A Look at COVID 19 in Terms of: 1. Respiratory Protection

Abstract

Evaluation of Selection and Use, & Re-use of Surgical Masks & N95 Filtering Facepieces (FF) for SARs-CoV-2

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ALookatCOVID19inTermsof:1.RespiratoryProtection

AndrewA.“Tony”Havics,CIH,PE
pH2,LLC
5250EUSHighway36,Suite830
Avon,IN46123
(317)7218‐7020Office
(317)409‐3238Cell

Introduction
TheworldhasbeeninundatedwithvariousmessagesaboutprotectionandcontrolsforCOVID‐19(more
correctlySARs‐CoV‐2(1),buthereaftercalledCOVID‐19forpubliccontinuity’ssake).Aswithany
biologicalagent,themechanismsforprotectionfromdiseasevary.Oneofthemostprominentand
highlydiscussedisthatofrespiratoryprotection.Considerationofrespiratoryprotectionduring
outbreaksorpandemicshasbeendiscussedtovariousextents[(2‐14)]giventheoutbreaksofSARs,MERs,
H1N1,in2003,2012‐2015,and2009.ThecurrentoutbreakofCOVID‐19isnodifferent.Thispaperis
intendedtoprovidethefactsandresearchsupportwhereavailable,andthendrawfromthataswellas
theauthor’sexperiencetoproviderecommendationsbasedtheweightingoftheevidence.Thedata
providedhereandtherecommendationscannotbemaintainedinavacuum,thusotherCOVID19
topicalpapersareintendedtofollowthisone,buteachwillhopefullybesufficientlyself‐containedtobe
usefulandreliable.Theintendedaudienceofthispaperisprofessionals.Thisincludesindustrial
hygienists,occupationalandpublichealthprofessionals,healthandsafetypractitioners,andmedical
personnel.Itisnotintendedforthegeneralpublic,thoughmanyindividualsmaybenefitfromreading
it.
RespiratoryProtectionClassification
Itisimportanttounderstandthecapacityofvariousrespiratoryprotectiondevicestoprotectagainst
particulateingeneralandbiologicalagentsasspecificbioaerosols,suchasCOVID‐19.Beforedoingso,
oneshouldseparaterespiratoryprotectionintheformofthoseintendedforonetimeorlimiteduse
suchasSurgicalMasksandFilteringFacepieces(FFs)fromotherrepeatuserespiratorssuchashalf‐face
negativepressurerespirators(1/2‐faceNPRs),full‐facenegativepressurerespirators(full‐faceNPRs),
andpositivepressurePoweredAirPurifyingRespirators(PAPRs).Duetothelackofrealneedinhealth
caresettingsrespondingtoCOVID19forotherhigherlevelsofprotectionsuchassuppliedair
respirators(SARs)andSelf‐ContainedBreathingApparatus(SCBA),thesewillnotbediscussed.The
needtodifferentiatethetypesofrespiratoryprotectiontobeemployedintheresponsetoany
pandemicisthatthesehavedifferentmethodsofconstruction,operation,regulatorycontrols,and
intendeduse.Inaddition,oneshouldunderstandthatthepurposeofasurgicalmaskistoprotectthe
wearerfromfluids,largedroplets,splashes,orspraysandprotectthepatientfromthewearer’s
respiratoryemissions.Thisfluidresistanceisimportantforprotectionfromcoughingandsneezing.The
purposeofanN95FFistoreduceswearer’sexposuretoparticlesincludingsmallparticleaerosolsand
largedroplets.OnedoesnotperformausersealcheckonasurgicalmaskbutitisrequiredforanN95

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FF.AnN95isintendedtobeatleast95%onamassbasisunderlaboratorytestingofNaClparticleswith
countmediandiameterof0.075um(per42CFR84.181).Thisisapproximatelythemostpenetrating
size(seebelow).
RespiratorEfficiency
Tobegin,onecanevaluatethegeneralaerosolcontrolbyafilteringfacepieceorarespirator.One
considersanaerosolasasolidand/orliquidparticledispersedinagaseousmedium(air)(15).Forthe
varioustypesofrespiratoryprotection,oneobservesthattherearedifferencesinthecapacityto
removeunwantedaerosolsingeneral,andbioaerosolsmoreappropriately.Inthecaseofbioaerosols,
thesemaybemoldspores,bacteria,bacteriophage,viruses,parasites,biofluids,etc.Thesizesofthese
rangefromvirusesat0.02‐0.5μmtobacteriaat0.2‐10μmtofungiat1‐500μm.Thelikelihoodofa
biologicalagentbecomingandstayingairbornewillvaryandisthesubjectofanotherpaper(16).Suffice
tosaythatabsentbeingpresentduringdirectaerosolization(cough,sneeze,surgicalormedical
proceduraldisturbance,etc.),theriskofaerosoltransmissionisnotexpectedtobeaprimaryrouteof
concern(16,17).Thedifferenttypesofrespiratoryprotectionhavebeentestedonbothgeneralparticulate
andspecificbiologicalagentsasseeninTable1below.Onemustrememberthatdespitetypicalsize
differencesinagents,theytendtoaggregateorattachthemselvestootherparticlesmakingthemoften
largerthantheiroriginalsize.Thisisclearfromreviewsofnumerousstudies(18).Whileitistruethat
someagents(fungi,bacteria,insects)canmoreeasilybecomefragmentedandstillpresentallergic
responses,theprimaryconcernisagent‐specificinfectivity,whichisrelatedtoviability.Physical
penetrationisnotthesameasviabilityafterphysicalpenetration(19,20).
Theauthorhasheardanumberofindividualsindicatethattheyareconcernedthatvirusesaresmaller
than0.3μminsizeandthusHEPAfilterswillnotefficientlycapturethem.HEPAfilters,usedin
respiratorsandairfiltrationdevices,aretestedtobe99.97%efficiencyat0.3μmaerosolsizebecause
themostpenetrableparticleisintherangeof0.2‐0.45μm,dependingonthefiltermediacharacteristics
andtheflowrate.Theefficiencybelowandabovethatmostpenetrablepointisbetterbecausethere
aremultiplecapturemechanisms(interception,inertialimpaction,diffusion,gravitationalsettling,
electrostaticattraction)andeachhasitsowncaptureefficiency.Thesumoftheseproducesacapture
curvethathasashapelikethatinFigure1(figurefromHinds(21)).

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Figure1.Filtrationefficiencyandmostpenetratingparticlesizebycapturemechanism.FromHinds,1982.
N95Filteringfacepieces(N95FFs)tendtohaveamaximumpenetrationbetween0.040‐0.200μm(22‐28).
TheefficiencyalsoissimilartotheHEPAinthatitincreasesatlessthanormorethanthemost
penetratingparticlesize.Theweightoftheevidenceclearlyindicatespoorperformancebysurgical
masks,andyetgenerallysufficientforN95FFuseswhenwornproperly(seeTable1below).
Considerationofnewdata(29)regardingaerosolsizing(byPCRanalysisofairsamples)inWuhan
Hospitalsindicatespeakconcentrationof40and9copiesSARS‐CoV‐2aerosolspercubicmeterinthe
0.25to0.5μmand0.5to1.0μmsizeranges,respectively.
Thisaspectofbeingwornproperlyhasbeendemonstratedbythevariabilitybetweenusers(30),
difficultiesfittingandintentionalattemptsatleakagecreationonmanikins,andbyanyonewhohas
performedtestingusingaparticlecounter(suchasTSI’sPortacountA)whereminoradjustmentsinmask
fitcanbringaboutsignificantchangesinFitFactor.FitFactor(FtF)isaratiobetweentheconcentration
outsidetherespiratoryprotectivedevicedividedbytheconcentrationinsidethemaskduringafittest,
oftenmeasuredintermsofverysmallparticles,asseeninequation1.
Equation1.FtF=Coutside/Cinside
Onenotesthatfiltrationefficiencyis:
Equation2: %E=100(Coutside‐Cinside)/(Coutside)
Onecanrearrangetheseequationstoshowthat:
Equation3: %E=100([1–(1/FtF)]

AAUseoftradenames,products,orproductmanufacturerdoesnotrepresentanendorsement,butratherare
usedforfactualexamplesorhypotheticalexamples.

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OnecancontinueandsolveforFtFintermsof%Etoarriveat:
 Equation4: FtF= 1_____
[1‐(%E/100)]
So,anoverallFitFactorof500isequivalenttoanoverallnominalefficiencyof99.8%whereasaFtFof
100isequivalenttoanefficiencyof99%.Similarly,anefficiencyof95%equatestoaFtFof20.When
performedinthefieldreal‐time,theFtFratioisreferredtoasaWorkplaceProtectionFactor(WPF).FtF
evaluatestherespiratoryprotectivedeviceundercontrolledlabconditionswhereasaWPFrepresents
real‐worldconditions.Toaccountfordifferencesbetweenlabtesting(FtF)aswellasvariabilityinactual
workplaces(asrepresentedbyWPF),onerequiresaFitFactorthatresultsinahigherefficiencythanthe
statednominalfilterefficiencyofarespiratoryprotectivedeviceinordertobeconsiderasuccessfulfit
test,e.g.,a100FtFforaN95FF.

Table1.Lab&FieldEfficiencyTestingofN95FF,SurgicalMasks,andImpromptuClothMasks
RespiratoryProtection
Device
Agent Efficiency(%) Ref.
SurgicalMask SM2Virus 15‐98 Balazy,2006a(31)
SurgicalMask M.Luteus(0.9‐1.8μm) 61.2‐75.3 Anon,1997
(restricted)
SurgicalMask B.subtilis(0.75‐2.5μm) 74.2‐90.6 Anon,1997
(restricted)
SurgicalMask Bacteriophage(0.06‐0.15
μm)†
21.8‐58.7 Anon,1997
(restricted)
SurgicalMaskw
Leakage
M.Luteus(0.9‐1.8μm) 31‐47.4 Anon,1997
(restricted)
SurgicalMaskw
Leakage
B.subtilis(0.75‐2.5μm) 4.7‐40.6 Anon,1997
(restricted)
SurgicalMaskw
Leakage
Bacteriophage(0.06‐0.15
μm)†
2.4‐6 Anon,1997
(restricted)
SurgicalMasks B.anthracis(1‐1.5x1‐8μm) 45‐65 Davidson,2006(32,33)
SurgicalMask Ambientparticles 66.7 Derrick,2006
SurgicalMask Ambientparticles ~51 Grinsphun,2009(34)
SurgicalMask BSubtilis(0.7‐0.8x1.5‐1.8
μm)
67 Johnson,1994(35)
SurgicalMask Ambientparticles 41.1‐80.8 Lee,2008(22)
SurgicalMask Mycobacteriumabcsesus
(0.3‐0.5x1‐4μm)
~0.5 McCullough,1997(36)
SurgicalMask Staphylococcusepidermis
(0.5‐1.5μm)
~0.6 McCullough,1997(36)
SurgicalMask Bsubtilis(0.5‐0.8x2‐3μm) ~7.5 McCullough,1997(36)
SurgicalMask Mycobacteriumabcsesus
(0.3‐0.5x1‐4μm)
8‐95.8 McCullough,1996

