United States
Environmental Protection
Agency
National Risk Management
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/SR-94/214 April 1996
4>EPA Project Summary
Demonstration of Split-flow
Ventilation and Recirculation as
Flow-reduction Methods in an Air
Force Paint Spray Booth
S. Hughes, J. Ayer, and R. Sutay
The report gives results of a demon-
stration of split-flow and recirculating
ventilation, individually and in combi-
nation, as safe and cost-effective meth-
ods of reducing paint spray booth
exhaust flow rates to lower the costs
of both conditioning intake air and con-
trolling volatile organic compound
(VOC) emissions in exhaust air.
This Project Summary was developed
by EPA's National Risk Management
Research Laboratory, Research Triangle
Park, NC, to announce key findings of
the research project that is fully docu-
mented in a separate report of the same
title (see Project Report ordering infor-
mation at back).
Background
This study was part of an extended
program of investigations into the cost and
efficacy of innovative approaches for bring-
ing U.S. Air Force industrial operations
into compliance with current and antici-
pated air pollution environmental stan-
dards. Adequate ventilation of paint spray
booths requires the movement of large
quantities of air, which are slightly con-
taminated during passage through the
booth. Air exhausted from this process
requires decontamination, which, although
technically achievable at operating flow
rates, can be prohibitively expensive. Be-
cause emission-control costs depend on
the volume of exhaust air being treated,
considerable savings can be realized
through the application of an acceptable
flow-reduction method.
A first principle of industrial hygiene is
to employ engineering controls to their
limit before invoking personal protection.
In dealing with exposures to airborne
toxics, the mainstay engineering device is
enhancement of ventilation. However, in-
creased ventilation creates enormous vol-
umes of slightly contaminated air, which
must be treated before discharge, and in
many situations the cost of such treat-
ment is excessive. In such circumstances,
a judgment must be made about the rela-
tive cost in increased exposure compared
to the economic benefit in decreased op-
erating cost. The goal of this study was to
provide experimental data to support the
development of a general Air Force posi-
tion and objective criteria for local deci-
sions about the acceptability of using
flow-reduction methods in paint spray
booths, based on local health-risk/cost-
benefit considerations.
Scope
The study consisted of two sets of ex-
perimental measurements in Booth 2,
Building 845, Travis Air Force Base, CA,
plus results of an ancillary effort conducted
at Research Triangle Institute (RTI) to
verify experimentally that the flame ion-
ization detector used in the ventilation con-
trol loop is within its linear response range
at the equivalent exposure limit for the
mixture of solvents present in the mixed
top coat. The first set of experimental mea-
surements was a baseline characteriza-
tion of the distribution of toxic pollutants at
the exhaust face and in the exhaust duct
of Booth 2. These data, the RTI results,
and the test plan for the second set of
tests were reviewed before approval was
given to proceed with the recirculation
tests. For the second set of tests, the
ductwork in Booth 2 was reconfigured to
separate exhaust streams from the top
and bottom of the booth (split-flow) and to
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return the upper exhaust stream to the
intake plenum for recirculation through the
booth. During separate painting sessions,
several sets of concentration measure-
ments were made of VOCs, particulates,
heavy metals, and isocyanates. Equiva-
lent exposures (Em) were calculated from
these data, and projections of Em were
made for larger recirculation ratios, to-
gether with an economic analysis of the
corresponding costs to apply VOC emis-
sion control devices.
Methodology
To determine exposure concentrations,
sampling was performed simultaneously
inside and outside the respirator, at 24
locations at the exhaust face, in the ex-
haust ducts, and, during the second set of
tests, at three locations at the face of
each of the two intake filters. To deter-
mine environmental contributions to the
load of pollutants, background air samples
were collected at the back of the booth
prior to the release of any paint-derived
materials. Standard sampling methods
were used. Paint usage was determined
by weighing the gun after each filling and
at the end of each painting session. The
percent volatile content of the paint was
determined gravimetrically, as percent
weight loss to evaporation. Airflows were
measured with an anemometer in the
booth and with a pitot tube in the exhaust
ducts. Painting start and stop times were
recorded manually by an observer, sta-
tioned at the rear of the booth, who also
noted the dimensions and locations of
workpieces painted, coatings applied, and
other details. Projections of equivalent ex-
posures at different recirculation ratios
were calculated by a Lotus 1-2-3 pro-
gram.
Test Description
In both test series, representative
workpieces were prepared and coated ac-
cording to normal operating procedures.
During each such painting run, measure-
ments were made of one of the four pol-
lutant classes using standard methods. A
typical painting session lasted 30 to
90 minutes, and included post-painting
cleaning of the paint spray gun with me-
thyl ethyl ketone and tidying up of the
area. In general, two sets of tests were
conducted during an 8-hour shift, corre-
sponding to a typical workday.
Results
Concentrations of airborne toxic pollut-
ants are recorded in the tables of the
report. Strontium chromate occurs as the
major contaminant during primer coating
and was the largest contributing factor to
the Em. Organic exposures were minor
during all painting, except that high isocy-
anate exposure occurred outside, but not
inside, the painter's respirator during top-
coat application inside a comfort pallet
(caused by airflow restrictions in the closed
space, and unrelated to the mode of ven-
tilation in the booth). The newly constructed
recirculation duct was a source of several
metals. These metals were included in Em
calculations, but the concentrations are
expected to decrease after the newly con-
structed surfaces are blown clean. Contri-
butions to Em from recirculation are
significantly less than the Air Force crite-
rion of 0.25 imposed for these tests, and
much less, in general, than the contribu-
tion from the painting process. The painter
showed no evidence of overexposure dur-
ing the post-test medical evaluation.
Conclusions
Data support the prediction that work-
place exposure levels during recirculation
of paint spray booth exhausts, especially
combined with split-flow extraction of the
pollutant-enriched lower portion of the ex-
haust stream, can be maintained at less
than an arbitrarily selected criterion (here,
Em = 0.25). Flow splitting alone is consid-
erably less effective, but, in combination
with recirculation, it acts to lower the con-
centrations in the recirculated stream at a
given rate of recirculation. Computational
projection of Em to larger recirculation rates,
and interpolation of results of an earlier
economic analysis of scale-related costs
to decontaminate exhaust air, indicated
that available cost savings allow projected
payback on the order of 1 year for thermal
or catalytic incineration.
Recommendations
Improvements should be examined to
augment or replace present-generation fil-
ter and water particulate control systems.
Concurrently, or when the improved tech-
nologies satisfy local standards, a combi-
nation of flow reduction and VOC control
should be implemented in an area of in-
tense regulatory pressure as the definitive
prototype. Standardized criteria should be
established to guide site selection, de-
sign, installation, and maintenance.
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S. Hughes, J. Ayer, and R. Sutay are with Acurex Environmental Corp., Mountain
View, CA 94039.
Charles H. Darvin is the EPA Project Officer (see below).
The complete report, entitled "Demonstration of Split-flow Ventilation and Recircu-
lation as Flow-reduction Methods in an Air Force Paint Spray Booth," is a two-
volume document:
Volume I (Order No. ABA 286 807; cost, subject to change, $31.00) contains
the main report and Appendices A through C.
Volume 11 (Order No. ABA 286 808; cost, subject to change, $38.00) contains
Appendices D through J.
Both volumes 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
National Risk Management Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
United States
Environmental Protection Agency
National Risk Management
Research Laboratory (G-72)
Cincinnati, OH 45268
BULK RATE
POSTAGE & FEES PAID
EPA
PERMIT No. G-35
Official Business
Penalty for Private Use
$300
EPA/600/SR-94/214
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