Abrasive Blasting Operations, Engineering Control and Work ...

1 ABRASIVEBLASTINGOPERATIONSE ngineeringControlandWorkPracticesManualE nviro-Management&Research, , "DEPARTMENTOFHEALTH,EDUCATION,ANDWELFARE P ublicHealthServiceCenterforDisceseContro lNationalInstituteforOccupationalSafetya ndHealthDivisionofPhysicalSciencesandEng ineeringCincinnati,Ohio45226 March1976 ForalllebytheSuperintendentofDocuments, , , , , , (NIOSH)76-179iiACKNOWLEDGDAENTSW eacknowledgewithgratefulappreciationthea ssistanceprovidedbytheAmericanFoundrymen 'sSocietyandTheAmericanIronandSteelInsti tute,a l'OUSmanufacturersofabrasl'veblastl'ngeq ul'pment, ,v rEngineeringBranch,DivisionofPhysicalSci encesandEngineering, ~~ ~itsinblastcleaningroomsHand-operatedcab inettypeblastcleaningmachinesAutomaticbl astcleaningmachLTlesWeiblastcleanL~ ~.

2 2 SpecificmhC~ ') ,000abrasiveblastersareexposedtosilicadu st,inhalationofwhichcanleadtosilicosis, ; blast. mach. type 107 Generalsafetycontrols125involved;methods toidentifyhazards; , **vi** ,Education,andWelfare'sNationalInstitute forOccupationalSafetyandHealth(NIOSH) , , ,ontheaverage, (ThresholdLimitValue) ,suchasopen-airabrasiveblasting, ;thepotentialsafetyandhealthhazardsinvol vedinthesepractices; :Abrasiveblastingcanbedefinedasaprocesso fcleaningfu~dfinishingofmaterialsbyforce fuldirectionofanabrasivemediaappliedeith erdryorsuspendedinaliquidmedium, **CURRENTMETHODSANDOPERATIONS cleanasurfacebyremovingunwantedrust,scal e,paint,etc.

3 ,inpreparationforpainting,anodizing,weld ing,orotherprocesseswhichrequireacleansu rface;deburr,removetoolingmarks,orotherw isefinishacrudeproduct;changemetallurgic alpropertiesorstressrelieveapartbythepee ningactionofmultipleimpactions;producead esiredmatteordecorativefinish;provideact ualcuttingorinscribingofpartiallymaskedp arts,suchastombstones,or;remove"flashing ll(excessmaterial) ~IOSH surveyundertakenfordevelopmentofthepUbli cation"AbrasiveBlastingRespiratoryProtec tivePractices"--andreferencedhereafteras litheNIOSH surveyll--indicatethatabrasiveblastillf. ! ~gtec~~iquesincludemaso~ry(brick,stone,c oncrete,etc.),sfu,dcastings,alwminum,cop per,brass,WOOd,glass, ~dsessentiallyonthenatureoft~esurfaceinv olved(includingitspre-cleanedsurfacecond itionwhichmayincludebeingcoveredbypaint, rust,etc.)

4 ,thetypeoftreatmentdesired(cleaning,debu rrL~g,etc.) ~ncompetitiveprocessesofpickling,electro chemicalcleaning,orhandfinishing, ,equipmentinvestmentisnotsUbstantiallyin fluencedbymodelchanges,operationalproced ures,orpersonnelturnover;trainingofopera torstakesplaceinaminimumamountoftime,and inmanycases--theabrasivemedia,orsubstant ialportionsofthem, ,shipyards,steelfabricationplants,specia lpurposejobandmachineshops,gastransmissi onstations,steelmills,structuralsteelsup plyyards,buildingcleaners,wineries,brewe ries,canneries,rubbermanufacturers,paint ingcontractors,plasticmanufacturers,weld ers,woodshopsandfurnituremanufacturers,p latingandanodizingshops,aircraftmanufact urers,electronicmanufacturers,petrochemi calcompanies,memorialmonumentmarkers, :Therearetwomethodsusedfordry-blastclean ing; , , (seeFigure11-1) ,generallyairwashedandgraded.

