Firearm Injuries PDF

Preview

Summary

My notes on firearm injuries for exam held in march 2016...

Description

Firearm Injuries Gunshot Injuries can be made by either a shotgun or a Rifle.

Shotgun The inner side of the barrel is uniformly smooth since they fire large number of small spherical lead shots. This is the reason they are known as shoter. In some shotguns, the muzzle end is constricted slightly, that is known as choking. It narrows the core of discharge, making greater impact of firing. Bore is the inner diameter of the barrel. It is defined as the number of spherical lead balls exactly fitting the barrel which can be made from 1pound of lead. The commonly used shotgun is the 12 bore (there is also the 16 bore).

Rifle The bell of the rifle contains spiral grooves and lands. These provide spinning effect on the bullet. The rifle fires single bullet at a time. Examples: revolver, Pistol, Rifle, and other types of military weapons. 3 types of movements occur in the bullet of the rifle gun on firing. These are: 1. straight movement (propulsion) 2. spin effect (grooves and lands) 3. bowling movement**pic

Types of cartridges**pic Gun powder can be of 2 types: 1. Semi smokeless- 80% black powder, carbon, and 20% smokeless powder 2. Smokeless- Nitrocellulose and Nitroglycerine

Shotgun Cartridge The case is made up of a cardboard or plastic tube with twisted anterior margins. The anterior surface is made up of cardboard and the posterior of brass. The contents from forward to backward are: 1. pellets(lead) 2. wad(cord) 3. gun powder(propellant) 4. percussion cap(containing the priming feature).

Rifle Cartridge It 1. 2. 3.

is made of metal. The contents from forward to backward are: Bullet Gun powder Percussion cap

Firearm Injuries Firearm injuries depend upon the type of firearm used. Every firearm wound is a punctured wound, with entry wound, a track, and sometimes an exit wound.

Medicolegal Significance is to determine: 1. Type of firearm used 2. Direction of firing 3. Range of firing

A.

Shotgun Injuries

Hot gases, flame, smoke, unburnt powder, wad and shots( pellets) all contribute for the appearance of shotgun wound. These produce the following 3 effects: 1. Flame effect- burn 2. Smoke effect- blackening 3. Powder effect- tattooing (washing differentiates it from blackening ) On the basis of distance of firing, it may be a contact shot, a closed range, intermediate, longer- range or long range wound.

Contact wound There will be muzzle impression. It can be single or double (if double valve is used). The impression is formed due to recoiling of the gun at firing. This may also produce a bruise. Since the pellets will enter the body in a single solid mass, the single entry wound will be of the same size as the bore of the barrel. There may be bursting effect at 2 sites: head and abdomen. The tissue will be blackened inside the track and the surrounding area pink due to CarboxyHb (CO is present in the discharged gas) Exit wound may be present because the shot in contact wound is in a solid mass. Except in contact wound, exit wound is not a feature of shotgun injury.

Close range wound (Near range) Within few cms from the surface skin There will not be any muzzle impression. There may be irregularity of the entry wound. The wound is larger than the barrel size. Tattooing will be present as unburnt powder is deposited into the epidermis. Blacking will be produced by soot deposition on the surface. Flame and hot gases will cause burn to the skin and singeing of hair. At this range, CO may produce pinkish discoloration of the tissue.

Intermediate range Between 20cm to 1m The smoke, flame, and powder effects diminish as the distance from the muzzle to wound increases. At this range, blackening diminishes while tattooing will still persist.

Longer range Critical distance- 2yards At this distance, tattooing is less visible and the wad may not penetrate the wound.

At the distance of 2-3m, satellite pattern may be present around the main entry wound. The range of firing can be assessed by the formula: Diameter of shot pattern in cm= 2-3 X muzzle distance from the wound in m

Long range firing It is at the range of about 20- 30m There will be dispersion of pellets and no central mass. It is less lethal.

B.

Rifle Injuries

Rifle injury is likely to have exit wound due to the high velocity and weight of the projectile. On the basis of range of firing:

Contact wound The features are the same as shotgun but an exit wound is more common.

