DTIC ADA534957: Filtration Effects Due to Bioassay Cage Design and Screen Type

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by  Defense Technical Information Center

Filtration Effects Due to Bioassay Cage Design and Screen Type
Author(s): Bradley K. Fritz, W. Clint Hoffmann, Muhammad Farooq, Todd
Walker, and Jane Bonds
Source: Journal of the American Mosquito Control Association, 26(4):411-421.
2010.
Published By: The American Mosquito Control Association
DOI: 10.2987/10-6031.1
URL: http://www.bioone.org/doi/full/10.2987/10-6031.1
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1. REPORT DATE 3. DATES COVERED
2010 2. REPORT TYPE 00-00-2010 to 00-00-2010
4. TITLE AND SUBTITLE 5a. CONTRACT NUMBER
Filtration Effects Due to Bioassay Cage Design and Screen Type
5b. GRANT NUMBER
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7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8. PERFORMING ORGANIZATION
Navy Entomological Center of Excellence,Box 43, Bldg REPORT NUMBER
937,Jacksonville,FL,32212-0043
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13. SUPPLEMENTARY NOTES
14. ABSTRACT
The use of bioassay cages in the efficacy assessment of pesticides, application techniques and technologies is
common practice using numerous cage designs, which vary in both shape and size as well as type of mesh.
The objective of this work was to examine various cage shapes and mesh types for their filtration effects on
air speed, spray droplet size, and spray volume. Reductions in wind speed and droplet size seen inside the
cages were measured by placing cages in a low-speed wind tunnel at air speeds of 0.5 m/ sec, 1 m/sec, 2
m/sec, and 4 m/sec and cage face orientations (relative to the air stream) of 0u, 10u, 22.5u, and 45u.
Reduction in spray volume inside a select number of cages was also evaluated under similar conditions.
Generally, greater air speed reductions were seen at lower external air speeds with overall reductions
ranging from 30% to 88%, depending on cage type and tunnel air speed. Cages constructed with screens of
lower porosities and smaller cylindrical-shaped cages tended to provide greater resistance to air flow and
spray volume. Overall, spray droplet size inside the cages was minimally reduced by 0?10%. There was a
32?100% reduction in concentration of the spray volume applied relative to that recovered inside the
bioassay cages depending on the cage geometry and screening material used. In general, concentration
reductions were greatest at lower air speeds and for cages with lower porosity screens. As a result of this
work, field researchers involved in assessing the efficacy of vector control applications will have a better
understanding of the air speed and spray volume entering insect bioassay cages, relative to the amount
applied, resulting in better recommended application techniques and dosage levels.
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JournaloftheAmericanMosquitoControlAssociation,26(4):411–421,2010
CopyrightE2010byTheAmericanMosquitoControlAssociation,Inc.
FILTRATION EFFECTS DUE TO BIOASSAY CAGE DESIGN AND
SCREEN TYPE1
BRADLEYK.FRITZ,2W.CLINTHOFFMANN,2MUHAMMADFAROOQ,3TODDWALKER3AND
JANEBONDS4
ABSTRACT. The useofbioassaycagesintheefficacyassessment ofpesticides,applicationtechniques,
andtechnologiesiscommonpracticeusingnumerouscagedesigns,whichvaryinbothshapeandsizeaswell
as type of mesh. The objective of this work was to examine various cage shapes and mesh types for their
filtrationeffectsonairspeed,spraydropletsize,andsprayvolume.Reductionsinwindspeedanddroplet
sizeseeninsidethecagesweremeasuredbyplacingcagesinalow-speedwindtunnelatairspeedsof0.5m/
sec,1m/sec,2m/sec,and4m/secandcagefaceorientations(relativetotheairstream)of0u,10u,22.5u,and
45u.Reductioninsprayvolumeinsideaselectnumberofcageswasalsoevaluatedundersimilarconditions.
