United States
Environmental Protection
Agency
Risk Reduction
Engineering Laboratory
Cincinnati, OH 45268
Research and Development
EPA/600/SR-92/039 June 1992
EPA Project Summary
Exposure and Release
Estimations for Filter Press and
Tray Dryer Operations Based on
Pilot Plant Data
Mary C. Marshall, James R. Scott, and Hinton K. Howard
This Project Summary discusses the
findings from a pilot plant facility using
a stationary tray dryer and a plate-and-
frame filter press which were operated
as part of the joint research effort be-
tween the U.S. Environmental Pro-
tection Agency (EPA) and Southwest
Research Institute. The worker expo-
sure data, chemical release data, and
observations from the pilot plant ex-
periments expand the database for mak-
ing engineering assessments of
Premanufacture Notice (PMN) materi-
als which are fine solids (powders) and
wet filter cakes.
Worker exposures and chemical re-
leases associated with a plate-and-
frame filter press and a stationary tray
dryer were studied in a pilot plant. The
equipment was representative of that
in a chemical manufacturing plant; the
filter press was previously used at a
chemical plant, and the dryer trays were
the same size used by dye manufactur-
ers. A randomized series of eight ex-
periments identified the most influen-
tial variables for inhalation exposure
during operation of the tray drying unit,
which used approximately 100 kg of
calcium carbonate. The range of con-
ditions studied in the eight experiments
provide inhalation exposure data with
more than two orders of magnitude for
evaluating the impact on a PMN of the
physical properties, the activities per-
formed, and the worker's technique.
The worker inhalation exposure for
the tray dryer unit operation was con-
trolled by the tray unloading activity;
92% of the time weighted average
(TWA) was attributable to the tray un-
loading exposure even though this task
only took 30% of the worker's time.
Even when the filter press was oper-
ated, the tray unloading activity domi-
nated. The pilot plant tray dryer TWA
ranged from 1.59 to 18.1 mg/m3 and
averaged 7.28 mg/m3. The inhalation ex-
posures associated with powders were
greater than those for wet filter cakes.
The worker technique could double the
inhalation exposure and in some cases
be responsible for more than an order
of magnitude difference. The particle
size distribution affected the physical
properties of the filter cake and caused
mixed results. Small particles gave
higher inhalation exposures during the
cake removal stage, but the large par-
ticles gave higher inhalation exposures
during the tray unloading stage. Excel-
lent linear correlations between inhala-
tion exposure and effective generation
rate for ithe large range of pilot plant
conditions indicate potential success
for building an inhalation exposure
model baised on generation rates.
Chemical releases for the tray drying
unit operation for powders and filter
cakes were 0.7 to 1.5 wt% of the batch
size in the pilot plant. The chemical
release for the disposal of used filter
media ranged from 0.37 to 0.85 wt% of
the batch size. Worker dermal expo-
sures for cake removal were 0.039 to
0.60 mg/cm2, for tray loading were
0.0076 to 0,063 mg/cm2, and for tray
unloading were 0.0048 to 0.067 mg/cm2.
This Project Summary was developed
by EPA's Risk Reduction Engineering
Laboratory, Cincinnati, OH, to announce
key findings of the research project
Printed on Recycled Paper
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that Is fully documented in a separate
report of the same title (see Project
Report ordering information at back).
Introduction
As one component of Section 5 of the
Toxte Substances Control Act (TSCA), the
EPA must estimate the exposures (inha-
lation and dermal) and releases associ-
ated with the manufacturing of a new
chemical. To assist engineers making
these estimates, EPA has compiled his-
torical, 8-hr TWA inhalation exposure data
for various job classifications. The PMN
includes a process f tow diagram and esti-
mates of the number of workers and time
required to perform a given task. Based
upon this information, EPA must select a
job classification which most closely re-
lates to the PMN and then extrapolate the
8-hr TWA to the new chemical. Inhalation
exposure data for unit operations would
Improve the workplace inhalation expo-
sure estimations.
Dermal exposure estimations suffer from
a lack of sufficient historical data for work-
place dermal exposures. Several experi-
mental research efforts have been con-
ducted for EPA with liquid compounds to
obtain dermal exposure data; however,
until now the data obtained on dermal
exposure to powders has not been spe-
cifically directed at improving the PMN
review process information.
Historical chemical release data are not
available to the PMN reviewer on a unit
operations basis. Guidelines for estimat-
ing releases to water and disposal of filter
media to landfill or incineration have been
developed for the PMN system; however,
a more complete database of chemical
releases is needed.
Research began in August 1986 to (1)
improve estimates for workplace exposures
and chemical releases and (2) explore the
feasibility of developing predictive models"
for chemical releases and worker expo-
sures for filtration and drying unit opera-
tions. These two unit operations were se-
lected because of their high frequency of
appearance on PMN forms. Ten principal
equipment types were considered within
the unit operations (six kinds of filtration
equipment and four kinds of drying equip-
ment). Fitter presses and tray dryers were
selected for study because of their high
potential for inhalation exposure. Because
of the expense and inability to identify
appropriate manufacturing sites for data
collection, it was decided to do the stud-
ies on a pilot plant scale.
