A
blast injury is the result of
physical traumaPhysical trauma refers to a physical injury, generally of a considerably severe degree. A trauma patient is someone who has suffered serious and life-threatening physical injury with the potential for secondary complications such as shock, respiratory failure and death.-Common causes:Comprehensive...
sustained in an
explosionAn explosion is a rapid increase in volume and release of energy in an extreme manner, usually with the generation of high temperatures and the release of gases. An explosion creates a shock wave. If the shock wave is a supersonic detonation, then the source of the blast is called a "high explosive"...
. Blast injuries occur with the detonation of high-order explosives, explosives that produce a
supersonicThe term supersonic is used to define a speed that is over the speed of sound . In dry air at 20 °C , the threshold value required for an object to be traveling at a supersonic speed is approximately 343 m/s, . Speeds greater than 5 times the speed of sound are often referred to as hypersonic...
over-pressurization
shock waveA shock wave is a type of propagating disturbance. Like an ordinary wave, it carries energy and can propagate through a medium or in some cases in the absence of a material medium, through a field such as the electromagnetic field...
, as well as low order explosives which produce a subsonic explosion with no over-pressurization wave. These injuries are compounded when the
explosion takes place in a confined space.
A blast wave generated by an explosion starts with a single pulse of increased air pressure, lasting a few milliseconds. The negative pressure (
suctionSuction is the flow of a fluid into a partial vacuum, or region of low pressure. The pressure gradient between this region and the ambient pressure will propel matter toward the low pressure area. Suction is popularly thought of as an attractive effect, which is incorrect since vacuums do not...
) of the blast wave follows immediately after the positive wave. The duration of the blast wave, i.e., the time an object in the path of the shock wave is subjected to the pressure effects, depends on the type of explosive and the distance from the point of detonation. The blast wave progresses from the source of explosion as a sphere of compressed and rapidly expanding gases, which displaces an equal volume of air at a very high
velocityIn physics, velocity is the rate of change of position. It is a vector physical quantity; both speed and direction are required to define it. In the SI system, it is measured in meters per second: or ms-1. The scalar absolute value of velocity is speed...
. The velocity of the blast wave in air may be extremely high, depending on the type and amount of the explosive used. Indeed, while a hurricane-force wind (approximately 200 km/h) exerts only 0.25
PSIThe pound per square inch or, more accurately, pound-force per square inch is a unit of pressure or of stress based on avoirdupois units...
overpressure (i.e. 1.72
kPaKPA may refer to:* Kenya Ports Authority* Kilopascal , a unit of pressure* Known-plaintext attack, a method of cryptanalysis* Korean People's Army* The Kosovo Property Agency* Also refers to the Montagnard name meaning "straight"....
), a lethal blast-induced overpressure of 100 PSI (i.e. 690 kPa) travels with a velocity of approximately 1500 mph (i.e. 2414 km/h). An individual in the path of an explosion will be subjected not only to excess barometric pressure, but to pressure from the high-velocity wind traveling directly behind the shock front of the
Blast waveA blast wave in fluid dynamics is the pressure and flow resulting from the deposition of a large amount of energy in a small very localised volume...
. The magnitude of damage due the
blast waveA blast wave in fluid dynamics is the pressure and flow resulting from the deposition of a large amount of energy in a small very localised volume...
is dependent on: 1) the peak of the initial positive pressure wave (bearing in mind that an overpressure of 60-80 PSI or 414-552 kPa is considered potentially lethal); 2) the duration of the overpressure; 3) the medium in which it explodes; 4) the distance from the incident blast wave; and 5) the degree of focusing due to a confined area or walls. For example, explosions near or within hard solid surfaces become amplified two to nine times due to shock wave reflection. As a result, individuals between the blast and a building generally suffer two to three times the degree of injury compared to those in open spaces.
Classification
Blast injuries are divided into four classes: primary, secondary, tertiary, and quaternary.
