that is to be painted. Airflow must be in a direction which will carry con-
taminated air away from the breathing zone of the painter. If necessary, work
platforms, product rotators, or other means must be provided in order that the
proper orientation of airflow can be maintained.

Air velocities of approximately 100 fpm are adequate to control most spray
painting operations. Lower air velocities (60 fpm) are appropriate where
airless spray equipment is used, paint delivery rates are low, and the paint
is formulated with relatively safe ingredients. Higher air velocities (150
fpm) should be considered where substantial quantities of highly toxic
materials are sprayed. It is preferable to supply make-up air directly to the
spray booth to avoid disruptions from stray room air currents and for reasons
of product quality control. Make-up air should be supplied from behind (or in
the case of a downdraft booth, above) the painter and in the same direction as
it is being exhausted. Make-up air velocity should be no greater than twice
the control velocity.

Fan noise in the spray booth should be minimized by use of a centrifugal fan
rather than a propellor type, and by locating the fan on an isolated surface
rather than the spray booth roof.

Application Equipment

Application equipment should be selected that minimizes the energy expended in
the atomization process, thus reducing the amount of stray mist that is gene-
rated. The recommendations of the paint formulator concerning the method of
application and the atomization parameters should be strictly followed.

Certain operations, such as painting deep recesses or internal cavities, can
not be effectively controlled by ventilation. Airless application methods are
suggested for these operations.

Health Studies

Respiratory problems have been reported among users of two-component urethane
coatings. The potential for the isocyanate prepolymers used in these coatings
to cause respiratory impairment or sensitization is unknown. In order to de-
fine safe levels of exposure to polymeric isocyanates, further development of
analytical techniques for the determination of these materials is necessary,
followed by environmental and medical investigations of respiratory impairment
in exposed individuals.

Health problems have also been associated with amine curing agents used in some
two-component epoxy coatings. As is the case with urethane coatings, develop-
ment of suitable analytical techniques is essential for any future research.

The extensive use of talc, diatomaceous earth, and silica (both crystalline and
amorphous) in paints and coatings suggests the possibility of fibrogenic lung
disease among painters using these materials. In light of the potential expo-
sure in spraying, epidemiological studies of lung disease in spray painters may
be warranted.

54


Cartridges are changed when the painter detects a solvent odor. Filters are
changed when breathing resistance is affected.

EVALUATION

One full time painter is employed in this shop. Total spraying time for com-
plete body repainting is approximately 45 minutes, and the painter will spray
from 6 to 8 cars on a typical workday (8-hour shift).

To determine control effectiveness, the breathing zone levels (outside the
respirator) of total spray mist, orangic solvents, and lead and chromium were
determined by personal air samples taken during the time required to repaint
each car. Total mist samples were collected by using closed-face cassettes,
with preweighed 37 mm polyvinyl chloride/acrylonitrile copolymer membrane
filters and personal pumps operated at 2.0 lpm. After weighing, the filters
were ashed and analyzed for lead and chromium by atomic absorption spectro-
scopy. Organic solvent samples were collected on 150 mg. charcoal tubes with
personal pumps at 100 cc/min. Tubes were subsequently desorbed and analyzed
by gas chromatography.

For polyurethane topcoats, consecutive, short-term samples were taken in the
painter's breathing zone in order to determine ceiling isocyanate concentra-
tions. Isocyanate samples were collected by using two midget impingers, which
were connected in series to a personal pump operated at 2.0 Ipm. Each impinger
contained 15 ml of a nitro reagent solution, which was subsequently analyzed
for the HDI/nitro reagent compound by high pressure liquid chromatography.

RESULTS

Sample results for total mist, lead, and chromium are reported in Table 5-2.
Mean paint mist levels are within the recommended maximums for an 8-hour expo-
sure to total particulates. Eight-hour time-weighted average (TWA) exposure
to lead was within the 50 ug/m? OSHA limit. However, none of the coatings
used on the vehicles painted during the survey contained significant quantities
of red or yellow pigments. This was not by the study's design, rather, red
and yellow colors are relatively unpopular for both new vehicle purchases and
repainting. The lead levels that were observed are a result using a lead soap
as the paint drier. For these reasons, all but one chromium sample were below
the limits of detection for chromium (3 ug per filter). Because the most
common chromium pigment is lead chromate, the one detectable chromium sample
is probably erronous because the corresponding lead level recorded for the
sample was quite low.

5-6


coating techniques can be utilized. Some primers are still applied by manual
or automatic spraying.

Top coating is usually accomplished by electrostatic spraying. Both automatic
and hand-held electrostatic guns are used. The automatic equipment is typi-
cally an electrostatic bell or disk. Manual spray equipment is used primarily
for reinforcement on less accessible surfaces and touch-up operations. The
commonly used resins, solvents and pigments are shown in Table 8.

Table 8. Major appliances (resins, solvents, and
pigments as percent of total consumption) .4

Per- Per- Per-
Resins cent Solvents cent Pigments cent
Acrylic 43 Glycol ether 21 Titanium 61
and ether dioxide
esters
Epoxy- 7 Xylene 20 Iron 10
ester oxide
Polyester 13 Aliphatic 16 Talc 8
hydrocarbons
Amino 9 Other an Silica 6
aromatics
Other 18 MEK 8 Chromium 5
n-Butanol 7 Lead 2
Toluene 7 Other 8
Other 10

TRANSPORTATION (non-automotive)

This section includes those industries covered by SIC major group 37 (Trans-
portation Equipment). Included here are establishments engaged in manufac-
turing truck and bus bodies, truck beds, truck cabs, and different types of
trailers, such as bus trailers, truck trailers, motor truck trailers, semi-
trailers for missle transportation, and so forth. It also includes establish-
ments mainly engaged in building and rebuilding locomotives, and equipment for
operation on rails for freight and passenger service, and establishments that
manufacture or assemble all types of aircraft.

20


CASE STUDY 8
FINISHING OF HEAVY EQUIPMENT

Hay stack wagons receive a single coat of an alkyd resin enamel in a three-step
finishing process. The enamel is applied using hot airless and hot airless
electrostatic equipment in a large downdraft spray booth. The booth features
a pit for underbody painting which incorporates a supply of fresh air. Powered
manlifts within the booth provide access to high areas of the wagon and allow
the painter to maintain proper orientation with respect to the airflow. The
sophistication of the application equipment and the excellence of the spray
booth design result in low levels of spray mist when the exterior of the wagon
is painted. When wagon interiors are painted, mist levels increase approxi-
mately tenfold.

PROCESS

A hay stack wagon is a two-wheeled agricultural trailer designed to be pulled
behind a tractor. Powered by the tractor's engine through a power take-off
system, it gathers hay and compresses it into a high density stack. The wagon
is box-like in shape, and fabricated from sheet steel and steel members; it
measures approximately 15 feet high, 12 feet wide, and 24 feet long.

Operations

The finishing process consists of a detergent wash, followed by paint appli-
cation and oven drying. The finishing department is shown in Figure 8-1.
Finishing begins in a 30 by 50 foot wash booth, where two operators remove
soil and manufacturing debris by spraying the wagons with a detergent solution,
After washing, the wagons are towed to a staging area, oven-dried, then towed
to the spray booth for painting.

EXHAUST DUCTS
PAINT KK
BUILDING WALL STORAGE,
FRESH AIR DUCT TO PIT Py Er
EAST
WEST aa
WASH MAKE UP SPROU ‘MAKEUP! DRYING OVEN
BOOTH pe BOOTH SRI
AIR SEAL x AIR SEAL
EXHAUST DUCTS
MANUFACTURING MANUFACTURING

AREA AREA

Figure 8-1. Finishing department layout.
8-1


Table 7-6. Airborne levels of paint mist and lead in light
aircraft finishing: topcoat application.

Sample
Ship duration Total mist Lead
number Operation Color (min) (mg/m3) (mg/m3)
3. Base coat, whole ship White 27 28.2 =
5 Base coat, whole ship White 35 24.7 =
6a Base coat, whole ship White 41 34.5 =
7a Base coat, whole ship White 45 41.2 5
6b Base coat, whole ship White 62 16.5 oO
7b Base coat, whole ship White 31 9.8 oo
Whole ship painting GM (GSD) 23.3 (1.7) --
8 Striping, Brown 25 8.5 --
painter's helper
8 Stripe, first coat, Brown 31 16.5 —
tail and cow]
8 Stripe, second coat, Brown 19 9.8 =
tail and cowl
9 Stripe, first coat, Red* 26 23.3 2.9
underbody and tail
9 Stripe, second, third Red* 35 38.8 5.0
coats, underbody and
tail
10 Stripe, side, Cream 29 6.4 =
three coats
Striping operations GM (GSD) 14.1 (2.0) --
OSHA PEL** 15.0 0.05
ACGIH TLV (1979)** 10.0 0.15
NIOSH ** -- 0.10

GM: Geometric Mean

GSD: Geometric Standard Deviation

* Molybdate orange pigment; 11.3 percent lead in dried film
**For full shift exposure

As was the case in ship priming, the airborne concentrations of organic sol-
vents in topcoat application are well below any existing or proposed standards.
These measurements are shown in Table 7-7.


AN EVALUATION OF ENGINEERING CONTROL
TECHNOLOGY FOR SPRAY PAINTING

Dennis M. O'Brien
Donald E. Hurley

U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES
Public Health Service
Centers for Disease Control
National Institute for Occupational Safety and Health
Division of Physical Sciences and Engineering
Cincinnati, Ohio 45226

June 1981

Fer sale by the Superintendent of Documents, U.S. Government
Printing Office, Washington, D.C. 20402



OFFICE
CUSTOMER
PREP
EXHAUST
FAN :
> BODY REPAIR
MAKE uP | [>
AIR UNIT EE AREA IV.
OVEN
9
SPRAY
BOOTH
MASKING
MAKE UP Iz AREA
AIR UNIT
Ko PAINT MIX
2¢ BENCH
ao
ar
wn

Figure 5-1. Paint shop layout.


CASE STUDY 1
POWDER COATING - SMALL PARTS

The formed steel panels used to mount control hardware for washing machines and
clothes dryers are coated with a thermosetting acrylic powder in an operation
that recycles both spray booth air and powder overspray. Low total dust levels
are maintained through careful attention to air distribution in the design of
the spray booths, dust-tight construction of the powder recovery equipment, and
good housekeeping.

PROCESS
Operations

Before entering the powder coating room, the steel panels undergo a seven-stage
pretreatment process: a chemical wash followed by two water rinses, an iron
phosphate bath, a water rinse, a chromic acid bath, and a final water rinse.

The powder coating room (Figure 1-1) contains two separate powder coating
systems, one for each color--dark brown and cream. This room is isolated from
other plant operations so that the powder will be contained; it is air condi-
tioned to prevent the powder from agglomerating.

(-"

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RECIPROCATOR RECIPROCATOR: y
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Figure 1-1. Layout of powder coating room.

The operator of the pretreatment process brings 100-pound drums of powder paint
to the powder unit. The powder unit operator opens the drums, attaches a vib-
brator to the drum, and transfers the powder to the first of two fluidized beds
(Figure 1-2). An aspirator connected to this fluidized bed transfers the
virgin powder to a sieve that removes oversize particles. The powder Passing
through the seive is discharged directly into a second fluidized bed, which
serves as a powder reservoir for the spray guns.

1-1


As shown in Table 7-9, airborne concentrations of tin were sufficiently low to
preclude any hazard from its application.

Table 7-9. Airborne levels of dibutyltin dilaurate
in light aircraft finishing.

Sample
Ship duration Tin
number Operation (min) (ug/m3)
4,5 Base coat 69 4
6a,7a Base coat 83 7
6b, 7b Base coat 93 2
OSHA PEL* 100
ACGIH TLV (1979)* 100
NIOSH* 100

*For full shift exposure
DISCUSSION

The exterior finishing of helicopters is not unlike that done in an automobile
repair shop or in a factory that produces bus or truck bodies in low volume,
(Application techniques, coating materials, and spray booth design are all
similar.) While the sheer volume of air exhausted provides more than adequate
control of the solvent hazard, the size and shape of the helicopter does not
permit the same degree of control of the stray mist in the immediate vicinity
of the painter, particularly during underbody painting. A comparison of total
mist concentrations in Table 7-6 lends credence to this observation. Mist
concentrations are highest for underbody painting operations, and lowest for
side striping.

Ventilation is compromised in underbody painting. In order to improve over-
spray control during this task fresh air should be supplied to the painting
pit (not currently used). Because only a small section of the pit should be
open at any time, additional fresh air requirements’ would be minimal. A
sidedraft-style booth, similar to that used in auto body shops, might be a
better choice for finishing helicopters and other light aircraft, if the paint-
ing required on the downstream side is minimal. In this type of booth, a flow
of air away from the painter could be maintained at nearly alls points of the
aircraft, with a possible decrease in total exhaust volume. Sidedraft ventila-
tion might be all that is possible with fixed-wing aircraft, when under-wing,
as well as underbodies may require painting.

Improvements in paint application techniques are limited. The conventional
air-atomized spray equipment is operated within the pressure recommendations
of the coating suppliers. Portions of the ship are made of fiberglass, lim-
iting the utility of electrostatic techniques. Many of the striping colors
are metallic finishes, ruling out the use of airless equipment. Lastly, the

7-15


9.

10.

11.

12.

13.

14.
15.

16.

7.

18.

19.

Dry--The finish is dried for four minutes in a 160°F oven.

Glaze (Booths 4 and 5)--A spray painter applies a coat of glaze to
the top, sides, interior, and rear edges of the cabinet. In the
next booth, a robot sprays a heavy coat of stain to the underside
of the lid, and the cabinet sides and front.

Wipe, Rub, Brush--The freshly stained surface is wiped with clean
rags, rubbed with steel wool, and brushed to produce grain high-
lights and promote adhesion of the stain. Unlike natural wood,
the plastic surface does not absorb the glaze. Thirteen wipers
are engaged in this operation.

Dry--The glaze is dried for four minutes in a 165°F oven.

Lacquer (Booths 6 and 7)--The entire surface of the cabinet is
sprayed with a clear lacquer. In the first booth, engravings may
receive black or gold highlights.

Dry--The cabinets enter a short flash-off tunnel followed by a
four minute dry in a 160°F oven.

Second glaze (Booths 8 and 9)--A second coat of glaze is applied
followed by a wiping operation (three wipers).

Fly specking (Booth 10)--An operator scatters dark paint droplets
over exterior surfaces using a special air gun.

Lid lacquer (Booth 11)--Models with a smooth top receive a second
coat of lacquer on the top only.

Dry--The finish is dried for four minutes in a 160°F oven.

Interior barrier coat (Booth 12)--Cabinet interiors receive a
second application of the barrier coating. A coat of black
"veiling lacquer" is applied with a compressed air gun to the
interior corners.

Veiling lacquer (Booth 13)--All visible interior surfaces receive
a decorative treatment with black lacquer using a compressed air
spray gun.

Final lacquer (Booths 14 and 15)--A heavy coat of clear lacquer is
applied to the entire cabinet surface.

Dry--The cabinets enter a short flash off tunnel followed by a
four minute dry in a 160°F oven.

Inspection--The finish is inspected for imperfections and rerouted
for correction if it is necessary.

2-2


Vinyl Resins--

Vinyl resins for surface coatings are based on the following monomers: vinyl
chloride, vinylidene chloride, vinyl acetate, and other vinyl esters. These
resins are used in coatings as solutions in volatile organic solvents, as dis-
persions in plasticizers or volatile organic non-solvents, as dry powders, and
as latexes. !

Vinyl solution coatings contain vinyl resins with low to medium molecular
weights. Copolymers are more readily ‘soluble and are preferred for solution
coatings. Vinyl resins may be modified with carboxylic acid groups in order
to increase adhesion to metal substrates, or hydroxyl-modified in order to im-
prove adhesion to cellulosic materials, wash primers, or alkyd resins. Phthal-
ate, adipate, and phosphate plasticizers are incorporated at levels of 5 to 30
percent of the resin weight in order to improve flexibility and impact resis-
tance. Because vinyl] resins are sensitive to heat and ultraviolet light, a
variety of organo metallic compounds are used to inhibit resin degradation.

In vinyl dispersion coatings, resins with very high molecular weights are dis-
persed as discrete particles in a liquid. If this liquid contains only plas-
ticizers, the dispersion is called a “plastisol". If this liquid contains
organic solvents, the dispersion is called an “organosol". Dispersion coatings
cure by baking; the high temperature softens the resin particles and increases
the solvent action of the liquid portion, causing the particles to fuse. Vinyl
powder coatings are similar to vinyl dispersions. Film formation also requires
a fusion step; however, greater melting and flow are required for powders.

Vinyl latexes are emulsions of resins in water. The major use for latexes is
in exterior house paints; they are not industrially important.

The most important coating application for polyvinyl butyral resins is in the
preparation of corrosion inhibiting "wash primers." These coatings consist of
polyvinyl butyral, phosphoric acid, and a corrosion inhibiting chromate pigment
carried in a mixture of alcohols.

Pigments

Pigments are finely powdered insoluble solids dispersed in a liquid medium.
Pigments significantly effect the properties of a coating system, and may be
used for corrosion inhibition, reinforcement, and filler, as well as for color
and opacity. Overall pigment use in paint and coatings is reported in Table 3.
Pigments fall into three general classes: white, colored, and metallic.

White pigments reflect incident light completely, if the refractive index is
greater than that of the binder. The important white pigments can be divided
into two main categories--reactive and non-reactive.

The reactive pigments include lead carbonate, sulfate, and silicate, and the
oxides of antimony and zinc. They react with oleoresinous and acidic binders.
The use of these pigments is mainly limited to construction, bridges, and in-
dustrial maintenance. The main non-reative pigments are titanium dioxide and
lithopone. Pigments that appear white when exposed to the air, but exhibit
little hiding power because of low refractive indices are termed "supplemental"
or “extender” pigments. They are used to control gloss, texture, or viscosity.

10


CASE STUDY 6
APPLIANCE FINISHING

Refrigerator and chest freezer cabinets are painted with a thermosetting
acrylic enamel in an operation that features both manual and automatic paint
application. The levels of paint mist and organic solvents when paint is
applied by conventional and electrostatic means were compared. Painters who
used electrostatic guns for a greater Percentage of their work were found to
have lower potential exposures, despite lower booth airflow. Greatly elevated
paint mist and organic solvent levels were found when the internal surfaces of
chest freezer liners were painted.

PROCESS
Operations

Sheet metal components for refrigerator freezers and chest-type freezers are
finished in white, gold, almond, avocado, or copper, with a thermosetting
acrylic enamel. The finishing process begins with an eight step pretreatment
consisting of two alkaline washes, followed by a hot water rinse, a zinc
phosphate bath, a cold water rinse, a chromic acid rinse, and two deminera-
lized water rinses. Then the parts are oven dried and transferred manually to
the overhead paint line conveyor.

The paint line is shown schematically in Figure 6-1. It consists of two manual
spray booths and two automatic electrostatic spray systems. The line first
enters a sidedraft, water wash spray booth. In this booth, two painters apply
a prime coat of acrylic enamel to the corners, recesses, and interior flanges
of the doors, lids, and cases using air-atomized, electrostatic (70,000 volt)
spray guns. Embossed steel doors require a slightly heavier coat, which makes
a third painter necessary for these runs. The additional painter uses a con-
ventional air-atomizing spray gun.

The first coat is completed in an automated electrostatic system that is con-
tained in a downdraft spray room. Spray units in this system consist of
rapidly rotating bells, charged to 100,000 volts, into which paint is intro-
duced and atomized by the action of the electrostatic and inertial forces.
The units are grouped into headers of 3 spray units. The system is composed
of two opposed sets of three reciprocating headers, for a total of 9 spray
units on each side of the conveyor. An additional 3-unit header is mounted on
the floor to coat the top of the refrigerator cases (the cases are suspended
upside down from the conveyor).

After leaving the spray room, the workpiece travels through a short flash-off
tunnel and into a second spray room. This system is identical to the previous
one, except that there is one less spray header on each side of the conveyor
line. Each of the automated electrostatic spray systems is operated by an
attendant who changes paint colors and maintains the equipment as necessary.
Two painters in a sidedraft booth that is similar to the first booth apply
paint to light areas; one works with a conventional air-atomized, spray gun,
and the second works with both conventional and electrostatic guns. After
painting, all items are baked in a 365°F oven for 12 minutes.

6-1


RESULTS

As reported in Table 6-2, the mean 8-hour TWA concentrations of organic sol-
vents were less than both legal and current recommended maximums. Individual
TWA levels were also all below recommended maximums. The prime contributor to
the average solvent level was the liner painting operation. Solvent levels of
300 to 600 ppm were measured with a combustible gas indicator during liner
painting, as opposed to 1 to 10 ppm during the painting of refrigerator case
exteriors. All measurements were taken in the breathing zone of the spray
painter outside the respirator. Supplied-air respirators were worn during
liner painting.

Table 6-2. Airborne levels of organic solvents in appliance finishing.

8-hr time-weighted average
concentration (mg/m3)

Number of Toluene Xylene Cex
Operation -__ samples GM GSD oH GSD
Manual prime booth
Painter 1** 3 130 od) 148 1.2 0.52
Painter 2 3 104 Vcd) 113 1.4 0.40
Manual finish booth
Painter 3 3 204 1.2 225 1.2 0.79
Painter 4 2 88 1.7 12 1.9 0.38
Automatic prime booth 3 262 1.3 76 1.5 0.54
(area sample)
Automatic finish booth 3 W7 1.1 31 1.6 0.23
(area sample)
OSHA PEL 750 435 1
ACGIH TLV (1979) 375 435 --
NIOSH 375 -- --
GM: Geometric mean
GSD: Geometric standard deviation
*Combined exposure: Ce = oO <P Co + sae Cy
tT wy Th

where C is the concentration of the individual contaminant, and
L is the exposure limit


Table 10-1. Solvent levels for selected paint mix room operations
as measured by a combustible gas indicator.

Concentration (ppm)

Location

10 to 20
25

75

100

40

10

30 to 40

30 to 50

Center of mix room

One ft above 55-gal paint drum, with
integral agitator and top cover

One ft above 55-gal paint drum, with
clamp on agitator and loose fitting
lid

Directly above floor drain

Breathing zone above four 5-gal
solvent pails

Directly above solvent spigots
with safety cans

Breathing zone during filling of
5-gal pails with xylene

Breathing zone while adding solvent
to paint mix tanks

10-6


The automatic stages of the process are accomplished by air-atomized, electro-
static spray guns mounted on reciprocators. Each reciprocator is equipped with
six guns and is housed in an individual sidedraft water-wash spray booth. The
reciprocators are installed as pairs and located on opposite sides of the con-
veyor system in each stage, thus eliminating the need to rotate component parts
during paint application. The electrostatic spray guns operate at 90,000
volts, with an air-atomizing pressure of 25 to 30 psi. Individual coating sys-
tems are supplied to the guns from a central mix room under a pressure of 15 to
20 psi. At the entrance to each pair of spray booths is an array of electric
eyes and a logic device that controls operation of the reciprocators.

The manual steps of the process consist of individual downdraft water-wash
spray booths. One person is stationed inside these booths to touch up and as-
sure adequate coating on non-uniform component surfaces. Much less manual
spraying is required in this operation than in Process A because of the simpler
product shape. Manual spraying is accomplished by electrostatic spray equip-
ment operating with an air-atomizing pressure of 95 psi, and a paint pressure
of 60 psi.

One operator/mechanic tends each of the operating reciprocator systems. The
responsibilities include continuous visual inspection for paint and solvent
line leaks, and appropriate scheduled or unscheduled maintenance.

The component parts are then routed through a roof-mounted curing oven that is
operated at 350°F. Both (flash-off after pretreatment and curing) oven tem-
peratures are automatically monitored at a station located in the paint shop
supervisor's office.

Coatings

The coating materials used in this plant are the same as those previously des-
cribed in Process A of this case study. Specifically, thermosetting acrylic
resins and medium high-solids polyester baking enamels are used in colors that
are common to the file cabinet plant so that finishes on the various components
of metal office furniture will match.

SPRAY BOOTHS
Manual Spray Booth Design

All manual spray operations are performed in one of two identical spray booths
identified as Booths I and J in Figure 9-4. These booths are similar in design
to the booths of Process A, with the following exceptions: centrifugal, rather
than duct fans, are used and the fans are mounted on the building roof, rather
than on the booth. This change creates a noticeable difference in noise inside
the booth. These fans are driven by a 15 hp motor and are rated at 12,000 cfm.
Two pumps are required in each of the booths to power the water wash. These
pumps are rated at 5 hp and 350 gpm.

Automatic Spray Booth Design

The automatic electrostatic spray booths in this plant resemble those of
Process A. These booths are identified as Booths G, H, K, and L in Figure 9-4.

9-13


Table 1-1. Job descriptions.

Position Duties

Spray operator --manually sprays the edges of the part
not accessible to the automatic unit

Equipment operator --start up and shutdown of equipment for
color changes
--loading of new paint
--cleaning of paint lines
--monitoring of equipment

Utility man --start up and shutdown of equipment at
shift beginning and end
--minor repair
--relief man for spray operator
(approximately 30% of shift
in powder unit)

Pretreatment --paint drum delivery from paint
operator storage room (less than 10 percent
of shift in powder unit)

Table 1-2. Total dust levels.

8-hour time-weighted average (TWA)

Number concentration (mg/m3)

of days
Worker or location sampled GM GSD
Sprayer* 3 lod) 1.1
Equipment* 3 1.5 1.4
Reciprocator (brown linet) 3 1.9 1.4
Filter exhaust (brown linet) 3 1.4 oll
Reciprocator (cream linet) 3 1.0 1.1
Filter exhaust (cream linet) 2 0.5 2.2
Control panel (general area) 3 1.3 1.9
West wall (in AC airstream) 3 0.8 1.1

GM: Geometric mean

GSD: Geometric standard deviation

*Personal samples

+Production approximately 70 percent brown, 30 percent cream

1-7


Be had comparitively few abnormalities that could be attributed to this
metal.

Zinc and Zinc Oxide--
No acute or chronic illness has been attributed to zinc oxide dust or metallic
zinc. Zinc oxide dust is considered a nuisance particulate.

Organic Pigments

Toxicity data for the majority of these materials is limited to acute oral
toxicities. In terms of the mean lethal dose (L059), most organic pigments
are innocuous; in rats they pgssess acute oral toxicities greater than 10 grams
per kilogram of body weight. 19

The chronic hazards posed by these materials are largely unknown. Many of the
pigments are based on dyestuffs; the dyestuff is combined with an inorganic
compound to produce an insoluble pigment. The dyestuffs have been studied more
extensively than the pigments, and several have been implicated as cancer
risks, In paint the biological availability of these materials is probably
limited by the insolubility of the Pigments and their partial encapsulation in
the paint resin matrix. Fat and/or water soluble dyes are used in some wood
stains, increasing the potential hazard.

