Aerosol production during autopsies

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Delft University of Technology

Aerosol production during autopsies

The risk of sawing in bone

Pluim, Jip M.E.; Jimenez-Bou, Lucas; Gerretsen, Reza R.R.; Loeve, Arjo J.

DOI

10.1016/j.forsciint.2018.05.046

Publication date

2018

Document Version

Final published version

Published in

Forensic Science International

Citation (APA)

Pluim, J. M. E., Jimenez-Bou, L., Gerretsen, R. R. R., & Loeve, A. J. (2018). Aerosol production during

autopsies: The risk of sawing in bone. Forensic Science International, 289, 260-267.

https://doi.org/10.1016/j.forsciint.2018.05.046

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Aerosol

production

during

autopsies:

The

risk

of

sawing

in

bone

Jip

M.E.

Pluim

a,b,1,

*

,

Lucas

Jimenez-Bou

a,1

,

Reza

R.R.

Gerretsen

a

,

Arjo

J. Loeve

b,c

a

DepartmentofForensicAnthropology,NetherlandsForensicInstitute,LaanvanYpenburg6,2497GBTheHague,TheNetherlands b

DepartmentofBioMechanicalEngineering,FacultyofMechanical,MaritimeandMaterialsEngineering,DelftUniversityofTechnology,F-0-200,Mekelweg2, 2628CDDelft,TheNetherlands

c

CovanLedden-HulseboschCentrum,ScienceParkBuilding904,1098XHAmsterdam,TheNetherlands

A R T I C L E I N F O

Articlehistory: Received7April2018

Receivedinrevisedform8May2018 Accepted26May2018

Availableonline6June2018

Keywords: Aerosol Bonedust Oscillatingsaw Autopsy Pathology Biosafety A B S T R A C T

Whensawingduringautopsiesonhumanremains,ﬁnedustisproduced,whichconsistsofparticlesof sizesthatmayfallwithinthehumanrespirablerange,andcanactasvectorsforpathogens.Thegoalof thisstudywastoexplorethepotentialeffectsofsawbladefrequencyandsawbladecontactloadonthe numberandsizeofairborneboneparticlesproduced.Themethodologyinvolvedtheuseofanoscillating sawwithvariablesawbladefrequenciesanddifferentsawbladecontactloadsondryhumanfemora. Released airborne particles werecounted per diameterbya particle counter insidea closedand controlledenvironment.Resultscorroboratedwiththehypotheses:higherfrequenciesorlowercontact loadsresultedinhighernumbersofaerosolparticlesproduced.However,itwasfoundthateveninthe best-casescenariotestedondrybone,thenumberofaerosolparticlesproducedwasstillhighenoughto provideapotentialhealthrisktotheforensicpractitioners.Protectivebreathinggearsuchasrespirators andbiosafetyprotocolsarerecommendedtobeputintopracticetoprotectforensicpractitionersfrom acquiringpathologies,orfromotherbiologicalhazardswhenperformingautopsies.

1.Introduction

Autopsies are surgical procedures performed in thefield of pathology that are used to find a deceased person's cause or mannerofdeath.Different diagnosesaskfordifferent examina-tions,someofwhichrequiringincisionsinsuperficialtissuesto provideaccesstodeeperinternaltissuesofthebody.Sinceforensic practitionersaregenerallyawareofpotentialhazards,protective clothingisusedandprotocolsarefollowedtominimisecontact withpathogens[1,2].Somecontaminationroutesmayseemmore obviousthanothersduetoexplicitinteractionwithcontaminants, such as through cuts by scalpels or punctures with needles. However, inhalation of infectious airborne particles during an autopsycouldbeasharmfulasanaccidentalcut[2–4].Powered surgical instruments, such as saws and drills, are greatly responsiblefor aerosolisation(solidorliquidairborneparticles) ofbodytissues,exposuretotheseaerosolsmaybeconsideredan oftenoverlookedcontaminationroute[5,6].

Oscillating saws are routinely used during autopsies, when forensicpractitionersarerequiredtomakedeepincisionsthrough boneorcartilagetissues,oscillatingsawshaveanadvantagedueto anincreasedeaseof useand accessibilitycompared tohand or bandsaws.Thereishoweveraconcernabouttheproductionof suspendedparticles(aerosols)whenoperatingthesaw.Aerosols producedbysawingcanbedispersedwideinthesurroundingsof thesiteofoperation,possiblyreachingtherespiratorytractofthe operator [5,7–9]. The aerosol's particle size determines the potentialinvasiondepthoftheaerosolintheinhaler'srespiratory tract,asreported in[3],and canpossiblyact asa pathwayfor hazardousdiseases[10].Forexample,forparticlesof0.1

m

mabout 2.1% will only reach the head airways, 2.7% will reach the tracheobronchial regionand 14% willend upinthealveoli.For particlesof10

m

mthiswouldbe81%,1.5%and1.9%,respectively. Particlessmallerthan10

m

marewithintherespirablerange[3]

and havethepotentialtoremainsuspended in theairfor long periodsoftime,increasingthetimeduringwhichtheairaround theworkingareaiscontaminatedwithpossiblyinfectiveaerosol

[9]. Among the hazardous pathogens are Hepatitis B and C, Streptococci,andHumanImmunodeﬁciencyVirus(HIV),ofwhich transmissionshavealreadybeenrecordedduringautopsysessions

[11–14].Wheninhalingsuchpathogens,aminimalinfectivedose (MID)isrequiredtoactuallyproduceaninfection.Mostrespiratory virusesappeartohaveinfectiouspotentialinhumansevenwith

*Correspondingauthorat:DepartmentofForensicAnthropology,Netherlands ForensicInstitute,LaanvanYpenburg6,2497GBTheHague,TheNetherlands.

