LESSONS LEARNT FROM EXPLOSIVE ATTACKS - ?· Lessons Learnt From Explosive Attacks SE Harrisson, E Kirkman,…

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  • LESSONS LEARNT FROM EXPLOSIVE ATTACKS

    SE Harrisson1, E Kirkman1, P Mahoney2

    1DSTL Porton Down, 2Academic Department of Anaesthesia and Critical Care RCDM, Birmingham

    IntroductionA vast amount of material has been published about terroristattacks using explosives. Contained within these papers arevaluable clinical and operational lessons. Some of these lessonscan be applied to the current UK military and civilian situationand be used to help to refine our clinical and organisationalresponses.

    Explosive Injury Mechanisms - a briefoverview.The damage created by a conventional explosion depends on anumber of factors, including the type of explosive, the amountof explosive, and the environment within which the detonationtakes place.

    Whenever and wherever an explosion occurs in air, theprinciples are the same. An understanding of the principlesenables a prediction of likely injury [1][2].

    As a substance explodes it rapidly expands from a solid (orliquid) state to a gas, increasing in volume by up to 100,000times. The speed of expansion depends on the type of explosive.This expansion pushes out whatever is surrounding theexplosive, such as casing (which may or may not be designed tofragment) or other items, for example nails or ball bearings.

    The explosion also compresses the surrounding air to form ashock-wave. This is a wave of very high pressure which expandsaway from the explosive at a speed greater than the speed ofsound in air. The high pressure lasts for a very short period oftime (milliseconds) and in an open air explosion, is relativelyshort-lived. As a result the peak overpressure decreases rapidly.

    For single shock waves in air, after the initial rise in pressure,the pressure drops to sub-atmospheric levels for a short time dueto the elasticity of air (Figure 1). Under water, the shock wave ispropagated for a much greater distance and the distance from thedetonation at which injury may occur consequently increases.

    It should be noted that the shock wave travels through air it is not the mass movement of air and products.

    Shock waves can be reflected and will then interact with theoriginal wave, leading to complex waves [3] which have a longerduration, multiple pressure peaks and enhanced pressure-related effects in comparison to the original wave. This is ofparticular significance for an explosion in a confined space,where the initial shock wave will reflect several times, increasingthe direct pressure effect considerably.

    The explosion will also set the surrounding gas (ambient airand explosive products) in motion, causing the dynamicoverpressure or blast wind. The pressure of the blast wind is less

    Corresponding Author: Lt Col P MahoneyAcademic Department of Military Anaesthetic and Critical CareRoyal Centre for Defence Medicine, Vincent Drive,Birmingham B15 2SQT: +44 121 415 8848E: Prof.ADMEM @rcdm.bham.ac.uk

    REVIEW

    278 JR Army Med Corps 153(4): 278-282

    Figure 1: Schematic representation of a shock wave a. pressure v time at asingle point b. pressure v distance from point of detonation

    1a

    Figure 2: An explosive detonation. Note the shock wave (solid arrow)

    1b

  • Lessons Learnt From Explosive Attacks SE Harrisson, E Kirkman, P Mahoney

    than that of the shock-wave, but the blast wind has a muchlonger duration. It will move more slowly than the originalshock-wave, but may continue for considerable distances(although the products are confined to the fireball). The blastwind will pick up pieces of debris (or people) in its path andcause the whole, or parts of them to move. The explosion mayalso cause injury due to the release of toxic fumes, as a result ofthe radiant and convective heat created by the detonation or asa result of ignition of the environment.

    Blast injuriesBlast injuries are classified as shown in table 1. [4][5].

    Primary blast injuriesThese are caused by the shock wave. Injuries are dependant onthe power of the explosion, the proximity of the casualty to theexplosion and the environment (open or confined) [6]. Theshock wave causes most damage to tissues where there isfluid/air interface predominantly the lungs, and bowel, - butdamage does occur in other tissues.

    In the lungs the shock wave can cause the alveoli to bedamaged, leading to a progressive respiratory impairment. Itcan also lead to the introduction of air into the pulmonaryvasculature leading to embolic injury.

    It was previously suggested that eardrum perforation should beused as a marker for primary blast injury following an explosion.It is certainly true that the presence of eardrum rupture is anindicator of significant blast exposure, however the absence oftympanic rupture can not be used to exclude the possibility ofsignificant blast loading. Although it has been challenged [7], inthe operational environment it remains safe practice to admitpatients with a ruptured eardrum for a period of observationwhilst other more significant injuries are excluded.