Synthetic Resins

Acrylic Resins~-

No evidence exists that would Suggest any unusual toxicity for the acrylic
resins, although the potential does exist that unreacted monomer could be pre-
sent. Of these monomers, acrylonitrile represents the greatest hazard. Iso-
cyanates are used to cross-link or "harden" certain acrylic paint systems.
The hazards of isocyanates are discussed under the heading "Urethane Resins."
Dimethyl] ethanolamine, a cross-linking agent used in certain acrylic emulsion
coatings, has been reported to induce asthma and rhinitis.

Alkyd_Resins--

Piper!/ cites no major hazards from this group of resins, and notes that none
of the potentially noxious raw materials used in manufacture is likely to re-
main free. Alkyd resins have a long history of use with no reports of any
chronic hazards.

Alkyd paints employ metal soaps of organic acids to catalyze the oxidation of
the drying oi] component. Because lead soaps are commonly used, lead is a
potential hazard in any drying-oil-type Paint (alkyd, epoxy ester, oleoresin,
and urethane-oil). Lead used as an oxidation catalyst may comprise 0.5 to 1.0
Percent of the paint solids by weight.

Amino Resins--

These resins are used as cross-linking agents in alkyd, acrylic, and epoxy
baking enamels. Piper!” notes that traces of formaldehyde may be present,
but seldom in sufficient quantities to present a hazard.

Cellulose Resins--
Cellulose resins possess no known toxic hazards. Coatings produced from cellu-

27




own momentum rather than by a stream of air. Other advantages of airless or
high pressure spraying include high capacity, compatibility with high-solids
coating, adequate coverage of awkward shapes, and negligible stray mist. Some
disadvantages include relatively high cost, limited pattern and flow adjust-
ment, and difficulties in overlapping.

In electrostatic spraying, the paint can be atomized with compressed air, by
hydraulic pressure as in airless spraying, or solely by electrostatic forces.
Electrostatic spray guns can be used with waterborne, solvent, and powder
coatings. Although the equipment used for each of these applications differs
considerably, the operating principle is similar. Paint particles are electri-
cally charged as they leave the gun and are attracted to the grounded work-
piece. The chief advantage of electrostatic spraying is the improved working
environment and the paint economy that is achieved.42 Electrostatic systems
usually permit use of substantially less exhaust and make-up air than conven-
tional compressed air spraying for the same painted surface area. This tech-
nigue also provides significant wrap around, coats sharp edges, and can be
highly automated. However, null points in the electrostatic field (caused by
recesses or object interiors) may not be coated.

One function of the solvent in a coating material is to dilute the coating in
order to obtain a viscosity suitable for spraying. Another means to achieve
the same lowered viscosity is by applying heat. This concept can be applied
to both conventional and airless spray painting, which results in a decreased
solvent requirement. With lowered spraying viscosity, atomizing energy can be
reduced; this produces a more gentle spray with less bounceback. Limitations
include the heat tolerance of the paint and the necessity for more complicated
equipment 42

ISOLATION

Isolation can be achieved by the use of a physical barrier, or by the separa-
tion of the worker from the hazard by time or space.

Physical Barriers

Certain paint components can either penetrate or react with the surface of the
skin and cause injury either at the point of contact, or act as a systemic
poison. Protective clothing acts as a barrier between the hazard and the
worker's skin. Careful selection of gloves, aprons, and sleeves that are not
adversely affected by the resins and solvents is necessary. Key?! recommends
neoprene for gloves and vinyl for aprons and sleeves. He suggests white cotton
glove interliners to minimize sweating. Protective creams and ointments can
also be used, but are less effective than gloves.

Respirators are another type of physical barrier. There are basically two
kinds of respirators--those that provide the worker with a clean atmosphere
from an external source (supplied-air respirators), and those that attempt to
remove the contaminant(s) from the workroom environment before they are inhaled
(air-purifying respirators). The selection and use of an adequate respirator
requires knowledge of: the capabilities and limitations of the equipment, the
possible concentration and mode of action of the toxic materials, and the dura-

34


combined solvent levels did not exceed more than 5 percent of currently allow-
able levels. For the same reasons cited earlier, solvent levels in the breath-
ing zone of Painter B were approximately 5 times higher than Painter A.

The low concentration of paint mist and solvent vapors measured at the air
seals is indicative of the degree of containment. That any contaminants were
measured at all is due to the observed painting of some small parts within the
air seal area itself.

DISCUSSION

Paint mist levels were well controlled despite the size and complex shape of
the stack wagon and the high rate of paint delivery. The excellent control of
total paint mist was due to the use of sophisticated application techniques,
and a well designed spray booth suitably adapted to the painting of the stack
wagon.

The use of heated paint allows the airless atomization to take place at rela-
tively low paint pressures. This results in low droplet velocity with little
rebound. The addition of the electrostatic charge to the hand guns further
increases the efficiency of application.

Careful attention in design of the spray booth resulted in uniform air velo-
cities throughout the booth. The use of man lifts avoided the exposure to
paint mist seen in other case studies when tall objects were painted in down-
draft booths. The fresh air-supplied painting pit provided excellent protec-
tion in underbody painting, a problem also noted in other case histories.

There is little room for improvement in the control of paint mist. Spray gun
maintenance could be facilitated by use of a solvent Purge or soak, and more
frequent replacement of spray gun tips and charging wires. Although no commer-
cial electrostatic pole guns are currently available, perhaps a handgun could
be modified with an extension handle for painting wagon interiors.

Company blood lead data indicates that the present respiratory Program is ade-
quate. Nonetheless, a full facepiece style respirator is suggested for two
reasons. First, it would provide protection of the eyes, absent in the present
respirator. (The viewing window can be kept clear with plastic food wrap.)
Second, it offers increased wearing comfort because the load is distributed
over a larger facial area.

The substitution of a heavy metal free pigment for the lead chromate requires
discussion, The lead chromate is used primarily for its color stability and
low cost. An organic pigment may provide a good color match, but is liable to
cost more. Company blood lead data would indicate that the painters are not
at a significant risk due to lead, and that an immediate change to a lead-free
material is not warranted. In light of proposed rule making on chromium, con-
tinued investigation of possible substitutes would be prudent.


45.

46.

47.

48.

49.

50.
51.

52.

Industrial Ventilation: A Manual of Recommended Practice, 15th Edition.
Committee on Industrial Ventilation, American Conference of Governmental
Industrial Hygienists, Lansing, Michigan. 1978.

American Standard Safety Code for the Design, Construction and Ventila-
tion of Spray Finishing Operations. ANSI A9.3-1964 (Reaffirmed 1971).

U. S. Department of Labor. 1976. OSHA Safety and Health Standards (29
CFR 1910).

Hemeon, W.C.L. 1963. Plant and Process Ventilation. Industrial Press,
New York. pp 115-6. 1963.

Baturin, V.V. 1972. Fundamentals of Industrial Ventilation. Pergamon
Press, Elmsford, New York. 3rd Edition. pp 457-460.

Gaynes, N.I. 1976. The Organic Corner. Metal Finishing. pp 25-9.

Muirhead, J. 1975. Spray Application Methods of Surface Coatings. Pro-
duct Finishing. pp 10-11.

Taylor, D.G. (Editor). 1977. NIOSH Manual of Analytical Methods. Vol.1.
DHEW (NIOSH) Publication No. 77-157-A. U.S. Department of Health, Educa-
tion, and Welfare, Public Health Service, Center for Disease Control,
National Institute for Occupational Safety and Health.

59


Table 7-5. Airborne levels of organic solvents in light
aircraft finishing: primer application.

Sample Concentration (mg/m3)
Ship duration
number Operation (min) 2-Butanone Toluene Ethanol IspropanoT Cex

1 Prime 25 al 54 21 7 0.14

2 Prime 40 92 72 46 33 0.31

2 Prime 4] 37 55 18 13 0.16
GM (GSD) 42(2.1) 60(1.2) 26(1.6) 19(1.6) .19(1.5)
OSHA PEL** 590 750 1900 980 1.0
ACGIH TLV (1979)** 390 375 1900 980 1.0
NIOSH** 590 375 -- 980 --

GM: Geometric mean
GSD: Geometric standard deviation

*Combined exposure: C. = “1 +©2 + wee fn

where C is the concentration of the individual contaminant, and
L is the exposure limit
**Full shift exposures.

Topcoat Application

Breathing zone (outside respirator) levels of paint mist and lead are reported
in Table 7-6. As might be expected, the mean concentrations of total mist in
applying the base coat to the whole ship are equal to those in ship priming.
As base coats are primarily white or off-white colors, all lead-in-air measure-
ments for whole-ship painting were below the limits of detection. For the
sampling conditions used, this corresponds to an airborne concentration of less
than 50 ug/m’. Paint mist levels varied more greatly in striping operations
than in whole ship painting. Ventilation was compromised in underbody paint-
ing, with mist exposures far greater than those experienced in striping the
ship's sides. Only one ship was painted with a lead-containing pigment. This
paint, a red hue, contained 11.3 percent lead by weight (dried film). It was
used to paint an underbody, resulting in a lead concentration several times the
current 8-hour limit for lead. Other colors may contain up to 20 percent lead.
Variations in the lead content of the paint and the quantity sprayed make real-
istic estimates of 8-hour averages difficult.


used as paint solvents. On contact with the skin, these solvents may produce
a dermatitis after repeated exposure. High vapor concentrations are irrita-
ting to the conjunctiva and mucous membranes of the nose and throat and can
produce narcosis. No chronic systemic effects are known to exist.2

Petroleum Distillates--

Petroleum distillates are the materials in greatest use as paint solvents. The
term includes complex mixtures of solvents distilled from petroleum and dis-
tinguished by their boiling ranges and aromatic content. These materials are
irritating to the skin, to the conjunctiva, and to the mucous membranes of the
upper respiratory tract. One fraction, hexane, is reportedly associated with
peripheral neuropathy. The lower boiling mixtures may contain benzene, a well
known blood poison.@

Toluene and Xylene--

Toluene and xylene are the most important aromatic hydrocarbons used as paint
solvents. Both compounds may cause irritation of the eyes, respiratory tract,
and skin, and high concentrations produce depression of the central nervous
system. Commercial grades of toluene may contain benzene. High concentra-
tions of xylene may cause pulmonary edema, anorexia, nausea, vomiting, and
abdominal pain.

Additives

Other products added to paint include driers, anti-skinning agents, surfac-
tants, plasticizers, and fungicides. With the exception of the plasticizers,
these materials represent only a small fraction of the coating formulation.
Toxicity data for many of those substances is limited to acute oral toxicities.
Because of the variety of paint additives, only the most common materials are
discussed here.

Paint Driers--

These materials include the metallic salts of tall oi] and naphthenic acids.
Fassett22 reports that the acute oral toxicity of the metal naphthenates is
Tow; the oral LD5q in rats ranges from 4 to more than 6 grams/kilogram.

Plasticizers--

This group of additives includes castor oil, dibutyl phthalate, dioctyl phtha-
late, tributy] phosphate, tricresy] phosphate, polyester resins, sulphonamides,
and chlorinated diphenyls. Tributy] paospnate excites the central nervous
system and is a respiratory irritant.22 * The chlorinated diphenyls have been
implicated in cancer of the skin and liver.28 The phthalates are relatively
inert materials.

30




Table 10-2. Mix room solvent concentrations -
(8-hr time-weighted average values).

Concentration (mg/m3)

n-Butyl Aromatic

Sample Xylene acetate Naphthalene n-butanol distillate Ce*
Senior

attendant 12 1 <0.5 13 30 0.15
Attendant 22 2 <0.5 12 20 0.15
Center of room 38 4 <0.7 15 80 0.34
OSHA PEL 435 710 50 300 435 1.0
ACGIH TLV 435 710 50 150 -- 1.0
(1979)
NIOSH 435 -- -- -- -- --
*Combined exposure: 5 Gl + Cy toe Cn

ty ly ty

where C is the concentration of the individual contaminant, and
L_is the environmental limit
**By analogy with xylene

10-7


CASE STUDY 4
RAILROAD CAR FINISHING

Hopper cars are finished in the paint shop of a manufacturer and rehabiTitator
of railroad freight cars. Exterior surfaces are finished with air drying alkyd
enamels by two painters using airless spraying equipment. All painting is per-
formed in a semi-downdraft, water-wash spray booth, equipped with a longitudi-
nal pit to facilitate underbody painting. Full-facepiece, supplied-air respi-
rators are worn during all spraying operations. The respirator is prevented
from fogging with spray paint mist by covering the viewing window with layers
of clear plastic food wrap.

PROCESS
Operations

This plant is engaged in the manufacture and rehabilitation of railroad freight
cars, primarily hopper cars. These cars are painted chiefly to protect them
against corrosion; aesthetic considerations are secondary. Therefore, applica-
tion techniques are geared to providing a high film build in a minimum time.

The steel surface of these cars is prepared for finishing by blasting with
commercial grit or steel shot. After cleaning, the cars are moved from the
blasting area into the spray booth shown in Figure 4-1. Prior to painting,
the car's trucks and couplers are wrapped and access platforms are dropped
into position at each end of the car. The booth doors are closed when
painting begins.

Two painters apply the finish, using airless spray equipment operated at 3,600
to 4,000 psi. Light colors require both a prime and a finish coat; darker
colors require only a single coat. A typical car requires about 45 minutes of
actual spraying time, and 40 to 50 gallons of paint.

The painters begin by descending into the pit and painting the underbody.
They start in the middle and work toward opposite ends of the car. After
completing the underbody, painters proceed to the main level and access plat-
forms to paint the sides and ends of the car. The interiors of the hopper
cars are not finished.

After spraying, the rail cars are moved to an enclosed drying area where mark-
ings and manufacturer's identification numbers are added. The process layout
allows one car to be prepared while a second is being painted, and a third is
curing in the dry-off area. About 3 cars are painted per shift. During the
survey, 3 types of cars were painted: a wood chip car, a coal hopper, and an
aggregate car. All 3 have the same basic configuration, except that the wood
chip car has a 50 percent larger volume.

Coatings

Color, coating type, and film thickness are specified by customer order; alkyd
enamels are used most frequently. Light color topcoats are preceded by a zinc

4-]


FILE CABINETS (Process "

PROCESS
Operations

Cases for file cabinets and associated sheet metal parts are finished on a high
speed (22 fpm) conveyor line. Cases represent approximately two-thirds of the
line finishing time.

Prior to finishing, the prefabricated sheet metal components are hung on an
overhead conveyor system and routed through a 4-stage washer, a single stage
rinse unit, and a 360°F dry-off oven. The four washer stages consist of two
detergent/phosphatizing baths, followed by water and chromic acid rinses.

A 1.5 mil polyester or acrylic finish is applied in two coats (wet-on-wet) in
a 4-step application process. These steps consist of manually spraying the
case interiors and edges, applying two coats electrostatically (using
reciprocators) to flat surfaces, and again manually spraying the edges and
light areas. A layout of this finishing line is shown in Figure 9-1.

BREAK CENTRAL
anca | Mik ROOM

@ MANUAL WORK. STATION

Figure 9-1. Process A layout.

The application process begins in a downdraft booth where one manual sprayer
applies a gray reclaimed paint to the interiors of the file cabinet cases with
an airless spray gun operating at 1,800 psi. The airless equipment was
selected for use in this operation specifically for reduction of overspray.

A second painter stationed in this booth (on the opposite side of the conveyor)
applies the exterior color to the edges and recesses with a conventional, air-
atomized spray gun. When drawer dividers and other small flat pieces are to
be painted, both operators use conventional air-atomized equipment. Compressed
air guns for the booth are operated at an air-atomizing pressure of 60 psi, and
a paint delivery pressure of 15 psi. Because of bleed-through of the gray

9-2


Organic solvent concentrations are reported in Table 5-3. Solvent levels are
well below any existing or proposed exposure limit.

Table 5-3. Airborne levels of organic solvents
in automobile refinishing.

Sample Concentration (mg/m3)

duration
Car size (min) (ay (by (ce) Cd) fe) (FY) (a) Cg*
Subcompact. 42 25 7 2 -- -- -- -- 23 0.06
Standard 44 44 7 9 -- -- -- -- 27 (0.10
Compact 40 67 10 10 -- -- 7 5 24 0.15
Subcompact 45 42 10 4 -- -- -- -- 21 0.09
Subcompact. 40 24 7 -- -- -- -- 24 0.07
Fender only 15 69 6 6 6 -- -- 63 0.16
Compact 43 25 2 -- -- 2 5 23 0.07
Geometric mean 39 10 5 -- -- 4 5 -- 0.09
Geo standard deviation 1.6 1.0 2.0 .-- -- 2.4 1.0 -- #165
OSHA PEL 750 435 710 590 410 1400 540 2950 1.0
ACGIH TLV (1979) 375 435 710 590 410 1400 270 -- 1.0
NIOSH 375 -- -- 590 200 --  -- 3500 +e

a) toluene, b) xylene, c) n-butyl acetate, d) methyl ethyl ketone, e) methyl
isobutyl ketone, f) ethyl acetate, g) 2-ethoxy ethyl] acetate, h) petroleum
distillates

*Combined exposure: C-. = “1 +02 + ee fn

where C is the concentration of the individual contaminant, and
L is the exposure limit.


fpm for a distance between the spray gun and object of 39 inches, 158 fpm for
32 inches, 296 fpm for 24 inches, and 640 fpm for 20 inches. However, those
gun-to-object distances are not consistent with actual practice. The spray
gun is generally held 6 to 10 inches from the surface for conventional com-
pressed air spray painting, according to Gaynes.50

Table 13. Ventilation requirements, spray
booths (cfm/sq ft cross section).

ACGIH ANSI /OSHA
Airtess/
Air spray Airless Air spray electrostatic

Bench-type spray booth 1504-200 1008-1255 150¢-2004 100
Large spray booth

Walk-in 100€ 60 100¢-1504 --

Operator outside 100 -150 60 -100 100¢-1504 --
Auto spray paint booth 100 60 -- o>

a. Booth cross section less than 4 sq ft

b. Booth cross section more than 4 sq ft

c. Cross drafts up to 50 fpm

d. Cross drafts up to 100 fpm

e. 75 for very large, deep booth; (operator may require approved respirator)

Air cleaning

The air cleaning section of the spray booth not only removes paint mist from
the exhaust air, but acts as a means of air distribution within the booth. An
arrangement of metal baffles is the simplest form of air cleaner. Specific de-
sign criteria for baffle-type booths are listed in Industrial Ventilation: A
Manual of Recommended Practice.45 The baffle-type booth provides a constant
flow of air. Mist removal and clean-up difficulties limit its use to low pro-
duction applications. Dry filter booths combine low cost with highly efficient
paint mist removal, but have the disadvantage of a variable airflow. The air-
flow is at a maximum when the filters are clean, but continuously decreases to
a point where the filters require replacement. Like baffle-type booths, the
dry filter booth is best suited for low production operations. Water wash
booths incorporate various combinations of water curtains and sprays to scrub
the paint mist from the exhaust air. They have the advantage of constant air-
flow, inherent fire protection, and high mist removal efficiency, but at a
greater cost than dry-type booths. Maintenance is necessary to retain the high
rate of mist removal. Cost of maintenance may equal or exceed that of the dry-
type booths.

WORK PRACTICES

Inadequate training and supervision in the techniques of spray finishing can
result in a poor work environment as well as a faulty finish and a waste of

40


were determined for the finish wipers. Area samples for organic solvents were
taken in solvent flash-off and drying oven areas to determine the impact of
these sources on employee exposure.

The 8-hour TWA exposures were calculated from separate morning and afternoon
samples. With the exception of the crew chief, all employees spend their
entire workshift in the finishing department, excluding 2 scheduled 15-minute
breaks and a 30-minute lunch.

Total mist samples were collected using closed-face cassettes with preweighed
37 mm polyvinyl chloride/acrylonitrile copolymer membrane filters and personal
pumps operated at 2.0 lpm. Organic solvent samples were collected on 150 mg
charcoal tubes with personal pumps operated at 50 cc/min. Tubes were subse-
quently desorbed and analyzed by gas chromatography.

Solvents for analyses were selected based on the stated composition of the
finishing materials and qualitative analysis of selected charcoal tube samples
by mass spectroscopy. No benzene was detected in any samples. The effects of
the solvents were assumed to be additive, and a combined exposure factor calcu-
lated.

To determine the presence of crystalline silica as a contaminant in the amor-
phous silica present in the clear lacquer, dried lacquer residue was obtained
from the booth filters and analyzed qualitatively by x-ray diffraction. The
sample yielded no crystalline diffraction patterns, indicating a crystalline
silica concentration of less than 0.25 percent of the paint solids.

RESULTS

Air sampling results are reported in Tables 2-3 through 2-7. In all cases the
exposure of workers to total paint mist and to organic solvents was less than
25 percent of allowable levels.

DISCUSSION

The low concentrations of paint mist and organic solvents can be attributed to
adequate ventilation of the spraying operation, proper orientation of the
worker with respect to the booth and the workpiece, and the inherent low bounce
back of the airless spray guns. Because no makeup air is supplied directly to
the spray booth, solvent exposures cannot be reduced below the concentration
of solvents present in the background air. On the other hand, the spray booths
act as a source of general exhaust ventilation, keeping the background levels
to a minimum. No attempt was made to correlate mist and solvent levels to
spray booth airflow because of significant differences in paint characteris-
tics, paint usage, and cabinet areas finished in each work station. In addi-
tion, only those spray booths in operations that had proven to be troublesome
had been modified to increase airflow.

The glaze wipers had the highest exposure to petroleum distillates, but still
far below hazardous levels. A supply air duct running underneath the conveyor
at the wiping station circulates room air to provide relief during warm weather
months (Figure 2-3). This system was not in use at the time of the study but
might prove to be useful in the further reduction of solvent exposure to the
glaze wipers. as

-10


e Evaluation and discussion

The diversity of spray finishing operations, coating formulations, and the
materials to be coated make it difficult to apply general engineering control

design to specific operations.
methods exactly as it is found in the case studies.

Thus, it may not be possible to use one of the
Therefore, emphasis in

the case studies has been placed on the principles of control employed, rather
than on specific design requirements.

Hazard Application Ventilation
Case Study Page Paint Type Evaluated Method Equipment
Case Study 1 1-1 Thermosetting Total dust Compressed air Bench type spray
Powder Coating - acrylic powder electrostatic booth; air re-
Small Parts circulation
Case Study 2 2-1 Acrylic lacquer; Mist, solvents Airless; some Open side draft
Wood Furniture oleoresin stain; compressed air; booth
Finishing nitrocellulose robot

Jacquer

Case Study 3 3-1 Alkyd baking enamel; Mist, lead, Compressed air; Side draft booth

Metal Furniture:
Solvent and
Waterborne Coatings

Case Study 4
Railroad Car
Finishing

Case Study 5
Auto Refinishing

Case Study 6
Appliance
Finishing

Case Study 7
Light Aircraft
Finishing

Case Study 8
Heavy Equipment
Finishing

Case Study 9
Metal Furniture:
Conventional and
High Solids
Coatings

Case Study 10
int, Storage
and Mixing

4-1

6-1

7-1

8-1

9-1

10-1

acrylic emulsion

Air dry alkyd
enamel

Air dry alkyd;
urethane modified
alkyd

Thermosetting
acrylic enamel

2-part epoxy primer
2-part urethane
topcoat

Air dry alkyd enamel
Thermosett ing
acrylic and high-

solids polyester
enamels

Various

solvents

Mist, lead,
chromium,
solvents

Mist, lead,
chromium,
isocyanates,
solvents

Mist, lead,
solvents

Mist, chromium
lead, isocyanates,
organotin,
solvents

Mist, lead,
chromium, solvents

Mist, lead,
solvents

Solvents

manual and
reciprocator

Airless

Compressed air

Electrostatic
bell with com-
pressed air and
electrostatic re-
inforcement

Compressed air

Airless electro-
static; airless
pole gun; paint
heated

Airless electro-
static on recipro-
cators with air
spray reinforcement,
airless on interiors

w/intergal supply air

Semi -downdraft
spray booth

Drive-through side
draft booth

Downdraft spray room;
side draft booth w/
integral supply air.

Downdraft booth w/
integral supply air

Downdraft booth w/
integral supply air.
Ventilated pit for
underground paint ing

Downdraft booth;
Side draft booth

General ventilation

Table 1. Paint/process/control matrix.

3




Table 7-7. Airborne levels of organic solvents in light
aircraft finishing: topcoat application.

Concentration (mg/m3)

Sample Ce*
Ship duration Ethyl Ethoxyethyl Aliphatic
number Operation (min) acetate acetate hydrocarbons
3 Base coat, whole ship 27 92 54 <40 0.19
4 Base coat, whole ship 34 74 38 <30 0.14
5 Base coat, whole ship 35 76 41 <30 0.15
6a Base coat, whole ship 41 78 50 30 0.16
7a Base coat, whole ship 45 120 70 50 0.24
6b Base coat, whole ship 62 49 27 30 0.10
7b Base coat, whole ship 31 66 38 30 0.13
Whole ship painting GM (GSD) 77 (1.3) 44 (1.4) 34(1.2) 0.15 (1.3)
8 Striping, 25 69 21 80 0.13
painter's helper
8 Stripe, first coat, 31 70 33 70 0.15
tail and cowl
8 Stripe, second coat, 19 21 VW 100 0.09
tail and cowl
9 Stripe, first coat, 26 85 65 100 0.23
underbody and tail
9 Stripe, second,
third coats, 35 160 94 80 0.33
underbody and tail
10 Stripe, side, 29 19 i 37 0.03
three coats
Striping GM (GSD) 52 (2.5) 30 (2.7) 73 (1.5) 0.13 (2.5)
OSHA PEL** 1400 540 2000 1.0
ACGIH TLV (1979)** 1400 270 1800 1.0
NIOSH** -- -- 350 --

GM: Geometric mean
GSD: Geometric standard deviation

*Combined exposure: Ces 1+

Where: C is the concentration of the individual contaminant, and
L is the exposure limit.

**For full shift exposure.


DRY TYPE WATER WASH TYPE

Pree
\\\
SS=

OPEN
7h
= _- A
—
W/ ENCLOSURE W/FILTER DOOR
tL
}
= Hs
_—
BENCH TYPE W/INTEGRAL SUPPLY AIR

Figure 2. Sidedraft booth configurations.

37


25
60 70 100
90 75

150 100 90 40 100
200 200 160 110 170
225 225 170 100 130
225 175 170 150 1to
150 25 150 130 80 100
150 100 110 130 40 110
WAGON IN BOOTH WAGON ABSENT FROM BOOTH

Figure 8-6. Air distribution through horizontal section
of booth (air velocity in fpm).

