Bk083 Fire Investigation PDF

BOOK 83  From the office of The Chief Engineer… October 11, 1996 TO ALL UNIFORMED MEMBERS SUBJECT: BOOK 83 Each year, approximately 20,000 fires occur in the City of Los Angeles. As a result of these fires, approximately 53 fatal...

BOOK 83  From the office of The Chief Engineer… October 11, 1996 TO ALL UNIFORMED MEMBERS SUBJECT: BOOK 83 Each year, approximately 20,000 fires occur in the City of Los Angeles. As a result of these fires, approximately 53 fatalities occur annually. Determination of cause and origin is one of the most challenging and interesting duties of any Officer. To assist you in performing these duties, the Department is providing Book 83, Fire Investigation Manual. The topics covered are: Introduction to Fire Investigation Fire Chemistry and Behavior Incident Indicators Cause Determination Conducting Investigations Evidence Motives Reports and Records Courtroom Testimony Officers shall possess a thorough knowledge and members a working knowledge of the material contained in this Manual. This will ensure uniformity and effectiveness in the performance of cause and origin determination. WILLIAM R. BAMATTRE WILLIAM R. BAMATTRE Chief Engineer and General Manager WRB:ss: Book 83  TABLE OF CONTENTS I. Introduction to Fire Investigation A. Fire Department Responsibility....................................................1 B. Incident Commander Responsibility............................................2 C. Arson Investigation Section Responsibility..............................................................................3 II. Fire/Chemistry Behavior A. Introduction..................................................................................4 B. Fire/Chemistry Terms...............................................................4-6 C. Chemistry of Fire....................................................................6-11 D. Building Construction...........................................................11-26 III. Incident Indicators A. Introduction................................................................................27 B. Structures.............................................................................27-38 C. Vehicles................................................................................38-43 D. Wildland...............................................................................43-58 E. Explosions............................................................................58-63 IV. Cause Determination A. Elements of a Fire Cause......................................................64-66 B. Accidental Fire Causes 1. Electrical Fires...........................................................67-89 2. Cigarette-caused Fires..............................................89-93 3. Other Accidental Fires............................................93-107 C. Incendiary Fire Causes.....................................................107-112 V. Conducting the Investigation....................................................113-122 i VI. Evidence A. Types of Evidence...................................................................123 1. Direct Evidence.....................................................123-124 2. Circumstantial Evidence..............................................124 3. Evidence Handling................................................124-126 4. Chain of Evidence.........................................................126 VII. Motives A. Motive Types....................................................................127-131 VIII. Reports and Records A. Introduction..............................................................................132 B. Definitions of Fire Causes.......................................................133 C. Fire Loss Estimation.........................................................133-137 D. Fire Report Requests.......................................................137-138 E. Subpoena Service............................................................138-139 F. 902 Operation..................................................................140-143 G. Fire Incident Report Requests..................................................143 IX. Courtroom Testimony A. Subpoenas.......................................................................144-145 B. Preparing for Court...........................................................145-146 C. Testifying..........................................................................146-147 D. Testifying as an Expert Witness.......................................147-149 E. Definitions........................................................................149-150 X. Arson Laws A. California State Penal Code.............................................151-156 B. California State Insurance Code..............................................156 C. Los Angeles Municipal Code...................................................157 ii XI. Glossary...................................................................................................158-168 XII. Bibliography............................................................................................169-170 XIII. Arson Bulletins........................................................................................171 iii I. INTRODUCTION TO FIRE INVESTIGATION A. THE FIRE DEPARTMENT'S RESPONSIBILITY The Fire Department, under the City Charter, has the authority to investigate fires occurring within the City of Las Angeles. The responsibility for the investigation of fires is shared between the Bureau of Fire Suppression, which has the primary responsibility for the cause determination of fires, and the Bureau of Fire Prevention. In arson fires, this responsibility is translated into the protection of the public from those people who set fires. Under a written Letter of Agreement with the Los Angeles Police Department, the Fire Department, with the exception of associated major crimes such as a homicide, is responsible for the prevention, enforcement and prosecution of the crime of arson within the City of Los Angeles. In non-criminal fires, this follow-up responsibility translates into a moral and ethical obligation of the Fire Department, as the first responder who possesses the most immediate facts and evidence as to the cause and circumstances of the fire, to make an adequate investigation. In recent years, the most probable cause of a fire and the facts of the investigation as determined by the Fire Department have been increasingly used as a basis for subrogation in small and large loss fires, and fires resulting in injury and death. 1 B. THE INCIDENT COMMANDER'S RESPONSIBILITY The Bureau of Fire Suppression and Rescue has the primary responsibility to determine the cause of all fires, criminal and non-criminal. They will complete the preliminary investigation on all incidents. In doing so, they may request the Arson Investigation Section for assistance or an Arson Unit may automatically be dispatched by OCD. The Bureau of Fire Suppression and Rescue also has the follow-up investigation responsibility of fires where the total loss is less than $25,000. This Fire Investigation Manual is designed to assist you, the Incident Commander, in: Determining Fire Cause and the Point of Origin Incident Indicators How to Conduct the Investigation Identification and Preservation of Evidence Motives of the Firesetter Documentation Needed for Reports and Records Preparation for Testifying as an Expert Witness Arson Laws Terminology Used in the Fire Service 2 C. THE ARSON INVESTIGATION SECTION'S RESPONSIBILITY As per the Manual of Operation, the responsibility for determining the most probable cause of a fire rests with the Incident Commander. These investigations are to determine the cause of the fire. The purpose of fire cause determination is to establish how the fire started and the motive for starting it. For the purpose of assigning investigation responsibility, the term investigation as applied to a fire will be divided into a preliminary and follow-up investigation. The preliminary investigation will refer to the fire scene investigation and subsequent investigation needed to establish the cause. The follow-up investigation, of an arson fire, refers to the criminal investigation necessary to seek the prosecution of an arsonist. In an accidental fire, the non-criminal investigation necessary to determine the contributing factors, liability, fire code violations and needed fire code revisions. The Arson Investigation Section is organized to provide limited fire investigation service for the City of Los Angeles on a 24-hour basis. The Arson Section is responsible for the investigation of fires in which there is knowledge or suspicion the crime of arson has been committed or attempted. The responsibility also extends to the detection and apprehension of those who are involved in criminal fires. The Arson Section is required to complete a narrative report on all fires investigated and to maintain these records as a source of documentation for use in criminal and civil cases. 