Explosions and Blast Injuries

???????????? ????????????EXPLOSIONS AND BLAST INJURIES(C)

????????????????????? ??????????????Martin Greenberg, MD

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???????????????? ????????????????????????INTRODUCTION

Scenario 1:?

???? A 9 story high reinforced concrete building is torn apart by a Ryder truck bomb parked in front.?? A crater 30 feet wide and 8 feet deep is left by the blast.? Responding fire departments entered a scene resembling a war zone with over 800 surrounding buildings sustaining blast damage; 50 ultimately require demolition.? Windows are broken 2 miles away and the explosion is heard for 50 miles.??? 60 cars in a parking lot across the street are destroyed; the blast measures 3.5 on the Richter scale in an adjoining state.? Property loss is thought to be $250 million.? 1000 firefighters and hundreds of police, EMS, and medical volunteers arrive within minutes.? Within 60 minutes, 204 victims are transported to hospitals in 66 ambulances.? Communications and rescue are hindered by fear of activating a secondary explosive device.? The bomb is later discovered to be a 4000 lb. ammonium nitrate/fuel oil mixture.? 169 people eventually die and 600 more are injured.? It could have been worse… if chemical nerve agents were added, over 5000 citizens may have died.? This amazing scenario is not a Tom Clancy fictional account.? It accurately describes the bombing of the Oklahoma City Alfred P. Murrah Federal Building on April 19, 1995.

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Scenario 2:

???? 4 teams of Islamic Fundamentalist terrorists hijack 4 fuel laden, transcontinental, commercial jet-liners using only box cutters and plastic knives.? Almost simultaneously, the planes crash at full throttle into the New York City World Trade Center and into the Pentagon.? The twin towers soon collapse. A fourth plane crashes into a Pennsylvania strip mine thanks to a heroic passenger insurrection.? Over 6000 innocent victims in the World Trade Center perish.? Master terrorist Ausama Bin Laden is implicated in the attack.? The United States officially declares war on terrorism.? September 11, 2001 will be forever burned into our memories as the date of the worst domestic terror incident in our history.

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???? How would your community deal with such catastrophic events? This article hopes to present a brief history of conventional terrorism, describe the physical properties of bomb blasts, and summarize the medical aspects and treatment of explosive injuries.

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??????????? A BRIEF HISTORY OF CONVENTIONAL TERRORISM ON AMERICAN SOIL

?? ????Despite the notoriety given to nuclear, biological, and chemical (NBC) unconventional “WMD” (Weapons of Mass Destruction), it should be understood that 70% of all terrorist incidents are of a conventional nature.? Unlike rare NBC attacks, there were over 10,000 bombings worldwide in the years 1990-95!? The human toll exacted from these episodes included 3,176 injured and 355 killed.?? The goal of terrorists to induce panic and apprehension were successfully achieved worldwide multiple times.? The terrorist’s motivation? is multi-factorial.? The Oklahoma City Murrah Federal Building bombing was felt to be in retaliation to the Federal management of the Waco, Texas and Ruby Ridge, Idaho confrontations.?? In 1975, Croatian nationals attempted to draw attention to their plight by bombing LaGuardia Airport in Queens, New York City injuring 75 and killing 11.? The terrorist may also be mentally ill, and act alone. The “Unabomber” managed to elude law enforcement agencies for 17 years while completing 14 successful letter and pipe bomb attacks.?

???? The number of conventional bombings increased dramatically during the 1990s.? On February 26, 1993, the World Trade Center in New York City was bombed by an Islamic Fundamentalist cult.? The World Trade Center is comprised of two 110 story towers which house about 150,000 people when fully occupied.? The attack occurred at 12:17PM when the center was most busy in order to inflict maximal casualties.? The goal of the attack was to undermine US support of Israel and to show that our country was not immune to terrorism.? The 1200 pound nitrate/fuel oil bomb created a crater 180 feet deep, 100 feet long, and 200 feet wide that encompassed 6 levels of the parking garage.? Amazingly, the twin towers were destroyed on September 11, 2001 when 2 teams of Islamic terrorists flew fuel laden commercial jets into their upper structures.? Over 3000 lives were lost.? For the first time in history, air travel over the United States ceased, and thus began our first declared war in over 50 years.?

???? There is a very real threat of a secondary explosion directed at responding law enforcement and rescue personnel in terrorist incidents.? On January 30, 1998, a bomb exploded near the front door of an abortion clinic in Birmingham, Alabama, drawing the attention of authorities.? As the responding personnel gathered, it is believed that the bomber was watching and intentionally detonated a secondary bomb, killing a security guard and seriously injuring a counselor.