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RespiratoryProtection
Device
Agent Efficiency(%) Ref.
SurgicalMask Staphylococcusepidermis
(0.5‐1.5μm)
8‐94.4 McCullough,1996
SurgicalMask Bsubtilis(0.5‐0.8x2‐3μm) 12‐97.4 McCullough,1996
SurgicalMasks Ambientparticles 1Mask63.0
2Masks73.7
3Masks78.3
5Masks81.8

Derrick,2005(37)
SurgicalMask NaCl(0.3μm)
LatexSpheres(0.8μm)
LatexSpheres(2μm)
LatexSpheres(3μm)
9.8‐96.04
18.3‐99.96
22.8‐99.99
32.6‐99.98
Oberg,2008(38)
SurgicalMask LatexSpheres(0.03,0.1,0.5,
1,2.5μm)
78‐94 Shakya,2017
SurgicalMask Cornoil(0.02‐1μm) 0‐80 Weber,1993(39)
SurgicalMask A.baumannii,E.faecalis,
andB.subtilis
98.4‐98.6 Tseng,2016(40)
Surgicalmask Mycobacteriumabcsesus 76.9GM Brousseau,1997(41)
SurgicalMask Ambienthomehealthcare 50‐88.89 Elmashae,2017(42)
SurgicalMask NaCl(0.02‐0.50μm) 89‐93% He,2014(43)
SurgicalMask MS2phage 91.7‐92.0 Eninger,2009(44)
SurgicalMask NaClparticles 0‐98.5 Guha,2017(45)
SurgicalMask Staphylococcusepidermidis
(0.93μm)
~86‐99 Jeong,2019(46)
SurgicalMask Escherichiacoli(0.82μm) ~82‐98 Jeong,2019(46)
SurgicalMask Steptococcussalivarus(0.8‐
1μm)
~90 Willeke,1996(47)
SurgicalMask Psuedomonasfluorescens
(0.3‐0.5x1.0‐1.5μm)
~92 Willeke,1996(47)
SurgicalMask CornOil ~69 Willeke,1996(47)
SurgicalMask Bacillusalcalophilus(0.7‐0.9
x3‐4μm)
~94 Willeke,1996(47)
SurgicalMask Bacillusmagetherium(1.2‐
1.5x2‐5μm)
~95.8 Willeke,1996(47)
SurgicalMask NaClParticles(0.02‐1μm) 8‐92 Rengasamy,2009b(48)
SurgicalMask NaClParticles(0.04‐0.60
μm)
90.96‐99.25 Rengasamy,2013(49)
SurgicalMask LatexParticles 0.5μm47.78‐51
1.0μm71.06‐84.22
2.0μm69.76‐85.26
Sanchez,2010(50)
SurgicalMask,
Unsealed
LatexParticles,1um 0.5μm3.83‐43.81
1.0μm58.3‐75.58
2.0μm58.87‐79.67
Sanchez,2010(50)
SurgicalMask MS2phagedroplets(0.54‐
100μm)
78.69‐80.43 Vo,2012(51)

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Device
Agent Efficiency(%) Ref.
SurgicalMask M.Luteus(0.9‐1.8μm) 17.2‐99.64 Wake,1997(52)
SurgicalMask B.subtilis(0.7‐0.8x2‐3μm) 30.4‐>99.9 Wake,1997(52)
SurgicalMask P.alcaligens(0.5x2‐3μm) 75‐85 Wake,1997(52)
SurgicalMask Cornoil(0.1‐4μm) 0‐80 Weber,1993(39)
SurgicalMask NotSpecified 0‐80 Willeke,1994(53)
ClothMask LatexSpheres(0.03,0.1,0.5,
1,2.5μm)
15‐57(countbasis)
13‐40(massbasis)
Shakya,2017
T‐shirts,scarvesand
clothmasks
NaCl(0.020‐1μm) 10‐60 Rengasamy,2010(54)
Shirt
Towel
Handkerchief
Nylonhosiery
DOP 4
14
2
67
Cooper,1983(55)
GFFilterSheet Mycobacteriumchelonae
(0.65‐0.22μm)
86,1Layer*
99.9,2Layers
99.95,3Layers
99.999,4Layers
Brousseau,1994(56)
DM Mycobacteriumabcsesus 96.3GM Brousseau,1997(41)
DMF Mycobacteriumabcsesus 99.39GM Brousseau,1997(41)
FF Cornoil 25‐>99 Chen,1992(57)
N95FF SM2Virus 94.5‐99.5 Balazy,2006a(31)
N95FF 0.02‐0.2μmNaClPM 94‐99.9 Balazy,2006b(58)
N95FF 0.02‐0.2μmNaClPM 95‐98.5 Brochot,2015(59)
N95FF B.anthracis(1‐1.5x1‐8μm) 49‐62 Davidson,2006(32,33)
N95FF Ambientparticles 99.03 Derrick,2006
N95FF MS2Bacteriophagevirus 98.2‐98.3 Eninger,2008(19)
N95FF MS2Bacteriophage ~96.5 Eninger,2008(60)
N95FF Bsubtilisphage ~98.1 Eninger,2008(60)
N95FF T4Phage ~99.1 Eninger,2008(60)
N95FF Ambientparticles ~91 Grinsphun,2009(34)
N95FF NaCl(0.006‐220μm) 97.5‐99.5 IRSST,2013(23)
N95FF Ambientparticles ~91‐96 Lee,200822)
N95FF Culturablebacteria ~64‐98 Lee,200622)
N95FF Culturablefungi ~87.5‐99.7 Lee,200622)
N95FF TotalFungi ~62‐99.7 Lee,200622)
N95FF Bsubtilis(0.7‐0.8x2‐3μm) 99.5+ Qian,1998(61)
N95FF Mycobacteriumtuberculosis
(0.3‐0.6x1‐4μm)
99.5+ Qian,1998(61)
N95FF BMegatherium(1.2‐1.5x2‐
5μm)
99.5+ Qian,1998(61)
N95FF NaCl 94.9‐97.2 Ramirez,2015(24)
N95FF NaCL(0.02‐1μm) 94.8‐98.6 Rengasamy,2011(25)
N95FF NaCl(0.2μm) 96.2‐96.8 Willeke,1998(62)
N95FF BSubtilis(0.8μm) >99.5 Willeke,1998(62)

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Device
Agent Efficiency(%) Ref.
N95FF NaCl(0.020‐1μm) 99.88 
N95FF Ambientparticles 96‐99+ Bergman,2015(63)
N95FF Ambienthomehealthcare 96.55‐97.5 Elmashae,2017(42)
N95FF MS2phage 98.9‐99.9+ Gardner,2013(64)
N95FF MS2phage 99.28‐99.30 Eninger,2009(44)
N95FF LatexSpheres 79.2‐99.3 Eshbaugh,2008(26)
N95FF NaClparticles ~99.75 Han,2012(27)
N95FF LatexSpheres 99.17‐99.995 Harnish,2016(28)
N95FF H1N1Virus 99.26‐99.997 Harnish,2016(28)
N95FF H1N1Virus 98.56‐99.996 Harnish,2013(65)
N95FF LatexSpheres 98.37‐99.999 Harnish,2013(65)
N95FF NaCl(0.02‐0.50μm) 99‐99.6% He,2014(43)
N95FF Ambientparticles(IV
treatment&Woundcare)
99.42‐99.91% Hauge,2012(66)
N95FF Staphylococcusepidermidis
(0.93μm)
Avg99.6 Jeong,2019(46)
N95FF Escherichiacoli(0.82μm) Min90.5
Avg99.1
Jeong,2019(46)
N95FF NaCl(0.02‐0.4μm) 99.435‐99.99 Rengasamy(67),2009a
N95FF SilverParticles(0.004‐0.02
μm)
81.9‐99.98 Rengasamy,2008(68)
N95FF NaClParticles(0.04‐0.60
μm)
99.386‐99.986 Rengasamy,2013(49)
N95FF NaClParticles(0.02‐0.4μm) 98.76‐99.39 Rengasamy,2007(69)
N95FF LatexParticles(0.025‐0.099
μm)
~95.3‐96@65nm Hurata,2008(70)
N95FF MS2phagedroplets(0.54‐
100μm)
96.17‐98.18 Vo,2012(51)
N95FF InfluenzaA 99.6‐99.7 Zhou,2018(71)
N95FF Rhinovirustype14 99.6‐99.9 Zhou,2018(71)
N95FF BacteriophageΦΧ174, 99.5‐>99.9 Zhou,2018(71)
N95FF Staphylococcusaureus 99.7‐>99.9+ Zhou,2018(71)
N95FF Paraffinoil >99.3 Zhou,2018(71)
N95FF NaClParticulate >99.3 Zhou,2018(71)
N95FF NaClParticulate(0.02‐2μm) 99.26‐99.36 Zhuang,2013(72)
N95FF NaClParticulate(0.04‐0.06
μm)
99.27 Zhuang,2013
N95FF Humanadenovirusserotype
1(0.048‐0.052μm)
95.27‐98.15§
Physical
Zuo,2013(73)
N95FF swineinfluenzaH3N2virus
(0.048‐0.052μm)
94.76‐97.04§
Physical
Zuo,2013(73)
N95FF M2phage 99.949‐99.984
ViralRNA
99.976‐99.992
Zuo,2015(20)

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Device
Agent Efficiency(%) Ref.
Viable
N95FF&½‐faceN95 Endotoxininfield 99.64 Cho,2011(74)
N95FF&½‐faceN95 Fungiinfield 97.45 Cho,2011(74)
N95FF&½‐faceN95 1‐3‐β‐D‐Glucaninfield 97.11 Cho,2011(74)
*OnemightexpectaHEPAfiltertohave10layers
†Notindividual,butextractedE.Coli
§LowestefficiencyfromaN95FFthatisnotNIOSHcertified

