Forensic science

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  • Created by: Sophie153
  • Created on: 11-02-16 10:53
what is substrate?
the surface on which the trace evidence or print mark is laid
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what are four types of marks?
Extrusion marks, Moulding marks, Coatings, Machine marks (on grinding wheel, unlikely to ever be put on at same time-scratches get different marks...)
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when do impressed tool marks occur?
Produced when a hard object is impacted onto a softer surface with no lateral movement occurring between the objects. Impressed marks produce a negative image of that portion of the harder object. May be left by:–face of piler blade–Tipofscrewdriver
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what are single contact marks?
Marks produced by implements which contact the surface once on each application. Each application leaves a mark indicative of the working edge of the specific implement. Example - marks left by: – Hammers – Pliers – Axes – Screwdrivers etc.
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what are striated (scratched) toolmarks?
Produced when a hard object is moved laterally across the surface being marked. The marks produced are a series of parallel striae (lines of ridges & valleys) of varied width & depth. Minute irregularities onthe surface ofthe harder objectwill scratc
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what can these marks be left by?
Bolt cutters – Tin-snips Shearing type implements. Can be readily duplicated as their mechanism is designed to produce marks of this nature. Screwdrivers – Jemmybars -knives. May have spacing and depth depending on direction of travel& angle of appli
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what are multiple contact marks?
Marks produced by implements which touch the surface being marked, many times during a single application. Such as: – Saws – Files – Drills • The loss of ‘individual’ identifiable characteristics. as repeated application, limited to type of weapon
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tool marks sum up, how comparison and evidential value
How – forcing / cutting – 'jemmies', bolt croppers – recovered by SOCO / laboratory • Comparison – direct, microscopy – test marks • Evidential value – moderate conclusive – often with other evidence – photographs to demonstrate
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is a perfect tool shaped mark essential?
A perfect tool shaped mark is not an essential pre-requisite to obtaining a positive result,and identifications can be made from marks as small as one millimetre..
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what are impressed marks?
mpressed marks are caused when a tool is forced into softer material
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what are cutting marks?
These are marks made by double-bladed tools(e.g bolt croppers,wire cutters etc
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what are scratches?
Scratchesare produced when a tool is scraped across a surface leaving a series of parallel lines, better evidence
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what are manufacturing defects?
Small, often microscopic defects caused by slight imperfections in the machine tools and other equipment used to form and finish the product, are normally passed by the quality control because they do not effect either performance or appearance.
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what are three options to recover tool mark?
remove entire item, carefully cut out the marks,cast marks using a silicone rubber moulding compound (Always photograph mark with scale before retrieving)
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Excellent rendering of small detail. • Highcontrastfor subsequent microscopical examination. • Available in several colours. • Short setting time
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what do you need to do?
take a photo first to show no evidence, fine details are best to to recover that looks you can barely see like dust on smooth surface... overshoes aren't that useful
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footwear evidence overview, how/comparision/evidential value
ow: most surfaces: debris/impressed, apparent/latent, recoveredbySOCO/laboratory ñ enhancement Comparison: pattern,size& wear,damage. Evidential value:moderate-conclusive; often very good, FSSdatabase, identify footwear from marks, linking offences
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what are the type of footwear marks?
Three-dimensional (Three ñdimensional marks are those where the sole and/ or a heel or a shoe sinks into a soft material such as soil, snow and sand.get upper&lower heel), Two-dimensional(generally much better as dusty marks normally much better.
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about footwear marks on a scene?
It is the quality of the mark not the size of it that counts, Not all shoes have patterned soles and many identifications have been made on plain, some best quality marks occur on light deposits on floors, furniture...
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what are recovery methods?
Photography ñ Electrostatic Lifting ñ Powdering ñ Crownstone casting ñ Other chemical techniques ñ Adhesive Lifting ñ Gelatine Lifting
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Commence early 80ís. n Constraints: Bulky, Wired, Suffered from mechanical defects.
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what is a pathfinder?
put large device on floor, then lift up the film and it will show ups any marks e.g. footprints...
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what is adhesive lifting?
get marks of the floor again with adhesive paper
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what is brownstone and kaffa plaster?
write name, sale number, date to know had to be made then
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why are shoe marks good?
Unlike fingerprints,which depend on ridge characteristics that do not alter ridge characteristics that do not alter with time, most show mark identifications are made because changes over time due to way we walk...
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what are the stages of assessment?
Patterns, General Wear, Specific (Random Wear), Marks on bodies or clothing, Feet in shoes
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what are tyre marks?
Tyre marks can be left at the scene in both two-dimensional and three dimensional situations in the same way as that of footmarks. They can be found on clothes of victims of fatal road accidents. retrieval same way as footwear
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components and information of tyres
Determine the manufacturer. Track width or stance - from centre of one tyre to the centre of the other. n Wheel-base-front to back. Turning radius. Determine the tyre.