3 II. FIRE CHEMISTRY/BEHAVIOR A. INTRODUCTION Members that are responsible for or the investigation of fire scenes must have a working knowledge of the behavior of fire since: The member is often required to interpret the aftermath of a fire. The member is frequently required to use both technical and/or general explanations of fire behavior in legal proceedings. A knowledgeable understanding of the behavior of fire helps to demonstrate the member's expertise in the area of fire cause determination. A member's understanding and ability to explain the behavior of fire will add credibility to court testimony and to the member's opinion. A basic understanding of the behavior of fire is the foundation from which any fire cause investigation will be developed. One of the more popular tactics of arson defense attorneys is to attack the member's credibility with regard to fire behavior, therefore, a good basic understanding of the subject adds to the credibility of the member as an expert witness. B. FIRE CHEMISTRY 1. Terms relating to Fire Chemistry British Thermal Unit (B.T.U.) The amount of heat required to raise the temperature of one pound of water one degree Fahrenheit (measured at 60 degrees F.). Combustible liquids Liquids having a flash point at or above 100 degrees F. 4 Fire Rapid oxidation of a substance accompanied by the release of energy usually in the form of heat and light. Fire point The lowest temperature of a liquid in an open container at which vapors evolve fast enough to support continuous combustion. Flammable limits The term "lower flammable limits" (LFL) describes the minimum concentration of vapor-to-air below which propagation will not occur in the presence of an ignition source. The "upper flammable limit" (UFL) is the maximum vapor-to-air concentration above which propagation of flame will not occur. Flammable liquids Liquids having a flash point below 100 degrees F. Flash Point The minimum temperature at which a liquid gives off vapors in sufficient concentrations to form an ignitable mixture with air near the surface of the liquid. Heat A form, of energy associated with the motion of atoms and molecules. Heat of combustion The amount of heat released during the complete oxidation of a substance. Ignition temperature The minimum temperature to which a substance must be heated in air in order to initiate or cause combustion, independent of the heating element or source. The ignition temperature of ordinary combustibles is between 300 and 1000 degrees F. 5  Oxidation As a substance burns, it mixes with oxygen and produces heat. Specific gravity The ratio of the weight of a solid or liquid substance to the weight of an equal volume of water. Temperature The quantity of heat concentration. The intensity of heat is measured in degrees (Fahrenheit or Celsius). Vapor density The weight per unit volume of a pure gas or vapor. In fire protection, vapor density is reported in terms of the ratio of the relative weight of a volume of vapor to the weight of an equal volume of air under the same conditions of temperature and pressure. A vapor density less than 1.0 indicates a vapor lighter than air. A vapor density more than 1.0 indicates a vapor heavier than air. C. CHEMISTRY OF FIRE 1. Classification of fires Class "A” fires are fires involving ordinary combustible fuels. Class "B" fires are fires involving liquid fuels. Class "C" fires are fires involving energized electrical equipment. Class “D" fires are fires involving combustible metals. 6 2. The fire triangle Heat Fuel Oxygen 3. The fire tetrahedron In reality, fire has four parts which are necessary for self-sustaining, open flaming combustion: Heat Fuel Oxygen Uninhibited chain reaction among all parts of the tetrahedron. In the flame, many chemical reactions occur which produce additional heat. When certain extinguishing agents are introduced, it breaks up this chemical reaction and extinguishes the fire without affecting the heat, fuel, or oxygen sides of the fire triangle. These extinguishing agents are: Dry chemical Halon 4. Pyrolysis Pyrolysis is the chemical decomposition of matter through the action of heat. Early indications of the pyrolysis process are usually observed as discoloration of the fuel. As pyrolysis continues, combustible gases are released and a black carbon residue called "char" remains. The fuel continues to dry and char as the fuel continues to absorb heat. As pyrolysis continues, sufficient combustible gas is evolved to produce an atmosphere rich enough to support combustion. If the fuel continues to be heated slowly, but there is not sufficient heat present to reach ignition temperature, pyrophoric carbon may result. 7  Normally, minimum- temperature associated with development of pyrophoric carbon may become hot enough to cause surrounding fuels to reach ignition temperature. At the point of origin, combustible materials may be totally carbonized while adjacent areas may be undamaged. 5. Ignition and Combustion of Wood Products As fuel is first heated to a point where its surface reaches the* boiling point of water, flammable vapors are released. As heating continues/increases, the drying process continues and ignition of the flammable vapors occurs when the temperature is sufficient to cause these vapors to ignite. 6. Heat Transfer The transfer of heat is usually the key element in ignition (and extinguishment) of most fires. Heat is transferred in four ways. a. Conduction The transfer of heat from one object to another through direct physical contact. Examples: Metal pipes in the fire area conducting heat and spreading the fire through walls or other combustible assemblies to involved areas. Heated steel structural members spreading the fire to uninvolved areas. b. Convection The transfer of heat by some circulating medium (liquid or gas). This is the form of heat transfer most responsible for fire spread in structural fires. Example: The spreading of fire from lower to upper structural areas when upper areas become heated to their ignition temperature. 8  c. Radiation The transfer of heat as energy traveling through space or materials as waves. Example:Exposure problems in large fires. d. Direct flame impingement Direct flame contact with combustibles. 7. Phases of fire Most fires (and especially those in structures) can be divided into three separate phases: a. Incipient phase (Growth) Although actual flame temperatures can reach 1000 degrees F., temperatures in the surrounding area are not greatly increased. There is free burning with open flame. Oxygen in the area remains near 21%. Thermal updraft causes heat to accumulate at the higher portions of the area. b. Free burning phase (Fully developed) Air from the surrounding atmosphere is drawn into the fire. "Mushrooming" may take place and flame is present. oxygen content of area is usually reduced to 16% - 18%. Fire gases which may be present are carbon, carbon monoxide, carbon dioxide, water, sulfur dioxide, etc., depending on fuel, heat, and general environment. "Flashover" frequently occurs during this phase. c. Smoldering phase (Decay) Free burning may cease in the fire area. Area fills with dense smoke. Oxygen may drop below 15%. Temperatures may reach 1000 degrees F. throughout the area. Improper/uncontrolled air admission may result in "backdraft". 9 8. Backdraft A backdraft is defined as an explosion or rapid burning of heated fire gases resulting from the introduction of oxygen when air is admitted into a building heavily charged by smoke from a fire which has depleted the oxygen content of a building. Cause of backdrafts: Carbon monoxide is one of the most common gases found in structural fires and is highly flammable. (Explosive limits = 12.5% - 74%). Carbon monoxide usually collects at the upper areas of a fire-involved structure and the introduction of air from below may produce the necessary air-to-vapor mixture to bring the carbon monoxide into its flammable limits. The ignition temperature of carbon monoxide (1128 degrees F.) is well below the temperature found at the upper areas of a structure involved in fire. Flammable gas + explosive (flammable) range + ignition source = explosion. Backdrafts (explosions) often produce injuries to fire personnel. Questioning fire personnel may help identify a backdraft: Heavy smoke conditions on arrival. Lack of visible flame. Improper method of entering a structure may cause a backdraft. Movement of smoke prior to explosion. Structure may appear to breathe. Whistle, jet or train sound 10  9. Flashover Flashover is the stage of the fire when all combustibles in an area have become heated to their ignition temperature, then ignite simultaneously. Flashover occurs when heat produced by-'the fire collects at ceiling level and is returned to lower areas by thermal radiation feedback. Combustible materials are heated to their ignition temperatures and fire flashes over-large areas (may involve all combustibles in the area). Flashover may cause an area to appear to have been exposed to flammable accelerants. Careful examination, however, should indicate: Burning over top surfaces of materials. Lack of normal fire spread from point of origin. Lack of accelerant residue. D. BUILDING CONSTRUCTION 1. Types of Buildings (Title 24) Type I - Fire Resistive The structural elements in Type I Fire-resistive buildings shall be of steel, iron, concrete, or masonry. Walls and permanent partitions shall be of noncombustible fire-resistive construction except that permanent non-bearing partitions may have fire-retardant treated wood. Type II - Noncombustible/fire-resistive, one-hour, or no-hour construction. Construction in which walls, partitions, and structural members are of noncombustible material but do not qualify as Type I Fire-resistive. Type III - Ordinary construction Construction in which exterior bearing walls or bearing partitions of exterior walls are of noncombustible materials and have a minimum hourly fire-resistive rating. Wood allowed for interior use. 11  Type IV - Heavy timber construction Construction where exterior bearing and non-bearing walls are noncombustible and have a minimum fire-resistive rating of four hours. Columns, beams and girders are commonly heavy timber with wood floors and roof construction built without concealed spaces. " Type V - Wood frame construction Construction in which exterior walls, bearing walls, partitions, floors and roofs as well as their supports are wholly or partly wood or other combustibles. 