Wound Ballistics and Tissue Simulants Notes - lect 21
Ballistics Lab Reminders
Labs are scheduled for tomorrow and Friday.
Ensure preparation and familiarity with assigned tasks before attending.
Assessment components for labs are due one week after completion.
Deadlines vary per group; verify submission dates.
Consistent weekly progress is advised for timely completion.
Additional Lecture
An extra lecture has been added next Monday immediately after the regular session.
This is to ensure sufficient time to cover all material, including exam question types.
The lecture will be recorded for those unable to attend.
The confirmed schedule should appear overnight.
Exam Timetables
Exam timetables are now available.
Ballistics is scheduled as one of the earlier exams.
Wound Ballistics and Tissue Simulants
Understanding injury mechanisms caused by bullets.
Recognizing wound profiles related to different projectile types.
Studying key tissue simulants and testing methodologies.
Slide Packs
Main slide pack.
Secondary slide pack on experiments, available on Moodle.
Trigger Warning
The slides contain gruesome images of wounds.
Viewers sensitive to such content should exercise discretion.
Key Principles of Wounding
Understanding wound processes is complex.
Multiple factors influence bullet behavior and tissue reaction.
Energy transfer from the bullet is a significant damage factor.
Higher energy doesn't automatically equate to more trauma; the amount of energy transferred is key.
Energy is neither created nor destroyed, but redistributed.
Energy Transfer
Kinetic energy from the bullet transfers to kinetic energy in tissues.
More energy transfer leads to more tissue movement and damage.
The ability to transfer energy depends on tissue type (hard/soft).
Different organs have varying mechanical properties affecting impact response.
Bullet Design and Stability
Bullet design influences energy transfer (e.g., full metal jacket, hollow point).
Bullet stability during passage through the body affects energy transfer.
Range and Forensic Evidence
Different ranges provide different forensic evidence.
Close ranges allow analysis of propellant deposits (gunshot residue).
Contact wounds leave distinct marks or imprints.
Civilian firearm wounds are typically inflicted at close range with handguns.
Gunshot Residue (GSR)
At close range, GSR particles embed in the skin, creating a tattooing effect.
Spread of GSR indicates shot range.
Angle of shot can be inferred from GSR patterns.
Tattooing: Permanent embedding of GSR particles in the skin.
Contact Wounds
Contact wounds, especially on the head, often produce a stellate (star-like) pattern.
GSR is concentrated inside the wound without dispersion.
High-pressure gases enter the head cavities, causing skin tearing.
Gases expand between the skull and skin, leading to the stellate pattern.
Muzzle Imprints
Contact wounds may leave muzzle imprints around the wound.
Imprints vary based on firearm characteristics.
Documentation is crucial as imprints may not last long.
Range Determination Limitations
Beyond a few meters, range determination based on GSR becomes difficult.
After 5-10 meters, range estimation is generally unreliable.
Gunshot Detection Technology
High-resolution microphones in urban areas detect gunshots.
Microphones triangulate the source of the gunshot based on sound wave arrival times.
Sound waves travel at approximately 340-350 meters per second.
Shotgun Wounds
Shotgun wounds have larger impact sites compared to single bullet wounds.
Pellet size varies, with birdshot having smaller pellets and buckshot having larger pellets.
Pellet distribution follows a normal distribution, with higher concentration in the center.
Bone Impacts
Skull impacts provide valuable information due to its structure.
Beveling: A beveled edge indicates the direction of the bullet.
Exit wounds show larger openings on the external surface of the skull.
Bullet direction causes funneling damage to the skull.
Beveling
Bullet travels through the skull causing stress, and there's an opening and funneling of the bone itself.
Keyhole Wounds
Keyhole wounds occur when bullets enter at an angle, with beveling on one edge and a clean wound on the other.
Skull Fractures
On the entry side, the bullet causes more significant damage to the inner table (tabula interna).
Entry wounds have more bone fragments due to the bullet driving fragments inward.
Gutter Wounds
Gutter wounds are shallow skims across the skull surface.
They create a channel and may cause additional cracking and fracturing.
The entry point is cleaner, while the exit is less defined.
Bullet Ricochet
Bullets can ricochet off the inside of the skull.
Comminuted fractures: The bullet impacts the far side of the skull, potentially deviating its direction due to the curvature of the skull.