5 Orubbermatsoftenareusedonworktablestocus hiontheimpactanddippervalvewhichmeterst 'lC',0::oQ)t:>V'l,_JV'l-0':':.. )Q)Q). ,,-~o~3'Vi001+=..(1). :,,-~ZVi:2=>0w:r:Z::;-'Cf:.~ww4:0:r:w-'~ ~ 'a=> )wZw=> , ,abrasivevelocity(approximately250feetpe rsecond) , , ,andtocleanstripsteelandautomotivecranks hafts,axleshafts, :Indirectairpressureblasting,theabrasive isfedfromapressurizedcontaLier(pressurev essel)intoablasthose, (usually80to90psi)toboththehoseandpressu revesselareequalthuspermittingthefreefal loftheabrasivethroughanaperture(feedpoin t) ~~ , ~~~~!:~f~=1~C~fr~o~m~compressor,Controll inefilterTankremains~underpressure~atall times; ,SanFrancisco, ,~henabrasivebein gusediseXhsusted, sthenexhaustedfromthepressur evesse~and,whenitreacheszeropressure,the fillervalvedro~ssot !

6 Nductjon-SiphonMethod:Theblastgunofinduc tion-siphonequipmentisconnectedtoacompre ssedairpipeandaflexiblehoseYihichcarries t ::~ATM05PI1[f',j(A "EfA~~~~~,.:"- ' .AGRASIVEHOPPErIgunwhereitispropelledthr oughthenozzlebythejettheabrasivehosecrea tesapartialvacuuminthehoseofthemachineho pper(seeFigure11-3).Asaresult, ,inturn,drawsorinducestheabrasiveintothe Therubberabrasivefeedhoseisusuallysix-to eight-feetl ,Figure11-3:Conne ctionofAbrasiveFeedhosetotheAb rasiveHopperpassesthrought heblastnozzlebutdoesnotreachthefullveloc it yoft heabrasiveleavingt henozzleisapproximately40%of - 9 widerangeofhand-operatedabrasiveblastin heyalsoareusedincon-:,inuousoperationaut omatice quipment,theyaregenerall ylimitedtoapplic ationofl i :Induction-gravityequipmentisverysimilar toinduction-siphonequipmentinthatalIgunl lisusedtomixairandabrasivemedia(seeFigur e11-4).)]

7 Withinduction-gravityequipment,however, , '.BLASTUNITBODYBLASTNOULEABRASIVEFEEDTUB ECO : ,eventhoughtheyallc ! , :Wetblastinginvolves:1i~h-velocity, , . ,take-offconveyors, ,horizontalplaneturntable,shuttlewithrai lorcarextensions,chainorbeltconveyors,se lf-containedturningmechanismsdesignedfor shaftsandtubularparts, , (seeTable11-1)thats&~ ,steelgrit,aluminum,flint/garnet,glassbe ads,carbides,slag,andorganicmaterials( ,groundcorncobsandcrushedpecanshells).Ab rasiveBlastingEquipmen~ fabrasiveblastcleaningsystemsnowincommon useare:portableblastcleaningma(?hines;ha nd-operatedunitsinblastc1eaI"lingrooms;- 13-TABLEII-ITheNIOSHS urveyResultsbyAbrasiveUsehand-operatedca binet,--cypeblastcleaningmachines;automa ticblastcleaningmachines,andwet- (Figure11-5):Portableblastcleaningmachin esgeneraRlyrequireahigh- volumeairsupply(usuallyintheAbrasiveSand SteelShotSteelGritAluminaFlint/GarnetGla ssBeadsCarbidesSlagOrganics(Cobs,PecanSh ells,etc.)))