2. Structural Loads and Loading Dead loads The weight of the building and any equipment permanently attached or built-in. Live loads Any load other than a dead load. Live loads vary with intended or actual use of the structure. Examples of common live loads are occupants, storage, and furnishings. Fire operations increase the live loads both in water accumulation and fire personnel. Impact loads Loads which are delivered in a short period of time. Impact loads may be more harmful when supported as dead or live loads. Examples of common impact loads are explosions, wind (lateral analysis), and earthquakes. Fire loads The total number of British Thermal Units (BTU) which might be evolved during a fire in the building or area under consideration and the rate at which the heat will be evolved. Occupancy type has a direct relationship to fire load and generally dictates the possible fire load. 12 3. Building elements and considerations for the fire scene investigation. Walls and Partitions Rating of fire walls. Wall finish and certifications. Wall integrity. Ceiling assemblies Concealed spaces acting as flues. Ceiling integrity. Floor assemblies Floor coverings. Floor integrity. Concealed spaces acting as flues. Attic and roof assemblies Usually susceptible to fire spread. Often constructed of unprotected materials. Storage of combustibles. Attic areas (Unprotected concealed space) cannot exceed 3000 square feet without fire walls. 13 4. Roof Construction Gable Roof Conventional or ordinary construction consists of a ridge board and rafters from the ridge board down to and across the outside walls (studs). Ridge and rafters are usually 2 by 6 inches Or larger. Rafters are usually 16 inches to 24 inches "on center". Additional support is provided by collar beams and ceiling joists. Roofs are constructed in semi-flat to steep pitches. RIDGE BOARD RAFTER CEILINGLING JOIST TOP PLATES STUD GABLE ROOF 14  Hip roof Similar to gable roof. Ends of roof terminate in "hip". conventional or ordinary construction consists of ridge pole and hip rafters from the ridge board down to and across the corners at the outside walls. Valley rafters are utilized where two roof lines are joined together. Ridge and rafters are usually 2 by 6 inches or larger. Rafters are usually 16 to 24 inches "on center". Various degrees of pitch are utilized. RIDGE BOARD HIP RAFTER JACK RAFTER PLATE VALLEY RAFTER COMMON RAFTER 15  Flat roof Wood joists (rafters) of various sizes laid across the outside walls or outside walls to interior walls or structural supports. Joists may also be suspended by metal hangers. Joists are covered with 1 by 6 inch sheathing or plywood and composition roofing material. ROOFING MATERIAL 4' X 8'PLYWOOD OR 1" X 6" SHEATHING WOODEN JOIST FLAT ROOF 16 Bridge truss roof Wooden truss members constructed from 2 by 12 inch lumber with sloping ends. Usually a heavy grade of construction. Metal tie rods may be used vertically for additional support. Joists are 2 by 6 inches and 2 by 8 inches covered with 1 by 6 inch sheathing and composition roofing material. ROOFING MATERIAL WOOD SHEATHING RAFTERS TOP CHORD COMPRESSION METAL SUPPORT RODS BOTTOM CHORD TENSION BRIDGE TRUSS ROOF 17 Arched roofs Bowstring arch roof Arch roof with tie rods and turnbuckles offering lateral support. Tie rods with turnbuckles are used-below each arch member to support the exterior walls. Tie rods may pass through exterior walls to an outside plate facilitating identification. Tension is maintained by the turnbuckles. Top chords of arch members may utilize laminated 2 by 12's or larger. Two by 10 inch rafters are covered by 1 by 6 inch sheathing and composition roofing material. TOP CHORD COMPRESSION RAFTERS OPTIONAL WOOD SHEATHING ROOFING MATERIAL STEEL ROD BOTTOM CHORD TENSION TURNBUCKLE BOWSTRING ARCH 18 Ribbed (trussed) arch roof Usually large size (2 by 12, 2 by 14 inch) wooden members utilized to construct truss arch. Some arches have multiple laminated beams to form one arch. Rafters (2 by 10 inch or larger) are covered with 1 by 6 inch: sheathing and composition roofing material. TOP CHORD RAFTERS COMPRESSION WOOD SHEATHING ROOFING MATERIAL DETAIL BOTTOM CHORD TENSION RIBBED ARCH ROOF 19  Sawtooth roof Constructed in commercial buildings to yield additional light and ventilation. Constructed with rafters of 2 by 8 inches or larger, and utilizes wood and/or metal supports for bracing to provide additional strength. Vertical portion is usually "wired" glass with openable panes. Sloping portion is covered with 1 by 6 inch sheathing or plywood and composition roofing material. ROOFING MATERIAL GLASS WOOD SHEATHING RAFTER SAWTOOTH 20 Panelized roof This roof may be found on structures constructed of woody masonry, or concrete tilt-up slabs. This roof consists of four major components. Laminated beams Purlins 2 by 4 inch joists ½ or 5/8 inch plywood decking. ROOFING MATERIAL 4’ X 8’ PLYWOOD PURLIN JOIST 12’ TO 40’ BEAM DETAIL METAL HANGER PANELIZED ROOF 21 Metal Gusset Plate Construction Drawing "All (Residential) Rough carpentry wood trusses used both in residential (Drawing "All) and commercial (Drawing "B") applications utilize 2 X 4's held together by metal gusset plate connectors. Trusses are constructed of top chords, bottom chords, and webbing (supports between the top and bottom chords). The trusses are held together by metal gusset plate connectors. Trusses are supported at their outside edge only unless used as a cantilever truss. Eighteen gauge roof truss clips are nailed to the bottom chords and to the top plate of the interior wall. Common on-center spacing is 2 feet and may be covered with 1/2 inch plywood. METAL GUSSET PLATE TOP CHORD WEBBIN COMPRESSION G PLYWOOD ROOFING MATERIAL BOTTOM CHORD TENSION METAL GUSSET PLATE CONSTRUCTION 22  Metal Gusset Plate Construction Drawing "B" (Commercial) WEBBING PLYWOOD TOP CHORD COMPRESION METAL GUSSET PLATE BOTTOM CHORD TENSION METAL GUSSET PLATE CONSTRUCTION 23 Open Web Construction Open web construction consists of bottom and top parallel wooden supporting beams (chords) which are cross connected by steel tube web members. The steel, tube web members are prefabricated from 1 to 2-inch cold rolled steel tubing with the ends pressed flat into a semicircular shape and a hole punched through each end. These flattened ends are then inserted into slots in the chords. Steel pins (up to 1 inch) are driven through the chord members and through the flattened ends of the web members completing the assembly. PLYWOOD TOP CHORD ROOFING COMPRESSION MATERIAL METAL OPEN WEBBING BOTTOM CHORD TENSION UNSUPPORTED OPEN WEB CONSTRUCTION 24  Wooden "I" Beam Construction Wooden "I" beam construction consists of three main components: top chord, bottom chord and a 3/8 inch plywood stem. The stem is joined to the top and bottom chords by a glued edge joint. 2 X 4 Is are used as chords. Some chords resemble plywood because of laminations. The laminations run horizontally in the chords. Common on-center spacing for this construction is 2 feet. Half -inch plywood is utilized for the decking. PLYWOOD TOP CHORD COMPRESS ROOFING MATERIAL PLYWOOD BOTTOM CHORD TENSION END VIEW WOODEN “I” BEAM 25 5. Building construction Illustration The following illustration is an example of construction terminology and techniques that are useful in developing a basic knowledge of construction fundamentals-. WALL FRAMEWORK 1. TOP PLATE 2. KICKER BLOCK 3. HEADER 4. STUD 5. TRIMMER 6. FIRE BLOCKING 7. DIAGONAL BRACING 8. SILL HERDER 9. TRIMMER 10. SUDFLOORING 11. SOLE PLATE 12. FLOOR JOIST 13. SOLID BLOCKING 14. CRIPPLE STUDS 15. TREATED PLATE 26 III. INCIDENT INDICATORS A. INTRODUCTION In most cases, damage from fire leaves behind distinctive patterns. The type of material burning, the manner in which it was ignited and how long it burns dictates the pattern(s) that remain. The burn patterns may be very obvious or extremely subtle, requiring an exhaustive search. The fire scene Investigator must be able to follow the path of the fire by reading these patterns. The area of origin can best be determined by having the knowledge and experience to recognize these patterns or incident indicators. Burn patterns and the ability to recognize them are fundamental to the fire scene investigator. There are definite relationships between the point of origin and the fire cause. Conclusions should be based on the preponderance of the indicators and the total fire scene. B. STRUCTURES 1. Preliminary observations The process of determining cause and origin of a fire starts prior to arrival on the fire scene. Some considerations are as follows: Type of occupancy Timeof day and day of week Color of fire and smoke Complete combustion often produces little or no smoke. Dense, heavy smoke often indicates incomplete combustion as the lack of sufficient oxygen usually causes flames to be darker. The color of flames may indicate the types of materials being burned. As the amount of hydrocarbons increase, the flames will become darker and more orange in color. The process continues through the extinguishment phase. How well developed was the fire upon arrival? How fast was the fire developing? How difficult was the fire to extinguish? How did firefighting tactics and strategy affect the fire travel? 27 2. Scene investigation Accurate cause and origin determination requires the fire scene investigator to develop a well organized and coordinated procedure. First, examine the entire exterior of the structure. Then examine the interior of the structure, working from. the LEAST to the MOST damaged fire areas. It is imperative that ALL areas be examined, to insure that nothing of significance is overlooked. ONE INDICATOR IS NOT SUFFICIENT. TAKE ALL AVAILABLE INDICATORS INTO CONSIDERATION. CLEAR YOUR MIND AND TAKE A SECOND LOOK. MENTALLY, MOVE THE POINT OF ORIGIN TO DIFFERENT PLACES AND TRY TO DISPROVE YOUR OWN THEORY. 3. Burn patterns Burn patterns are the burned areas as opposed to unburned areas and their relationship to each other. This will be indicated by the angle, or where the burn IS as opposed to where it is NOT. Convection and radiation play a major role in producing burn patterns. Factors that may influence the burn patterns: Fuel load Venting Firefighting activities Weather Complete and systematic removal of debris may be necessary to obtain a clear, unobstructed view of patterns. a. General The fire scene investigator should work backwards in relation to the fire's travel or spread. Examine the areas of least damage and work toward areas of most severe damage. Entire structure must be examined and conditions recorded. Ceiling damage may help locate the point of origin. 