Onequestionthatoftencomesupinconsiderationforfiltrationefficiencyishowlongcanamasksit
aroundbeforeitsfiltrationefficiencydegradesbeyondacceptable.Rottach(10)foundthatstraptension
capacitywasreducedovertimefor1of2modelsofN95FFwhenevaluatingthemafter1‐10yearsof
storage.Fitfactoreffectwasnotevaluated.Robergemeasuredtherestorativeforcesofstrapsforfive
simulateddonningsandreportedreductioninthestraploadforeachsuccessivedonningwiththe
majorityofthereductionoccurringafterthefirstdonning(75).However,theN95FFmodelwiththe
lowestrestorativestrapperformanceloadwasstillabletopassfit‐testing(anychangeinfitfactorwas
notreported).Viscusi(76)assessed21modelsofN95FFsrespiratorsthathadbeenstoredintheir
originalpackagingforaperiodofatleast6yearsinresearchlaboratoriesanddrywarehousefacilities,
rangingintemperaturebetween15.8Cand32.8CandRHbetween20%and80%.Ofthese,19of21had
minimumefficiencies>95%(96‐98.99),theothertwowereat94.17and94.51%.Theredidnotappear
tobeanycorrelationbetweenthelengthofstorageandfailuretopassthefiltrationtest.
Thereareseveralstudiesthatsupporttheuseofanykindofrespiratoryprotectiontoreduceriskof
disease.ThisincludesInfluenzaA(4,7,8,13)&B(13),TB(77),pH1N1(78),adenoviruses,human
metapneumovirus,coronavirus229E⁄NL63,parainfluenzaviruses1,2or3,influenzavirusesAorB,
respiratorysyncytialvirusAorB,rhinovirusA⁄BandcoronavirusOC43⁄HKU1(79),Streptococcus
pneumoniae,Bordetellapertussis,Chlamydiapneumoniae,MycoplasmapneumoniaeorHaemophilus
influenzatypeB(80),andgeneralinfectioncontrolatahospital(81).MacIntyre(82)hasperformedameta‐
analysisofmanyoftheseanddemonstratedthevalueofrespiratoryprotection.
Althoughrespiratoryprotectionisbeneficialforreducingpotentialinhalationexposure,itmaybecome
contaminatedwithbiologicalaerosols(seebelow).Threeaspectsofthiscontaminationneedtobe
addressedwhenconsideringappropriatenessfordeployment.Thefirstisre‐aerosolizationfromthe
devicebackintothepotentialbreathingzoneofothers.Thesecondiscontactcontaminationbetween
thedeviceandhands,fingers,forearms,orfomites(cellphones,pens,paper,tags,keys,etc.)(83‐85)ofthe
wearer.Thethirdisdecontaminationofthedeviceifpossibleorpreferred.
Thesecondaspect,contactcontamination,canbeaddressedbyclassicaltime‐distance‐shielding
protectivecontrols:appropriatehygienetechniques,limitingthetimeofuseandreuse,proper
selectionfortheseparametersgivenamountandfrequencyofusecombinedwithpotentialfor
exposure.Theseprotectivecontrolsarenottreatedfurtherinthispaper.Detailsonhygieneaspects
willbeprovidedinanotherpaper(86).Thethirdaspect,decontaminationwillbereviewedafterRPD
selectionundertheheadingDecontaminationofRespiratoryProtectionDevices.

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ContaminationPotential
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Thepremiseforconsiderationofcontaminationmustfirstbeacceptedbeforetransferisevaluated.
Fisheretal.(87)modeledthecontaminationofN95FFandSurgicalMasks(SMs)usingtheNicas‐Jones(88)
model.Forthesimulatedaerosolcontaminationscenarios,estimatedfacemaskcontaminationranged
from19to202,549virusesandfrom13to182,477virusesforFFsandSMs,respectively.They
demonstratedcontaminationbydropletsprayproducedbyadirectcoughwouldleadto19viruses
becomingtrappedontheFForSM,givenadistanceof0.6m,aconcentrationof355virus/cough,a
particlespreadof3,800cm2,andanFilteringFacepieceareaof200cm2.Heimbuch(89)investigated52
N95FFswornbyhospitalstaffduringapproximately20minutecleaningofroomswhosepatientshad
beendischarged.Thesewereanalyzedandfoundtocontainanaverageloadingofmicrobesranged
from6.2×102to4.8×103CFU/mask.Approximately97%ofthecontaminationwasfoundonthe
externallayer.Mostoftheisolatesrecoveredwerecoagulase‐negative,Gram‐positivestaphylococci
andMicrococcusspp.Additionaldata(90)fromthissamestudyrevealedloadingofupto24.15CFU/cm2
and3.33CFU/cm2forthetwotypesofN95FFsused.Jackowicz(91)evaluatedsurvivalonFFsbyanalyzing
in‐field(15‐120minusage)FFsfromagriculturalusageandthesameFFmaterialunderlabtreatments
for3bacteriaE.Coli,B.subtilis,B.subtilis,andtwofungi,C.albicans,andA.niger.Airsamplingduring
activitieswas7.5x103to7.2x104CFU/m3culturablebacteriacountand3.9x103to1.7x104CFU/m3
culturablefungalcount.FungionFFsrangedfrom10,000to~315,000CFU/cm2whereasbacteria
rangedfrom~30,000‐200,000CFU/cm2.Inlabtesting,E.Coliincreasedwithinthefirst24hoursthen
heldsteadyuntildecreasingafter72hours.B.subtilisincreased3ordersofmagnitudewithinthefirst
24hoursthenheldsteadyuntildecreasingafter72hours.B.subtilisstayedconsistentlythesame
throughthelengthofthetest(120hours).C.albicansincreasedslightlywithinthefirst24hoursthen
heldsteadyuntildecreasingafter96hours,andA.nigerstayedconsistentlythesamethroughthe
lengthofthetest(120hours).
Aspartofdesigningatestmethodology,Fisher(92)aerosolizedMS2phageontoN95FFcoupons.The
N95shadthreelayers.Outerandmiddlelayerdepositionvariedbymediumusedbutrangedfrom20‐
80%,whereastheinnerlayer(closesttoawearer)had<2%deposition.Tseng(40)directlyapplieddrops,
usedaspraybottle,andanebulizertoapplA.baumannii,E.faecalis,andB.subtilistosurgicalmasksat
10E3to10E8CFU/m3.Filtrationefficienciesforall3taxawerefoundtobe98.4‐98.6%.Thesemasks
werethentestingusingNaClparticlesandfoundtobe77.6‐79.4%efficient.
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Inastudyatastudenthealthcenter,12participantswereassessedforinfluenzavirusexposureover12
days.Only3of127airsampleswerepositive,2of483surfacesamplesandnoneofthe54surgical
maskswerefoundtohaveviralcomponents(byPCR)(11).
Clearly,thepotentialforexternalcontaminationofsurgicalmasksandN95FFsexists.
AlthoughnotofrelevancetoCOVID19exposureoutsidethemask,butrelevantforsharingof
respiratoryprotection,inonestudy(93)self‐contaminationfrom1hourusageon3menrevealed7.8x104
to2.8x106CFU/maskonhalf‐facerespirators.Inthefacecontactarea,therewasa75%reductiontoa
50%increaseafter1dayofstorageinaplasticbagwith2of25testsshowinganincrease.Onthe
exhalationvaluearea,therewasa98%reductiontoa31%increaseafter1dayofstorageinaplastic
bag;with3of25testsshowinganincrease.Similarly,anotherstudybyHigami(94)revealedself‐
contaminationfrom1hourusageatlevelsof100‐4,000CFUbacteriapermlofwashing.Johnson(95)also
discoveredenvironmentalbacterialcontaminationontheinsideofN95FFsafter1dayofuse.
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AerosolizationPreventionbyRPD
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Asmentionedearliersurgicalmaskspreventinhalationoflargeraerosols,whereasanN95FFprevents
bothlargeandveryfineaerosols.Anotherdesignaspectofsurgicalmasksistopreventthepatientfrom
exposuretothewearer’srespiratoryemissions.OnequestionishowwelldosurgicalmasksandN95FF
preventtransmissionfromthewearer.
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Firstoneexaminesthenatureofcoughing&sneezing.OnemightexpectaTBpatienttocough2.6‐26
timesperhour(96).AlthoughWilliamsmeasuredthemediancoughfrequencyat466per24hour(19.4
cough/hr).Twoparticipantsproducedgreaterthan2000coughsoverthe24hoursamplingperiod(83.3
coughs/hr),nearly20‐foldmorethanthelowestvalueof39(1.625coughs/hr).Loudon(97)found12
cough/hratthe40%percentileinpneumoniapatients.Socoughingisfrequentenough,giventhe
aerosolamountsreleased.ForatypicalsneezeseeFigure2belowfromJennison.
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Figure2.Imageofaerosolsgeneratedduringasneeze.(fromJennison,1942)
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Nextonecanassessthetypesofaerosolsproduced.Nicas(98)modeledaerosolproductionbasedon
threestudies:Druett(99),Loudon(100),andPapineni(101).Thepattenisadispersedonewithlargerand
smallersizefractionsthat,obviously,reactdifferentlyaerodynamically.Otherauthors,suchas
Morawska(102),Lee(103),havefoundsimilardistributionsforcoughsandsneezeswithverificationof
microorganismsaswell(104).
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Regardingcoughs,Nishimura(105)showedthatduringthefirst0.08s,thevelocityoftheparticleslocated
atthedistalend(i.e.,75–80cmfromthemouth)washighestinthemistcloud,andthereafter,
deceleratedtobecomeslowerthantheparticlesfoundattheinnerpartofthemistmass,andfinally
almostlostvelocityby0.15s,about85cmfromthemouth.Similarresultsweredocumentedby
Bouriub(106),Jennison(107),andVansciver(108).Tang(109)showedvisually,usingschlierenimaging,theeffect
ofamaskonreducing(butnoteliminating)emissionsfromcoughing(seeFigure3).

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Figure3.Cough(fromTang,2008)
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Usinganoldtechnique
(110)
,Williams
(111)
evaluated24hospitalizedpatientswithnewlydiagnosed
pulmonaryTBwhoworeFFP1masks(Britishfilteringfacepiecedesignation)foronehouroutofevery
threefor24hours.AerosolwascapturedinagelatinefilterprocessedforM.tuberculosisquantitation
byPCR.Serialsputumwascollectedandobjectivecoughfrequencymonitoringperformedoverthe
sameperiod.M.tuberculosiswasdetectedin86.5%of192masksamplesand20.7%of38assessable
sputumsamplesobtainedfromthecohort.Williams
(112)
continuedthisworkwithanother37patients
showingsimilarresults.

Lindsley
(113)
evaluatedtheefficacyoffaceshieldsincoughtransmissionprotection.Duringtestingofan
influenzaladencoughaerosolwithavolumemediandiameter(VMD)of8.5μm,wearingafaceshield
reducedtheinhalationalexposureoftheworkerby96%intheperiodimmediatelyaftera
cough.Thefaceshieldalsoreducedthesurfacecontaminationofarespiratorby97%.Whenasmaller
coughaerosolwasused(VMD=3.4μm),thefaceshieldwaslesseffective,blockingonly68%ofthe
coughand76%ofthesurfacecontamination.Intheperiodfrom1to30minutesafteracough,during
whichtheaerosolhaddispersedthroughouttheroomandlargerparticleshadsettled,thefaceshield
reducedaerosolinhalationbyonly23%.Increasingthedistancebetweenthepatientandworkerto183
cm(6ft)reducedtheexposuretoinfluenzathatoccurredimmediatelyafteracoughby92%.Hencethe
6ftofsocialdistancing.