8 TotalNumberReported% 'ange);acontain e rorpressurevesseltocontaintheabrasive; a meteringdevicetocontrolair-to-abrasivera tioandflow; aflexibl ehosetodelivertheabrasive,andahand-heldn ozzlet oaimtheabrasiveO:cl~ "pot " machineshavecontr olswhichstartandstopoperationsbyuseofafl owcontrolvalveora"deadman" ,themachinestartsandtheairandabrasivemix tureise heoperatorreleasestheflowcontrolvalve, (NIOSH)74-104-14-intothedryblastdischarg e.'l'hewatersaturatestheabrasiiTeandthus convertsadryblastoperationintoa i t sinBlastCleaningRooms(Figure11-6):Althou ghhand-operatedunitsinb lastcleaningroomsusuallyusealargehopperf orstorageofabrasive,t heunitsthemselvesareessentiallysimilar-1 5-FIGURE11- 5 PortableBlastCleaningUnit C1ementina, , (1)abilitytoprovideanduseadustcontrolven tilationsystem,(2)costsavingsfromrecycli ngtheabrasive,and(3) (inoneofthenation'slargershipyards) , ~chines(Figure11-7) ,semi-automatically, , CourtesyofWheelabrator Frye, ~ ,theabrasive-to-waterratiousuallyis25% (Figure11-$) ~ , ,SwingTableBlastCleaningMachine-20--21- ,heavy-dutycompressorsand0' (300everyfiveminutes).

9 (Figure11-9):passedthrougha ,wet, , ,specialpurpose(whichisrecycleduntilitca nnolongerbeused). :3-Someofthenewerwater-jetblastcleani ,awaterfilter ,apressuregauge, f 4t 'It_191wae rpressuresplaceconsiderablestr a i lizealimitedsupplyofabrasivedrawnfromano pensupplyht' , ,however,numeroushazardscanbegreatlymini mizedifnoteliminatedaltogetherbyapplying mownoperatingandmaintenancetechniquesand engineeringcontrols, ,noiseandchemical& :Dustsresultfrombroken-downabrasives,pUl verizedsurfacecoatingsandencrustedsubsta nces,andabradedmaterialfTOmtheobjectbein gblasted,Thesolidparticleswhichcompriset hedustsrangeinsizefromlessthanonemicron( 1/25,000inch) , ~ (Si02) }aslowlydevelopinglungdiseasewhichoftenl eadst odeathyearsafterexposurehas~ (referredtoearlier)showssandtobefarandaw aythemostcommonlyusedabrasiveandthatexpo suretosilicadustinmanyoftheindustriesinv olvedisext~emelyhigh(seeTableIII-I).

10 Anotherserioushealthhazardiscreatedwhent oxicmetalsoralloyscontainingtoxicmetalss uchaslead,cadmium, ~sarenotgenerallyinvolved,italsoshowedth atmanyofthematerialscleanedarelikelytobe coatedbypaintorothersubstanceswhichcould containsuchmetalsorothertoxicsubstances( seeTable111-2). }ears}noseandthroatandcancause,attheleas t, , ;throughingestion(eatingdust-affectedfoo ds),and(rarely) ) 'drla:l.> <P::1H+-'~ooH+-'(f) (.)oorloorlH+-'C/) or--rl Q)rloH+-'Q) '0o~ ~tlc:ou-27-rl(V\ )c:J5oC/)"Becausedustalsoisairborne,heav yconcentrationsmayaffectthosenearthework areaaswellasthoselocatedatevenarelativel yremotedistance,dependingontheventilatio nsystemor,inthecaseofopen-airblasting,pr evailingwindconditions,humidity, ,infact, , , ,particlesonceagainbecomeairborneexample ,unprotectedworkersfrequentlyaregiventhe taskofbeatingandcompositionofblastingare a,thetypeofequipment(includingareas,neit herofwhichenableseasyconfinementorcontro lofdustnozzle)involved,theangleofworkpie ce,andsoon.