PROTECTIVE EQUIPMENT

At the start of each workshift painters don clean coveralls and safety glasses.
Before painting they don head socks, painters' hats, gloves, and respirators,
then they coat exposed areas of their faces with petroleum jelly. Gloves have
the palms cut out so that the painters are grounded to the handle of the
electrostatic guns. Respirators are of the haif-facepiece variety, with twin
organic vapor-removing cartridges and mist filters.

EVALUATION

Two painters are engaged in painting the hay stack wagons. Total spraying time
for a stack wagon is approximately 60 minutes, and the painters will spray up
to 5 stack wagons on a typical workday. In addition to painting, these work-
ers are responsible for paint mixing, skimming paint sludge from the booth
water tank, maintaining spray guns, and general housekeeping in the spray
booth. These tasks are all of short duration and were judged not to contribute
significantly to the painters' exposure.

To determine control effectiveness, the breathing zone concentrations of spray
mist, lead, chromium, and organic solvents were determined by personal air
samples taken during the time required to paint each stack wagon. Total mist,
lead, and chromium were collected using closed face cassettes with a pair of
matched weight, 37 mm cellulose ester membrane filters of 0.8u pore size at a
sampling rate of 2.0 lpm. After weighing, the filters were ashed and analyzed
by atomic absorption spectroscopy for lead and chromium, Organic solvent sam-
ples were collected on 150 mg charcoal tubes with personal pumps operated at

8-8


Figure 1-4. Cleanup with central vacuum system.

were made, using preweighed 0.8 u PVC/AN membrane filters in closed cassettes
and portable pumps operated at 2.0 lpm. Results of these measurements are
reported in Table 1-2.


Table 2-1. Coating composition.

Clear Lacquer

15% solids:

Resin: nitrocellulose modified with natural
resins and oils 11%

Pigment: amorphous silica 4%

85% volatile:
Tsopropanol 11%
Isobutyl acetate 18%
n-Butanol 12%
VM&P naphtha 22%
Toluene 12%
Ethylene glycol monobuty] ether 2h
Isobuty] isobutyrate 3%
Aromatic 100 3%
Isopropyl acetate 2%

Barrier Coat

23% solids:

Resin: thermoplastic acrylic plasticized with

dioctyl phthalate
Pigments: synthetic iron oxide, lampblack, burnt sienna

77% volatile:

MethyT ethyl ketone 40%
Isopropyl acetate 55%
Xylene 5%
Barrier coat mixed 1:1 with following reducer:
Tsopropanol 32%
Methyl ethyl ketone 40%
Methyl] isobutyl] ketone 6%
Toluene 12%
Isobuty] isobutyrate 10%

GLAZE
21% solids:
Resin: oi 1-based
Pigments: iron oxide, lampblack, burnt sienna

77% volatile:

VM&P naphtha 50%
Mineral spirits 35%
Toluene 10%
Ethylene glycol monobuty1] ether 5%
Xylene 5%

2-5


Nish

TECHNICAL REPORT

An Evaluation of Engineering
Control Technology for |
Spray Painting

U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES
Public Health Service

Centers for Disease Control

National Institute for Occupational Safety and Health


‘Table 4-2.

Semi-downdraft booth airflow summary.

Exhaust air
NE section
NW section
SE section

SW section

Supply air
North unit

South unit

Total

Total

Design
15,000

15,000
15,000
15,000
60,000

36,000
36,000
72,000

Actual
cfm 14,000
cfm 14,600
cfm 12,600
cfm 11,300
cfm 52,500
cfm 39,000
cfm 27,000
cfm 66,000

cfm
cfm
cfm
cfm

cfm

cfm
cfm

cfm

30"
FAN

ACCESS
PLATFORM

a

hws)

°

WATER LINE

[ELIMINATOR

S"WATER
HEADER

JGGEST AIR

;

possce———J ~)
WATER LINE]

30°
FAN

Figure 4-3. Cross-section of railway car, semi-downdraft booth.

4-5


Table 9-8. Airborne levels of organic solvents in
metal furniture finishing (Process B).

8-hour time-weighted average concentration (mg/m3)

Buty? Naphtha- Aromatic
Number of Xylene acetate lene n-Butanol distillate

Operation samples GM GSD GM GSD GM GSD GM GSD ce GSD Cex
Manual prime booth
Painter 1 2 6 1.3 0.81.3 <1 1.1 <1 1.6 30. «(1.6 10
Manual finish booth
Painter 2 2 10 1.3 1 2.7 <1 1.0 1 1.6 30.«1.6 oli)
Electrostatic booth H
Entrance 2 2 2.8 3 40 1 40 2 2.1 40 2.7 18
Electrostatic booth K
Face 2 7 1.0 1 V1 <td 1.2 1 12 45 8.3 +13
Exit 2 68 1.1 24 1.6 7 1.2 11 1.2 200 «1.1 83
OSHA PEL 435 710 50 300 435** 1.0
ACGIH TLV (1979) 435 710 50 150 - 1.0
NIOSH 435 -- -- - -- -

*Comb ined Exposure: Ce = cil + Cy Foose Cy
ty Lo Ly

where: C is the concentration of the individual contaminant, and
L is the environmental limit.

**By analogy with xylene
DISCUSSION

Although this process is far removed from the physical location of Process A
of this case study, it is operated under the same corporate management, with
similar safety and health direction. This process is much newer than Process
A; it has been in production only four years.


—— EXHAUST

SUPPLY (2 bucts)
oucT
Le 3)
WATER
S-FILTER HEADER
+ WALL [ WATER
0 CURTAIN
10" 0
i fe
‘ | WATER
‘ HEADER
_— . }—wATER
7 LEVEL
\ is

>

Figure 6-2. Cross-section of manual spray booth.

Table 6-1. Manual spray booth airflow rates.

Prime booth Finish booth
Exhaust (cfm) 19,000 25,000
Supply (cfm) 16,000 28,000
Control velocity (fpm)
Average 70 150
Low 25 75
High 125 250

Automatic Spray Operations

A spray room for the automatic electrostatic paint systems is shown in Figure
6-3.

Fresh air is supplied from a ceiling plenum through two rows of 20 in by 20 in
fiberglass filters, located on each side of the overhead conveyor. A 4 foot
wide exhaust grate is located in the floor directly beneath the conveyor. The
prime and finish spray rooms exhaust 18,000 and 20,000 cfm respectively, for a
nominal exhaust rate of 20 cfm per square foot of horizontal area. While an
air velocity this low would not be adequate for conventional spray equipment,
the extremely high transfer efficiency of the electrostatic bell system pro-
duces little or no overspray.

6-4


Figure 8-5. Interior of stack wagon spray booth.

Air is exhausted from the booth through floor grates located on each side of
the pit area. A flooded pan 2-1/2 feet below the grate collects the overspray.
Water from the pans drains down through 16 inch diameter venturi cones into a
collecting tank. Booth air is drawn at high velocity (5,000 fpm) through the
water swirling down the cone, effectively scrubbing entrained mist from the
exhaust stream. These points of high velocity also serve to evenly distribute
the exhaust. Six 25,000 cfm centrifugal fans are located on a platform near
the top of the booth.

For any spray booth to be effective, it is essential that the painter be upwind
of the object being painted. When painting a product that is 15 feet high, it
becomes necessary to provide access to elevated areas. This booth is equipped
with powered manlift platforms, which not only make all exterior surfaces read-
ily accessible but also allows the painter to maintain the proper orientation
with respect to the airflow. This arrangement is far superior to a fixed
access platform where, more often than not, the painter will be spraying above
his head.

8-6


ABSTRACT

A series of field surveys of 11 finishing operations provided information for
an evaluation of control technology for spray painting and coating processes;
this information was supplemented by a literature review. The field studies
were conducted in the automobile refinishing, wood and metal furniture, trans-
portation equipment (non-automotive), heavy machinery, and appliance finishing
industries. The processes that were selected provide representative coverage
of spray finishing operations relative to the number of exposed workers, dif-
ferent control techniques, physical size of the workpiece, and the coating sys-
tems that are typically used. The level of control of selected health hazards
is discussed, and available control options evaluated. Case study summaries
presented for each of the sites surveyed include:

@ An analysis of the hazard
@ Engineering controls and work practices
e@ Ventilation measurements
e@ Air sampling data
@ Personal’ protective equipment
@ Evaluation and discussion
The results of this study should be usable as a reference source for anyone

interested in the adequate protection of the worker who sprays paints and
coatings.

iii


Table 10-3. Methy] chloroform concentrations
using a combustible gas meter.

Methyl Chloroform (ppm) Location

90 to 180 Breathing zone of sweeper
450 Directly over bucket
675 to 900 "Cleaned" area, 30 ft from sweeper

3,000 to 4,500 Directly over drain grate
350 OSHA PEL (8-hr TWA)
350 ACGIH TLV (1979 8-hr TWA)
350 NIOSH (15 min ceiling)

DISCUSSION

The data in Table 10-1 indicate that the integral agitator with top cover is
far more effective in preventing solvent evaporation than a clamp-on agitator
and loose fitting lid. The safety cans appeared to be an effective means of
preventing solvent evaporation from dripping spigots. As might be expected,
areas where solvent was exposed to the air (floor drains and open pails) showed
the highest airborne solvent levels. Open floor drains require construction
with a steep slope, and frequent cleaning in order to prevent pooling and sub-
sequent evaporation of solvent.

Cleanup of paint spills requires the use of a solvent for easy removal. Mop-
up operations, using hydrocarbon solvent, could produce a fire hazard, thereby,
methyl chloroform was selected because it is nonflammable and is only moderate-
ly toxic. Prospective users are cautioned, however, that high concentrations
are rapidly disabling. The NIOSH Pocket Guide lists the concentration of 1,1,1
trichloroethane (methyl chloroform) immediately hazardous to life as 1,000 ppm.

10-8

‘te U.S. GOVERNMENT PRINTING OFFICE: 1981--757-074/1078


Control velocity was determined at an elevation of 5 feet, with the car in the
booth, and again on the access platforms, at an elevation of about 12 feet
above floor level. Because the make-up air units apparently had an adverse
effect on air distribution, the measurements were repeated again with the
supply air shut off. Both sets of measurements are presented in Figure 4-4.

15 10 50 7S

as) (10) 10) ISO}

) 20 150 110

(5) (5) (30) K25)}

CAR CAR

50 10 100 125

(10) (10)) 115) as)

70 100} 50 100

(5) to) {10)) (10)

90 so so

ie (5) (20 (oy
MAKE-UP AIR ON MAKE-UP AIR OFF
5‘ ABOVE FLOOR 5' ABOVE FLOOR
() 12"ABOVE FLOOR () 12‘ABOVE FLOOR

Figure 4-4. Control velocity (fpm) in railroad
car, semi-downdraft booth.

The adverse air distribution caused by the make-up air location is depicted in
Figure 4-5. With the make-up air units on, air is apparently directed under-
neath the car, short circuiting the area alongside the car,and resulting in a
dead air space in the center of the booth. An alternate location for the make-
up air inlets is shown in Figure 4-3. By locating the air inlets above the car
sides the dead air space would be eliminated. :

PROTECTIVE EQUIPMENT

Before painting each car, the painters don heavy cotton hoods, overpants, and
hip-length coats. They wrap masking tape around openings of these suits at the

4-6


SECTION V. HEALTH HAZARDS IN SPRAY FINISHING
ROUTES OF ENTRY

Toxic substances can gain entry to the body through inhalation, skin contact,
and ingestion, although this last route is of little industrial importance.
Many industrial chemicals penetrate or react with the surface of the skin, and
cause injury either at the point of contact or act as a systemic poison. In
spray finishing operations, contact with chemicals that are likely to penetrate
the skin most often occurs during mixing and cleanup operations, Because many
contaminants can be inhaled easily and remain in the lung or be absorbed into
the bloodstream, inhalation ranks as the most significant route of entry in
spray finishing.

CONTAMINANT GENERATION

In evaluating the hazards of spray finishing, both the method of application
and the paint formulation require analysis. The method of application deter-
mines the degree of atomization, the relative efficiency in depositing the
coating material on the object, and the site of deposition in the respiratory
tract.

Compressed air spraying atomizes liquid paint by directing a high velocity air
jet at the paint stream as it exits from a fluid nozzle. The flow of air con-
veys the finely atomized droplets to the object being painted. Hama and
Bonkowski note that approximately 20 percent of the droplets are smaller
than 12 microns. In airless spraying, the paint is atomized by forcing it
through a small orifice under very high pressure. This method Produces less
fog than compressed air spraying because not as many fine droplets are pro-
duced. Hama and Bonkowski note that: only 2 percent of the spray droplets in
airless painting are less than 12 microns. In electrostatic spraying, the
paint can be atomized with compressed air, by hydraulic pressure as in airless
spraying, or solely by electrostatic forces. Because the charged paint par-
ticles are directed to a grounded object by electrostatic forces, Paint de-
livery is more efficient.

TOXIC SUBSTANCES
The toxic substances encountered in spray finishing fall into the broad cate-
gories of pigments, synthetic resins, solvents, and additives. The substances

in widest use in each of these categories are discussed in the following sec-
tions.

25


Table 2-4. Airborne solvent levels in barrier coat operations

8-hour time-weighted average (TWA) concentration (mg/m3)

Isopropyl TsobutyT
Booth Date MEK Acetate Xylene Isopropanol MIBK Toluene isobutyrate  C_*

1 9/10 6 13 1 3 <6 9 <7 0.11
1 g/l 4 V 2 2 <4 8 <6 0.09
3 9/12 <3 3 1 1 3 3 <5 0.06
3 9/13. <3 4 1 1 <3 4 <4 0.05
OSHA PEL 590 950 435 980 410 750 150* 1.0
ACGIH TLV oS a a -- -- 375 -- --
NIOSH 590 -- - 980 200 375 -- --

*Combined exposure: C, = G +02 tee Cy

where C is the concentration of the individual contaminant, and
L is the exposure limit.

**No OSHA standard for isobutyl isobutyrate exists; 150 mg/m? is used by
analogy with n-butanol; see text.


Figure 2-2. Dry filter booth used in cabinet lacquering.

GENERAL VENTILATION

Make-up air is provided to the finishing department by two 46,000 cfm make-up
air heaters that are direct fired with natural gas and a third 60,000 cfm unit.
Fresh air inlets for the make-up air heaters are located at ground level, far
removed from booth exhaust stacks. Tempered air is introduced into the fin-
ishing department through three grille boxes. The volume and high discharge
velocity of these distribution points, together with 20 percent deficiency in
the volume of supply air, produce substantial crossdrafts in areas near doors
and supply air points.

Because all air exhausted from the booths must be supplied from the finishing
department, the booth exhausts have the effect of providing dilution ventila-
tion for any solvents that are evaporated from the open conveyor lines.

A fan supplies room air to a plenum running underneath the conveyor in order
to provide cooling for the finish wipers during the summer months (Figure
2-3). The system was not in operation during this survey.

2-7


paints. The resins used in thermosetting acrylic emulsions are similar to
those used in solution-type coatings.

Alkyd Resins--

Alkyds are oil-modified polyester resins made by the condensation of a poly-
carboxylic acid with a monoglyceride. The monoglyceride is produced by the
reaction between a polyalcohol and a fatty acid. Glycerol and pentaerythritol
are often used for the polyalcohol, and phthalic anhydride is typically used
for the polycarboxylic acid.

Variations in the type and amount of the fatty acid that is used can produce
variations in the final film and drying properties. Alkyds with low oil con-
tent are commonly combined with amino resins to produce industrial baking
enamels. Alkyds with higher oi] content are used in air drying finishes.
Finishes made from. these materials cure by oxidation and the subsequent poly-
merization of unsaturated double bonds in the drying oil.

Polyester resins, on the other hand, are considered "oil-free" alkyds. Poly-
ester resins can be combined with amino resins to produce high quality baking
enamels, _or used alone as the polyol component in two-package urethane
coatings.7

Amino Resins--

Amino resins are based on the reaction of formaldehyde with urea or melamine.
These resins are seldom used alone, but are generally used as cross-linking
agents in baking enamels. They can be used with alkyds, epoxies, and thermo-
setting acrylic enamels. ' .

Cellulosic Resins--

Cellulose is a natural polymer characterized by pendent hydroxyl groups. As
such, it can form esters of inorganic and organic acids as well as ether com-
pounds. Cellulose nitrate, or nitrocellulose, is the only inorganic ester of
cellulose that is used in large volume. Nitrocellulose is manufactured by
treating purified wood pulp or cotton linters with a mixture of nitric and
sulfuric acids. Nitrocellulose lacquers are used for finishing furniture and
refinishing automobiles, largely because of their rapid air-drying character-
istics.

Cellulose is reacted with acetic anhydride to form cellulose acetate. It is a
useful component of heat resistant coatings because of its high melting point.
A mixed ester, known as cellulose acetate butyrate, is obtained by the reaction
of cellulose with acetic and butyric acids and their anhydrides. Cellulose
acetate butyrate, modified with acrylic resins, is used in both furniture and
automobile finishes. Cellulose derivatives by themselves produce coatings with
inferior properties, so they are combined with modifiers, either plasticizers
or compatible resins, to enhance their performance. The phthalates, ary] phos-
phates, polymerized oils, and liquid resins are all used to plasticize cellu-
losics.

Epoxy Resins--
The most commonly used epoxy resins are derived from the condensation of bis-
phenol A with epichlorohydrin. Resins with increasing molecular weight are

7


soaps for paint drying did not exceed the 50 ug/m3 standard when minimum ven-
tilation requirements were met (case study 5).

Based on the maximum paint mist concentration of 5 mg/m? found in well-con-
trolled finishing operations, up to 1 percent lead could be tolerated in the
dried film and the OSHA standard for airborne lead would still be met. This
is not a practical concentration for the pigments typically used. However,
where a variety of colors are painted, the "average" paint for the workshift
may be well below this figure and the subsequent average exposure for the shift
below 50 ug/m3.

The lead pigments provide durability to exposure, and thus find greatest use on
transportation and heavy equipment. Of the operations in these categories, the
heavy equipment finishing operation described in case study 8 comes closest to
meeting the 50 ug/m3 standard, with an 8-hour time-weighted average concen-
tration of about 100 ug/m3 during painting of equipment exteriors.

While lead should be eliminated where possible, suitable substitutes are not
always available, and lead pigments will continue to be used. Safe usage of
these materials dictates the use of respiratory protective equipment and the
biological monitoring of the painter in addition to engineering controls.

Chromium

Chromium is used in both trivalent and hexavalent forms in paint pigments.
Trivalent chromium occurs primarily in the pigment chromium oxide green.
Hexavalent chromium most frequently appears as lead chromate in chrome green,
chrome yellow, and molybdate orange pigments, and in the corrosion inhibiting
pigments zinc and strontium chromate.

All of the spray painting operations studied meet the 1 mg/m3 OSHA standard
for chromium metal and insoluble salts. Conversely, nearly all that employ
chromium pigments exceed the OSHA ceiling level of 0.1 mg/m3 for chromic acid
and chromates. The applicable standard is unclear, as these pigments are both
insoluble salts and chromates. The OSHA ceiling standard of 0.1 mg/m3 was
adopted from the American National Standard 237.7-(1971), which was a time-
weighted average limit for chromic acid and chromates of alkali and alkaline
earth metals. The situation is further complicated by the state-of-the-art of
analytical methods. Presently available methods do not allow an unambiguous
determination of which chromium species are present. For the purposes of this
study, analytical results are reported as total chromium.

The ACGIH has suggested a limit of 50 ug/m3 (time-weighted average) for the
chromates of lead and zinc. NIOSH has proposed a time-weighted average limit
of 15 ug/m3 for non-carcinogenic hexavalent chromium, and a 1 ug/m3 ceiling

concentration for those compounds considered carcinogenic. Most hexavalent
chromium compounds used in paint fall in the latter category. The levels re-
commended by NIOSH can only be met by eliminating hexavalent chromium from the
coating formulation, or by automating the process and removing the painter.

As is the case for lead, hexavalent chromium-containing pigments should be
eliminated where possible. However, suitable substitutes are not always avail-

49


Table 9-1. Manual spray booth data (Process A).

Total Average control velocity (fpm)
Booth airflow (cfm) 4' above grate SD
Booth A
(no filter) 27,000 100 55
(clean prefilter) -- 90 55
(dirty filter) -- 80 55
Booth F 30,500 100 37

Automatic Spray Booth Design

One of the four automatic spray booths for electrostatic application is shown
in Figure 9-3. These identical sidedraft water wash booths measure 20 feet
wide by 12 feet high. They are equipped with thick mesh filters, fitted over
the water curtain to prefilter exhaust air. These filters are changed at the
end of each workshift. The booths house four electrostatic spray guns mounted
on reciprocators. An additional electrostatic spray gun is mounted just inside
the conveyor entrance vestibule in order to coat the tops (in one instance)
and bottoms (in the other instance) of the file cabinets.

AIR_INLET DRY PREFILTER
UGHT ADJUSTMENT VANES
FIXTURES —
Ny

La BNIB

WAY
[-HEAI

WATER
LEVEL

ELECTROSTATIC
APPLI Fi ‘VENTURI
iy , ane Bor rom BAFFLE

Figure 9-3. Automatic electrostatic spray booth.

9-6


than 30 seconds. All the waterborne coatings and small runs of other paints
are delivered to the booths in portable pressure pots.

HAZARD ANALYSIS

With more than 700 different coating formulations in use, employees are poten-
tially exposed to a wide variety of paint materials. The organic solvents that
are used produce similar physiological effects. In general, they are irritants
to the conjunctiva and to the mucous membranes of the upper respiratory tract.
They all produce depression of the central nervous system and, at high concen-
trations, produce symptoms of headache, nausea, and drowsiness followed by
unconsciousness.

The hazards of organic solvents are drastically reduced when waterborne
coatings are employed, because these substitute materials typically contain
less than two percent organic co-solvents. Dimethylethanolamine is used in
the waterborne formulation as an emulsion-stablizer, surface active agent,
producing a slight fishy odor noticeable in the flash-off areas. Dimethy1-
ethanolamine has been demonstrated to induce asthma and/or rhinitis. No
standard exists for exposure to dimethylethanolamine, however, animal studies
indicate that it is of the same order of acute toxicity as monoethanolamine
which has a Permissable Exposure Limit (PEL) of 3 ppm. Because of the low
vapor pressure of dimethylethanolamine, the chief hazard would be associated
with inhaling the paint aerosol rather than the vapors of dimethylethanolamine.

The non-volatile components of the coating formulations that are utilized are,
for the most part, physiologically inert. Exceptions are the lead- and
chromium-containing pigments that are present in certain color formulations.
The reactive resins, polyurethane and epoxy, and their associated catalysts,
are only used to a limited extent but are potential irritants or sensitizing
agents to the skin and/or respiratory system. Their limited use did not permit
evaluation during this survey.

SPRAY BOOTHS
Design

The five spray booths that are in operation at this facility are of nearly
identical design. The only difference is the in-line configuration of the
prime and finish booths as opposed to the detached "special" booth. The booths
were originally installed as sidedraft booths with an oil-flooded sheet and
wash section. However, most paints would not float on the oil, which created
severe problems in removing paint sludge from the oi] reservoirs. The oil also
caused slippery conditions in and around the booth. A switch to a water wash
design would have required replacement of both pumps and reservoirs. Because
of the problems associated with such a change, the oil-flooded sheet and air-
wash section was replaced with an 8 foot by 20 foot filter bank for collection
of the paint solids. This modified design is shown in Figure 3-2. Note that
make-up air is supplied through 5 air inlets located on the wall opposite the
exhaust filter bank, and through two filtered-air inlets in each conveyor inlet
and supply exit vestibule. Design specifications called for an exhaust flow
rate of 27,800 cfm and a make-up air flow rate of 31,600 cfm. The excess make-

3-3


all colors are equally popular, some paints are stored in 350-gallon bulk con-
tainers, others in 5-gallon buckets, and the majority in 55-gallon drums. Nine
80-gallon paint containers and seventeen 55-gallon drums are continuously agi-
tated, and the paint is pumped to the spray guns and returned back to the con-
tainer. All but one of the drums is equipped with a heavy barrel cover, with
an integral agitator, sealed pipe openings, and a closable access door. This
cover is pictured in Figure 10-2. The larger paint containers have a similar
arrangement. The single paint drum without this feature uses the clamp-on agi-
tator and partially closed drum lid shown in Figure 10-3.

Coatings

Typical paint formulations in this plant required thinning with 10 to 15 gal-
lons of additional solvent per drum of raw paint. Xylene and an aromatic
petroleum distillate are the most commonly used solvents in this operation.
These materials are stored in remote tanks and pumped to the mix room. Those
solvents used less frequently are stored in drums equipped with spigots. All
solvents are transported within the mix room in 5-gallon containers.

Figure 10-2. Paint mixing drum with integral cover and agitator.

10-2


ROOF LINE.

LNA NZ NAN YN

SUPPLY AIR TO OPEN
TOP OF SPRAY BOOTH

FAN

WATER waren

SPRAY . SPRAY
HEADER NS SL HEADER

GRILLE
WATER
— LEVEL
p30 —21.0'

Figure 9-2. Manual spray booth.

mist from the exhaust air stream. The floor of each booth contains a 5 foot
wide exhaust grate running its entire length. Parts to be coated enter and
exit the booths through conveyor vestibules.

The first manual booth on this paint line was fitted with a prefilter to the
water wash that was similar to the prefilter on the automatic spray booths.
The prefilter assembly did not significantly affect the total airflow, but did
reduce the average control velocity between 10 and 20 percent. This reduction
was because of the filter assembly's adverse effect on the air distribution in
the booth. The results of these measurements are presented in Table 9-1.

9-5


In order to identify trace metals and determine free silica, two bulk samples
of the paint were qualitatively analyzed. X-ray diffraction analysis indicated
the absence of silica patterns. Although both samples did show patterns indi-
cative of crystalline material, the diffraction patterns were not identified.

The x-ray fluorescence analysis of both samples of bulk material are reported
in Table 1-3. An inductively coupled plasma, atomic emission spectrometer
(ICP-AES) was used to further examine the ash of the two powder samples. This
procedure identified the presence of lead and selenium in trace quantities; no
chromium was detected. Air samples were subsequently analyzed by atomic
absorption spectroscopy for lead and selenium. All analyses were below the
limits of detection for these metals, corresponding to concentrations in air
of less than 2 ug /m3 for lead and 10 ug /m3 for selenium.