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alcohol summary
What:analysis, back calculation, technical defence. how: requirefullinformationfrompolice, analysisofbeverages,examination of drinking vessels, calculation. Evidential value: moderate- conclusive; depending on circumstance, burden of proof on defe
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what was DR. Nehemiah Drew interested in?
First documented interest in the skin's ridges in the western world, a paper written in 1684 by an Englishman
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what about Sir William Herchel?
commenced placing the inked palm impressions and, later, thumb impressions of some members of the local population on contracts.. These prints were used as a form of signature on the documents because of the high level of illiteracy in India and freq
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what about Sir Francis Galton?
ublished an accurate and in-depth study of the fingerprinting science.ecame the foundation of modern fingerprint science and technology
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Sir Edward Henry?
ublished his book Classification and Uses of Fingerprint, introduced finger print system and he first British court conviction by fingerprints
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what are fundamental principles of fingerprints?
A fingerprint is an individual characteristic.Fingerprints have general ridge patterns that permit them to be systematically classified. A fingerprint will remain unchanged during an individuals lifetime.
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what is value of finger print evidence?
Confirmation of identity of suspect in custody. Identity of suspect in custody with prints left at crime scene. Matching of prints left at scenes with known criminal records.
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what is friction skin?
The specialised configuration of ridged skin resembling corduroy, which appears only:On the inner surfaces of the hands (thenar surface)& Bottoms of the feet (plantar surface). collectively referred to as solar surfaces.
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where is true friction found?
Marsupials, Primates
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what about sweat?
Sweat pores are found in higher concentrations on friction skin than other surfaces of the body. • Secretions from these pores combine with the ridged surface to give superior walking and grasping ability.
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whats the papillary layer?
Only the hairless parts of the body - the inner surfaces of the hands and the soles of the feet. Covered with patterns formed by raised ridges of skin known as friction or papillary ridges.The study of fingerprints, or dactyloscopy, forms only one pr
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papillary layer continued
Patterns cannot be altered, except by accident, mutilation, or very serious skin desease, as they are formed in deep layers of the dermis.the skin consists of two main layers: the outer skin or epidermis
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about epidermis?
The epidermis is constantly being worn away and replaced by new skin generated by the upper layer of the dermis - a papillary layer (stratum mucosum) which is the source of the ridges known as 'papillary ridges'.
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what are pores?
Pore holes are critical to the production of latent prints Sweat reaches the surface of the hand and efficiently coats the tops of the fingerprint ridges with sweat. Sweat glands serve as small chemical reservoirs and contain a variety of water-solu
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how are fingerprint patterns formed?
ingerprint patterns are not formed at the surface of the skin but are determined by the arrangement of various elements, such as sweat glands, nerves, and blood vessels found below the surface of the skin.
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On the inner surface of the hands (thenar) and the soles of the feet (Plantar) the skin surface differs from that of the rest of the body. Flowing across these surfaces are minute ridges generally referred to as friction ridges, which run parallel
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what are latent impressions?
98%water, 2%amino acids and fatty tissue
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why do they mark ridge ends and bifurcation points?
develops picture of the person-builds up a strucute
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what are papillary marks?
Marks made by the ridge pattern of the skin surface. A deep skin layer (the stratum mucosum of the dermis) constantly generates new skin to replace worn away surface skin or epidermis maintaining the ridge pattern.Each line/ridge is called a papailla
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what are ridge characteristics?
Bifurcation • Hook • Scar • Downthrust ridge ending • Upthrust ridge ending • Ridge crossing • Enclosure • Island
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what are arches?
5% of prints are arches • Ridges run from one side of the finger to the other with no backward turn. • No delta.
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what are loops?
60% of prints are loops. • Radial and ulnar loops
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what are tented arches?
Upward thrust of spine
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what are whorls?
35% of prints are whorls or compounds. • Ridges complete tun through one complete circuit. • Two deltas.
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what are capillaries?
Capillaries are fine blood vessels, which connect arteries and veins. They allow water, proteins, gases and white cells, from the blood, to pass through the single-cell wall, to and from body tissue
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what is blood?
Blood contains red (half the blood) and white cells and platelets. • Red cells carry oxygen around the body. White cells ingest invading bacteria, protect the body from disease.White cells produce antibodies-provide immunity.Platets assist clotting
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what evidence do you get from bloodstains?
At the scene:•location of attack •method of assault •sequence of events •more than one source.On exhibits:•how it could have arisen •more than one source Evidence of contact: species of origin (what) & from whom
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blood volumne
On average, accounts for 8 % of total body weight –5/6l of blood for males – 4/5l for females. 0 percent blood volume loss, internally or/and externally is required to produce irreversible shock (death). loss of 1.5l causes incapacitation
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why is it red?
from the presence of haemoglobin.
