United States
Environmental Protection
Agency
Industrial Environmental Research
Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S2-81-126 Sept. 1981
Project Summary
Characterizing Baghouse
Performance to Control
Asbestos Manufacturing
Source Emissions
David R. Jones
This study is part of a research
program designed to improve the
effectiveness of airborne asbestos
fiber removal by baghouses. A typical
fabric filter baghouse control system,
shown in Figure 1, was automated and
modified to facilitate the use of the
EPA Method 5 sampling train, shown
in Figure 2 to monitor the output of the
baghouse during the commercial
fabrication of asbestos containing
materials. Single-point near isokinetic
inlet samplers were installed on each
of four inlet ducts. The baghouse mass
loadings, the outlet fiber concentra-
tions, and operating conditions of the
fabrication process were monitored.
Each of three operating parameters of
the baghouse was observed at three
levels. The baghouse research param-
eters were shake amplitude, shake
duration and shake interval.
Two test series were conducted.
The first was a statistically designed
test series, the results of which were
interpreted using multiple linear
regression analysis on the 1 /3 facto-
rial test design. The linear regression
analysis showed shake duration to be
the most important parameter, fol-
lowed by the shake amplitude and the
shake period. The results indicated
that, at optimum shake interval and
shake duration, a 6-fold improvement
in asbestos fiber emission control was
achieved. The second test series was
run to determine whether extending
shake intervals would produce an
equivalent 6-fold reduction in fiber
emissions, and if the mass loading or
waste type were more significant
characteristics. Extending the shake
intervals did result in low emissions;
however, no significant effect on
control was achieved by extending
shake duration. No detectable change
in pressure drop was noted up to a 12-
hour shake interval.
Statistical evaluation of the first test
series data indicated interactions
between the baghouse parameters.
The fiber emissions were reduced at
longer shake intervals. The major
conclusion reached regarding asbestos
emission control was that fiber
emissions were minimized by the least
frequent disturbance of the bags.
The Project Report was submitted in
fulfillment of Contract No. 68-03-
2558 by I IT Research Institute under
the sponsorship of the U.S. Environ-
mental Protection Agency. The report
covers the period from June 27.1977
to September 30, 1979.
This Project Summary was devel-
oped by EPA's Industrial Environ-
mental Research Laboratory. Cincin-
nati. Ohio, to announce key findings of
the research project that is fully
documented in a separate report of the
same title (see Project Report ordering
information at back).
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Figure 1. Baghouse for asbestos removal, showing plenem. ducting and effluent
sampling station.
Figure 2. HVSS sample train and effluent monitor.
2
Introduction
Processes involving asbestiform
minerals are known to produce signif-
icant quantities of waste materials
which release airborne asbestos fibers.
Airborne asbestos fibers have been
associated with asbestosis and other
respiratory diseases. The prevalent
control device used to minimize the
emission of airborne asbestos fibers to
the environment is a fabric filter used in
a form known as a baghouse.
This report describes a field research
program whose objective was to mini-
mize asbestos fiber emissions. The
program demonstrated that, even
though a baghouse has an extremely
high mass efficiency, literally billions of
fibers per ho(ur are emitted from a well-
controlled source.
While current asbestos data do not
permit the determination of the health
effects, it is prudent to maximize the
control of asbestos emissions using the
most feasible, economical and effective
methods available.
Asbestos fibers are implicated in the
development of diseases with 20-40
year latency periods, and to date no
threshold exposure value has as yetj
been defined. It is possible that even'
very small asbestos fiber emissions
could have a long-term impact on the
national health.
Previous studies had shown that
fabric filters were the most common and
effective method of controlling emissions
from asbestos processes. Variations in
the operating baghouse parameters
were believed to affect the degree of
control achieved. In'this study, a full-
scale commercial baghouse was oper-
ated at specified conditions, and its
degree of control measured by moni-
toring emission fiber counts.
The objective of the study was to
identify the significant operating pa-
rameters, and to determine what
conditions provide maximum control of
asbestos fiber emissions. The fiber
count method was used, since the
variations on a mass basis are too small
to measure.
This research study has origins in
past projects done at IITRI and in EPA's
continued interest in the improvement
of control technology for asbestos fiber
emissions from industrial sources. The
initial effort was a two-phase program
performed under EPA Contract No. 68-
03-1353. Phase I results are reported in
EPA-650/2-74-088 and Phase II result^
in EPA-600/2-76-065. ^
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Statistical Evaluation of Bag-
house Test Data
The pri mary objective of the f ractiona I
factorial statistical evaluation was to
define guidelines for the optimum
operation of baghouses for control of
asbestos emissions. This was done on a
full scale baghouse in use on an actual
operation generating asbestos emis-
sions. The parameters selected for
investigation were:
• the period of time between shake
cycles,
• the duration of the shake cycle, and
• the shake amplitude.
During the first series of tests on the
program a data base was assembled
permitting statistical analysis of the
three baghouse parameters, monitoring
of the baghouse condition, baghouse
inlet loading, and data permitting a
check on the validity of the samples.