Generally,greaterairspeedreductionswereseenatlowerexternalairspeedswithoverallreductionsranging
from 30% to 88%, depending on cage type and tunnel air speed. Cages constructed with screens of lower
porosities and smaller cylindrical-shaped cages tended to provide greater resistance to air flow and spray
volume.Overall,spraydropletsizeinsidethecageswasminimallyreducedby0–10%.Therewasa32–100%
reductioninconcentrationofthesprayvolumeappliedrelativetothatrecoveredinsidethebioassaycages,
depending on the cage geometry and screening material used. In general, concentration reductions were
greatest at lower air speeds and for cages with lower porosity screens. As a result of this work, field
researchersinvolvedinassessingtheefficacyofvectorcontrolapplicationswillhaveabetterunderstanding
oftheairspeedandsprayvolumeenteringinsectbioassaycages,relativetotheamountapplied,resultingin
betterrecommendedapplicationtechniquesanddosagelevels.
KEYWORDS Bioassaycages,sprayflux,sprayfiltration
INTRODUCTION material (Breeland 1970, Boobar et al. 1988,
Barber et al. 2006).
Evaluatingtheefficacyofinsectvectorcontrol
Constructionmaterialsandgeometryhavealso
treatments relies on accurate measurements of
been found to affect the spray and air flow
both the amount of spray material applied and
penetrationintothecage(Breeland1970,Boobar
insect mortality within a treated area. Bioassay
et al. 1988, Bunner et al. 1989, Hoffmann et al.
cages confine mosquitoes to specific spatial
2008).Screensplacedacrossanyairflowprovide
locations downwind of an application site per-
a resistance restricting flow (Kosmos et al. 1993,
mitting repeated and controlled assessments of
Miguel 1998, Teitel 2009). Screens also have an
insecticide and/or machine treatment efficacies,
efficiency with which they collect spray material
which provide a basis for pest management
that is a function of the screen characteristics,
programs.Althoughmeasurementsoftheportion
spray droplet spectrum, and airspeed (Foxet al.
of spray material aloft is well documented (May
2004, Fritz and Hoffmann 2008a).
and Clifford 1967, Miller 1993, Cooper et al.
Boobar et al. (1988) found that confined
1996, Fritz and Hoffmann 2008a, Bonds et al.
mosquitomortalityratesdidnotalwayscorrelate
2009), the interaction of the bioassay cage with
well with the observed parameters used to
theambientairstreamandappliedsprayandthe
monitor wild mosquito populations and suggest-
resulting insect dosage rates inside the cage are
ed that filtering of the spray via deposition onto
not understood. Reports have found that screen
the screen surfaces contributed to these inconsis-
materials with larger porosities filtered less spray
tencies. Boobar et al. (1988) also observed that
the mortality data between cages with varying
screen types could not be compared without
accounting for the differing filtering effects. This
1Mention of a trademark, vendor, or proprietary
productdoesnotconstituteaguaranteeorwarrantyof can also be extended to screens of varying
the product by the USDA or US Navy and does not geometrical design and orientation to mean air
imply its approval to the exclusion of other products flow based on results from Bunner et al. (1989).
thatmayalsobesuitable. Hoffmann et al. (2008) conducted a series of
2USDA-ARS-AreawidePestManagementResearch studies for 2 bioassay cage designs, one a flat
Unit,2771F&BRoad,CollegeStation,TX77845.
disk,theotheracylinder.Airspeed,spraydroplet
3NavyEntomologicalCenter ofExcellence,Box43,
size, and spray concentrations were measured
Bldg.937,Jacksonville,FL32212–0043.
inside and outside the cages. The results showed
4Florida A&M University, Public Health Entomol-
ogy Research and Education Center, 4000 Frankford that concentrations inside the cage ranged from
Avenue,PanamaCity,FL32405. 50% to 70% of those measured outside the cage.
411
412 JOURNALOFTHEAMERICANMOSQUITOCONTROLASSOCIATION VOL.26,NO.4
However, the measured concentration data re-
ported by Hoffmann et al. was not corrected for
thecollectionefficiency(CE)ofthesamplerused,
which would have differed for the external and
internal samplers as a result of the reduced air
speed inside the cage (May and Clifford 1967).