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what is white blood cells for?
White blood cells are part of the immune system produced in the lymph glands and bone marrow and help to protect the body against foreign organisms.
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what is main function of blood?
The main function of the blood is to transport nutrients absorbed from the gastrointestinal canal to other parts of the body and to carry oxygen from the inhaled air to all cells and tissues.
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clotting process of blood
Fresh untreated whole blood will begin to clot within about five minutes after sampling forming a clump of red cells. • The clotting process can be prevented by adding an anticoagulant to the blood specimen immediately after sampling.
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what happens if add blood to reaction Phenolphthalein+HydrogenPeroxide
no reaction- pinkbecause blood contains peroxidase, an enzyme that rapidly breaks down H202 & phenolphthalein responds to this reaction.
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what is the Kastle-Meyer test?
Sequence of drops: Alcohol, hydrogen peroxide & phenolphthalein. Purple reaction indicates the presence of blood
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blood patterns can help the investigation by:
origin of the bloodstain, type of instrument to cause the bloodstain,direction object struck the victim,relative position of the victim assailants & bystanders, location and movements of victim during the attack,no of blows,truthfulness ofsuspect&wit
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what is the plane?
The acute angle formed between the direction of a blood drop and the plane of the surface it strikes.
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what are components of impact?
direction, plane, receptive surface
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different categories of blood patterns
drops, splashes (with well defined tables indicate blood struck surface
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what does elliptical show
Elliptical shows drops struck obliquely
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what do spurts and pools suggest?
Suggestsvictimwas static and still alive since death stops blood flow.
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what do trails and smears suggest?
Suggests that the object pressed against the surface will also be smeared
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what is third dimension?
hape of the ellipse reveals the angle at which the blood hit.
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about reconstruction
Theconvergenceof lines indicates the position of the source in two dimensions.
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what is blood splatter dependant on?
volume and height fallen and type of surface it strikes
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what does angle it drops at mean?
perpendicular:the bloodstain will be circular.
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what is an impact splatter?
as a result of beating
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how can you tell if it is aspirated (coughed) blood?
air bubbles will be visible in blood impact. Blood that is blown out of the nose, mouth, or wound as a result of air pressure and/or air flow which is the propelling force.
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what is cast off blood?
Blood that is flung from a surface, usually a hand or a weapon during movement
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what are cast-off stains?
Blood released or thrown from a blood-bearing object in motion. Line Pattern, Blood spots all roughly the same size
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how do you know if its a punching?
Spatters are consistently found around the cuff of the punching arm • May also be on the upper arm and across upper chest • Depends upon the type of punch and the volume of blood at the impact site
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how do you know if its a beating?
Usually little blood on assailant, but increases with no of blows •Depends upon the type of weapon,often the blood spatter will be deposited to the side of the assailant (path of least resistance) and void areas can result •Cast off on walls/ceilings
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how do you know it is kicking and stamping?
Blood within seams and crevices of footwear - indicating forceful contact Blood on bottom of trousers Presence of impact spatter, which may show directionality
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what is acid Phosphatase used for?
presumptive testing, its a protein found in high concentrations in *****.turns purple if present. be careful teabags.. give positive results too.An enzyme found in many tissues but is 500 to 1000 times more active in ***** than any other bodily fluid
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how do you look for and test *****?
Body swabs - clothing - scene - contraceptive devices
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what are problems with it?
Vasectomy • Aspermia • Menstruation • Time since intercourse • Withdrawal and non *********** • Washing • Sampling errors
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what is Bayesian Approach?
Evaluate how the findings affect the hypotheses • E.g. The presence of fibres on the clothing of the defendant, matching those of the injured person, supports the proposition that these people had been in physical contact.
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how long is Spermatozoa found in the ******
Should be found for 24 hours after intercourse • May be found up to 3 days • Occasionally are found up to 7 days
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how long does alcohol last in blood and urine
blood (18 hours) in urine (24 hours)
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how long does drugs of abuse last in blood and urine
12/24 hours in blood and 48 hours in urine.
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how long can GHB be detected for?
detected in blood only within 4 hours, 6/12 hours in urine
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how long can Rohypnol( flunitrazepam) be detected for?
n blood for up to 18 hours and 72 hours in urine
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how long can Saliva be found for on skin?
up to 48 hours
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condom lubricants?
7% of sexual offence submissions request a test for condom lubricant • Samples taken more than 6 hours after offence are mostly negative • Max detection limit up to 50 hrs on penis • Max detection up to 30 hours in the ******
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what about fibre evidence?
