Fires and explosions Flashcards
What is the activation energy of a fire?
The energy required to elevate fuel and oxygen molecules into an excited state to undergo reactions
What is the ignition temperature of a fire?
The temperature required for combustion to begin
What is the flash point of a fire?
The temperature required to convert enough of the fuel into a vapor for combustion
What is the flame point of a fire?
The temperature required to sustain a fire
What features of accelerants allow them to support combustion?
Easily vaporized and burnt easily
What are the three types of fires?
Natural, accidental and deliberate
What is self ignition?
Spontaneous combustion leading to lighting self on fire
What is direct ignition
The direct application of sparks of flames to fuel to light a fire
What is indicated about the point of origin by low burning of fire?
Fires generally start in a low area of a building to do more damage
What is indicated about the point of origin by V-patterns of smoke?
Origin is near a wall or corner, leaving smoke damage in the v-shape
What is indicated about a fire by the charring of wood?
Depth of the charring depends on heat intensity therefore more charring indicates closer proximity to fire
What is indicated about a fire from the spalling of plaster or concrete?
Occurs where the heat is most intense, surface destruction or concrete explosion from trapped moisture
What is indicated about a fire from material distortion?
Metal and glass distorts under high heat and therefore can indicate proximity and temperature of the fire
What is indicated about a soot staining by the soot staining?
Indicates fire origin and direction of travel
What are indications of arson?
Presence of accelerant near origin, elimination of natural and accidental causes, multiple points of origin and fire trails from accelerant being poured in a trail
What methods can be used to detect accelerant?
Dogs trained to sniff out hydrocarbons, gas chromatography to detect hydrocarbon
What is commonly used to package accelerant residue?
Air tight containers including paint cans and glass jars
How are hydrocarbons isolated in ignitable liquids?
Hydrocarbons are insoluble and therefore are easily extracted
How are hydrocarbons isolated in partially burnt samples?
Most volatile compounds have evaporated and therefore remaining compounds with a high boiling point can be extracted
How are hydrocarbons isolated in nearly completely burnt samples?
Nearly all the compounds have evaporated and therefore it is difficult to extract sufficient evidence
What is involved in passive adsorption?
Placing a charcoal or synthetic material to adsorb the hydrocarbons with the sample and leaving overnight
What is involved in active adsorption?
Charcoal or synthetic material to adsorb the hydrocarbons is placed in a tube and the sample is pumped through
What is the blast pressure of an explosion?
The formation of a partial vacuum as compressed air from the explosion rushed back, creating a negative pressure phase
What is the fragmentation effect of an explosion?
Propelling pieces with great force from the explosion, including shattered bomb or metal wrapped around bomb
What is the thermal effect of an explosion?
The large ball of fire produced at the instant of detonation
What is a low explosive?
Explosion with velocity less than 3280 fps where the oxygen and fuel is mixed
What is a high explosive?
explosion with velocity greater than 3280 fps where a shock is required to break the bonds between oxygen and the fuel
What type of explosive aims to push rather than shatter?
Low explosive
What leads to a low order explosion, where the explosion occurs at less than optimal efficiency?
Using an old explosive, exposure to moisture and improper construction
What is in explosive residue?
Undetonated explosive and exploded residue products
