SN2 SHORT NOTE 5M ★ High-yield

Describe explosion and blast injuries.

Forensic Medicine · 2nd Professional — Para-Clinical

Mechanism of Blast Injury

An explosion is the sudden conversion of a solid or liquid into a large volume of gas with the release of enormous energy, producing a blast wave — a sharp rise in pressure travelling faster than sound, followed by a negative (suction) phase.

Category	Mechanism and injuries
Primary blast injury	Direct effect of the pressure wave on gas-containing organs, where the pressure differential at tissue interfaces tears them. Affects the lungs ("blast lung" — contusion, haemorrhage, oedema and alveolar rupture with air embolism), the tympanic membrane (the most sensitive and the commonest finding, rupturing at low pressures), and the bowel (perforation and haemorrhage, often delayed by hours or days). There may be NO external injury
Secondary blast injury	The commonest and the greatest cause of death — penetrating and lacerating injury from flying fragments: the casing of the device, deliberately added shrapnel such as nails and ball bearings, and secondary missiles of glass, masonry and metal from the surroundings
Tertiary blast injury	The victim is thrown by the blast wind against a surface, or a structure collapses on them — blunt trauma, fractures, crush injury and traumatic amputation
Quaternary (miscellaneous)	Burns, both flash and flame; inhalation of hot gases, smoke, dust and carbon monoxide; toxic effects; and exacerbation of pre-existing disease. Also crush syndrome and psychological trauma
Quinary	Effects of additives — radiological, chemical or biological material deliberately incorporated in a "dirty bomb"

Effects vary greatly with the environment — the same charge is far more lethal in an enclosed space because the wave reflects from the walls and is reinforced; and underwater blast is more dangerous than blast in air, since water transmits the pressure wave more efficiently and over a greater distance
Very close to the charge, the body may be disrupted — fragmented, with traumatic amputation and dispersal of parts over a wide area, so that identification and even the number of victims becomes the first problem

CLINICAL PEARL

A person may die of blast lung with no mark on the body at all. The pressure wave passes through the chest wall and tears the alveoli at the air-tissue interface, so the lungs are haemorrhagic and oedematous while the skin is intact. Ruptured eardrums are the clue — they are the most pressure-sensitive structure and are therefore the marker that a significant blast wave was experienced, prompting a search for lung and bowel injury that may otherwise be missed.

Autopsy and Investigation

The autopsy has two purposes — to establish identity and cause of death, and to recover evidence about the device, which makes the pathologist part of the criminal investigation in a way that is unusual
Radiograph the body and all fragments before dissection; this is essential and locates metallic fragments, ball bearings, nails, detonator components and timer parts embedded in the tissues, which may identify the type of device and its maker
Recover, label and preserve every fragment separately with its site, handling metal with rubber-tipped instruments; and preserve the clothing, on which explosive residue is often best detected
Examine for the suicide BOMBER — who characteristically shows complete disruption of the trunk with the head relatively intact and often thrown some distance; and severe damage to the hands and lower limbs where the device was carried. Establishing which body was the carrier is a specific and important question
Examine the tympanic membranes, the lungs and the bowel in every survivor and every victim, since primary blast injury may be occult
Estimate the position relative to the charge from the pattern and distribution of injuries and fragment wounds, which may reconstruct where each person was standing

Applied Aspects

Examine the eardrums in every blast survivor; perforation indicates exposure to a significant pressure wave and mandates observation for blast lung, which may deteriorate over hours
Beware delayed bowel perforation; it may present 24 to 48 hours after the event in a patient who appeared uninjured, and a survivor of a significant blast requires admission and observation rather than discharge
Radiograph before you dissect; fragments are the physical evidence of the device, and cutting blindly loses them into the tissues or the drain
Do not wash the body or clothing before residue sampling; explosive traces are recovered from the skin, hair and garments and are destroyed by washing
Treat it as a mass-disaster identification problem — number and photograph every fragment in situ, take DNA from each, and do not release remains until reconciliation is complete; body parts from several victims are commonly intermingled
Blast lung can kill without any external injury, so a body recovered intact from an explosion still needs a full internal examination and should never be assumed to have died of something else
An enclosed space multiplies the effect, because the pressure wave reflects from the walls; the same charge indoors is far more lethal than in the open

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