Calvarria Fracture
High energy impacts may cause the calvarria (skull cap) to pop off due to increased pressure inside the cranium.
A temporary cavity is created
Long Bone Impacts
Smaller bones (radius, ulna, clavicle) undergo explosive fragmentation.
Bones store energy and release it upon significant damage, causing fragmentation.
Fragments become micro-projectiles, causing additional trauma.
Larger bones (femur, pelvis) chip rather than explode, depending on energy transfer.
Bone Fragmentation
High-energy impacts cause multi-fragmentary fractures and secondary missiles.
Primary missile: Bullet itself.
Secondary missiles: Bone fragments energized by the impact.
Forensic Analysis
Finding the bullet and jacket is crucial for forensic analysis.
Jackets may contain rifling marks for linking to firearms.
Bullets can be deflected by bones, leaving and re-entering the body.
Trajectories can change even through soft tissue.
Soft Tissue Impacts
High-velocity bullets tend to over-penetrate at close to medium ranges.
Autopsy can reveal bullet paths and differentiate between single or multiple shots.
Wound Cavities
Permanent wound cavity: The path taken by the bullet through the body.
Temporary wound cavity: Caused by energy transfer moving the soft tissues.
Permanent Wound Cavity
Typically the most significant wounding mechanism.
Bullets crush and tear through tissues, impacting blood vessels and causing internal bleeding.
Damage depends on bullet stability. Unstable bullets create larger cavities.
The size of the permanent cavity is smaller than the bullet's caliber because the tissues are elastic.
Tissue Damage and Treatment
Crushing and tearing causes tissue necrosis (death).
Surgeons must remove dead tissue to prevent infections because the bullets are dirty.
Bullets introduce bacteria, leading to potential infections without antibiotics.
Ballistics Lab Reminders
Labs are scheduled for tomorrow and Friday.
Ensure preparation and familiarity with assigned tasks before attending.
Assessment components for labs are due one week after completion.
Action Required: Deadlines vary per group; verify submission dates.
Consistent weekly progress is advised for timely completion.
Additional Lecture
An extra lecture has been added next Monday immediately after the regular session.
This is to ensure sufficient time to cover all material, including exam question types.
The lecture will be recorded for those unable to attend.
The confirmed schedule should appear overnight.
Note: Review the recording if you are unable to attend to stay up to date with the materials.
Exam Timetables
Exam timetables are now available.
Ballistics is scheduled as one of the earlier exams.
Wound Ballistics and Tissue Simulants
Understanding injury mechanisms caused by bullets.
Recognizing wound profiles related to different projectile types.
Studying key tissue simulants and testing methodologies.
Examples: Gelatin, clay, and other materials that mimic human tissue.
Slide Packs
Main slide pack.
Secondary slide pack on experiments, available on Moodle.
Trigger Warning
The slides contain gruesome images of wounds.
Viewers sensitive to such content should exercise discretion.
Key Principles of Wounding
Understanding wound processes is complex.
Multiple factors influence bullet behavior and tissue reaction.
Energy transfer from the bullet is a significant damage factor.
Higher energy doesn't automatically equate to more trauma; the amount of energy transferred is key.
Clarification: The efficiency of energy transfer matters more than the absolute energy.
Energy is neither created nor destroyed, but redistributed.
Energy Transfer
Kinetic energy from the bullet transfers to kinetic energy in tissues.
Impact: Measured in terms of velocity and mass (KE = arc{1}{2}mv^2).
More energy transfer leads to more tissue movement and damage.
The ability to transfer energy depends on tissue type (hard/soft).
Different organs have varying mechanical properties affecting impact response.
Bullet Design and Stability
Bullet design influences energy transfer (e.g., full metal jacket, hollow point).
Elaboration: Hollow point bullets are designed to expand upon impact, increasing energy transfer.
Bullet stability during passage through the body affects energy transfer.
Details: Yawing or tumbling bullets transfer energy differently than stable bullets.
Range and Forensic Evidence
Different ranges provide different forensic evidence.
Close ranges allow analysis of propellant deposits (gunshot residue).
Contact wounds leave distinct marks or imprints.
Civilian firearm wounds are typically inflicted at close range with handguns.
Note: Military or hunting scenarios might involve longer ranges and different types of firearms.
