Forensic Chemistry Flashcards
What does forensic chemistry analyze?
- non-biological trace evidence
ex: fibres, paint, glass, arson, explosives
What types of crimes does forensic chemistry cover?
- break and enter
- hit and run
- arson
- bombings
- terrorism
What are the 5 steps for analysis?
- determine substance (gasoline)
- determine distributor (Esso)
- determine batch (specific location and date)
- qualitative analysis (what substances were present?)
- quantitative analysis (% of each)
What are 5 types of non-destructive analysis?
- visual inspection (colour, design, surface quality)
- microscopy (opacity, reflectance, refractive index)
- UV-Visible micro-spectrometry (pigments)
- Fourier-transform infrared spectrometry (wavelengths)
- micro x-ray fluorescence (inorganic materials)
What is chromatography? List and describe the different types
- separates substances into components (purifies them)
1. Gas chromatography (GC) - separates based on distribution between liquid and gas phase
- sample is injected, heated, broken down into gas, and analyzed
2. Thin Layer Chromatography (TLC) - uses solid and liquid phase to separate components of mixture
3. High-Performance Liquid Chromatography (HPLC) - liquid pumped through column filled with solid particles
- as liquid moves through, sample in injected and carried through liquid
- various components will be slowed as it passes through
4. Pyrolysis - paint chips are heated into gaseous products and sent through GC
What is spectrophotometry?
- analyzes how different substances absorb light in different ways
- GC + MS = positive ID
- GC alone is tentative ID
How is significance evaluated?
- identifying substance
- class evidence
- may have low or high significance (rare = more significant)
- how common is the evidence?
- develop database and determine parent population
- how valid is database?
What are the two types of fibres?
- natural - animal, mineral, vegetable
2. manmade - synthesized or originate from natural materials (made of polymers)
How are fibres examined?
- colour, striations, cross section shape, refractive index
What dictates the significance of a fibre?
- circumstances of the case
location found, number and nature of fibres examined
Where can paint be found?
transportation - cars, bikes, boats, planes
household objects - walls, doors, window frames, paintings
What are some methods of paint examination?
- visual and microscopic examinations
- colour, shapes, surface properties, thickness of layers
- physical match based on contours, scratches
What are the 4 layers of car paint? How can it be used as class evidence?
- primer, primer surface, colour, base coat, clear coat
- can match paint in database down to make, model, and year (PDQ)
How is glass examined?
- comparing control sample from scene to recovered sample from suspect
- need to look at thickness, elemental composition, refractive index, colour
What are 3 things fire investigators are responsible for at a fire scene?
- determining origin of fire (using fire patterns)
- determine cause of fire (what fuel was ignited first and fuel source)
- determining if arson or accidental
Why are fire crime scenes more complex than regular crime scenes?
- more dangerous, hot, and unstable
- scene is destroyed by fire then water (destroy evidence of accelerants)
What is the role of a forensic chemist for a fire scene?
- detect accelerants
What are the 3 components of fire?
- fuel (combustible material)
- oxygen
- source of heat (activation energy)
List 6 things fire investigators need to look for/determine at a fire scene
- assumption of arson
- check for human remains
- identify point of origin
- search for accelerants
- search for ignition devices
- determine significance of accelerant
How are samples collected from a fire scene?
- debris is placed in a sealable gas-tight container
Describe flame over and flashover
flame over:
- unburned fuel from originating fire has accumulated in ceiling layer and ignites and burns
flashover:
- surfaces exposed to thermal radiation reach ignition temps at the same time leading to full room involvement
What are the disadvantages of flashover?
- dangerous for firefighters
- obscures fire origin and consequently the cause
What is an explosion? How does it differ from a fire?
- product of combustion accompanied by creation of gases and heat
- difference between fire is speed
List and describe the 3 effects of an explosion
- blast/pressure wave
- does the most damage
- pressure wave that radiates outward from seat of explosion - Fragmentation
- device casing breaks into pieces
- primary: shrapnel/fragments
- secondary: other objects like glass struck - incendiary/thermal component
- high temps and localized
How are explosions classified? Describe the 2 categories
- classified based on speed at which explosive decomposes
1. Low explosives: speed of deflagration - rapid oxidation, heat, light, subsonic pressure wave
- slow burning rate = suitable for throwing or propelling action
- unconfined = burns
- confined = lethal due to shrapnel
2. high explosives - speed of detonation - creates supersonic shock wave, and build up of heat and gases
Primary: - ultra-sensitive to heat, shock, friction
- detonate violently (used as detonators)
Secondary: - insensitive to heat, shock, and friction
- Burn rather than detonate in open air
What is dynamite composed of? What are the disadvantages for forensic chemists?
- composed of a ammonium-nitrate (manure)
- washes away easily, easily available, low significance
What are common components of a bomb?
- explosive
- timer
- detonator
- fuses
- batteries
- casings