To evaluate the potential for hydrolysis in the lung of the caprolactam isocya-
nate group, regenerating caprolactam, a bulk sample of the powder was
extracted with an isotonic saline solution (1 9/5 ml) over a period of time,
taking 1-m] aliquots at intervals of 0, 2, 8, 24, and 48 hours. To determine
the caprolactam recovered, the aliquots were then extracted with methylene
chloride before analysis by gas chromatography The bulk material yielded very
little caprolactam in the recovery procedure. The 24- and 48-hour aliquots
displayed an irregularity in the baseline output of the flame ionization
detector. If the irregularity represents caprolactam, it could be concluded
that perhaps a milligram of caprolactam per gram of bulk powder may go into
saline solution. Note that the irregularity may have been because a small
amount of the bulk material contaminated the saline aliquot. In this case no
conclusion could be drawn. In either case, no hazard from caprolactam should
exist at airborne powder paint levels below the limits for nuisance materials.

RESULTS

The total dust exposure of both the sprayer and the equipment operator are low,
approximately equal to the dust concentration in the general area (Table 1-2).

Dust concentrations at the brown line are nearly double those of the cream
line, which reflects the approximate production ratio of 70/30 for these
colors. The concentration of dust in the discharge of the final filters is
higher than might be expected, especially when compared with dust levels at
the west wall.

Dust levels at the west wall are strongly influenced by the quality of air that
is returned by the air conditioning system, a unit that recirculates 100 per-
sent of the powder department air through only a rough fiberglass filter. The
higher-than-expected concentrations could be a result of mechanical damage to
the filter from a periodic manual cleaning with compressed air.

1-8


SECTION VI. CONTROL OF HEALTH HAZARDS

This section presents the control methods that were discussed in the litera-
ture or studied in the field surveys. These methods involve the application
of the basic control principles of substitution, isolation, ventilation, and
work practices.

SUBSTITUTION

Substituting less hazardous materials, equipment, or even a less hazardous
process, may be the least expensive, as well as the most positive, method of
controlling an occupational hazard. In order to minimize the hazards in spray
finishing, coating materials should be formulated with relatively safe ingre-
dients, and with a minimum amount of solvent.

Substitution of Materials

Pigments--

Organic pigments can be used in place of the principle lead- and chromium-
containing pigments used in industrial finishes. However, the organic pigments
are less durable, have reduced corrosion resistance, and have a tendency to
fade. Besides lead and chromium, other heavy metals (cadmium, antimony,
arsenic, and water soluble barium) are used to a limited extent in paint pig-
ments. Most of these pigments also contain lead, thus, eliminating lead may
remove other heavy metals.

Webb29,30 describes available lead-free pigments and their properties. He
notes that a lead-free color with properties exactly matching a lead-contain-
ing color will cost more. To hold down costs, he suggests changing the color
of the product to the browns, blues, violets, whites, grays, blacks, or certain
shades of green that can be made inexpensively with lead-free pigments. Simi-
larly, costs can be held down in a switch to a lead-free pigment if some re-
duction in pigment performance, such as bleed resistance, color intensity,
light fastness, and heat resistance, is accepted.

Panush3! discusses the shortcomings of some traditional non-chromate pigments
for use in automotive finishes, citing poor color matching, increased cost, and
weakened durability to exposure. He lists those pigments that have potential
for non-chromate automotive colors.

Considerable interest has been shown in the automobile and ship building in-
dustries in metal primers that contain metallic zinc dust in place of zinc
chromate. Metallic zinc protects the metal substrate by galvanic action rather
than by inhibition and, unlike zinc chromate, zinc dust is of low toxicity.

31


Table 9-7. Airborne levels of spray mist, lead, and chromium
in metal furniture finishing (Process B).

8-hour time-weighted average concentration

Paint mist Lead Chromium
Number (mg/m3) (ug/m3) — (ug/m3)
Operation of samples GM GSD GM GSD GM = GSD
Manual prime booth
Painter 1 2 0.5 1.2 5.0 1.0 5.0 1.0
Manual finish booth
Painter 2 2 0.9 2.2 5.0 1.0 5.0 1.0
Electrostatic booth H
Face 2 0.2 2.7 5.0 1.0 5.0 1.0
Entrance 2 4.0 2.0 2.3 3.0 7.0 2.0
Electrostatic booth K
Face 2 0.2 2.2 5.0 1.0 5.0 1.0
Exit 2 17.8 1.2 6.0 1.3 5.0 1.0
OSHA PEL 15 50 1,000
ACGIH TLV (1979) 10 150 100
NIOSH -- 100 1

GM: Geometric mean
GSD: Geometric standard deviation

9-16


SECTION VII. EVALUATION PROCEDURES
INTRODUCTION

This section presents the methods for sampling, analysis, and engineering eval-
uation that were used during the course of this study to measure workplace
levels of airborne contaminants and to evaluate the effectiveness of control
measures.

AIR SAMPLING AND ANALYSIS
General Principles

Air samples were collected in order to determine the effectiveness of a control
measure based on the environmental levels achieved, and to lend support to the
observations made during the study. Prior to sampling, a study of the particu-
lar finishing process and the associated control measures was made in order to
provide an understanding of the variables which could effect sampling results.

Basically, three different types of samples were taken, each for a specific
purpose:

1. Personal air samples--This type of sample permitted an eval-
uation of the potential exposure of the spray painters to
various airborne hazards. Where respiratory protection was
used, samples were collected outside of the respirator. The
results of these samples were directly compared to allowable
limits. By themselves, however, these samples did not always
give a direct indication of the functioning of a particular
control measure.

2. Short duration breathing zone samples--In several finishing
processes, the preliminary observations indicated that a
specific operation contributed heavily to the overall conta-
minant levels. To determine this contribution, breathing
zone air samples were collected for the duration of the sus-
pect operation. These short duration measurements were made
by using either direct reading instruments or conventional
personal sampling equipment.

3. Bulk air samples--These fixed area samples were collected in
the spray booth and analyzed qualitatively to determine the
contaminants present. Bulk air samples were collected where
material safety data sheets were either unavailable or judged
to be inadequate, or where many types of paints were used in
a single workshift.

43




tive success in maintaining proper airflow orientation as the painter changes
position and the degree of sophistication of the paint application equipment.
The paint mist concentration for the majority of these operations could be con-
trolled to below 10 mg/m3 if ventilation and/or application techniques were
improved. An exception would be the finishing of relatively enclosed spaces,
such as vehicle interiors.

Table 15. Summary of paint mist concentrations
in selected finishing operations.

Operation Paint mist (mg/m3)

I. Mean time-weighted average concentrations
of paint mist in continuous painting

operations

Powder coating small parts (electrostatic) los}

Wood furniture (airless and compressed air) 0.1 - 2.5
File cabinets and panels (compressed air) 4.2

Metal furniture (compressed air) 3.7 - 27.6
Appliances (compressed air/electrostatic) 21.7 - 39.2

II. Mean concentrations of paint mist during
spraying of internal cavities

Freezer liners (compressed air) 320.0
File cabinet interiors (airless) 2.9
Walk-in spraying of large vehicles 36.5
(airless)

III. Mean concentrations of paint mist in
intermittent painting operations
Heavy equipment exteriors (airless electro- 2.0
static with heated paint)
Automotive refinishing (compressed air) 8.7
Light aircraft (compressed air) 23.3
Railroad freight cars (airless) 43.3

Lead

Lead is used in paints as both a pigment and as a catalyst to accelerate the
drying of alkyd and oleoresinous paints. Chrome green, chrome yellow, and
molybdate orange were the principle lead pigments found in this study. The
amount of lead, by weight, in the dried film of paints using these pigments may
reach 15 percent. In no case where the lead content approached this figure was
the 50 ug/m3 limit for lead met. Alkyd resin enamels employing lead only as

48


CASE STUDY 7
LIGHT AIRCRAFT FINISHING

Helicopter exteriors are finished with an epoxy/polyamide primer and a two-com-
ponent polyurethane topcoat. Conventional air-atomized spray equipment is used
in large, downdraft spray booths. Breathing zone levels of organic solvents
and dibutyltin dilaurate, a paint accelerator, were well below recommended
maximums. Breathing zone levels of lead greatly exceeded allowable levels when
certain colors were used. Control of total mist, chromium, and isocyanate was
marginal, particularly when helicopter underbodies were painted. Air-purifying
respirators were worn during all spraying operations.

PROCESS
Operations
Helicopters are finished in a paint shop adjacent to the manufacturing build-

ing. This shop contains 5 spray booths and 3 open bays. A layout of the paint
shop is shown in Figure 7-1.

DESIGN LAYOUT. tn ~

co

SOUTH CENTRAL

BAY BAY

AREA AREA

PAINT I PAINT BREAK
L ——— MIX ROOM STORAGE AREA
a INDICATES
ROLL-UP DOOR

Figure 7-1. Layout of helicopter finishing area.

The North Bay Area of the paint shop is reserved for all pretreatment pro-
cesses. In this area the ships are cleaned, masked, repaired with body putty,
sealed, rinsed with a dilute chromic acid solution, and tested with water for
leaks. All doors, cowls, and air foils are removed and hung on portable parts
racks. The ships are then manually transported by dolly to one of the three
north spray booths. The small parts racks are positioned over the exhaust
grates inside the spray booth.

Each spray booth can accommodate 2 to 4 painters and 1 or 2 helicopters, de-
pending on the size of the ship. After tack wiping and black light inspection,
all ships and small parts receive a single coat of a yellow-green epoxy primer,
which requires approximately 1 hour for application and another hour for
curing. The small ships receive 2 to 3 gallons of primer while larger ships
require 3 to 4 gallons.

7-1


Sampling rates and duration were based on the applicable permissible exposure
limit, the sensitivity of the analytical procedure, the estimated airborne con-
centration of the contaminant to be sampled, and the length of the actual
painting operation. In general, continuous (conveyorized) painting operations
were sampled for two consecutive periods of about 4 hours each. For intermit-
tent operations, such as heavy equipment painting or automobile refinishing,
separate air samples were taken for the duration of each painting activity.
Measurements that were taken to determine exposure to ceiling standard sub-
stances were taken during periods of maximum expected concentrations; each
measurement consisted of approximately a 15 minute sample. When possible,
three days of sampling were performed. The extent of sampling was limited by
the necessity to restrict all of the evaluations within a particular plant to
a period of several days.

Non-Volatile Paint Components

Air samples for the aerosols of the non-volatile components of paint (total
mist, lead, and so forth) were collected using closed face cassettes with pre-
weighed 37 mm membrane filters and personal sampling pumps operated at 2.0 lpm.
Total mist was determined by weighing the samples plus the filters on an elec-
trobalance and subtracting the previously determined tare weights of the
filters. The tare and gross weighings were performed in duplicate. For analy-
sis of metals, the filters were subsequently wet-ashed with both nitric and
perchloric acids to insure their complete dissolution. The ashed samples were
diluted to a final volume of 25 ml and aspirated into an atomic absorption
spectrophotometer, as described in NIOSH method P&CAM 173,52

Three types of filter media were employed in these samples. The majority of
samples were collected on 0.8u polyvinyl chloride/acrylonitrile membrane
filters. These filters showed high resistance to the common paint solvents,
low blank values for lead and chromium, and freedom from blinding at reasonable
filter loading. NIOSH detected significant weight loss in some lots of these
filters; therefore use of these filters was discontinued. The remaining filter
samples were collected on 5u polyvinyl chloride or matched weight 0.8u cellu-
lose ester membrane filters. The PVC filters did not exhibit the same degree
of solvent resistance as the other filters.

Volatile Paint Components

Air samples for the organic solvents employed in paints were collected on 150
mg charcoal tubes, with personal pumps operated at either 50 cc/min or 100
cc/min. The lower sampling rate was used for continuous painting operations
where samples were collected for the duration of one-half a shift. The higher
rate was used for non-continuous finishing operations -where sampling (and
painting) times were typically 1 hour. A lower total sample volume was col-
lected for these operations because of anticipated higher concentrations. The
A and B sections of each sample were separately desorbed and analyzed by gas
chromatography as outlined in a modified version of NIOSH P&CAM 12792 or in
P&CAM $5622, Chromatographic conditions are reported in Table 14. Except
as noted, all desorptions were performed with carbon disulfide.

44


CASE STUDY 2
WOOD FURNITURE FINISHING

Stereo cabinets of polystyrene and wood are finished with a base coat, a glaze,
and a clear lacquer in a multi-step, conveyorized operation. The application
equipment includes both conventional compressed-air and airless spray guns,
although the latter predominates. All finishing operations are performed in
sidedraft spray booths, with either dry filters or sheet metal baffles. Make-
up air is supplied externally to the spray booths. The Operations at this
facility are characterized by good housekeeping and a high rate of exhaust ven-
tilation; this result is that employee exposure to solvent vapors and spray
mist is low.

The glaze operation features a robot applicator, which was installed to remedy
an employee morale problem resulting from the messiness of the glaze applica-
tion.

PROCESS
Operations

The stereo cabinets are made in a variety of designs, but all are of basically
the same configuration; they open from the top with hinges at the rear. The
cabinet interiors contain a composition board shelf that receives the record
changer and radio amplifier. The cabinets are roughly the same height and
depth (approximately 30 in x 20 in), with widths ranging from 30 to 60 inches.
The walls and lids are made of thin polystyrene sheets, reinforced with back-
up panels of composition board. Rims and bases are natural wood moldings.

The cabinets enter the finishing department on a steel mesh conveyor travelling
at 10 feet per minute, with an interval of 2 to 3 feet between cabinets. Be-
cause the conveyor cannot rotate the cabinet, spray booths are paired on oppo-
site sides of the conveyor to allow better coverage of product sides and edges.
Not all product designs nor all of the finishing steps require the use of a
second booth.

The finishing process begins with the application of a barrier coat, followed
by successive coats of glaze and clear lacquer. The entire process can involve
up to 15 spray painters and 16 glaze wipers. The layout of the finishing
department is shown in Figure 2-1. The finishing sequence follows:

1. Dust--Dust and wood chips from the assembly operation are removed
from the cabinet with a compressed air jet.

2. Barrier coat (Booths 1 and -2)--The acrylic base coat is applied to
the entire cabinet surface.

3. Sand--The wooden rim molding is lightly sanded.

4. Top barrier coat (Booth 3)--Both sides of the cabinet lid receive
a second application of barrier coat with a compressed air gun.

2-1


Table 2-3. Airborne levels of paint spray mist
in wood furniture finishing.

Paint mist (mg/m3)*
D

Booth Operation GM GS

1 Heavy coat of barrier 0.8 1.4
finish

3 Second coat of barrier 0.4 1.6

finish to top and sides

4 Manual coat of glaze 1.0 1.2
to top and sides

5 Robot application of 0.1 2.0
heavy coat of glaze
(area sample)

6 Heavy coat of lacquer 0.5 1.2

7 Second coat of lacquer 0.4 1.8
to top and sides

8 Light coat of glaze 0.1 5.0

12 Barrier coating of 0.5 1.1
interior surfaces

13 “Veil lacquer applied 0.1 1.5
to interior

14 Final heavy coat of 2.5 1.0
lacquer

GM: Geometric mean
GSD:Geometric standard deviation
*8-hour time-weighted average (TWA)


L
OPEN
- \
TM ;
ENCLOSED

W/INTEGRAL SUPPLY AIR

Figure 3. Downdraft booth configurations.

38


— t—
AUTOMATIC PRIME ao MANUAL PRIME 4
{ B0oTH BOOTH ~
4 =)
' |
o Y
'
4 [contro
FLASH-OFF | | | ROOM
AREA —J> '
,
, _—
\ AUTOMATIC. FINISH MANUAL_ FINISH
coats as Do seep ees o eo oe
BOOTH BOOTH
—_—

Figure 6-1. Layout of appliance finishing area.

Liners for chest-type freezers are painted with a white acrylic enamel on the
same paint line. However, they are manually sprayed by air-atomized guns; the
automated systems are not used. The liners represent approximately 10 percent
of the units painted, and occur in short runs of about 5 minutes each, inter-
spersed during the day. Air-supplied helmets are worn during the painting of
the liners because of the fog generated in this operation.

Coatings

Lids, doors, and cases are coated with a thermosetting acrylic enamel in a
choice of five colors. The basic paint consists of a pigmented acrylic resin
in a solution of organic solvents. The coating material, as received from the
manufacturer, contains approximately 60 percent volatile materials by volume,
and is further reduced with toluene and/or xylene. Coatings for the automated
system are reduced with toluene and xylene at a ratio of 2 gallons of paint to
1 gallon of thinner; the exact thinner mix varies slightly with color.
Coatings for manual spraying are thinned with xylene at a ratio of 3 gallons
of paint to 1 gallon of xylene.

A white acrylic enamel from a second supplier is used for the interior surfaces
of chest freezer liners. This material is a pigmented acrylic resin mixed with
a phenolic resin to confer thermosetting properties. It is thinned at a 3:1
ratio, with a mixture of xylene and other aromatic solvents.

Coating materials are mixed in a separate paint mix room and piped to the spray
guns at 20 psig. Each 3-unit electrostatic spray header applies approximately
4 gallons of paint per hour. Each painter applies approximately 3-1/2 gallons
per hour with the manual equipment. All the manual guns are operated at an
atomizing-air pressure of 60 psig.

6-2


There were no major differences observed between mean total mist levels among
the painters. Mean concentrations of lead and chromium for the individual
painters were not calculated because of variations in the content of these me-
tals in the paints used.

Arrangements had been made to evaluate a heated (160°F), electrostatic
(76,000 volt) spray gun during this survey. Time and equipment constraints
allowed only one sample for comparison, This sample is identified in Table
4-4, Mist concentration was 33.2 mg/m3 as compared to a mean concentration
of 44.4 mg/m3 for the other samples. Visible overspray appeared to be less,
but the time required for painting was twice as long, in part because of the
lower paint delivery rate. It is unclear from this single sample whether im-
proved application techniques would significantly lower exposure.

Airborne concentrations of aliphatic hydrocarbons, toluene, xylene, and other
aromatics are reported in Table 4-5. Solvent fractions eluting from the gas
chromatograph before toluene are listed as "aliphatic hydrocarbons." Solvents
eluting after xylene are reported as “other aromatics." Combined solvent con-
centrations range from 70 to 200 percent of the maximum allowed for a full
shift exposure, based on current legal maximums. Because of the short spraying
time, the 8-hour time-weighted average concentrations would be below the legal
maximum. However, both NIOSH and the ACGIH have Recomended lower exposure
limits for toluene, and NIOSH has recommended a 350 mg/m3 maximum for refined
petroleum solvents.

As a rule of thumb guide to the maximum concentration allowed for short periods
of time, the ACGIH has established excursion factors. The appropriate 8-hour
limit, multiplied by the excursion factor, yields the maximum concentration re-
commended for exposures of short duration. For the solvents employed, a maxi-
mum excursion of 1.25 times the 8-hour limit is permitted. Approximately one-
half the solvent samples exceed this recommended maximum excursion.


SPRAY BOOTH

All complete body repainting as well as the spot painting of areas greater than
2 square feet are performed in a standard-make spray booth, similar to that
shown in Figure 5-2. °

Figure 5-2. Spray booth and oven.

The working area of each booth is approximately 14 feet wide by 26 feet long
by 9 feet high. The booth is the "drive-through" variety, with the exit doors
connecting directly to a drying oven. Air is supplied to the booth through
20 in x 20 in foam filters mounted in the doors and door bulkhead. Air is
exhausted through two exhaust chambers that are located on either side of the
exit doors and connected to a single duct fan on the roof of the spray booth.
Each exhaust chamber contains six 20 in x 20 in and three 10 in x 20 in paint
arrestor filters. Pressure drop is monitored by a manometer and the filters
are changed when the pressure drop exceeds a predetermined point. It is esti-
mated that total airflow declines about 10 percent after a set of five to six
complete body repaintings.

The booth was designed for a nominal 100 cfm/sq ft of booth cross-sectional
area. Measured air velocities are presented in Figure 5-3. The presence of
an automobile raises the actual air velocity in the painter's breathing zone.
Also, the placement of the exhaust openings at the booth sides tends to in-
crease the air velocity there.

PROTECTIVE EQUIPMENT

Protective equipment is limited to the use of a half-facepiece, air-purifying
respirator, with organic vapor-removing cartridges and mist prefilters.

5-5


Sampling results for hexamethylene diisocyanate (HDI) are reported in Table
5-4. All three samples were below the 10-minute ceiling concentration limit
for HDI that is recommended by NIOSH. For current levels of usage, 8-hour
time-weighted average exposure limits would also be met. An analysis for HDI
oligomers was not attempted.

Table 5-4. Airborne levels of hexamethylene diisocyanate
in automobile refinishing.

Sample Hexamethylene diisocyanate
Car size duration (min) (ug/m3)
Compact 13 (Coats 1 + 2) <50
Subcompact 7 (Coat 1) <93
5 (Coat 2) <130
NIOSH (10 minute ceiling) 140

DISCUSSION

The spray booth used at this facility is typical of that found in most refini-
shing shops and automotive dealers. The design appears adequate in keeping
solvent and total paint mist concentrations within acceptable maximums. Usin
the mean total mist concentration of 8.7 mg/m3 of Table 5-2, the 50 ug/m
lead standard can only be met if the lead content of the paint solids is less
than about 0.5 percent by weight. Unfortunately, many shades of yellow and
red will contain many times this amount of lead. Eliminating lead from these
colors is not feasible at this time, because the use of lead-containing pig-
ments is required in order to match factory colors. Only when all vehicle
manufacturers, both foreign and domestic, have switched to heavy-metal-free
factory finishes, and all the current vehicles are no longer in use, will it
be possible to reduce the lead hazard for all paint colors in the automotive
finishing trade.

While no respiratory protection would be needed for a majority of the painting
operations when they are performed in a effectively functioning spray booth,
use of certain colors poses a risk of overexposure to lead and other metals.
Good industrial hygiene practice suggests that all painters wear an approved
air-purifying respirator while painting. Because the sensitization potential
of the polyisocyanate is not well understood, respiratory protection will also
minimize this hazard.

5-10


Sampling results for hexamethylene diisocyanate are reported in Table 7-8. All
but one sample are below the 10 minute ceiling concentration limit for HDI re-
commended by NIOSH. The single value in excess of this limit was for the final
coat to the underbody and tail. As was noted before, ventilation is compro-
mised in this operation.

The first two samples reported in Table 7-8 were taken jn parallel, with the
second sample preceded by a filter. This was done to determine if the isocya-
nate was present as a vapor, or as a constituent of the paint aerosol. Insuf-
ficient material was collected to enable a judgement to be made.

Table 7-8. Airborne levels of hexamethylene diisocyanate
in light aircraft finishing.

Sample Hexamethy lene
Ship duration diisocyanate
number Operation (min) (ug/m3)
5 Base coat, whole ship 15 27
5* Base coat, whole ship 15 <26
5 Base coat, whole ship 21 19
9 Stripe, first coat, 13 <30
underbody and tail
9 Stripe, first coat, 7 <57
underbody and tail
9 Stripe, second coat, 10 67
underbody and tail
9 Stripe, second coat, 8 <47
underbody and tail
9 Stripe, third coat, W 250
underbody and tail
NIOSH Recommendation
Ceiling (10 Minutes) 140
8-hour time-weighted average 35

*Sample taken parallel to preceding sample, but with
prefilter.


Two painters apply a single coat of an alkyd enamel in a 32 by 40 foot down-
draft spray booth. The booth is equipped with five airless electrostatic hand
spray guns and two airless pole guns. The pole guns are used to allow the op-
erator access to hard-to-reach areas. All guns are operated at a paint pres-
sure of 1000 to 1200 psi and the electrostatic guns operate at a charging
potential of 60,000 volts. The paint is heated to 100 to 130°F, which allows
paint formulation at a lower solvent content, and application at a lower pres-
sure than would be possible with a cold airless system. The paint is distri-
buted with a loop-type system, from an adjacent paint storage room.

The two painters require one hour to apply the 10 to 12 gallons of paint that
are necessary to cover the product. Both painters begin coating the bottom
frame and lower edges with the pole guns. Painter A enters the pit for about
5 minutes to spray the remaining members with an electrostatic gun (Figure
8-2). He returns to the floor, sprays the front of the wagon, then raises the
manlift to paint the top with a pole gun. Then he works his way down the side

Figure 8-2. Underbody finishing operations.

8-2


DISCLAIMER

Mention of company names or products does not constitute endorsement by the
National Institute for Occupational Safety and Health.

DHHS (NIOSH) Publication No. 81-121

ii


Figure 7-5. Helicopter in booth after striping.

While providing excellent protection, the coverall material does not readily
breathe, which causes complaints from the painters during hot weather. How-
ever, because few painting operations at this plant require more than one
hour, use of this type of clothing should not produce undue thermal stress.

The size and shape of the helicopter and the toxicity of the paint materials
require the use of respiratory protective equipment. Again, the short duration
of actual spraying make respirators more acceptable to the employees. At this
facility line supervisors have the responsibility for enforcing and training in
the use of respirators. Several employees noted respirator leakage. These
same employees were found to be wearing respirators with one headband either
missing or improperly adjusted, which underscores the need for training as a
function of the safety or hygiene management.

EVALUATION

Approximately 130 people are employed in the finishing department, with the
majority working the day and afternoon shifts. Many have no exposure to paint

7-8


Table 4-1. Paint composition.

Paint Blue alkyd enamel
0.25 % CrVI (in pigment)
0.19 % Pb (in drier)
40 % mineral spirits
10 % aliphatic hydrocarbons
5 % toluene
5 % aromatic naptha
Paint "B": Zinc chromate primer
3.7 % CrVI (in pigment)
4.7 % Zn (in pigment)
25 % mineral spirits
5 % toluene
Paint "C": Brown alkyd enamel
0.24 % Pb (as litharge) —
0.2 % Pb (in drier)
40 % mineral spirits
5 % toluene
5 % xylene

Paint “D": Zinc chromate primer

0.72 % CrVI (in pigment)
0.91 % Zn (in pigment)

0.22 % Pb (in drier)

45 % mineral spirits

5 % aromatic naphtha

Paint "E". Gold Alkyd Enamel

0.24 % CrVI (in pigment)
0.29 % Pb (in drier)

40 % mineral spirits

% aliphatic hydrocarbon

% toluene _
% aromatic naptha
% VM&P naphtha

ana

*AIT percentages shown are by weight of total paint.

the hazard of lead poisoning, lead chromate (and zinc chromate) has been impli-
cated as a lung carcinogen in workers who produce chromate pigments.

Alkyd resins have been used in paints for some time with no reports of any
chronic hazards.

4-3


APPENDIX


SECTION VIII. CONCLUSIONS AND RECOMMENDATIONS

In this section a summary of the conclusions and recommendations based upon
the case studies is presented. The level of control of selected hazards is
discussed; available control options are evaluated; and recommendations are
presented.

CONTROL OF HEALTH HAZARDS
Paint Mist

Paint mist refers to the non-volatile component of the coating aerosol. Its
concentration in the breathing zone of spray painters was determined gravimet-
rically as an index of overspray control. Geometric mean paint mist concentra-
tions for selected finishing operations are reported in Table 15. The concen-
trations reported for continuous painting operations are 8-hour time-weighted
averages. Results from intermittent painting operations are reported for the
duration of the specific painting operation.