The samplers used in this study were relatively
large in diameter (0.6 cm) and, for the droplet
spectrum sampled, had approximate CEs of 6%
and 30% at 0.5 m/sec and 4 m/sec, respectively
(calculated after Fritz and Hoffmann 2008a).
Like many of the studies cited, Hoffmann et al.
(2008)waslimitedinscoperelativetothevariety
of cages tested. Fig. 1. Images of screening material tested: (a)
Giventhenumberofbioassaycagesinusewith aluminum screen, (b) copper screen, (c) fiberglass
screen, (d) nylon tulle T-310, (e) nylon tulle T-1720,
multiple cage geometries and screen mesh types,
(f) amber lumite screen. Note: Screen pictures are not
there is a need to quantify these effects. The
toscale.
objectives of this study were to determine the
influenceofbioassaycagesontheairspeed,spray
system then converted image to black and white,
droplet size, and amount of spray material
with fibers being white against a black back-
penetrating the cage under multiple air speeds ground. Mesh images were then analyzed for
and cage orientations relative to the mean air fiber diameter, distance between fibers, and
stream. percentopenarea.Foreachscreentype the fiber
diam, distance between fibers, hole percentage
MATERIALS AND METHODS area,andporositywasmeasuredacross40unique
locations and averaged (Table 1). Giving the
Wind tunnel testing facility multithread weave design of the T-310 and T-
1721 tulle materials, additional characteristics
The study was conducted in the United States
were measured and recorded. Where the alumi-
Department of Agriculture, Agricultural Re-
num, copper, and fiberglass materials consist of
search Service (USDA-ARS) Aerial Application
singlefibersinperpendicularcrossingweaves,the
Technology research group’s low-speed wind
2tullefabricsconsistofsmallerdiameterfibersin
tunnel at College Station, Texas. The tunnel is a
multithread, twisted interlocking perpendicular
push system with dimensions of 1.2 3 1.2 3
weaves, which result in less uniform screen
9.8m.Usinganelectronicvariablespeedcontrol,
structures(Figs. 1d,1e).Forthesescreens,single,
tunnel air speed can be varied across a range of
double,andclusterfiberdiamarereportedalong
0.5–6.5 m/sec. A gridded flow straightener
with distance between fibers, large- and small-
positioned in the tunnel 0.75 m downwind of
hole percentage areas, and total porosity (Ta-
thefanoutletprovidesforsmoothairflowwithin
ble 2).
the tunnel.
General descriptions of cage construction and
screen material and overall cage dimensions
Bioassay cages follow. The general descriptions follow the
following format: Full cage name; abbreviated
A selection of 12 mosquito bioassay cages
name usingtheformat ofa 3-letterabbreviation;
along with 2 prototype sand fly cages were
XX (where XX is a numerical value equal to
selected for testing (Figs. 1 and 2). The sand fly
porosityofscreenused);YZZ(whereYequalsC
cages are prototypes and were constructed using
[cylindrical cage] or D [disk cage] and ZZ is a
thecardboardbodiesfromtheNavyEntomolog-
numericalvalueequaltothediam[cm]ofthedisk
ical Center of Excellence and Clarke cages with
or cylinder). The letters in the listing below
amber lumite screen (BioQuip Products, Rancho
correspond to those associated with the cages
Dominguez, CA) in place of the normal screen
pictured in Fig. 2.
materials(T-1721tulle[Walmart],andT-310tulle
[Walmart], respectively. Prior to testing, cage A. Naval Entomological Center of Excellence
geometries and screen mesh characteristics were (NECE) Cage—NEC-74-D9: constructed
measured using an image analysis system devel- from 237-ml Neptune paper cans. Screen
oped for sizing droplets deposited on water- material is T-1721 tulle (Walmart). Dimen-
sensitive papers (Hoffmann and Hewitt 2005). sions: 9 cm diam 3 6 cm depth.
