Fire and explosions Flashcards
What are fire and explosions?
Combustion; chemical reaction
Combustion is the reaction of what with what?
A fuel with oxygen
What does complete combustion create?
Carbon dioxide, water, and energy
What is a chemical reaction that releases energy?
Exothermic
What is a reaction that requires the input of energy in order to take place?
Endothermic
All combustion reactions are what reactions? (endothermic/exothermic)
Exothermic
In order to start a reaction, what is required? - the name of input of some energy
Activation energy
What two factors determine whether combustion results in fire or explosion?
(1) the nature of the fuel
(2) how close the oxygen and the fuel are to each other
What are 4 elements in fire tetrahedron?
A source of heat, fuel, oxygen, chain reaction between the fire and the oxygen.
What do fire investigators need to know about fire?
what a fire is, how fire can be started, types of fires, how to investigate fire scenes, fire residues and its origin, role of the forensic science laboratory
What is the lowest temperature that will allow a liquid to produce a flammable vapor?
Flash point
What is the minimum temperature to which a substance must be heated before it will sustain a burn?
Ignition temperature
What has higher temperature? (Flash point/Ignition temperature)
Ignition temperature
When does smoke occur?
When there is incomplete combustion
What is smoke made up of?
carbon particles and unburned and partially burned gasses
What is a flashback?
Fire burns with a limited supply of oxygen is suddenly ventilated, resulting in an explosive fire
What are accelerants
Fuels that are easily vaporized, support combustion, and are highly exothermic
When are accelerants used?
to make a fire burn quickly
What are the types of fires?
Natural; Accidental; Deliberate
What are natural fires?
Chief natural cause for a fire is lighting
What are accidental fires?
May arise from a number of different sources and may be difficult to distinguish from deliberate fires
What is the most important evidence?
Point of origin, cause of fire
Generally, where can investigator find the most intense burning and damage?
Point of origin
What are char patterns?
created by very hot fires that burn very quickly and move fast along its path; so that there can be sharp lines between what is burned and what isn’t.
What are V-patterns?
Fire burns up, in a V-shaped pattern, so a fire that starts at an outlet against a wall leaves a char pattern that points to the origin.
What are Heat Shadows
Occur when heavy furniture shields part of a wall; can help determine the origin point.
What is Chimney effect?
Since fire burns upward, there can be a chimney effect where the fire ignites at a point, the super heated gases rise upward and form a fireball, which continues straight up to burn a hole in the ceiling.
What must you find to identify the cause of fire? (3)
- fuel 2. source of heat 3. how the two came together
Where should investigators focus on when finding a trace evidence?
Points of entry, exil and origin
Where will acceleants most often be found?
at point of origin or along fire trails
What should you use to detect accelerant?
Hydrocarbon-sniffing dog
What is a less sensitive method to detect accelerant?
stripped-down gas chromatograph with a gas sensor
What kind of container must be used for packaging fire scene evidence? why?
Airtight; it prevents evaporation and contamination
What kind of container is used to package fire scene evidence?
Metal; airtight, rugged, easy to use
What signs indicate non-accidental fire?
odors, furnishing, clothing, locked windows, blocked doors, two or more points of origin, narrow V-pattern, floor charred, trailers
What is furnishing?
Removal of personal objects and valuables
What are 6 common motives for arson?
Crime concealment, revenge or spite, monetary gain, malicious vandalism, mentally disturbed, serial arson
What kind of motive for arson accounts for the largest percentage or arson fires?
Malicious Vandalism.
What is Monetary gain?
Arson-for-profit fires are set to burn a building, vehicle, or some other object in order to gain profit from the fire.
What is the bomb seat?
origin of the explosion
What is blast pressure?
escaping gases that can travel as much as 8,000 miles per hour
What results in negative pressure?
Partial vacuum that is created in wake of blast wave, which causes air to rush back toward the bomb seat.
What is the most destructive part of the explosion?
negative pressure phase
What are fragmentation effects?
shattered bombs result in pieces that are propelled way from the bomb seat with great force
What are thermal effects?
large ball or fire or flash produced at bomb seat
What is the least damaging effect from an explosion?
thermal effects