Wood
(114)
evaluatedsurgicalmasksforpreventionofaerosolizationofPseudomonasaeruginosain
dropletnucleiduringcoughsfrom25adultswithcysticfibrosis.Atotal19of25(76%)participants
producedaerosolscontainingP.aeruginosa.TherewasareductioninaerosolP.aeruginosaloadduring
coughingwithasurgicalmask(2of25),coughingwithanN95mask(4of24),andcoughetiquette
(coughingintothehandorarm),comparedwithuncoveredcoughing.Asimilarreductionintotalcolony
formingunitswasobservedforbothmasksduringcoughing;yet,participantsratedthesurgicalmasksas
morecomfortable.Coughetiquetteprovidedapproximatelyhalfthereductionofviableaerosolsofthe
maskinterventionsduringvoluntarycoughing(13of25patients).Talkingwasalowviableaerosol–
producingactivity(only1in24patientsrevealedemissionsoutsideamask).Thevisualeffectoftheuse
ofasurgicalmask(albeitaveryoldstyle)isseeninFigure4below.

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Figure4.Sneezethroughasurgicalmask(fromJennison,1942)
Lai(115)evaluated(non‐specified)FFssealedindifferentwaysonamanikinandfoundemission
reductionsof33‐100%.Milton(116)measuredexhaledviralparticlesemittedwithandwithoutsurgical
masks.Fineparticles(≤5μmdia)contained8.8foldmoreviralcopiesthandidcoarseparticles(>5
μm).Surgicalmasksreducedviralcopynumbersinthefinefractionby2.8foldandinthecoarsefraction
by25fold(e.g.,captureefficienciesof~64.3%and96%,respectively.Overall,masksproduceda3.4fold
reduction(e.g.,captureefficiencyof~70.6%).reductioninviralaerosolshedding.

Diaz(117)evaluatedN95FFsonbothsymptomaticperson(manikin)andreceiver(manikin)aswellasa90
degreeheadturnusingparticlegeneratorandparticlemeasurementsystems.UsinganN95FFonthe
symptomaticpersononlyresultedina~46.5%effectivecollectionefficiency.UsinganN95FFonthe
receiveronlyresultedina~50%effectivecollection(prevention)efficiency.UsinganN95FFonthe
symptomaticpersonandhavingthepersonturn90degreestothesideresultedinonly~14.5%
effectivecollectionefficiency.Interestingly,usinganN95FFwithaVaseline®sealonthesymptomatic
persononlyresultedina~93.8%effectivecollectionefficiency.UsinganN95FFonthereceiveronly
withaVaseline®sealresultedina~99%effectivecollection(prevention)efficiency.

ThebottomlineisthatsurgicalandN95FFssignificantlyreducesourceemissions,asdoesafaceshield.
Thenextquestionisonthereductionofexternalemissionsfromcapturedbioaerosolsonmasksand
FFs.

Release/Reaerosolization
Afewstudieshaveevaluatedthepotentialreleaseofagentsfromrespiratoryprotectivedevices(RPDs)
forpotentialinhalationtothoseinthenear‐bodyarea.Theseagentsincludelatexpaticles(118,119),M2
phage(85,120),polystyrenespheres(121),andB.subtilis(62,122).Inanevaluationofreleasingmicrospheres
(0.59‐1.9μm)fromdroppingarespirator,only6in100,000particleswasreleased(118).Insimilarworkby

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thesameauthor,inanevaluationofreleasingmicrospheres(0.59‐1.9μm)frommockremovalofaFF,
only1.5‐2particlesin100,000particleswasreleased(119).Kennedy(121)alsolookedatmicrosphere
releasefromdroppingN95FFsataheightof3feetandfound160‐290in100,000particleswas
released.Fisher(120)demonstratedreleaseof0.08‐0.21%(8to21particlesin1,000)fromdropletnuclei
and<0.0001%(<1in10,000)fromdropletsfromaN95FFduringsimulatedcoughing(120).Qian(122)used
B.subtilissporestosimulateM.tuberculosisandB.megatheriumwhileattemptingtoreaerosolizethese
at22%RHfromaN95duringasimulatedsneeze.HealsousedNaClparticlesandlatexspheres.The
resultsshowedthatthelargerparticleshadmoreaerosolizationpotentialof0.01,0.025,and0.04%(1,
2.5,and4particlesin100,000)forNaCL,B.subtilis,andB.megatherium,respectively.Wileke(62)usedB.
subtilistoevaluatereaerosolizastionfromN95FFs.Nobacteriawerereaerosolizedduringnormal
exhalation.Somereaerosolization(0.022‐0.025%orless[22‐25in100,000])wasobservedonlyatlow
humidityandextremelyhighairflowthroughtherespirator,correspondingtoviolentcoughingor
sneezing.LowerRHandlowerflowproducednodetectablebacteria.Theweightoftheevidence
suggestslittleopportunitytoreaerosolizesignificantbioaerosols.
SurvivabilityonFilterMaterial
Brousseau,etal.testedtheabilityforbacteria(MabscessusandSepidermis)togrowonfilters5days
aftercaptureatroomtemperatureand85%RH(123).Almostallfiltersrevealedculturablebacteriaafter
capture,butonly20%offiltersrevealedculturableMabscessusafter5daysand61%Sepidermis.
CouilletefoundthatMS2coliphagepersistedafter48hoursonN95FFandviruspH1N1wasviableafter
6days(124).FishershowedthatforM2Phage,Atleast10%oftheinitialMS2loadwasabletosurvivefor
4daysontheFFRandallsampleshaddetectablelevelsafter10days(125).Johnson(95)testedseveral
respiratoryprotectivedevicesforsurvivabilityofH37Raandfoundthattherewasasharpdropoffafter
day3withonly1of6showinganydetectableH37Raafter28days.
CoulliettedistributedpH1N1ontoN95couponsandextractedthevirusesbyavortex‐centrifugation‐
filtrationprocesstoanalyzebyELISAforsurvivalovera6dayperiodat20%RH(126).Reductionsin
pH1N1were40%,70%,and82%at12,72,and144hours,respectively.Fisherappliedbacteriophage
MS2toN95FFcouponsasanaerosolorliquiddropsandstoredat22°Cand30%RH(125).Viabilityofthe
viruswasmonitoredevery24hoursfrom1to5daysandthenagainonday10.Dropletsshowedless
reductionthandropletnucleiwith10dayvaluesat22%and99.97%,respectively.Asignificantdecrease
indropletnucleididnotoccuruntilafterday4.Koevaluatedthesurvivalofmycobacteria(M.chelonae,
MTBH37Ra,andMTBH37Rv)onHEPAfiltersbothwithoutandwithairflow(127).Miaskiewicz‐Peska(128)
tested4typesofFFmaterialswithchallengesfromaerosolizedStaphylococcushominisbacteria.In
untreatedfiltersthenumberofbacteriaincreased100‐foldandreached1.3×105cfu/cm2within8h.
Rengasamy(129)evaluatedMS2phageonN95FFcouponsat22Cand30%RHat8and12hourspost
inoculation.Theresultsshowedan~54%decreaseafter8hoursand~84%after20hours.Rengasamy
alsoevaluatedMS2phageonN95FFcouponsat37Cand80%RHat8and12hourspostinoculation.
Theresultsshowedan~90%decreaseafter8hoursand~99.68%after20hours.Reponen(130)usedM.
smegmatistotestsurvivabilityonN95FFat37Cand85%RH.Theyevaluatednutrientloading,no
nutrients,andsaliva,fordays1‐6.Withoutnutrients,theresultswere>99%reductionafter24hours,
withsaliva~99.74%reductionat24hoursand>~99.87%at72hours,withnutrients~85.5%reduction
after24hoursand~98.2%at72hoursand~99.6at6days.Wang(131)studiedPseudomonasfluorescens
andB.subtilissurvivalonN95filtersat37Cand85%RHforBsubtilisand28Cand85%RHfor
Pseudomonasfluorescens.Theyweretestedwithnutrients,withoutnutrients,sandwithsaliva.

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Culturalbacteriacountsdroppedbelowdetectionafter3days.ResultsforAll3conditionsrevealed>
99.92%decreasein3days.
Majchrycka(132)investigatedthesurvivalofEscherichiacoli,Candidaalbicans,andAspergillusnigerin
dust‐loadedpolypropylenenonwovens(atypicalouterlayermaterialofN95FFs).Materialsweredust
loadedfromvariousindustrytypes,inoculatedandthenheldat80%RHandatatemperatureof30Cfor
7days.Controlsurvivalsrangedfrom228to5,692%whereasdustloadedsurvivalwas261–150,946%.
Thedustcreatedbothincreasesandsuppressioncomparedtocontrols.TheresultsforCandidaalbicans
andAspergillusnigerweresimilarinthatthedustcreatedbothincreasesandsuppressioncomparedto
controls.Majchrycka(133)inanotherstudyinvestigatedEscherichiacoli,Staphylococcusaureus,Bacillus
subtilis,CandidaalbicansandAspergillusnigersurvivabilityonFFfabricsatmoisturecontentsof4‐,80,
and200%.Evaluationsweremadeat0,8,24,48,72and120hours.B.subtilissurvivedthebeston
filtermaterialswith40%–200%moisturecontent.AdecreaseinsurvivabilitywasobservedforE.Coli
andC.albicanswhenmasshumiditydecreased.TheyfoundthatB.subtilisandA.nigerproliferatedfor
48–72hofincubationandthendiedregardlessofthemoisturecontent.Inyetathirdstudyby
Majchrycka(134),E.Coli,B.subtilis,B.subtilisbacteria;andC.albicansyeastandA.nigermoldwere
testedonsamplesofnonwovensforFFs.Evaluationsweremadeat0,4,8,24,48,72,and96h.The
testswerecarriedoutinaccordancewiththeAATCC100‐1998method.Survivaldependedstronglyon
microorganismspecies.E.ColiandB.subtilisbacteriagrewthemostonallnonwovenstested.The
structuralparametersofthenonwovenstested(massperunitareaandthickness)andcontactangledid
notsignificantlyaffectmicroorganismsurvival.
AlthoughHEPAfiltersareconstructeddifferentlythanFFs,thereshouldbesomeparallelsin
performance.Ko(127)foundthatanRHof75%resultedinafasterdecreaseofsurvivableM.chleonae
beginningat2hoursthrough24hourswithfinalvaluesof0.05survivalfor75%RHversus0.5for55%
RH.Withoutairflow,H37RaandH37Rvshowedsurvivalratesof10and17%after24hoursandratesof
1.1and1%after72hours.SurvivalratesofH37Raafter24hoursaerosolizedontoaHEPAfollowedby
airflowwere~0.6%.Lin(135)evaluatedthesurvivabilityofB.subtilisandE.ColionN95FFsupto96
hoursatRHsof40,60,and95%,andwithsalivaandartificialperspiration.ResultsatallRHsshowan
increaseinthefirst24hoursfollowedbydeclines.Salivaclearlyenhancedsurvival.ForB.subtilisat
37Csurvivalratesofapproximately23,36,and39%wereobservedat40,60,and95%RHat24hours.
ForB.subtilis25Csurvivalratesofapproximately13,16,and16%wereobservedat40,60,and95%RH
at24hours.ForB.subtilis25Csurvivalratesofapproximately2,2,and4%wereobservedat40,60,and
95%RHat96hours.ForB.subtilis25Csurvivalratesofapproximately6,8,and7%wereobservedat
40,60,and95%RHwithsalivaat96hours.ForE.Colisurvivalrateswereconsistentlybelow10%.At
37Cand95%RH,B.subtilisincreased300%in24hourswithartificialperspiration.
Theweightoftheevidenceindicatesthatbioaerosolswillgrowonfilteringfacepieces,andthatsalivais
animportantfactorinsurvivability.
MicrobialTransferfromRespiratoryProtection
GiventhatN095FFsandSurgicalmaskshavethepotentialtoacquireandgrowmicrobesonthem,a
wearercanexpecttocontactandtransfersomeofthesetoeitherfingers,hands,clothing(pockets),etc.
Thisprovidesanopportunityforspreadofcontaminationtoselfandothers.Inaddition,itlimits
potentialextendeduseandlimitspotentialreuseunlesscleaned.