Procedure
A filter press was obtained which had
baen used in a chemical manufacturing
process, and a new stationary tray dryer
was purchased. In the pilot plant, a series
of randomized experiments were con-
ducted in a controlled environment (i.e.,
modified ventilation systems and one unit
operation per room to prevent cross-con-
tamination). During the pilot plant experi-
ments, sampling protocols for effective
generation rate, short term area concen-
tration data, dermal exposures, and chemi-
cal releases were evaluated to identify
whether the methods and prediction mod-
els would be practical for field work.
Calcium Carbonate was the chemical
used in these experiments; because it is
inexpensive, non-toxic, available in a range
of particle sizes, and has low water solu-
bility.
Eight experiments were performed uti-
lizing a factorial design for two levels for
each of three factors: two research tech-
nicians as operators, two size distribu-
tions of CaCO3, and two initial conditions
of the material. Regarding the last factor,
the initial condition was either a dried pow-
der or a filter cake (the latter was pro-
duced by processing a 10 wt% slurry of
CaCOg in water through the plate-and-
frame filter press). The drying experiments
consisted of: loading approximately 100
kg of CaCO3 onto 11 trays, drying the
material in a mechanical convection oven,
and unloading the dried material into a
single container. The tray loading and un-
loading areas were located in a room that
possessed a high air exchange rate and
well-mixed air circulation, but no local ex-
haust ventilation systems.
As preparation for a pilot plant experi-
ment with an initial condition of wet filter
cake, the CaCO3 was mixed with water jn
a 380-gal tank to give a 10 wt% CaCO3 in
water slurry. An 18-in. by 18-in., 15-cham-
ber, plate-and-frame filter press was used
to filter this slurry. The mixing and filtra-
.- tion -activities were performed within a,,
metal-frame building in an area which was
separated from a warehouse by floor-to-
ceiling black polyethylene sheets. No modi-
fications were made to the general venti-
lation system in this filtration area.
A mechanical convection oven (Blue M
Model DC-136C)* with an internal volume
of 0.75 m3 was used as the stationary-tray
dryer. The oven was located in a second
room which was significantly modified to
provide a well-mixed, high exhaust turn-
over rate for the detailed study of genera-
tion rate. One tray dryer batch consisted
of approximately 100 kg of CaCO3 (dry
weight basis) loaded onto eleven 94 x 48
cm trays.
The factorial experiment was designed
to study the response variable, worker
inhalation exposure (mg of CaCO. / m3 of
air). The analysis of variance (ANOVA)
tables were also developed for two other
response variables, dose [(mg of CaCCy
(minute) / (m3 of air)] and mass of chemi-
cal spills [kg spill / kg product]. The dose
variable is calculated by multiplying the
inhalation exposure for a given activity
(cake removal, tray loading, or tray un-
loading) and the activity's duration. Other
response variables of interest for the pilot
plant experiments were generation rate
(mg CaCO3/sec), chemical release (kg of
CaCO3), and worker dermal exposure (mg
CaCO3/cm2 skin). These variables were
assessed for linear correlations with vari-
ous parameters.
Results and Discussion
One of the factors that can affect the
airborne concentrations within a work area,
and subsequently the inhalation exposure
of the operators, is the ventilation charac-
teristics of the work area. To enhance the
evaluations associated with the genera-
tion rate models, the drying room was
deliberately equipped with a ventilation
system that would create a well-mixed air
flow pattern inside the room. The drying
room was designed to have an average
room air exchange rate of 8.7 changes
per hr and an average mixing factor of
1.03 which indicates perfect mixing condi-
tions within the error range of the mea-
surements. The air exchange rate and the
mixing factor of the drying room may be
better than those values found in typical
industrial facilities. Conversely, the filtra-
tion room's average air exchange rate of
5.0 changes per hr and mixing factor of
0.88 are probably more consistent with
the levels existing in actual chemical manu-
facturing plants.
To. characterize a .worker's;, inhalation
exposure for an entire unit operation, the
TWA exposure is commonly used. The
TWA inhalation exposure to CaCO3 in-
curred by the pilot plant workers during
the tray dryer operation can be calculated
using the following formula:
tucu)/T
where:
' Mention of trade names or commercial products does
not constitute endorsement or recommendation for
tL = time of the loading stage
CL= calcium carbonate concentration
measured in the breathing zone of
the operator during the loading
stage
tu o time of the unloading stage
c = calcium carbonate concentration
measured in the breathing
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zone of the operator during the un-
loading stage
T - total time operator was involved
with the tray dryer operation
Since the operator was not present dur-
ing the drying stage (i.e., the inhalation
exposure was zero), this stage is not in-
cluded in the TWA calculation. The geo-
metric mean TWA inhalation exposure for
the drying unit operation was 7.28 mg
CaCO3/m3. The unloading activity ac-
counted for 92% of the overall inhalation
exposure even though it accounted for
only 30% of operator's time. This com-
pares with a previous in-plant study of a
recessed filter press where 72% of the
TWA inhalation exposure for the entire
filtration operation was attributable to the
cake removal stage even though only 1 5%
of the operator's time was required for this
activity. Therefore, for the two unit opera-
tions of interest, filtration and drying, one
worker activity for each unit operation is
attributable to the majority of inhalation
exposures.