Close range Within 20cm from surface There is no muzzle impression. At this range, the bullet will enter the body leaving a small entry wound with inverted margin and this diameter of the entry wound may not correspond to the diameter of the bullet due to elasticity of the skin. Blackening, singeing of hair, tattooing will be present. There will be an abrasion/ contusion collar. A grease collar may also be present. A swab around the entry wound should be preserved.

Intermediate range 20cm to 1m At this range, there will be tattooing and abrasion collar around the entry wound. Blackening will diminish. Flame effect may be absent.

Long range Only entry wound and an abrasion collar around the entry wound will be present. Beyond the range of 1- 1.3m, tattooing will be absent. At very long range, the diameter of the wound will be greater than the bullet size.

Differences in Entry and Exit wounds Feature 1 Size 2 Margin 3 Singeing of hair, tattooing, burn,

Entry

Exit

Usually smaller in size Inverted

Usually larger in size Everted

Present

Absent

blackening

4 5 6 7 8

Abrasion collar Dispersion of pellets Redness due to CO staining Metallic ring shadow bursting

Features in skull- at the outer table, the margins will be clean cut and at the inner table there will be bevelling. In the exit wound, the inner table will be clean cut and the outer will be bevelled. Medicolegal information obtained from examination of firearm wounds (medicolegal questions that may be asked in court while conducting a firearm wound) 1.

Nature of death- suicidal, homicidal, accidental

Suicidal firearm injury is commonly present over accessible sites of the body. Example in a right handed person: the right temporal area, palate, chin, forehead, left side of chest. Entry wound is usually contact range, but may be near range also. There will be muzzle impression. Gun will be present in hand in cadaveric spasm. Apart from this, circumstantial evidences are important (closed room locked from inside, presence of weapon at site of incidence and suicidal note). Dermal nitrate test of the hand will be positive. Homicidal nature will be indicated by more than 1 firearm wound placed anywhere over the body and it may be contact, near or a distant shot. Homicidal firearm used may be from long as well as shot barrel. In this case, circumstantial evidences are also important. For example: the place of occurrence is disturbed, weapon of offence usually missing but occasionally present in victim’s hand but not in cadaveric spasm. Accidental nature may occur with muzzle being in contact with the body or in close range: example while cleaning a loaded gun, while playing with a gun, or due to wrong firing.

2.

direction of firing

Margin of entry wound In case of shotgun injury, the dispersion of pellets may give direction of firingdispersion is more on the opposite side of firing. In rifle gun, abrasion collar will give direction. It is thicker in the direction of firing. Track of bullet Track inside the body may also be helpful for giving the direction as well as the entry and exit wounds. It is applicable only in rifle injury. In shotgun, there is dispersion of pellets and also the chance that the bullet change track inside the body.

3. 4.

distance of firing identification of firearm used

Gun powder used in the cartridge can help in identification of the weapon used. If the chemical analysis reveals that the nature of gun powder present on the inner surface of the barrel and that present around the entry wound or corresponding cloth is the same, then this is the indication that this suspected gun might have been used for that injury. If grease material from the grease collar around the entry wound and corresponding cloth is similar with the grease material found in the inner surface of the barrel, then this may also give indication of the gun used. Comparative study of the bullet- recovered bullet from the site of entry or the site of crime and test bullet fired from the suspected gun are studied for markings. There are 2 types of markings: primary and secondary. Primary markings are produced by lands and grooves present on the inner surface of the barrel. The secondary markings are caused by certain specific features of the inner surface of the barrel (minor projections, elevations, depressions). Examination of suspected gun- if the gun is examined after use and before cleaning, then evidence can be established by physical and chemical examination of swaps taken from the inside of the barrel.

5.

identification of assailant

Apart from circumstantial evidences, a laboratory test is recommended for identification of assailant. Dermal nitrate test (Paraffin test) Paraffin impression from the medial surface and base of the thumb and lateral surface and base of the index finger of the right hand if the person is right- handed is subjected to test for nitrate. It is performed with Diphenyl amine reagent. In case of recent use of gun, the hand is contaminated with nitrogenous compound of the gun powder and a bluish discoloration occurs over the paraffin cast. Spectrophotometry and Neutron Active Analysis (metal present in priming mixture) are advanced identification techniques....