forensic medicine - firearm injuries

7/29/2019 Forensic Medicine - Firearm Injuries

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FIREARM

INJURY


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Firearm injuries occur when someone is shot

by a bullet or other sort of projectile from a

firearm.They vary hugely depending on anatomical

location and ballistic factors.


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Mechanism of injury

Terminal ballistics (the study of the dynamics of bullets in gunshot injury) is acomplex and difficult area. Bullets are composed of a casing enclosing an explosive

powder charge, which, on striking, forces the end projectile element out at speedsof up to 1500 metres/second, dependent on the ammunition and type of gun. Theyinflict injury in a number of ways. Firstly, the projectile crushes structures along itstrack, similar to other forms of penetrating injury. Temporary cavitation causesshearing and compression, sometimes tearing structures (as with solid abdominalviscera) or stretching inelastic tissue (the brain is particularly susceptible), analogousto blunt trauma. As tissues recoil and hot gases dissipate, soft tissue

collapses inwards with the permanent cavity being the resultant defect. Secondly,kinetic energy transfer occurs during retardation of the bullet and this may cause

damage outside the tract.

Factors influencing the efficiency of kinetic energy transfer include:

-The kinetic energy of a bullet is proportional to mass and velocity (mv);

-Projectile's deformation and fragmentation;

-Entrance profile and path travelled through the body;-Biological characteristics of the transit tissues ;

Projectiles tend to be classified as low velocity (300m/second).


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FIREARM

Every firearm has a chamberin which the cartridge is

normally lodged. The chamber leads into a hollow

steel tube called the barrel. The projectile releasedfrom the cartridge in the chamber is forcefully pushed

through the barrel by the expanding gases produced

by the explosion of gun powder. The proximal end of

the chamber has a minute hole, through which apinmoves forward to strike the base of the cartridge.

This striking action produces heat which ignites the

primer. This pin, known as firing pin is activated by aspring connected to a trigger mechanism. The spring

is released on pulling the trigger.


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Types of

weapons

andammunition


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Classification of firearms1. Rifled firearm

a.High velocity: shoulder arms - e.g., rifle

automatic weapons - e.g., machine gun

b.Low velocity: hand arms - e.g., revolver, pistol

2.Smooth bore firearm (Shot gun) e.g.single

barrelled, double barrelled

3.Air or gasoperated firearm4. Country made firearm


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Cross-section of a barrel of rifled firearms

Caliber of rifled firearms : distance measured by

opposite lands or the inner diameter of the barrel.

Caliber of shotgun-the number of balls (pellets) oflead which can be made out of 1 pound(450 gms) of

the lead

grooves

lands caliber


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Action

Chamber

Barrel

Rifling

Bore

Caliber

Muzzle

HammerMagazine

(Clip)

Anatomy of the Gun


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CARTRIDGE

A cartridge consists of an outercase in which the explosive is

stored together with the chemicals required to ignite it, and theprojectile. The explosive is called gun powder, while the igniting

chemical is calledprimer. The projectile is either a bulletor

pellets (shot).

Cartr idge = Case + Pr imer + Gun powder + Projectile

(Bulletorshot*pellet*)


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1. CASE

function: expands and seals chamber against rearward

escape of gases.

2. PRIMER

function: explodes on compression igniting the

powder3. GUN POWDER

function: burns to produce large volumes of gases

under pressure.4. BULLET OR PELLETS (SHOT)

function: the part of the cartridge which exits the

muzzle.


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The appearances of the most common cartridges

are shown here. In general, it is difficult to tell from the

wound exactly what cartridge was used.


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Anatomy of the Cartridge

ShotgunHandgun Rifle

Primer

Flash Hole

Powder

bullet

Powder

Primer

Wad

Shot

WOUND BALLISTICS


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WOUND BALLISTICS

Definitions:

Ballistics is the science of the motion of projectiles.

Interior ballistics is the study of projectiles in weapons.

External ballistics is the study of projectiles in the air.

Terminal ballistics is the study of projectile penetration of solids.Wound ballistics is the study of projectile penetration of tissues.

A moving projectile has kinetic energy proportional to its weight

and velocity. KE=WV/2.

The wounding effect of a projectile is produced by transfer of

kinetic energy from the projectile to the tissues.Kinetic energy increases in proportion to

increases in the velocity squared; hence the wounding

potential depends on the velocity of projectiles

If a projectile does not exit the body, then all its kinetic energy has

been transferred to the tissues. If the projectile exits the body,then only some of its kinetic energy has been transferred to the tissues. The woundproduced by a projectile (bullet or shot) as it enters the body is called the entrywoundand that by which the projectile leaves the body is the exit wound. The pathtraversed by the projectile between the entry and exit wounds is called the track.

