Exam questions Flashcards
What conclusions can be made when comparing between animal blood and human blood?
A Study to Compare and Contrast Animal Blood to Human Blood Product (1997) Daniel V. Christman (ME)
• Study looked at blood from: bovine, equine, swine, sheep
• Study compared: drip stains, impact patterns – MVIS, impact patterns – HVIS, reproducibility, composition
• “One thing that is sure, blood is a fluid and whether it’s human blood, animal blood, or ink for that matter, there is a negligible difference in the results.”
• “In conducting controlled experimentation and studying the resulting stains it became apparent the fluids used were reacting in a similar fashion.”
• “In comparing the mean scores for those stains tested, all of the fluid stains compared favorably to the ‘standard,’ human blood.”
What is blood?
- Blood is the fluid that circulates through the heart, arteries, veins and capillaries of the human body.
- It carries nourishment and oxygen to the tissues and takes away waste products and carbon dioxide.
- In an average adult male there is approximately 4-6 liters of blood
- The ability of blood to reproduce specific patterns is not affected to any significant degree by: age, sex, body temperature, alcoholic content, disease process
What is the consistency of blood?
Blood constituents: • Blood plasma (fluid) 55% • Erythrocytes (red bloods cells) ~45% • Leukocytes (white blood cells) <1% • Thrombocytes (platelets) <1%
What is Bloodstain Pattern Analysis?
Bloodstain Pattern Analysis is the examination of the size, shape, location and distribution pattern of bloodstains, in order to provide an interpretation of the physical events which gave rise to their origin.
What are two premises of Bloodstain Pattern Analysis?
- Bloodstain patterns are predictable and reproducible.
- When blood leaves a body, its behaviour will follow the laws of physical science, specifically the science of projectiles in motion.
- Is a combination of Applied and Empirical Science.
- Based on Biology, Physics and Mathematics.
What type of crimes is BPA most commonly used for?
BPA is most commonly used in the following incidents:
• murder
• attempted murder
• assault causing grievous bodily harm
• sexual assaults
• suicide (used to determine suicide vs. homicide)
• death due misadventure
What is preferred when a BPA examines a scene?
When a BPA examines a scene it is preferred:
- The analyst attends and the body is still at the scene.
- The analyst attends the scene after the body has been removed.
- The analyst conducts their examination based on scene images.
- Examination of exhibits.
What may be established through Bloodstain Pattern Analysis?
- Movement and direction of persons or objects while they were shedding blood
- Position of persons or objects during bloodshed
- Movement of persons or objects after bloodshed
- The mechanism or object used to create a specific pattern
- The direction a stain was traveling when it was deposited
- The area of origin of an impact pattern
- The minimum number of impacts during an incident
- The sequence of events
What are the three basic bloodstain pattern groups?
Bloodstain patterns can be classified into these basic bloodstain pattern groups:
• Gravity Patterns
• Spatter Patterns
• Transfer Patterns
Name different types of Gravity Patterns (5)
- DRIP STAIN: A bloodstain resulting from a falling drop due to gravity.
- ACCOMPANYING DROP: A small blood drop produced as a by-product of drop formation.
- DRIP PATTERN: A bloodstain pattern resulting from a liquid that dripped into another liquid, at least one of which was blood.
- SATELLITE STAIN: A smaller bloodstain that originated during the formation of the parent stain as a result of blood impacting a surface.
- DRIP TRAIL: A bloodstain pattern resulting from the movement of a source of drip stains between two points.
- FLOW PATTERN: A bloodstain pattern resulting from the movement of a volume of blood on a surface due to gravity or movement of the target.
- SPLASH PATTERN: A bloodstain pattern resulting from a volume of liquid blood that falls or spills onto a surface.
- POOL: A bloodstain resulting from an accumulation of liquid blood on a surface.
Name different types of Spatter Patterns (6)
• SPATTER STAIN: A bloodstain resulting from a blood drop dispersed through the air due to an external force applied to a source of liquid blood.
• IMPACT PATTERN: A bloodstain pattern resulting from an object striking liquid blood.
• CAST-OFF PATTERN: A bloodstain pattern resulting from blood drops released from an object due to its motion.
• Cessation Cast-off Pattern: A bloodstain pattern resulting from blood drops released from an object as it suddenly stops.
• PROJECTED STAIN: A bloodstain pattern resulting from the ejection of blood under pressure.
• EXPIRATION PATTERN:
A bloodstain pattern resulting from blood forced by airflow out of the nose, mouth or a wound.
Name different types of Transfer Patterns (4)
- TRANSFER STAIN: A bloodstain resulting from contact between a blood-bearing surface and another surface.
- SWIPE PATTERN: A bloodstain pattern resulting from the transfer of blood from a blood-bearing surface onto another surface with characteristics that indicate relative motion between the 2 surfaces
- WIPE PATTERN: An altered bloodstain pattern resulting from an object moving through a pre-existing wet bloodstain.
- SATURATION STAIN: A bloodstain resulting from the accumulation of liquid blood in an absorbent material.
What are two important physical properties of blood?
Surface Tension:
• The elastic like property of the surface of the liquid that makes it tend to contract, caused by the forces of attraction between the molecules of the liquid.
• A liquid in free flight has no surface to rest upon.
• To achieve the maximum volume possible with the least surface area a liquid forms a sphere (the net forces draw the liquid molecules inward)
Viscosity:
• Viscosity is the resistance of a fluid to flow (thickness).
• It occurs due to the frictional forces between layers of the fluid as they flow past each other.
• The flow of liquid blood decreases as its viscosity increases.
• Blood is three times more viscous than water.
What is projectile motion?
• Projectile motion is a form of motion in two-dimensions.
• In analyzing this form of motion there will be two assumptions:
– the free-fall acceleration (gravity) is a constant
– the affect of air resistance is negligible
• To analyze projectile motion separate the object’s motion into two components, vertical and horizontal.
• In the vertical motion the object has a constant acceleration (gravity).
• In the horizontal motion the object has no acceleration and velocity remains constant.
What is Trigonometry and how is it applied to BPA?
• Trigonometry is a branch of mathematics that studies triangles and the relationships between the 3 sides and the 3 angles between these sides.
• There are six basic trigonometric functions: sine, cosine, tangent, cosecant, secant, cotangent
• The functions are defined by the sides and their relationship to the right angle.
• Bloodstain Analysts utilize the sine and tangent functions
• The sine function is the trigonometric function that will be used to determine the angle of impact.
α = sin-1 width/length
