A bomb is a container filled with an explosive mixture and missiles, which is fired either by detonator or a fuse. Terrorist bombs often involve only 2 to 10 kg of explosives. When an explosion occurs, the explosive material produces a large volume of gas, and releases a large amount of energy.
Pressure of up to 1,000 tons per sq. inch. can be generated. A minimum pressure of about 700 kilopascals (100 lb/sq inch) is necessary for tissue damage in humans. A person can be injured by an explosion in a number of ways.
If the victim is almost in contact with a large bomb he may be blown to pieces, e.g., when the victim is carrying it. The pieces can be scattered over an area of 200 meters radius. Many parts of the body are never found, having been disrupted into tiny fragments and mixed with the masonry and other debris of the bomb site. A bomb exploding on the ground may cause severe damage or traumatic amputation of the lower legs. A bomb which explodes when the victim is bending over it, may cause severe damage to arms, face and front of the chest. When the victim is a few meters away or with smaller explosion, disruption is usually limited to mutilation of a localized area.
The temperature of the explosive gases can exceed 2000°C., and the radiated heat can cause flash bums. It bums nearby objects and clothing. The flame causes extensive bums, which involve irregular area of skin to a different degree. Tight clothing protects, so that beneath collars, bras, waist bands, socks and shoes the skin may be quite normal.
An explosion produces a ‘shock wave’ which spreads concentrically from the site of explosion at about the speed of sound (1 l20ftJsec). This wave of very high pressure is followed by a weak wave of negative pressure (below atmosphere), a suction which lasts about five times as long.
A shock wave exceeding 700 kilopascals (100 lb/sq. inch) pressure is necessary to cause serious damage to a body. The shock wave can throw the victim against a wall or toss him through the air causing blunt force injuries. The clothes may be blown off by the blast. The clothing should be retained for chemical analysis. The shock wave passes through the body. The homogeneous tissues like liver and muscle are not damaged.
Blast injury of lungs is seen if the victim is within a few meters of explosion, and at such range, the victim usually dies from other injuries. Lungs show sub pleural patchy hemorrhages, scattered at random, often in the line of ribs.
Sectioning of lungs shows more discrete scattered areas of hemorrhage, often with a tendency to be more central than periphery. Microscopically, alveolar ruptures, thinning of alveolar septae, enlargement of alveolar spaces and circumscribed sub pleural, intra-alveolar and perivascular hemorrhages are the main findings.
Desquamated alveolar and bronchial epithelium is seen lying free. This causes reactive pulmonary edema and bloodstained froth is found in the air-passages, and later bronchopneumonia. This specific pulmonary injury of air blast is called ‘blast lung’. The tympanic membrane may rupture with hemorrhage in the ear.
Damage to cochlea is more frequent. Subperitoneal hemorrhage and hemorrhages in mesentery and momentum vary in size and laceration of abdominal organs may occur. Intracranial hemorrhage, contusion of the brain, injuries of heart and aorta, pneumothorax, ruptured stomach and bowel may occur.
Death may occur from systemic air embolism, from air which enters the pulmonary veins after blast damage to the lungs. When the explosion is in the water, the pressure changes are called underwater blast. The physical changes are similar to those of explosion in air. Injuries occur mostly in gastrointestinal tract and less commonly in lungs. Most of the lung injury is due to pressure transmitted from abdomen through the diaphragm.
Solid blast refers to a wave of energy that spreads through a rigid structure when an explosive is detonated near it and people in contact with its structure can be injured. Steel construction of tanks and warships conduct shock wave well and cause solid blast injury. The injuries are mostly skeletal. The fractures depend on the position of the person. Fractures of legs and vertebral column are more common. Gastrointestinal damage is more common than lung damage. In some cases, death may occur without any external injury.
The blast may drive multiple fragments of bomb or pieces of nearby objects, e.g., gravel, glass, wood, brick, plaster, etc. through the air into the skin and cause bruises, abrasions and puncture lacerations intimately mixed on the skin. This triad of injury is diagnostic.