Gunshot Residue (GSR)
At close range, GSR particles embed in the skin, creating a tattooing effect.
Spread of GSR indicates shot range.
Angle of shot can be inferred from GSR patterns.
Tattooing: Permanent embedding of GSR particles in the skin.
Additional Information: GSR composition can help identify the type of ammunition used.
Contact Wounds
Contact wounds, especially on the head, often produce a stellate (star-like) pattern.
GSR is concentrated inside the wound without dispersion.
High-pressure gases enter the head cavities, causing skin tearing.
Gases expand between the skull and skin, leading to the stellate pattern.
Muzzle Imprints
Contact wounds may leave muzzle imprints around the wound.
Imprints vary based on firearm characteristics.
Documentation is crucial as imprints may not last long.
Recommendation: Photograph and cast imprints for detailed analysis.
Range Determination Limitations
Beyond a few meters, range determination based on GSR becomes difficult.
After 5-10 meters, range estimation is generally unreliable.
Factor: Environmental conditions (wind, humidity) can affect GSR dispersion.
Gunshot Detection Technology
High-resolution microphones in urban areas detect gunshots.
Microphones triangulate the source of the gunshot based on sound wave arrival times.
Sound waves travel at approximately 340-350 meters per second.
Advancement: Some systems also incorporate video and infrared sensors.
Shotgun Wounds
Shotgun wounds have larger impact sites compared to single bullet wounds.
Pellet size varies, with birdshot having smaller pellets and buckshot having larger pellets.
Pellet distribution follows a normal distribution, with higher concentration in the center.
Consideration: Spread patterns can indicate the distance from the target.
Bone Impacts
Skull impacts provide valuable information due to its structure.
Beveling: A beveled edge indicates the direction of the bullet.
Exit wounds show larger openings on the external surface of the skull.
Bullet direction causes funneling damage to the skull.
Beveling
Bullet travels through the skull causing stress, and there's an opening and funneling of the bone itself.
Keyhole Wounds
Keyhole wounds occur when bullets enter at an angle, with beveling on one edge and a clean wound on the other.
Skull Fractures
On the entry side, the bullet causes more significant damage to the inner table (tabula interna).
Entry wounds have more bone fragments due to the bullet driving fragments inward.
Gutter Wounds
Gutter wounds are shallow skims across the skull surface.
They create a channel and may cause additional cracking and fracturing.
The entry point is cleaner, while the exit is less defined.
Bullet Ricochet
Bullets can ricochet off the inside of the skull.
Comminuted fractures: The bullet impacts the far side of the skull, potentially deviating its direction due to the curvature of the skull.
Calvarria Fracture
High energy impacts may cause the calvarria (skull cap) to pop off due to increased pressure inside the cranium.
A temporary cavity is created
Long Bone Impacts
Smaller bones (radius, ulna, clavicle) undergo explosive fragmentation.
Bones store energy and release it upon significant damage, causing fragmentation.
Fragments become micro-projectiles, causing additional trauma.
Larger bones (femur, pelvis) chip rather than explode, depending on energy transfer.
Bone Fragmentation
High-energy impacts cause multi-fragmentary fractures and secondary missiles.
Primary missile: Bullet itself.
Secondary missiles: Bone fragments energized by the impact.
Forensic Analysis
Finding the bullet and jacket is crucial for forensic analysis.
Jackets may contain rifling marks for linking to firearms.
Bullets can be deflected by bones, leaving and re-entering the body.
Trajectories can change even through soft tissue.
Soft Tissue Impacts
High-velocity bullets tend to over-penetrate at close to medium ranges.
Autopsy can reveal bullet paths and differentiate between single or multiple shots.
Wound Cavities
Permanent wound cavity: The path taken by the bullet through the body.
Temporary wound cavity: Caused by energy transfer moving the soft tissues.
Permanent Wound Cavity
Typically the most significant wounding mechanism.
Bullets crush and tear through tissues, impacting blood vessels and causing internal bleeding.
Damage depends on bullet stability. Unstable bullets create larger cavities.
The size of the permanent cavity is smaller than the bullet's caliber because the tissues are elastic.
Tissue Damage and Treatment
Crushing and tearing causes tissue necrosis (death).
Surgeons must remove dead tissue to prevent infections because the bullets are dirty.
Bullets introduce bacteria, leading to potential infections without antibiotics.