Fire and Explosive Investigations Flashcards
(32 cards)
What is oxidation?
oxygen combining with substances to produce new products
What is energy and how is heat achieved
- the ability to do work
- by breaking (absorb E) and forming (releasing E) bonds
What is combustion?
more energy is released than needed to break bonds
excess energy is heat and light (heat of combustion)
What is the minimum temperature at which a fuel burns?
ignition temperature
in what state will fuel create a flame?
gaseous
the lowest temperature that a fuel will create enough vapour to burn is what?
the flash point
what is pyrolysis?
the chemical breakdown of a solid material to a gaseous product (wood)
what is the flammable range?
the lower and upper limits between which a mixture of gaseous fuel and air will burn if an ignition source is introduced
what is it called when a fuel burns without a flame
glowing combustion
true or false: the rate of a chemical reaction increases with the temp
true
what is the process called when a fire is created by a natural heating process in a poorly ventilated area?
spontaneous combustion
can a fire scene be searched immediately without a warrant?
yes
why might a fire scene investigator be working against time?
- accelerants after extinguishing evaporate over hours to days
- accelerants in soil can be degraded by bacteria
how is a fires origin determined?
typically the lowest point with the most burn damage, V-pattern, or use streamers to determine locations
what is a flashover and why is it a problem?
- temperature causes the ignition of all flammable objects
- creates the illusion of multiple fires
what device can rapidly screen for volatile residues?
a sniffer that sucks up fumes, dogs can also be used
how is evidence collected from a fire scene?
- 2-3qts of ash and soot from the origin and all porous materials
- fill an airtight paint can 2/3
- collect a control sample, used to test for normal maintenance chemicals
- collect any ignitor devices
what is the headspace method?
- heating the airtight container to create a vapour in the ‘headspace’
- extract with a syringe and inject into the GC
- compare with known samples
what is the vapour concentration method?
- charcoal strip is heated in the sample
- extracted and washed with a solvent to remove accelerant
- inject into GC
how does GC and MS work?
- GC creates discernable patterns based on number of C molecules or boiling point range
- may be complicated by mixed samples
- MS fragments samples into ions
- can filter to see peaks associated with a particular accelerant
what is an explosion?
- rapid combustion + the creation of a large volume of gas
What is an oxidizing agent and why is it used?
- a chemical that supplies oxygen
- reaction occurs so rapidly that environmental oxygen can’t participate, need its own source of oxygen
What is a low explosive?
- relatively low rate of reaction called deflagration
- explosive and lethal only when confined
- produces subsonic pressure waves
- includes blackpowder (potassium nitrate, charcoal and sulfur), smokeless powder, chlorate mix, and gas-air mix
What is a high explosive?
- react at a higher rate, called detonation, supersonic
- Primary: very sensitive, violently detonate
- Secondary: insensitive, burn