28  The area above the point of origin is usually exposed to heat and flame for longer periods and may result in holes in the ceiling. The normal growth of a fire is usually upward and outward. This burning usually produces a “V" pattern. “V" patterns may help to identify point of origin and are usually found on walls, therefore, once ceiling damage has been identified, walls should be evaluated next, then patterns at floor level. “V" patterns will usually point toward the origin of the fire. Shape/characteristic of “V" pattern: Wide “V" pattern with diffused line of demarcation usually indicates a slow smoldering combustion. Narrow “V" pattern with sharp line of demarcation may indicate flaming, rapid combustion. Inverted “V" pattern with sharp line of demarcation may indicate flaming, very rapid combustion; possible presence of flammable accelerants. “V" may only be identifiable from a distance in larger structure fires. In some cases, “V" may be vertical, horizontal or a combination of both. “V" patterns may extend around corners, walls and doors. Interior structural elements may form “V" patterns. b. Char patterns The chemical composition of wood and modified wood consists primarily of carbon with other elements such as hydrogen and oxygen with lesser amounts of nitrogen. 29  Douglas fir burns at the rate of approximately one inch in 40-45 minutes. Hardwoods burn at the rate of about 3/4 inch in 40-45 minutes and pine burns at a faster rate than fir. CHAR DEPTH MEASUREMENTS SHOULD BE USED AS AN INDICATOR ONLY! PYROLYSIS CHAR BASE ZONE BASE PYROLYSIS CHAR LAYER ZONE NORMAL WOOD CHAR DEPTH 30 If a cross section of the wood is cut and the line of demarcation examined, it will show a sharp line of charring between the burned and unburned areas for high temperatures. However, if the area between the burned and unburned is overlapping showing a grey or brown area, then this is a good indication of a slow fire with lower temperatures. DEPTH OF CHAR MEASURING TOOL WOOD CHAR 31 A fast fire does not give heat time to penetrate the wood. A slow fire would give the heat time to penetrate and there would be a "gradual" decline from unburned to charred wood. Wall coverings must be taken into consideration in regards to flame spread. How long would these coverings protect the wood? When exposed to high temperatures, such as those associated with flammable liquids, wood will usually develop deep, shiny, rolling, alligatoring blisters. Relative depth of char usually indicates length of time materials have been exposed to the flame. Deep char is usually found near the point of origin and may be a good indicator to help locate the point of origin. LENGTHWISE CUTS INDICATIVE OF SLOW BURN: INDICATIVE OF FAST BURN: GRADUAL DECREASE FROM SHARP LINE OF DEMARCATION CHARRED TO UNBURNED WOOD BETWEEN BURNED AND UNBURNED AREAS 32  The char patterns will vary based upon the fuel load. Other factors that may effect charring are: Ventilation Age of the product Moisture content Hardness/density of the product Temperature of the fire Existing fuel load around the product Firefighting tactics & strategy Expect deeper char around doors, windows and other openings. This will usually be caused by the flames venting out these openings as the fire seeks additional oxygen. c. Low burns Fire penetrates floor Consider fuel load. Consider venting. Consider floor covering. Consider radiant heat patterns. Consider sharp lines of demarcation which may indicate the presence of flammable liquids. Fuel load Table/chair legs Undersides of tables/chairs Door bottoms d. Lowest level of burning Burning in a downward direction is usually very slow. The point of origin is usually located at or near the lowest level of burning. 33  Remove debris in layers when searching for lowest level of burning. Determine if debris is normal for given occupancy or area. Establish times when various fuels/materials were heated/burned and fell to floor. Examine undersides of contents for fire damage. Fire damage to the underside of contents may indicate point of origin at lower level (chairs, sofas, tables, etc.). Examine undersides of structural elements for fire damage (shelves, doors, window sills etc.). e. Spalling Spall is the explosive breaking off of pieces of masonry materials such as concrete or brick during exposure to fire. Great care must be used while evaluating the significance of concrete spalling. Spall only suggests a possibility of the presence of flammable liquid, and in and of itself, does not prove the presence of a flammable liquid. Spalling can be caused by rapid contraction of the surface of the concrete as a result of application of hose streams. It may also be caused by expanding moisture pre-existing in the concrete prior to the fire. f. Ghost marks Asphalt tile is usually applied by use of a mastic adhesive. Most flammable liquids are petroleum-base and will be a solvent to the mastic. As the flammable liquid soaks into the joints of the tiles, it will mix with and liquefy the mastic. The tightness of the joints regulates the amount of liquid seeping under the tile. In most cases, ghost marks are caused by the application of a flammable liquid to a surface covered with asphalt tile. Ghost marks will leave a dark, discolored mark where the tile edge was located. 34 g. Smoke residue color-and density Black, sooty smoke usually indicates a hydrocarbon product (flammable liquid or foam). Dark, gray smoke adheres to surfaces and is usually sticky and difficult to wipe off. It is usually indicative of a slow or smoldering fire. The farther away from the origin, the higher the smoke line. This will-vary with the fuel load. h. Light bulbs When subjected to 900 degrees F., may swell toward the point of heat. Under fire conditions, the gas pressure in the light bulb increases while the glass is softened on the side which is heated most by the fire. i. Light fixtures Improperly installed light fixtures may cause fires in nearby combustible construction materials (joists, studs, insulation, etc.). The fire may be slow starting and may be characteristic of low temperature ignition. There may be deep charring or pyrophoric carbon in the area of origin. In fluorescent fixtures, the ballast transformer can often cause fires when the pitchblende inside the transformer breaks down. The transformers are designed to operate continuously at approximately 90 degrees F, but the temperature often goes higher. This heat can melt and vaporize the pitchblende sometimes igniting combustible ceiling material. Ballast transformers have a life expectancy of 15 years. Many older ones still in use are beginning to break down. Check for the odor of the burned ballast. Check for leakage of ballast filler material. 35 j. Glass as an indicator. Factors that effect glass behavior Age Thickness Type Temperature variation (inside to outside) Country of manufacture Glass objects located throughout the structure can be affected by smoke, heat and flame, and therefore assist with point of origin identification. The effects of these products vary with: Heat buildup Intensity of fire Speed of fire spread Distance from the fire Smoke stain and glass Smoke production varies with the type of material burned, rate of burning, and duration of burning. Smoke stains must be used as an indicator only due to the many variables affecting its presence. Accumulates on cool/cold surface. Stops forming when temperatures reach 700 degrees F. Baked on smoke stain (soot) will burn off when exposed to direct flame. Crazing of glass as an indicator. Crazingis usually caused by rapid buildup of heat during the fire. Extent and size of crazing varies with the thickness of glass, relative exposure to fire, and type of glass. 36  Heat fracturing of glass Usually larger than crazed glass. Usually caused by slower heat buildup. Checkering of glass (half-moon shape found on surface of glass). Usually results from water being applied to heated glass. Usually indicates glass was in its frame when fire streams were used. Broken glass due to mechanical force Requires careful examination. Check the glass for concentric fractures and radial fractures. Can indicate forced entry prior to fire. May produce protected areas under the glass. Explosion will cause shards of glass to be found at various distances outside of structure. Location of glass within debris Level that glass is located in debris. Determine what time during the fire the glass became part of the debris. k. Annealing of springs The term annealing, when applied to spring steel, means to make less brittle. This condition is the result of the steel being subjected to heat and allowed to slowly cool. Annealing can occur to any type of spring, whether in a vehicle or in furniture. The annealing temperature is dependent on the type and mass of the steel. 37  l. Melting points of metal Melting of metal within the structure may indicate an intense fire. Possible indicator of extreme heat at or near floor level. Extreme heat may be the result of the use of flammable liquids. The melting of different materials in the structure can be an indicator of the type of temperatures reached during the fire. m. Calcination of drywall/sheetrock Naturally contains 21% water which is chemically bound in the product. Dehydration of gypsum is called "calcination". Heat exposure causes it to undergo calcination (105+ degrees F.). The calcination process causes distinct lines to appear. This can be observed by looking at the edge of the board (cross section). C. Vehicles The average automobile contains over 300 pounds (approximately 13%) of plastics which are derived from petroleum products. Vehicles also contain other materials, such as gasoline, diesel fuel, motor oil, transmission and brake fluids, and battery acids, which among other things, are subject to combustion. In addition to these components, a normal vehicle contains mechanical systems which generate electrical sparks and heat during its normal operation. These sources of ignition are capable of starting a fire under the proper conditions. Engineering and safety designs by the manufacturer play an important role in protecting these vehicles from accidental fires. Accordingly, accidental fires involving vehicles are not as frequent as commonly believed. 