E-mailaddresses:jip.pluim@gmail.com(J.M.E. Pluim),lukebou.lb@gmail.com

(L.Jimenez-Bou),r.gerretsen@nﬁ.minvenj.nl(R.R.R.Gerretsen),a.j.loeve@tudelft.nl

(A.J. Loeve). 1

Theseauthorscontributedequallytothiswork.

https://doi.org/10.1016/j.forsciint.2018.05.046

ForensicScienceInternational289(2018)260–267

ContentslistsavailableatScienceDirect

Forensic

Science

International

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lowdoses[15].ConcernalsoemergestowardsunknownMIDs,as thisservesasmotivationforprophylaxis,seeTable1.

The goalof this study was to investigate the production of aerosol when sawing dry long bones under different sawing conditions,simulatinganautopsyprocedure.

2.Materialsandmethods 2.1.Experimentalsetup

Acustomsetupdesignedforease-of-useandcleanabilitywas manufactured.Intheexplanationofthesetupbelowtheletters usedtorefertospecificpartscorrespondwiththoseinFigs.1–3. Anoscillatingsaw(DeSoutterNS3,DeSoutterMedicalLimited) (a),withabladeof76mmindiameter(DeSoutter16892,DeSoutter Medical Limited), fixed toa sliding platform (b) by a 12536 40mmaluminiumblockwithacylindricalholethediameterof the saw handle. The platform housed three cylindrical brass cylindersthatslidalongthree20mmdiametersurgicalstainless steelrods(c)actingasguides, allowingthesawtofreelymove verticallywitharangeof270mm,whilebeingfixatedintheother planes.Thebonespecimen(d)wasfastenedina705060mm aluminiumblockwithav-shapedgrooveinitsbase.Anu-shaped clampwithathreadedboltclampedthefemurintothev-groove, securingittothesetup(e).Boththev-grooveblockandthesteel rods were fixed to a 440260mm aluminium base plate (f). Interchangeableweights(g)wereusedtovarythecontactloadof thesawbladeagainstthebonespecimen.

Thesawingdepthofthesawblade(h)wascontrolledtoalways be10mmbya depthcontrolstopper(i)placednexttothesaw blade. Thestopper consistedof a 3mm thick,66mm diameter (10mmlessthanthesawbladediameter)roundaluminiumplate.

Fig.2showsthesawbladeandstopperreachingthepresetlimit afteracut.Acustom-builttachometer(j)usingahall-effectsensor (GeartoothspeedsensorGS100701,ZFElectronics)wasclampedto thesawwitha504020mmaluminiumblock(k),andwasused toaccuratelysettheinitialfrequencyineachexperiment,aswellas to observe the frequency change during sawing. Due to the resistanceoftheboneagainstthesawit wasexpectedthat the sawingfrequencywoulddropduringsawing.Aclose-upviewof thesawbladeisshowninFig.2.

Thewholeplatformwasplacedinsideanacrylicglassbox(l)of 780470500mm,asshowninFig.3.Anentrancehole(110mm diameter)(o)inthesideoftheboxprovidedaccesstothesetup withouthavingtoopentheboxandcauseanydisturbanceduring

Table1

SizesandMinimalInfectiveDoses(MID)ofzoonoticpathogens.CourtesyofWenneretal.[7].

Microorganism Pathogen Size MinimalInfectiveDose

Viruses InﬂuenzaA 120nm Unknown

Lyssa(rabies) 65180nm Unknown

Avula(NDV) 150–250nm Unknown

Herpesvirus(eg,herpesB) 150–200nm Unknown(CHV-1) Coronavirus(eg,SARS-COV) 80–160nm Unknown

Bacteria Mycoplasmasp. 0.05–0.50.3–2mm <100CFU(M.pneumoniae) Francisellatularensis 0.2–0.70.2mm 5–10organisms Brucellasp. 0.5–0.70.6–1.5mm Unknown Coxiellaburnetti 0.2–0.40.4–1mm 1–10

Staphylococcussp. 0.5–1.5mm >1,000,000(S.aureus) Streptococcussp. 0.5–1mm Unknown

Mycobacteriumtuberculosis 0.2–0.61–10mm <10bacilli Bacillusanthracis 0.4–1.80.9–10mm 8000—50,000 Leptospirainterrogans 0.16–12mm Unknown Salmonellasp. 0.75–1.52–5mm 103_–105 Escherichiacoli 0.6–11.2–3mm 10EHEC106

EPEC108 ETEC Yersiniapestis 0.5–0.81–3mm Unknown

Fungi Histoplasma 2–4mm,8–15mm 5yeastcells

Aspergillussp. 3–8mm Unknown

Cryptococcus 3–5mm Unknown

Parasites Toxoplasma 10–12mm <10sporulatedoocysts(T.gondii) Echinococcussp.(eggs) 3427mm Unknown

CFU,colony-formingunits;CHV-1,CercopithecineHerpesvirus-1;EHEC,EnterohemorrhagicE.coli;EPEC,Entero-pathogenicE.coli;ETEC,EnterotoxicE.coli;NDV,Newcastle DiseaseVirus;SARS-CoV,SARSCoronavirus.