Links in the absence of body fluids • Very strong evidence (especially if 2 way transfer) • Source of fibres-database • Difficult to avoid fibre transfer
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how many pubic hairs do you need for evidence? what needs to happen before taken?
25, brushed and pulled
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In the living person: – In the ****** - 2-3 days. – In the **** - 1 day. – In the mouth < 1 day. – On clothing/bedding - indefinitely, provided the item is dry and has not been washed.
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In living persons: – In the ****** - 7 days. – Anus - 3 days. – Mouth 2 days. – Clothing/bedding - indefinitely, provided the item is dry and has not been washed.
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what is crime scene managers role?
“The Crime Scene Manager is “The Crime Scene Manager is responsible for all matters relating to responsible for all matters relating to the examination of a crime scene” the examination of a crime scene”The Crime Scene Manager should be senior SOCO
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what is order of incident importance?
major incidence- senior investigating officer- deputy SIO/ management team-scientific support/co-ordinator/crime scene manager- scene examination- scenes of crime/photographic dept/technical support/FFS...
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what is the role of Crime Scene Co-ordinator?
MULTIPLE Scenes or Incidents.Head of SOCO/S.S.M. Member of the SIO’s Management Team. co-ordinated scientific support, Assess, prioritise & Co-ordinate Scientific resources.Brief & advise SIO on all aspects of Scientific Support.Provide a focal point
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what should a crime scene manager do?
Ensure scene security Should Should – Confirm/establish scene guards – Confirm/establish Log – Confirm/establish R.V. point(s) – Establish best approach routes (CAP) – Minimise access – Confirm/establishcordons(inner&outer)
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what do need to record on a log?
Name of officer keeping record 2. Name of person entering/leaving the scene 3. Date/time of entry/departure 4. Reason for entry
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how should crime scene manager minimise destruction?
Climatic conditions (rain, snow, wind, dew- point) – Interference by police & their agents n steppingplates/scenetent n protectiveclothing n crosscontamination n helicopterdown-draughtetc. – Animals / public/ press
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how should they manage speaclists?
Knowing who & when to call in – Strategy meeting before examination – Frequent tactical discussions during exam – Mediating on examiners needs (sequential) – Ensuring specialists stay of their competency – Maintenance of information flow
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what would they do to take responsibility for health and safety?
Risk assessment (competent person) – Dissemination of assessments – Correct equipment is available – Protective equipment is worn – Items are correctly packaged & labelled
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how do you ensure full examination carried out?
Record scene – Video – Photograph – Plans – Notes & sketches – Readings (temperature, meters, timers etc)wha
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what should crime scene manager do?
Be responsible for QC & QA Be responsible for QC & QA –Check the work of staff n Documentation – Carry out scene walk-through with n Scene examiners Scene examiners n Supervisor or peer Supervisor or peer n SIO (prior to handover of scene) SIO (prior
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prior to handover of scene, Carry out Debriefings, Consider counselling
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four types of death
natural (strokes..), accidental (falls...), suicidal (gunshot, overdose...), homocodal(hands of another)
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how to co-ordinate a scene
scene evaluation-specialists within the scene/scientific co-ordinator/health&saftey
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initial death scene evaluation
talking to the officer who was first on the scene and learning from them of any changes that might have been made to the scene since their arrival: Turning lights on or off. Opening doors or windows.Start by determining life extinct.look up
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how does body temp show time since death
Normal body temperature - measured body temperature  1.5 = time since death. therefore work out what is room/ambient temp
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what does UN estimate for total cost of fire and explosions?
1% GDP
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what % of crime have malicious cause?
15-20% of dwellings and 30-40% of other fires
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why is arson important to forensic investigator?
insurance fraud, malicious destruction of property, attempt to harm, juvenile disorder, metal health problems, to destroy evidence (e.g. fingerprints...), to conceal other crimes,
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what percentages of arsonists are male
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number of deaths as a result of fire?
200 UK, 7500 in W. Europe, 3500 USA
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how many fires where attended by fire brigade in 2012-2013 and total fire death? highest death count
192600, 350 people killed-lowest total for 50 years. highest number was 1096 in 1979, 1/3 caused by burns alone.
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how many people a yeah in UK die from deliberately started fires
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what % of fires were accidental in dwellings?
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what % of fires in other buildings were accidental?
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how many fires are smoke alarms absent in working
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about arson statistics in UK?
detection and conviction rates for arson is low
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about Arson control forum
set up 2001, government run chaired by chief inspector of fire services. sought to reduce arson related deaths, injuries, damage. target to reduce no of deliberate fires by 10% in 10 years, did this in a year and 50% in 10 years.
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invested £11.6 million in 100 local arson reduction initiatives. helped to produce an Arson Toolkit as part of Home Office Crime reduction programme.
