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| Questão | Responda |
| What does CFA stand for? | Common Fire Accelerant |
| Which associations agreed to who was present at a fire? | The National Agreement for fire investigation 2005 By association of chief police officers, chief fire investigators association and the Scottish forensic science liaison |
| What is the fire brigades role at a fire scene? | Save lives, extinguish fire, assess level of investigation, hand over to police |
| What is the role of the police at a fire scene? | Take charge of all suspicious/fatal scenes, assess level of investigation, do crime scene management, bring in forensic team |
| What is the forensic teams role at a fire scene? | To investigate the fire with police and FB. investigate suspicious/ fatal/high value fires |
| What are some common causes of fire? | Candles, smoking materials, cooking, electrics, children with matches, deliberate fire-setting |
| What are the reasons for deliberate fire-setting? | Revenge, fraud, suicide, cover up another crime |
| What is hypothesis testing? | Considering the various causes then ranking them based on likelihood |
| What is the aim of a fire investigation? | To determine and test hypotheses, to find the seats of a fire, to determine how the fire started, to determine how the fire spread, to recover evidence, analyse suspects and compare |
| What are fire debris samples collected in? | Nylon bag, if doubled, polythene on outside, then put in cardboard box |
| Why are nylon bags used for fire debris? | Hydrocarbons are small and volatile, can pass through polythene lattice |
| What are measures used to stop false positives in the nylon bag? | Each batch made in factory is tested for measurable levels of contaminant, control bags are taken at scene to prove bag and person not contaminated. |
| Why can tape, sticky labels or pen not be used on a nylon bag? | Tape and sticky labels contain toluene/xylenes (in petrol) and white spirit Pen contains a mixture of solvents |
| What is the purpose of the control nylon bag? | Proves no contamination since batch test, samplers hands are not contaminated. |
| What is the meaning of a positive control bag? | If the levels of control and sample are similar then there is contamination, +ve result not reported. If control bag levels a lot lower, and only contains CFA, suggests cross contamination and +ve result reported. |
| How can there be proof there is no contamination? | Control bag is negative, blanks run prior to analysis, analysed against known standards, peak area and heights. |
| How can you avoid cross contamination? | Make sure separate samples are contained separately, different samples examined in different rooms, different samples analysed by different scientists |
| Describe headspace sampling | Nylon bag heated to 110C for 10min, tenax syringe attached and 10mL taken, bag sealed and tube inserted into ATD-GC-MS |
| What does ATD-GC-MS stand for? | Automated Thermal Desorption Gas Chromatography Mass Spectrometry |
| How does ATD work? | Tenax tube leak tested, heated to 220C, sample desorbed from tube and trapped on cold trap (-30C), rapidly heated to 200C, transferred to GC |
| How does GC work? | Mixture is separated by column, then ionised by electron beam, each frgament has a different mass, the ions are focused and drawn into quads by charged plates (lenses), each mass passed through and abundance measured |
| What are the two modes of MS? | Total Ion Count (TIC) and Selected Ion Recording/Monitoring (SIR/SIM) |
| What are the advantages of TIC mode of MS? | Lots of info, can identify using mass spec databases (NIST), can quantify using peak area |
| What are the disadvantages of using TIC mode of MS? | Can only collect each fragment for a short time (ms), not very much is collected in that time, not sensitive, cannot quantify or identify unresolved peaks |
| What is selected ion recording/monitoring (SIR/SIM)? | A MS mode where only specific ions are allowed through the quadrupole to the detector |
| What is the advantages of the SIR/SIM mode of the MS? | simpler chromatograms, can collect each fragment for longer (20-200 ms), collects more ions, more sensitive (lower LOD), can quantify using peak area |
| What are the disadvantages of SIR/SIM mode of MS? | Provides very little info, cannot use libraries, not all masses are unique to a single compound, can mis-identify/mis-quantify if interferences |
| What does EIC/EIP stand for? | Extracted ion count, Extracted ion profile |
| What does the EIC/EIP do? | It produces chromatographs of specific mass ions that are commonly present in the compounds being analysed |
| What are the 5 hydrocarbon groups used to identify crude oil? | Aromatic Hydrocarbons Alkanes Naphthalenes Indanes Alkenes/Cycloparaffins |
| What are some characteristics of a petrol chromatogram? | short alkanes (C2-C5) Aromatic compounds (toluene, ethyl benzene, xylene, substituted benzenes) |
| What are some characteristics of white spirit? | 3 alkane hydrocarbons (C9-C11) with smaller substituted benzene and branched/cyclic alkane peaks in between |
| What are some characteristics of diesel? | alkane hydrocarbon large peaks (C8-C30) with small branch/chained alkanes, alkenes, cycloparaffins and substituted benzenes |
| What is the most abundant fragment on a mass spectrometry graph? | [M]+-1 Molecular ion minus one hydrogen |
| What does pyrolysis mean? | When all objects in a room burn |
| What makes a CFA chromatogram complicated? | 1. Possible CFA mixtures 2. components present due to other sources (non-CFA) 3. Partial evaporation due to heat of fire or time taken to recover |
| What are the main causes of fires? | Electrical (appliance, wiring, fuses) Human error (smoking, candles Unguarded fires Nature (lightning, spontaneous combustion) Deliberate (revenge, insurance, cover, fun, terrorism) |
| What is the definition of fire? | A chemical reaction involving the oxidation of a fuel which results in the release of energy in the form of heat and light |
| What is the fire triangle? | |
| What are some ignition sources? | flames, arcs (charge from +ve to -ve), sparks, heated objects, electrical heating |
| What is the explosion triangle? |
Image:
explosion (image/png)
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| What volume does one mole of gas occupy at STP (standard temperature and pressure) and SATP (Standard ambient temperature and pressure)? | STP - 22.41L (273K, 1atm) SATP - 24.8L (25C, 1x10^5 Pa) |
| What does the mode of burning depend on other than chemical nature? | physical state distribution of fuel environment |
| What type of fuel burns? | Only gaseous fuel, other states can be heated to burn |
| What is pyrolysis? | the chemical decomposition of a substance through heating which is irreversible in the absence of oxygen |
| What is sublimation? | the transition from solid to vapour without chemical decomposition |
| What is chemical decomposition? | The breakdown of a compound into its elements |
| What are the four aspects of combustion? | Thermodynamics (reaction feasibility) Kinetics (speed of reaction and mechanisms) Heat transfer Mass transfer |
| What are flammability limits dependent on? | Temperature and Pressure |
| What is the FLl? | lower flammability limit, the % concentration below which fuel cannot burn in air (too lean) |
| What is the FLu? | upper flammability limit, the % concentration above which fuel cannot burn in air (too rich, not enough O2) |
| What is flashpoint? | The lowest temperature that a vapour can be produced by fuel and ignited (FLl) |
| What is fire point/flame point? | The temperature at which the vapour from a fuel can be ignited to produce a continuous flame |
| What is the spontaneous ignition temperature (SIT) or autoignition temperature (AIT)? | The temperature at which fuel can ignite on its own without an external source |
| What defines a combustible liquid from a flammable liquid? | flammable flashpoint lower than 37.8C combustible flashpoint higher than 37.8C |
| What is flaming combustion? | when the liquid fuel vapourizes to gas which is igniting |
| What is glowing combustion/smouldering? | There is no flame, just heat, occurs in low oxygen, is very slow, increases with less water and smaller particles |
| What is spontaneous combustion? | A fire caused by natural heat produced in the presence of enough air and fuel |
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