Primary injuries are due to high-order explosive over-pressurization shock wave as it moves through the body targeting gas-containing organs such as the ear, lungs, and
gastrointestinal tractThe human gastrointestinal tract , digestive tract, guts or gut is the system of organs within humans that takes in food, digests it to extract energy and nutrients, and expels the remaining matter...
) or those containing structures with different specific weights. In general, primary blast injuries are characterized by the absence of external injuries; thus internal injuries are frequently unrecognized and their severity underestimated. According to the latest experimental results, the extent and types of primary blast-induced injuries depend not only on the peak of the overpressure, but also other parameters such as number of overpressure peaks, time-lag between overpressure peaks, characteristics of the shear fronts between overpressure peaks, frequency resonance, and electromagnetic pulse, among others. There is general agreement that
spallSpall are flakes of a material that are broken off a larger solid body and can be produced by a variety of mechanisms, including as a result of projectile impact, corrosion, weathering, cavitation, or excessive rolling pressure...
ing, implosion, inertia, and pressure differentials are the main mechanisms involved in the pathogenesis of primary blast injuries. Thus, the majority of prior research focused on the mechanisms of blast injuries within gas-containing organs/organ systems such as the
lungThe lung or pulmonary system is the essential respiration organ in air-breathing animals, including most tetrapods, a few fish and a few snails. In mammals and the more complex life forms, the two lungs are located in the chest on either side of the heart...
s, while primary blast-induced brain injury has remained underestimated.
Blast lung refers to severe
pulmonary contusionA pulmonary contusion is a contusion of the lung, caused by chest trauma. As a result of damage to capillaries, blood and other fluids accumulate in the lung tissue. The excess fluid interferes with gas exchange, potentially leading to inadequate oxygen levels...
, bleeding or edema with damage to alveoli and blood vessels, or a combination of these. It is the most common cause of death among people who initially survive an explosion.
Secondary injuries are due to bomb fragments and other objects propelled by the explosion.
These injuries may affect any part of the body and sometimes result in
penetrating traumaPenetrating trauma is an injury that occurs when an object pierces the skin and enters a tissue of the body, creating an open wound. In blunt, or non-penetrating trauma, there may be an impact, but the skin is not necessarily broken. The penetrating object may remain in the tissues, come back out...
with visible hemorrhage (bleeding). At times the
propelled objectA projectile is any object propelled through space by the exertion of a force which ceases after launch. Although a thrown baseball could be considered a projectile, the word more often refers to a weapon...
may become embedded in the body, obstructing the loss of blood to the outside. However, there may be extensive blood loss within the
body cavitiesBy the broadest definition, a body cavity is any fluid filled space in a multicellular organism. However, the term usually refers to the space, located between an animal’s outer covering and the outer lining of the gut cavity, where internal organs develop...
.
ShrapnelFragmentation is the process by which the casing of an artillery shell, bomb, grenade, etc. is shattered by the detonating high explosive filling. The correct technical terminology for these casing pieces is fragments , although shards or splinters can be used for non-preformed fragments...
wounds may be lethal and therefore many anti-personnel bombs are designed to generate shrapnel and fragments.
Tertiary injuries result when a person becomes a missile and is thrown against other objects. The injuries sustained are then similar to those that are sustained by
blunt traumaIn medical terminology, blunt trauma, blunt injury, non-penetrating trauma or blunt force trauma refers to a type of physical trauma caused to a body part, either by impact, injury or physical attack; the latter usually being referred to as blunt force trauma...
, including
bone fractureA bone fracture is a medical condition in which there is a break in the continuity of the bone...
s and
coup contre-coup injuriesIn head injury, a coup injury occurs under the site of impact with an object, and a contrecoup injury occurs on the side opposite the area that was impacted. Coup and contrecoup injury is associated with cerebral contusion, a type of traumatic brain injury in which the brain is bruised. Coup and...
.
Quaternary injuries are all other injuries not included in the first three classes. These include
burnA burn is an injury to the skin caused by heat, cold, electricity, chemicals, or radiation.Burn may also refer to:*Concrete things and phenomena:**Combustion**Burn , type of watercourses so named in Scotland and north-eastern England...
s, crushing injuries and respiratory injuries.