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what idid arson control forum commissioned research into?
motivation of arsonists, link between car arson, abounded vehicles... social rexculsion, risk of fire, why arson prosecutions "fail"
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even if fire accidental can be legally liable for example when:
infringement of safety legislation and regulations (unlicensed storage of fuel or in inappropriate containers...) failure to undertake safety inspections -duty of care, fire caused by consequence of another crime
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the fire triangle, what three conditions are necessary for combustion?
fuel, oxygen, heat(enough to imitate combustion) forensic science concerned with imitation source was it stated deliberately and was an accelerant such as petrol added?
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what is combustion?
oxidation process. it consumes oxygen not releases it!the combination of substances with oxygen to produce new substances (oxides) accompanied by production of heat and light. oxygen can be from the air.
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what gas can create flaming combustion?
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how can iron be oxidation process?
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what does a chemical reaction involve?
activation energy required to imitate the process
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what type of process is oxidation?
exothermic process- heat is liberated Called heat of combustion)
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what might the heat of combustion do?
release further energy to fuel the process and sustain the fire
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what is a flame?
A region in which chemical interaction between gases occurs, accompanied by the evolution of heat and light It’s the gas phase that burns.
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what can a gas be?
gas, vapour from a liquid, gases/vapours pyrolyse from a solid (pyrolysis : the decomposition of organic matter by heat)
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how much are fuel vapours capable burning in air
21% oxygen. If the concentration of flammable gas is too low, it cannot burn.Combustion does not generate enough heat to sustain the flame.
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what is The lowest concentration of flammable gas in air that can sustain combustion called?
lower flammability limit, below this is fuel lean
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If the concentration of flammable gas is too high, it cannot burn. There is not enough oxygen to sustain the reaction. The highest concentration of flammable gas in air that can sustain combustion is called what
“upper flammability limit”. Above this is “fuel rich”; e.g. a flooded petrol engine.
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what is flash point?
The minimum temperature at which the vapour produced by a liquid can be ignited momentarily in air
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process of flash point
liquid emits sufficient vapour to form a mixture with air that will support combustion, ignition is by an external source, ie a small flame, it supplies the initial activation energy & then quickly removed, the resultant flame does not necessarily
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the resultant flame does not necessarily self-sustain at this temperature. Several factors influence this, including the balance between the heat generated from combustion and the rate of heat loss from the flame by radiation.
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what is Fire Point (Flame Point)?
The minimum temperature at which sufficient vapour is produced by a liquid to sustain combustion after ignition in air”. it is few degrees higher than flashpoint, After the ignition source is removed, heat produced by combustion balances heat loss fr
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loss from the flame, so that the temperature does not drop Vapour must also be produced at a rate sufficient to maintain concentration above the lower flammability limit. This depends on the volatility of the liquid
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what is Ignition Temperature Also called Self-ignition or Auto-ignition Temperature?
The minimum temperature at which a fuel will ignite on its own without any external source of ignition. the activation energy required to initiate the combustion reaction with oxygen is supplied by ambient heat energy, without a specific ignition sou
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where is petrols flash point?
below room temperature
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do fuels with low/high flash points make good accelerants?
Fuels with low flash points make good arson accelerants. A fire can be started by an ignition source without having to pre-heat the accelerant!
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are ignition temperatures higher or lower than flash point temperatures
much higher, substances cannot catch fire at room temperature without an external ignition source. Some chemicals have ignition temperatures below room temperature. These are very hazardous to handle. Example: diethyl ether
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what is smouldering/glowing combustion?
A type of flameless combustion, Takes place at surfaces of material: fuel-air interface, e.g a burning ember or cigarette. Occurs in substances that can form a solid char e.g. wood,
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what happens if fire in closed room and oxygen concentration falls to low enough value
the flames will die out to be replaced by smouldering or glowing combustion. Flaming fire can restart suddenly if more oxygen is supplied e.g. braking down the door
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what is spontaneous combustion?
Fire initiated by a natural heat-producing process in the presence of sufficient fuel and air, without an external ignition source. Natural exothermic reactions (chemical oxidation or biological fermentation) sawdust, coal dust, hay, municipal waste
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certain types of “unsaturated” oils soaked into rags, paper towels etc e.g. fish oils, linseed oil This may resemble an arson attack (e.g. fire starts in rubbish bin outside shop)
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what is initial limiting factor of a typical fire?
enough heat to sustain the combustion
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why does the rate of chemical reaction increase by?
factor of 2/3 for each 10 degrees risen
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what is next limiting factor?
oxygen, if there is lack of ventilation (closed room i.e.)
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what is the third limiting factor?
fuel-ends when fuel is used up
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what contaminates evidence?
fires, explosions, fire-fighting (high pressure water, break doors...)