The level of airborne paint mist is a more reliable indicator of the degree of
control in manual spray finishing than the concentration of solvent vapors.
Solvent concentrations were well below the recommended maximums even when paint
mist levels exceeded the maximum concentration permitted for nuisance dusts.
In no case was the reverse true. If the paint composition is known, the con-
centration of paint mist can also be used as a guide in estimating the poten-
tial exposure to specific non-volatile paint components. For example, if the
concentration of paint mist is 5 mg/m3, and lead represents 1 percent by
weight of the paint solids, then the airborne concentration of lead could be
estimated at 50 ug/m3,

Continuous operations include both manual and automatic application processes
where the painter remains in one location as the workpiece passes by on a
conveyor. The concentration of total paint mist for the Majority of continuous
spray finishing operations did not exceed 5 mg/m3 provided that spray booth
ventilation rates met minimum OSHA requirements (specified in 29 CFR 1910.94)
and good spray painting practices were observed. The continuous painting
operations (listed in Table 15) that exceeded this concentration involved
either the spraying of internal cavities (case study 6) or faulty ventilation
and work practices (case study 3). With the corrections suggested in these
case studies, paint mist levels could be controlled to below 5 mg/m3.

Intermittent operations are non-conveyorized processes where a relatively large
workpiece is positioned in a booth; after finishing operations are completed by
a mobile painter, the workpiece is removed and replaced by the next unit. The
concentrations of paint mist reported in Table 15 for intermittent painting op-
erations range from 2.0 to 43.3 mg/m3. Differences were due to the relative

47


solvent samples were collected on 150 mg charcoal tubes with personal pumps
operated at 50 cc/min.

Organic solvents selected for analysis were based on the composition stated by
the manufacturer and on qualitative analyses of selected charcoal tube samples
by gas chromatography/mass spectroscopy. Major components identified were
xylene and higher molecular weight aromatics, such as trimethyl benzenes,
diethyl benzenes, dimethyl] ethyl benzenes, tetramethyl benzenes, pentamethy]
benzenes, ethyl trimethyl benzenes, and naphthalene. Minor components identi-
fied were toluene, n-butyl acetate, n-propyl] benzene, methyl amyl ketone,
butyl-Cellosolve, and Cellosolve acetate. No benzene was detected.

RESULTS

Results of air sampling for total paint mist, lead, and chromium are reported
in Table 9-3. Mean concentrations of all contaminants are within the maximum
levels allowed by OSHA and recommended by the ACGIH for an 8-hour exposure to
total dust, lead, and chromium. A primary factor in the low levels of lead and
chromium that were measured is the limited popularity of red and yellow colors
in office-type furniture.

Organic solvent concentrations are reported in Table 9-4. Solvent levels are
well below all recommended maximums. The highest concentrations were recorded
at electrostatic Booth D. The elevated solvent levels measured at this booth
were probably a result of an extensive manual cleanup with a xylene spray of
the spray equipment in this booth.

9-8


Because the paint wets the respirator hood fabric, Consideration should be
given to switching to a respirator with a hood made of an impervious material.
A respirator that is certified by NIOSH should be used. In any event, contin-
ued use of respiratory protection is warranted, as long as any lead-containing
paints are used, or when two-component urethane or epoxy paints are applied.

Table 3-2. Airborne levels of organic solvents
in metal furniture finishing.

8-hour time-weighted average (mg/m3)

2-Ethoxy-
n-Buty] Diisobutyl ethyl Aliphatic
Painter Toluene Xylene acetate ketone acetate hydrocarbons Cr*

U 61 30 109 23 14 180 0.46

Vv 57 36 56 <1 1 170 0.34

W 59 48 82 6 10 120 0.44

X 12 7 22 3 4 33 0.10

Y 52 48 56 3 1 170 0.37

OSHA PEL 750 435 710 290 540 1800 1.0

ACGIH TLV 375 435 710 150 270 -- 1.0

(1979)

NIOSH 375 435 -- -- -- =D =
*Combined exposure: Ce = G) + age eee
Ly ly Ly

where C is the concentration of the individual contaminant, and
L is the exposure limit.

Table 3-3. Airborne levels of paint spray
mist in metal furniture finishing.

8-hour TWA (mg/m3)

Painter GM GSD
U 27.6 1.9
Vv <12.9 2.0
W <18.9 2.0
x 3.7 1.8
Y 23.5 1.4
Zz 7.0 Ld

GM: Geometric mean
GSD: Geometric standard deviation

3-8


Because of the size and shapes of these products, both primers and topcoats are
generally applied by hand spray equipment. Railroad cars are painted primarily
for protection against corrosion; aesthetic considerations are secondary. Ap-
plication techniques (primarily airless) are therefore geared to Providing a
high film build in a minimum time. Truck finishes are also applied by hand-
held spray guns and cured by baking or air drying. Alkyd-type finishes predo-
minate in this industry.

In the aircraft industry two component epoxy and urethanes predominate because
of their ability to produce a baked quality finish without baking. Airless
spray equipment is generally not accepted because of aesthetics. The most
commonly used resins, solvents and pigments are shown in Tables 9, 10, and 11.

Table 9. Trucks and buses (resins, solvents, and
pigments as percent of total consumption) .4

Per- Per- Per-
Resins cent Solvents cent Pigments cent
Alkyd 40 Aliphatic 26 Titanium 35
hydrocarbons dioxide
Acrylic 30 Acetone 14 Barytes 15
Amino 16 Xylene 13 Lead 9
Epoxy ester 6 Other 12 Chromium 8
aromatics
Other 8 Toluene 7 Talc 8
Butanol 7 Iron oxide 8
MEK 7 Other V7
Other 14

21


for both natural wood and unfinished exterior or interior grades of plywood.
Some materials may require solvent wiping and sanding. Coating material is
generally applied in several layers, which requires intervening steps like
sanding, rubbing, daubing, and polishing. These procedures are performed by
hand and, therefore, the workers are exposed not only to the liquid coating
material itself, but to the wood dust that may also contain the coating
material. Coating materials are predominately applied by hand. Sometimes
electrostatic spray techniques are used; they require the use of a conductive
primer (applied by dipping), or controlled moisture content.

Table 5. Automobile refinishing (resins, solvents, and
Pigments as percent of total consumption) .4

Per- Per- Per-
Resins cent Solvents cent Pigments cent
Alkyd 47 Xylene 32 Titanium 33
dioxide
Acrylic 31 Ethyl 12 Tale 14
acetate
Cellulosic a Toluene 10 Clay 12
Urethane 7 MEK 10 Barytes 12
Other 4 Buty] 9 Chromium 8
acetate
Other 27 Iron oxide 6
Lead 6
Other 9

7


Figure 4-1. Railroad car in booth ready for painting.

chromate primer. Darker colors are generally applied directly to the metal
substrate.

The compositions of the coatings used during this survey are presented in
Table 4-1. Although these coatings are supplied by different manufacturers,
composition varies only slightly. All are approximately 50 percent solvent by
weight. Metallic soaps employed as driers allow a tack-free surface in 3 to 5
hours. As with all alkyd resin paints, the film cures by the oxidation and
subsequent polymerization of the resin. The principal solvent used is mineral
spirits, along with lesser quantities of toluene and xylene. Up to 5 gallons
of additional mineral spirits may be added to each 50-gallon drum of paint to
reduce it to application viscosity.

HAZARD ANALYSIS

Lead compounds are the main hazard associated with the coatings in use at this
facility. These compounds include both inorganic lead (lead chromate, lead
monoxide) used as pigments and lead soaps employed as driers. In addition to

4-2


100 cc/min. Tubes were subsequently desorbed and analyzed by gas chromato-
graphy.

Initial observations indicated that Painter B was exposed to considerably more
overspray, primarily from painting the interior of the wagon. To determine the
impact of this operation on his overall exposure, a second sample for total
mist was collected for the duration of the interior painting, which was approx-
imately 17 minutes. A preweighed polyvinyl chloride filter was used for this
determination.

To determine the ability of the booth air seals to contain the spray mist and
solvent vapors within the booth, area air samples were taken at the booth
exits. Sampling and analyses were identical to the personal samples noted
above, except for duration and a charcoal tube sampling rate of 50 cc/min.

RESULTS

Airborne levels of paint mist, lead, and chromium in the breathing zone of the
spray painters (outside of the respirator) and in the area of the booth exits
are reported in Table 8-2. The breathing zone samples were collected for the

Table 8-2. Airborne levels of total paint mist, lead,
and chromium in heavy equipment finishing.

Concentration (mg/m3)#

Number of Total mist Lead Chromium
samples GM GSD GM GSD GM GSD
Painter A 5 2.0 1.4 0.23 1.3 0.031 1.5
Painter B 6 N69 (1.3 1.300 1.2 0.230 1.2
Painter B 4 36.5 1.2 -- -- -- --
(interior only)
Booth Exits 4 0.3 «21.9 0.006 =1.8 0.003 1.0
(area sample)
OSHA PEL* 15 0.05 1.0**
ACGIH TLV (1979)* 10 0.15 0.050
NIOSH Recommendat ion* -- 0.10 0..001

GM: Geometric mean

GSD: Geometric standard deviation

# Results are reported for short term samples. 8-hour time-weighted averages
would be approximately 50 percent lower; see text.

* For full shift exposure

**Chromium metal and insoluble salts

8-9




contains less total solvent and a comparatively greater percentage of butyl
acetate.

The high-solids material is formulated for application performance similar to
conventional coatings. These performance parameters include no increase in
air-atomization pressure, cure in 8 to 10 minutes at a peak oven temperature
of 340°F, and dry to touch in 30 minutes at ambient conditions.

All colors of waste paint collected in the spray booths are combined with addi-
tional solvent to produce a gray-colored paint. This recycled paint is used
to coat the interior of file cabinets and other unseen areas where protection,
but not appearance, is required.

All colors of paint (except for the gray interior paint described above) are
supplied directly to the spray guns from a central paint mix and storage room
through circulating paint lines. The gray interior paint is supplied to a
single airless spray gun by a 30:1 paint pump, and 55 gallon drum located
directly outside of the spray booth where the coating system is applied.

HAZARD ANALYSIS

The principle hazard associated with the coatings used is a result of the vola-
tile organic materials that they contain. These substances, chiefly xylene,
butyl alcohol, and butyl acetate, are employed in the coating formulation as
solvents. They can produce irritation of the skin, the conjunctiva, and the
mucous membranes of the upper respiratory tract. Repeated or prolonged dermal
contact with these finishes should be avoided because they can cause drying and
defatting of the skin, which may lead to dermatitis. Acute exposure to xylene
vapor may cause central nervous system depression and minor reversible effects
upon the liver and kidneys. At high concentrations, xylene vapor can cause
dizziness, staggering, drowsiness, and loss of consciousness. At very high
concentrations, this substance can cause pulmonary edema, loss of appetite,
nausea, vomiting, and abdominal pain.

The majority of the colors are natural or earthtone shades. However, a limited
amount of reds and yellows are used and these colors contain lead chromate pig-
ments. The other pigments that are used are essentially inert from a physio-
logical standpoint. To date, no evidence of harm has been demonstrated by the
thermosetting acrylic resin or baking enamel systems that are used. However,
as a minimum, these materials should be controlled to below the maximum levels
recommended for nuisance materials.

SPRAY BOOTHS
Manual Spray Booth Design

All manual spray operations are performed in one of two identical downdraft
booths similar to the one shown in Figure 9-2. The exterior of each booth
measures 21 feet wide by 17 feet long with an interior height of 10 feet.
Filtered fresh air is supplied through the open top of the booths, and removed
at the bottom through a water curtain by two exhaust fans mounted on the roof
of the booth. Spray headers located in each exhaust air plenum clean paint

9-4


reacted isocyanate groups may impair respiratory function or give rise to
sensitization. They cite many cases of respiratory distress among automobile
refinishers in the United Kingdom since two-component urethane coatings
containing aliphatic isocyanates were introduced in 1976.

In his review of the hygienic aspects of urethane coatings, Ziegler25 reports
on aerosol inhalation studies in rats of monomeric toluene diisocyanate (TDI),
hexamethylene diisocyanate (HDI), and polyisocyanates based on these materials.
While TOI and .HDI possessed comparable acute toxicities, the polyisocyanates
did not. The toxicity of the monomeric materials was an order of magnitude
greater than the TDI-based polyisocyanate, but only slightly greater than that
based on HDI. He also reports that Ames tests conducted on these polyisocya-
nates indicate that they are not mutagenic.

Vinyl Resins--

The principle hazard associated with vinyl resins used in surface coatings is
the potential for residual vinyl chloride monomer. Like cellulosic coatings,
vinyl resins are combined with substantial quantities of plasticizer to improve
their properties as film-formers.

Solvents

Alcohols--

Ethanol, n-butanol, and isopropanol are the alcohols most used in paint. Their
principal physiological effect is irritation of the mucous membranes of the
eyes and upper respiratory tract. Methanol receives limited use as a paint
solvent. It is a poison to the central nervous system and to the optic
nerve.

Esters--

Ethyl, butyl, and propyl acetate are aliphatic esters used in large quantities
as lacquer solvents. The aliphatic esters are irritants to the mucous memb-
ranes of the eyes and upper respiratory tract; at high concentrations they can
cause headache, drowsiness, and unconsciousness. Prolonged exposure to the
skin can cause irritation, which is a result of the defatting action of these
solvents. No chronic hazards have been associated with these solvents.26

Glycols and Glycol Derivatives

Ethylene and propylene glycol are the principle glycols used in paint. Inha-
lation of ethylene -glycol may result in central, nervous system depression and
hematopoietic dysfunction. Propylene glycol posseses very low toxicity and is
unlikely to pose any hazard.26

Ethylene glycol ethers are mildly irritating to the skin. The vapor may cause
conjunctivitis and upper respiratory tract irritation. Temporary corneal
clouding may also result and may last several hours. The acetate derivatives
cause greater eye irritation than the parent compounds. The butyl] and methy1]
ethers may penetrate skin readily.

Ketones--
Acetone, methyl ethyl ketone, and methy] isobutyl] ketone are the ketones most

, 29


Table 9-4. Airborne levels of organic solvents in metal
furniture finishing (Process A).

8-hour time-weighted average concentration (mg/m3)

Buty] Naphtha- Aromatic

Number of Xylene acetate lene n-Butanol distillates
Operation samples GM GSD GM GSD GM GSD GM GSD Gt GSD Cex

Manual prime booth 3

Painter #1 22. 1.3 3° «1.3 0.7 1.1 2 «21.5 30. «1.0 «14
Painter #2 55 1.4 6 1.4 1.01.1 4 1.3 60 1.4 3
Manual finish booth 3
Painter #3 10 4.1 2 2.5 0.71.3 2 2.3 10 (1.2 07
Painter #4 2461.1 4 #+21.0 0.7 1.1 2 2.0 8 iol) 09
Electrostatic booth C
Face 3 10 3.4 0.91.1 0.71.5 0.7 1.5 7 6.8 06
Entrance 3 65 1.2 7 1.4 1. 1.8 4 1.3 80 1.2 +38
Electrostatic booth D
Face 3 121. 2.4 4 1.7 1.51.7 2 1.0 84 «1.3 5]
Entrance 3 26 41.6 3 1.3 1.01.5 2 1.6 20. 32
OSHA PEL 435 710 50 300 435** 1.0
ACGIH TLV (1979) 435 710 50 150 -- 1.0
NIOSH 435, -- -- -- -- --
*Combined Exposure: Ce 5 GL + Cy @ 000 cy

Ly Ly ty

where: C is the concentration of the individual contaminant, and
L is the environmental limit.

**By analogy with xylene


Table 4-5. Airborne levels of organic solvents
in railroad car finishing.

Concentration (mg/m3)
Sample . Aliphatic

Car time Other hydro-
type Painter Paint (min) Toluene Xylene aromatics carbons *Cp
Pulp x A 50 120 12 160 720 0.96

Y A 50 150 <4 190 920 1.16
Pulp A 57 160 30 300 890 1.4

Y A 60 130 4 150 770 0.96
Pulp X A 24 230 25 330 1400 1.90

Zz A 24 120 <9 180 730 1.00
Coal Z 8,C 40 350 90 320 790 1.84

Y B,C 49 310 80 350 780 1.84
Gravel Y D,E 23 270 <8 250 1200 1.62

Z D,E 22 330 <10 300 1500 1.99
Gravel Zz E 15 110 <14 <140 430 0.74

Y E 16 130 <13 <130 500 0.78
Gravel X E 31 210 <5 170 890 1.18

Zz E WV 230 13 250 880 1.40
Geometric mean 188 14 217 840 tos}
Geometric standard deviation 1.5 2.6 1.4 1.4 1.4
OSHA PEL** 750 435 435%e* 1800**** 1.0
ACGIH TLV (1979)** 375 435 -- -- --
NIOSH** 375 -- -- 350 --
*Combined exposure: Cp = cm 402° tase Cy

ty le Ly

where C is the concentration of the individual contaminant, and
L is the exposure limit

** For full shift exposure

*ek Xylene

wee eHEXane


Only those painters with the highest total mist levels had measureable concen-
trations of lead in their breathing zones. These results, shown in Table 6-3,
along with the corresponding mist levels, were well below the 50 ug/m3 stan-
dard for lead.

Solvent levels in the automatic prime booth were twice the levels in the auto-
matic finish booth. Approximately 40 percent more paint is applied in the
prime booth than the finish booth and this, along with 10 percent less exhaust
in the prime booth, accounts for the difference in solvent concentration.
Because the equipment operators spend one half of their workshift in a control
room, their. average exposure would be somewhat less than that indicated by
these area samples.

Mist levels in both automatic spray rooms were extremely low, because of the
high transfer efficiency of the electrostatic bell spray equipment.

Table 6-4. Airborne levels of spray mist
during liner painting.

Sample
Duration Total Mist
Ident ification (min. ) (mg/m3)
5164 6.4 350
5158 6.0 320
5157 6.1 330
5152 4.4 300
5168 6.0 310
Geometric mean -- 322
Geo std deviation -- 1.1

DISCUSSION

During the finishing of freezer liners, the painters are surrounded by a cloud
of paint mist. Solvent and paint mist concentrations in this cloud are high
enough to require the use of respiratory protection. Supplied-air respirators
are provided and used during this operation. Conventional air-atomizing guns
produce a mixture of air and paint particles that rebounds from the surface
being painted. As is the case with the freezer liner operation, this charac-
teristic is particularly troublesome when internal surfaces or cavities are
being painted. Airless spraying could accomplish this task without the over-
spray currently encountered and with little or no reduction in finish quality.
In addition to the reduced overspray, more rapid paint build with less paint
waste could be achieved with the airless method.

6-9


OFFICE PARTITIONS (Process B)
PROCESS
Operations

Office partition panels and associated sheet metal parts are finish-coated on
a high speed (26 fpm) conveyor line. The processes and operations in this
plant have been in use for four years. Small sheet metal parts represent
approximately 70 percent of the conveyor footage. Large, flat sheet metal
panels that are either 3 by 6 feet or 4 by 6 feet represent the remaining 30
percent.

All components that are to be finish-coated are hung on the overhead conveyor
and are transported through a totally enclosed 4-stage metal pretreatment pro-
cess: a detergent phosphatizing bath, water rinse, chromic acid rinse, and a
final water rinse. They are then routed through a roof-mounted flash-off oven,
operating at 400°F.

A 1.0 mil, high-solids, polyester baking enamel or acrylic finish is applied
to the component parts. This is accomplished by a 2-coat (wet-on-wet), 4-step
application process (Figure 9-4). The first coat is applied by air-atomized
electrostatic spray guns mounted on reciprocators, followed by a manual
touch-up operation also using air-atomized electrostatic guns. Application of
the second coat is by a process similar to that of the first coat.

FIRST COAT AUTOMATIC FIRST MANUAL
ELECTROSTATIC BOOTHS DOWNDRAFT BOOTH
[8] ba |
BOOTH G
BOOTH Ht BOOTH |
SECOND MANUAL FIRST COAT
SECOND COAT AUTOMATIC ea
DOWN GRAFT BOOTH Y ELECTROSTATIC BOOTHS rl

O@ fe)

( fice om)
O vel |
TST on Roaial?
BOOTH J STATIC.

TO ROOF ‘SPRAY EQUIPTMENT BOOTH L
MOUNTED

BAKE OFF BOOTH K

OVEN Ne wy

® MANUAL WORK STATION

Figure 9-4. Process B layout.

9-12


There is some reluctance to accept high technology application equipment,
especially where appearance is a critical factor. This is due either to the
greater versatility of conventional air-atomized spray equipment or to some
inherent limitations combined with higher costs for the more sophisticated
techniques. However, in many operations, ventilation is impractical, and effi-
cient application techniques are the only logical choice.

Respiratory Protection

Respiratory protection is required in those spray finishing operations that em-
ploy significant quantities of highly toxic materials, such as lead, chromium,
or reactive compounds (isocyanates and epoxy curing agents). It is also
necessary for protection against paint mist and organic solvents in painting
enclosed spaces or other areas where ventilation is compromised.

A conventional half facepiece respirator, with mist-removing prefilters and
organic vapor-removing cartridges, should provide adequate respiratory pro-
tection in cases where the hazards can be identified and quantified. In many
instances, the variety of paints employed on a given workshift make quantifi-
cation of the hazard impractical. In other cases, painting may be done in an
enclosed area. These situations warrant the use of a supplied-air respirator.

Many paint constituents can be injurious to the eyes and the skin as well as
to the respiratory system. Full facepiece or hood-type respirators are recom-
mended where these constituents are present. In addition, the full facepiece
is more comfortable than a half-mask because the pressure of the attaching
straps is distributed over a larger facial area and no goggles are required to
protect the eyes. Case study 4 describes a railroad car painting operation
that successfully employs a respirator program using full facepiece, supplied-
air respirators.

RECOMMENDAT IONS
Paints and Coatings

Paint formulations should be selected for use that contain relatively non-toxic
materials and a minimum amount of solvent. Lead and other toxic metal pigments
should be eliminated where possible.

Paint users should establish a file of material safety data sheets for all
coatings. Material safety data sheets should be reviewed by the purchaser and
rejected if incomplete or found to be inaccurate. The paint and coatings in-
dustry should establish strict material safety data sheet guidelines and
labeling requirements.

Spray Booths
Spray booths should be selected to provide the maximum enclosure of the
painting operation in order to contain the spray mist with a minimum volume of

air and to avoid disruptions from stray room air currents. The choice of a
downdraft or sidedraft booth depends largely on the configuration of the object

53


by mass spectroscopy. Major peaks identified were aliphatic hydrocarbons,
toluene, xylene, and higher molecular weight aromatic hydrocarbons. No ben-
zene was detected.

Table 4-3. Qualitative analysis of bulk
air samples for metals.

Element Paint A Paint B Paint C Paint D Paint £
Al Mix T T T T
Ca Mi Mi T Mi Mi
Co T ND ND ND ND
Cr T Mi ND Mi T
Cu T ND ND ND ND
Fe T M i} M Mi
Mg Mi Mi T Mi T
Mn T T ND T ND
Na Mi Mi Mi Mi Mi
P ND T ND T ND
Pb T T T T T
Sn ND ND ND ND ND
Ti T ND ND ND T
W ND T ND T ND
Zn T Mi T Mi T

*Key: Mi - minor
T - trace
ND - not detected
M - major

RESULTS

Airborne concentrations of total paint mist, lead, and chromium are reported
in Table 4-4, The levels for both paint mist and lead exceeded those that
would be allowed for a full shift's exposure. Because actual spraying time
does not exceed 2 hours per shift, 8-hour time-weighted average levels of total
mist and lead would be below legal limits. It should be noted that while the
concentration of chromium does not exceed the legal maximum, it is signifi-
cantly higher than the levels proposed by NIOSH and the American Conference of
Governmental Industrial Hygienists (ACGIH).

4-9


Table 1-3. X-ray fluoresence analysis of powder paint.

Element Brown powder Cream powder

Fluorine
Aluminum
Silicon
Sulfur
Chlorine
Calcium
Titanium
Chromium
Tron
Copper
Zinc
Lead
Strontium
Barium

>< >< > 1 KDE > Oe De OOK
$< S<

d<
DS >< >< >< DE DK HY OC OK OK OE OK VD

X

element present

element present in large amounts

element was not detected .

instrument not sensitive enough to detect the element or
interference present

DISCUSSION

Total dust levels could be further reduced by several modifications. These in-
clude the use of absolute filters for final filtration and the use of vesti-
bules at the entrance/exit of the conveyor to the booth. The vestibules should
be added because present design permits the spraying of powder directly out of
the conveyor entrance if an operator works ahead of the conveyor.

The aspiration of the powder paint from the 100 pound drums caused a visible
release of dust. Because the drum is lined with a plastic bag, this dust
source could be easily eliminated by loosely wrapping the bag around the
aspirator tube.

1-9


Table 11. Other transportation (resins, solvents, and
pigments as percent of total consumption) .4

Per- Per- Per-

Resins cent Solvents cent Pigments cent

Urethane 33 Aliphatic 23 Titanium 47
hydrocarbons dioxide

Epoxy 19 Other aro- 18 Talc 16
matics .

Alkyd 14 Acetone 9 Silica i
Glycol ether 6 Barytes 6
and ether
esters

Acrylic 10 Toluene 6 Iron oxide 6

Other 24 Xylene 6 Chromium 4
n-Butanol 6 Lead 4
Isopropanol 5 Other 6
Ethanol 5
MEK 5
MIBK 5
Other 6

MACHINERY AND EQUIPMENT

This section is included in the SIC major group 35 (Machinery except Electri-
cal). The categories covered here are: SIC 3523 (Farm Machinery and Equip-
ment) and 3531 (Construction Machinery and Equipment). The establishments
considered here are engaged in manufacturing all kinds of farm machinery and
equipment for use in the preparation and maintenance of the soil, planting and
harvesting, and for use in performing other farm operations and processes.
The category also includes the heavy equipment that is generally used in con-
struction industries, such as bulldozers, sgrapers, concrete mixers, cranes,
dredging machines, pavers, and power shovels.

23


CASE STUDY 3

METAL FURNITURE:
SOLVENT AND WATERBORNE COATINGS

This modern sheet metal job shop manufactures custom cabinetry for office
equipment, automatic data systems, and electronic products. In this shop, base
and finish coatings are applied in over 700 different colors and various tex-
tures. Both solvent and waterborne coating systems are used. The application
equipment includes conventional spray guns, air-atomized electrostatic hand-
guns, and electrostatic guns mounted on reciprocators. All of the coating
operations are performed in sidedraft, dry filter spray booths that are en-
closed on all sides. Make-up air is introduced into the booths through a
distribution plenum in the back wall and into conveyor entry and exit vesti-
bules. The high levels of paint mist that were measured at this facility are
attributable to infrequent replacement of paint filters, improper distribution
of supply air, and relatively high atomizing-air pressures.