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BradyinvestigatedtransferofM2phagefromcontaminatedFFandfoundtransfertohandsat7.6‐
15.4%and2.2‐2.7%fordropletanddropletnuclei,respectively(85).Asexpected,Bradyalsofound
improperdoffingandreusetoresultinahighertransferthanimproperdoffingalone.Cassanova
evaluatedtransferofM2phageby10volunteersfromprecontaminatedgowns,N95FF,goggles,and
dominanthandpalm(136).Transfertoother(initiallynon‐contaminatedsites)werenondominantglove
(80%),righthandskin(90%),lefthandskin(70%),scrubshirt(100%),scrubpants(75%),andface(0%).
Rebmann(137)studiedN95FFextendeduseandfoundthatduringtwo12‐hrshiftsthenumberof
touchesperpersontotheface,eye,N95,undertheN95,N95adjustmentswere3.6‐5.8,0‐0.8,6.6‐14.6,
0‐0.8,and3.2‐6.6(rangefromday1&2).
Theauthorhasusedfluorescenttracers(powders,liquids,creams)toevaluatebothtransferofagents
anddecontaminationprocedurestoremovecontaminants.DuringatrainingexercisewiththeNCID
Bioterrorismresponseteam(in2003duringtheSARsoutbreak)involvingthecollectionofa
contaminatedenvelope(withpowderedtracer),evenafter3successivedecontaminationsequences,
thetransfertohands,head,andotherbodypartswasstillevident.Others(85,138)havealsousedthese
tracers.Cassanova(136)didindicatethevirusesmaynotcorrelatedwithfluorescenttracer.

SuggestedSelectionMatrix

Selectionoftheappropriatelevelofrespiratoryprotectionshouldbetiedtominimizingexposurebythe
inhalationroutebasedonthemostprobablerisk.Nicas(88)estimatedtheriskofinfectionassociated
with4pathwaysofexposureforinfluenza(assumingthatdepositioninthelowerrespiratorytractto
upperrespiratorytractwas3200:1Bandassuming0.5ACHintheroomC):(1)virus‐contaminatedhand
contactwithfacialmembranes,(2)inhalationofrespirable(<10μm)coughparticles,(3)inhalationof
inspirable(10μm<da<100μm)coughparticles,and(4)sprayofcoughdropletsontofacial
membranes.Therelativeriskofinfectionbypathwaywas31%,17%,0.52%,and52%,respectively.
Thus,thebulkoftheriskisassociatedwithshort‐termcoughingdirectlyonorimmediatelyadjacentto
theinfectedpersonversusfromsmallrespirableaerosolscontinuingtocirculateintheroom.Nicas
estimatedthatmorethan99.9%oftheemittedvirusarenon‐respirableparticles(baseduponcough
studies).Watanabe(139)prepareddose‐responsecurvesforoftheSARS‐CoV(asimilartothecurrent
SARS‐CoV‐2)withcorrespondingto10%and50%responses(illness)estimatedat43and280PFU
[PlaqueFormingUnits],respectively.Theyindicatedthatitsestimatedinfectivitywascomparableto
thatofHCoV‐229E,knownasanagentofhumancommoncold,andalsosimilartothoseofsomeanimal
coronavirusesbelongingtothesamegeneticgroup.Nicas(140)modeledinfectionriskreductionafforded
bytheuseofrespiratoryprotectionwithhalf‐face,full‐face,andPAPRrespirators.Basedonthe
filtrationcapacityoftheN95FF,itwouldfallbetweennoprotectionandahalf‐face,butstillprovidean
orderofmagnitudereductioninrisk.Basedonthisandreviewofaerosoltransmission,risk,andreuse&
cleaningpotential,amatrixofrespiratoryprotectionselectionisprovidedinTable2.Alsoin
considerationisthatwhensurveyed,reusablerespiratorsweresignificantlymorelikely(oddsratios2.3‐

BIftheratiowas1:1,thenhandcontactwoulddominate.
CThisisaresidentialrate.Hospitalswouldbeexpectedtobeinthe4‐15ACHdependingontheusageandageof
construction.

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7.7)tobepreferredoverN95filteringfacepiecerespiratorsinhigherriskscenarioscomparedto“usual
circumstance”scenarios(141).

Table2.RespiratoryProtectionSelectionMatrix
Class Population WorkingExample Recommended
Respiratory
Protection
RecommendedUse
&Hygiene
Practices
1 IndividualsinDirect
ContactwithInfected
Persons
CDCHighRisk‖=Level
1HealthCarewith
routinehandson
contact

1APreferred½‐face
1BPreferredsplash
resistantN95‡
1CAcceptableN95
SeeHavics(86)1A
SeeHavics(86)1B

SeeHavics(86)1C
2 Individualinrooms
adjacenttoInfected
Persons
CDCMediumRisk=
Level2HeathCare
withoutroutinehands
oncontact
N95 Personalhygiene
(seeHavics(86)Class
2).
Hygieneprotocols
forsurfacesare
necessary.
3 Individualswith
IndirectRisk
CDCLowRisk=Level3
GeneralBusinesswith
occasionofcasual
contactwith
symptomaticperson
None Personalhygiene
(seeHavics(86)Class
3).
Cleaningofsurfaces
isrequired
promptlyand
thoroughly
4 GeneralPublic CDCVeryLowRisk=
Level4General
Businesswith
occasionofcasual
contactwith
asymptomaticpersons
None Personalhygiene
(seeHavicsClass4)
‡Forexample,TBapprovedRPD
‖RisklevelstoparallelCDC,InterimUSGuidanceforRiskAssessmentandPublicHealthManagementofPersons
withPotentialCoronavirusDisease2019(COVID‐19)Exposures:GeographicRiskandContactsofLaboratory‐
confirmedCases,March22,2020

Onenotesthatunlessthereisdirectcontact,anN95FFisnotrecommended.Asre‐statedbythe
NationalAcademyofSciencespanel(83),CDCestimatesthatintheeventofasevereinfluenzapandemic,
atleast1.5billionmedicalmaskswouldbeneededbythehealthcaresectorandanadditional1.1billion
wouldbeneededbythepublic.DemandforN95respiratorsbythehealthcaresectorcouldexceed90
millionfora42‐dayoutbreak.N95sshouldbereservedformedicalpersonnel(142)engageddirectlywith
symptomaticpersonssoastoprovidesufficientresourcesforthosemostatriskofinfection.
Inordertoworkeffectively,oneneedstofittestanN95FF.ThisauthordisagreeswiththeFDA’s
policy(143)onhavingaminimumcriteriaforpublichealthemergencyrespiratorsofaminimumFitFactor

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of2.Wecanandshoulddobetterthanthat,becauseitmeansweacceptonly50%efficiencyfor
healthcarepersonnelwhenatdirectriskofinfection‐justonapolicybasis.Aspointedoutby
Janssen(144),onewouldexpectaNIOSHcertifiedN95toeasilyexceedthatvalue,buttheregulatory
policyitselfsendsapoormessage.Thatsaid,trainingandinstructionareimportantforproperfitting
anduse.ThefindingsofBrosseau(145)pointtothis,wherewithoutinstructionalmostabout3%didnot
properlyplacetherespiratorontheirface(i.e.,rightsideup,overthechin,andcoveringthenoseand
mouth)andabout3%didnotproperlyformthenosecliptothenose.Theauthor’sownexperience
testingothersandhimselfareaconstantreminderofaneedfortesting.Similarly,andnotsurprisingly,
Lam(146)andFrost(147),bothrevealedsignificantfailingsoftheUserSealCheckwithFilteringFacepieces.
Itshouldbeconsideredaminimumscreeningtool,notoneofabsolutereliance.Italsocreatesan
opportunityforcontaminationofthehandsduringextendeduseorreuse.Inthepasttheauthorhas
suggestedapossiblealternativeistouseaplasticsandwichbagoverthehandtolimitcontamination
duringreuse.AsforfittestingN95FFs,qualitativefittestshavelimits(148,149),butshouldbeconsidereda
minimuminunderstandingwhatagoodfitisandhelpingtoachievethat,whereasquantitativefit
testingisabetterpracticeandprovidesmorerealtimeinsightintohowwellaFFworks(ornot).
DecontaminationofRespiratoryProtectionDevices

InrecognitionofthefactthatRPDsareexpectedtobecomecontaminatedatsomepoint,andthat
suppliesonN95sarelikelylimited,onehastoconsiderextendeduse(usingforawholeday/shiftand
notjustwhenvisitingasymptomaticpersonfollowedbydisposal)andreuse(morethanoneday).
CDC(150)definesextendedasthepracticeofwearingthesameN95respiratorforrepeatedclosecontact
encounterswithseveralpatients,withoutremovingtherespiratorbetweenpatientencounters.
Extendedusemaybeimplementedwhenmultiplepatientsareinfectedwiththesamerespiratory
pathogenandpatientsareplacedtogetherindedicatedwaitingroomsorhospitalwards.Reuserefers
tothepracticeofusingthesameN95respiratorformultipleencounterswithpatientsbutremovingit
(‘donning’)aftereachencounter.Therespiratorisstoredinbetweenencounterstobeputonagain
(‘donned’)priortothenextencounterwithapatient.

Thereareafewstudiesthathaveassessedreuseandextendeduse.Rebmann(137)evaluatedlong‐term
dailywearofN95FFsfortwo12‐hrshiftson10nursesandfound90%tolerance(1nurseworethe
maskfor30minutesandthenwithdrewfromthestudy).Noclinicaleffects,norsubjectiveperceptions
werenotedafter1hourofsurgicalmaskwearing(151).Tensubjectsworehalf‐maskrespiratorswhile
exercisingfor1hourandshowedonlyaslightdecreaseinbreathingratethatwaswelltolerated(152).
Bergman(153)studiedmultipleconsecutiveuseonN95FFsbytestingFitFactorsaftermultipleuses.No
statisticaldifferencewasfoundafter5re‐donnings,butthereafterthereweremorefailurestowards
achievingthedesiredFitFactorof100.ThiseffectwasN95FFmodeldependentbutwas53‐75%across
allmodelsbydonnings16‐20.

