Lecture 16: Fire and Explosions Flashcards
What is fire in relation to oxidation?
Fire is a form of oxidation where oxygen combines with other substances, releasing energy in exothermic reactions.
Describe the energy manifestation in oxidation reactions.
Energy in oxidation reactions can manifest as heat and light, with reactions releasing more energy than needed to start.
Explain the concept of flash point.
Flash point is the lowest temperature at which a liquid generates sufficient vapor to ignite and burn.
What is combustion?
Combustion is a chain reaction requiring fuel vapor, oxygen, and heat to initiate and sustain fire.
What are the heat transfer mechanisms in fire?
Heat transfer in fire involves conduction through solids, radiation via electromagnetic radiation, and convection through fluid movement.
What role does oxygen play in combustion?
Oxygen must be present in sufficient quantity to combine with the fuel for combustion to occur.
Why is heat necessary in combustion reactions?
Heat is essential to initiate and sustain combustion reactions by raising the temperature of the fuel to its ignition point.
In what physical state does combustion to produce a flame typically occur?
Combustion to produce a flame usually occurs when the fuel is in a gaseous state.
What is the flash point of a liquid fuel, and why is it significant?
The flash point is the temperature at which a liquid fuel vaporizes enough to ignite; it indicates the temperature needed for combustion.
Explain the process of glowing combustion or smoldering.
Glowing combustion occurs at the fuel-air interface, seen in examples like a cigarette or embers of a fire, where slow oxidation takes place.
What challenges do arson investigations pose?
Arson investigations pose challenges due to meticulous planning, absence during the act, and extensive destruction.
What is the role of criminalists in arson investigations?
Criminalists detect and identify chemical materials at the scene and reconstruct igniter mechanisms.
What does determining the cause of a fire require?
Determining the cause of a fire requires an investigator with specialized training and experience in fire investigation.
What is fire in terms of chemical reactions?
Fire is a form of oxidation, involving the combination of oxygen with other substances to produce new substances.
What is an exothermic reaction in the context of oxidation?
Oxidation reactions release more energy than needed to start the reaction, known as exothermic reactions.
What are some indicators of arson in a fire scene?
Indicators include separate fires, streamers to spread fire, and irregular patterns from accelerant pouring.
How can the probable origin of a fire be determined?
Fires typically move upward, with the lowest point showing the most burning indicating the likely origin.
What type of residues suggest the use of flammable liquids in arson cases?
Severe burning on the floor suggests flammable liquid use, as they are usually not fully consumed in a fire.
What are some ignition devices that arsonists may use to start fires?
Arsonists may use matches, burning cigarettes, firearms, or other ignition devices to start fires.
How are accelerant residues collected at the fire’s origin for analysis?
Ash, soot, and porous materials with residues are gathered in airtight containers like paint cans or glass jars for analysis.
How should ash, soot, and porous materials with potential accelerants be stored?
In airtight containers like new paint cans or wide-mouth glass jars, avoiding plastic containers.
What are recommended for detecting flammable liquid residues at a fire scene?
Using a vapor detector (sniffer) or trained canines.
Why is substrate control important when collecting materials suspected of containing volatile liquids?
To have uncontaminated controls from another area of the scene for comparison and analysis.
How are accelerant residues from fire scene debris recovered in the laboratory?
By heating the airtight container holding the sample to drive off volatile residues, then analyzing the vapor collected.