PROCESS
Operations

Prior to finishing, semi-assembled sheet metal fabrications are hung on an
overhead conveyor in the "load area" (Figure 3-1). They then receive an auto-
matic seven-stage metal pretreatment. This process consists of a detergent
wash followed by two water rinses, an iron phosphate bath, a third water rinse,
a chromic acid rinse, and a final rinse with deionized water. The workpieces
are then routed to an elevated multi-zone oven for drying.

Following this, they are transported through a sidedraft spray booth designated
"Special booth" in Figure 3-1. In this booth, speciality paints, such as con-
trasting colors for the insides of cabinets, are applied. Because not every
production run requires the application of contrasting colors, this subprocess
is not always in operation during a regular shift. After a 10-minute air
flash-off period, the workpieces enter two in-line sidedraft spray booths
(designated "Prime Booths A" and "B" in Figure 3-1). Both sides of each work-
piece receive a base or prime coat. This can be applied either manually with
hand-held spray equipment or by equipment mounted on a reciprocator. The se-
lection of an application method is influenced primarily by the physical confi-
guration of the production-run workpieces.

Electrostatic equipment is used only for conventional solvent-type paints.
Following a second 10-minute air flash-off period the workpieces enter an
identical set of in-line spray booths. These booths are designated "Finish
Booths A" and "B" in Figure 3-1. In these booths, a finish coat is manually
applied over the wet prime coat using hand-held equipment Textured and
wrinkled finishes, when they are required by customer order, are applied in
these booths. As an alternative, the workpieces from the prime booths can be
routed to the elevated baking ovens before they receive the finish coat. The
majority of workpieces receive both prime and finish coats before baking.

3-1


SECTION II. INDUSTRIAL COATING TECHNOLOGY
INTRODUCTION

Coatings can be defined as liquid or liquefiable materials that can be con-
verted to solid protective, decorative, or functional adherent films after
application as a thin layer. The term "coating" includes paints,
varnishes, and powders.

CLASSIFICATION

Liquid coatings can be classified into two broad groups, those that use organic
solvents as the primary liquid and those that employ water. The main differ-
ence is that most solvent-type coatings exist as true solutions, where the
polymer is dissolved in the liquid solvent, whereas most waterborne coatings
are emulsions of pigments and binders in water.

Coatings can also be classified according to their end use as “trade sales”
paints and “industrial finishes." "Trade sales" products are stock-type com-
modities, generally distributed through wholesale and retail channels.
"Industrial finishes" are products that are specifically formulated to meet
conditions of application and use of the products to which they are applied.
They are produced for manufacturers, rather than for contractor or general
public use.

For the purposes of industrial health, it is most useful to categorize coatings
according to the mechanism of film formation. These mechanisms give some indi-
cation of the hazard involved. These mechanisms can be categorized as either
thermoplastic or convertible. A thermoplastic material is one that becomes
soft or fluid when heated, and regains its original properties upon cooling. A
convertible material is one that undergoes an irreversible chemical change
during film formation. :

Thermoplastic Film Formation

Thermoplastic materials can form coating films by solvent evaporation, by heat
fluxing, or by coalescence.

Coatings that form films solely by the evaporation of a solvent are termed
"lacquers". The film that is formed by this process is susceptible to deterio-
ration by the solvent used in manufacture. Lacquers are noted for quick drying
properties. These coatings may be baked to accelerate drying, to improve adhe-
sion, or to increase gloss.

Thermoplastic films can also be formed by heat fluxing. In this method, a
coating material is changed from a solid to a liquid then back again; this
phase change is brought about by a change in temperature.

4




SPRAY BOOTHS
Design

Eight spray booths were included in the original design of the finishing de-
partment. These booths consist of a water pan extending from the conveyor edge
into a dry plenum chamber. Air is exhausted into a 9-inch slot at mid-level
and a 4-inch opening above the water pan. A change of air direction in the
plenum is intended to drop particulate matter into the water pan for collec-
tion. Air is moved with an axial flow fan and discharged through a "coolie"
style weather cap a few feet above roof level. The fan is rated at 15,900 cfm.
To improve airflow, five booths were modified by removing the steel spray
curtain, slots, and internal baffles, and installing a 5 x 5 array of dispos-
able 20-inch square filters and turning vanes in the plenum. Each of these
five booths has a smaller booth paired with it, situated on the opposite side
of the conveyor to allow better paint application to the sides and back of the
stereo cabinet. These booths are also of a dry filter design, with a 3 x 5
array of disposable filter pads. Fans for the smaller booths are rated for
10,930 cfm. Filters on all booths were changed at the end of the 8-hour shift.
A typical booth is shown in Figure 2-2.

With the exception of two dry filter booths used for glaze application, all the
booths are open on three sides. The two booths used for glaze application have
sheet metal side curtains with openings for the conveyor and cabinet passage.
It was necessary to close the sides on these booths because of the proximity of
the finish wipers to these operations.

Airflow Measurements

Total airflow was measured on each of the booths that were in use. The airflow
in the dry filter booths was recorded with both clean and dirty filters. Con-
trol velocity was measured with a hot wire anemometer at 12 points in the ver-
tical plane occupied by the paint sprayer and the measurements were averaged.
Results of these measurements are presented in Table 2-2.

Total airflow for the slot-type booths was 10 to 20 percent below the design
value of 15,900 cfm. Airflow for the slot booths that had been reworked with
filters was 1.5 to 2 times the design value. A maximum decrease in airflow of
about 25 percent was observed for the large (5 x 5) dry filter booths with
heavy loadings. The smaller (3 x 5) booths experienced larger decreases in
flow. While airflow with clean filters was 150 percent of design, it dropped
over one half when the filters loaded.

Average air velocities ranged from 130 to 230 fpm in the larger dry filter
booths, from 60 to 110 fpm in the smaller filter booths, and from 40 to 150
fpm in the slot booths. The glaze booths, which were partially enclosed,
exhibited a higher velocity than the more open booths with the same total
airflow. In most cases, increased airflow meant increased air velocity at the
operator's platform, but other factors (including location of doors, walls,
process equipment, and airflow patterns established by the make-up air units)
affected the control velocity.

2-6




Figure 4-6. Full-facepiece respirator window protected by food wrap.

by atomic absorption spectroscopy for lead and chromium. Organic solvent sam-
ples were collected on 150 mg charcoal tubes with personal pumps operated at
100 cc/min. Tubes were subsequently desorbed and analyzed by gas chromato-
graphy.

Metals for analysis were selected based on the stated composition of the fini-
shing materials and a qualitative analysis of air samples for each type of
paint. Trace metals indicated by these analyses are reported in Table 4-3.
The material safety data sheet from one supplier did not indicate the presence
of any toxic metals. After the qualitative analysis indicated the presence of
lead, the supplier was queried. He admitted that litharge was added to the
paint in the amount of 2 pounds per 100 gallons of paint, and that a lead soap
drier was used.

Solvents for analysis were selected based on the stated composition of the
finishing materials and on a qualitative analysis of area charcoal tube samples

4-8


duce a decorative effect. Black or gold lacquers are used on some product
lines to highlight engravings or other details.

HAZARD ANALYSIS

The principal hazard associated with the coatings in use in these operations is
because of the volatile organic materials employed as solvents. These materi-
als fall into the different categories of alcohols, aromatics, esters, ketones,
and naphthas, but all exhibit similar physiological effects. These manifesta-
tions include irritation of the skin, the conjunctiva, and the mucous membranes
of the upper respiratory tract. At high concentrations, these materials can
produce the symptoms of headache, nausea, and drowsiness, followed by loss of
consciousness and death. Dermal contact with these finishes should be avoided,
because toluene and the ketones are known to be absorbed through the skin.
Benzene is a potential hazard as a contaminant in formulations containing tolu-
ene, xylene, or refined petroleum solvents.

No federal standard exists for isobutyl] isobutyrate, a minor constituent of
both the clear lacquer and the reducer for the barrier coating. Acute inhala-
tion studies on animals indicate that this material is slightly more toxic than
isobutyl alcohol; these results suggest a working limit of 25 to 50 ppm for an
8-hour exposure.

The non-volatile coating components include resins, plasticizers, and pigments.
The oleoresins, nitrocellulose, and the thermoplastic acrylics are all nonre-
active components which are relatively inert physiologically. Diocty] phthal-
ate, used to plasticize the acrylic resin, possesses low toxicity. The pigment
materials (natural and synthetic iron oxide, lampblack, and amorphous silica)
are either of low toxicity or they represent such a minor constitutent of the
coating solids that they do not present a hazard under normal conditions of
use. Crystalline silica, a highly toxic mineral, is a possible contaminant in
the amorphous silica material.


crete floor is washed down periodically with methyl chloroform in order to
remove any paint residue. Spill cleanup is facilitated by a sewer grate run-
ning the length of the paint mix tank area. Methyl chloroform was selected
because of its low flammability and high solvency. Considerable attention is
paid to keep access ports on mix containers closed, and to replace all lids
and bungs on empty drums. Housekeeping is assisted by roller conveyors for
both paint and empty drum storage.

EVALUATION

Because a majority of the operations involve sporadic rather than continuous
exposure, a combustible gas meter was used in order to determine approximate
solvent levels during short duration operations, such as pail filling and sol-
vent addition, and in order to evaluate the significance of various solvent
sources.

Eight-hour time-weighted average (TWA) breathing zone and background concen-
trations were determined using 150 mg charcoal tubes and portable personal
sampling pumps operated at 50 cc/min. Following desorption with carbon disul-
fide, the resultant solution was analyzed by gas chromatography for n-butanol,
buty] acetate, xylene, and petroleum distillates.

RESULTS

The exposure of mix room attendants can be characterized as a continuous low
exposure to solvents evaporating from multiple small sources, punctuated by
brief, higher exposures from various manual operations. Combustible gas indi-
cator measurements of solvent levels are reported in Table 10-1. Results of
full shift sampling are reported in Table 10-2.

Combustible gas indicator measurements of methyl chloroform concentrations are

reported in Table 10-3. The values reported were obtained by multiplying meter
readings by a factory-specified correction factor.

10-5


The organic solvents employed in these formulations all exhibit similar physio-
logical effects. In general, they are irritants to the conjunctiva and the
mucous membranes of the upper respiratory tract. They all produce irritation
of the central nervous system and, at high concentrations, produce symptoms of
headache, nausea, and drowsiness, followed by unconsciousness and death. Poly-
neuropathy, associated with the lower molecular weight alkanes, may occur from
chronic inhalation of mineral spirits.

SPRAY BOOTH
Design

The railroad cars are painted in the semi-downdraft spray booth shown in
Figures 4-2 and 4-3. The booth measures 20 feet wide, 22 feet high, and 96
feet long, and will accommodate the largest freight cars made in this shop.
The booth entrance and exit are equipped with automatic roll up doors. Three
emergency doors are located along each side. Two 36,000 cfm, make-up air units
supply fresh air to the 4 corners of the booth through banks of filters running
from ceiling to floor. Two exhaust grates, each 2.5 feet wide, straddle the
track for about 60 percent of the booth's length. Four water-wash sections,
each equipped with a 15,000 cfm fan, scrub overspray from the air before it is
discharged to the atmosphere.

MAKE UP AIR MAKE UP AIR

a | Cx 4 cc ‘ACCESS PLATFORM 2 T =)
BEKEKEKEK KAKA aE

exit feernance
GooR = UNDER CARRIAGE = PAINTING PIT ‘b00R

ExnausT Os
Manare DODO MRK KR
[ ewe! ACCESS PLATFORW. Lr
wate UF am SS PAINE ORORS POP NT nan uP an

Figure 4-2. Plan view of railway car, semi-downdraft booth.

Each side of the booth has an elevated, open-mesh platform 8 feet above the
floor level. Ladders located at both ends of the booth provide access to
these platforms. Manually operated, counterbalanced cross platforms are kept
at ceiling level until the car is in place. These platforms are lowered in
order to provide access to the upper half of the cars at both ends. A pit that
is 4 feet deep is provided between the rails in order to facilitate painting
the under carriage.

Airflow Measurements

Air velocity was measured at the supply air inlets and exhaust grates using a
hot wire anemometer. Velocities were averaged, and the total volume of air
that was supplied and exhausted was determined. Results of these measurements
are presented in Table 4-2.

4-4


Table 2-7. Airborne solvent levels in veil lacquer operations.

8-hour time-weighted average (mg/m3)

Booth Date (a) (by) (ce) (dy) fe) (FY) (a) Sth) ~SCCT)—séCzy,

12 9/10 <1 25 13 12 3 <26 <23 3 <14 0.24
12 9/11 <1 23 9 12 3 <16 <14 4 10 0.18
13 g/l2 <1 3 <5 5 1 12 <1) <i <7 0.10
13 9/13 <l 4 <4 6 1 10 <9 <l <5 0.09
OSHA PEL 140 700 300 750 435 240 1900 590 2950 1.0
ACGIH TLV (1979) 25 700 150 375 435 120 1900 590 -- 1.0
NIOSH 23 -- -- 375 435 -- -- 590 3500 --

(a) Isophorone; (b) Isobutyl acetate; (c) n-Butanol; (d) Toluene; (e) Xylene;
(f) Ethylene glycol monobutyl ether; (g) Ethanol; (h) MEK; (i) Petroleum
distillates.

*Combined exposure: C. =

where C is the concentration of the individual contaminant, and
L is the exposure limit.


EVALUATION

Two employees are potentially exposed to organic solvents or paint mists in
this process: one spray painter in each of the manual spray booths. Potential
sources for exposure include paint mist and solvent vapors from spraying and
solvent vapors evaporating from finished panels.

Eight-hour time-weighted average (TWA) concentrations of total spray mist and
selected organic solvents were determined for the paint sprayers. This was
accomplished to provide an index of control. The spray painters spend their
entire workshift in the finishing area, excluding scheduled breaks and lunches,
Area samples were collected at the entrance vestibule of automatic electro-
static Booth H and at the exit vestibule of automatic electrostatic Booth K.
Area samples were also collected at the face of these booths (reciprocator in-
let venturi baffle). These area samples were collected to document the perfor-
mance of the booths.

The 8-hour TWA concentrations were calculated from separate morning and after-
noon samples that were collected over a two-day period. Sampling procedures
were identical to those used in Process A except that no qualitative analyses
were performed.

RESULTS

As reported in Table 9-7, the 8-hour TWA concentrations of total particulates
for the manual spray painters was less than both legal and current recommended
maximums. These low levels were to be expected because each manual booth has
only one painter per shift. The responsibilities of these painters is pri-
marily a touch-up function to cover light areas, and the Majority of surfaces
to be coated are large flat pieces. Therefore, there is no overspray from
opposed spraying and little bounce-back of paint mist from irregular surfaces.
These facts, combined with the excellence of booth design, work practices, and
maintenance, are primary reasons for the low mist levels.

One of the automatic electrostatic booths did exhibit a high level of particu-
late at the exit vestibule (Table 9-7). This is probably attributed to a mis-
aligned spray head on one of the reciprocators in that booth. Visual observa-
tions of the process did not indicate this as a problem area. The physical
size of the workroom and distance of manual work stations also do not indicate
that this situation is a potential exposure area.

Airborne levels of organic solvents in the breathing zone of the spray painters
and in the face and entrance or exit vestibules of the automatic electrostatic
booths are reported in Table 9-8. These samples were taken in parallel to the
particulate samples. Maximum combined solvent levels were well below current
allowable airborne concentrations.


The air exhaust fans for each spray booth are located on the roof of the
facility. This differs from Process A where the fans were mounted inside the
plant building. The roof-mounted fans provided a noticeable reduction in the
noise level inside the booths, with the system exhaust equipment operating.

Medium high-solids polyester paints require exceptional housekeeping techniques
because they do not readily air dry. At this facility high traffic areas are
covered with tar paper in order to prevent the spreading of semi-dried material
throughout the rest of the plant. In order to be most effective, the paper must
be changed at frequent invervals. All of the tar paper was neatly trimmed and
secured in place with tape, to prevent safety hazards associated with tripping
and falling.


Respiratory Protection

Further evaluation of the effectiveness of half facepiece respirators is
needed. NIOSH certification tests for spray paint respirators need significant
review to reflect current coating technology.

Material Safety Data Sheets

The quality of material safety data sheets was found to vary considerably among
suppliers. In one case even lead was omitted from the safety data sheet al-
though the lead content was significant. The number of coating types and
suppliers employed by some users make the establishment of a file of material
safety data sheets a formidable task. Improved labeling requirements could
ease this burden for the purchaser of industrial coatings.

55


The aerosols of these paints contain a substantial quantity of isocyanate pre-
polymer with unreacted isocyanate groups. The potential of these prepolymers
to cause respiratory impairment and/or sensitization is unknown; however, the
prepolymer of HDI possesses approximately the same acute inhalation toxicity
as the monomer. If the polymeric material poses the same sensitization poten-
tial as the monomer, a paint mist level of about 1 mg/m would be required
to maintain the prepolymer concentration below 140 ug/m3. This mist concen-
tration approaches the lowest mist levels measured in this study, and is quite
a bit lower than mist concentrations measured in auto refinishing and aircraft
painting. Respiratory protection is therefore recommended wherever reactive
urethane coatings are applied. The use of these materials should be restricted
in enclosed spaces or other areas where ventilation may be compromised.

Epoxies

Most reports of health problems associated with epoxy paints have been related
to the amine curing agents used rather than the epoxy resins themselves. Many
of these curing agents are of low volatility and therefore the hazard is asso-
ciated with the inhalation of the paint aerosol. Present analytical techniques
do not permit the evaluation of the presence of these amines in a curing agent/
paint aerosol. As is the case with urethane coatings, development of suitable
analytical techniques is essential for any future research. It is recommended
that, when possible, the less toxic polyamide resins be used in place of the
more aggressive amine curing agents.

CONTROL OPTIONS

In the following paragraphs, some observations about the various available con-
trol options described in Section VI are noted.

Spray Booths

Spray booths that meet OSHA design requirements are capable of controlling
total paint mist and organic solvent vapors to within recommended maximums.
Spray booths are partially effective in the control of toxic metals and other
dangerous materials, insofar as they contain the hazard within the booth.

Several factors not addressed by the OSHA standard have a significant bearing
on the effectiveness of a booth in protecting the health of the painter.

The distribution of air within the spray booth is apparently at least as sig-
nificant as the average air velocity. It was noted that supply and exhaust
air chambers were often built without regard to accepted criteria for plenum
design. Particular problems were noted where fresh air was supplied at a
velocity that was too great, introduced in a direction other than what was
being exhausted, or introduced between the painter and the point of exhaust.
The spray booths of case studies 1 and 8 are examples of booth design for
proper air distribution.

In order for protection to be maintained, the spray painter must not position
himself between the object being painted and the point of exhaust. Where all
sides of an object require painting, the operator can maintain proper position

51


additives, and rarely exceed 1 or 2 percent of the total formulation. They can
be classified by function as paint driers, anti-skinning agents, mildew inhibi-
tors, rheological modifiers, and latex paint additives.

Paint Driers--

The oldest and most important class of paint additive is the paint driers.
They promote the drying, curing, or hardening of oxidizable coating vehicles,
such as those found in alkyd, oleoresinous, epoxy ester, and urethane-oil
paints. The principal materials used as paint driers are metal soaps of
naphthenic acid or tall oil fatty acid. Cobalt is the most active of the metal
driers, followed by manganese. Lead is the most commonly used metal soap
because of its through drying properties. Cobalt and manganese are used at
levels ranging from 0.02 percent to 0.06 percent metal, based on total vehicle
solids. Lead is used at levels of 0.5 to 1.0 percent. Other metals used in
driers include barium, calcium, cerium, iron, zinc, and zirconium, !2

Anti-Skinning Agents--

These agents act as anti-oxidants, inhibiting skin formation in the package,
but they are volatile enough that drying proceeds after paint application.
Oximes and substituted phenols are two chemical classes used as anti-skinning
agents in paint; the oxime is the most common by far. Oximes also function by
forming complexes with metal driers, impairing their action until the oxime has
evaporated. !2

Mildew Inhibitors--

Fungicides are incorporated in exterior house paints and in some interior in-
dustrial maintenance paints in order to prevent mildew growth on the dried
paint film. The phenyl mercury compounds are the most widely used fungicides.
Mercury concentration levels in paints normally range from 0.5 to 2.0 percent
of the total paint. Other fungicides used in paints include cuprous oxide,
copper-8-quinolinolate, and phthalimides.

Rheological Modifiers--

This group of paint additives includes compounds used to prevent the settling
of pigments or the sagging of the applied paint film. Materials used for these
purposes include soaps, modified drying oils, and clays. !2

Latex Paint Additives--

In contrast to solvent-type paints, latexes consist of both pigment and binder
dispersed in a liquid medium. Anionic surfactants are used to maintain pigment
dispersion and non-ionic surfactants are used to stabilize the total dispersed
system. Because of the presence of the surfactants, anti-foaming agents are
required to prevent foam formation in manufacture and use. Proteins, cellulose
derivatives, polysaccharides, and water-soluble acrylic polymers are used to
modify paint consistency. Ether alcohols, tributyl phosphate, pine oi], and
other solvents are incorporated as temporary plasticizers, which promote coa-
lescence of the latex particles. Alkyl mercury compounds, tributyltin oxide,
and chlorinated phenols are common latex preservatives. !2

13


POOR GOOD

-

- 4)
(a) = a
a S
; |
y H
(b) < ss
(c)

Figure 4. Spray booth work practices.

42


Other Materials

Where two component polyurethane enamels were used, consecutive short term
samples were collected in the breathing zone of the spray painter to determine
ceiling concentrations of hexamethylene diisocyanate. These samples were col-
lected using 2 midget impingers connected in series to a personal pump that was
operated at 2.0 Ipm. ach impinger contained 15 ml of a nitro reagent solu-
tion, which was subsequently analyzed for the HDI/nitro reagent derivative by
high pressure liquid chromatography. The solvent was removed from each
impinger solution using a rotary evaporator and the residue taken up in 2 ml
of methylene chloride. Aliquots of each resulting solution were injected onto
au Porasil column. The mobile phase was an isooctane-methanol-isopropanol
solvent gradient. Detection was accomplished by UV absorbance at 254 nm.
Although the nitro reagent will react with any reactive isocyanate group, the
present method allows quantification of the monomer only.

Analyses of other components and bulk materials were performed on an as-needed
basis. Sampling and analytical procedures for these materials are presented in
the individual case studies.

AIRFLOW MEASUREMENTS

The effectiveness of spray booths was determined in part by the measurement of
air velocities and flow patterns within the booth. These measurements included
as a minimum the total quantity of air supplied to and exhausted from the spray
booth and the air velocity within the booth. Total exhaust and supply volume
were determined by either a pitot tube traverse of the exhaust or supply ducts,
or, if duct access was limited, by measurement of face velocities at supply or
exhaust grilles. The air velocity in the booth was measured in an imaginary
plane occupied by the painter, a vertical plane in the case of a side draft
booth. For downdraft booths, an imaginary horizontal plane at face level was
used. Velocities were measured at a minimum of 12 points in these planes.
The results were averaged and reported as “control velocity." Where appro-
priate, the standard deviation of the air velocity measurements was reported
as an index of the variability of the air velocity within the booth.

46


Co oo ge rp fag EE,

3
SANDER OVEN
Sage ®

poorer nnn cornea ene nee nec anne ¢-~- SRG oo

sooo PM 2p fees} fea

& OVEN x bh OTs
MAKE UPAR CLEAR
"26,000 CFM, — INTERIOR, BARRIER URCOUER

u

Figure 2-1. Wood furniture finishing room layout.

In step 6 of the above finishing sequence, a heavy coat of glaze is applied to
the cabinet exterior and lid underside by a robot spray painter. The robot
was installed because of high employee turnover in this messy operation. In
addition to eliminating the operator from an unpleasant function, using the
robot reduced waste from overspray and increased material utilization by 15
percent. The company expects that the robot should pay for itself in 5 years.
Robots are being examined for other spraying operations where visual feedback
about the finish appearance is not required.

Coatings

Three types of coatings constitute the bulk of the finishing materials used:
an acrylic barrier coat, an oil-based glaze, and a clear lacquer. The barrier
or base coat provides color, promotes topcoat adhesion, and protects the plas-
tic furniture substrate from attack by the subsequent coats. The barrier
coating is a pigmented acrylic lacquer that has been plasticized with dioctyl
phthalate. Iron oxide, lampblack, and burnt sienna provide color. Prior to
use, the barrier coat is mixed with equal parts of a reducer. Like all lac-
quers, the barrier coat cures through the evaporation of its solvent fraction.
An oil-based glaze or stain is used to highlight the natural features of the
wood surfaces and the molded-in grain of the plastic panels. This oil-based
material requires oxidation of the drying oils to complete a cure. A clear
nitrocellulose lacquer topcoat is used to provide a protective seal and a
semi-gloss finish.

Constituents of the three major coatings are identified in Table 2-1. All
three of these coatings are stored and/or reduced as necessary in a building
separate from the main plant and finishing department. High pressure pumps
located in this building circulate these coatings at 1400 psi to the airless
guns. For the compressed-air guns, limited quantities of these coatings are
hand delivered to the pressure pots in 5 gallon pails.

Smaller quantities of other coatings are also used. A black lacquer is applied
to the record changer compartment in a net or "veil" pattern, in order to pro-

2-3


Ethoxyethy] acetate and ethy] acetate are the major solvent hazards associated
with the urethane enamel. The chief toxic manifestations of both compounds are
eye and nasal irritation. At high concentrations, headache, drowsiness, and
unconsciousness may occur.

SPRAY BOOTHS
Design

All spray painting operations are performed in 1 of 5 identical downdraft
booths similar to that shown in Figure 7-2 and 7-3.

<_
=>

378 SUPPLY.
20'x20'x 2" PLENUM
FILTERS

tyobouaN

"GRE GRATE GRATE
PIT
FILTER
roa) MEDIA

Figure 7-2. Cross-section of helicopter spray booth.

EXHAUST DUCTS
TYPICAL OF 5

EXIT EXIT

\

EXHAUST GRATES

AE A I EI SH RE EE ) ES BY
CS BE RE BB

EXHAUST GRATES

Figure 7-3. Plan of helicopter downdraft spray booth.
7-5


**Painters 1 and 2 used electrostatic guns for exterior panels, conventional
guns for liners; painter 3 used conventional spray equipment continuously;

painter 4 used both electrostatic and conventional guns for exterior panels,
conventional guns for liners.