Vuma(154)studiedtheeffectonFitFactorofmultipleconsecutivedonninganddoffingofN95FFsby25
persons.After3doffings,6individualsshowedasignificantdeclineinFtFresults.After6doffings,7
individualsshowedasignificantdeclineinFtFresults.Resultssuggestthatproperadjustmentmustbe
carriedoutforeachsequenceofdonning.Suen(155)evaluatedN95FFreuseon120nursesperforming
10minsofsuctioning&NGtubeinsertionwithpreandpostprocedurefittesting.Theaveragefitfactor
droppedsignificantlyafternursingprocedures(184.85vs134.71)asdetectedbythequantitativefit
testing.One‐thirdofFtFsfellbelow100(40of120nurses)afteruse.Kim(156)assessedworkplace
protectionfactorsduringvariousscenarios:1)checkbloodpressure,raise‐lowerstretcher,cleanhands,

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2)Upperairwaysuction,notifyaspirator,knockchestsandputongloves,raise/lowerstretcher,
performaspirator,3)AdministerIV,injection,cleanwithalcohol,tietourniquet,pushIVmed,
raise/lowerstretcher.Fittestingbeforehandrevealed73.5%passrate(FtF>100)withaGMFtFof
256.3forhosepassingand37.0forthosefailing.Duringworkplaceusage(Scenarios1,2,3)thefactors
forthosewhopassedthefittestwas68.8(GM)andthosewhofailedwas39.6(GM).Sothosewho
passeddeclinedinprotectionduringtasksandthosewhofailedremainedthesame–stillfailing.
Sietsma(157)studiedfitfactorsfortheshorttasksofcardiopulmonaryresuscitation(CPR),ultrasound
examination,andmakingahospitalbed.Fitfactorsrangedfrom58‐1,368(98.3‐99.93%efficiency)with
anaverageof285(99.65%).Inanalternativeway,Zhuang(158)lookedatFitFactorson10subjectsat
week0,2,and4,toevaluategeneralchangesovertimeinfit.Thecoefficientofvariationassociated
withbetweenvisitsandbetweensubjectswas2.4‐7.7%.Thisisrelevantinthatoneneedstoshowa
smallvariationinnon‐reusesituationswithfittestingtobeabletodetectchangesduringreuse.

Severalstudieshavelookedatdecontamination.Bessesen(159)evaluated21personsandfoundthat12
ofthemmadeatleastoneerrorinthedisinfectionprocesswhilecleaningahalf‐facerespirator.This
clearlyindicatestheneedfortrainingandsupervision.

Bergman(160)evaluatedtheparticlepenetrationonN95FFmaterialafter3‐cyclesofvarioustreatments:
ultravioletgermicidalirradiation,ethyleneoxide,hydrogenperoxidegasplasma,hydrogenperoxide
vapor,microwave‐oven‐generatedsteam,bleach,liquidhydrogenperoxide,andmoistheatincubation
(pasteurization).Onlythehydrogenperoxidegasplasmaprocessingcausedlevelshigherthanexpected
ofinitialaerosolpenetration(>5%)in9of36(25%)samples.Bergman(161)alsotestedN95FFsafter
multipleapplicationsofultravioletgermicidalirradiation(UVGI),moistheatincubation(MHI),or
microwave‐generatedsteam(MGS).After3cyclesoftreatment,nostatisticaldifferenceswerefound
betweentheuntestedresultsandthatafterthethirdcycleontentestsubjects.Fisher(162)conducted
testsonUV‐Cdecontamination.Circularcoupons,excisedfromtheFFRs,wereexposedtoaerosolized
particlescontainingMS2coliphageandtreatedwithIFM‐specificUV‐Cdosesrangingfrom38to4707J/
m2.ModelsexposedtoaminimumIFMdoseof1000J/m2demonstratedatleasta3logreduction
(LR)inviableMS2.Model‐specificexposuretimestoachievethisIFMdoserangedfrom2to266min.
Fisher(92)alsotestedtreatmentsonN95FFcouponsinoculatedwithaerosolizedMS2phage.Sodium
hypochlorite(bleach)concentrationof0.6%andsteamtreatmentsof45secondsandlongerresultedin
logreductions(>4log)whichreachedthedetectionlimitsforbothlevelsofprotectivefactors.

Fisher(163)againevaluatedtheuseoftwocommerciallyavailablesteambags,marketedtothepublicfor
disinfectinginfantfeedingequipment,forFFdecontamination.TheFFs(surgicalN95andN95)were
decontaminatedwithmicrowavegeneratedsteamfollowingthemanufacturers’instructionsthen
evaluatedforfiltrationefficiencyforuptothreesteamexposures.ThesteamhadlittleeffectonFFR
performanceasfiltrationefficiencyofthetreatedFFsremainedabove95%.Thedecontamination
efficacyofthesteambagwasassessedusingbacteriophageMS2asasurrogateforapathogenicvirus.
Thetestedsteambagswerefoundtobe99.9%effectiveforinactivatingMS2onFFs.

Fisher(164)testedtheefficiencyof3cyclesofdecontaminationbymicrowavegeneratedsteamandUVGI
underartificialsoilloading(protein).Microwave‐generatedsteamdecontaminationefficacywassimilar
forallthreecyclesregardlessofthesoilaccumulation(p=0.34)[thelogreductionwaspractically
speakingverysimilarforbothtreatmentsandallthreecycles].UVGIdecontaminationdemonstrateda
differenceinefficacyamongthecyclesofboththelowandhighsoilloadsamplesets(p<0.01)and
performedanorderofmagnitudepoorerinreductiongoingfromcycles1to3.


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Heimbuch(2)assessedsixcommerciallyavailableFFmodelsthatwerecontaminatedwithH1N1influenza
virusasaerosolsordropletsthatarerepresentativeofhumanrespiratorysecretions.Asubsetofthe
FFRswastreatedwithmicrowave‐generatedsteam(2min),warmmoistheat(30min),andultraviolet
germicidalirradiation(5min)at254nmtodecontaminateH1N1influenzavirus.All3decontamination
technologiesprovidedgreaterthan4‐logreductionofviableH1N1virus.In93%oftheexperiments,the
viruswasreducedtolevelsbelowthelimitofdetectionofthemethodused.

Heimbuch(165)assessed3modelsofsurgicalN95FFscontaminatedwithaerosolsofmucinorviable
Staphylococcusaureus.Thesewerecleanedwithhypochlorite(OCL),benzalkoniumchloride(BAC),or
on(inert)antimicrobialwipes.Eachofthe3testedFFswaswiped3timesinturnwith4facesofafresh
wipeproductfoldedovertwice.TotalcleaningtimeperFFwas~30seconds.Aftercleaning,FFswere
separatedintocomponents(nosepad,fabrics,andperforatedstrip),andcontaminantswereextracted
andquantified.Mucinremovalwas<1logforallwipeproductsonallcomponents.Inertwipesachieved
~1logattenuationinviableSaureusonfabricsfromallFFRmodelsremovalwaslesseffectivefromnose
padsandperforatededges.Bothantimicrobialwipesachieved3‐5logattenuationonmost
components,withsmallerreductionsonnosepadsandgreaterreductionsonperforatedstrips.Particle
penetrationfollowingcleaningyieldedmeanvalues<5%.Resultsofparticlefiltrationefficiencywere
~95.8‐98%forBAC,~98.3‐99.6%forOCL,and~87.5‐99.85%.Thehighestpenetrationswereobservedin
FFscleanedwithbenzalkoniumchloridewipe.Theseresultsshouldbeplacedincontext.All3are
surgicalFFRswithfluidresistantexteriorsurfaces,whichisnotcommontotypicalindustrialN95FFs.
ImmersionofFFsin10%householdbleachoxidizedmetalandleftanodor.

Lin(166)investigatedtheeffectsoffivedecontaminationmethodsonthefilterqualityofthree
commerciallyavailableelectretmasks,aN95,GauzeandSpunlacenonwovenmasks.Penetrationof
0.0156‐0.594μmlatexsphereswereusedtoassesstheeffectsonthedecontamination.The
decontaminationmethodswere1)physicaldecontaminationusingatraditionalelectricricecookerthat
wasmadeinTaiwantoprovidedryheat(3min),2)physicaldecontaminationusinganautoclave(15
min)toprovidemoistheat,andlowtemperaturechemicaldecontaminationusing3)70%ethanol(10
minsoak),4)isopropanol(10minsoak)and5)bleach(0.5%sodiumhypochlorite,10minsoak).The
bleachdestroyedtheGauzemask.Afterdecontaminationthericecookerrevealed~24%efficiencyfor
thespunlace,~76%forGauze,and~97%fortheN95FF.Afterdecontaminationtheautoclaverevealed
~19%efficiencyforthespunlace,~50%forGauze,and~97%fortheN95FF.Afterdecontaminationthe
ethanolrevealed~19%efficiencyforthespunlace,39%forGauze,and~71%fortheN95FF.After
decontaminationthebleachrevealed~12%efficiencyforthespunlace,0%forGauze(destroyed),and
~82%fortheN95FF.AfterdecontaminationtheIPArevealed32%forGauzeand~30%fortheN95FF.

Lin(167)alsodeterminedtherelativesurvivalofBsubtilissporesloadedonanN95filteringfacepiece
respirator(FFR)afterdecontaminationbyfivemethodsunderworst‐caseconditions.Relativesurvival
wasobtainedbytestingafterdecontaminationandafterstoringtheFFsat37°Cand95%RHfor24
hours.Thedecontaminationmethodsinvolvedethanol,bleach,ultravioletirradiation(UVA365nm,UVC
254nm),anautoclave,andatraditionalelectricricecooker(TERC)thatwasmadeinTaiwan.Without
decontamination,59±8%oftheloadedsporessurvivedfor24hours.When70%ethanolwasaddedto
theN95FFatapackingdensityof0.23,thesurvivalwas73%initiallyanddecayedto22%in24hours.
Relativesurvivalremainedabove20%after20minutesofUVAirradiation.Theotherfour
decontaminationmeasuresachieved99%‐100%reduction.

Lindsley(168)exposedbothsidesofmaterialcouponsandrespiratorstrapsfromfourmodelsofN95FFs
toUVgermicidalirradiation(UVGI)dosesfrom120–950J/cm2.UVGIresultedinasmalldecreasein

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efficiency(1.25%)andnochangeinairflow.UVGIdidreducestrengthofthefiltermaterial(upto90%).
HigherUVGIdose(2,360J/cm2)resultedin20‐51%strengthreductioninstraps.Ingeneral,thefindings
indicatethatevenlowdosesofUVGIwillresultinaminimumof10%reductioninstrapstrength.