1. Fire scene investigation a. Fires involving vehicles require both a fire scene examination and a detailed vehicle examination. 38 b. As in other fires, vehicles should be worked from the area of least damage to the area of most damage in an attempt to locate the point of origin. c. Begin your investigation PRIOR to overhaul. d. Survey of the surrounding area may help in the overall fire scene examination. The following indicators may be of importance: Gas cap missing. Accelerant residue under or near vehicle which may be taken from the soil. Fire damage to the surrounding area should be noted. An accelerant container may be found in the immediate area. A remote area may indicate vehicle was possibly stolen and taken to that location to be burned. e. Exterior vehicle examination may be helpful in the fire cause determination. This should include an examination of the following: Fire damage relating to roof, tires, wheels and other body components. Make note of collision damage. Check for multiple fires, although strict attention must be given to prove that one fire did not communicate to the other. Burn patterns may be evident on the vehicle especially when a flammable liquid was used to accelerate the fire. Check for obvious missing parts such as tires, wheels, doors, etc., which may possibly indicate a motive for the fire. Check for flammable liquid residue around the moldings of fenders, doors, hood, trunk and windows. Check trunk for the usual contents (spare tire, jack, etc.). An empty trunk should be considered suspicious on older model vehicles. 39 f. Examination of the vehicle's interior may reveal indicators as to the cause of the fire to include the following: A fire that is intentionally accelerated with flammable liquid in the passenger compartment will have a total, even burn from front to rear. The roof line will be severely distorted if allowed to burn for ten to fifteen minutes. Generally, the seats will show evidence of annealing (weakening and collapsing). Flammable liquid containers may be left in the vehicle by the suspect thinking they will be consumed in the fire. Regardless of the container used (metal, glass or plastic), some portion will be left as evidence. Flammable liquid residue may be present in floor carpets, under mats, in seat cushions or along door panels. Check for annealing of springs in seat cushions which is an indicator of extreme heat, but in and of itself is not necessarily an indicator of an incendiary fire. Examine the windows of the vehicle, noting their position and if they had been broken out prior to the fire (lack of heat/smoke damage). Examine doors to establish if forcible entry had been made prior to the fire. Examine interior of vehicle to establish if accessories may have been removed/stolen prior to fire. Check to see if ignition key is in its proper place or if the vehicle may have been "hot-wired". Make a complete search of the vehicle for evidence of incendiary devices. 40 g. Examination of vehicle's fuel system should include the following: Inspect the integrity of the fuel tank and its components. Examine the tank fill cap and spout. Examine fuel lines and connections (check for tool marks or tampering). Vehicles equipped with catalytic converters present special fire-related problems. A properly operating catalytic converter can reach internal temperatures of 1600 degrees. An improperly operating converter may generate an external temperature of approximately 2500 degrees Fahrenheit. This heat can be conducted through the bottom of the vehicle causing combustible material in the interior to ignite. Fires in grass and brush have been caused by vehicles parked off the road where the heat from a catalytic converter has been the source of ignition. h. Examination of the engine compartment area may reveal evidence as to the cause of the fire. Electrical engineers have greatly reduced the possibility of a fire from a short circuit in a "factory" (non-modified) vehicle. "After-market" additions to the electrical system (stereo components, etc.), however, do cause fire related problems. (1) Fuses Fuses are replaceable conductors with a low melting point. If the current passing through the fuse exceeds its capacity, the conducting material will melt and stop the flow of electricity. 41 (2) Circuit breakers Circuit Breakers are generally used to protect electric motors that are used intermittently. They are normally found on auxiliary items such as power windows and tailgate windows. (3) Fusible links Fusible links are a section of wire approximately four gauges smaller than the regular wire being used. If an overload occurs, the link will burn out before the regular wire is damaged. (4) Battery Although uncommon, batteries have been known to explode, thereby being a source of ignition. This can be caused by an excessive charging rate that causes hydrogen gas to be released. If there is inadequate ventilation, a spark can easily ignite this gas. Determine if battery was connected or missing. Examine the electrical system making certain that fuses, circuit breakers, and fusible links were operating correctly. Examine fan, generator, and air conditioner belts, as these belts are seldom destroyed in accidental fires. Check for missing motor accessories indicating that vehicle was inoperable, thus diminishing many accidental fire causes. Examine the carburetor to determine if it caused the fire or was merely an exposure of the fire (newer vehicles may not have carburetors). 42  i. Vehicle fires other-than automobiles. Recreational vehicles and trailer-mounted boats are usually of fiberglass construction and may add to the fire load and fire damage. Additional hazards of these type vehicles may be related to power generators, cooking appliances, or bilge areas. The presence of auxiliary fuel tanks may tend to alter normal burn patterns making the cause of the fire more difficult to determine. Establish if different types of fuels are present at fire scene which may also alter burn patterns. Vehicle registration and Ownership. Make note of the vehicle license plate or other descriptive indicators. Attempt to locate VIN (vehicle identification number) which is usually located on or near the dashboard. Check the glove compartment for paperwork which may aid in establishing ownership or detailed information about vehicle. D. Wildland Fires in open land covered with grass, brush, or timber are often termed wildland fires. Although they are often terrifying in their destructive power and intimidating in their coverage, they begin, like almost every other fire, with suitable fuel and a small, localized source of ignition. All fire investigations require thorough and systematic examination of the suspected area of origin and logical and analytical assessment of the evidence found. Wildland fires are no exception. The fire personnel who understand fuels, fire behavior, and the effects of environmental conditions are in a better position to interpret the subtle and sometimes delicate signs of fire patterns in wildland fires, and therefore are better able to identify the origin and cause, no matter what type of fire is involved. 43 1. Fire behavior a. Fire not influenced by strong wind will usually burn uphill in a fan-shaped pattern (“V" pattern). b. In the uncommon circumstance of a strong, downhill wind, the fire will burn down the hill only to the degree that the ambient wind can overcome the fire's tendency to burn uphill. c. On level ground, in the absence of a wind, fire will spread from the center in all directions but its spread will be inhibited by the wind it creates, blowing back into the base of the fire from all directions. Such a fire will spread very slowly. d. Ambient wind will modify the patterns by adding an additional spreading component, so that the fan shaped pattern on the hillside will deflect to one direction or the other and a predominant direction of travel will be created on level ground. e. In a fire having an extended perimeter, the direction of burning may vary locally in almost any direction depending on the interdependence of the terrain, the air currents created by the fire itself, and the ambient wind. f. Fire travel is controlled by weather, wind, fuels, and topography. g. As with structure fire investigation, no single indicator will identify cause and origin of a wildland fire. Several indicators must be identified and used to trace fire travel back to the point of origin. 44 2. Burn indicators a. Charring of a tree trunk, plant stem, or fence post is deeper on the side facing the oncoming fire. Char depth can be checked with a knife blade, pencil point, ice pick, or screwdriver. It is strictly a comparative indicator, so absolute depth is of little consequence. Tree trunks and fence posts may have been subjected to prior fire, so take that into consideration. FIRE FIRE CHAR DEPTH DEEPER ON SIDE FACING FIRE 45 b. Destruction of a -bush or tree will be more extensive on the side facing the fire. FIRE TRAVEL 46 c. The beveling effect of a fast fire may influence the appearance of branches or twigs remaining upright. Twigs and branches facing the fire may be flat or rounded stumps while those facing away from it (downwind) will be tapered or pointed. FIRE TRAVEL 47  d. A fast- moving fire creates a draft around large objects which creates an angled pattern around tree trunks, posts, plant stems, and the like. FIRE SPREAD FIRE SPREAD e. A slow-moving fire, especially one that is "backing" against the wind or down a slope, will create a burn pattern approximately level with the ground. Note that such patterns can be influenced by local fuel load such as needles, leaves, and debris around the base of the tree. FIRE SPREAD FIRE SPREAD  f. If the vertical stem is burned away, the remaining stump will be beveled or cupped on the side facing the fire. This will be true even for stems or weeds. FIRE SPREAD 50  g. When the back of the hand is brushed lightly against such stubble, the beveled tops will allow the skin to pass smoothly across in the same direction as the fire but resist with sharp points a hand passing in the opposite direction'. SMOOTH FIRE TRAVEL ROUGH 51 h. Rocks, cans, signs, and other non-combustibles will provide a barrier to the flow of the flames and show greater heat discoloration on the side facing the fire. Lichen, moss, and close-growing grass may survive on the side away from the fire. FIRE TRAVEL 52 i. Tall weeds and grass, when burned by a slow-moving fire (particularly as it backs along the flanks) will be undercut by the fire moving along the ground. The stems, if vertical, will then fall toward the fire with the heads of grass stems pointing back toward the fire origin. This effect is highly dependent on the wind conditions prior to and during the fire. Tall grass that is already matted down pointing away from the fire will fall in that direction, so there is often conflicting directions from such indicators. FIRE TRAVEL j. The height of remaining stems and grasses is roughly proportional to the speed of the fire. The effect is dependent on the moisture content of the plants and will not be visible in areas that have re-burned. 