HomeMy WebLinkAboutBlastingAirQualityBLACKRIVERQUARRYRENTON,WASHINGTONRECEIVED22R[-1UW’ü)ii:EJLVICESBLASTINGANDAIRQUALiTYEVALUATIONPreparedBySublerra,Inc.8112304thAvenueSEPreston,WA98050ProjectNumber98-09March20,2000SubTerra,Inc.
SubTerra,Inc.BlackRiverQuarryMarch20,2000BlastingandAirQualityEvaluationTableofContentsSectionDescriptionPageNo.No.IINTRODUCTIONI1.1FocusandScopeofStudyI7.2ApproachI2QUARRYOPERATIONSandREGULATORYCRITERIAGOVERNINGBLASTOPERATIONSI2.7ApplicableRegulationsandRegulatingAgenciesI2.2QuarryOperations32.3ControlofGroundVibrations32.4BlastMonitoringandBlastingRecords43POTENTIALIMPACTSFROMQUARRYBLASTING43.1EvaluationofImpactsofBlastingonStructures43.2EvaluationofPotentialforFlyrockImpacts533NoiseImpactsandEffectsofBlastingonHumans54AIRQUALITYIMPACTS65FINDINGSANDCONCLUSIONS66REFERENCES7
Sublerra,Inc.BlackRiverQuarryMarch20,2000BlastingandAirQualityEvaluationListofFiguresFigureDescriptionPageNo.No.15-YearQuarrySiteDevelopmentPlan2USBMRl8507“SafeLimit”Criteria3PeakParticleVelocityvs.ScaledDistance(WesternWashingtonQuarryData)4PeakParticleVelocityvs.ScaledDistance(BlackRiverQuarryData)5SoundOverpressureConversionListofTablesPlateDescriptionPageNo.No.IScaledDistanceCriteriaforBlasting2NationalStandardforAirBlastLimits3SummaryBlastMonitoringDatafortheBlackRiverQuarry4ComparisonofStrainLevelsInducedbyHouseholdActivitiesandBlasting1
Sublerra,Inc.BlackRiverQuarryMarch20,2000BlastingandAirQualityImpactEvaluationIINTRODUCTIONThisreportdocumentsanevaluationofblastingandairqualityimpactsforaportionofStonewayRockandRecycling’sBlackRiverQuarrynearRenton,Washington.TheBlackRiverQuarryisanactiverockquarrythathasbeeninoperationforabout50yearsandhasrecentlyundergoneaKCDDESperiodicreviewpursuanttoKCC21A.22.1.1FocusandScopeofStudyConditionofApproval3oftheSeptember3,1999KingCountyHearingExaminer’sReportandDecisiononAppealofPeriodicReviewDecisionrequiresanalysisofoffsiteimpactsattributabletoStoneway’soperationsanticipatedwithintheportionofthesitelyingeastofthewesternboundaryoftheadjacentEmpireEstatesparcelduringa5yearstudyperiod.Thoseoperationsaresetforthona“SupplementalSitePlan”preparedbyBarghausenConsultingEngineers,Inc.thatcoversthatportionofthesite(seeaccompanyingDrawingdatedMarch20,2000).ThisreportdealswithBlastingandAirQualityimpactsstemmingfromthatportionofthesite.TheremainingtasksconcerningCondition3arebeingundertakenbyothers.1.2ApproachOurapproachtoevaluatingthepotentialforblastingimpactsattheBlackRiverQuarrysitehasinvolved:adetailedreviewoftheregulatorybasisforblasting,areviewofpastblastingpracticeatthesiteincludingtheperformanceofeachblastwithrespecttooff-siteimpacts;andanevaluationofpotentialfutureoff-siteblastingimpacts.AirqualityissueshavebeenaddressedforthoseoperationsthatwillbeconductedwithintheSupplementalSitePlanarea.2QUARRYOPERATIONSandREGULATORYCRITERIAGOVERNINGBLASTOPERATIONSAnunderstandingoftheplannedblastingoperationsattheBlackRiverQuarryandtheregulationsthatgovernblastingpracticesintheStateofWashingtonisimportantbackgroundtounderstandingthenatureandextentofblast-relatedimpacts.2.1ApplicableRegulationsandRegulatingAgenciesTherearecurrentlynodirectlyapplicableStateorFederalregulatoryrequirementsaddressingairblastorblastvibrationsemanatingfromrockquarries.However,theStateofWashingtonDepartmentofLaborandIndustries(WADL&I)iscurrentlyworkingonamodificationtotheStateofWashingtonexplosivescodetoincorporatecriteriadevelopedfromregulationspromulgatedbytheFederalOfficeofSurfaceMinesReclamationandEnforcement(OSMRE).AlthoughthoseFederalregulationsapplyonlyI
Sublerra,Inc.BlackRiverQuarryMarch20,2000BlastingandAirQualityAnalysistosurfacecoalmines,thecriteriaforcontrollinggroundvibrationisoftenusedtoguideblastingactivitiesatothertypesofsurfacemines.ExpandedOSMREblastvibrationcriteriahavebeenadoptedbytheInstituteofManufacturer’sofExplosives(IME)andformthebasisforproposedamendmentstotheWashingtonAdministrativeCode(WAC)atWAC-296-52.TheproposedBlastVibrationStandardsprovide2possibleapproachesfordemonstratingthecomplianceofablastingprogramwithrespecttostructuraldamage.Method1:Requiresthatshotsbedesignedusingthescaleddistanceformula;W=(DISD)WhereWsafeweightofexplosivesperdelayfIbs)D=distanceoftheblasttoadwellingorstructurefft)SD=scaleddistancefactordefinedas;Table1:ScaledDistanceCriteriaforBlastingDistanceofStructurefromBlastScaledDistancetobeusedSite(ft)WithoutSeismicMonitoring0-30050301-5,000555001—beyond65Method2:Allowsparticlevelocitylimitstovarywithfrequency(seeFigure1).Themethodrequiresbothfrequencyandpeakparticleanalysisofeachblast.BlastsareinitiallydesignedusingMethod1andmonitored.Monitoringdataarethenused,inconjunctionwithscaleddistance,togenerateagraphicalrelationshipbetweenPPVandscaleddistance.ThegeneralizedrelationshipbetweenPPVandscaleddistanceisdefinedasfollows:PPV=Kx(SD)b=Kx(DNW)b(1)Where,bandKareconstants.ThisrelationshipisplottedinFigure2usingvaluesofbandKforquarryblastsinigneousrocksinthePugetSoundarea.Fordesignpurposes,thechartindicatesthatascaleddistanceof50wouldresultinaPPVof0.4in/secunderaverageconditions(0.8in/secat90%confidencelimits).2