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why might insurance investigator and loss adjuster be involved?
financial fraud for buildings or content insurance, tax fraud,
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what chemical evidence is there from fire scenes?
chemical analysis of trace residues presence of accelerants? (anything that speeds up the spread of a fire)
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what other related (circumstantial) evidence might there be?
evidence of forced entry to building? Removal of goods before fire? witness statements about starting point of fire, and rapidity of spread (“rapid spread of fire” does not prove arson)
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what is physical evidence?
smoke records and temperature indications (surface flaking of plaster) debris layer sequences remains of ignition devices and suspicious containers?
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what must you do before enter site?
Risk of structural collapse of building live electrical cables dust hazards (asbestos?) unknown contents of building : toxic chemicals? Biohazards? industrial warehouse clandestine laboratory used to make drugs or explosives
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how can tell if body was dead in fire or before?
, the presence of smoke in the lungs and carbon monoxide in the blood is consistent with death from smoke inhalation (most fire deaths are caused by this rather than actual burning). The absence of this suggests the victim was dead before fire-arson?
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what shape does raid upward circulation give?
V shape on adjacent walls, pointing downwards to possible seat, examine floors... but watch out for draughts, examine stairways...
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what are directional indicators?
typically face of the material that is directly exposed to fire shows greater damage
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what do you look for in fire scenes?
Trail evidence - ‘streamers’ from liquid accelerants, trails of paper, etc used in starting the fire and speeding up its spread Containers capable of holding accelerants Ignition devices- lighters, timing devices... Signs of forced entry
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what is evidence for arson?
fire starting in more than one place simultaneously but not proof
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what was there until 2009
Council for the Registration of Forensic Practitioners (CRFP) maintained a register of competent forensic practitioners in various specialties. Fire Scene Examination was one of these. This also covered explosions.
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what was this replaced by?
the Forensic Science Regulator
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what is the prime aim?
determine whether accelerants were present or not, Although liquid accelerants are combustible enough residues remain after a fire to be detected by modern chemical analysis methods. Water from fire-fighting delays evaporation of accelerants.
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what happens to liquid combustions?
Liquids seep into porous materials, so unburned accelerant is most likely to remain in carpets, upholstery, plaster, rags, floor cracks. Some types of concrete flooring are surprisingly porous.
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what are common accelerants?
volatile liquids. Time is of the essence before the residues evaporate. Portable hydrocarbon detector (“sniffer”).
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what is a fire sample?
a sample from near as possible to seat of fire, to be tested for accelerant
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what is comparative control sample?
same material as from fire sample, but from elsewhere on the room and therefore uncontaminated with accelerant. (substrate control)
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what are negative control samples?
Tools and empty containers of the same type used in the sampling process Other samples from suspect (if there is one): clothing from suspect, material from suspect’s premises (remember, it is not illegal to possess accelerant substances such as petro
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What must sample containers be like?
be airtight, and able to retain volatile hydrocarbons used as accelerants, avoid contamination(from gloves, tools..), accurate labelling and documentary evidence
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what and why are other containers bad?
Ordinary plastic bags are too porous to hydrocarbon vapours. Special double layer nylon (inner) and polypropylene (outer) bags. Closed by knotting the neck, sealed with cable tag - not with adhesive tape. Glass jars or metal cans, especially for s
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why is negative control samples within lab important?
swab workbench... guard against contamination, should be regularly monitored
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what is Recovery of accelerants by “Passive headspace analysis”?
Apparatus for accelerant recovery by vapour concentration. The vapour in the sealed container is exposed to activated charcoal, a chemical adsorbent, where it is trapped for later analysis. temperature 60 - 80 0C time typically 2 hours
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how can samples be recovered through gas chromatography?
Samples injected into a separating column with a stream of chemically inert carrier gas (helium...) It separates the volatile hydrocarbons on the basis of how volatile they are that depends on no of carbon atoms.Most volatile through first-less carbo
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what are most commonly used accelerants and what type of substances are they?
petrol and kerosene - these are not pure substances, but complex mixtures of hydrocarbons, can recognise patterns in chromatography of common fly,mmable liquids.
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what about molecules in petrol?
Molecules in petrol have fewer carbon atoms than those in diesel fuel, and are more volatile.The more volatile components come through the column first, and are on the left hand side of these charts
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what is weathering?
The most volatile components of the petrol are missing from the fire sample, because they have evaporated before the sample could be collected.