Fig.1.Experimentalsetup used to cut thebone, the setup consisted of: an oscillatingsaw(a)fastenedtoaverticalslidingplatform(b)guidedby3stainless steelrodsandbrassslidingbearings(c).Thebonespecimen(d)wasclampedina v-groove holder (e), that was connected to an aluminium base plate (f). Interchangeableweightscouldbeattachedtotheplatform(g).Thesawingaction isfurtherillustratedinFig.2.

Fig.2. Close-upofthesawbladeandbonespecimen,thesetupconsistedof:the bonespecimen(d)wasclampedinplacebythev-grooveholder(e).Thesawblade (h)cutintheboneuntilthestopper(i)reachedtheboneforaconsistentdepthof cut.TheHall-effectsensor(j)actedasatachometer,andwasclampedtothesaw withanaluminiumblock(k).

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themeasurements.Whentheentranceholeisnotused,alidwas used to seal it. By conducting the experiment inside a closed environment,theinvasionofforeignaerosolwas minimised,as wellastheleakageofproducedparticles,andthedisturbanceof anyairﬂowfromexternalinteractions,suchasfromresearchers walkingby.Also,itwasmuchmorefeasibletocleantheinsideof theboxthananentireautopsyroom.

Thenumberofaerosolparticlespresentintheairintheboxwas measuredusingaFluke985particlecounter(Flukecorporation, Everett,WashingtonUSA)(m),showninFig.3.Theparticlecounter wasplacedontopoftheboxwithafoamcasttoholditinplace.A small hole in the acrylic glass provided access tothe particle counter'ssensor.Thedistancebetweenthebonespecimenandthe particle counter's sensor was about 450mm, to replicate the breathingzoneofthesawoperator.Particleswerecountedata ﬂowof 2.83l/min sixdifferentsizes: 0.3,0.5,1.0, 3.0,5.0, and 10

m

m.Itwasdecidedthatsizesover10

m

mwerenotofrelevance tothecurrentstudy,asparticlesofthesesizesaremostlikelyto depositintheheadairwayregionoftherespiratorytract,whereas smaller particles will primarily deposit in the alveoli (see Introduction)[3,5,12,16].

Twohumanfemorafromanarchaeologicalbonecollectionof theNetherlandsForensicInstitute(TheHague,theNetherlands) wereused.Thefemuris alongtubularbone withareasonably consistentcortexthickness,andmorphologyalongtheshaft.Both femorawereindryconditionandcleanofanysofttissues.Forthis experiment,thebonemarrowcavitiesofthefemorawerescraped to remove gross trabecular bone tissue, together with other residuesthatcouldeasilyshakelooseduringcuttingandinterfere asunwantedsuspendedparticles.

2.2.Experimentaldesign

For this study, two hypotheses were formulated: H1, the frequencyofthesawbladehasapositiveeffectonthenumberof aerosolparticlesproduced.H2:thecontactloadofthesawblade hasanegativeeffectonthenumberofaerosolparticlesproduced. Itwashypothesisedthatbyincreasingthefrequency,orlowering the contact loads, a relative small amount of new bone is encounteredbytheteethofthesawblade,removinglittlebone, producingasmoothercutwithmoresuspendedﬁneparticlesand

lesscoarseheavydust.Reversely,itwashypothesisedthatwith lowerfrequencyorhighercontactloads,arelativelylargeamount ofnewboneisencounteredbytheteethofthesawblade,breaking off bigchunksof bone,resultingin a roughercut, morecoarse heavydustandlesssuspendedﬁnedust.

Theexperimentwassetupsuchthatsawbladefrequencyand sawbladecontactloadweretheindependentvariables,andthat thenumberofaerosolparticlesproducedduringsawing,wasthe dependentvariable.Threedifferentvalueswereselectedforboth sawbladefrequencyandsawbladecontactload.Athreebythree experimentalcondition(EC)matrixwasmade,asshowninTable2. Thevalueschosenrepresentarangeofloadsandfrequenciesused inpractice,asfoundduringapilottestwithforensicpractitioners. Atotalof90cutsweremade,withn=10foreachEC.

Theloadexertedbythesawonthebonewas setbyadding dumbbell weights of 1 or 2kg (actually 1.003 and 2.004kg respectively)tothesawplatform,whichtogetherwiththesawand itsclamping blockweighed 3kg.This resultedin threecontact loadsthatweretested:3kg,4kg,and5kg.

The saw blade frequency was setusing an external control panel.Byturningapotentiometeranyfrequencybetween30Hzor 250Hzcouldbechosen.Thesawbladefrequencieschosenwere 150Hz,200Hz,and250Hz.