SubTerra,Inc.BlackRivetQuarryMarch20,2000BlastingandAirQualityAnalysisCriteriahavealsobeendevelopedbytheInstituteofManufacturersofExplosivesforpermissibleairblastorsoundoverpressure.TheIME’srecommendedlimitsareprovidedinTable2.Table2:NationalStandardforAirBlastLimitsLowerFrequencyofMeasuringSystem(Hz)MeasurementLevel(decibels)0.1HzorLower...FlatResponse134peak(UBL)2HzorLower...FlatResponse133peak(dBL)6HzorLower...FlatResponse129peak(dEL)C-Weighted...slowresponse105peak(dBC)Theapparentlyhigherproposedstandardfor“L”weighteddataisduetothefactthatthelinearmicrophonetypicallyusedinblastmonitoringstudiesrecordstheverylowfrequenciesthatareanimportantcomponentoftheblastwave.Conversely,“C”and“A”weightedmicrophonesdonotincorporatethelowfrequencydataandthereforereportalowerintensity(indecibels)fortheairblast.ThereisnosimplewayofcalculatingthedifferencebetweencIBAordBCandUBL;however,differencesaretypicallyintherangeof10to25decibels.2.2QuarryOperationsTheBlackRiverQuarry,originallyopenedin1949,hasbeenoperatingunderaKingCountygradingpermitsince1971.Onsiteactivitiesincludedrillingandblastingbenchesfrom30to60-fthighandcrushingandsizingthefinalproduct.Blastholespacingandburdenvarywiththequalityofrocktobeminedbutaretypicallyintherangeoffrom6to10feet.Holesaretypicallydrilled3to5feetbelowtherequiredbenchfloor.Eachholeisloadedwithexplosiveandstemmedwithdrillcuttings.Aminimumstemminglengthof6feetistypicallyemployed.DryholesaretypicallyloadedwithANFO(AmmoniumNitrateandFuelOil)whilewetholesareloadedwithslurryexplosives.Eachholeistypicallybottom-primed;however,doublepriminganddeckedchargesaresometimesused.Holesarefiredusingamilliseconddelaysequencewiththemaximumweightofexplosivesperholedeterminedusingscaleddistancecriteria.Roundsarefiredatatimepre-arrangedthroughthepermitprocess.Awindowbetween12:00pm(noon)and3:00pmiscurrentlyutilizedandlocalresidentsarenotifiedofpendingblastsbymail,fax,ortelephone.Pre-shotwarningsirensaresoundedon-sitepriortoeachblast.2.3ControlofGroundVibrations3
SubTerra,Inc.BlackRiverQuarryMarch20,2000BlastingandAirQualityAnalysisPeakparticlevelocityiscontrolledinthevicinityofnearbystructuresusingthe,scaleddistancedescribedinMethodIabove.Inaddition,eachblastismonitoredusingcommercialseismographsincompliancewithMethod2.2.4BlastMonitoringandBlastingRecordsSinceearly1996,eachblastatthequarryhasbeenmonitoredbySubTerra,Inc.usingtwoormorecommercialseismographstodeterminepeakparticlevelocity,acceleration,anddisplacement,peakairoverpressure,andairandgroundvibrationfrequencies.RecordsofeachblastaremaintainedbySubTerra,Inc.andprovidedtoKingCountyandtoEmpireEstatesattorneyBrianLawleronamonthlybasis.Recordsinclude:layoutofblastholes,locationsofblastsrelativetopropertyboundaries,amountsandtypesofexplosivesused,locationsofblastmonitoring,weatherdata,andgeneralnotesonblastperformance.Table3containssummaryrecordsforblastsbetweenApril,1998andtheendofFebruary,2000.Thepeakparticlevelocitydataarealsoplotted,usingthelog/logformat,inFigure3.Thefollowingsummarydatahavebeenextrapolatedfromthetable:•Withoneexception(May29,1998),thepeakparticlevelocityhasbeenmaintainedbelow0.9in/secwithanaverageof0.4in/sec(thehighestmonitoredvalueis1.3in/sec).•Airbiastvalueshaverangedfrom100dBL(triggerlimit)to125dBLwithanaverageof116dBL.3POTENTIALIMPACTSFROMQUARRYBLASTINGPotentialimpactsfromquarryblastingcanbebrokendownintothree(3)maincategories:1.EffectofBlastingonStructures2.FlyrockHazards3.NoiseImpactsandEffectsofBlastingonHumansSuchpotentialimpactsarediscussedbelow.3.1EvaluationofImpactsofBlastingonStructuresAsillustratedintheattachedSupplementalSitePlan,theEmpireEstatesApartmentsarethecloseststructurestothequarrypropertyboundary.BuildingCisthecloseststructureandislocatedapproximately60-ftnorthoftheQuarry’snorthernpropertyline.Currentpracticehaslimitedscaleddistanceatthepropertyboundaryto50andattheapartmentcomplexto60withacceptableresults.However,wheneverpossible,werecommendthatthescaleddistancebasedontheapartmentlocationbesetat70.Onaverage,thisshouldmaintainpeakparticlevelocitiesattheapartmentcomplexwellbelowlevelsofconcernforstructuraldamage.4
SubTerra,Inc.BlackRiverQuarryMarch20,2000BlastingandAirQualityAnalysisWealsorecommendthatthefollowingproceduresbeimplementedandmonitoredforeffectivenesswithregardtothedesignandlayoutofblastpatterns:A.Thestiffnessratio(BenchHeight/Burden)shouldbemaintainedabove3whenblastingclosetothepropertyboundaryandproximateresidences.B.Holesthataremostlikelytobeover-confinedondetonationshouldbelocatedfurthestfromthepropertyboundarytoavoidunusuallyhighpeakparticlevelocity.Thisconditionmayexistonthelastdelayinthelastrowofmulti-rowblasts.C.Blaststhataredetonatedwithin300-ftofthenorthpropertyboundaryshouldbemattedtoprotectagainstthepossibilityofflyrock.Theseprocedureswillservetominimizeimpactsfromtheblastingactivities.3.2EvaluationofPotentialforFlyrockImpactsCurrentblastingpracticeshavebeenoptimizedwithregardtothecontrolofflyrock.Thishasincludedutilizingaminimumstemminglengthof6-ftandtheuseofblastmatswhenblastingontheupperquarrybenchesorwhenevertheBlasterinChargeconsidersthattheremaybeapotentialforflyrock.Anecdotally,blastmatshavebeenusedelsewherebyStoneway’sBlastingContractor,McCallumRockDrilling,whenblastingwithin50-ftoflarge,residentialstructureswithoutanyimpacts.ContinueduseoftheseBestManagementPractices(BMPs)willeliminatethepotentialforflyrock.AppendixAprovidesfurtherindustryguidanceinthisarea.3.3NoiseImpactsandEffectsofBlastingonHumansTherearenostandardsforblast-relatednoiseinKingCounty.However,theWashingtonStateDepartmentofLaborandIndustriesiscurrentlyconsideringadoptionofamaximumairbiastnoiselevelof134dBLintheirrevisionoftheWashingtonBlastingCode.Currentpracticemaintainsblasting-relatednoisewellbelowthisstandardasillustratedinFigure4.Forthelasttwoyears,peakparticlevelocitiesatthecornerofBuildingChaveaveraged0.4in/secand,withoneexception,beenmaintainedbelow0.9in/sec.Comparisonbetweentheseobservedvibrationlevelsandlevelsassociatedwithvarioustypesofcommonhouseholdactivities,areprovidedinTable4.5
SubTerra,Inc.BlackRiverQuarryMarch20,2000BlastingandAirQualityAnalysisTable4ComparisonofStrainLevelsInducedbyHouseholdActivitiesandBlastingHouseholdActivityMicrostrainInducedbyActivityCorrespondingBlastLevel(in/inIQ6)(in/sec)Walking9.10.03HeelDrops16.00.03Jumping37.30.28DoorSlams48.80.50PoundingNails88.70.88Source:Stagg,M.S.,Siskind,D.E.,Stevens,M.G.,andDowding,C.H.,1984Therecommendeduseofascaleddistanceof70withregardtoBuildingCshould,onaverage,maintainvibrationslevelsbelow0.4in/secandwouldprovidefurthermitigationofpotentialimpactstonearbyresidents.4AIRQUALITYIMPACTSActivitiesoccurringintheSupplementalSiteAreathatwillpotentiallyactassourcesofdustinclude:clearingandgrubbing,grading,blastholedrilling,blasting,rockhauling,andstockpilingofrawandprocessedmaterials.BestManagementPractices(BMPs)areusedfordustcontrolattheBlackRiverQuarryunderafugitivedustsuppressionplanimplementedin1998thatcomplieswithSection9.15ofthePugetSoundAirPollutionControlAgency’sRegulation1.Currentpracticesincludeutilizationofapermanenton-sitewatertruckformaintainingpotentialdustproducingsurfaces.ContinuationoftheseBMPsorBestAvailableControlTechnologies(BACT5)willminimizethepotentialforairqualityimpacts.Inaddition,furtherimpactmitigationcouldincludetheapplicationofchemicalstabilizerstohaultoadsandtheuseofwaterspraysonstoragepiles.Further,DDESstaffcouldrequestPSAPCAinspectionsundercircumstancesofobserveddustemission.5FINDINGSANDCONCLUSIONSWedonotexpectanysignificantimpactsfromblastingatStoneway’sBlackRiverQuarryifexistingpracticeismaintainedandtherecommendationscontainedinthisreportarefollowed.Carefulblastingshouldbepracticedwhenminingtheupperbenchesonthenorthernsiteboundarytominimizevibrationandair-blasteffectsonproximateresidenciesandminimizeblastdamageeffectstothefinalhighwall.Werecommendthatthecurrentarrayofblastingseismographsbeusedtomonitoreachblast.Thiscurrentlyinvolvesplacingmonitorsat(a)thenorthpropertyline,fb)the6
SubTerra,Inc.BlackRiverQuarryMarch20,2000BlastingandAirQualityAnalysissouthwestcornerofEmpireEstatesBuildingC,fc)attheEmpireEstatesmanager’soffice,and(U)neareachblast.Thislastmonitorisusedtoensurethatatleastonerecordisretrievedforeachblast.6REFERENCES1.Crum,S.V.andSuskindD.E.,1993ResponseofStructurestoLowFrequencyGroundWbrations.APreliminaryStudy.ProceedingsoftheNinthAnnualSymposiumonExplosivesandBlastingResearch,SanDiego,California,February,1993.2.Konya,C.].,andWalter,E.J.,1990.SurfaceBlastDesign.PublishedbyPrenticeHall,EnglewoodCliffs,NewJersey.3.Stagg,M.S.,Siskind,D.E.,Stevens,M.G.,andDowding,C.H.,1984.EffectsofRepeatedBlastingonaWoodFrameHouse.ReportofInvestigations8896,USBureauofMines,Washington,DC,1984.4.Siskind,1994.PersonalCommunication.5.Siskind,D.E.,andStagg,M.S.,1997.EnvironmentalEffectsofBlastingandTheirControl.Proceedingsofthe23rdAnnualConferenceonExplosivesandBlastingTechnique,LasVegas,Nevada,February19976.Siskind,D.E.,1997.SafeBlastVibrationCriteriaforHomes.JournalofExplosivesEngineering,page38,July/August,1997.7
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Figure 1:USBM RI 8507 “Safe Limit”Criteria
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SubTerta,Inc.Stoneway,Inc.
Black River Quarry
3/17/00
Table 3:Summary Blast Monitoring Data for the Black Rivet Quarry
Date Monitor Peak Frequency Peak
Particle Sound
Velocity Pressure Notes
Level
(inlsec)(mmlsec)(Hz)(UB(L)(pa)
Instrument located on site nearInstantel4114/98 0.08 2.09 70 111 property line approximately 750 feetMinimatePlus
from blast.
Instrument located at base ofInstantel4/14/98 0.14 3.59 17 6 Apartment foundation approximatelyMinimate
750 feet from blast.
Instrument located on site nearInstantel4/22198 0.08 2.15 20 113 property line approximately 750 feetMinimatePlus
from blast.
Instrument located at base ofInstantel4/22/98 0.16 4.03 18 2 Apartment foundation approximatelyMinimate
750 feet from blast.
Instantel Instrument located at property line4/24/98 0.09 2.20 30 115MinimatePlus between blast and apartments..
Seismograph did not tr gger so Instrument located at base ofInstantel4/24/98 that PPV was less than 0.05 Apartment foundation approximately
.Minimate in/sec (1.27 mm/sec).750 feet from blast.
Instantel Instrument located at property line5/1/98 0.19 4.77 22 113MinimatePlus between blast and apartments..
Instantel Instrument located at base of5/1/98 0.17 4.38 19 112Minimate Apartment foundation.
