THE THREAT TO BUILDINGS FROM EXPLOSIVE …

1 NewYorkCityPoliceDepartment11lthoughterr oristsemployawidevarietyoftacticsandstra tegies,theirattackshave often targeted BUILDINGS in urban environments. BUILDINGS in denselypopulatedareasareattractivetarget sforseveralreasons:theytendtobetallstruc tureswithhighconcentrationsofoccupants,a llowingformasscasualtiesandinjuriesfroma singletargetedstrike;andtheytendtobevalu ableassets, devices can cause casualties and property damage in a variety of scollapse,anexplosioncaninitiateuncontro llablefiresthatspreadrapidlythroughoutth ebuilding;producestructuraldamagethattra pspeoplewithinthe building ; and cause debris, broken glass, and fragmented furniture to DevicesConventional EXPLOSIVE devices used in terrorist attacks on BUILDINGS are calledimprovisedexplosivedevices(IEDs). IEDsvaryinsize, design ,andmaterial. Themeans by which an IED reaches its target has broad implications for the type andextent of damage it can cause; for this reason, IEDs are often characterized ONETHE THREAT TO BUILDINGS FROMEXPLOSIVE DEVICESA12 EngineeringSecurityVehicle-BorneImprovis edExplosiveDevicesAvehicle-borne improvised EXPLOSIVE device (VBIED) has the capacity to holdenough EXPLOSIVE material to significantly damage or even destroy a ,terroristshavechosentodetonateVBIED sinvehiclesparkedoutsideofbuildingsorwit hingarages,orinvehiclesthatstrikebuildin gs.

2 Themass-casualtypotentialofaVBIED becameclearin1983, BUILDINGS in Beirut, Lebanon: onApril 18, a VBIED delivered by apickup truck destroyed the Embassy in Beirut, killing 63 people;1and, onOctober23,atruckbelievedtohavebeencarr yinga12,000-poundTNT-equivalentVBIED crashed into the Marine Corps Barracks at the Beirut InternationalAirport, attacks have also been carried out in the United States. On February 26,1993,RamziYousefledaterroristcellthat detonateda900-poundTNT-equivalenturea-ni trateVBIED delivered in a rented Ryder van in the underground garage ,injuredmorethan1,000,andcausedsignifica ntstructuraldamagethatresultedinover$ April 19, 1995, Timothy McVeigh detonated a 4,000-pound , attacks in urbanenvironments have thepotential to causeconsiderable financial 2006, for instance, theAmerican Academy ofActuaries estimated that atruck bomb attack in NewYork city could produce$ billion in attackscan also have Marine Corps Barracks, Beirut, Lebanon 1983 NewYorkCityPoliceDepartment13financial implications, such as exposing building owners to liability for failure (MPIEDs)aregenerallyusedtotargetpeoplera therthanstructures.

3 TheytendtobesignificantlysmallerthanVBIE Ds,andmay be concealable in backpacks and suitcases, allowing for ease of entry into abuilding. Victims of such attacks are often injured by shrapnel and projectiles,including furniture fragments and shattered glass, rather than building range in size from under five pounds to as much as 100 pounds and aregenerally used against soft targets, such as shopping malls, nightclubs, and Forexample, on November 9, 2005, a team of suicide bombers carried out nearsimultaneousattacksonthreehotelsinAm man,Jordan, Theblastsalsocausedconsiderabledamagetot hehotels interiors. MPIED susedintheChapterOneBox 2: Port Authority Liability in 1993 World Trade Center BombingIn the aftermath of the 1993 World Trade Center bombing, the victims and theirfamilies sued the Port Authority of New york and New Jersey for failing toimplement security enhancements in response to known vulnerabilities.

4 From1984 to 1986, five separate reviews of the World Trade Center site, includingreviews conducted by the Port Authority and Scotland Yard, found that theunderground public parking garage presented a potential risk. At the PortAuthority s request, three reports on the site s security were written, eachproviding risk mitigation recommendations. On April 29, 2008, the New YorkState Appellate Division upheld a 2005 New york County Supreme Courtruling, finding the Port Authority liable for failing to meet its basic proprietaryobligation to its commercial tenants and invitees by not securing its facilities inthe face of ample notice that a VBIED attack was possible in the publicparking garage. The 2005 and 2008 decisions held the Port Authority liable fordamages potentially upwards of $100 :Nash v. PortAuthority of New york and New Jersey,51 3d 337 (First Dept,NY 2008); Anemona Hartocollis, Port Authority Liable in 1993 Trade Center Attack, TheNewYorkTimes, April 30, 2008, ,buckledceilingpanels, ,whenmultipleMPIED sare simultaneously employed against primary structural elements, such a result physics of EXPLOSIVE blasts may be used to determine the types of protectivesecuritydesignmeasuresthatbuil dingsshouldemploy.

5 Anexplosivesattackcreatessignificant pressures and impulses that vastly exceed normal loads. Unlikeenvironmentalconditionssuchashighw inds,whichcanexertsustainedpressureonbui ldings,explosionsdamagebuildingsbyexerti ngtremendousair-blastpressureoverarelati velyshorttimespan ontheorderofmilliseconds. Thistremendouspressureand its associated impulse can affect primary structural elements, such as columnsand beams, which contribute to overall structural stability, potentially leading ,whichoccurswhenabnormalloadingcausesind ividualstructuralelementstofaillocally,s hiftingthe loads to remaining structural elements unequipped to provide the requisitestructuralsupport; ,leadingtofacadefragmentation,shatteredw indows, subjected to an explosion is affected by several types of pressures thatoccur in two phases. The positive pressure phase refers to the rapid outwardexpansionofenergyastheshockwavesr adiateinalldirectionsfromthesourceofthe explosion; these waves are amplified by waves that reflect off the ground orsurroundingbuildings.