Lore(169)examinedH1N1appliedasanaerosolto2modelsonN95FFs.Theeffectivenessofthree
energeticdecontaminationmethods[ultravioletgermicidalirradiation(UVGI),microwave‐generated
steam,andmoistheat]ontwoNIOSH‐certifiedN95FFs.UVGIconsistedof15‐WUV‐C(254‐nm
wavelength)at25cmfor15min(dose18kJ/m2).A1250‐W(2450MHz)commerciallyavailable
microwaveovenwasusedalongwithaplasticboxfilledwith50mlofroomtemperaturetapwater.A
perforatedsystemallowsteamtotreattheFFsfor2miatfullpower.Formoistheat,a6‐lsealable
containerwasfilledwith1loftapwater,placedinanovenandheatedto65"Cfor3h.AsallFFs
displayed>95%efficiencyby300‐nmparticles,withnoprofoundreductioninfiltrationperformance.

Mills(170)tooktwelvesampleseachof15N95FFmodelsandcontaminatedthemwithH1N1influenza
(facepieceandstrap),thencoveredwithasoilingagent—artificialsalivaorartificialskinoil.Foreach
soilingagent,3contaminatedFFsweretreatedwith1J/cm2UVGIforapproximately1minute,whereas
3othercontaminatedFFsremaineduntreated.Allcontaminatedsurfaceswerecutoutandviruses
extracted.Theresultsrevealedsignificantreductions(≥3log)ininfluenzaviabilityforbothsoiling
conditionsonfacepiecesfrom12of15FFmodelsandstrapsfrom7of15FFmodels.

Salter(171,172)evaluated8decontaminationtechniques:1)UVirradiation(2547302nm@~2.7E5J/m2),
2)vaporizedhydrogenperoxide(VHP),3)3%hydrogenperoxide,4)dilutedhouseholdbleach(0.6%
hypochlorite),5)Moistheat(65Cand85%RH),6)mixedoxidants(10%oxone,6%sodiumchloride,5%
sodiumbicarbonate)7)Dimethyldioxirane(DMDO)(10%oxone,105acetone,5%sodiumbicarbonate),
8)ethyleneOxide(EtO).Peroxidetechniques(VHP&3%)andUVresultedinnosignificantoff‐gassingor
residue.Bleachoxidizedmetalandleftastrongodor.DMDOandmixedoxidantsalsocausedissues
withcorrosion.EtOtreatmentofFFsproduced2‐hydroxyethylacetate,(ahazardouschemicalby‐
product),possiblyformedbyareactionofEtOwithrubberpartsoftherespirator.Additionally,EtO
requiresalongoff‐gassingperiodthatwilllimitthroughput.ThroughputisalsoaproblemfortheVHP
technology—theauthorsindicatedtestingwiththeVHPsterilizerwasasterilizationcycleabortionif
morethansixFFRswereloadedinthechamberduringtheone‐hoursterilizationcycle.Also,itisknown
thatcellulosicmaterialwillabsorbperoxide.

Viscusi(173)testedtwomodelsofFFRs(oneN95andoneP100)withseveraldecontaminationprocesses
attwoconditionseach.Theseincluded:1)submergingthetestrespiratorsintapwaterfor30minutes,
2)Liquidchemicaldecontamination[hydrogenperoxide;Fisher30%stabilizedH2O2,Bleach;Fisher
5.25%SodiumHypochlorite(NaOCl)with0.20%SodiumHydroxide(NaOH);HenrySheinIsopropyl
alcohol(IPA),70%;Ivorybarsoap,1g/L,shavedfromthebaranddilutedintapwater]3)Ultraviolet
radiation(0.24mW/cm2)bothsides,4)dryheat(oven),5)Microwave26mW/cm3(750W/ft3)for2‐4
min,5)Autoclave121°C(15psi),6)EtOforonehourfollowedbyafour‐houraerationinterval,7)
VaporizedHydrogenPeroxide(VHP).Thestandarddryingtimewas72hoursforeach.Filtration
performanceofthetreatedrespiratorsplustwocontrolswasassessedusingapoly‐dispersedsodium
chlorideaerosoltestmethodsimilartothatusedbytheNIOSHforrespiratorcertification.
Decontaminationusinganautoclave,160⁰Cdryheat,70%isopropylalcohol,andsoapandwater(20
minutesoak)causedsignificantfilterdegradationtobothN95andP100FFs.Theparticlepenetration
levelsweregreaterthanallowedforNIOSHcertification.Filtrationperformanceafterdecontamination
usingbleach,ethyleneoxide,andamicrowaveovenwasdegradedforbothrespiratormodels,although
particlepenetrationlevelswerestilllessthantheNIOSHcertificationcriteria.Thedecontamination

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methodsthathadtheleasteffectonparticlepenetrationinvolvedhydrogenperoxide(vaporizedand
liquidforms)andUVradiation.

Viscusi(174)evaluatedfivedecontaminationmethods:1)ultravioletgermicidalirradiation(UVGI)40‐W
UV‐Clight(averageUVintensityexperimentallymeasuredtorangefrom0.18to0.20mW/cm2)2)
ethyleneoxide(EtOexposurefor1hfollowedby4hofaeration),3)vaporizedhydrogenperoxide
(VHP),4)microwaveovenirradiation(750W/ft3experimentallymeasured;2‐mintotalexposure;1min
eachsideofFF;papertowelwasplacedontherevolvingglassplateforinsulationtoprotecttheFFRs
frommeltingontotheglassplate),and5)bleach(30minutessubmersionin0.6%).Theyusednine
modelsofNIOSH‐certifiedrespirators(threemodelseachofN95FFRs,surgicalN95respirators,and
P100FFRs).MicrowaveovenirradiationmeltedsamplesfromtwoFFmodels.TheremainderoftheFF
samplesthathadbeendecontaminatedhadexpectedlevelsoffilteraerosolpenetrationandfilter
airflowresistance.Thepoorestresultshowedaleast98.14%efficiency.Thescentofbleachremained
noticeablefollowingovernightdryingandlowlevelsofchlorinegaswerefoundtooff‐gasfrombleach‐
decontaminatedFFswhenrehydratedwithdeionizedwater.Thechlorineoff‐gasconcentrationwas
initially2‐12ppmbutdroppedto~0.05ppmovernight.TheOSHAPELforChlorineis1ppmasaCeiling
limit.TheACGIHTLVis0.1ppmasan8‐hourlimitand0.4ppmasaSTEL.Rinsingafter30min
submersiondidnotappeartochangetheoff‐gassing.Perhapsthemosttellingwasthatefficiencies
declinedafterovenheattreatmentover100⁰C.Thisindicatesacriticaltemperaturetoavoid.

Viscusi(175)againevaluatedultravioletgermicidalirradiation(UVGI),moistheatincubation(MHI),or
microwave‐generatedsteam(MGS)decontaminationaffectsthefittingcharacteristics,odor,comfort,or
donningeaseofsixN95filteringfacepiecemodels(seepreviousstudiesbythisauthorfirdetailsonthe
decontaminationprocedures).Fiton10subjectswerefittestedusingaparticlecountingmethod.
Interestingly,testtechniciansdidnotreportanyunusualorstrongodorfromFFRsfollowinganyofthe
decontaminationmethods.WhilefiveofthesixFFRmodelsincludedinthisstudycontainedmetallic
nosepieces,nosparkingoccurredfrommicrowavingduringtheMGSprocessing.Therewasnomelting
ofanFFRoranyofitscomponents.Onesubjectcomplainedofintolerableodorissuesafter
decontaminationcycles4&5byUVGI.Therewerealsoanumberofheadstrapbreakages.Allmodels
underalldecontaminationprocedurescontinuedtomeet100FitFactor.

Vo(51)usedMS2coliphagewasusedasasurrogateforpathogenicviruses.Aviraldroplettestsystem
wasconstructed,andthesizedistributionofviraldropletsloadeddirectlyontorespiratorswas
characterizedusinganaerodynamicparticlesizer.Thesizesrangedfrom0.5to15μm.Relative
efficienciesofdecontaminationofsodiumhypochlorite(bleach)andUVirradiationwereassessed.
Sodiumhypochloritedosesof2.75to5.50mg/literwitha10‐mindecontaminationperiodresultedin
approximately3‐to4‐logreductionsinthelevelofMS2coliphage(99.90‐99.99%decrease).When
highersodiumhypochloritedoses(>8.25mg/liter)wereusedwiththesamecontacttimethatwasused
forthedilutesolutionscontaining2.75to5.50mg/liter,allMS2wasinactivated.ForUV
decontaminationatawavelengthof254nm,anapproximately3‐logreductioninthelevelofMS2virus
wasachievedwithdoseof4.32J/cm2(3hoursofcontacttimewithaUVintensityof0.4mW/cm2),while
withhigherdosesofUVirradiation(>7.20J/cm2;UVintensity,0.4mW/cm2;contacttimes,>5hours),all
MS2wasinactivated.

Moyer(176)tooknewN‐95respiratorsfromthreedifferentmanufacturersandloadedthemwith5mgof
sodiumchlorideaerosolonedayaweek,overaperiodofweekswhilestorageinanoffice.Results
showedthatsomeofthemanufacturers’modelshadpenetrationsofgreaterthan5percentwhen
intermittentlyexposedtosodiumchlorideaerosol.Itisconcludedthatintermittent,low‐levelsodium

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chlorideaerosolloadingofN‐95respiratorshasadegradingeffectonfilterefficiency.Thisreductionin
filterefficiencywasnotaccompaniedbyasignificantincreaseinbreathingresistancethatwouldsignal
theuserthatthefilterneedstobereplaced.However,itwasn’tuntilday40(4applications)that5%
penetrationwasreachedbyoneofthemanufacturer’sfilters.Thissuggestssometolerancetochloride.
Moyeralsodeterminedtheeffectduetowater,acomparisonwasdonebetweennewfiltersandnew
filterswhichweredippedfor15secondsinabeakerofdistilledwater.Thewater‐dippedfilterswere
allowedtoairdryovernightbeforetesting.Boththenewfiltersandthewater‐dippedfiltersweretested
forfilterpenetration.Thewatertreatmentwasperformedtoascertainwhat,ifany,effectitwouldhave
ontheseN‐95serieselectrostaticfilters.TheeffectofthewaterdipwasminimalformanufacturersB’s
andC’sfilters.ThereappearstobeanincreaseinthefilterpenetrationvaluesforthemanufacturerA
filterswhencomparingthenewtothewater‐dippedpenetrationvalues.Practicallyspeakinghowever,
themanufacturerA’sfilterswerestillat96.48%efficientafter20days,thuswashinginwateris
tolerable.