?????? Explosive terrorism is still the weapon of choice of the domestic terrorist.? Disturbingly, Burke points out that “acts of explosive terrorism almost doubled from 1989 to 1994.”?? For every successful explosive act of terror, many others are narrowly averted.? The time, energy, and dollars invested in counter-terrorist activities is staggering.

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???????????????????????????????? ??PHYSICAL PROPERTIES OF BOMB BLASTS????????

???? What defines an explosion?? Most authorities will agree that an explosion may be described as “a rapid release of high-pressure gas into the environment.”? This energy is released as a blast, or shock wave, heat, and flying debris.? The rush of air caused by the movement of blast gas is termed the shock wave, or blast wind.? The magnitude of this wave of compressed air can be measured, as overpressure, or direct impulse.? The magnitude of overpressure is proportional to the amount of explosive used, and is measured in pounds per square inch (psi).? It can be calculated by multiplying PSI x the duration (milliseconds) of the impulse.

????? How much blast wave does it take to cause death?? The expected injury to the blast victim is dependent upon several factors including the distance from the point of detonation, the duration of the blast (milliseconds), the size of the detonation, and the environment in which the explosion occurs.

???? Powerful conventional explosives have high overpressures of relatively long duration, while small-arms weapon noise will generate negligible peak overpressures of short duration (<1 atmosphere; <0.5msec.)?

???? Closed spaces will magnify the effects of the direct impulse.? The shock wave “bouncing” off a hard surface or wall is termed the “reflected impulse”.? This “bounced” blast wave may combine with the direct impulse and may cause injuries at a greater than expected distance from the blast site.? An example is the Israeli bus explosion (6 kilogram explosive) in Jerusalem that caused more severe injuries in passengers located further away from the explosion.? 30% of these blast victims sustained multiple trauma, while 10% died.? Blast pressures can be measured; the higher the overpressure, the worse the injury.? An overpressure of 58 - 80 psi. is more than 95% lethal.? Overpressures of only 0.5 - 1.0 psi break windows and “knock down” people.? 5 psi. can rupture eardrums while 7-8 psi from a sizable explosion may overturn rail cars and shears brick walls.?

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???? How does compressed air cause all this damage?? The molecules of all types of gases in our atmosphere are in constant motion.? At sea level, there are 30 million, billion molecules in each cubic millimeter of air, traveling at 300 meters/sec.? They strike each other 100 million times each second, although each molecule has traveled only 0.001 mm!? When an explosion occurs, molecules of air are “bumped” outward by the release of explosion energy. Moving at the speed of sound, molecules bump into each other over a very short distance.? The energy is transferred outward as a “ripple” or ring-like effect away from the blast epicenter.? This causes tissue damage as compressed air strikes the victim and stretches, tears, and ruptures tissues inside the body.? The injuries produced by this blast wave are termed “Primary Blast Injury”.

??? What are the differences between “high and low explosives?”? Explosives are described as “high” or “low” depending upon the speed of reaction and the psi generated.? HIGH EXPLOSIVES change from a solid to a gas almost instantly (microseconds,) and generate 50,000-4,000,000 psi at the immediate blast site.? LOW EXPLOSIVES incompletely burning over a period of time (milliseconds or longer, termed a deflagration,) can generate <50,000 psi.? Low explosives such as black powder are used as propellant charges and powder trains (fuses,) while high explosives, such as trinitrotoluene (TNT) create a blast wave that creates a shattering effect and can move large objects.? Only a detonation creates a true blast, or shock wave.? The pressure and heat waves travel equally in all directions at supersonic speed (>1,250 ft./sec.) and may carry deadly shrapnel.??? Blast wind speeds in a detonation may actually reach 20,000 mph.??? The yield of a material describes the rate at which an explosion involving the material occurs.? When high yield explosives detonate, including TNT, dynamite, detchord, semtex, C3, and C4, the blast wave may destroy objects it strikes.

??? Blast wave pressure can also be described in 2 phases.? The POSITIVE PHASE occurs as the blast wave travels in an outward direction away from the blast epicenter.? In a detonation, the blast will travel equally in all directions.?? A partial vacuum is then created near the epicenter due to the outward movement of air, and the consumption of oxygen by the burning process.? This vacuum sucks smoke, gases, and debris back towards the epicenter and is termed the NEGATIVE PHASE.? The negative phase may last three times as long as the positive phase, and is described by a “standard” waveform termed the Friedlander Waveform.? The thermal wave then carries explosion products up vertically and downwind.? A detonation blast wave will usually be preceded by a thermal wave that may ignite local combustible material.???? Explosive devices, which contain nails, screws, flechettes or other debris are termed ‘anti-personnel munitions’.? The injuries caused by flying debris (pipe bomb metal fragments, nails, glass, rocks, etc.) are called Secondary Blast Injuries.? Secondary Blast Injury is the most common cause of death in explosions.? The use of ballistic vests will greatly protect the officer from flying debris.? During the Vietnam War, soldiers who wore their “flak vests” had a much greater statistical chance of survival from artillery, grenade, and mortar shrapnel.? Explosives have been mixed or attached to unconventional hazardous materials and used as “hybrid” weapons that disperse radioactive material, or biological/chemical agents.? In larger explosions, nearby victims may actually be “blown away” and physically hurled through the air by the blast wave. ?Injuries resulting from being thrown are termed Tertiary Blast Injuries.? When responding to an explosive incident, it is very important to remember to screen the site with a Geiger counter, and carefully observe for signs of chemical agents or other potential threats.? Secondary explosive devices should be sought and expected; thus only essential personnel should be allowed near the explosion site.