Othervariablesthatwereobservedandnoteddown; tempera-ture,humidity,residualandforeignaerosols,boneweightbefore andaftercutting,andthesawbladefrequencyduringcutting.Any potentialeffectsofbonepropertiessuchasmechanicalproperties, surfacetopography,marrowcavity,cortexthicknessanddensity, andsaw bladewearandany unknownchangesover timewere considered tobe averaged out bycreating a randomised block experiment.

Fiveblocksof9cuts,withtoeachrandomlyassignedoneofthe 9experimentalconditions,weremadeoneachofthetwoselected humanfemora.Penmarkings weremadeonthebonespriorto sawingtoprovidevisualguidanceduringthetests(seeFig.4).Each cutwasspaced5mmfromitsneighbouringcuts.Thisdistancewas safeenoughtoavoidﬂaking,bendingorcrackingofthebonecortex duringsawing.Blockswerespaced10mmsotheycouldbeeasily distinguished.Thetotalof10blocksprovidedthe10repetitionsof allECsandwithineachblocktheECswererandomised.

Eachcutwascodedusingthetemplate[Bonetype][BoneID] [Block][ECCutnumber]toeasilyidentifyandrecordthetestruns. ThetwofemoraweregiventheIDsAorB,markedonthebackof thebone,eachblockwasnumbered1to5onthesideofthebone, andtheexperimentalconditionswerenumbered1.1to3.3onthe frontsideofthebone.Asanexample,acutinfemurAblock2with experimentalconditionnumber3wascodedasFEM-A2.3. 2.3.Experimentalprotocol

2.3.1.Sawingprotocol

Thefemurwasinsertedandfastenedsothesawbladelinedup withthe preparedpenmarkingon thebone. Following theEC number,thedesiredfrequencywasselectedwiththeuseofthe tachometerandthesawcontrolpanel,andweightswereaddedto theslidingplatform.Theboxwasclosedwiththeparticlecounter

Fig.3.Frontviewofthesetupenclosedinthebox;anacrylicglassbox(l)wasused tocreateanexperimentalspaceisolatedfromtheenvironment.TheFluke985 particlecounter(m)wasplacedontopoftheboxwithafoamcast,withthenozzle insertedintotheboxthroughaholeontopofthebox(n).Aclosableholewitha socketedcapwasusedforhandlingthesawduringoperationsinsidethebox(o).

Table2

TheExperimentalCondition(EC)matrix.EachnumberrepresentsanEC,i.e.a combinationofsawbladefrequencyandsawbladecontactload.Thenotation correspondswiththesamplenotationmadeontheboneshaft,asseeninFig.4.

150Hz 200Hz 250Hz

3kg EC1.1 EC1.2 EC1.3

4kg EC2.1 EC2.2 EC2.3

5kg EC3.1 EC3.2 EC3.3

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placedontop.Room temperature,roomrelativehumidity, date andtimewererecorded.Theparticlecounterprotocolwasstarted, asdescribedbelow.AtthestartofM1thesawwaslifted,switched onandgentlybroughtdowntocontactthefemurandthenleftto freelymovedown,untilthestopperhitthesurfaceofthefemur. Thenthesawwasswitchedoff.Thetimebetweenthestartingof thesaw,andthemomentthestopperhitthebonewasrecorded. After the particle counter protocol was ﬁnished, the cleaning protocolstarted,asdescribedbelow.

2.3.2.Particlecounterprotocol

The Fluke 985was programmedfor 7 measurements of 60 secondseach.EachmeasurementwascodedasM0,M1,...,M6. Thebasemeasurement(M0)recordedthebaselevelsofparticles alreadysuspended insidetheboxdirectlyafterclosing thebox. Thiscouldinclude bothresidualaerosol fromprevioustests,or foreignaerosolfromtheroomorthecleaningprocess.Including the sawing process described earlier, measurements M1-M6 recorded the suspension and settling down of particles from sawing.Aftereachtestrun,theparticlecounterwaspurgedusing themanufacturer'sﬁltertoguaranteethatresidualparticlesinthe particlecounterwerenotcountedagain.

2.3.3.Cleaningprotocol

OncemeasurementM6wasﬁnished,theinsideoftheboxwas vacuumedfor1minuteviathesideopeningoftheboxtoavoid scatteringofunwantedparticlestotheoutsideenvironment.Next, the box was lifted, the bone specimen was removed from the clamp,vacuum cleanedto remove residualdust and weighted. Boththeboxandthesetupwerevacuumcleanedandwipedoff using fresh multi-purpose disinfectant wipes, so all residual particleswereremoved.Boththeboxandsetupweredriedwith kitchenpaperandfurtherlefttoair-dryfor2minutes,afterwhich the sawing protocolfor the next run could start. Pilot testing showedlesssuspendedﬁnedustparticlesintheboxaftercleaning, thanpresentintheenvironmentoutsidethebox.