All of the data were associated with
93 individual samples taken during the
test program. The specific data base
used in the statistical analysis consisted
of fiber concentration in number of
fibers/SCM. The data were obtained
using electron microscopy (EM) on each
of the 93 samples obtained. Additionally,
each of the inlet loading values obtained
from all but combination 2 was also
entered into the analysis as a possible
co-variate variable.
Prior to the linear regression analysis
of the design, statistics on each of the
combinations were obtained. These
statistics were used to verify the
homogeneity of the fiber counting data
and various transforms. The variance of
the fiber count data varied widely from
combination to combination (P>.001).
The variance of the square root transform
also fluctuated (0.10 > P>0.05), while
the log transform was more stable (0.3>
P> 0.2). On the basis of Bartlett's test,
the log transform was considered
suitable for use in obtaining a pooled
estimate of the standard deviation. The
estimated pooled standard deviation
obtained on the basis of 81 degrees of
freedom was s = 0.49.
The summary of major conclusions
based on linear regression analysis of
the primary data base were:
• Two of the selected parameters,
shake duration and shake amplitude,
showed the maximums in their
output curves. The existence of a
maximum rather than a minimum
implies either that there is no
optimum, or that the optimum is
outside the experimental range of
the parameters.
• The shake period showed a mini-
mum at the midpoint of the values
studied.
• A positive correlation between
mass loading of the baghouse and
the output concentration has been
obtained.
• The lowest output concentration
obtained is equivalent to the
baseline concentration. The base-
line conditions are outside the
range of parameters studied.
• All values of concentration mea-
sured were at approximately 10 x
10" to 50 x 106 fibers/SCM. This is
equivalent to 10-50 fibers/cc in
the baghouse outlet. Also, since
about 10 percent of the total fibers
are above 5 /urn in length, the
OSHA concentrations measured in
the baghouse plenum would be 1 -5
fibers/cc.
There were two conclusions which
required additional study. The first was
that a previous study had showed, by
similar statistical analysis, that the type
of waste was more significant than the
mass loading. The second was that the
baseline data, obtained at a 12-hour
shake period and 300-sec shake dura-
tion, showed an output concentration
equivalent to the lowest obtained in the
experimental design. The shake period
and shake duration were greater than
those studies, while the shake ampli-
tude was identical to the longest ampli-
tude used in the design.
From the data taken, the conclusions
are:
• Extending the length of the period
between shakes is beneficial.
• For some applications, the pressure
drop is not significantly affected by
extended shake interval.
• Automation of the shake cycle
leads to better performance of the
baghouse.
• Shake duration at extended inter-
vals between .shakes is not a
significant parameter.
• The duration of the shake cycle
seems to be the most important
parameter, both from statistical
and observed standpoints.
• Interactions between variables are
important, but cannot be computed
from the partial factorial experi-
ment. The interactions make for-
mulation of a design equation
impractical.
Conclusions
The single most important variable in
the level of asbestos fiber emissions
from a baghouse is the duration of the
shake time for the bags during the
cleaning operation. The next variable in
importance is the amplitude of the
shake, followed by the shake period.
These three variables account for about
40% of the output variability from a
baghouse.
The interactions between the three
design parameters of shake period,
shake amplitude and shake duration are
important in operating a baghouse. The
measured asbestos fiber emission rate
from a baghouse is dependent on the
material being processed and the
process rate.
The lowest values of baghouse output
measured were 6 million fibers/m3 and
the highest 32 million. The lowest value
showed fiber concentration of 0.3
fibers/cc >5 fjm (300,000 fibers/m3 >
5/um) on the average. However, one
sample included in this average approx-
imated the OSHA limit of 2 fibers/cc (2
million fibers/m3> 5jum) of air. Fiber
counts exceeding the current OSHA
limitof 2 fibers/cc of air >5|/m in length
were numerous.
The lowest concentrations of fibers
emitted were achieved when the
baghouse was operating at conditions
which favored greater cake build-up on
the bags. The combination was: short
shake/small shake amplitude and long
shake period. No detrimental effect on
pressure drop was noted at the most
efficient conditions. In fact, no correla-
tion of performance with pressure drop
was found. The baghouse, even though
it has an extremely high mass efficiency,
does emit literally billions of fibers per
hour under optimum conditions.
Recommendations
The baghouse exit air fiber levels
must be reduced below 100,000 fibers
> 5//m per cubic meter to be considered
for recycle. In lieu of current optimum
conditions as defined by this research,
the baghouse alone cannot produce the
levels of control required. Additional
research is necessary to assess what if
any control technology is capable of
producing an emission of less than
100,000 fibers >5^m per cubic meter.
The use of statistical design tech-
niques when evaluating or optimizing
control device performance is recom-
mended. Statistical designs for con-
tinuous data are quite efficient to use
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and provide cost effective programs.
The data obtained on a statistically
designed program will provide, at a
minimum, guidance for future work and
trends; at its best, when all assumptions
are correct, the maximum information is
extracted from the data.
David R. Jones is with IIT Research Institute, Chicago, IL 60616.
Mary K. Stinson is the EPA Project Officer (see below).
The complete report, entitled "Characterizing Baghouse Performance to Control
Asbestos Manufacturing Source Emissions,"(Order No. PB81 -231 250; Cost:
$8.00, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Industrial Environmental Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
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