Fire Arm Injuries 4th Yr Forensic

8/8/2019 Fire Arm Injuries 4th Yr Forensic

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FIRE ARM INJURIES

DR MACHARIA

MBchB (uon),Mmed Path (uon),Dip. Forensic Path (SA)


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OBJECTIVES

Broad classification of firearms

Mechanisims by which missiles cause injuries

Factors that can be determined from firearminjuries

Range

Exit and entrance wounds

Number of shots Type of weapon used.

Direction from which the missile was fired.


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Classification

1) Classification accordidng to velocity

Low velocity missile (760m/s)


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2) In the context of wounds guns arecategorised into:

Rifled guns

They have parallel spiral grooves on theinner aspect of the barrel and a single

missile is fired at a time. They include

Pistols, revolvers, AK47, submachine guns


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Shot guns ( Smoothbore firearms)

The inner lining of the barrel is smooth

Multiple pellets are usually discharged at

once.


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Mechanisms of injury Missiles cause injuries in three ways.

Mechanical damage

This is by laceration and crushing of tissues

This is the principle mechanism especially

with low velocity missiles since most of the

energy is transmitted into the tissues.


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Shock waves

High velocity missiles generate shockwaves thatcompress tissues ahead of the missile.

This compression causes damage especially tofluid filled organs like the bladder, heart, and the

bowel.


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Cavitation

A high velocity missile causes tissues to fling

away from the center creating a temporary cavitythat lasts afew miliseconds.

The cavity may be upto 40 times the size of the

bullet.

This affects mainly the solid organs like the brain

and liver.


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A cartridge is made of

Cartridge case

Primer- It ignites the propellant.

propellant and

the missile.


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When the trigger is pulled, the following areemitted.

Projectile Burnt propellant

Unburnt propellant

Hot gasses

Flames

Grease and oil.

Cartridge case


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Factors that can be determined from firearm

injuries

Range

Entry and exit wounds

Direction from which the missile was fired.

Type of missile used.

Number of shots that struck the body.


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Range

Broadly categorised into three.

Contact

Near

Distant


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Contact wounds over hard surface

The gun is held tight against the skin.

Characteristics of the entry wound

Usually stellate in shape

The edges are everted

Edges are seared by heat and have soot Muzzle imprint

May be larger than the exit wound.


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Close range ( near ) wounds

Up to an arms-length

The entry wound will have the followingcharacteristics

Smaller than the exit wound.

Inverted edges.

Usually round to oval in shape

A collar of abrasion

Soot around the wound


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High levels of co in tissue around thewound.

Singeing of the hair due to heat so theyappear club shaped

Tattooing These are small focal punctate

abrasions caused by burnt and unburntpropellant particles.

Not found on the palms and the soles


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Distant wounds

Distances greater than 35 to 60 cm

Usually small and round to oval.

Inverted edges.

A collar of abrasion No soot/blackenning

No tattooing


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Exit wounds.

Generally larger and irregular than the entry

wound. Usually do not have a collar of abrasion except in

shored exit wounds. ( where skin was in contactwith a hard contact like a belt)

Exit wounds may be more than the entry wounds. Normal levels of co in the tissues around the

wound.


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Direction from which missile was fired.

This is done by examining the following

Shape of collar of abrasion

Pattern of distribution of blackenning and

tattooing.

Trajectory between the entry and exit

wounds.


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Shot guns.

The contact wound over a hard surface resembles

that of a rifled gun.

The close range entry wound differs with that of a

rifled gun since many pellets are fired.

In close range the entry wound is round

From around 30cm the entry wound has a rat-hole

appearance


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As the distance increases, satellite small holes

start appearing with a central hole.

With further distance, the central hole

disappears leaving only the satellite holes.

So for distant range wounds, there are many

small wounds on the skin .


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Rat-hole appearance


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A central hole with small multiple satellite wounds.


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Distant range. Multiple small wounds.


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Autopsy

Should be preceded by a visit to the scene of

crime. Photography

There should be a consent from relevantauthorities.

Obtain proper history as to the circumstances ofthe shooting.

Pre autopsy X Ray if possible.


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Samples and exhibits retained.

Pieces of clothing for possible gunshot residue and

blood Blood may be taken for alcohol level DNA

analysis can be done then compared with thatfound at the scene.

The skin wound may be removed for ballistics. Bullets recovered. Should not use metal forceps to

remove bullets-rubber-tipped forcepsrecommended.Wrap it with cotton wool then into

a container.


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Calibre

It is the distance between the lands, a land

being the metal between the grooves. The

land projects in to the barrel.


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EXPLOSIVES

An explosion is a sudden release of previously

confined energy.

Death and injury are due to the following.

Primary blast injury.

This is due to direct effect of blast wave that

radiates from the center. A secondary blast injury

This is caused by objects e.g. glass falling stones


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Injuries due to inhalation of toxic substances.

Burns


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Why carry out an autopsy

Identity of the victims

Number of victims

Cause of death


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Fire Arm Injuries 4th Yr Forensic

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