The three main factors (worker, particle
size distribution, and material condition)
significantly affected (p < 0.05) worker
inhalation exposures for all three unit op-
eration activities with the exception of the
particle size distribution for the loading
activity. In the performance of all activities
associated with the stationary-tray dryer
and the plate-and-frame filter press,
Worker B consistently experienced higher
inhalation exposures. During the removal
of filter cake from the filter press, inhala-
tion exposures were higher for the smaller
particle size distribution. The particle size
distribution had no significant effect on
inhalation exposures during the tray load-
ing activity. During the tray unloading ac-
tivity, inhalation exposures to the larger
particle size distribution were greater than
those to the small particle size distribu-
tion. Finally, inhalation exposures to the
powdered material (i.e., dry initial condi-
tion) for the tray loading and tray unload-
ing stages were higher than for the mate-
rial which was processed through the plate-
and-frame filter press.
For the manual filter press and tray
drying unit operations, one worker activity
for each unit operation is attributable to
the majority of inhalation exposures (92%
of tray dryer TWA and 30% of the worker's
time is associated with tray unloading ac-
tivity).
When both filter press and tray drying
unit operations are being performed, the
inhalation exposures are overwhelmingly
controlled by the tray unloading activity.
The tray unloading inhalation exposure
(8.63 to 49.4 mg/m3) was one to two or-
ders of magnitude greater than those re-
ceived during the remaining tray dryer
(0.20 to 2.38 mg/m3 for tray loading and
negligible for drying) and filtration (0.13 to
0.73 mg/m3 for cake removal) operations.
In the tray dryer operations, worker tech-
nique, particle size distribution, and mate-
rial condition significantly affect worker in-
halation exposures and are each capable
of producing a range of inhalation expo-
sures greater than one order of magni-
tude.
Pilot plant tray dryer overall TWA inha-
lation exposure was 7.28 mg/m3 with a
range of 1.59 to 18.1 mg/m3. It is conceiv-
able that different workers and greater
distinctions in CaCO3 size ranges could
make exposures even more variable. Con-
sequently, data collection activities with-
out development of predictive models will
not provide the PMN reviewer with a reli-
able order of magnitude estimate for inha-
lation exposures.
Inhalation exposure concentrations are
approximately the same for the cake re-
moval (0.13 to 0.73 mg/m3) and the tray
loading (0.22 to 0.68 mg/m3) activities for
wet filter cakes which may imply that the
physical principles responsible for genera-
tion of the aerosols are similar for these
tasks.
Total chemical releases for the tray dryer
unit operation when fine solids (powders)
are being handled (0.7 to 1.5 wt%) are
higher than the current PMN guidelines of
-0.1% to 1.0% of batch size (i.e., product
yield).
The mass of wet filter cake lost from
trays during! their transfer into and out of
the dryer shelves is the greatest source
for chemicail releases during tray drying
operations and are as high as 2.84% of
product yield.
For filter cloths that are washed prior to
disposal, the current PMN guideline for
chemical releases to the landfill or incin-
erator (i.e., 0.5% of a batch) is an appro-
priate estimate for the amount of material
retained within the filter cloth.
For unwashed filter cloths, the chemical
release associated with cloth disposal is
0.7% of a batch.
Worker dermal exposures during cake
removal operations (0.039 to 0.60 mg/cm2
skin) are less than the criteria stated in
current PMN guidelines (1 to 3 mg/cm2
skin developed from contact with liquids).
The pilot plant data of 0.0076 to 0.063
mg/cm2 skin for dermal exposures associ-
ated with tray loading activities can be
used for PMN materials which are fine
solids or filter cakes.
The pilot plant dermal exposures from
activities associated with high tempera-
tures (e.g., Ithe tray unloading activity) are
higher than the current PMN guidelines
(the pilot plant exposures were 0.0048 to
0.067 mg/cm2 skin and PMN guidelines
advise "negligible" exposure). The dermal
exposure during high temperature opera-
tions stems from fine solids falling into the
worker's gloves, and from contamination
between experiments since the gloves
were not exchanged for new ones be-
tween experiments.
This report was submitted in partial ful-
fillment of Cooperative Agreement CR-
813355 by Southwest Research Institute
under the partial sponsorship of the U.S.
Environmental Protection Agency.
•U.S. Governmant Printing Office: 1992— 648-080/60023
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Mary C. Marshall and James R. Scott are with the Southwest Research Institute,
San Antonio, TX 78228; and Hinton K. Howard is with the Risk Reduction
Engineering Laboratory, Cincinnati, OH 45268.
John O. Burckle is the EPA Project Officer (see below).
The complete report, entitled "Exposure and Release Estimations for Filter Press
and Tray Dryer Operations Based on Pilot Plant Data," (Order No. PB92-
158450/AS; Cost: $43.00; subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Risk Reduction Engineering Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
United States
Environmental Protection
Agency
Center for Environmental
Research Information
Cincinnati, OH 45268
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POSTAGE & FEES PAID
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EPA/600/SR-92/039
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