    JR Army Med Corps 153(4): 278-282 279

    Table 1: A classification of blast injury

    PrimaryInjuries due to the interaction of the blast (shock) wave withthe body

    SecondaryInjries due to fragments

    TertiaryInjuries due to the blast wind (dynamic overpressure)

    QuaternaryBurns, crush injury, toxic chemical injury

    Secondary blast injuriesSecondary blast injuries are caused by objects energised by theexplosion colliding with the casualty. The objects can be splitinto two groups primary fragments (part of the explosivedevice prior to explosion (for example casing or other objectssuch nails or ball bearings-packed around the explosive) andsecondary fragments (objects from the environment picked upand moved by the blast wind including glass from shatteredwindows).

    Some of the fragments might be human tissue (for examplebombers in suicide attacks) [8]. These injuries require earlyrecognition because of the potential risk of transmission ofblood borne diseases (including HIV and Hepatitis B).

    Tertiary injuriesTertiary injuries are caused by the body of the casualty beingmoved by the force of the explosion, and colliding with thewall, floor or other objects. Gross disruption of the body andlimb amputation may also occur in those very close to the pointof detonation (see below). Some authorities include injuriescaused by a building or structure collapsing in the tertiarygroup. In structural collapse casualties can become trappedleading to delayed evacuation and the possibility of thedevelopment of crush syndrome.

    Quaternary injuriesQuaternary injuries are other miscellaneous injuries, forinstance burns or inhalation of hot or toxic gases.

    Location Date Comments Further reading

    Aldershot,Hampshire

    22nd February 1972 The first major attack by the IRA on the UK mainland. Six werekilled five female kitchen staff and a Roman Catholic Padre.

    Guildford,Surrey

    5th October 1974 Bombs were placed by the IRA in two public houses. Five peopledied and 69 persons injured.

    [9]

    Birmingham,West Midlands

    21st November 1974 21 deaths and 119 others injured in two separate IRA bombattacks on a bar and a public house.

    [9, 10]

    Musgrove ParkHospital,Northern Ireland

    November 1991 IRA bomb targeted at the military wing of a hospital. [11]

    Canary Wharf,London

    10th February 1996 This IRA attack ended a seventeen-month ceasefire. Two peopledied and 39 injured. During the next ten weeks five furtherdevices detonated in London (including the Aldwych Bus bomb)and then in June 1996 a bomb was detonated in centralManchester.

    Omagh,Northern Ireland

    15th August 1998 29 deaths and 336 injured. An unclear warning message meantpeople were next to the car when it exploded.

    [12]

    Figure 3: Secondary blast injury from energised environmental debris

    Table 2: Selected key Irish Republican Army (IRA) attacks

  • UK ExperienceA major feature of UK domestic history in the late 20th centurywas the situation in Northern Ireland involving terrorist attacksby both Republican and Loyalist groups. British troops weredeployed in to the province in the late 1960s to support thelocal police services. What was initially envisaged as a short-term deployment resulted in the deaths of 452 militarypersonnel between 1969 and 2006.

    According to figures released by the Police Service ofNorthern Ireland (PSNI), the year when the highest number ofbombing devices were detonated or found was 1972 when 1853devices were deployed. In total the PSNI state that between1969 and 2006 there were a total of 16457 bombing incidentsin Northern Ireland alone [9].

    The bomb attacks were not always in Northern Ireland, andnor indeed only within the boundaries of the UK mainland. Alist of some of the major Irish Republican Army (IRA) attacksis given in table 2.

    The Good Friday Agreement (or Belfast Agreement) wasreached in Belfast on Friday, April 10 1998 and set out a planfor devolved government in Northern Ireland on a stable andinclusive basis and provided for the creation of Human Rightsand Equality commissions, the early release of paramilitaryprisoners, the decommissioning of paramilitary weapons andfar reaching reforms of criminal justice and policing.

    There were still attacks after this by dissident groups, includingin August 2001 when a car bomb was detonated in west London.

    Types of explosive devices.Hull described the common types of explosive devices seen inNorthern Ireland [13]. While all explosives have similar actions,the amount and type of explosive and construction of the bombalter the effect produced.

    Hull described four main types

    Car bombs.Car bombs generally contained between 1 and 3 kg ofcommercial explosive, placed beneath the drivers seat.Detonation (normally by a mercury tilt