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what is mass spectrometry?
identification technique: for individual separated components. measures mass of individual molecules
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what is an explosion?
a sudden and violent release of physical or chemical energy, often accompanyd by the emission of light, heat and sound. rapid increase of pressure. normally caused by exothermic chemical reactions in relatively large amounts
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what are gas explosions?
the explosive forces comes mainly from the thermal expansion of the product gases caused by the heat of combustion
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what are Condensed phase explosions?
produce large volumes of hot gases from a solid or a liquid explosive (an extra factor of about 1500-fold increase in volume). Much more powerful than gas explosions
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what is explosive act 1875?
controls explosives used for legitimate purposes : manufacture, sale, storage and conveyance legislation passed after an explosion at a munitions factory attempts to define “explosives” by listing some examples, beginning with gunpowder, and then
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“every other substance, whether similar to those above-mentioned or not, used or manufactured with a view to produce a practical effect by explosion”. hard to make watertight definitions, but issues with "legal highs"
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legal act 1883?
deals with criminal use of explosives and devices for injuring persons or damaging property : manufacture, possession and use passed after several bombing outrages “Causing explosion likely to endanger life or property…. whether any injury to person
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/property has been actually caused or not”. Penalty of life imprisonment.places burden of proof on the accused,to show that manufacture/possession of explosive which gives rise to “reasonable suspicion” of an unlawful object,was for a lawful purpose
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1983 classification and labelling of explosive regulations?
much more scientific definition of explosive, in terms of exothermic chemical reactions, heat and pressure.
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what is an explosion?
a chemical explosion can be regarded as a form of combustion – an exothermic oxidation reaction. Reaction products are (mostly) gaseous. The distinguishing characteristic of an explosion is that it takes place extremely rapidly:within a fraction of s
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Explosion reactions are too rapid to allow time for oxygen to be drawn in from the air. The source of the oxygen atoms for the oxidation must be within the explosive substance itself. The hot gases produced are produced at very high pressure at the
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origin of the explosion. This leads to a blast wave which produces the violent physical disruption of the surrounding environment. The blast wave damage falls off rapidly with distance. But debris, shrapnel etc are thrown great distances.
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what is an explosion?
mica explosion can be regarded as a form of combustion- an exothermic oxidation reaction.reaction products mostly gaseous. it takes place in fraction of a second-too rapid of oxygen to be drawn from air(oxygen atoms for oxidation must be within expol
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-sion. hot gases are produced thigh pressures at origin. leads to a blast wave which produces to violent physical disruption of surrounding environment. damage gets less with distance, but debris thrown far which causes most injuries
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what is deflagration?
a very rapid oxidation reaction with the evolution of heat and light as well as low intensity pressure wave of moving gas. propagation of reaction is at surface of material and subsonic velocity. e.g. gunpowder
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when is a substance classed as a deflagrating explosive?
a small amount of the substance in an unconfined condition suddenly ignites when subjected to a flame/spark/shock/friction or high temperatures. they burn faster and more violently than ordinary combustible materials. called low explosives
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what is detonation?
extremely rapid oxidation reaction resulting in a high speed shock wave with violent disruptive disruptive effect. shockwave transmitted through the material at supersonicpeed (faster than sound between 1500-9000ms-1). can be initiated by burning/
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mechanical shock/ electrical impulse. called high explosives e.g. dynamite
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how can blackpowder explode in different ways?
if spread thin layer in open air, it burns violently. when partially confined, it will deflagrate and use as propellant for gun/rocket. if ignited in pressure tight container it will detonate e.g. firework
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what are propellents?
materials which deflagrate in a controlled fashion to allow their energy to be used in propelling rockets/projectiles from guns
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what are pyrotechnics?
used for production of light/sound/smoke. for fireworks and signalling flares e.g. marine distress flares. might contain metal powders and various metal nitrates
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what are primary explosives?
sensitive explosives which undergo a rapid transition from burning to detonation and are rapidly detonated by heat/friction/mechanical shock. low activation energy, used in relatively small quantities
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what are secondary explosives?
less sensitive, cant be detonated but heat/shock.generally more powerful-higher detonation velocities. more difficult to detonate. designed to be easier/safer to handle/store/transport. insensitive to shock/flame but explode when set off by primary e
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what is aim of chemical design for explosives?
oxidation must be within substance so incorporate oxygen atoms into explosive substance. many explosives contain nitrite groups in molecular structure
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what is gunpowder/blackpowder?
a physical mixture of potassium nitrate, carbon, sulphur
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what is nitroglycerine?
NO2, made from vegetable oils and animal fats
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what is TNT?
Trinitrotoluene, from coal tar
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what is ammonium nitrate?
a chemical compound which is ionic
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what is RDX?
research development explosive, a military explosive-synthetic chemical
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what is TATP?
Triacetate Triperoxid/ acetone peroxide, on london bombings 2005. easysyntheiss from readily available materials. very sensitive to primary explosive- v dangerous to handle.very volatile: it will evaporate/degrade over a few days at room temp.useless
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who invented dynamite and by mixing what?