Blasting Data:Table 3 PNo:98-09
SubTerra,Inc.Stoneway,lflC.3/17/00BlackRiverQuarryTable3:SummaryBlastMonitoringDatafortheBlackRiverQuarryDateMonitorPeakFrequencyPeakParticleSoundVelocityPressureNotesLevel(in/sec)(mm/sec)(Hz)(dB(L)(pa)lnstantelInstrumentlocatedatpropertyline5/6/980.369.2423116MinimatePlusbetweenblastandapartments..lnstantelInstrumentlocatedatbaseof5/6/980.184.6419110MinimateApartmentfoundation.InstantelInstrumentlocatedatpropertyline5/8/980.348.6340120MinimatePlusbetweenblastandapartments..InstantelInstrumentlocatedatbaseof5/8/980.143.6040120MinimateApartmentfoundation.InstantelInstrumentlocatedatpropertyline5/15/980.276.8730115MinimatePlusbetweenblastandapartments..InstantelInstrumentlocatedatbaseof5/15/98Seismographdidnottrigger.MinimateApartmentfoundation.InstantelInstrumentlocatedatpropertyline5/20/981.5038.2040128MinimatePlusbetweenblastandapartments..InstantelInstrumentlocatedatbaseof5/20/980.389.7335125MinimateApartmentfoundation.InstantelInstrumentlocatedatpropertyline5/27/98OutofRangeor>1.5in/secMinimatePlusbetweenblastandapartments..BlastingData:Table3PNo:98-09
SubTerra,Inc.Stoneway,Inc.
Btack Rivet Quarry 3/17/00
Table 3:Summary Blast Monitoring Data for the Black River Quarry
Date Monitor Peak Frequency Peak
Particle Sound
Velocity Pressure NotesILevel
(in/sec)(mm/sec)(Hz)(dB(L)(pa)
Instantel Instrument located at base of5/27/98 0.65 16.40 40 119Minimate Apartment foundation.
Instantel Instrument located at property line5/29198 2.60 66.1 40 124MinimatePlus between blast and apartments..
Instantel Instrument located at base of5/29/98 1.29 32.70 40 117Minimate Apartment foundation.
Instantel Instrument located at property line6/5/98 1.08 27.50 35 125MinimatePlus between blast and apartments..
Instantel Instrument located at base of6/5/98 0.41 10.30 30 117Minimate Apartment foundation.
Instantel Instrument located at property line6/10/98 0.90 22.91 34 119MinimatePlus between blast and apartments..
lnstantel Instrument located at base of6/10/98 0.40 10.24 34 118Minimate Apartment foundation.
Instantel Instrument located at property line6/12/98 1.17 29.72 30 120MinimatePlus between blast and apartments..
Instantel Instrument located at base of6/12/98 0.49 12.45 30 114Minimate Apartment foundation.
Blasting Data:Table 3 PN0:98-09
SubTerra,Inc.Stoneway,Inc.BlackRiverQuarry3117/00Table3:SummaryBlastMonitoringDatafortheBlackRivetQuarryDateMonitorPeakFrequencyPeakParticleSoundVelocityPressureNotesLevelfinlsec)fmmlsec)(Hz)(dB(L)(pa)InstantelInstrumentlocatedatpropertyline6/17/982.2456.9050118MinimatePlusbetweenblastandapartments..InstantelInstrumentlocatedatbaseof6/17/980.5413.7240121MinimateApartmentfoundation.Instantel6/24/981.0225.9135131Instrumentlocatedatpropertyline.MinimatePlusInstantelInstrumentlocatedatbaseof6/24/980.6416.2630125MinimateApartmentfoundation.Instantel6/26/981.1930.2340125Instrumentlocatedatpropertyline.MinimatePlusInstantelInstrumentlocatedatbaseof6/26/980.6316.0040119MinimateApartmentfoundation.Instantel7/1/980.399.9145119Instrumentlocatedatpropertyline.MinimatePlusInstantelInstrumentlocatedatbaseof7/1/980.215.3330114MinimateApartmentfoundation.Instantel7/8/982.1053.3430124Instrumentlocatedatpropertyline.MinimatePlusBlastingData:Table3PNo:98-09
SubTerra,Inc.Stoneway,Inc.
Black River Quarry 3/17/00
Table 3:Summary Blast Monitoring Data for the Black Rivet Quarry
Date Monitor Peak Frequency Peak
Particle Sound
Velocity Pressure Notes
Level
(in/sec)(mm/sec)(Hz)(UB(L)(pa)
Instantel Instrument located at base of7/8/98 0.63 16.00 30 119Minimate Apartment foundation.
Instantel7/10/98 2.80 71.12 50 127 Instrument located at property line.Minimate Plus
Instantel Instrument located at base of7/10/98 0.85 21.59 50 124Minimate Apartment foundation.
Instantel7115/98 2.10 53.34 33 123 Instrument located at property line.Minimate Plus
Instantel Instrument located at base of7/15/98 0.69 17.53 30 120Minimate Apartment foundation.
I nsta ntel7/17/98 0.16 4.06 30 112 Instrument located at property line.Minimate Plus
Instantel Instrument located at base of7/17/98 0.25 6.35 25 114Minimate Apartment foundation.
•Instrument located at base ofSeismographdidnottriggersothatPPVwaslessthanApartmentfoundationapproximately4123/99 Minimate (Apt)0.05 in/sec (1.27 mm/sec).
1,100 feet from blast.
Blasting Data:Table 3 PNo:98-09
SubTerra,Inc.Stoneway,Inc.3/17100BlackRiverQuarryTable3:SummaryBlastMonitoringDatafortheBlackRivetQuarryDateMonitorPeakFrequencyPeakParticleSoundVelocityPressureNotesLevel(infsec)(mmlsec)(Hz)fdB(L)(pa)Instrumentlocatedonsitenear4/23/99Minimate(PB)0.153.7820112propertylineapproximately850feetfromblast.Instrumentlocatedatbaseof4/29/99Minimate(Apt)0.082.1326114Apartmentfoundationapproximately1,100feetfromblast.Instrumentlocatedonsitenear4/29/99Minimate(PB)0.287.0627114propertylineapproximately850feetfromblast.Instrumentlocatedatbaseof5/14/99Minimate(Apt)0.328.0834116Apartmentfoundationapproximately480and1,000feetfromblastcenters.Instrumentlocatedonsitenear5/14199Minimate(PB)2.2958.1737116propertylineapproximately210and800feetfromblastcenters.Instrumentlocatedatbaseof6/4/99Minimate(Apt)0.389.7027114Apartmentfoundationapproximately510feetfromblast.Instrumentlocatedonsiteneat6/4/99Minimate(PB)2.6366.8027123propertylineapproximately250feetfromblast.BlastingData:Table3PN0:98-09
SubTerra,Inc.Stoneway,Inc.3/17/00BlackRiverQuarry
Table 3:Summary Blast Monitoring Data for the Black Rivet Quarry
Date Mdnitor Peak Frequency Peak
Particle Sound
Velocity Pressure Notes
Level
(in/sec)(mm/sec)(Hz)fdB(L)(pa)
Instrument located at base of6/25/99 Minimate (Apt)0.56 14.10 37 118 Apartment foundation approximately
.425 feet from blast.
Instrument located on site near6/25/99 Minimate (PB)1.65 41.91 47 121 property line approximately 160 feet
from blast.