????????????????????????????????????????????? TYPES OF CONVENTIONAL EXPLOSIVES

?? ?Conventional explosives are compounds of nitrogen, oxygen, carbon and hydrogen.? They may exist in any physical state (solid, liquid, or gas.)? There are two categories of materials used in explosive devices.?? Primary explosive materials are sensitive to heat or pressure.? They include substances such as lead azide or mercury fulminate.? They are difficult to handle for this reason.? Secondary explosive materials are less sensitive to prevent unintended explosions, and can be handled relatively safely.? These include compounds such as trinitrotoluene (TNT), pentaethyltrinitride (PETN), and C4 plastic explosives.? These less-sensitive explosives are not usually affected by high temperatures.? Most military munitions consist of a fuse (a sensitive primary explosive,) a booster (a less sensitive secondary explosive,) and a main charge (an insensitive explosive.)? Most conventional terrorist weapons are improvised or assembled from individual dual use components.? For example, ammonium nitrate is an agricultural fertilizer, but it is also the oxidizer in an ammonium nitrate/fuel oil bomb.? These materials were used in the New York and Oklahoma City attacks, and were transported to the sites as Vehicle Borne Improvised Expolsive Devices (VBIEDs).? These bombs are usually large and destructive.? Rental trucks were used in both cases.??? The most common type of improvised explosive is the PIPE BOMB.?? This bomb has been used in about 1/3 of all conventional terrorist attacks made by filling a pipe, or metal “Mag-light” style flashlight with black powder.? Alternately, a simple cannon-type fuse may be lit or a timer may be used.? The flashlight switch itself may serve as a booby trap!? As flashlights are an increasingly popular pipe bomb booby trap, do not disturb flashlights encountered at a bombing scene, but consider them to be bombs until proven otherwise.? According to the BATF (Bureau of Alcohol, Tobacco, and Firearms,) 20 such devices have been discovered in the years 1997-98.? The ubiquitous backpack is a convenient method of concealment that was successfully employed at the Olympic Park bombing in 1976.????

???????????????????????? ??????MEDICAL ASPECTS OF EXPLOSIVE TERRORISM

??? ??The severity of blast injury is dependent upon characteristics of the blast, the surroundings and the victim.?? Blast intensity is directly proportional to the level of inflicted trauma.?? Hybrid elements of the explosion will also adversely impact victims.? Characteristics of surroundings include the size and magnifying effects of the enclosure.?? A small enclosure will greatly magnify the reflected impulse and create a large combined impulse (direct plus reflected impulse.)? The reflected or combined impulse may injure victims distant from the epicenter.? Victim characteristics include the distance from the epicenter, body orientation to the blast, and clothing factors such as the use of body armor or a bomb suit.? Even the use of a bomb suit will not completely protect against blast wave effects.? In fact, the use of a bomb suit/ballistic vest may actually slightly worsen the severity of blast lung injury, but the benefits of protection from shrapnel and penetrating trauma override this risk.?

???????? ?Body positioning in relation to the advancing blast wave is also important.? The end-on position (lying down with the head or feet pointing towards the blast) offers the best protection against blast injuries.? For example, “the threshold for lung injury is about 12 psi. for blast waves of 20-30 msec. duration…Subjects end-on to the blast would require an incident shock of 12 psi….to cause this lesion.? If the subjects are oriented side-on, an incident shock of 10 psi…. would cause equal damage.”? Adding a nearby wall to “bounce” the blast wave into the body would also cause more damage, thus decreasing the injury threshold to 5 psi.?

?????? ??Repeated exposure to explosive blasts dramatically increases tissue damage.? For example, a blast that causes a 1% mortality when experienced once, causes a 20% mortality when experienced twice, and a 100% mortality when experienced three times.????