P j til di t ti b t i i l h i


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Projectiles disrupt tissues by two principal mechanisms:

1.Direct laceration of the tissues as occurs with any penetrating object

("drilling effect"). This is the main mechanism in low velocity gunshot wounds

e.g. from a pistol, and in such cases the permanent cavity seen at autopsy

accurately reflects the tissue damage produced by the path of the bullet.

2. In high velocity rifle wounds, there is an additional effect oftemporary cavityformation. Produced by the large amount

of kinetic energy transferred to the tissue, this cavity may be up to 30 times the

diameter of the projectile, has a lifetime of 5 to 10 milli-seconds, produces

pressures of 100 to 200 atmospheres. The diameter of the resultant permanent cavity isvariable but usually larger than the diameter of the bullet. At autopsy, the evidenceof temporary cavity formation may be a wide zone of haemorrhage around a small

permanent cavity. If the pressure of temporary cavity formation exceeds the elasticlimit of the tissue, then the organ may be disrupted ("bursts").

Organs which are dense (and thus cause greater loss of projectile KE) andrelatively inelastic are most susceptible to this bursting effect e.g. liver. Organs withlow density and high elasticity are relatively protected e.g. lung. High

velocity gunshot wounds of the head produce bursting injuries of the skull due totemporary cavity formation.


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Cavitationtemporary

cavity

permanent

cavity

direction of motion bullet

directinjury


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Other wounding mechanisms include:

1.Secondary projectiles such as shattered bone

fragments e.g. gunshot wounds to the head.

2.Discharge gases exiting the muzzle of the

weapon pass into the wound track in hard contact

wounds and produce tissue disruption e.g.

contact shotgun wounds to the head.

3. Additional components of the shot flame, smoke, gunpowder particles (unburnt or burnt)


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Gunsmoke ejected from the muzzle of a revolver at the time of discharge. The volume

of gas created is equal to the weight of gunpowder burn. The light streaks are glowing

particles of gunpowder. The bullet in seen on the left side of the photograph.

SKIN SURFACE CHARACTERISTICS OF GUNSHOT (BULLET) WOUNDS


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SKIN SURFACE CHARACTERISTICS OF GUNSHOT (BULLET) WOUNDS

(a) Exit wound is typically larger and more irregular than entry due to bullet tumbling and deformation.

(b) May be absent in the palm or sole, and re-entry wounds of axilla and scrotum Typically absent from exitwounds, allowing their distinction from entry wounds. May be seen in "shored" exit wounds.

(c) The term "powder burns" is variably used to include one or more of these features.

Term Synonyms Cause

Skin defect Permanent cavity Passing of the projectile through the skin (a).

Abraded margin Abrasion collar, Marginal abrasion,

Contusion ring, Abrasion ring

Forward motion of bullet indenting the skin and

abrading the margin of entry wound (b).

Micro-tears High velocity centre fire rifle bullets tend to produce

these rather than an abrasion ring.

Grey ring Contact ring, Bullet wipe Lubricant and debris on bullet surface wiped off onto

the wound edge.

Smudging (c) Fouling, Blackening Deposition of soot from partially burnt gases.

Tattooing (c) Stippling, Peppering Unburned, partially burned and burning gun powder

abrading and embedding in skin (sine qua non of

intermediate/ close/near range).

Singeing (c) Branding/Burning Hot gases from muzzle at close range

Muzzle impression Muzzle contusion, Muzzle imprint Skin impact against muzzle produced by discharge

gases or temporary cavity formation in contact and

near contact wounds


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BULLET WOUNDS

RANGE OF FIRE OF BULLET WOUNDS-The distance between the muzzle end of


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RANGE OF FIRE OF BULLET WOUNDS-The distance between the muzzle end offirearm and the target is called the range. This may be:

Range Muzzle-target distance Entry wound characteristics

1. Contact -Muzzle in contact with body Contact wound is generally large and cruciate( stellate, or star shaped), due to explosive effects of

the gases liberated. The imprint of the muzzle of the

weapon may be found stamped on the skin. Burning,

fouling by smoke, and tattooing are slight or absent

in the adjacent skin, since all the components of the

explosion are driven into the wound. The tissues are

often saturated with carbon monoxide and therefore

cherry red in colour.