Instrument located on site near
6125/99 Minimate (Ma)1.26 32.00 47 130 property line approximately 170 feet
from blast (approx.65 ft to east of
main property line station).
Instrument located on site near crest6/25/99 Minimate (Mb)5.45 138.43 37 124 of bench above blast area,
approximately 60 feet from blast.
.Instrument located at base of7/16/99 Minimate (Apt).0.50 12.70 10 117 Apartment foundation approximately
410 feet from blast.
Instrument located on site near7/16/99 Minimate (PB)2.48 62.99 34 122 property line approximately 155 feet
from blast.
Instrument located at base of7/30/99 Minimate (Apt)0.33 8.38 20 122 Apartment foundation approximately
390 feet from blast.
Blasting Data:Table 3 PNo:98-09
SubTerra,Inc.Stoneway,Inc.3/17/00BlackRiverQuarryTable3:SummaryBlastMonitoringDatafortheBlackRiverQuarryDateMonitorPeakFrequencyPeakParticleSoundVelocityPressureNotes.Level(infsec)(mmlsec)(Hz)(dB(L)(pa)Instrumentlocatedonsiteneat7130/99Minimate(PB)2.6767.8218.132propertylineapproximately155feetfromblast.Instrumentlocatedatbaseof8/27/99Minimate(Apt)0.092.3534110Apartmentfoundationapproximately640feetfromblast.Instrumentlocatedonsiteneat8/27/99Minimate(PB)0.102.4322110propertylineapproximately390feetfromblast.Instrumentlocatedatbaseof10/1/99Minimate(Apt)0.5413.7234122Apartmentfoundationapproximately375feetfromblast...Instrumentlocatedonsitenear10/1/990.7619.3047124propertylineapproximately220feetus(fromblast.MinimateInstrumentlocatedatsouthbaseof10/22/99PIus(south0.184.5722111ApartmentOfficeapproximately745sideofoffice)feetfromblast.Instrumentlocatedapproximately44011/5/99Minimate42470.348.6457116feetfromblastonnorthsideofquarry.BlastingData:Table3PN0:98-09
SubTerra,Inc.Stoneway,Inc.
Black River Quarry 3/17/00
I
Table 3:Summary Blast Monitoring Data fot The Black River Quarry I
Date Monitor Peak Frequency Peak
Particle Sound
Velocity Pressure Notes
Level
(in/sec)(mmlsec)(Hz)(dB(L)(pa)
Instrument located approximately 44011/5/99 Minimate 4247 0.42 10.67 32 120 feet from blast on north side of
quarry.Cutoff Blast
Instrument located at south corner of11/5/99 Minimate 4403 0.35 8.89 30 112 Apartment Building approximately
770 feet from blast.
Instrument located at south cornet of1115/99 Minimate 4403 0.28 6.99 28 116 Apartment Building approximately
770 feet from blast.Cutoff Blast
Instrument located at propertyMinmatePlusboundaryapproximately540feet11/5/99 5671 0.31 7.75 64 117 from blast.
Minimate Plus Instrument located at Apartment11/5199 6670 0.08 1.91 47 104 Office 1250 feet from blast.
Instrument located at Apartment
Minimate Plus Office 1250 feet from blast.Failed to11/5/99 6670 na na na na detectCutoff Blast.
...Located 900 feet from blast area andSeismographdidnottriggersothatPPVwaslessthan.Minimate Plus 0.05 in/sec (1.27 mm/sec).failed to exceed the trigger level of1/28/00 6713 .O5in/s
Blasting Data:Table 3 PNo:98-09
SubTerra,Inc.Stoneway,Inc.BlackRiverQuarry3/17/00Table3:SummaryBlastMonitoringDatafortheBlackRiverQuarryDateMonitorPeakFrequencyPeakParticleSoundVelocityPressureNotesLevelfin/sec)(mm/sec)(Hz)(dB(L)(pa)Located1100feetfromblastareaSeismographdidnottriggersothatPPVwaslessthanMinmatePlusandfailedtoexceedthetriggerlevel0.05in/sec(127mm/sec).1/28/005671of.O5inIsLocated1600feetfromblastareaSeismographdidnottriggersothatPPVwaslessthanMinimatePlusandfailedtoexceedthetriggerlevel0.05in/sec(1.27mm/sec).1/281006708of.051n/sLocated970feetfromblastareaatMinimatePlusthewestsideoftheApartment2/18/0067080.194.8320109BuildingOffice.MinimatePlusLocated580feetfromblastareaat2/18/0056710.4511.30320117nearestcornerofApartmentBuilding.MinimatePlusSeismographwastriggeredsecondsbeforeactualblastLocated330feetfromblastareaat2/18/006670andrecordedanunrelatedvibration.PropertyBoundary.BlastingData:Table3PNo:98-09
SubTerra,Inc.BlackRiverQuarryMatch20,2000BlastingandAirQualityAnalysisAttachmentAFlyRockData8
Everyoneintheblastingindustryknowswhatismeantbyflyrock,butthereareseveralperspectivesorwaystoviewfly-rock.Insomecases,flyrockhassimplybeendescribedasANYrockthrownintheairbyablast.Usingthisdefinition,evenrockthatroseonlythreefeetofftheground,couldtechnicallybeconsideredflyrock.Obviously,suchflyrockisnotthekindablasterneedstobeconcernedwith.Incertainothertexts,flyrockisdefinedas“anydirt,mud,stone,fragmentedrockorothermaterialthatisdisplacedfromtheblastsitebybeingthrownintheairorcastalongtheground.”Severalpointstonoteaboutthisdefinitionare:1.Flyrockcanbemudordirt,itdoesnotnecessarilymeanonlyrockorstone.2.Thematerialcanbedisplacedfromtheblastsitebytravelingalongthegroundaswellasthroughtheair.Thatis,fly-rockdoesn’tnecessarilyhavetofly.Ifyoualsoexaminethisdefintionofflyrock,itsaysnothingaboutflyrockbeingdangerous.Therefore,castblastingcouldfitthisdefinitionsincethematerialisdisplacedfromtheblastsitebytheforceofthedetonation.However,evenifcastblastingmaymeetthisdefinition,itisnotthenightmarereferredtoearlier,becauseitisbothexpectedandcontrolled.Whendonecorrectly,castblastingisapositiveoutcomeoftheblastdesign.However,theflyrockthattheblastermustbeconcernedaboutisneithercontrollednorplanned,andwouldnormallybeconsideredasexcessive.Whentheblasterisconcernedwithflyrockandsafety,therearetwopossibleproblems:eithertheamountofmaterialthrown,orthedistancethematerialtravelsisexcessive.Wheneitherorbothofthesethingsexceedwhatmostexperiencedblasterswouldreasonablyexpectfromablast,theremaybeseriousproblems.Somelawsarewrittentospecifywhatisconsideredtobeexcessivedistanceforflyrock.Theymaysaythat“flyingrocksshallnotbeallowedtofallgreaterthanone-halfthedistancebetweentheblastandadwellinghouse,publicbuilding,school,church,commercialorinstitutionalbuilding.”Thisisaquantitativewayofevaluatingthedegreeofflyrock,whichhastheadvantageofflexibilityinthatftdoesnotsetaspecificdistanceandapplyittoallblastingoperations.Itwouldsimplynotbefeasibletosetaparticulardistanceasthelimitforflyrodcforeverycase.Forinstance,if300feetwaschosenasauniversallimitBACKBASICSbyLarrySchneiderFlymcktPàrt1:SafetyaiRd£uses18TheJournaloff.xptosivesEngineeringNovember/December1996