?????? ??Blast injury is described as primary, secondary, and tertiary.? Primary blast injury (PBI )? is caused by the physiological effects of the blast wave upon the human body.? Primary blast injuries occur through 3 basic mechanisms.? SPALLING describes the tissue injury caused when the blast wave rapidly changes velocity as it moves through tissues of different densities.? The lung is prone to this type of trauma.? Implosion is the result of the air filled intestines (the gastrointestinal track) rapidly stretched beyond its elastic limit and rupturing after being compressed by the passing shock wave.? INERTIAL EFFECTS describe the injury occurring when connected tissues of different densities move at different velocities such as the bowel on its mesentery (connective tissue and blood vessels attaching the bowel to the abdominal wall).

???? ???If the victim is close to the explosion, skin burning may occur. Fortunately, this is rare unless materials such as gasoline or organic chemicals are used.?

????? ?An 8- year study of over 500 victims of bomb blasts in Northern Ireland revealed different injury constellations in survivor and non-survivor groups.? The fatal injury constellation included brain damage (66%,) skull fracture (55%,) blast lung (47%,) ear drum (tympanum) rupture (45%,) and liver laceration (34%.)?? Interestingly, brain damage frequently occurred without skull fracture.? Survivor’s injuries included fractures (18%,) burns (15%,) and concussions (15%.)? Blast lung is a severe form of pulmonary contusion (lung “bruise”) where lacerated, crushed lung tissue fills with blood and cannot exchange oxygen.

??????????????????????? ?????????????????????????????MEDICAL BLAST TREATMENT

???? ?When responding to the explosion scene, the first consideration of the first responder is simple but extremely important… self-preservation!? You should ALWAYS FIRST ask yourself… “Is the scene safe for me to enter?? Are radiation, biological or nerve agents present?? Are the victims on the ground the result of the actual explosion or are their secretions, tears, and vomit the result of a nerve agent release?”? Adhere to the Incident Command protocol.?? Do not enter the scene unless you have a definite role, and only then after you are certain you won’t be joining the ranks of victims.

??? ?The blast victim should have his “ABCs” (Airway, Breathing, Circulation) evaluated.?? Make sure the victim can breathe through an open airway, check pulses, and treat for possible shock.? Remember that penetrating trauma? (secondary blast injury) causes most injuries.? Attempt to stop major bleeding.? Victims with altered mental status, in shock or having sustaining penetrating torso trauma are “load and go” requiring immediate transportation to a Level 1 Trauma Center. The victim may have suffered spine or extremity fractures. An EMS backboard, stretcher, or even a wooden door may be used for transportation.?

?? ??In a disaster with multiple victims, most or all of the “walking wounded” will likely be gone by the time you arrive.? Therefore most of the blast victims remaining on-site will be dead or critically injured.? Triage (‘to sort’) should occur during the initial evaluation and repeated often during subsequent care and transport.? One rapid triage “tool” to remember is that victims with blood or reddish fluid coming out of their ears (ruptured eardrums) have a 50 percent chance of life threatening internal injuries. The overriding triage rule is “to do the most good for the greatest number of people”.

??? For patients who have severe lung or brain injury, intubation (breathing tube placed in their trachea) will be required.? If heat injury or burns occur to the throat or trachea, the victim’s airway may rapidly swell and close.? Therefore, early intubation should rapidly be performed if difficulty talking or swallowing is present.????????????????????????????????????????????????

? ??Bleeding needs to be controlled.? If bleeding continues without success in using pressure bandages, then the previous dressings should be removed and the wound re-inspected.? Old school teaching was to simply add more and pile up dressings and never remove the prior dressing.? This is no longer true. Get a good look at the wound, remove the old dressings, apply direct pressure with a fresh bandage, and you should be able to stop extremity trauma in most circumstances and consider the use of an approved tourniquet.

?? Penetrating trauma to the chest may be treated with a new bandage called a chest seal..? This device is easily applied, and allows rapid treatment that may prevent a tension pneumothorax (high pressure developing in one half of chest).? A variety of hemostatic agents are also commercially available in the form of a powder, impregnated gauze or tampons.

? Burns may be encountered in caring for blast victims, and if the skin or material is still hot (and causing injury) cool water / non-flammable liquids should be applied to prevent further skin damage.? Care should be taken to avoid hypothermia (low body temperature) that is a real threat.? Once the skin is at body temperature, non-adherent burn dressings or dry loose sheets/clean blankets may be used.? Transportation to a burn center should then occur.

????????????? ?????????????????????????????????????????SUMMARY

??The blast victim will likely survive if his airway and breathing are maintained, bleeding is stopped, shock is treated, and rapid transportation to a Level 1 Trauma Center occurs.? The mechanisms of injury include primary (shock wave) blast injury, secondary (flying projectiles) blast injury, and tertiary (blunt trauma from being thrown by explosion) blast injuries.? The physician first responder may be required to manage blast injury victims.?? Their survival may depend upon your blast injury knowledge, and the rapid application of appropriate medical skills you employ.

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