Most of the bruises and abrasions are less than one cm. in diameter, although they tend to unite. The puncture-lacerations are also usually of this size. They are ragged, sometimes with soiled margins, and may contain foreign material, such as scraps of clothing, wood or metal.
The skin can be darkened by an explosion which drives dust into the skin and causes fairly uniform tattooing. The force of the explosion is extremely directional and the pattern of injury might indicate that the person was carrying the bomb or bending over it or sitting to one side of it.
When a building is destroyed by a blast, the persons inside sustain multiple injuries and die of traumatic asphyxia.
If a bomb explodes in a confined space, enough CO is produced to cause asphyxia. In a victim of bomb death, X-rays of tissues should be taken, as pieces of metal especially the detonating mechanism may be seen.
Incendiary bombs, e.g., napalm bombs primarily cause burns. A temperature of about 10000 C is produced. In incendiary type, usually phosphorus and magnesium are added. The Molotov cocktail is an incendiary type which is thrown by the hand.
In a crude type, a bottle is filled with gasoline and a rag to serve as a wick. The wick is lighted and thrown at the target. Various acids and chemicals are sometimes added to increase the destructive effects.
BOMBING INCIDENTS INVESTIGATION
(1) Whether the explosion was caused by a bomb?
Dispersed explosion usually occurs in houses when domestic gas leaks into the atmosphere and mixes with the air to form an explosive mixture that then catches fire. A dispersed explosion can blow off clothing and burn the exposed skin. All the exposed parts of the body are affected and all the burns are of same depth.
A bomb explosion (localized explosion) never causes extensive burns. Injuries by blast force, and the fragments are seen on the body. A part of a limb is blown off or a localised area of the body is mutilated. The triad of bruises, abrasions and puncture-lacerations with tattooing of part of the body also indicate explosion.
(2) Identification of the dead.
(3) Number of dead persons.
(4) Cause of Death
Death may result from multiple injuries, burns, shock or cerebral air embolism.
(5) Circumstances of Death
To differentiate the terrorist from the peaceful citizen, the reconstruction of the scene and the circumstances of the deaths from the autopsy findings are helpful. The injuries on the victims, particularly their type, severity and distribution are of much help.
(a) Explosive Force Declines Rapidly
Injury due to the explosive force itself is likely within a few meters of the bomb. With a terrorist bomb, when a person is blown to pieces he must have been in contact with it, i.e., either carrying the bomb, sitting with it or arming it. Persons can be injured by flying fragments and collapsing structures when at considerable distance from a terrorist bomb.
(b) Explosive Force is Highly Directional
The parts of the body directly exposed to explosive force only are injured. An explosion at ground level injures mainly lower legs and feet. When a person is in front of a bomb when it blows up, the face, chest, forearms, hands, inner thighs and the legs below the knees are injured, but the back of the body, the lower legs and face escape.
If a person is bending down over the bomb, the face, chest, lower legs and hands are severely damaged. The legs may be blown off or the abdomen disrupted or the hands and arms torn away in the person who was planting it. If the thigh, pelvic region and abdomen are damaged, it may have been carried on the lap.
If a parcel bomb is opened by a person sitting at a desk, his face, chest and hands are injured. If it explodes behind a person sitting in a chair, injuries will be produced on the back of the legs below the knee and on the back of the trunk.
All bodies should be X-rayed before autopsy to identify any radio.opaque objects including those from the bomb mechanism, such as small springs or contacts from the timer or detonator.
DOMESTIC GAS EXPLOSIONS
They occur due to leaks in the gas supply. Natural gas explodes at concentrations in air between 5 to 15 percent. Ignition is usually caused by matches or candles, fires, sparking electric switches. The explosion is accompanied by a momentary flame that sets fire to furnishings.
The air pressure usually rises to less than 10 psi, due to venting through broken windows and doors. Deaths are rare. The person can be thrown off their feet and injured. The damage is haphazard or diffuse. The flame singes hair and causes localized superficial burns of exposed surfaces. Most deaths occur when the building collapses and the victims are buried in the debris.
Mechanical explosion occurs when a steam boiler bursts due to increased pressure. Heat and large volumes of gas are produced. The effects are similar to those of chemical explosion.