OnenotesthatOSHA[29CFR1910.134AppendixB‐2]hasamandatoryRespiratorCleaningProcedure
asfollows:

“A.Removefilters,cartridges,orcanisters.Disassemblefacepiecesbyremovingspeaking
diaphragms,demandandpressure‐demandvalveassemblies,hoses,oranycomponents
recommendedbythemanufacturer.Discardorrepairanydefectiveparts.
B.Washcomponentsinwarm(43deg.C[110deg.F]maximum)waterwithamilddetergentor
withacleanerrecommendedbythemanufacturer.Astiffbristle(notwire)brushmaybeused
tofacilitatetheremovalofdirt.
C.Rinsecomponentsthoroughlyinclean,warm(43deg.C[110deg.F]maximum),preferably
runningwater.Drain.
D.Whenthecleaneruseddoesnotcontainadisinfectingagent,respiratorcomponentsshould
beimmersedfortwominutesinoneofthefollowing:
1.Hypochloritesolution(50ppmofchlorine)madebyaddingapproximatelyone
milliliteroflaundrybleachtooneliterofwaterat43deg.C(110deg.F);or,
2.Aqueoussolutionofiodine(50ppmiodine)madebyaddingapproximately0.8
millilitersoftinctureofiodine(6‐8gramsammoniumand/orpotassiumiodide/100ccof
45%alcohol)tooneliterofwaterat43deg.C(110deg.F);or,
3.Othercommerciallyavailablecleansersofequivalentdisinfectantqualitywhenused
asdirected,iftheiruseisrecommendedorapprovedbytherespiratormanufacturer.
E.Rinsecomponentsthoroughlyinclean,warm(43deg.C[110deg.F]maximum),preferably
runningwater.Drain.Theimportanceofthoroughrinsingcannotbeoveremphasized.
Detergentsordisinfectantsthatdryonfacepiecesmayresultindermatitis.Inaddition,some
disinfectantsmaycausedeteriorationofrubberorcorrosionofmetalpartsifnotcompletely
removed.
F.Componentsshouldbehand‐driedwithacleanlint‐freeclothorair‐dried.
G.Reassemblefacepiece,replacingfilters,cartridges,andcanisterswherenecessary.
H.Testtherespiratortoensurethatallcomponentsworkproperly.”

Havingreviewedthefindingsofvarioustests,itisclearthatextendeduseandre‐usearecertainly
possibleandworthwhileprovidedgoodhygienetechniques,andproperstorage(cleandryplaceoutside
facingup)areusedforextendeduseanddecontaminationisperformedwhensignificantandknown
bioaerosolshavebeenencountered.Thisisnotbestpracticebutratheranacceptablepracticegiven
resourcelimitations.Thethreetechniquesmostuseablearebleach,UVGI,andsteam.Howevercareful

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attentiontotheconditionofmaterialsofconstruction(straps,edges)mustbetakenseriously.See
attachedAppendixforexamplesofeach.

ConcernoverSodiumHypochloriteUsage

Variousauthorshaveraisedconcernsregardingpotentialskinandvaporexposureduringthe
decontaminationofRespiratoryProtectivedevices.Thevapordataabovesuggested0.05ppmafter
dryingisoneconcern(174).Onemightexpectatriplerinseaftertreatmentorextendeddryingwould
reducethisrisk.Ignoringforthetimedifferencesinconcentrationresponse,onenotesthattopical
hypochloriteat0.05%appliedtobothsidesofthethoraxofdogswerewell‐toleratedwithoutsignsof
skinirritation(177,178).

HazeltonLaboratoriesexamined1.1%sodiumhypochloritesolutionusingastandardtestforpredicting
sensitizationorallergicreactions,theGuineaPigMaximizationTestwithnosensitization(179).Twotests
byAmuchinaonhumansubjectsat0.11%and0.1%revealednosensitizationandnosignificant
irritation(179).InanotherhumanprimaryirritationpatchtestbyBillhimerinaclinicalexaminationofthe
irritationpotentialofsodiumhypochloriteeachtestsubjectwasexposedtothreeconsecutive24‐hour
applicationsof0.11%sodiumhypochloritesolutionwithobservationstakenaftereachapplication.Only
transient,slighttomoderateirritationwasobservedduringthestudy(179).

Giventhewidespreaduseofsodiumhypochlorite,itisapositivesignthattherearelimitedreportsof
variouseffectssuchasurticariatohypochloriteinthepoolwater(180),andacoupleofcasesofbleach
usage(181),andacaseinvolvingatheatretechnician(182).Hostynek(183)suggestedthatanon‐irritant
concentrationfordiagnosticpatchtestingforallergiccontactdermatitisusing17ulto20ultestvolume,
couldbeashighasI%NaOCI.

Thesestudiesdiscussedabovedemonstratethatsodiumhypochloriteisnotaskinirritant,nora
sensitizeratlessthan1%.


Somekeyfindings:

1. N95FilteringFacepiecesworkfairlywellagainstbiologicalaerosols.

2. Surgicalmasksdonotworkwellagainstbiologicalaerosols.Handkerchiefs,clothmasks,etc.do
notworkwellagainstbiologicalaerosols.

3. Veryfewvirusesorbiologicalmaterialencompassingviralmaterialisexpectedtobereleased
fromtheoutsideofN95FF.

4. Variousbiologicalagentshavepotentialtogrowonfiltrationmediaoncedepositedthere(with
orwithoutdustadded).

5. BiologicalagentshavepotentialtogrowontheinsideinRPDstoo.

6. ProperhygienepracticesandproperPPE(RPDandotherapparel)doffingisamust.

7. BestpracticeistoproperlyremoveandthendisposeofanN95afterone‐timeuse.

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8. AcceptablepracticeistouseanN95forextendeduseprovidedtheN95FFishandledwithcare
(includesaggressivetrainingbytheauthorityhavingjurisdiction,andstoringproperlyinaclean
dryplaceoutsidefacingup).

9. Riskassessmentindicatesvaryinglevelsofrespiratorycontroldependingonthewearerand
his/heractivities.

10. Thehighestriskisforthoseindirectcontactandinrangeofcoughing/sneezingsymptomatic
persons.

11. Althoughnotbestpractice,extendeduseofN95FFsisacceptableprovidedproperhygiene
practicesandproperPPEdonning/doffingisperformed.

12. Althoughnotbestpractice,norevengoodpractice,re‐useofN95FFsisacceptableprovided
properhygienepractices,properPPEdonning/doffing,anddecontaminationisperformed
(includesaggressivetrainingbytheauthorityhavingjurisdiction,performancedemonstrationof
sanitizationpracticesbythedevicewearer,andstoringproperlyinacleandryplaceoutside
facingup,andjudicioussupervision).

13. TheuseofsurgicalmasksorN95FFsonsymptomaticpatientsisbeneficial.

Acknowledgements
ThankstoElsevier,Springer,andthosepublisherswhohavemademanyrelevantarticlesavailablefree.
AldothankstoPurdueUniversity,IUPUI,andIUSchoolofMedicinewhohaveallowedmethrough
variousadjunctfacultyandlecturingpositionsaccesstoanumberofthearticlescitedherein.Also,a
heartyshoutouttoSteveJahnandScottArmourfortheirencouragementtowritethisandtheirreview
ofthetext.Finally,thankstomybetterhalfTami,whoindulgesmeinmyscientificendeavors.

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171 Salter,W.,K.Kinney,W.Wallace,A.Lumley,B.Heimbuch,andJ.Wander:Analysisofresidual
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172 Salter,W.,K.Kinney,W.Wallace,A.Lumley,B.Heimbuch,andJ.Wander:"Analysisofresidual
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173 Viscusi,D.J.,W.P.King,andR.Shaffer:EffectofDecontaminationontheFiltrationEfficiencyof
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174 Viscusi,D.J.,M.S.Bergman,B.C.Eimer,andR.E.Shaffer:Evaluationoffivedecontamination
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175 Viscusi,D.J.,M.S.Bergman,D.A.Novak,K.A.Faulkner,A.Palmiero,J.Powelletal.:Impactof
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182 Zhe,G.C.S.,A.Green,Y.T.Fong,H.Y.Lee,andS.F.Ho:RarecaseoftypeIhypersensitivity
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solutionsinhumanskin.ContactDermatitis23(5):316‐324(1990).
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AppendixA
AppendixA.N95FFandSurgicalMaskRPDCleaningProcesses
(recommendlimitingto5decontaminationcycles)

SodiumHypochloriteProcess

1. Preparea0.06%to0.1%solutionofsodiumhypochlorite;placeinContainerB.
 [sizesufficienttosubmergetheRPD]
2. Prepareapan/container[ContainerA]with1%Alconoxsolution*inroomtemperaturewater.
[sizesufficienttosubmergetheRPD]
3. Prepareapan/container[ContainerC]withroomtemperaturewater.
[sizesufficienttosubmergetheRPD]
3. Useanon‐alcoholwetwipeandwipeoffstrapsandanyvisibledebrisfromRPD.
4. PlacetheRPDinpan/containerwith1%Alconoxsolution[ContainerA].
5. GentlyagitatetheRPD.
6. RemoveRPDfromContainerA.
7. RinseRPDonceinContainerC.
8. RemoveRPDanddrainexcesswater.
9. PlaceRPDinContainerB.Soaksubmergedfor10minutes.
10. WhileRPDissoakingchangewaterinContainerC.
11. After10minsoak,removeRPD.
12. PlaceRPDinContainerC.
13. GentlyagitatetheRPDfor30sec.
14. RemoveRPDanddrainexcesswater.[Ifskinsensitive,repeatsteps12&13twomoretimes
withfreshwatereachtime]
15. RemoveRPDanddryinanareawithreasonablecleanairflow(e.g.,hood,sterileopenchamber,
etc.).
16. ExamineRPDfordegradationofstraps,edges,fraying,etc.beforereusing.Donotreuseif
damaged.


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UltravioletGermicidalIrradiation(UVGI)Process
1. DoffRPD.
[Wearlatexornitrileglovestominimizehandcontactduringthisprocess]
2. Useanon‐alcoholwetwipeandwipeoffstrapsandanyvisibledebrisfromRPD.
3. PlaceRPDfaceupindrychamberwithUVshieldingcapacity(oruseproperPPE,e.g.,goggles).
4. ApplyUV‐Cat25W/m2totheoutersurfacefor10min.
5. TurnRPDoverandplacefacedown.
6. ApplyUV‐Cat25W/m2totheinnersurfacefor5min.
7. RemoveRPDanddryinanareawithreasonablecleanairflow(e.g.,hood,sterileopenchamber,
etc.).
8. ExamineRPDfordegradationofstraps,edges,fraying,etc.beforereusing.Donotreuseif
damaged.
CheckefficacyofUV‐C(254nm)sourcedailytoensure25W/m2acrossareatheRPDwillbeplaced.

MoistHeat(MH)Process
1. DoffRPD.
[Wearlatexornitrileglovestominimizehandcontactduringthisprocess]
2. Useanon‐alcoholwetwipeandwipeoffstrapsandanyvisibledebrisfromRPD.
3. PlaceRPDfaceupincubatororsteamingdevice.
4. Appl60‐65⁰C(uppertemp.limit),80‐85%RHfor30min.
5. Removeanddryinanareawithreasonablecleanairflow(e.g.,hood,sterileopenchamber,
etc.).
6. ExamineRPDfordegradationofstraps,edges,fraying,etc.beforereusing.Donotreuseif
damaged.

*Onecansubstituteamilddetergentatlowconcentrationifnecessary.