onflyrock,itobviouslywouldnotbeappropriatewhenblastinginthemidstofaresidentialarea.However,whenblastingonaminesiteinanisolatedareawhichmaybethreemilesfromyournearestneighbor,300feetisunnecessarilyrestrictive.Thedisadvantagetothistypeoflawisthatitdoesmeanthatflyrockcanremainwithintheboundariesofajobsiteorminepermitandstillbeinviolation.Inmostjurisdictions,therewillbelawsandregulationsthatrestrictflyrockinthevicinityofhighways,waterways,thatendangerpropertyorconstituteahazardtoemployeesorthepublic.Manyoftheselawsaremoredirectlyconcernedwithsecuringtheareaaroundablastsite.Providedablasterdoesagoodjobofclearingandsecuringthearea,evenifablastgeneratesalargeramountofflVrockthanusual,itshouldhavenoeffect.Iftheblasterislaxinclearingtheareaorblockingaccess,evenawellcontrolledshotcanresultinenoughflyrocktoinjureorkillsomeone.InfactaU.S.BureauofMinesstudydoneinthelate1980’s,showedthatthetwoleadingcausesoffatalitiesinblastingoperationsare1)failuretosecurethearea2)Excessiveflyrock.Therefore,inadiscussionofflyrockandsafety,thereshouldbesomeconsiderationgiventosecuringthearea.Immediatelybeforedetonation,theblaster’smostcriticalconcernmustbethattheareaiscompletelyclearandaccesstothesiteiscontrolled.Heshouldhaveapre-determinedplanforsafeguardingallpersonnelandthepublic.Thisisamatteraboutwhichtheblastercanmakenoassumptions,hemustbeabsolutelysurethattheareaisclear.Flyrockhasbeenknowntotravelremarkabledistancesfromablast,andaplantoprotectagainstflyrockmusttakeintoaccounttheworstcasescenario.furthermore,whenblastinginapublicarea,theblastermustrealizethatthepublicisbothcuriousanduninformedabouttheuseofexplosives.Theywillsometimesplacethemselvesindangeroussituationsinanattempttoseewhatishappening.InthesurfacecoalminesofAppalachia,therehavebeenanumberdosecallswherepeojMewhoride“fourwheelers”intheseisolatedareas,drivedirectlyuponablastsite.Therearealsoreportedinstancesofhuntersorback-packerswalkinginwoodedareasnearblastsitesandwhodeliberatelyremainnearbyinattempttowatchablastbeingsetoff.Allroadsleadinginto-thevicinityoftheblastareamustbephysicallyguarded,andallpersonnelandequipmentmustberemovedfromtheareatoalocationwhichisbothatasafedistanceandwell-protected.Athoroughvisualinspectionofallpossibleareasthatcouldbeaffectedisessentialpriortosoundingthewarningsignals.Itisimperativethatcontrolofaccesstothesitebemaintainedcontinuously;ifsuchcontrolislostorremovedforevenafewseconds,arepeatedinspectionoftheareaismandatorytobesurenoonehasenteredtheareaduringthetimethataccesscontrolwaslost.Theneedforprotectionfromflyrockismostseriousfortheblasterhimself,sinceheisusuallythepersonclosesttothedetonation.Eventhoughmostblasterswanttofiretheblastfromapositionwithadearvantagepointtoseetheentireblastareaandtheblastitself,itisimperativethattheytakeadequateprecautionstoprotectthemselves.Thismeansthattheblastermustbeatasafelocation,andundersubstantialcover.Lightbuildings,pickuptrucks,andothervehicleswhichareoftenusedascover,havealsooftenbeenpenetratedbyflyrock.Theuseofspeciallydesignedblastsheltersarebecomingmorewidelyavailableandused,andrepresentastepforwardinprovidingforthesafetyoftheblaster.Asafelocationandsufficientcoveriscriticaltotheblaster’sprotectionbecauseleadlinesortheshocktubeisseldomlongenoughtoallowtheblastertobebeyondflyrockrange.Anothercriticalpointisthatnoone,includingtheblaster,shouldeverbelocatedinfrontoftheshot.Sincesomanyinjuriesarecausedbyflyrock,anydiscussionofsafetyshouldNovember/December1996TheJournalofExptosKvesEngineering
BACK10BASiCSemphasizethemeanstopreventit.Someofthecommoncausesofflyrockareasfollows:1)Excessiveamountofexplosivesused.InadequateBurden.Explosivesloadedintovoids,crevices,mudseams,oranyincompetentmaterial.4)Spacingandburdenexceedthedepthoftheborehole.5)Inadequateamountortypeofstemming.6)Liftshotsorshotswhichareover-confined.7)Poordelaytiminginthepatternordetonatorsfiringoutofsequence.Fromthislist,itshouldbeobviousthatthebestprecautionagainstflyrockisagoodblastpattern,onewhicheffectivelydistributestheexplosiveenergyintotherocksothattheenergyisnearlyallusedtofragmenttherock,andwhateverenergyisleftoverdisplacestherockinacontrolledmanner.Apoorblastdesigncanresultinablastwhichtheexplosiveisunder-confined,thatis,thestrataofrockisnotstrongenoughtocontaintheforceofthedetonation.2)3)IFIT’SDUST-FREE,YOUKNOWITMEANSANINCREASEINPRODUCTWITYEliminateDustProblems‘thYourAirTrackAncLincreaseDrillingProductionAtTheSameTime.InstallASafeAndReliableILMEGDustCollectorCalltollfree1-800-526-3837THEIN.DUSTRYSPREFERR£DCH0ICETRAMAC4>TheJournalofExplosivesEnglneerngNovember/December1996