53 k. In the immediate vicinity of the origin, the fire will not have developed any particular direction and the indicators will be confused or contradictory. Fuels in the form of grass or weeds may still be upright or only partially 'burned in the immediate area of origin. l. Extension of a fire beyond a barrier, for example, a road or river, will cause the appearance of a brand new origin. This is particularly true when the "new" fire is started by airborne embers or burning debris from an established fire rolling downhill (sometimes called "spot fires"). 54 3. Determine the Area of Origin a. Utilize firefighters and witness statements to determine the area at which the fire was first observed. b. Depending on the nature of the terrain and the extent of the fire, a fan-shaped or V-shaped pattern may be visible from a short distance away. The apex of this pattern can then be selected as the focal point for the search pattern. LATER DEVELOPING STAGE START SEARCH TYPICAL “V” PATTERN 55  c. Identify burn indicators and work backward to identify the area of origin. d. Take into consideration the wind direction at the time of the fire and the relative humidity. e. once an area of origin is located, rope it off This will control access to the area and limit damage to the physical evidence. f. Conduct a slow and systematic search of the area of origin to determine the source of ignition. 4. Sources of Ignition a. Unattended fires or fires inadequately extinguished by campers, hunters, and others. b. Carelessness with smoking materials, including burning tobacco and matches. Cigarettes may not ignite dry vegetation unless the relative humidity is under 22%. c. Trash burning and, in some areas, controlled grass and brush burning. d. Sparks from vehicles, especially locomotives or other motor-driven equipment. e. Heat and/or fragments from a disintegrating catalytic converter. f. Lightning, which is a major cause of timber fires. g. Power transmission lines and accessories such as transformers. (1) Transformer short circuits and malfunctions (2) Leakage over dirty insulators and supports (3) Fallen wires (4) Arcing between conductors (5) Grounding of in-place conductors (6) Birds coming in contact with conductors 56  h. Arsonists generally- use a lighter or match, but may use a variety of devices, i.e., road flares, matchbook devices, etc. Look for multiple points of origin. i. Firearms, which under certain circumstances may blow sparks of burning powder into dry vegetation. j. Spontaneous combustion, limited to very specific types of circumstances. k. Overheated machinery which may be in contact with combustibles. l. Miscellaneous objects, sometimes present among trash, including glass that can focus the sun's rays (burning glass effect). m. Sparks from any source, such as, impacts of metal with rocks or static discharge. n. Fireworks and/or explosives igniting dry vegetation or wood shingles. 5. Evidence a. Identify human and/or animal travel in the area. b. Photograph fire scene and the burn indicators that lead to the area of origin. c. Photograph footprints and tire tracks. d. Identify evidence of haste in leaving the area. e. Evidence of area use by humans. f. Evidence of accidental fire cause. g. Evidence of incendiarism: flares, device remains, placement of types of fuels, multiple points of origin and accelerants. 57  h. Evidence collection: (1) Use proper containers. (2) Photograph all evidence prior to picking up. (3) If possible, sketch the scene and the location of the evidence. E. Explosions An explosion is defined as the sudden and rapid escape of gases from a confined space, accompanied by high temperatures, violent shock, and a loud noise. To clarify, an explosion is the result of an unstable compound or condition returning to a more stable condition with great speed. It will be accompanied by the release of energy, heat, light, and noise. Two pressure waves result from an explosion. The first is positive wave which is the force of the explosion travel away from the center of the explosion in all directions. second or negative pressure results from the first and is air rushing back toward the center of the explosion to the to fill the vacuum created by the passage of the positive wave. The negative wave has about 60 percent of the power developed by the positive wave. When responding to a possible explosion, keep alert as the scene is approached. The clues to look for in an explosion are any physical evidence of forces exerted on the structural components of the structure. This could include broken glass or debris from the structure located some distance from the involved structure. Having determined an explosion has occurred, the next step is to determine the origin of the explosion. 58 1. Types of explosions a. Mechanical A mechanical explosion is any explosion that occurs within a container or vessel. This. type of explosion must involve an unstable physical condition which consists of pressure on one side of the container and a pressure on the other side of the container that is higher or lower. This condition might only occur for a millisecond as in the case of a pipebomb. b. Chemical A chemical explosion is caused by the rapid conversion of a chemical compound into gases. This compound may be either solid or liquid. The conversion takes place in an extremely short span of time and is accompanied by shock waves, a loud noise, and high temperatures. c. Nuclear A nuclear explosion occurs within the atom of an element and may be either nuclear fission or nuclear fusion. 2. Common sources of explosions Gases - natural gas, sewer gas (methane) , LPG, and other flammable gases. Flammable Liquids - gasoline, solvents, cleaning fluids, and other low-flash point flammable liquids. Dusts - combustible metal, agriculture material, plastics, and carbonaceous dusts. Unstable or explosive chemicals. Steam, air and electrical explosions. Explosives and blasting agents - commercial types of dynamite and TNT, bombs, and improvised explosive devices (IED). 59 3. Indicators of accidental-explosions Types of explosions and their indicators depend on what caused the initial explosion. a. Natural gas Depending on the amount of natural gas that fills the structure before it reaches a source of ignition will determine the amount of damage. Natural gas will travel from room to room filling all areas. Because it is lighter than air, it will travel upward until it reaches an area that is blocked. It will continue to fill the structure even flowing into a basement area or sub-floor. It often finds its way into sewers, pipe chases, and tunnels. It will continue in this manner until it dissipates or reaches a source of ignition. You will frequently find the structure bulging from all sides where the explosion has traveled from room to room. You might find external walls blown outward with interior walls still intact. This phenomenon occurs due to the pressure being equal on both sides of the interior wall at the moment of the explosion. Since natural gas is lighter than air you will normally find the upper portion of the structure more heavily damaged than the lower areas. A natural gas explosion will not always cause a fire. b. Liquid petroleum gas Liquid petroleum gas such as butane and propane are heavier than air and tend to seek lower levels in structures such as basements, sub-floors, and crawl spaces. The walls of a structure will frequently be blown outward from the bottom floor plate or sub-floor. Another danger of LPG is that when its container is heated, it is subject to a B.L.E.V.E.. This usually occurs from direct flame impingement on the container. 60 c. Gasoline Gasoline vapors are heavier than air and tend to flow along at floor level. If a source of ignition ignites the vapors, the resulting explosion will usually blow out the lower portions. of the structure depending on the amount of vapors present. You will usually have a fire after a flammable liquid explosion. d. Dust explosions Under favorable conditions, a dust explosion can occur in any industrial occupancy where combustible dusts are created and allowed to accumulate. Many materials are innocuous when intact, but become explosive when finely divided to dust. Almost all dusts are explosive with the exception of sand, rock, earth, and similar materials. In some ways dusts are more violent than flammable liquid vapors. vapors are usually dissipated by normal air currents where dusts seem to settle and build up throughout the interior of a structure. Consequently, a very small explosion may dislodge the dust and put it into suspension throughout the interior. A secondary explosion may occur and cause much greater damage. The probability of a dust explosion is directly related to the type of business and the structure involved. A dust explosion would tend to cause damage throughout the interior as opposed to one specific area. This type of explosion will not necessarily result in a fire. e. Backdraft A backdraft is the rapid combustion of flammable gases that have been heated above their ignition point. This condition develops due to insufficient oxygen. It usually occurs during the smoldering phase of a fire as oxygen is introduced into the confined space. 