Macroscopic images were recorded for a section B. Kline Cage—KLI-59-C9: constructed from
of each of the meshes placed over a dark folded and stapled mesh screening. Screen
background such that the mesh fibers and material is plastic-coated fiberglass mesh (16
backgroundwerecontrastingcolors.Theimaging mesh). Dimensions: 20 cm 3 9 cm diam
DECEMBER2010 BIOASSAYCAGEEFFECTS 413
Fig.2. Mosquitobioassaycages.A:NECECage—NEC-74-D9;B:KlineCage—KLI-59-C9;C:Syke-Janousek
Cage 1—SYJ-84-D17; D: Meisch Cage—MEI-72-C9; E: PHEREC Cage—PHE-58-D14; F: PHEREC Field
Cage—PFC-72-D14;G:ClarkeCage—CLA-84-D16;H:PHERECFieldBioassay—PFB-58-C12;I:Syke-Janousek
Cage1—SYJ-84-D9;J:DVECCenterPVCCage—DVE-74-D11;K:Cooperband-AllanUSDACage—CAU-84-
C26; L: Chaskopoulou/WHO Cage—WHO-72-C5; M: NECE Sand fly Cage—NSC-47-D9; N: Clarke Sand fly
cage—CSC-47-D16.NOTE:CagesMandNareadaptedfromtheAandBcages,withoriginalscreeningmaterial
replacedwith amber lumite screen(BioQuip Products).Side views arenot shownforthese cages as they arethe
sameasthoseshownforAandB.
(center)312cm(ends).Note:Althoughthis dowscreen.Dimensions:9cmdiam321cm
cageisdefinedhereasacylindricalcage,itis length.
an irregular volume whose ends taper to a E. Public Health Entomology Research and
sharp edge. Education Center (PHEREC) Cage—PHE-
C. Syke-Janousek Cage 1—SYJ-84-D17: con- 58-D14: constructed from copper ring with
structed from cardboard ring with mesh copper screen soldered to each face. Screen
gluedtoeachfacealongtheringedge.Screen material is copper mesh. Dimensions: 14 cm
material is T-310 tulle (Walmart). Dimen- diam 3 3.5 cm depth.
sions: 17 cm diam 3 4 cm depth. F. PHEREC Field Cage—PFC-72-D14: con-
D. MeischCage—MEI-72-C9:constructedfrom structed from stainless steel ring with steel
screenedplastic ringsenclosingtheendsofa mesh welded to each face. Screen material is
cylinder constructed from metal screen. stainlesssteelmesh.Dimensions:14cmdiam
Screen material is 16-mesh aluminum win- 3 3.5 cm depth.
414 JOURNALOFTHEAMERICANMOSQUITOCONTROLASSOCIATION VOL.26,NO.4
Table1. Imageanalysisofmeshpropertiesforsingle- Screen material is amber lumite screen
weavematerials. (BioQuip Products). Dimensions: 9 cm diam
3 6 cm depth.
Distance
N. Clarke Sand fly cage—CSC-47-D16: con-
Fiberdiam betweenfibers Porosity
structed from concentric, friction-fit card-
Screentype (mm) (mm) (%)
board rings that secure screen material to
Aluminum 0.26 1.7 71.7
each face. Screen material is amber lumite
Copper 0.48 2.0 57.9
screen (BioQuip Products). Dimensions:
Fiberglass 0.40 1.7 58.8
16 cm diam 3 4 cm depth.
Amberlumite 0.26 0.81 46.6
Air speed reduction testing was conducted on
all 12 cages, and the spray volume penetration
testing was conducted on 4 mosquito bioassay
G. Clarke Cage—cLA-84-D16: constructed
cagesandthe2prototypesandflybioassaycages.
from concentric, friction fit cardboard rings
The selected cages for the spray penetration
that secure screen material to each face.
testingfrom thislist wereA,E,G,L,M,andN.
Screen material is T-310 tulle (Walmart).