2.4.Dataanalysis

Statistical analyses were performed in three parts using MATLAB(MATLAB 2014a,TheMathWorks Inc.).First for oneof eachoftheproducedindividualparticlesizes(0.3,0.5,1.0,2.0,5.0, and 10

m

m), then for the total number of produced aerosol particles,and ﬁnally for thetotal surface areaof theproduced aerosol particles. In all analyses the production of aerosol was summedoverthe6minofmeasurements(M1toM6)fromthe moment the saw was commenced. The base level (M0) was subtractedtoseparatethebackgroundaerosolfromtheaerosols

thatwereactuallygeneratedbysawing.Theeffectsofsawblade frequencyandsawbladecontactloadwereanalysedusinga two-wayANOVAtoevaluatetheireffectsontheproductionofaerosol. Effectswereconsideredsigniﬁcantwhenp<0.05.

By summationof thenumberofparticles producedforeach individualparticlesize,thetotalnumberofproducedparticlesper EC was calculated. By summation of the number of particles produced foreachparticlesize,multipliedbythesquareofthe particle's size times pi, the total surface areaof the produced particlesperECwerecalculated.Thiscalculationassumesthatthe particlesareperfectspheres,foranyothershapesthetotalsurface would bebigger,buttheratiobetweentheECswould staythe same.

3.Results

3.1.Individualparticlesizes

Stackedbargraphsforeachofthe6particlesizesareshownin

Fig.5.Forallcutsthenumberofsmallerparticlesoutrankedthe number of bigger particles. The mean numbers and standard deviationsoftheindividualsizesofaerosolparticlesproducedper eachexperimentalconditionareshowninTable4.

A cleartrend was visible in theresultsof all theindividual particlesizes,exceptforthe10

m

mparticles.Thehighestnumber ofaerosolparticleswasconsistentlyproducedinEC1.3,withthe highesttestedfrequency(250Hz)andthelowesttestedcontact load(3kg). Thelowestnumber ofaerosol particles was consis-tently produced in EC 3.1, with the lowest tested frequency (150Hz) and the highest tested contact load (5kg). This only deviated for particle size10

m

m, where the highest number of particleswasfoundatEC1.2(200Hz,3kg),andthelowestnumber ofparticlesatEC3.2(250Hz,5kg).

Thetwo-wayANOVAshowedsigniﬁcanteffects offrequency andofcontactloadonthenumberofaerosolsparticlesforparticle sizes0.3,0.5,1.0and2.0

m

m(p<0.001).Forparticlesize5.0

m

m the effects werealso signiﬁcant for frequency (p=0.0096) and contactload(p<0.001).Forparticlesize10.0

m

monlytheeffectof contactloadwas statisticallysigniﬁcant(p<0.001),theeffectof frequencywasnot(p=0.21).Theinteractioneffectwasinallcases not statisticallysigniﬁcant. Table3 showsanoverviewofall p-valuesfortheeffectsoffrequencyandcontactloadaswellasthe interactioneffect,forallparticlesizes.

3.2.Totalproducedparticles

By summation of the number of particles produced in all particlesizes,thetotalnumberofproducedparticlesperECwas

Fig.4. Topviewofoneofthefemorathatwasusedintheexperiment.Thenotationsoftherandomisedexperimentalconditionnumbers(EC1toEC9)areshownasused duringtheexperiments,dividedin5blocks.TheECnotationwaschangedtoamatrixnotationaftertheexperimentsforreasonsofvisibility:EC1ischangedto1.1,EC9to3.3, andcorrespondstotheECmatrixshowninTable2.

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calculated,asshowninFig.6.Bymultiplyingthesquareofeach particlesizewithpiandthenumberofparticlescountedforthat size,andsummingtheseproductsforallparticlesizes,thetotal surface area of the produced particles per EC was calculated,

showninFig.7.Themeannumbers,standarddeviationsandthe maximum and minimumvalue of thetotal number of aerosol particlesproducedpereachexperimentalconditionareshownin

Table5,themeannumbers,standarddeviationsandthemaximum

Fig.5.Stackedbargraphsofthenumberofaerosolparticlesproducedperexperimentalcondition(markedcolumns)duringthetotalofn=10measurements(coloured layers)foreachparticlesize(0.3mmtopleftto10mmbottomright).EachlayercorrespondswithoneblockofECs,thebottomlayerswerefromBlockA.1,thetoplayersBlock B.5.Notethatforreasonsofvisibility,theverticalaxesarescaleddifferentlyforeachparticlesize.(Forinterpretationofthereferencestocolourinthisﬁgurelegend,thereader isreferredtothewebversionofthisarticle.)

Table3

p-Valuesoftheeffectsofsawbladefrequencyandsawbladecontactloadonthenumberofaerosolparticlesproduced.Signiﬁcantvaluesaremarkedinitalics. Numberofparticlesproducedofparticlesizes Totalnumberofparticles

produced

Totalsurfaceareaofparticles produced

0.3mm 0.5mm 1.0mm 2.5mm 5.0mm 10.0mm

Effectofsawbladefrequency p<0.001 p<0.001 p<0.001 p<0.001 p=0.0096 p=0.21 p<0.001 p=0.027 Effectofsawbladecontact

load

p<0.001 p<0.001 p<0.001 p<0.001 p<0.001 p<0.001 p<0.001 p<0.001 Interactioneffect p=0.37 p=0.40 p=0.36 p=0.37 p=0.56 p=0.70 p=0.38 p=0.63 264 J.M.E.Pluimetal./ForensicScienceInternational289(2018)260–267

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andminimumvalueofthetotalsurfaceareaofparticlesproduced areshowninTable6.