As shown in Table 6-3, the 8-hour TWA concentrations of paint mist exceeded the
legal maximum for total dust. Again, the liner operation was a heavy contribu-
tor to the average concentration, as is evidenced from the results of the short
term mist samples reported in Table 6-4. Based on these results and a mean
mist concentration of 35 mg/m3 for all spray painters, mist concentrations
would be less than the 15 mg/m3 total dust standard during exterior painting
operations.

Table 6-3. Airborne levels of spray mist and
lead in appliance finishing.

8-hour time weighted
average concentration

Number of
Operation samples Paint mist (mg/m3) Lead (ug/m3)
GM GSD GM GSD
Manual prime booth
Painter 1* 3 21.7. 1.1 <7 1.0
Painter 2 1(Pb-3) 31.4 -- <6 1.0
Manual finish booth
Painter 3 3 54.5 1.3 20 1.4
Painter 4 2(Pb-3) 39.2 1.4 13 2.2
Automatic prime booth
(area sample) 3 0.1 =#1.9 <6 1.0
Automatic finish booth
(area sample) 3 0.1 1.0 <6 1.0
OSHA PEL 15 50
ACGIH TLV (1979) a 150

NIOSH - a

GM: Geometric mean
GSD: Geometric standard deviation

*Painters 1 and 2 used electrostatic guns for exterior panels, conventional
guns for liners; Painter 3 used conventional spray equipment continuously;
Painter 4 used both electrostatic and conventional guns for exterior panels,
conventional guns for liners.


Produced by increasing the ratio of bisphenol A to epichlorohydrin. Resins
employed in the paint industry have molecular weights varying from 400 to
4,000. Liquid resins with molecular weights of 400 are modified by the addi-
tion of reactive diluents (glycidyl ethers) for use in solventless, two-pack-
age coatings. Solid resins with molecular weights of about 1,000 are dissolved
in solvents or dispersed in water as one component of two-package coatings.
Resins with molecular weights of around 1,400 are applied as powders, together
with dicyandiamide, or are used as reaction partners with fatty acids for pro-
ducing epoxy esters. Resins with molecular weights ranging from 2,900 to 4,000
are combined with phenolic resins, melamine, and carbamides to form high qual-
ity baking finishes.9

Epoxy coatings can be classified into three principal categories, based on the
method of cure: 1) two-package or amine-cured coatings, 2) epoxy baking ena-
mels, and 3) epoxy esters.

Two-package epoxy coatings consist of two separate components that are mixed
just prior to use. One component consists of either a solid resin in solution,
or a modified liquid resin; the other component is a curing agent, most com-
monly a polyamino compound. The coating cures by the room temperature reac-
tion of the terminal epoxide groups with the hydrogen atoms of primary or
secondary amines.

The principal types of amine curing agents that are available are polyamines,
polyamine-adducts, and amine-terminated polyamide resins. Typical polyamines
are diethylene triamine, triethylene tetramine, and tetraethylene pentamine.
Polyamine-adducts are amine-terminated epoxy resins that are formed by pre-re-
acting an epoxy resin that is relatively low in molecular weight with an excess
of polyamine, resulting in a curing agent with little free amine. Polyamides
are the reaction products of polyamines and dimerized vegetable fatty acids.
Polyamide-cured systems are not quite as chemically resistant, nor do they cure
as rapidly, as the polyamine systems, but they are less irritating and offer
longer pot-life.

Epoxy resins with molecular weights ranging from 2,900 to 4,000 may be combined
with thermosetting phenolic and amino resins to produce high quality baking
finishes. The large number of reactive groups in both the epoxy and the phe-
nolic or amino resin gives a highly cross-linked structure which, when cured,
is hard, tough, and solvent resistant. Epoxy powder coatings belong to the
thermosetting category and exhibit the same general properties as epoxy baking
enamels. The curing agents are usually friable solids, dry blended with the
powdered resin, pigments, and additives. Curing agents include dicyandiamide,
aromatic amines, and polyanhydrides.

Epoxy esters are prepared by reacting solid epoxy resins with drying oil fatty
acids. Curing takes place at ambient temperatures, through the oxidation of
the oil, as in alkyd paints, or it may be accelerated by baking. Although
these esters are superior to alkyds in certain respects, they have the same
handling and processing characteristics as alkyds.

Urethane Resins--
Urethanes are polymers that result from the reaction of isocyanates with mate-
rials that possess hydroxyl groups. Toluene diisocyanate is the most widely

8




able. Safe usage of these materials dictates the use of respiratory protection
in conjunction with engineering controls.

Other Toxic Metals

Besides lead and chromium, other toxic metals like antimony, arsenic, cadimum,
and mercury are used in some paints. These materials were not encountered in
any of the field studies.

Silica and Silicates

Talc, diatomaceous earth, and silica (both crystalline and amorphous) are used
in paints as extender pigments. These materials may represent up to 20 percent
of the non-volatile coating components in certain formulations. Except for
crystalline silica, all of these components would be controlled to safe levels
in typical spray booth installations, based on the total paint mist concentra-
tions measured.

Organic Solvents

When spray booth ventilation rates meet the minimum requirements set forth by
OSHA, exposure to organic solvents is readily controlled to less than 25 per-
cent of currently allowable levels. NIOSH recommendations for lower exposure
limits for alkanes, refined petroleum solvents, and toluene are also met in
most instances. Except for painting in enclosed spaces (such as vehicle
interiors), the operations studied that did not meet the above limits could be
brought into conformance by a change in application techniques (case study 6)
or increased ventilation (case studies 3 and 4).

No benzene was indicated in any bulk air samples collected and analyzed by gas
chromatography/mass spectroscopy. Bulk air samples were collécted where re-
fined petroleum solvents were included in the paint formulation or employed as
reducers, and in cases where many paints were used during a single workshift.

Organic solvent levels were noticeably higher in paint mixing and storage
rooms. These rooms can generally be characterized as small and inadequately
ventilated with poor housekeeping. Solvent levels are high because of poor
equipment and bad work practices, with open containers of paint and solvents
in abundance. Solvent exposures can be controlled by use of paint mixers with
loose fitting covers, elimination of solvent leaks and drips, good house-
keeping, and general ventilation. A model paint mix room is described and
evaluated in case study 10.

Isocyanates

Breathing zone concentrations of hexamethylene diisocyanate (HDI) were deter-
mined ‘in automobile refinishing (case study 5) and in light aircraft finishing
(case study 7). Except for a single sample, all concentrations of monomeric
isocyanate were below the ceiling level for HDI (140 ug/m3) recommended by
NIOSH. The single sample exceeding this value occurred when ventilation was
compromised during the painting of aircraft underbodies.

50


CONTENTS

Abstract... 2... 2s eee es B /
Acknowledgment. .........2-4 res 2 © §
I. Introduction. .........2- 0000000 09000000000 0al
II. Industrial Coating Technology. .......2.6- 9ad00000c0000%
III. Spray Application Methods... . 2... 2.2.22 eee S0000000 ok}
IV. Industrial Finishing Practices. ....... 6 6 we oo oo 16

V. Health Hazards in Spray Finishing. . 2... 2 ee ee we ew eww 025

VI. Control of Health Hazards... . 1... ee ee 0000000000 oll
VII. Evaluation Procedures... 2... 2... 220 ee eee ee ee we 243
VIII. Conclusions and Recommendations. ....... eee we eee ew ww M7
References. . 2. 2 ee ee eee rere ne eee wee ew ee tw te wt OF
Appendix. . 2. 2 ee eee ee eee 6)

Case Study 1. Powder Coating - Smal] Parts. ............ 1-1
Case Study 2. Wood Furniture Finishing. .........6.2..6.22. 2-1
Case Study 3. Metal Furniture: Solvent and. ..........4.. 3-1
Waterborne Coatings
Case Study 4. Railroad Car Finishing... 1... 6. eee ee ew 4H
Case Study 5. Auto Refinishing. ... 2... e222 ee eee eee Sel
Case Study 6. Appliance Finishing. ........20.00.200. 26-1
Case Study 7. Light Aircraft Finishing. ............2.. 7-1
Case Study 8. Finishing of Heavy Equipment. ............ 8-1
Case Study 9. Metal Furniture: Conventional and... ....... 9-1
High Solids Coatings
Case Study 10. Paint Storage and Mixing... .......2..2..2.. 210-1


Table 9-3. Airborne levels of total paint mist, lead, and
chromium in metal furniture finishing (Process A).

8-hour time-weighted average concentration

Paint mist Lead Chromium
Number of (mg /m3) (ug /m3) (ug /m3)
Operation samples oy GSD cM GSD om GSD
Manual prime booth
Painter 1* 3 2.9 1.3 22 1.1 6.0 1.2
Painter 2 3 6.2 1.3 22 3.4 9.0 2.0
Manual finish booth
Painter 3 3 4.0 1.4 19 1.6 6.0 1.2
Painter 4 3 4.2 1.1 26 1.6 6.0 1.6
Electrostatic booth B
Face 3 0.1 1.7 5.0 1.0 5.0 1.0
Exit 3 0.1 1.6 9.0 2.0 4.0 1.3
Electrostatic booth C
Face 3 0.3 2.0 5.0 1.0 5.0 1.0
Entrance 3 0.1 1.2 7.0 2.0 6.0 1.3
OSHA PEL 15 50 1,000
ACGIH TLV (1979) 10 150 100
NIOSH -- 100 1

*Painter T uses airless for cabinet interiors, compressed air for other items ;
other manual painters use only compressed air guns.

GM: Geometric mean

GSD: Geometric standard deviation

9-9


duration of the wagon painting, a period of approximately 60 minutes. An addi-
tional gravimetric sample was taken on Painter B for the duration of painting
the interior of the wagon. The area samples were collected over the time re-
quired to paint several wagons.

The mean concentration of total paint mist, lead, and chromium in the breathing
zone of Painter B was six times that of Painter A. This can be explained by
the high mist levels measured during the painting of the wagon interior. The
concentration of paint mist in the breathing zone of Painter B during exterior
painting operations was determined by calculation to be 2.2 mg/m3, a level
virtually identical to that of Painter A.

Eight-hour time-weighted average (TWA) concentrations would be approximately
one-half the values reported in Table 8-2. Levels of paint mist are well below
the maximum allowed by OSHA for total dust. Lead concentrations exceed the 50
ug/m3 standard; however, both painters wear half-facepiece respirators, with
organic vapor-removing cartridges and mist filters. As half-mask respirators
offer a protection factor of ten, Painter A would be well protected, but
Painter B would not be as well protected.

Airborne levels of organic solvents in the breathing zone of the spray painters
and in the area of the booth entrance and exit are reported in Table 8-3.
These samples were taken in parallel with the particulate samples. Maximum

Table 8-3. Airborne levels of organic solvents
in heavy equipment finishing.

Concentration (mg/m3)

TetramethyT Ref ined

Number of Xylene benzene solvents Ce*

samples GM GSD GM GSD GM GSD
Painter A 6 3 1.3 <2 1.0 21 1.5 0.01
Painter B 6 5 1.3 <2 1. 96 1.8 0.05
Booth Exits 4 <0.5 1.0 <0.5 1.0 <6 -- = <0.01
(area sample)
OSHA PEL 435 oo 2,950 1
ACGIH TLV (1979) 435 -- 1,350** --
NIOSH Recommendation 435 -- 350 --

GM: Geometric mean
GSD: Geometric standard deviation
**VM&P Naptha

*Combined Exposure: Ce =O + Cy <P? D0 cy

where C is the concentration of the individual contaminant, and
L is the exposure limit.

8-10


PREVENTION OF FIRE AND EXPLOSION

Although the measured total exhaust rate is approximately 20 percent less than
the design value of 4500 cfm, fire and explosion hazards are minimal; the maxi-
mum duct powder concentration (0.014 ounces/cubic foot) is less than 30 percent
of the lower explosive limit (0.05 ounces/cubic foot). Each booth is equipped
with two ultraviolet fire detectors that, if activated, shut off the entire
system and close a guillotine damper isolating the booth from the dust collec-
tor. Fire detector windows are purged with 100 cubic feet/hour of air to pre-
vent fouling. Each dust collector is provided with an 8 square foot explosion
relief, vented to the roof.

GENERAL VENTILATION

Process humidity requirements necessitate that the powder unit area be air
conditioned. The room is equipped with two units, a 15-ton, 6,000-cfm unit,
located just outside the north wall, and a 10-ton, 4,000-cfm unit, located
just outside the south wall. Return air inlets are located above the doors on
the respective walls. Supply air from the larger unit is well distributed
with six outlets just below ceiling level. The smaller unit supplies air
through a-single outlet next to the first powder booths. Louvers are adjusted
to direct air away from the booth so the air does not adversely affect control.
A single, fresh (outside) air outlet located in the northeast corner supplies
250 cfm or approximately one air change per hour.

HOUSEKEEPING

Accumulation of powder on equipment or accidental spillage is inevitable, and
prompt removal is necessary in order to prevent entrainment into the shop air.
The powder department is equipped with a high capacity, turbine-type vacuum
system, with a filter bag separator. The vacuum unit is located outside the
enclosed area and has four vacuum outlets in the powder unit. This system per-
mits immediate cleanup of spills and periodic vacuuming of walls and equipment
(Figure 1-4).

SAFETY

The danger of electrical shock from the 90-kV equipment is minimized by lim-
iting the available current and by grounding both equipment and personnel.
The current is restricted by limiting resistors located in the spray guns and
cables. All equipment is interconnected with grounding cables to prevent
static buildup and subsequent sparking. Likewise, personnel are grounded by
contact between bare hands and the metal gun handle to prevent static buildup.

EVALUATION

As an index of control, the 8-hour, time-weighted average exposure (TWA) to
total dust was determined for the spray operator and the equipment operator
(Table 1-1). Both individuals spend their entire workshift in the powder-unit
area, excluding two 10-minute, scheduled breaks and a 30-minute lunch period.
Area samples were taken in the vicinity of the potential exposure sources to
determine their relative impact on worker exposure. Total dust measurements

1-5


Table 10. Railroads (Resins, Solvents and Pigments

as Percent of Total Consumption).

Per- Per- Per-
Resins cent Solvents cent Pigments cent
Alkyd 50 Aliphatic 38 Titanium 43
hydrocarbons dioxide
Epoxy 16 Other 12 Talc 13
aromatics
Urethane 8 Glycol ether 10 Silica 8
and ether
esters
Acrylic 7 Xylene 9 Chromium 8
Amino 6 n-Butanol 8 Barytes 5
Other 13 MEK 10 Tron oxide 8
Acetone 8 Lead 3
Toluene 5 Other 12
Other 5
ketones

22


In this operation, lead- and chromium-free pigments (titanium dioxide, iron
oxide, and carbon black) are used. Filler materials (amorphous silica, non-
asbestiform talc, and calcium carbonate) represent less than 10 percent of the
formulation.

HAZARD ANALYSIS

Powder paint eliminates the hazard of inhaling the solvent vapors associated
with the spray application of conventional coatings. It does not eliminate the
danger of fire and explosion but, rather, presents special problems in this
regard.

The hazards associated with pigments, filler materials, and resinous binders
are similar to the hazards of conventional liquid paints with like composition.
The use of lead- and chromium-free pigments minimizes the risk posed by these
materials. Trace quantities of lead and chromium may still be found in heavy
metal-free formulations because of contaminants in the raw materials or as
contaminants introduced in manufacture. In the absence of toxic metals, the
filler materials are the most dangerous constituents, but their relatively low
concentration in the formulation precludes any serious hazard as long as air-
borne powder levels are kept below recommended maximums for nuisance materials.

Respiratory irritation, or sensitization, or both, resulting from the polymeric
isocyanate should not occur because the active isocyanate groups have been
blocked by their reaction with caprolactam. The caprolactam released in the
curing oven presents no hazard to the painters. However, there is a possibi-
lity that when inhaled, the caprolactam-isocyanate complex could hydrolyze and
regenerate caprolactam, a respiratory irritant. However, the isocyanate would
not be regenerated because the hydrolysis yields a carbamate.

POWDER BOOTH

The configuration of the powder booth is shown in Figure 1-3. Panels enter and
exit through openings that are 5 square feet in size and located on both ends
of the booth. The conveyor does not enter the booth, but panel hangers pass
through a 6 1/2 inch wide slot running the length of the booth. The spray
operator works through an 11 square foot opening with his head and body out-
side the booth. A 16 square foot opening is provided for removing the recip-
rocator assembly. Hinged doors reduce this opening to an 8 inch width during
spraying.

No powder losses are visible from any booth opening. Average indraft velo-
cities vary from 120 to 135 fpm, depending on the loading of the filter media,
based on measurements of total airflow that ranged from 3400 to 3700 cfm. In-
draft airflow is well distributed, with the velocity exceeding 100 fpm at all
points. A good distribution of flow is obtained by the large horizontal cross
section (68 square feet). When compared with the total open area, this cross
section results in low internal hood air currents in relation to the indraft
velocity. Distribution is further enhanced by placing the exhaust takeoff at
the hopper bottoms and incorporating turning vanes at those points.


spraying. Of those individuals employed as spray painters, a maximum of 6
paint at any time. The actual time that these workers Paint varies with the
size of the helicopter and the complexity of the color scheme, but a daily
exposure of 2 hours or less is an estimate. This exposure time is low because
of the slow pace of finishing necessary to attain a virtually flawless finish,
the extensive preparation of the ship for priming, and the time-consuming lay-
out of the custom color schemes.

To determine control effectiveness, the airborne levels of total spray mist,
toxic metals, and organic solvents were determined by personal air samples
taken during the time it took to paint each aircraft.

Total mist, lead, strontium, and chromium were collected using closed-face
cassettes with preweighed, 0.8 u pore size, 37 mm polyvinyl chloride/acrylo-
nitrile membrane filters and personal pumps operated at 2.0 Ipm. After
weighing, the filters were ashed and analyzed by atomic absorption spectro-
scopy for metals. Air samples taken during ship priming were analyzed for
strontium and chromium. Samples taken during topcoat application were
analyzed for lead.

Organic solvent samples were collected on 150 mg charcoal tubes with personal
pumps operated at 100 cc/min. Tubes were subsequently desorbed and analyzed
by gas chromatography.

For polyurethane topcoats, consecutive short term samples were taken in the
painter's breathing zone to determine ceiling concentrations of HDI. These
samples were collected using 2 midget impingers connected in series to a per-
sonal pump operated at 2.0 lpm. Each impinger contained 15 ml of a nitro
reagent solution, which was subsequently analyzed for the HDI/nitro reagent
derivative by high pressure liquid chromatography.

Dibutyltin dilaurate, used as an accelerator in the urethane enamel, was col-
lected using closed-face cassettes with 37 mm glass fiber filters and personal
pumps operated at 2.0 lpm. Because of the anticipated low airborne concentra-
tion of tin, sampling times were increased to encompass the finishing of 2 air-
craft. Following collection, the samples were analyzed by x-ray fluorescence
for total tin content.

RESULTS
Prime Application

Breathing zone (outside respirator) levels of paint mist, strontium, and chro-
mium (strontium chromate) are reported in Table 7-4. (NOTE: Ship numbers are
included in tables so that samples for mist, solvents, and so forth, can be
compared). Both concentrations of total mist and total chromium exceed allow-
able limits for a full shift's exposure. On a 8-hour, time weighted average
basis, however, levels of total mist and chromium are below legal limits. It
should be noted that both NIOSH and the American Conference of Governmental
Industrial Hygienists (ACGIH) have recommended exposure limits well below the
current OSHA standard for chromium.

7-9


28.

29.
30.

31.

32.

33.

34.

35.

36.

37.

38.
39.
40.

41.

42.

43.

44,

for Disease Control, National Institute for Occupational Safety and
Health. 1977. 247 pp.

Crieria for a Recommended Standards....0ccupational Exposure to Poly-
chlorinated Biphenyls. DHEW (NIOSH) Publication No. 77-225. U. S.
Department of Health, Education, and Welfare, Public Health Service,
Center for Disease Control, National Institute for Occupational Safety
and Health. 1977. 224 pp.

Webb, R.J., Jr. 1977. Get the Lead Out! Products Finishing. pp 74-7.

Webb, R.J., Jr. 1976. How to Hold Down Costs with Lead-Free Coatings.
Materials Engineering. pp 90-1.

Panush, H.S. 1977. Non-Chromate Pigments for Automotive Finishes. Jour-
nal of Coatings Technology. pp 38-44.

Craig, R.W. 1977. Waterborne Coatings....Fact or Fantasy? Industrial
Finishing. pp 26-8.

Anon. 1975. Waterborne Coatings and Their Place Among ‘Ecology' Finishes.
Products Finishing. pp 70-5.

DeVittorio, J.M. 1975. Waterborne Coatings-Application of Film. Metal
Finishing. pp 46-9..

Pettit, P.H. 1978. High-Solids Coatings, Evaporating the Low Solids/High
Solvent Transition. Canadian Paint and Finishing. pp 24-6.

Anon. 1977. The High-Solids Route to Pollution Control. Products Fin-
ishing. pp 63-7.

Brown, P. 1975. Non-Aqueous Dispersion Finishes in the Automotive Indus-
try. Metal Finishing. pp 38-40. :

Anon. 1976. Powder Coating '76. Products Finishing. pp 46-52.
Anon. 1978. What's New in Powder Coating? Products Finishing. pp 90-7.

Berger, D.M. 1975. Urethanes for Coatings have Many Positive Assets for
Finishing Operations. Metal Finishing. pp 44-7.

Key, M.M. 1969. Control of Epoxy Dermatitis in Industry. Journal of Paint
Technology. pp 304-7.

Norin, M. 1975. The Needs of the Working Environment. Product Finishing.
pp 24-8.

Munger, C.G. 1974. Safe Application of Protective Coatings. Plant Engi-
neering. pp 73-5.

Reichenbach, G.S. 1953. Ventilation for Ship Construction and Repair.
Industrial Hygiene Quarterly. pp 307-11.

58


with similar advantages. In addition, with airless systems, lower hydraulic
pressures can be used and finer atomization can be achieved.

The high pressures associated with the airless method carry with it the hazard
of hypodermic injection for persons who may accidentally contact the spray.
Because the paint may spread under the skin through even a tiny wound, immedi-
ate medical attention is required.

ELECTROSTATIC METHOD

In electrostatic spraying, an electrical charge is applied to the atomized
coating particles, either by the creation of an ionized zone within the spray
cone area, or by imparting a charge to the fluid stream prior to its release
from the spray gun head. The charged, atomized paint particles are attracted
to the conductive object being finished by the electrostatic potential between
the paint and the object.

The atomization can be achieved by the use of air-atomizing or airless type
equipment, or solely by the use of electrostatic means. In this last method,
the coating material is introduced into the center of a rapidly spinning disk
or bell, which is charged to a high potential. As the coating reaches the
edge of the disk or bell, the repulsive forces of the like charges causes the
coating to atomize.

15


Solvents--

Several alternatives exist for either reducing or eliminating organic solvents
in industrial finishing. These include waterborne, non-aqueous dispersion,
high solids, or powder coating techniques. Development of these techniques has
been hastened by legislation that limits the release of volatile organic hydro-
carbons into the environment, and by the increasing cost of the solvent
materials.

Waterborne finishes have some distinct advantages over high solids, powder, and
other types of solvent-substitute coatings for many applications. These ad-
vantages include low flammability, reduced solvent toxicity and odor, water
cleanup, reduced environmental pollution, and lower energy requirements32,
The greatest advantage is that, in many cases, waterborne coatings can be
applied and air-dried or oven-cured in existing coating lines with little or
no modification. On a cost-per-square-foot painted basis, waterborne coatings
are competitive with solvent-based.33 waterborne coatings can take the form
of emulsions or solutions. In general, the emulsion systems allow a higher
solids content and lower levels of organic co-solvents than the water soluble
coatings. Two problem areas arise in waterborne coatings: 1) waterborne
coatings are applied at higher viscosity, making atomization more difficult,
and 2) waterborne coatings are conductive, requiring special precautions in
electrostatic spraying. The atomization difficulties may require the use of
higher air pressures for atomization, which may increase the spray painter's
exposure to overspray and noise.34 In addition, questions have been raised
about the coupling solvents and pH control materials used in waterborne
coatings.

A second option for the reduction of solvent content is the use of high-solids
coatings. The effect of increasing solids content from the 20 percent that is
typical of solution coatings to 60 percent is to reduce solvent consumption for
equal coverage by a factor of 6. The resins used in low solids finishes are
generally not suitable for high-solids coatings. In formulating sprayable
high-solids coatings, it is necessary to use lower molecular weight polymers to
minimize the rise in viscosity. In addition to molecular weight reduction, the
resin manufacturer must incorporate reactive groups to each small polymer
chain, because at some point, it is necessary to combine the shorter chains,
to assure satisfactory performance of the applied coating. The more the mole-
cular weight of the resin is reduced, the higher the solids content can be
raised. However, when more combination is required, more catalyst and/or
curing agent must be added. As catalyst content is increased, paint stability
decreases to the point where it is necessary to package the two components
(resin and curing agent) separately. Unfortunately, the more reactive fast
curing products are also generally more toxic. 35 Current high-solids
coatings are dominated by alkyd and oil-free polyester resins, but high solids
acrylics, epoxies, and polyurethanes are in. the development stage. 36

Non-aqueous dispersions (NADs) are a third option to reduce total solvent con-
tent. NAD systems can achieve a higher usable solids content of 50 to 60 per-
cent, compared to the the 20 percent of a typical solution system. Non-
aqueous dispersion finishes are sometimes considered hybrids of solution
systems and conventional emulsions. The aliphatic hydrocarbons, which in
general are lower in toxicity than oxygenated solvents, can be used as the main

32


Calcium naphthanate, cobalt naphthanate, and zirco catalyst are employed as
driers, catalyzing the oxidation and subsequent polymerization of the paint
film. Solvents used in formulation include VM&P naptha, mineral spirits,
tetramethyl] benzene, and xylene in order of decreasing percentage. Up to 2
gallons of tetramethyl benzene per 53 gallons of raw paint are used to adjust
the viscosity of the paint.

HAZARD ANALYSIS

The principle hazard associated with the coating in use at this facility is the
lead chromate (chrome yellow) pigment employed. Because the inorganic pigments
are generally weak tinting colors, a substantial amount of pigment is required.
In this particular coating, the chrome yellow pigment amounts to approximately
20 percent of the total paint solids by weight. Lead chromate is one of the
least toxic lead compounds with respect to plumbism because of its low solubi-
lity; nonetheless, the hazard is still present and must be treated seriously.
In addition, lead chromate has been implicated as a lung carcinogen in workers
who produce chromate pigments, although a similar situation has not been docu-
mented in painters.

The alkyd resin has no unusual toxic properties. Alkyd resins have been used
in paints for some time with no reports of any chronic hazards.