Alfred Nobel, 1867, by mixing nitroglycerine and kieselguhr
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what are industrial explosives based around?
ammonium nitrate- NH4NO3. it is a fuel oil (ANFO) contains ammonium nitrate mixed with liquid hydrocarbons-its waterproof. can be used in waterbed emulsions or can be used to boost explosion
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what type of bombs are in bombings normally?
home-made explosives and incendiary devices, but can be stolen form military premises tho high security
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How do you del with a SCENE?
Safety, cordon (place around where want to protect), evidence, nominal (keep record), evaluate
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collection of explosion residue
need to wear overalls, gloves... crater shows point of detonation usually. evidence may be scattered considerable distance. package all loose soils/residue embedded in nearby soft objects or nearby metal objects
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what can having high explosives do to you?
it is illegal taken as prima facie evidence of criminal/terroist intent
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is possession of arson accelerants illegal?
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what does DSTL stand for?
Defense science lab and technology
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what does FEL stand for?
Forensic explosive lab. they can look for timing devices, wire remains, chemical traces,.. as evidence. can look for clothes fibre on device if other lines failed.
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what is optical microscopy used for?
seek particles of explosives and taggants ( tiny colour0-coded plastic chips added to commercial explosives)
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what can organic residues be further characterised by?
gas chromatography, mass spectrometry, when sufficient quantities recovered infra read spectroscopy as confirmatory tests. IR produces unique fingerprint of vibrations of chemical bonds in a molecule
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what is the Griess test?
specific for nitrite anion. uses complex ,mixture of reagents with breaks down molecules containing NO2groups o form nitrite anion. if red/pink it is present. can be applied as spray. doesn't mean not explosive if doesn't contain this. preliminary th
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why do dead bodies undergo decomposition?
Enzymatic, Bacterial, Fungal attack
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what does decomposition result in?
a softening and liquefaction of tissues (autolysis) by the action of various enzymes.
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the does decomposition first become visible?
visible in the abdominal wall owing to the spread of gut bacteria. The skin turns a greenish colour and the body starts to swell owing to gas formation( Carbon dioxide, Ammonia, Methane). outside invasion of maggots
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what is decomposition characterised by?
Discolouration, Swelling of tissue, Generation of a bad smell when the material becomes putrefied.
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what is end result of putrefaction and what is it brough on by?
decomposition. brought on by bacteria or yeast/other micro-organisms
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what do need to determine in dead body?
identity,cause, how long in water (submergence and then float), whether live on entry (water in lungs if alive when enter:pulmonary edema, dry drowning: 15% of drowning may be intake of water on throat causing laryngeal spasm)
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what is wet drowning?
person drowns when water enters lungs. mixture of air and water comes up from lungs to fill mouth and nostrils
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whats vagal inhibition?
Water enters the nose. Causes spasm of larynx. To press on vagus nerve. Stops heart.
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what is shock?
sudden exposure to cold=heart attack
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what are hypothermia?
Cause - prolonged immersion in water. < Body core temperature. Unconsciousness & death.
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what are diatoms?
Single celled organisms that reside in water. if person is alive on entry to water, diatoms pass through lungs and collect in bone marrow inferring live on entry
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what are the four manners of death?
natural(strokes, heart attacks) accidental (fall) suicidal (gunshot, overdose) homicidal(in hands of another)
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what do need to take fr toxicology from deceased?
blood, urine,liver, stomach
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type of samples need/might take?
blood (preserved&unpreserved) for DNA, alcohol, urine (preserved&unpreserved) for alcohol and drugs,stomach and contents(drugs/food), liver(drugs), deep muscle tissue (DNA),bone marrow (DNA), lungs(drowning/petrol), vitreous humour (drugs/alcohol)
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CSI equipment
sample contaners, sterile swabs, permanent marker, air sanitiser, magnifying glass, screwdriver, fingerprint brush, powder, lifting tape and template
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what is point of entry?
entry usually refers to that point where an offender entered a building prior to committing an offence. However, it also sometimes refers to the entry point of police, fire brigade and other persons after the incident.
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what are three types of prints?
patent (blood, ink, paint, grease on fingers), plastic (3D- wax, putty dust), latent (invisible, requiring special processing or lighting)
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why is portion of finger prints important
could show pulling self in to building through window...
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Card 2


what are four types of marks?


Extrusion marks, Moulding marks, Coatings, Machine marks (on grinding wheel, unlikely to ever be put on at same time-scratches get different marks...)

Card 3


when do impressed tool marks occur?


Preview of the front of card 3

Card 4


what are single contact marks?


Preview of the front of card 4

Card 5


what are striated (scratched) toolmarks?


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