61  A backdraft condition can usually be recognized by the heavy, thick, yellow/gray smoke puffing out of the structure with little or no signs of flame. As entry is made, a whistling sound can be heard as air is sucked into the structure. f. Boilers and water heaters These explosions occur when the internal pressure becomes too great for the container. There will not normally be a fire and evidence of the container should be found. Examine the container as it should show signs of an internal explosion. g. Electrical vaults and transformers The location of the incident itself should lend some clue as to the source of the explosion. An example would be where an explosion occurs in an underground vault. You might find the steel cover completely lifted off and some distance away from the vault. 4. Indicators of criminal explosions When responding to the scene of a possible explosion, approach the scene carefully. Conduct a preliminary examination and attempt to determine the source of the explosion. If an explosive device (pipebomb, etc.) is found or it is determined the explosion was caused from an explosive device, follow the procedures outlined in the Fire Department Manual of Operations. Pipebombs are the most common type of Improvised Explosive Device (IED). The container can be common galvanized pipe or PVC plastic pipe which is being used with more frequency. Pipebombs are usually filled with either black powder or smokeless gun powder. These powders are a low order explosive (3000 feet per second or less velocity). The shattering effect is much less than found in high order explosives (3000 feet per second or greater velocity). 62  Low order explosions can- usually be recognized by the non-shattering, pushing type effect. Walls appear to be pushed outward, ceilings are raised, and windows and doors may be intact even though they are blown out of their frames. A black powder pipebomb explosion will usually leave black carbon deposits in the area where the bomb or device was placed. The fragments of a pipebomb will usually be long, ripped-type fragments. High explosives devices - typical high explosives are Nitroglycerin, TNT, Dynamite, Military C-3 and C-4 plastic explosives. High explosives have a shock wave of approximately 25,000 feet per second. High explosives shatter nearby windows and even windows at a greater distance. Walls will be blown out and fragmented. Debris will be found in small pieces at a great distance from the scene. There may be a crater where the device was located. The device will shatter and fragment into very small sharp-edged pieces. 5. Safety at the scene of a bombing A bomb scene is an extremely dangerous area. The possibility of a second, unexploded device must be considered. In recent years, numerous bombing incidents have been complicated by the presence of a secondary device designed to detonate at such a later time as to injure police and fire department personnel. The chance of undetonated explosives remaining in the immediate area presents imminent danger. Downed power lines, gas leaks, weakened structures, and other bomb devices also pose potential danger to persons at the scene. The Incident Commander should expend every effort to secure the scene and protect the evidence. 63 IV. CAUSE DETERMINATION A. Elements of a Fire Cause All fires must be investigated. A critical fact to keep in mind is that all fires should be considered ACCIDENTAL at the beginning of each investigation. Examination of the fire scene will either confirm the accidental nature of the fire or will establish circumstances to the contrary. An arsonist's main line of defense rests with the possibility of an accidental cause. As a result, efforts must be made to rule out all reasonable causes for the fire. There are three main elements involved in the determination of every fire cause. These elements include Heat, Fuel, and an Event which brings the two together. 1. Heat Heat energy can result from: a. An exothermic (heat-producing) reaction between fuel and an oxidant where "heat" is one of the products of combustion. b. Spontaneous heating when characteristics of certain materials cause a heat-producing reaction with or without exposure to an external heat source. This process can exist as a straight chemical interaction (such as sodium metal with water), a process of oxidation or a fermentation (known as "thermogenesis"). Some common substances subject to spontaneous heating are: alfalfa products, charcoal, fish oils and by-products, and certain metals in fine particle form. c. Electrical activity such as: (1) Overcurrent Heat buildup in insulation adjacent to wiring. (2) High Resistance Fault and material Heat buildup caused by imperfect electrical path such as frayed wires or poor points of contact. 64  (3) Arcing/Sparking Heat buildup caused by an arc, where a spark travels across a gap. This is a normal occurrence in an electrical device, where the glowing particles are confined within the unit. If this happens in an extension cord, a fire may result. (4) Lightning The discharge of electrical energy from a cloud to an opposite charge on another cloud or the ground. d. Mechanical activity (1) Frictional Heat The mechanical energy used in overcoming the resistance to motion when two solids are rubbed together. Example: a drive belt slipping against the surface of a pulley. (2) Friction Sparks Resulting from the impact of two hard surfaces, one of which is usually metal. Depending on the metal, the temperature of these sparks can range from 500 to over 2500 degrees Fahrenheit, normally above the ignition temperatures of flammable materials. Example: a tool striking the surface of a concrete floor and causing sparks. e. Heat of Compression Heat energy released when a gas is compressed. Temperature of a gas will normally increase when compressed. 65  f. Nuclear activity Heat energy is released from the nucleus of an atom along with pressure and nuclear radiation. In the process of nuclear fission, energy is released by splitting the nucleus of an atom. In nuclear fusion, energy is released by the joining of two nuclei. The energy released by nuclear means is commonly a million times greater than the energy released by an ordinary chemical reaction. 2. Fuel The ignition of a fire is dependent upon: a. Mass (amount) of the fuel b. State of the fuel (1) The fuel can consist of any solid material such as wood products or plastics. (2) Fuel can be in the form of a liquid such as any flammable fluid, either acting as a primary fuel or as an accelerant. (3) The fuel can be in gaseous form such as hydrogen gas, methane gas, propane etc. 3. Event An event which brings the heat source and the fuel together can be: a. an Action (Acts) b. a Lack of Action (omissions) 66 B. Accidental Fire Causes 1. Electrical a. Introduction Electricity is blamed for being the cause of many fires only because it may be present in a suspected area of origin. Electricity is capable of, and responsible for, causing fires. However, its mere presence at the area of origin is not sufficient to allege it is responsible for the fire. A thorough investigation of the electrical system in question must be undertaken to corroborate or eliminate the probability of an electrical failure. b. Basic Electricity All matter is composed of molecules which, in turn, are composed of atoms. The atom is the building block of matter. An atom is composed of a positive nucleus (protons and neutrons) surrounded by the negative electrons which rotate around the nucleus of positive charges in the same manner that the planets revolve around the sun in our solar system. To comprehend electricity, an understanding of the following terms is essential. c. Definitions ELECTRON - The very small negatively charged particles which are practically weightless and circle (orbit) the nucleus of an atom. FREE ELECTRONS - Electrons that have left their orbit in an atom and are wandering free through a material. ELECTRIC CURRENT - The movement of free electrons. POSITIVE CHARGE - A deficiency of electrons. NEGATIVE CHARGE - A surplus of electrons. CONDUCTORS - Materials that permit the free movement of many electrons such as silver, copper.- aluminum, zinc, brass, and iron (listed in order of ability to conduct). 67 INSULATORS Materials that do not permit the free movement of many electrons such as dry air, glass, ceramics, mica, rubber, and plastics (listed in order of their ability to insulate). POTENTIAL (VOLTS) - The ability of a source of electrons to overcome resistance. As compared to a water system, it would be water pressure. CURRENT (AMPERES) Rate at which electrons pass through a circuit. As compared to a water system, it would be gallons per minute. RESISTANCE (OHMS) - Opposition offered by a material to the flow of current. As compared to a water system, it would be friction loss. POWER (WATTS) - Rate of energy use or dissipation. The product of POTENTIAL x CURRENT (115 volts x 1 amp = 115 watts). DIRECT CURRENT - Current that always maintains a direction of electron flow. ALTERNATING CURRENT - Current will periodically change the direction of electron flow (regulated at 60 times per second in the United States). FAULT - A partial or total failure in the insulation or continuity of a conductor. GROUND FAULT - An insulation failure between a conductor and ground, where the failure is not to a grounded conductor normally intended to carry current in the circuit. SHORT CIRCUIT - A fault where there is an abnormal connection between two points of different voltage in a circuit. A short circuit occurs between conductors that are intended to carry current under normal operating conditions. 