Dimensions: 16 cm diam 3 4 cm depth.
H. PHEREC Field Bioassay Cage—PFB-58- Air speed reduction testing
C12: constructed from rigid screen material
Thecagesweremountedinthetunnelapprox-
with solid copper bottom and screened top.
imately5mdownwindofthefaninthecenterof
Screen material is copper screen. Dimen-
the cross-sectional area as shown in Fig. 3.
sions: 11.5 cm diam 3 13.5 cm height.
Internal and external air speeds were measured
I. Syke-Janousek Cage—1–SYJ-84-D9: card-
simultaneously using 2 Kanomax Clinomaster
board ring with mesh glued to each face
(ModelA533;KanomaxUSAInc.,Andover,NJ)
alongtheringedge.ScreenmaterialisT-310
high-precision hot-wire anemometers (measure-
tulle (Walmart). Dimensions: 9 cm diam 3
ment range: 0.05–5.0 m/sec; resolution: 0.01 m/
4 cm depth.
sec; accuracy: 62% of reading or 60.015 m/sec,
J. DiseaseVectorandEcologyControl(DVEC) whichever is greater). One anemometer was
Center PVC Cage—DVE-74-D11: construct- positioned within the center of each cage, and
ed from PVC ring with secure clips formed theotherwaspositionedoutsideandupstreamof
from PVC ring strips. Screen material is T- the cage (approximately 10 cm) at the same
1721 tulle (Walmart). Dimensions: 11 cm height. The anemometers were inserted into the
diam34cmdepth. cages, from the bottom, either through an insect
K. Cooperband–Allan United States Depart- insertion hole or, if not available, an incision in
ment of Agriculture (USDA) Cage—CAU- the screen.
84-C26: constructed from screen material Foreachcage,3replicatedmeasurementswere
sewed into 26 mm diam cylindrical sleeve made at 4 air speeds (0.5 m/s, 1 m/s, 2 m/s, and
and held to shape using sewing rings at top 4m/s)and4orientationsofthecagefacerelative
and bottom. Screen material is T-310 tulle tothemeanairdirection(0u,10u,22.5u,and45u).
(Walmart).Dimensions:26cmdiam332cm Thecages were mounted in a frame that allowed
length. forrotationaroundtheairspeedprobe.Airspeed
L. Chaskopoulou–World Health Organization measurements were taken over a 30-s period,
(WHO) Cage—WHO-72-C5: constructed during which the instruments sampled in 1-s
from WHO insecticide resistance test kits intervals. Average, maximum, and minimum air
and screen secured into cylindrical shape speeds were recorded for each replication. Aver-
with screened plastic cap on top end and ages and standard deviations were determined
plastic gate valve on bottom end. Screen across each set of replications, and the percent
materialis16-meshaluminumwindowscreen reductionofinternalversusexternalairspeedwas
material. Dimensions: 4.5 cm diam 3 12 cm determined using Equation 1. Significance of air
length. speed and cage orientation changes on the
M. NECE Sand fly Cage—NSC-47-D9: con- percentreductionofinternalairspeedwastested,
structed from 237-ml Neptune paper cans. using SYSTAT (v. 13.00.05, Systat Software,
Table2. Imageanalysisresultsofmeshpropertiesformulti-weavematerials.
Fiberdiam Distancebetween Holepercentarea Porosity
Screentype (single/double/cluster)(mm) fibers(mm) (large/small)(%) (%)
T-310tulle 0.051/0.086/0.257 1.1 81.5/2.1 83.6
T-1721tulle 0.12/0.30/0.40 1.4 71.7/2.6 74.3
DECEMBER2010 BIOASSAYCAGEEFFECTS 415
size external to the cage. For all screen types, air
velocityandorientationcombinations,3replicated
dropletsizemeasurementsweremade.
