a location do not indicate aparticular fuel source. Can sometimes determine duration andintensity of a fire– There are many additional factors. Postfire analysis can use exemplars andundamaged portions of an object. As fire intensifies, mass loss increases.44Char (2 of 2)Char (1 of 2) Factors affecting rate of char:– Rate and duration of heating– Ventilation effects– Surface‐to‐mass ratio– Direction, orientation, and size of wood grain– Species of wood– Moisture content of the wood product– Any surface coating Carbonaceousmaterial that hasbeen burned– Wood char is mostcommon.– There is no standardrate of char.4Spalling (1 of 2) Chipping or pitting of concrete or masonry4Spalling (2 of 2) Spalling on the floor of a garage.– Founds on floors, walls, ceilings– May show different coloration– May have existed prior to the fire– May be caused by heat or mechanical stress2

12/20/201344Oxidation (2 of 2)Oxidation (1 of 2) More pronounced oxidation can be caused by: Basic chemical process associated withcombustion Oxidation of noncombustible materials canproduce:– Higher temperature– Longer exposure– Color and texture changes– Fire patterns4Melting4Alloying of Metals Physical change of material from solid to liquidcaused by heat Demarcation lines between melted andunmelted portions of a material can be useful. Each solid material has its own meltingtemperature. Can be difficult to distinguish from oxidation Two metals, one in liquid state, come intocontact and form a new material. Can look like melting4Thermal Expansion and Deformation Heat causes most materials to expand andchange shape.– Temporarily or permanently Structural failures can occur as a result. Distortion indicates that melting temperaturewas never reached.4Smoke Deposits (1 of 2) May collect on cooler surfaces such as wallsand windows– Especially during smoldering fires Color and texture do not indicate burning orheat release rate As fire grows, it consumes smoke depositsfrom earlier in fire– Referred to as a clean burn3

12/20/20134Smoke Deposits (2 of 2)4Calcination Occurs in plaster or gypsum wall surfaces Chemically bound water is driven out by heat. Gypsum wallboard reacts to fire in predictablemanner Clean burn– Created when fireoxidizes smokedeposits andconsumes carbon– First paper burns off, then color changes Rate and depth do not indicate burn times.Courtesy of Jamie Novak, Novak Investigation Inc. and St. Paul Fire Department44Glass Effects (2 of 3)Glass Effects (1 of 3) Glass deposits free of soot usually indicateearly failure of the glass before accumulationof smoke. May result from: Light bulb damage can indicate direction ofheat source.– Rapid heating– Damage prior to fire– Direct flame impingement4Glass Effects (3 of 3) Fractured glass is found in most structurefires. Window panes may pop out of frames. Crazing results from rapid cooling of glass.– Not from heating, as previously believed4Furniture Springs Damage can provide clues to:– Fire intensity– Duration– Direction of travel Does not indicate type of fire4

12/20/201344Protected AreasHeat Shadowing Caused by object blocking travel of heat to asurface:– Radiated heat– Convected heat– Direct flame Object is shielded from:– Heat transfer– Combustion– Deposition Useful in reconstructingfire scene Creates discontinuous pattern44Fire Patterns (1 of 2)Rainbow Effect Visible or measurable physical changes, oridentifiable shapes, formed by a fire effect orgroup of fire effects Three basic causes: Hydrocarbons do not mix with water.– Float on the surface– Interference pattern produces rainbow effect Produced by many materials– Heat– Decomposition– Consumption4Fire Patterns (2 of 2) Analyze fire patterns within the context of allthe patterns. Used to determine the sequence of eventsthat occurred during the fire When fires increase in size or burn for anextended period, fire patterns at the originmay be more difficult to identify.4Plume‐Generated Patterns (1 of 3)Fire patterns are twodimensional, but thefire plume creatingthe pattern wasthree dimensional.5

12/20/20134Plume‐Generated Patterns (2 of 3)4Plume‐Generated Patterns (3 of 3) Pattern shapes include: When a fuel package is ignited, a plume ofgas, smoke, and flame rises upward until it iscontained or cooled. The heat release rate greatly affects the firepattern.– V‐shaped– Inverted cone– Hourglass– U‐shaped– Circular– Pointer and arrow As plume develops, size and shape of patternchanges4Ventilation‐Generated Patterns As pressure builds during combustion, hotgases and fire escape through openings withincreased velocity. Well‐ventilated fires increase the rate ofmaterial damage. Heavy damage is often found at ventilationareas, even if they are not the point of origin.4Hot Gas Layer‐Generated Patterns (1 of 2) Prior to flashover, hot gas layer begins todescend Level of descent can be determined byexamining the line of demarcation Sometimes referred to as containmentpatterns4Hot Gas Layer‐Generated Patterns (2 of 2)An example of a hotgas layer‐generatedpattern.4Patterns Generated by Full‐RoomInvolvement Usually found on all exposed surfaces in theroom Makes traditional patterns more difficult todocument and analyze Material damage is more extensive6