6 Thepressureenvelopesthestructure,loading thesidesandtheroof;itmaybefurtheramplifi edifthewavesarestagnatedbythestructure. Thepressuresinthepositivephasepushontheb uilding sexteriorandmayinducethelocalized failure of exterior walls, windows, floor systems, columns, and freestanding columns may benefit from pressures wrapping around theirsurface and minimizing the net loading. Downward pressure directly beneath theexplosion leaves a crater below the source, potentially damaging undergroundstructuralelementsandcreating intensevibrationsthroughthegroundsimilar totheChapterOneNewYorkCityPoliceDepartme nt15effects of an earthquake. The negative pressure phase refers to the low intensity,longer duration inward movement of air that fills the void created by the positivephase. Thepressuresinthenegativephasereversethe positivephaseloading,pullingstructural elements towards the source of the blast, which may dislodge windowsand sloped roofs.

7 Once the applied pressures deform building components, theelements attempt to rebound back to their original shapes, which may result is defined as the distance between the EXPLOSIVE THREAT location and sabilitytowithstandanexplosivesattackbec ausethepeakpressurepersquareinch(psi) ,thepeakpressurefallsroughlybythecubeoft heratioofincreaseddistance. Forexample,ifstandoffisdoubled,thepeakpr essurereducesbyafactorof23,or8;thismeans thatthepeakpressurefroman800-poundblast1 0feetChapterOneFigure 1: Peak Reflected Pressure and Standoff16 EngineeringSecurityawayfromastructureisa pproximatelyequivalenttothepeakpressuref roma100-poundblastfivefeetaway. basis THREAT (DBT) is the magnitude of the blast from an EXPLOSIVE devicethatabuildingorparticularbuildinge lementshouldbedesignedtowithstandataspec ified distance. The magnitude of this THREAT is expressed inTNT-equivalentchargeweight,andthedista nceinfeet.

8 Forexample,abuilding sDBTmaybestatedasa500-poundTNT-equivalen texplosivechargeat20feetofstandoff,meani ngthebuilding,ortheparticularbuildingele menttowhichtheDBTisassigned,mustbeableto withstandtheloadingassociatedwitha500-po undTNT-equivalentexplosivecharge,from20f eetaway. load a specific building element must withstand varies with both the distanceand magnitude of the THREAT from an EXPLOSIVE distance component ofDBTtakesintoaccountthemostprobablescen ario:thatattackerswillgetasclosetotheirt argetsaspossible. Forthisreason,thedistancecomponentofDBTt endstobenomorethanthestandoffaffordedthe buildingortheparticularbuildingelementun der consideration. The magnitude component of DBT takes into account thedifferenttypesofthreatsinurbanenviron ments, 2 presents a summary of the NYPD s DBT coding system, referenced insubsequent chapters as M-values. Each M-value represents a distinct order ofmagnitude, corresponding to the range of EXPLOSIVE threats BUILDINGS or particularbuilding elements should be designed to NYPD provides a rangeratherthanspecificvaluesforDBTcharg eweightstoavoiddisclosureofsensitivesecu rity information to potential terrorists and to account for variations amongbuildings in factors such as: amount of available standoff, type of access control,thresholdforscreeningprocedures, ,containingpotentiallylargeamountsofexpl osives.

9 Forabuildingthathasprotectionfromahardpe rimeter,ChapterOneNewYorkCityPoliceDepar tment17thetrueperimeterisdefinedastheant i-rambarrierline. Forabuildingthatlacksprotection from a hard perimeter, the true perimeter is generally defined as thebuilding s envelope. For threats from the true perimeter, the NYPD recommendsthatprimarystructuralelementsi nHighTierbuildings satisfy M3standards athreatinthethousands-of-poundsrange( satisfy meanstheelementinquestionisadequatelyrob ustthatthebuilding:doesnotengageinprogre ssivecollapse;meetsanindustrystandarddef initionofnon-disproportionatedamage;andp erformstoalevelthatallowsforevacuation,r escue,andrecoveryoperations). Bycontrast,threatsatzerofeetofstandoff,r epresentingcontactwiththecolumn,generall ycomefromMPIEDs, ,forthreatsfromacontactcharge,theNYPD recommendsthatcolumnsinHighTierbuildings satisfyM1standards srecommendedDBTstandardswillalmost certainly be greater than the load requirements set out in applicable localbuildingcodes.

10 Buildingownersshouldconsultwithblastengi neersandtheNYPDC ounterterrorismBureautodeterminebuilding -specificDBTstandards. OnceDBTlevels are established for a site, building owners, in consultation with appropriateexperts, specific DBT levels determined for each building are sensitive Code Order of Magnitude Charge Weight*Potential ThreatM110110 - 99 BombSuicide Belt/VestSatchel/SuitcaseM2102100 - 999 BagLuggageCompact SedanM3* Expressed in TNT-equivalent weight1031000 - 9,999 SedanCargo VanDelivery VanFigure 2: NYPD design Basis THREAT Coding System18 EngineeringSecurity