2a Close range

2b Near range

-if the range is within the distance

travelled by flame

- if the range is within the distance

travelled by unburnt or burnt

gun powder burns

Close shot: Flame travels approximately up to 7 cm in

the case of revolver or pistol, and 15 cm in the case

of rifle. The wound appears as a circular hole

surrounded by singeing, and smudging. These may

be absent if firing has occurred through clothing.Abrasion collar, Grey ring, and tattooing may be

present.

Near shot: The entry wound is circular or oval in shape.

Unburnt powder burns and small metallic particles

travel approximately up to 60cms in the case of

revolver and pistol, and 70 cm in the case of rifle.

In practical situations, tattooing is seen up to amaximum distance of about 90 sm. Singeing of hair


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Differences between Entry and Exit

wounds


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Contact entrance

wound


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A firm contact discharge against tissue overlying bone (such as the

skull) caused gas to rebound from the rigid base. This raises dome under

the skin can split to give a ragged entrance wound.

Contact entrance


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Diagram showing of a shot fired with the muzzle in tight contact with

the skin The pocketbetween the skin and the bone is filled with soot

and gunpowder.

Contact entrance

wound.


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Soot is frequently deposited on the underlying a contact bullet wound. The presence of the soot

can usually only be demonstrated after careful removal of the area`s soft tissues. Particular care

must be taken in stripping the periosteum in the immediate vicinity of the bullet hole.

Gunsmoke is often deposited on the bone after the periosteum has been elevated by the gas

pressure.

Suicidal bullet


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Suicidal bullet

wound of the

forehead. This shot

was firedwith the muzzle

pressed against the

skin. The abraded

ring around thewound is due to

impact of the

muzzle on the skin

by the recoil of theweapon.

This is an contact


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This is an contact

gunshot entrance wound.

Since the barrel contacts

the skin, the gases

released by the fired round

go into the subcutaneous

tissue and cause the star-

shaped laceration. Note

also the grey-black

discoloration from the

soot, as well as the faint

abrasion ring.

A b i i


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An abrasion ring

(arrow), formed when the

force of the gasesentering below the skin

blow the skin surface

back against the muzzleof the gun, is seen here in

this contact range

gunshot wound to the

right temple.


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The abrasion ring, and

a very clear muzzle

imprint, are seen in thiscontact range gunshot

wound.


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Contact gunshot woundon the chest. An abrasionring (arrows) around the wound.

The gunsmoke


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The gunsmoke(arrows) is deposited

around on the wound

between the sternumand the ribs.

Gunshot wound on


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Gunshot woundonthe heart.


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Un this intraoral shotgun wound, note the tissue tears extending from the

side of the mouth. These tears result from the large amount of the gases

exiting the end of the barrel at high pressure (see next slide).


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Similar case: (1)entrance wound; (2)exit wound.

1

2


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1.A man shot himself in the chest

with a 20-gauge shotgun.

Note the oval entrance wound

with oval marginal abrasion and

the eccentric rim of

soot on this contact wound.

2. Another example, this is

self-inflicted contact shotgun

wound of the chest shows

singeing of the skin from theflame that exited the end of the

barrel.

1 2


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Formation of entrance wound (close range) and exitgunshot wounds (see next slide).


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Diagram ofclose-range shot with a handgun. At distance of 2

to 5 cm from the target, gunpowder burns are around

the bullet hole, while wave of soot disperse over a much area.


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Two homicidal shots of the right side of the face. The upper shot show plentiful soot

and very little gunpowder burns around the wound. This shot was fired at near contactwith skin. The lower shot is surrounded by a small amount of soot, while gunpowder

burns are scattered over a diameter of about 5 cm. This shot fired from a distance

of a 15 cm.


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As the muzzle-to-target-distance increases, the dispersion of gunpowder

burns on the target increases in diameter, while density of gunpowderburns scattering decreases.


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Homicide. Close-range shot of the left temple. Densely scattered

gunpowder burns but no soot indicate a shot fired a distance of about 30

cm.

Powder tattooing is seen in this


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gnear range gunshot

wound. The actual entrance siteis irregular, because the

bullet can tumble in

flight.


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This is a near range gunshot entrance wound in

which there is powder "tattooing" around the entrance site. Distances

of 60 cm or less.


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An nearrange gunshot wound was on the left temple of a female

homicide victim (1). The man who shot the woman had an near range gunshot

wound to the right temple (2). The wounds in both the woman and the man were

inflicted with the same firearm and ammunition. Note the presence of black soot and

residue and increased concentration of stippling immediately around the gunshot woundin the female as compared with minimal soot residue and a wider, less concentrated

stippling pattern around the gunshot wound in the male. The range of fire was slightly

greater in the male.