12/20/201344Lines of DemarcationSuppression‐Generated Patterns Fire suppression actions may create or changefire patterns.– Water streams may change direction of fire spread– Ventilation actions affect fire patterns. Produce a border between affected and lessaffected areas Numerous factors dictate where these linesform.4Patterns Detected in Fire Victims’ Injuries(1 of 2)4Patterns Detected in Fire Victims’ Injuries(2 of 2) Body should not be moved until it has beendocumented and analyzed Heat effects on the body: Bodies found at fire scenes should be treatedas evidence and interpreted for fire patterns. Investigators should also document injuries tothose who have survived a fire.– Skin will redden, darken, blister, split, and char.– Muscle will dehydrate, contract, and shrink.– Pugilistic pose– Exposed bone will change in color and mass.44Pattern Location (2 of 2)Pattern Location (1 of 2) Fire effects can be three dimensional. Look for large‐scale patterns such as aerialviews of the roof. Look for small‐scale patterns such as heateffects on wiring insulation. Examine all areas in a building for patterns. Wall patterns usually V‐shaped or U‐shapedCeiling patterns above fire are usually circularFloor patterns depend on many conditions.Flashover and full‐room involvement canproduce relatively uniform burning.7

12/20/201344Beveling (2 of 3)Beveling (1 of 3) Fire penetration of a horizontal surface Beveling is anindicator of firedirection on woodwall studs. Bevel leans indirection of fire travel– Potential causes include radiant heat, isolatedsmoldering objects, and ventilation.– Downward movement is not necessarily from anignitible liquid.– Gas may have been forced through small holes inthe flooring.44Beveling (3 of 3)Irregular Patterns Direction of fire travel is determined byexamining the sides of the hole and the slopecreated by the fire.– Wide hole and downward slope indicates firetravel from above.– Wider on the bottom and sloped upward indicatesfire travel from below. Irregular patterns can be misinterpreted. Investigator should work to identify fuel thatcaused pattern If an ignitable liquid is suspected, samplesshould be submitted for laboratory analysis.4Pattern Geometry (1 of 2) Fire and smoke produce variety of distinctivepatterns Multiple interpretations possible4Pattern Geometry (2 of 2) Examples:– V‐shaped patterns from fire plume– Inverted cone patterns created by vertical flameplume not reaching ceiling level– Hourglass patterns from fuel package at the base,near a vertical surface– Truncated cone patterns from intersection of acone pattern on vertical and horizontal surfaces8

12/20/201344Heat (Intensity) PatternsFire Pattern Analysis Process of identifying and interpreting firepatterns to determine how they were created Two basic types– Heat (intensity) patterns– Fire spread (movement) patterns As a fuel item is exposed to heat and flames,patterns are created. Lines of demarcation indicate:– Direction of fire travel– Characteristics and amounts of fuel present4Fire Spread (Movement) Patterns Produced by growth, spread, and flow ofcombustion products Helpful in determining the original heatsource4Summary (1 of 5) The examination of fire patterns allows theinvestigator to determine the direction of firetravel as well as the point of origin. Fire patterns may be created by flameimpingement, hot gases, smoke, and otherproducts of combustion.4Summary (2 of 5) The area of most damage may not indicate thepoint of origin. Factors such as ventilation, fire suppressionactivities, and types of materials that areburning will influence the severity of damageas well as the direction of fire travel during afire.4Summary (3 of 5) Glass that displays crazing indicates rapidcooling. Spalled concrete, brick, and mortar mayindicate rapid heating of the surface.9

12/20/20134Summary (4 of 5) Incandescent light bulbs that are equal to orgreater than 25 watts will tend to pushoutward toward the heat source, whereasthose less than 25 watts will collapse inward.4Summary (5 of 5) Penetrations in floors may be the result ofignitable liquids; however, they can also becaused by smoldering items, the effects ofventilation, and areas exposed to flashoverconditions.10

Fire pattern visible or measurable changes or shapes formed by fire effects Fire investigator attempts to recreate fire development history and origin 4 Fire Effects and Fire Patterns (2 of2) Primary physical eviden