Stackedbargraphsofthetotalnumberofparticlesproduced, andtotalsurfaceareaoftheparticlesproducedshowsimilartrends astheresultsforindividualparticlesizes0.3to5.0

m

m,thehighest numberofparticlesisfoundatEC1.3(250Hz,3kg),thelowestat EC3.1(150Hz,5kg).

Theresultsofthetotalnumberofparticlesshowedsignificant effects of frequency and contact load (p<0.001). Similarly, the resultsofthetotalsurfaceareaoftheparticlesproducedshowed significant effects for frequency (p=0.027) and contact load (p<0.001).Theinteractioneffectwasinallcasesnotstatistically significant.Table3showsallp-valuesfortheeffectsofsawblade frequencyand sawbladecontactloadaswellastheinteraction effect,forthetotalnumber ofparticlesproduced, andthetotal surfaceareaoftheparticlesproduced.

3.3.Tachometerreadings

Themeasuredsawbladefrequencythroughoutthecuttingof theboneshowedadrop,asseeninFig.9.Theresistanceonthesaw bladewhenincontactwiththebonesurfaceseemedtohamper with the torque of the oscillating saw's engine. At higher frequenciesthedropsseemedbiggerthanwithlowerfrequencies, whereas higher contact loads used in a given frequency signiﬁcantlyincreasedthedropin frequency(two-wayANOVA, p<0.001).

3.4.Sawingtime

A signiﬁcanteffectfor bothsaw blade contactloadandsaw bladefrequencywasfound(p<0.001):asthesawbladefrequency orsaw bladecontactloaddecreased,thesawingtimeincreased (seeFig.8.Forreasonsofvisibility,inthisplottheECsarearranged inadifferentorderthanintherestoftheﬁgures).

4.Discussion

Oscillatingsawsareroutinelyusedduringautopsyprocedures, leadingtoproductionofconsiderableamountsofbonedust,and puttingforensicpractitionersandothersinvolvedatriskofbeing

Table4

Themeansandstandarddeviationsover10repetitionsforeachparticlesizeandallexperimentalconditions.

0.3mm 0.5mm 1.0mm 2.0mm 5.0mm 10mm

Mean SD Mean SD Mean SD Mean SD Mean SD Mean SD

EC1.1 3.47106 _0.283₁₀6 _3.18₁₀6 _0.395₁₀6 _2.56₁₀6 _0.437₁₀6 _1.99₁₀6 _0.420₁₀6 _0.775₁₀6 _0.235₁₀6 _0.322₁₀6 _0.111₁₀6 EC1.2 3.92106 0.182106 3.68106 0.240106 3.03106 0.272106 2.38106 0.268106 0.937106 0.149106 0.379106 0.0718106 EC1.3 4.33106 0.153106 4.07106 0.172106 3.34106 0.244106 2.62106 0.292106 0.980106 0.223106 0.376106 0.116106 EC2.1 3.32106 0.328106 2.98106 0.430106 2.35106 0.448106 1.80106 0.415106 0.691106 0.227106 0.281106 0.110106 EC2.2 3.59106 0.237106 3.26106 0.292106 2.59106 0.300106 1.97106 0.277106 0.720106 0.147106 0.279106 0.0705106 EC2.3 4.01106 _0.225₁₀6 _3.73₁₀6 _0.200₁₀6 _3.01₁₀6 _0.159₁₀6 _2.32₁₀6 _0.148₁₀6 _0.858₁₀6 _0.117₁₀6 _0.334₁₀6 _0.0686₁₀6 EC3.1 2.92106 _0.193₁₀6 _2.55₁₀6 _0.295₁₀6 _1.98₁₀6 _0.315₁₀6 _1.49₁₀6 _0.291₁₀6 _0.553₁₀6 _0.146₁₀6 _0.222₁₀6 _0.0622₁₀6 EC3.2 3.19106 0.192106 2.81106 0.269106 2.15106 0.289106 1.60106 0.272106 0.564106 0.150106 0.215106 0.0762106 EC3.3 3.51106 0.161106 3.11106 0.255106 2.39106 0.306106 1.77106 0.308106 0.618106 0.184106 0.238106 0.0906106

Fig.6.Stackedbargraphofthetotalnumberofaerosolparticlesproducedper experimentalcondition(markedcolumns)duringthetotalofn=10measurements (colouredlayers).EachlayercorrespondswithoneblockofECs,thebottomlayers werefromBlockA.1,thetoplayersBlockB.5.(Forinterpretationofthereferencesto colourinthisﬁgurelegend,thereaderisreferredtothewebversionofthisarticle.)

Fig.7.Stackedbargraphofthetotalsurfaceareaoftheaerosolparticlesproduced per experimental condition (marked columns) during the total of n=10 measurements(colouredlayers).EachlayercorrespondswithoneblockofECs, thebottomlayerswerefromBlockA.1,thetoplayersBlockB.5.(Forinterpretationof thereferencestocolourinthisﬁgurelegend,thereaderisreferredtotheweb versionofthisarticle.)