68 d. Types of Electricity (1) Static Electricity Static electricity means electricity at rest on the surface of a body as distinguished from the commonly recognized type of electricity known as electricity in motion. The terms are primarily used to describe effects, such as the sparks observed when one walks across wool carpeting on a dry day and touches a metal object. This is compared to the completely different effects of electricity in motion which are the production of heat and light and magnetic forces such as used to drive electric motors. Static has also been known as frictional electricity since it is generated by rubbing or contact and separation of the surfaces of two dissimilar bodies. When sufficient charge has accumulated, a spark or electrical discharge may be formed. It is this resulting spark which often causes the ignition of flammable materials. Any process that involves the storage and handling of flammable gases and liquids, combustible fibers and dusts, and similar easily ignitable materials can be subject to the fire hazard of static electricity. Although there is no generation of static electricity in the actual storage of flammable liquids, static charges are produced during the turbulence in mixing, flow, or discharge of liquids or gases. Sparks from static charges occur more frequently in the dry winter weather than in the hot, humid months of summer. 69 (2) Current Electricity Electrical energy is transferred through conductors by means of the movement of free electrons that migrate from atom to atom inside the conductor. Each electron moves a very short distance to a neighboring atom where it replaces one (or more) of its electrons by forcing it out of its outer orbit. This continues until the movement of electrons has been transmitted throughout the length of the conductor. Current electricity may be generated in various ways. One way is through the use of an electric generator. In this device, a magnetic field is brought near a coil of wire. As long as the magnetic field is changing, that is, the coil or magnet is in motion, a current will be produced in the coil. Another way of setting electricity in motion is by the use of chemical energies in an electrical cell (a group of cells is called a battery). If we wish to have the electrical energy do useful work, we must provide an appropriate electrical path for the current to flow through. In this respect, it is similar to a water circuit. If we want to do something with water, we must have a path to pass it through (a pipe). Voltage can be thought of as the electrical pressure forcing the electrons through the circuit and current as the electron rate. 70 Any time a current of electricity is flowing, a magnetic field will also be generated. A magnetic field is developed around any wire carrying an electric current. If the wire is wound into a coil, the magnetic field will be concentrated. This is the basis of an electromagnet. Whenever a conductor is moved through a magnetic field, an electric current will be generated in the conductor. An electric generator works on the principle that a coil of wire moves through a magnetic field. An electric motor is exactly the opposite. A coil of wire is in a magnetic field in the motor. When a current is sent through the coil, there is a magnetic field produced by the coil in the opposite direction to the magnetic field normally present in the motor. This causes the motor to rotate. The design of a circuit can be such that one of these effects (heat or magnetism) can be made greater than the other, but we can never completely eliminate any one of them. In electric heaters, the purpose is to convert electrical energy into as much heat as possible. We have no use f or the magnetism which is produced. However, it is present around the heating coils as well as around the conducting cable. In an electric motor, the desired product is magnetism, heat being undesirable. The electrons passing through a conductor constantly collide with other electrons. This causes heat to be produced. The greater the current, the more heat produced. If the size of the conductor is undersize, it can become very hot and become a possible ignition source. Some materials are better conductors of electricity than others. In other words they will transmit electrons better than other materials. 71  Metals are generally considered to be good conductors of electricity. On the other hand, materials such as glass, stone, plastics and synthetic textiles resist the flow of electricity, and as nonconductors, are used as insulators. (3) Conduction Heating The heating of conductors used to convey current is negligible under ordinary circumstances. The codes limit the current a conductor can carry and therefore the amount of heat generated. This limit depends upon the size of a conductor, its composition, and the type of insulating covering. Where these limiting currents are exceeded (where a conductor is overloaded), the generation of heat may become a hazard. A small overload has only a minor affect on overheating due to the "built-in" safety factor. For instance, a 30 ampere fuse used instead of a 20 ampere size is a 50% overload, but even with this amount of overload, some time would be required to feel the temperature rise of the conductor. Extension cords are easily overloaded because they are usually small in diameter and rated for less ampacity than the service they are plugged into, such as an 18 AWG lamp cord plugged into a 20 ampere receptacle circuit. Careful examination for signs of entrapped heat will be indicated where identification labels are around the cord, or where the card enters the plug. If the condition exists for a long period of time, the insulation will become separated from the wire conductor. Consider the situation where a small #18 AWG extension cord is plugged into an appliance circuit protected at 20 amperes. In case of a short circuit in the extension cord, possibly from frayed or cracked insulation, the current has to be 400% of rated value for the breaker to function (#18 AWG rated at 5 amperes). 72 This could cause overheating of the extension cord. The circuit feeding the receptacle would not be overheated since, if properly insulated, it would have been #12 AWG and rated at 20 amperes. Conduction heating heats the full -length of the wire all the way back to the box. Extreme overcurrent can cause the wires to reach fusion temperature and when the initial point fuses, an arc can form. If the insulation becomes destroyed first, the resulting bare wires will touch and arc. When these things occur inside metal boxes or conduit, the failures are usually trapped and of little concern. However, if the failure has sufficient energy to burn a hole through the metal enclosure, a fire may result. Frequently, the examination of the wiring in an unburned area can provide useful information such as its age and general condition. If it is older and the insulation has become brittle and cracked, electrical problems should be considered. If a section of undamaged wire between the suspected area and the supply can be found, the condition of the conductor can provide some useful information. If the insulation and wire are in a new condition with no tarnishing of the conductor, it would be unlikely that overcurrent occurred to the degree where ignition had taken place. Electrical arcing, however would still have been possible under these conditions. When an electric current flows through a single circuit path, the current (amperes) is the same in all parts of the circuit. The temperature at any point is dependent on the electrical resistance at that point and also upon the rate that heat can be transferred away. Referring back to the previous example, the #18 AWG wire has a higher resistance per unit length than the #12 AWG. Therefore, it will operate at a higher temperature. 73  Heating of electrical wires also occurs from loose or poorly made connections and terminations. Cords under rugs and carpets or cords left coiled up, entrap heat causing insulation overheating with subsequent degradation and possible failure. 1 (4) Contact Resistance In order to act as an ignition source, whether it be by overcurrent, sparks, or arcs, there must be a flow of current. AN ELECTRIC CIRCUIT HAVING VOLTAGE SUPPLIED TO IT BUT NO CURRENT FLOW WILL NOT CAUSE IGNITION. When current flows through a circuit, heat is produced throughout the circuit in proportion to the resistance at any particular point. The current flow through a circuit is inversely proportioned to the resistance: the greater the resistance, the less the current flow. The total resistance of a circuit determines the current flow (at a certain voltage) and thus the total rate of heat production (watts). The distribution of the resistance throughout the circuit determines where the heat will be concentrated. The points of high resistance can be where a portion of the conductor size is smaller, where the conductor material is different (as in an electric heater), and at connection points (ends) where poor electrical contact or splices are frequently made. Good practice calls for the latter to be made in protective enclosures. 74  In order to minimize heat buildup at connections, the following is mandatory: The full cross-sectional area of the conductor be maintained. Positive contact of the conductors be maintained. This means that no oxide or other film or foreign material appears between the conductors. An example of the first case would be the use of the inexpensive "zip" cord plugs that are installed by merely pushing the cord into a slot in the opened plug and them pushing it back together. The connection into the wire is made by needle-like points being pushed through the insulation and into the conductor. The cross-sectional area is diminished at this point and if used for anything other than perhaps a clock or small lamp, excessive heating can occur. e. Residential electrical systems Almost every residential building in the