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.