Table5

Means,standarddeviations,maximumandminimumnumbersoftotalnumberof particlesforeachexperimentalconditionover10repetitions.

Totalnumberofparticlesproducedduringsawing

Mean SD Maxvalue Minvalue EC1.1 12.3106 1.86106 14.8106 8.38106 EC1.2 14.3106 1.14106 16.4106 12.5106 EC1.3 15.7106 _1.04₁₀6 _17.3₁₀6 _14.1₁₀6 EC2.1 11.4106 _1.90₁₀6 _13.8₁₀6 _8.28₁₀6 EC2.2 12.4106 _1.26₁₀6 _13.9₁₀6 _9.59₁₀6 EC2.3 14.3106 0.667106 15.2106 12.9106 EC3.1 9.72106 1.27106 11.0106 7.27106 EC3.2 10.5106 1.20106 12.2106 8.66106 EC3.3 11.6106 1.22106 13.3106 9.94106

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contaminatedbypathogen-carryingaerosols.Aspreviousstudies have already demonstrated, there can be an alarmingly high productionofboneaerosolwhenusingoscillatingsaws[5,7,8,17]. Inthecurrentstudy,theeffectsofsawbladefrequencyandsaw bladecontactloadonaerosolproductionweredemonstrated.

Theresultssuggestthat,forallparticlesizes,contactloadsand sawingfrequenciestested,increasingthecontactloadexertedby thesawbladeonthebonehasaninverseeffectonthenumberof aerosol particles produced. The same effect was seen when consideringthetotalnumberofaerosolparticles,aswellasthe

totalsurfaceareaofaparticlesproduced.Analysingtheeffectof frequencyonparticleproduction,itwasdemonstratedthathigher frequenciesresultinahighernumberofaerosolparticlesproduced forthesmallerparticlesizes,exceptforparticlesofsize10.0

m

m. The deviating results for 10.0

m

m aerosol particles could be explained as these bigger particles are more susceptible to disturbances, such as air resistance. Therefore these bigger particles mighthavetaken moretime than smallerparticlesto evenlydiffusethroughouttheboxandreachtheparticlecounter. Among the selected frequencies and contact loads in the experimental conditionmatrix, EC 3.1 showed to be the most promising for minimising the number of aerosol particles produced.Theselectionoflowerfrequenciesinconjunctionwith highcontactloads showedtobetheoptimalsetting.Therewas howeveralimittothoseparameters,asitwasnecessarytoobserve the saw's torque threshold: frequencies lower than 150Hz or contactloadshigherthan5kgcouldleadtoenginehaltsorfailure tocutthroughthebone.Similarly,thecuttingtimewasaffectedby theusedsawbladecontactloadsandsawbladefrequency,which togetherwithapossiblechangeinqualityofcutcouldbeareason whyforensicpractitionersusethesesawingparameters.

Despite having produced the lowest number of aerosol particles,EC3.1stillgeneratedasigniﬁcantnumberofsuspended particles,averaginga total numberof 9.715106 _particles_over

16.98l of sampled air. Considering that in resting conditions humansbreatheabout6lofairperminute[18],thiswouldresult in the inhalation of 3.43106 _particles. _Together _with _[3]

observationsondepositionof aerosolin thehumanrespiratory track,differentamountsofparticleswillbedepositedindifferent partsoftherespiratorytract,allpotentiallyprovidinghealthrisks. Depending on a pathogen's survivability and the time period during which a person is in contact with the bone dust, it is plausibletoassumethatapathogencouldcauseaninfectiononits host,asseenby[15]and[7]instudiesonMinimalInfectionDose. Thetotalnumberofaerosolparticlesproducedisdominatedby theproductionofthe0.3

m

mparticles,asthey wereroughly10 timesmoreprevalentthanthe10.0

m

mparticles.Thestackedbar graphsofthe0.3

m

mparticlesandofthetotalnumberofparticles showsimilartrendsbetweenECs.Reversely,thetotalsurfacearea of the producedparticles was dominated by theproduction of 10.0

m

m particles, as their surface area is roughly 1000 times biggerthanthatofthe0.3

m

mparticles.Thestackedbargraphsof the10.0

m

mparticlesandofthetotalsurfaceareaofparticlesshow similartrendsbetweenECs.

The total number of particles produced is of interest as it indicatesa number of potentialpathwaysfor pathogens tothe humanbody.Similarly,thetotalsurfaceareagivesanindicationof thepossibleamountofpathogensthatcouldbeattachedtoone

Table6

Means,standarddeviations,maximumandminimumnumbersoftotalsurfacearea [m2

]oftheparticlesforeachexperimentalconditionover10repetitions. Totalsurfacearea[m2

]ofparticlesproducedduringsawing Mean SD Maxvalue Minvalue EC1.1 199106 60.110 6 277106 84.210 6 EC1.2 23610 6 38.3106 30010 6 18710 6 EC1.3 24310 6 58.3106 32210 6 15010 6 EC2.1 17610 6 58.710 6 273106 72.610 6 EC2.2 18110 6 _37.7₁₀6 ₂₃₃₁₀ 6 ₁₁₆₁₀ 6 EC2.3 21510 6 _31.8₁₀ 6 ₂₆₈₁₀ 6 ₁₅₈₁₀ 6 EC3.1 14110 6 35.6106 17910 6 84.610 6 EC3.2 142106 39.710 6 20410 6 88.010 6 EC3.3 156106 47.6106 247106 10310 6