Neurotrauma
Blast injuries can cause hidden
brain damageBrain damage, or acquired brain injury, is the destruction or degeneration of brain cells.-Causes:Brain damage may occur due to a wide range of conditions, illnesses, injuries, and as a result of iatrogenesis...
and potential
neurologicalNeurology is a medical specialty dealing with disorders of the nervous system. Specifically, it deals with the diagnosis and treatment of all categories of disease involving the central, peripheral, and autonomic nervous systems, including their coverings, blood vessels, and all effector tissue,...
consequences. Its complex clinical syndrome is caused by the combination of all blast effects, i.e., primary, secondary, tertiary and quaternary blast mechanisms. It is noteworthy that blast injuries usually manifest in a form of poly-trauma, i.e. injury involving multiple organs or organ systems. Bleeding from injured organs such as lungs or bowel causes a
lack of oxygenHypoxia is a pathological condition in which the body as a whole or a region of the body is deprived of adequate oxygen supply. Variations in arterial oxygen concentrations can be part of the normal physiology, for example, during strenuous physical exercise...
in all vital organs, including the
brainThe brain is the center of the nervous system in all vertebrate, and most invertebrate, animals. Some primitive animals such as jellyfish and starfish have a decentralized nervous system without a brain, while sponges lack any nervous system at all...
. Damage of the lungs reduces the surface for oxygen uptake from the air, reducing the amount of the oxygen delivered to the brain. Tissue destruction initiates the synthesis and release of hormones or mediators into the blood which, when delivered to the brain, change its function. Irritation of the nerve endings in injured peripheral tissue and/or organs also significantly contributes to blast-induced
neurotraumaThere is no single classification system that can describe all the many variations of nerve injury. Most systems attempt to correlate the degree of injury with symptoms, pathology and prognosis. In 1943, Seddon introduced a classification of nerve injuries based on three main types of nerve fiber...
.
Individuals exposed to blast frequently manifest
loss of memoryAmnesia is a memory condition in which memory is disturbed. In simple terms it is the loss of memory. The causes of amnesia are organic or functional. Organic causes include damage to the brain, through trauma or disease, or use of certain drugs. Functional causes are psychological factors, such...
for events before and after explosion, confusion, headache, impaired sense of reality, and reduced decision-making ability. Patients with brain injuries acquired in explosions often develop sudden, unexpected brain edema and cerebral
vasospasmVasospasm refers to a condition in which blood vessels spasm, leading to vasoconstriction. This can lead to tissue ischemia and death . Cerebral vasospasm may arise in the context of subarachnoid hemorrhage. Symptomatic vasospasm or delayed cerebral ischemia is a major contributor to...
despite continuous monitoring; however, the first symptoms of blast-induced neurotrauma (BINT) are latent, occurring months or sometimes years after the initial event. The broad variety of symptoms includes weight loss, hormonal imbalance, chronic fatigue, headache, and problems in memory, speech and
balanceEquilibrioception or sense of balance is one of the physiological senses. It helps prevent humans and animals from falling over when walking or standing still.-Normal balance functioning:...
. These changes are often debilitating, interfering with daily activities. Because BINT in blast victims is underestimated, valuable time is often lost for preventive therapy and/or timely rehabilitation.
See also
- Battlefield medicine
Battlefield medicine, also called field surgery and more recently combat casualty care, is the treatment of wounded soldiers in or near an area of combat. Civilian medicine has been greatly advanced by procedures that were first developed to treat the wounds inflicted during combat...
- Bomb
A bomb is any of a range of explosive devices that typically rely on the exothermic chemical reaction of an explosive material to produce an extremely sudden and violent release of energy. The word comes from the Greek word βόμβος , an onomatopoetic term with approximately the same meaning as...
- Explosive
- Suicide bombing
- Chest trauma
Chest trauma is a serious injury of the chest. Thoracic trauma is a common cause of significant disability and mortality, the leading cause of death from physical trauma after head and spinal cord injury. Blunt thoracic injuries are the primary or a contributing cause of about a quarter of all...
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