INJURIES BY EXPLOSIVES

The recent upsurge of terrorism for political and other purposes in many parts of the world has brought with it the use of explosives. It seems that in the general political unrest, which is prevalent in the world, the bomb will continue to be used to reinforce direct and indirect political objectives and therefore, a medico-legal expert needs to be conversant with some basic knowledge about the effects contributing towards injuries/death etc. Identification of the material used in the manufacture of the bomb and mechanism of its explosion, etc. are the domains of the forensic scientists.

Most of our knowledge of explosions has been gained through wartime events. There have also been some notable explosions affecting civilians such as the one in Texas City in 1947 when a ship loaded with ammunition exploded at the docks killing about 560 people and injuring over 3000.

Following an explosion, a person can be injured/killed in a number of ways:

1. If he is quite near the explosion, he can be blown to pieces.
2. He can be injured by a wave of pressure, called the ‘shock wave’, which spreads concentrically from the seat of the explosion. When the explosion is in air, the pressure wave is referred to as air-blast.
3. He can sustain ‘flash burns’ from the momentary heat radiation or, if his clothing or other material is set on fire, he can sustain ordinary burns.
4. He can be struck by ‘flying missiles’ propelled by the explosion.
5. He can be injured or crushed by debris, usually of building(s) demolished by the explosion.
6. He can be overcome by fumes generated as a result of the explosion.

The above factor(s) may operate solely or in varying combinations and the relative importance of each will depend upon the tye of detonation, the distance of the victim from the seat of explosion and the location of the explosion. Each factor is being discussed.

Disruptive Effects: If the victim is almost in contact with a large bomb (usually when he is carrying it or sitting with it in some vehicle), he may be blown to pieces.. a pre-mature explosion, sometimes during the act of setting the timer, may cause disruptive injuries. With smaller explosions or when the victim is a few feet away, disruption is limited to the blowing off of head or lib or the mangling of a localized area. therefore, sometimes a part of the body may be totally destroyed while the remainder of the victim being remarkably intact. The pieces can get scattered over an area of 100 metres or more from the seat of explosion. Many parts of the body may never be found having mixed with the masonry and other debris of the bomb-site.

Air Blast (Shock Wave): A blast comprises a wave of compression, which spreads concentrically from the blast-centre. The velocity of the shock wave depends upon the distance from the epicenter, being many times the speed of sound in the air at the start but rapidly decreases as it spreads out. This wave of compression/high pressure is followed by a week wave of negative pressure (below atmospheric), so that a rapid double change in pressure is suffered by the victim. The magnitude of the blast varies with the energy released and also with the distance from the epicenter. As the distance from the explosion increases, the peak pressure falls rapidly, almost exponentially. About 100 lb/sq. inch (690kPa) is the minimum threshold for producing serious damage to human beings.

Effects of Blast Wave/Shock Wave: The high pressure shock wave generated by an explosion can knock a person down and thus cause injury but the specific injury associated with blast is due to the shock wave being propagated through the body. It causes most damage at an interface between tissues in contact with the atmosphere and that is why the lung is usually the worst sufferer. The shock wave can pass through solid homogenous tissues like muscle and liver, causing little or no damage but in the lungs the damage is caused owing to marked variation in density between the alveolar walls and the contained air so that damping of shock wave occurs leading to disruptive effects. Its transit through the lungs can tear the alveolar septa and give rise to alveolar haemorrhage. Other findings in the lungs may include sub pleural patchy haemorrhages (often in the line of ribs) and intra-pulmonary haemorrhages. The air passages may be filled with bloody froth causing airway obstruction and hypoxia in addition to the primary damage. Later, neutrophilic reaction may develop around the haemorrhagic areas and those can progress onto brocho-pneumonia. The pulmonary injury is a specific injury of the air-blast and is sometimes called as ‘blast lung’. However, the lungs can also be bruised by direct blows on the chest and haemorrhagic areas can arise by aspiration of blood or regurgitation of stomach contents down the trachea. Rarely, when the victim dies soon after the explosion of a bomb, this finding may not be seen, presumably due to relatively small amount of explosive detonated and the victim being somewhat away from the seat of explosion so that the blast wave is unable to exert any serious effect.

Blast may also cause damage to the ears. Its effects tend to be capricious because the pressure on the tympanic membrane is modified by many factors but when the pressure rises excessively above the atmospheric, rupture is likely.

Gastrointestinal system often suffers from the effects of a blast because like the lung, it contains air and gases and is thus not a uniform medium for the transit of shock wave. The caecum and colon are more often hurt than the ileum, jejunum and stomach, presumably because they are larger and often contain more gases. Occasionally, ruptures of the gut can occur if the blast is violent and the victim is situated nearby.

Burns: When a bomb explodes, the temperature of explosive gases can exceed 2000^oC and the heat radiated momentarily can cause ‘flash burns’. The amount of thermal radiation received decreases with the square of the distance from the explosion and the intensity of explosion.