A Sympatec HELOS laser diffraction droplet
sizing system (Sympatec Inc., Clausthal, Ger-
many)wasused.TheHELOSsystemusesa623-
nm He-Ne laser and was fitted with an R5 lens,
resulting in a dynamic size range from 0.5 mm to
875 mm across 32 sizing bins. Tests were
performed within the guidelines provided by
ASTM Standard E1260: Standard Test Method
forDeterminingLiquidDropSizeCharacteristics
in a Spray Using Optical Nonimaging Light-
Scattering Instruments (ASTM, 2003). Droplet
sizingdataincludedvolumemediandiam(D ),
V50
and the 10% and 90% diam (D and D )
V10 V90
Fig.3. Hot-wireanemometerprobespositionedfor (ASTM E1620, 2004). D is the droplet diam
V50
airspeedmeasurementsinsideandoutsideoftheNavy (mm),where50%ofthesprayvolumeiscontained
Entomological Center of Excellence (NECE) bioassay indropletsofequalorlesserdiam.D andD
V10 V90
cage. values are likewise the droplet diam, where 10%
and 90% of the spray volume, respectively, is
Chicago, IL) general linear model analysis at the contained in droplets of equal or lesser diam.
alpha 5 0.05 significance level: Averages and standard deviations were deter-
mined and recorded. Reductions in D , D ,
V10 V50
%Reduction~(cid:1)1{ Airspeedinsidecage(cid:2)100: ð1Þ amnadteDriVal9,0,wreerleatailvseotdoettheremaibnseedn.cSeigonfitfhiceasnccreeeonfianigr
Airspeed
outsidecage speed and face orientation was tested using
general linear model analysis in SYSTAT (v.
13.00.05, Systat Software) at the alpha 5 0.05
Droplet size testing
significance level.
Droplet sizing measurements were made using
a laser diffraction system (discussed below),
Spray penetration testing
which required an uninterrupted line of sight
betweenthelaseremissionpointandthereceiving Spray penetration testing was conducted for
lens. To maintain this line of sight, 2 open-faced theselectedcagedesigns(asmentionedprevious-
(front and rear openings) chambers spanningthe ly) at 0.5 m/sec, 2 m/sec, and, 4 m/sec tunnel air
tunnel were constructed. These chambers en- speeds and at 0u and 22.5u orientations (screen
closed the distance between the laser outlet and face relative to the mean tunnel air stream, with
the lens detector while allowing for screening 0u being perpendicular to the wind direction).
materials to be attached over the front and back Five replication measurements were conducted
faces. One chamber was constructed with a flat for each cage/air speed/orientation combination.
faceandtheotherwitharoundedface(Fig. 4)to Anadditionalairspeedof1m/secwasexamined
represent the 2 cage geometries tested. The for the 2 sand fly cages due to below-detection-
chambers were mounted on a pivot to allow the threshold concentrations observed at the 0.5 m/
frontalfacestoberotatedtocorrespondwiththe sec air speed. For measurement of the spray
sameorientationanglesselectedfortheairspeed penetration, the cages were mounted within the
testing.Screeningmaterialsweresecuredinplace tunnelapproximately5mdownwindofthefanin
using magnetic tape that adhered to metal the center of the cross-sectional area. Spray
strappingattachedtotheframepinningtheedges concentrations inside the cages were measured
ofthescreen.Thisallowedscreeningmaterialsto usingsmalldiameterstainlesssteelwire(0.56mm
be replaced every 3 measurement replications to thickness 3 150 mm length) inserted into the
prevent material buildup on screens from affect- cages from below through access holes (Fig. 5).
ing droplet sizing results. Wires placed inside the cages were either bent in
For each of the bioassay cages selected, the half or in thirds, depending on cage height, to
corresponding screen type and frontal face shape accommodate fit. This was done, rather than
(flatorround)wastestedfordropletsizewithinthe using shorter wires, to maximize the sampling
screenedareaat4airvelocities(0.5m/s,1m/s,2m/ area due to the low spray concentrations being
s, and 4 m/s) and 4 frontal face orientations (0u, sampled. A second sampler was placed 0.5 m
10u,22.5u,and45u).Additionally,dropletsizewas upwind and external to the cage to measure the
measuredwiththechambersinplacebutwiththe concentration of spray material applied to the
screening material absent as a measure of droplet cage. The samplers were held using hemostats
416 JOURNALOFTHEAMERICANMOSQUITOCONTROLASSOCIATION VOL.26,NO.4
Fig. 4. Flat and round faces frames spanning wind tunnel walls for droplet sizing of spray penetration
screenmaterials.