1 2


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Entrance wounds near range. Generally found at distance

of 60 cm or less. Tattooing is pathognomonic. Density of tattooing isdependent on the distance & caliber

Diagram showing difference


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g g

configuration of the marginal

abrasion of

an entrance bullet wound,depending on

the angle at which the bullet

strikes the body:

(a)- bullet perpendicular to body;(b)-bullet at an acute angle.

The diagram illustrates


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The diagram illustrates

the basic differences

between

the skin appearance of a

contact, close (near),

and distantrange gunshotwound.


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Wounding characteristics in the skull-the wound of entranceshows a punched clean hole in the outer table. The innertable is a cone-shaped piece of bone is detached forming acrater that is larger than the hole on the outer table. Exitwound shows a contrary feature. This is a good indicator of

the direction of the bullet.


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Entrance wound on theouter table of skull.

Exit wound on on theouter table of skull.


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SHOTGUN WOUNDS

SHOTGUN WOUNDS: The smoke extends up to 30 cm., flame up to50 cm and unburnt powder burns up to 60 to 90 cm Wadding can


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50 cm., and unburnt powder burns up to 60 to 90 cm. Wadding canproduce minor injury, up to a distance ofthree metres.

The character of a SHOTGUN wound depends on :

1. The distance from weapon is discharged.

-contact wound

-close range-near range

- distant range

2. The nature of the explosive.

3. The gun itself

RANGE OF FIRE OF GUNSHOT wound. This may be:


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y

Range Muzzle-target distance Entry wound characteristics

1. Contact -Muzzle in contact with body Contact wound is usually a large, irregular hole,

resulting from the explosive blast effect. The edge

of the defect is scorched by flame, and the skin

surrounding it is blackened by smoke, and tattooed

by unburnt powder. An imprint abrasion produced

by the muzzle end may be seen. The shot passes

into the body as a solid mass. The injured tissue is

usually cherry red in colour.

2a Close range

2b Near range

-if the range is within the distancetravelled by flame ( up to one

metre)

- if the range is within the distance

travelled by unburnt or burntgun powder burns ( up to four

metres)

Close shot: This produces a circular defect withirregular inverted edges. The edges are scorched

due to flame, and smudged by smoke. A wide zone

of tattooing may surround the edges of the wound.

Tissues often appear cherry red in colour. The

pellets enter the track en masse.

Near shot: The wound is circular or oval in shape.

Smudging may be evident around the wound up to

a maximum distance of 30 cm. Tattooing is presentover a wide area. The pellets travel in a compact

mass up to a distance of about 50 cm, after which

they begin to disperse3. Distant -if it is beyond the range of flame,

smoke and gun powder burns

(above four metres)

produced by mechanical action of pellet penetration of

skin only; Beyond a range of 2 metres, there will

be no burning or blackening. Tattooing is also rare.The dispersion of pellets becomes significant at


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Shotgun wounds at varying distances: 1(a)- split woundcontact over bone( skull); 1(b)- usual round contact wound;

2- close but not contact range up to about 30 cm (variable);3- rat-hole wound from 30 cm to about a metre(variable); 4-satellite pellet holes appearing over a metre;5- spread of shot increases, central hole diminishes; 6-

uniform spread with no central hole over about 10 metres.


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A man used 12-gauge shotgun to inflict a contact shotgunwound on the chest. Note unique circular abrasion

adjacent to the entrance wound. This is seen in double-barrelshotgun in which only one of the barrel fires (see next

slide).


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Similar case.


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Contact shotgun wound on the head.


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Shotgun discharge at 2 m into the chest. Notethe scatter of the shot.


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Homicidal assault with a 12-gauge pump actionshotgun from a distance of20 cm to 30 cm.

Homicidal assaultwith a 12 gauge


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with a 12-gaugeweapon from adistance about 4

metres.


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Pellet injuries from a distant 12-gauge shotgun discharge. The range wasabout 20 metres and the injuries were shallow. Death was caused bycoronary heart disease due to the shock of injury.

Wound inflicted


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from a distance of 40metres (see nextslide).

X ray of the


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X-ray of theshot pattern

associated withwound inprevious slide.

MEDICOLEGAL ASPECTS OF FIREARM


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INJURIES

The kind of firearm used

The range of firing

The direction of fire

The place from where firing took place The cause of death

Whether the firing was an accident,

homicide or suicide.


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forensic medicine - firearm injuries

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