Fig.8.Stacked bargraphof thecumulative sawing timeover 10repetitions (coloured layers) per experimental condition (marked columns). Each layer correspondswithoneblockofECs,thebottomlayerswerefromBlockA.1,the toplayersBlockB.5.Notethatforreasonsofvisibility,inthisplottheECsare arrangedinadifferentorderthanintherestoftheﬁgures.(Forinterpretationofthe referencestocolourinthisﬁgurelegend,thereaderisreferredtothewebversionof thisarticle.)

Fig.9.Sawbladefrequencyduringsawingmeasuredbythetachometerdisplayedovertime,averagedover10ECrepetitions.Theerrorbarsshowthestandarddeviations. 266 J.M.E.Pluimetal./ForensicScienceInternational289(2018)260–267

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particle.AsdifferentpathogenshavedifferentsizesandMIDs,as showninTable1,itcouldwellbethatsomeofthecountedparticles arethe pathogenthemselves,orone particlecan carryenough pathogenstoacquiretheMID.Lastly,evennon-pathogen-carrying particlesmightposehealthrisksthroughmechanismssimilarto theriskofinhalingasbestosparticles.

Theeffectsofsawingindrybonecoulddifferfromfreshbone duetoincreasedpresenceoforganicmatterin freshbone. This organicmatterismainlycomposed ofcollagen, grantinggreater boneelasticity,whereasdiminishingorganiccontentindrybone changestheelasticpropertiesfromviscoelastictobrittle[19,20]. Eventhoughthecurrentexperimentwasperformedinaclosed andsigniﬁcantlysmallerenvironmentthanasincommonpractice, – a room with a ventilation system and constant turbulence disturbances by human movement–, the resulting production valuesstill clearlyshowthepotentialrisk ofaerosolsproduced duringautopsy.Addingthattheparticlescanremainairbornefor periodslongerthan15min[8,21],andastheparticlegetssmaller themore likelyit will remainsuspended [7,17],there is strong reason to further test the potential negative health effects of aerosolbonedustparticles.

The results obtained from the current study stress the importance of biosafety guidelines. Despite finding significant effects of saw blade frequency and contact load on the aerosolisationofdrybone,whichsuggeststhataerosolproduction couldbereduced,theoptimalexperimentalcondition(EC3.1)still resultedinanumberofparticlesthatisconsideredarisktoanyone potentiallyinhalingthebonedust.Combiningthesefindingswith recommendations from other studies could further reduce the intakeofbonedustwhenusingoscillatingsaws:i.e.adaptations withprotectivecasingaroundthesawblade[5]ormoisteningthe sawbladetoreducespreadofparticles[7,22].Similarly,theuseof protective gear, such as specialised, well-fitted respirators and filteringface pieces[16,23], aswellas guideline inspections to ensure proper infrastructure of autopsy facilities could greatly reducethenumberofaerosol particlesreachingtherespiratory tractsofforensicpractitioners.

Unfortunately,manypathologyinstitutessufferfrom precari-ousconditionsandgovernmentalnegligence[2,4,24].Howeverthe resultsprovided bythe current studycouldhelp minimise the occupational riskin autopsy practice,asfrom theresults some clearsuggestionscanbedistilled:decreaseaerosolproductionby reducingthesawbladefrequencyandbyincreasingthecontact loadonthebonesubject,ormoreradically,butprobablynotideal; switch to hand sawing. Similarly, workers in environments without means to acquire ventilation systems, or where the reductionthespreadingofdustishardtoachieve,e.g.infieldwork, emergencyresponsework,orpracticesinlessdevelopedorpoorer countries, couldimprove theirbone sawing protocols with the results of the current study. Future studies should investigate realistic scenarios faced by forensic practitioners, such as aerosolisationof freshboneinstead ofdryarchaeological bone. Furthermore,testing different bone types (e.g.long, short, flat, irregular or sesamoid bones), and testing additional sawing parameters(suchasthemorphologyofthesawblade),andtheir effects on aerosol production could be investigated. Lastly, followingthestepsof[17],futurestudiesshouldstudyinfluences ofventilationsystemsandairflowsinautopsyrooms.

5.Conclusion

Overall,increasingthesawbladefrequencyordecreasingthe sawbladecontactloadresultedinahigherproductionofaerosol bonedust.Futurestudiesareneededtodeterminetheinﬂuenceof other sawing parameters, other sawing materials, and other

practiceenvironments.Fornow,theresultssuggestthatinorderto limit bone aerosolproduction whenusingoscillating saws,one shouldtrytokeepthesawbladefrequencyaslowandsawblade contactforceashighaspossiblewithinthelimitsofsafetyand practicality.

Acknowledgements

TheauthorswouldliketothankHannesHabrakenforbuilding thesetup,andMaudvanVelthovenfortakingthephotographsof thesetup.

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