that were held in place in the tunnel on posts spectrofluorophotometer (Model RF5000U; Shi-
equipped with magnets. madzu, Kyoto, Japan) with an excitation wave-
After each replication, the samplers were lengthof372nmandanemissionat427nmand
collected and placed into individually labeled a minimum detection level of 0.00007 mg/cm2.
plastic bags and stored in an ice chest. Prior to Fluorometricreadingswereconvertedtoconcen-
placementofsamplers,hemostatswerecleanedin trationsofspraymaterialperareasampledusing
acetone and allowed to dry. New samplers were comparativeanalysiswithfluorometricstandards
handledwithafreshsetofglovesforpreparation of known tracer dye concentration.
and placement to eliminate contamination. Test Prior to comparison of the cage internal and
cages were replaced after 3 replications to external spray concentrations, concentration
minimize any possible bias from spray material data were corrected for the collection efficiency
buildup on the screens on spray penetration. (CE) of the samplers. May and Clifford (1967)
Samples were processed in a laboratory by demonstrated that cylindrical collectors had CEs
pipetting15mlofhexaneintoeachbag,agitating that varied with droplet size and air speed. The
thebags,anddecanting6mloftheeffluentintoa sampler CE values were calculated using the
cuvette. The cuvettes were then placed into a droplet spectrum and air speed data measured
DECEMBER2010 BIOASSAYCAGEEFFECTS 417
Fig.5. Spraypenetrationmeasurementinsidecagesusingstainlesssteelwiredepositionsamplersheldinplace
usinghemostats.
for each test condition following the methods Internal (C ) and external (C ) mea-
internal external
outlined by Fritz and Hoffmann (2008a, 2008b). sured concentrations were then adjusted for CE,
The droplet size spectrum data used to correct and the reduction in concentration determined
the internal and external samplers for CE were using Equation 2. Significance of air speed and
taken from measurements made for the different frontalfaceorientationwastestedusingSYSTAT
screening materials, air speeds, and orientations (SystatSoftware)generallinearmodelanalysisat
as discussed earlier. The external sampler CE the alpha 5 0.05 significance level:
calculation used the droplet size spectrum (cid:1) c (cid:2)
measured with no screen in place at the air Reductionð%Þ~ 1{ internal 100: ð2Þ
c
speed being tested. The internal sampler CE external
calculationusedthedropletsizespectrumforthe
screen, air speed, and orientation angle associat-
Spray generation
edwiththecageandconditionsbeingtested.For
example, to correct measured concentration The spray used in the droplet sizing and spray
taken inside the NEC-74-D9 (NECE) cage at concentrationstudieswasgeneratedusinganair-
2 m/s and 0u orientation, the droplet size assisted dual-venturi-style, stainless steel nozzle
spectrum measured for the T-1721 tulle at 2 m/ (Advanced Special Technologies, Winnebago,
s and 0u orientation was used. Air speed outside MN), which produces a DV50 of 21.7 mm for oil
the cage was measured using a hot-wire ane- sprays (Hoffmann et al. 2007). A BVA crop oil
mometer (Model 407119A; Extech Instruments, with Uvitex dye (BASF) added at a rate of 1 g/
Waltham, MA). The air speed data used in the liter was metered to the nozzle using a syringe
CE calculations were calculated using the reduc- pump(NE-4000DoubleSyringePump;NewEra
tion levels measured as part of the air speed PumpSystems,Wantagh,NY).Atotalof3mlat
testing. avolumefeedrateof25ml/minwasusedforeach