pBACKTOTHE.BASICLanySchneiderFlyrock(Part2:PreventionInpartoneofthisseriesonflytocksevencommoncausesofflyrockwerelisted.Thefirstcausewasdescribedasanexcessiveamountofexplosives.Whenyouhearthatdescription,theimplicationisthattheblasterloaded“TOOMUCHEXPLOSIVESINTI-IFHOLE”Infact,thisiswhatthepublicoftenaccusesblastersof,whenevertheyhaveacomplaintaboutthegroundvibration,noiseorflyrock;thatis,theblasterdeliberatelyputtoomuchpowderinthehole.Astheblastersthemselvesarewellaware,that-explanationistoosimplisticbecausethereisonlyacertainamountofexplosivesthatwillfitintoaboreholeofaparticulardiameteranddepth.Furthermore,duetotheeconomicsofblasting,theideaiscertainlynottouseanymoreexplosivesthannecessary.Sothestatementthattherewasanexcessivechargeinablastusuallymeansthattheremaybesomeotherproblems,suchastheblastwasloadedwithapowderfactor(asmeasuredinlbofexplosivesperyard1ofrock)thatwastoolargeforthetypeofrockbeingshot.Apowderfactorthatistoehighcancauseenormousmovementoftherock.Andanexcessivelylargepowderfactorcanactuallyoccurduetoanyofseveralofthecausesdescribedinthelist.Forinstance,iftheburdendistanceistOOsmallfortheboreholediameter,orifnotenoughstemmingisloadedintheborehole,thosefactorsalsoresultinanexcessivepowderfactorandanoverloadedblast.Thismayresultfrompoordesignwhenplanningtheburdenorspacing.Orsometimes,poorexecutioninthefieldoccurswhentryingtoimplementagoodblastdesign.Forinstance,ablastermayloadaholewherethepowderfactorhasbeencalculatedcorrectlyforagivenburden,spacinganddepth,hutthehoreholeswerenordrilledaccuratelyaccordingtothatdesign.Theblastermustalsobeawareofwhatthetrueburdenisoneachborehole,andwhetherornotthatburdenisconsistentthroughthelengthoftheborehole.Notethatthetrueburdenisdeterminedbythedelaytimingsequenceaswellastheblastgeometry.Ifwelookatsomeofthefollowingdiagrams,wecanseeinsomecasesclearlywheretheburdenturnsouttobelessthanthatwhichtheblasterexpected.Infigure1,thebenchhasagoodverticalfreeface,butthedrillingwasdonepoorly.Iftheblasterpro-Figure177n’jurnai“IExp1osizysEii’zneerinç]anwnY&br7tafl/99
ceedstoloadtheboreholeforthe12footburdenhehasatthetop,hewillheoverloadingthebottomoftheholewherehehasonly8.5ft.Aninaccuracysuchasthis,whenthedullisoffthevertical,willhemagnifiedthedeepertheboreholeisdrilled.Asanexample,aborehole40feetdeep,whichisdrilled5degreesfromtheverticalresultsinanerrorof3.5feetatthebottomofthehole.Thesameboreholedrilled100feetdeepwiththesame5degreeerror,willbeoffbynearly9feetatthebottomofthehole.Eveninthefirstinstance,wheretheburdenwasoffl)y3.5feet,thepowderfactormayvaivby20%fromtoptobottomoftheborehole.Asanexampleofthistypeoferror,considerablasterwhointendstodrilla12x15pattern,40feetdeep,using8ftofstemmingina51/2inchdiameter,andloadsitwithaloadingfactorof8.25poundsofANFOperfoot.Withthispattern.heexpectstohaveanaveragepowderfactorof1.00lb/yd3fortheborehole.If,however,thedrillereumby5degreesfromthevertical,hisburdenatthebottomisonly8.5ft.,andhisaverageburdenthroughouttheboreholewouldbe10.25feet.Hisactualpowderfactorfortheentireholewillbe1.16Ib/yd.Evenmorestriking,isthefactthatwhilethepowderfactorforthetoponefootofthepowdercolumnis1.29,thepowderfactoratthebottomoftheboreholeis1.75lb/yd,anincreaseofmorethan35%.figure2showsaperfectlydrilledvertical,holeonalevelbench,butduetotheequipmentexcavatingmaterialatthefrontofthebench,theblastermayencounterabenchwithaprofilelikethis.Inthisexample,iftheblasterdoesnotchecktheshapeofthefreeface,hemayloadtheshotfora15ftburdenandonlyhave8feetofrockconfininghisexplosivecharge.Asimilarinstanceiswheretheholesare“buffered”infrontheshot,andtheblasterUnearthefreefacetoensurehe“pullsthetoe.”Theprcmaylookliketheoneshowifigure3.Thefirstrowofhokdrilledclosetothecrestsitthereisalargebufferthatreaesnearlytothetopofbench.Subsequentrowsholesaresetbackareasonadistance,andthebiasassumesthatthebufferwillccfinetheblastontheoutsiboreholes.Anditmayworkplannedprovidedthepowocolumnisnotloadedtoohisothatthetopportionofchargeisnotnearorabovebuffer.Ifachargeisloadedsuthatthechargeisunconfinedthistopportion,itcanthrcrocksoveralongdistance.Accuracyindrillingextremelyimportantwhangledholesareused.Tsetupdistancefromtheface,t:angleofthedrillmustbemcsuredcarefullytoensureththeproperburdenexistsatttoe.failuretodosocanres.inchargesthatareplacedrclosetothefacewithlessccfinementthanintended.Ifexplosivesareloadedinfaults,crevices,ormudsearthattheboreholepasstthrough,theblastershou.expectexcessiveflyrock.Tdrillerhasacrucialroletophinthepreparationoftheb1aIqformationaboutanyunusuconditionssuchasmudseanorvoidsencounteredin±boreholemustberecordedlogged,andtheblastermurelyonhisdrillertocommuccateanyunusualconditionsFlguw2Januar,y&bruurl199TheJournalojf.rp1c,itisLng:nemng
BACKTOBASICStheboreholeshehasdrilled.ThedrillermustbeconstantlyawareOfwhatishappeningashedrills,SC)hewillknowifheencountersUsignificantmudseamf)tUvoidsuchasacavernoranabandonedundergroundmine.Ifexplosivesareloadedintoamudseam,themuddoesnothavesufficientresistancetoconfinetheenergyofthedetonation.Aslongastheblasterknowsinadvancethatamudseamintersectstheborehole,hecantakestepstoeliminatethedanger.Thisisnormallydonebystemmingthroughthemudwithinertmaterialtomaketwoseparatechartesinthel)Orehole.Acardinalruleforablasteristhatexplosivesshouldneverbeloadedintoarnihingexceptcompetentrock.Likewise,ifaboreholeisdrilledsothatitcutsintoacayemorundergroundmine,theblastermayloadhugeamountsofexplosives,andIt’detonatedwillcreateaViolentresult.Iftheblasteriscarelesswhileloadingtheborehole,especiallywhenusingbulkexplosives,hemaynotdeectthefactthatalargeamountofexplosivesaregoingintotheborehole.Itisalwaysmponantthatablasterconstantlymonitorstheriseofthepow-dercolumnintheboreholeusingatapeorothermethod.Adequatestemmingisrequiredtoconfinethehighpressuregasesreleasedbythedetonationoftheexplosivecharge.Thisstemmingmusthesufficienttopreventtheforceofthesegasesfromviolentlycrateringtothesurface.Theexplosiveforcewillalwaysbeinthedirectionofleastresistance,whichshouldbetheburdendistancetothefreefaceattheinstantofdetonation.However,ifthestemminglengthistoO)small,themostdirectpathforthegaspressuretoventmaybetothesurface.Inminoroccurrences,thisresultsinstemmingmaterialbeinglaunchedawayfromtheblast.Moreseriouscasesoccurwhenmaterialaroundthecollaroftheboreholecanhethrownsignificantdistances.Adequatestemmingdoesnotonlymeanthelengthofthestemming,butalsothecompositionofthematerialusedasstemming.DrillcuttingsC)tdustareusuallyayenpoorstemmingmaterial,particularlyiftheboreholeiswater-filled.Crushedstoneofasuitablesizesothatitinterlocksintheboreholeisarecommendedstemmingmaterialonmostoperations.Anotherpotentialproblemoccursifablastpatternisdrilledsuchthatthespacingandburdenisgreaterthantheboreholedepth.Inthissituation,theblastershouldexpectflyrock.Blastersoccasionallydrillthistypeofpatternwithoutrealizingthattheyarecreatingapotentialhazard.Forexample.ablasterusinga63/4inchdrillbittriestoblastanexcavationtogradethatisonly8feetdeep.Hemaybeconscientiousenoughtorealizethatheonlyneeds2feetofpowderinaboreholedrilledona12x14feetpattern,8feetdeeptogetaproperpowderfactor.However,suchadesignproducesaburdengreaterthandepth.sothatthenearestdirectionforreliefisthesurface,androckmayhethrownstraightupintotheair.Certainoperationsuseblastingpatternswheretheburdensaresometimescloseto,orslightlygreaterthanthedepth.Oneofthesearethe“partingshots”insurfacecoalmines,wheretheblasterhastobreakalayerofrockthatliesbetweentwocoalseams,thisstrataofrockmayheanywherefrom8to20feetthickandtheblastermayhavetousealargediameterdrillwitha12x12pattern.Itcanresultinagreatdealofmaterialthrown,butusuallysuchhlast.sarealargedistancefromhouses,androads.Occasionallyblastersinquarriesarerequiredtoshoot“teeshots’wheretheycomebackafterthemainhlast.shavefailedtopulltograde.Ontheseshot.s.thehoreholesmaybedrilledinanirregularpatternandveryshallow.Whentheyarefired,flyrockisadefinitepossibility.Socalled“liftshots”oran’shotsfiredtobeginanexcavationarealsopronetogenerateflyrock.Theseshotshavenofreefaceandareintendedtocausetherocktofragmentandswell,However,iftheyarenotcarefullyloadedandcontrolled,thefragmentedrockagainislaunchedupward.Onsmallerscaleblasts,suchasthoseforsettingelectricutilitypoles,theuseof“bumorcut”holesservetoprovideaplaceforthebroFigurc’3ThejournalofExplositt’sEngmc.er.ui.’Jauuari/Februarv199
BACK10BASICSkenrocktomoveandhelpcontroltheupwardthrow.Ontheseshots,blastingmatsmaybeuseful,butagoodblastdesignisstillcritical.Poordelaytimingcangenerateflyrock.Faultydelayrimemayhetheresultofbaddesign,butcouldalsobecausedbyinaccuratedetonatorfiringtime,orsimplyhumanerrorinlayingoutthedelaydetonators.Thetimingonallshotsmustallowenoughtimefortherocktomovesothemuckdoesnotpileupinfrontandpreventtheintendedhorizontalmovementofsubsequentcharges.figure4showstheeffectthattakesplaceasthedetonationproceedsdeeperintothebenchifthereisinsufficienttimefortherockinfronttomove.Thatis,theJmovementoftherockfromeachboreholeprogressivelymovesupwardatanincreasedangleuntilthebackrowsbecomealmostaliftshotandtherockmovementisclosetovertical.Normallythiscanbesomewhatcorrectedbyprovidinglongerdelaysbetweentherowsastheshotprogressesdeeperintothepattern.figure5showsadelaypatternwhichillustratesaverysimpietypeoftimingdelaythatresultsinthesameeffect.Inthiscase,amistakehasoccurredanda#10delayismisplacedintheshotpattern.Whenthisshotisdetonated,thechargeinthatholewillfirewithnoreliefatallandtheonlypossiblemovementoftherockarounditwillbevertical.Ablasterwouldbeincompetentifhelaidoutashotlikethatonpurpose,andattheveryleast,carelessifhediditbyaccident.However,withcomplextiminglayouts,bothelectricandnon-etectric,anyerrorintheconnectionscanresultinholesfiringoutofsequence.Thetimingmistakemaynotbeasblatantastheoneillustratedtohavethesameeffect.Regulationsusuallyrequirethatwhenblastingisdoneinproximitytobuildingsandroadswherenoamountofthrownmaterialcanbetolerated,blastingmatsorotherprotectivematerialsshouldbeusedtoconfineanypossibleflyrock.Buteveninthosecases,thebestmeansofcontrollingflyrockisstillthroughproperblastdesignanddelaytiming.Itisthereforeextremelyimportantthatwhenablasterworkingwithasuccessfulblastingprogrammakesanychangeintheblastdesign,hemustcarefullyconsideranychangesfromthestandpointofitspotentialeffectonflyrock.Whilemanyofthecausesofflyrockmentionedpreviouslycanbepredictedandavoided,itisalwayspossiblethatthereexistssomeunknownconditionthatwillcauseflyrock.Forthisreason,theblastermustalwaysassumetheworstpossibilityandformulatehisplanstodeartheareaforthiscase.Regardlessofhowmany“well-behaved”shotshehaspreviouslydetonated,thenextdetonationisalwaysthemostdangerous.Itistheultimateresponsibilityofeveryblastertooverseethesafetyandwell-beingofanyonethatcouldbeeffectedbytheblast.Theymustacceptthisresponsibilityanddowhateverittakestoprotectthepublic,theirco-workers,andthemselves.Whiletheexplosiveproductsweusetodayarethesafest,mostreliableeverproduced,theyareonlyassafeastheindividualsusingthem.Trainingandeducationinallaspectsofblastsafetymustalwaystakehighpriorityinourindustry,aswellasaccountabilityandresponsibilityinimplementingtheproceduresthatarelearned.figurr4Figure5:36TheJournalofExplosivesEngineeringJanuarr/Frbruar1997