The organic solvents employed in these formulations all exhibit similar physio-
logical effects. In general, they are irritants to the conjunctiva and to the
mucous membranes of the upper respiratory tract. They all produce depression
of the central nervous system and, at high concentrations, produce symptoms of
headache, nausea, and drowsiness, followed by unconsciousness and death.

SPRAY BOOTH
Design

The hay stack wagons are painted in the 40 by 32 foot downdraft booth shown in
Figures 8-4 and 8-5. This booth features a pit (for underbody painting) that
incorporates a supply of fresh air. In the design stage, careful attention was
given to good air distribution within the booth. Fresh, heated air is supplied
to the booth by two direct-fired, make-up air units with a combined, rated
capacity of 180,000 cfm. Approximately 80 percent of this air is supplied
through an overhead plenum. The floor of the plenum chamber is a perforated
plate to assist in air distribution to the filter bank. The shape of the
filter bank and the gentle slope of the booth's upper wall further diffuse the
supply air. Maximum supply air velocity at the filter face is 200 fpm. Except
for a small quantity of air supplied to the pit area, the remaining make-up air
is supplied to entry and exit vestibules or “air-seals." Because the total
quantity of air supplied to the booth exceeds that exhausted by 10 percent,
excess make-up air spills out of the air seals, effectively preventing dust-
laden plant air from entering the booth. Fresh air enters the pit area
through a fresh air plenum located beneath the open grate floor of the pit.
This plenum incorporates slots to achieve air distribution. The pit area is
covered with movable panels. To paint the bottom of the hay wagon, the painter
removes only one or two panels, sliding the cover panels as he progresses.

8-4


if the object is rotated, or if a downdraft booth is employed. Case study 8
describes a unique technique used to ventilate underbody painting operations,
and special lifts to allow proper operator position during other operations.

The air velocities recommended in the standard are useful guides in determining
air volume requirements, but may be either too restrictive or inadequate,
depending on the toxicity of the paint material, and the method and rate of
paint application. Higher airflow rates should be considered for highly toxic
materials in order to minimize exposure although even at these higher rates
control may not be complete. Baturin 3 recommends an air velocity of 220 to
260 fpm when lead-containing paints are sprayed. However, this recommendation
was not evaluated in this study because no spray booths with design air velo-
cities greater than 150 fpm were encountered. Such high velocities substan-
tially interfere with most spray processes, inhibiting the deposit of sprayed
material onto the intended surface. Lower airflow rates have been suggested
for airless spray finishing operations. Even with airless spraying, highly
toxic paints or high application rates might warrant higher velocities.

In spray booths equipped with dry filters, airflow must be monitored because
it decreases with the build-up of overspray on the filters. Manometers are
frequently used to monitor the pressure loss across the filter media. Filters
are changed when resistance reaches a predetermined level. Too often these
Manometers are broken, low on fluid, mounted where they can't be seen, or no
change point has been determined. A more positive means to ensure that the
filters are changed is the use of a pressure switch and interlock that pro-
hibits activation of the spray gun when the filter is fully loaded.

Application Methods

The working environment of the spray finisher can be improved by the use of
paint application methods that minimize the energy expended in the atomization
process. Electrostatic discs and bells atomize paint primarily by electro-
static forces and produce very little stray paint mist. An electrostatic bell
system was evaluated in case study 6. With minimal air movement in the auto-
mated spray room (for the purpose of diluting the evaporating solvents), the
mean concentration of paint mist was only 0.1 mg/m’.

Both airless and airless electrostatic methods, when they are used with heated
paint, can produce low levels of overspray, even when relatively large and
complex shapes are painted. In case study 8, paint mist concentrations of 2.0
mg/m3 were measured when these methods were used to finish the exteriors of
heavy equipment.

Airless techniques appear to be particularly useful in painting recesses or
internal cavities. Not only do they provide a cleaner work environment, but
they apply paint faster and cover inside corners better. The benefits of air-
less were demonstrated in case study 9, in which an airless gun was used to
finish the interiors of file cabinets. In a similar operation (case study 6)
using conventional spray guns, paint mist concentrations were over 10 times as
high. This higher level of paint mist was noted in spite the fact that the
total number of units requiring internal painting was significantly less.

52


The most common types of resins, solvents and pigments are included in Table 6.

Table 6. Wood furniture (resins, solvents and pigments
as percent of total consumption)4

Per- Per- Per-
Resins cent Solvents cent Pigments cent
Alkyd 42 Toluene 27 Titanium 26
dioxide
Cellulosic 27 Xylene 15 Talc 25
Amino 8 n-Butanol 12
Other 23
Ethanol 10 Silica 18
Isopropanol 10 Calcium 15
carbonate
MEK 8 Iron 8
oxide
MIBK 7 Other 8
Other VW

METAL FURNITURE

This industry is classified under SIC major group 25 (Furniture and Fixtures)
and 34 (Fabricated Metal Products except Machinery and Transportation Equip-
ment). These establishments are engaged in the manufacture of metal household
and office furniture, garden furniture, cabinets, chairs, storage and display
cases, metal partitions, shelving, metal doors, lockers, industrial and work
benches, and restaurant furniture. They also include products such as metal
doors, window and door frames, hardware cabinets and different types of hard-
ware (locks, hinges, and so forth).

The metal surface to be coated is cleaned and pretreated. Most plants use
automated three-stage or five-stage pretreatment processes, incorporating hot
water rinses, phosphoric acid baths, and chromic acid rinses.

Alkyd baking enamels are most used. Various acrylics (both thermosetting and
emulsion), high solids polyesters, and powders are: also used in lesser quan-
tities. Electrostatic spray guns are used in both automatic and hand-held
versions,

18


om

bo tod

.| |. \. |

50, 200 t 100 130) 25
\e =) \xe 200 50.

\

CUS

Figure 7-4. Spray booth airflow (ft/min).

Two factors influence this variation. First, the relatively small grate size
in proportion to the booth width induces a region of higher airflow above the
grate area. Second, supply air velocity appeared to vary because of poor dis-
tribution in the supply plenum.

Overspray control was facilitated by positioning the ship between the exhaust
grates as shown in Figure 7-5. The regions of highest air velocity thus coin-
cided with the cabin sides. Control was similarly aided by Placing racks
holding doors, cowls, and other small parts directly over the exhaust grates.
Observations indicated that control of overspray was compromised when heli-
copter underbodies were finished.

PERSONAL PROTECTIVE EQUIPMENT

Before entering the spray booth, all painters don a set of disposable coveralls
and a loose-fitting hood made of Tyvek R, During painting operations, they
wear a NIOSH-approved, half-facepiece respirator, with organic vapor-removing
cannisters and mist prefilters. Rubber gloves are available but not used by
all workers.

7-7


Table 2-5. Airborne solvent levels in glaze operations.

8-hour time-weighted average (mg/m3)

Ethylene glycol Petroleum
Booth Date Toluene Xylene monobutyl ether distillates  Ce*

4 9/10 3 1 19 20 0.10

4 9/11 2 2 12 12 0.06
Robot 9/12 3 2 19 13 0.10
Robot 9/13 1 1 am 20 0.06

8 9/12 4 1 14 6 0.07

8 9/13 5 1 15 6 0.08
Glaze wipers** 5 4 18 33 0.10
Background** 4 2 14 15 0.08
OSHA PEL 750 435 240 2950 1.0
ACGIH TLV (1979) 375 435 120 - 1.0
NIOSH 375 435 - 350 1.0
*Combined Exposure: Cp = a + Co tose Cy

a | Ly

where C is the concentration of the individual contaminant, and
L is the exposure limit.

**Geometric mean


The reciprocator opening, on the side of each booth, is fitted with a venturi
baffle that surrounds the operating equipment. This was installed to increase
the inlet velocity in the vicinity of the reciprocators. Two air inlet adjust-
ment vanes are located on each side of the venturi baffle. These vanes permit
adjustment of air velocity through the venturi, to reduce any adverse effects
on the spray pattern of the application system. The differences in adjustments
of these vanes may be a major contributing factor that affects the average con-
trol velocity data presented for Booths C and D in Table 9-2,

Table 9-2. Automatic electrostatic spray booth data (Process A).

Average control velocity (fpm)

Conveyor Reciprocator
Booth Total airflow (cfm) vestibule SD ventilation SD
Cc 5,400 31 21 90 32
D 11,200 7 39 61 23

Airflow Measurements

Total airflow was measured in both of the manual spray booths, and in two of
the automatic booths. Control velocity in the manual booths was measured with
a hot wire anemometer at 25 points in a horizontal plane at an elevation of 4
feet and the measurements were averaged.

EVALUATION

Four employees are potentially exposed to paint spray mist and organic solvents
in this process: two spray painters in the first manual booth, and two spray
painters in the finish, or second, manual booth. Potential sources for expo-
sure include spray mist and solvent vapors from spraying, and solvent vapors
evaporating from finished cabinets.

As an index of control, the 8-hour time-weighted average (TWA) concentrations
of total spray mist, lead, chromium, and selected organic solvents were deter-
mined for the paint sprayers. The spray painters spend their entire workshift
in the finishing department, excluding scheduled breaks and lunches. Area
samples were collected to determine the degree of containment in the automatic
spray booths. These samples were collected at the exit vestibule of the second
automatic electrostatic booth, and at the entrance vestibule of the third auto-
matic electrostatic booth. Area samples were also collected at the booth face
(at the reciprocator venturi baffle) of these booths.

The 8-hour TWA concentrations were calculated from separate morning and after-
noon samples over a three-day period. Samples of total spray mist were col-
lected using closed-face cassettes with preweighed 37 mm polyvinyl chloride
membrane filters and personal sampling pumps operated at 2.0 Ipm. Organic

9-7


Degree of Enclosure

Both sidedraft and downdraft booths are available in open or enclosed versions.
Overspray is easier to control in a closed booth; random room air currents may
upset the flow pattern designed for an open booth. In addition, an open booth
is more costly to operate than an enclosed booth, because a larger volume of
air is necessary in order to achieve a given air velocity at the operator's
location.

Air Make-up

The air exhausted from the spray booth must be replaced in order to achieve
optimum plant environmental control. Whether this air is supplied directly to
the spray booth or to the general workroom is largely a function of how dusty
the plant air is. Spray booths may be equipped with filter doors or fresh air
inlet plenums to prevent plant dust from settling on freshly painted surfaces.
Air should enter the booth at low velocity (200 fpm or less), and in the same
direction as it is being exhausted to avoid unnecessary turbulence. Fresh air
inlet plenums should be equipped with baffles or other positive means of air
distribution.

Air Velocity

A key parameter in local ventilation system design is the control velocity,
that is, the air velocity at the painter's position that is necessary in order
to overcome room air currents and any turbulence generated by the process it-
self. The American Conference of Governmental Industrial Hygienists (ACGIH)
Industrial Ventilation Manual45, and the American National Standards Insti-
tute (ANSI) Z9.3-1964, "American Standard Safety Code for the Design, Construc-
tion, and Ventilation of Spray Finishing Operations"46 contain design cri-
teria for spray booths. Occupational Safety and Health Administration (OSHA)
standards for the ventilation of spray finishing operations are presented in
29 CFR 1910.94.47 Their recommendations are summarized in Table 13.

An airless finishing process can be controlled at lower control velocities
than air spraying because it is a less turbulent operation. As the air pres-
sure is increased the turbulence of the spray action increases and more fine
spray particulates are generated. In discussing control velocities for spray
booths, Hemeon48 includes spray gun air pressure as a parameter in selecting
the control velocity. For large booths, Hemeon recommends an air velocity of
125 fpm for atomizing air pressures less than 65 psig. For air pressures of
75 to 95 psig, he suggests 150 fpm.

Several spraying variables are not addressed by the ACGIH and ANSI/OSHA. These
include the toxicity of the paint materials and the distance between the object
being painted and the spray gun. Baturin49 reports that a control velocity
of 150 fpm is sufficient to offer protection from paint or solvent vapors, but
that it is not sufficient when spraying lead-containing paint or primers. He
recommends a control velocity of approximately 220 to 260 fpm when spraying
lead-containing paints. Hama and Bonkowski!3 cite a German study that lists
control velocities for compressed air spray painting. Air velocities suggested
are: 69 fpm for a distance between the spray gun and object of 59 inches, 98

39


Table 2-2.

Spray booth airflow.

Rated Actual flow Average
Booth* Type flow(cfm) (cfm) Velocity Coating Comments
(range)
1 5x5 15,900 23,400(dirty) 130(40-250) Barrier Heavy paint
filter 28,700(clean) 160( 100-200) application
3 Slot 15,900 12,200 95(40-200) Barrier Air gun
4 3x5 10,930 6,900(dirty) | 110(60-140) Glaze Heavy paint
filter 14,650(clean) 105(60-150) application;
5 5x5 15,900 26,000(dirty) 230(90-300) Glaze Heavy paint
filter 28,600(clean) 220(80-350) application;
6 5x5 15,900 28,100(dirty) 210(100-350) Lacquer Heavy paint
filter application
7 3x5 10,930 6,500(dirty) 60( 10-90) Lacquer Heavy paint
filter 15,400(clean) 100(60-170) application
8 5x5 15,900 26,500(dirty)  230(70-400) Glaze Booth closed
filter on 3 sides
10 4x6 11,120 -- -- Fly Very light
filter speck paint appli-
cation
12 Slot 15,900 14,100 70(30-140) Barrier; Airless:
veil barrier coat
lacquer air gun:
veil lacquer
13 Slot 15,900 12,100 40( 15-65) Veil Air gun
lacquer
14 5x5 15,900 27,000(dirty) 150(100-200) Lacquer Heavy
filter application

*Booths 2, 9, Tl, T5 not in use.

2-8


DISCUSSION

In various other processes during this study, it has been shown that applica-
tion of a coating material to interior cavities contributes significantly to
the mist and solvent exposure of spray painters. Visual observation of the
airless techniques used at this plant indicated a marked reduction in bounce
back of the overspray while painting the interiors of the file cabinets. These
observations were confirmed by the sampling data (Note: the lower 8-hour time-
weighted averages of paint mist for Painter 1 in Table 9-3).

The dry mesh prefilters that are fitted over the water curtain in the automatic
electrostatic spray booths tended to load quickly; however, these filters are
changed at the end of each workshift to reduce the possibility of overloading
the exhaust systems. In addition, booth cleanup time and subsequent exposures
are drastically reduced.

A similar prefilter system was installed in the first manual spray booth. This
additional filter had an adverse effect of the airflow patterns in the booth,
as shown in Table 9-1. The major effect was a 10 to 20 percent reduction of
the control velocity at the painters breathing zone.

Part hangers which are free from accumulated paint deposits are essential for
any form of electrostatic painting, in order to maintain grounding for the part
being painted. These hangers are typically cleaned by immersion in a high
temperature bath containing caustic soda, often requiring extended periods of
soaking. This time consuming and hazardous process was eliminated in this
plant by the installation of a burn-off oven followed by a high pressure
washer.


14.

15.

16.

7.

18.

19.

20.

21.

22.

23.

24.

25.

26.

27.

Stockinger, H.E. 1963. Chapter 27-The Metals. Industrial Hygiene and
Toxicology, Vol. II. Interscience.

TLVs Threshold Limit Values for Chemical Substances... With Intended
Changes for 1979. American Conference of Governmental Industrial
Hygienists, Cincinnati, Ohio, 1979.

Hueper, W.C. and W.W. Payne, 1959. Experimental Cancers in Rats Produced
by Chromium Compounds and Their Significance to Industry and Public
Health. American Industrial Hygiene Association Journal. pp 274-280.

Piper, R. 1965. The Hazards of Painting and Varnishing 1965. British
Journal of Industrial Medicine. Vol. 22. pp 247-260.

Selikoff, I.J. 1975. Investigation of Health Hazards in the Painting
Trades. National Institute for Occupational Safety and Health. Contract
CDC 99-74-91.

Mone, J.G. 1968. Organic Color Pigments. Federation Series on Coatings
Technology, Philadelphia. Federation of Societies for Coatings Techno-
logy, Unit 9, 33 pp.

Vallieres, M., Cockcroft, D.W., Taylor, D.M., Dolovich, J., and F.E.
Hargreave. 1977. Dimethyl Ethanolamine-Induced Asthma. American Review
of Respiratory Disease. Vol. 115.

Lemon, R.C. 1972. Epoxy Resins in Surface Coatings. Annals of Occupa-
tional Hygiene. Vol. 15, pp 131-6.

Fassett, D.W. 1963. Chapter 40: Organic Acids, Anhydrides, Lactones,
Acid Halides and Amides, Thioacids. Industrial Hygiene and Toxicology.
Vol. II. Interscience.

Fassett, D.W. 1963. Chapter 44: Cyanides and Nitriles. Industrial
Hygiene and Toxicology. Vol. II Interscience.

Hardy, H.L. and J.M. Devine. 1979. Use of Organic Isocyanates in Indus-
try-Some Industrial Hygiene Aspects. Annals of Occupational Hygiene.
Vol. 22. pp 421-7.

Ziegler, P.D. 1979. Industrial Hygiene and Urethane Coatings, Modern
Paint and Coatings.

Key, M.M., Henschel, A.F., Butler, J., Ligo, R.W., and I.R. Tabershaw
(Editors). Occupational Diseases, A Guide to Their Recognition. HEW
Publication No. (NIOSH) 77-181. U. S. Department of Health, Education,
and Welfare, Public Health Service, Center for Disease Control, National
Institute for Occupational Safety and Health. Rev. 1977. 608 pp.

Criteria for a Recommended Standard....Occupational Exposure to Refined
Petroleum Solvents. DHEW (NIOSH) Publication No. 77-192. U.S. Depart-
ment of Health, Education, and Welfare, Public Health Service, Center

57


PLATFORM

AIR y)
PLENUM

Figure 2-3. Ventilation heat relief for glaze wipers.
PROTECTIVE EQUIPMENT

Protective equipment is limited to the optional use of aprons or shop coats and
gloves. No respiratory protection is required at the environmental levels mea-
sured. For cleanup, waterless hand cleaner is available at the work stations.

EVALUATION

At this facility, twenty-seven employees are potentially exposed to paint sol-
vents or spray mist. This number includes 10 spray painters, 16 finish wipers,
and a crew chief/relief person. Potential sources of exposure include spray
mist and solvent vapors from spraying, solvent vapors evaporating from finished
cabinets, and (for the crew chief only) solvent vapors from paint system cut-
ting or mixing operations.

As_an index of control, the 8-hour time-weighted average (TWA) exposures to to-
tal spray mist and selected organic solvents were determined for the paint
sprayers. Area samples for total mist and selected solvents were taken at the
booth face of the robot spray painter to evaluate the performance of that SyS-
tem. The 8-hour time-weighted average exposures to selected organic solvents

2-9


producing sensitization is unknown. Because both the monomer and the polymer
have low vapor pressure, the main isocyanate hazard is associated with the
inhalation of the paint aerosol.

Table 5-1. Composition of finishing materials.

Gray primer sealer
47% Solids:

Modified alkyd resins ” 28%
Pigment 19%

53% Volatile:

Xylene and mixed aromatic
solvents 50%
Ethyl alcohol 1%

2% Additives: wetting agents, driers

Note: Drier is a lead soap; Total paint
is 0.13% lead by weight.

Enamel topcoat

43% Solids:
Acrylic modified alkyd resin 37%
Pigment (variable composition) 6%

57% Volatile:

Mineral spirits 42%
Toluene 5%
Xylene and other aromatics 3%
n-Butyl acetate 7%

Urethane additive (Mixed 8-16 oz. per gal. of enamel)
45% Hexamethylene diisocyanate (HDI) prepolymer
55% Solvent

Ethylacetate 32%
2-Ethoxy ethyl acetate 16%
Xylene 7%

54


Ne

125 ( ) {75

100

75

D>

150

Pr 7

125

Ao fh y

150

90

Figure 5-3. Spray booth air velocity.

5-7



Inorganic Pigments

Aluminum--
Finely divided aluminum metal is used to produce "metallic" paints. No acute
or chronic toxicity has been demonstrated in humans from aluminum metal.

Barite (Barytes)--
Barite is a crystalline mineral consisting essentially of barium sulfate.
Because it is insoluble, the potential for barium poisoning is low.

le umoroMiCS has been reported in workers inhaling barium containing
dusts.

Calcium--
Calcium carbonate is widely used as an extender pigment in paint. It is con-
sidered a nuisance particulate. 5

Chromium--

Both trivalent and hexavalent forms of chromium are used in paint pigments.
The trivalent form occurs in the pigments chromium oxide green and Guignet's
green (hydrated chromium oxide). The trivalent compounds possess a low order
of toxicity. !4 Hexavalent chromium occurs as the chromates of barium, lead,
strontium, and zinc. Hexavalent chromium compounds have been implicated in
excess lung cancer death rates in workers who produce chromates from chromite
ore and in handlers of chromium pigments. Hueper and Payne 6 determined
that hexavalent chromium ‘acts as a carcinogenic agent when it is present in a
form that provides for adequate biological availability, and that its avail-
ability is a function of the solubility of the chromium compound.

Lead--

Various lead compounds are used as pigments in paints. These include the ace-
tate, antimonate, borate, carbonate, chromate, molybdate, oxides, oxychloride,
phosphite, phosphosilicate, and sulfate. Piper!7 notes that in spite of the
differing solubilities of these materials in water, the hazard of plumbism, or
chronic lead poisoning, is always present and must be treated seriously. The
toxic effects of lead exposure are well documented. Lead poisoning is mani-
fested by general weakness; anorexia; insomnia; pains in the muscles, joints,
and abdomen; and anemia.

Silica and Silicates--

Silica (both crystalline and amorphous), and the silicates clay, diatomaceous
earth, mica, and talc are widely used as extender pigments. With the exception
of clay, all have been demonstrated to produce fibrosis of the lung. A preli-
minary study of the health hazards in the painting trades suggested that "mixed
dust pneumoconiosis" is common among painters. 8 While extender pigments
are used in substantial quantitites in some paint formulations, these materials
may be at least partially locked up by encapsulation in the resinous binder.

Titanium Dioxide--

Titanium dioxide is the pigment in greatest use in paints. It is considered a
nuisance dust.!5 A preliminary study of the health hazards in the painting
trades conducted in 1974 found that individuals who were heavily exposed to

26


switching back to an electrostatic gun when the area to be painted is within
reach. Painter B enters the wagon and sprays the interior with a pole gun for
about 20 minutes (Figure 8-3). He then rides the manlift to the side that is
opposite Painter A and paints that side in the same manner. Both painters in-
spect their work and touch up light areas as necessary. Painter A used the
electrostatic gun for approximately 80 percent of his work. Painter B used the
electrostatic gun for only 40 percent of his work,

After painting, the wagon is towed to the oven and connected to a floor con-
veyor. The conveyor draws the wagons through the 175°F oven, allowing a 40
minute cure.

Coating Material

The stack wagons are available in only one color. That color is attained by
an alkyd resin enamel containing lead chromate, iron blue, and titanium
dioxide pigments. This paint consists of 45 percent solids by weight. Of
that solid material, lead represents 11 percent and chromium represents 4
percent.

Figure 8-3. Finishing of wagon interior.

8-3


Each booth is equipped with a single centrifugal fan. The fans are rated at
10 hp and 10,670 cfm . The water curtain of the booths is provided by a 5 hp
pump, which is rated at 350 gpm. Each of the automatic electrostatic spray
booths is fitted with a thick mesh prefilter assembly that is similar to those
booths in Process A of this case study.

Airflow Measurements

Total airflow was measured in both of the manual booths and in two of the four
automatic electrostatic booths used in this process. Air velocity was measured
in the manual booths with a hot wire anemometer at 25 points in a horizontal
plane at an elevation of 4 feet and the measurements were averaged. Inlet air
velocities were also measured at the reciprocator venturi and at the conveyor
inlet vestibule of the automatic electrostatic booths. The results of these
measurements are reported in Tables 9-5 and 9-6.

Table 9-5. Manual spray booth data (Process 8B).

Average velocity (fpm)

Booth Total airflow (cfm) 4' above grate SD
I 20,800 80 60
Vestibule indraft 20 to 80
J 20,700 80 65
Vestibule indraft 10 to 75

Table 9-6. Automatic electrostatic spray booth data (Process B).

Velocity at recipro-

Booth Total airflow (cfm) cator venturi (fpm) SD
H 8, 300 60 16
L 10,200 25 18



e@ Heavy machinery (SIC major group 35--machinery, except
electrica

Nineteen candidate plants were selected for walk-through surveys. The walk-
through surveys were conducted to further identify control measures, to select
plant locations for evaluating specific processes and controls, and to finalize
sampling and documentation strategies. in-plant studies of engineering contro]
technology were completed for 11 spray finishing proceses. Results of these
studies are included in this report as individual case studies. Each case
study involves a distinct process and evaluates the techniques used to reduce
or eliminate employee exposure to potentially harmful chemicals. The selected
Processes are directly related to one of the above industries. These processes
are representative of the industry based upon the number of exposed workers,
different control techniques, and diversity of operations.

Other considerations governing the selection of processes that were studied
include:

@ Coating type and toxicity

e@ Application techniques

@ Engineering controls and work practices

@ Personal protective equipment

@ Product size and shape

e Substrate materials 5

@ Required finish performance and appearance
The report is organized in two parts. The first Presents an overview of
coatings technology, application methods, and the finishing practices of the
industries studied. Also included are summaries of the potential health
hazards, control methods reported in the literature, and the procedures used
to evaluate these control methods. Closing this part are the authors' conclu-
sions and recommendations regarding these control methods. The second part,
or appendix, of this report contains the case studies upon which these conclu-
sions and recommendations are based. Immediately following this introduction
is a paint/process/ control matrix (Table 1) that is intended to serve as a key
to the individual case studies. Each of these case studies includes:

@ A description of the process

@ An analysis of the hazard

@ Engineering controls, protective equipment, and work practices

@ Ventilation measurements

e@ Air sampling data


All coating materials are applied with conventional air-atomizing spray guns
operating at 50 to 65 psig. Either siphon or pressurized feed (at 15 psig) is
used; however, siphon-fed guns are generally restricted to striping or let-
tering operations. In order to coat the undersides Of the helicopter cockpit
area, the painter is required to lay on his back on a mechanic's creeper and
spray directly upward to the work area. A stepladder is used to gain access
to the tail and upper body sections of the helicopter. After the primer has
cured, a minimum of 2 coats of white or off-white base color are applied, using
the same equipment and application techniques. A 20- to 30- minute drying time
is provided between each coat. Base color use is approximately 4 gallons for
small ships and 6 gallons for the larger ships.

After application and curing of the base coat, the ships are manually tran-
sported to the Central Bay Area where color schemes, striping, and identifi-
cation markings are laid out and masked. Striping, identification markings,
and interior painting is generally performed in Booth 4 or 5 (Figure 1).
These spray booths are identical to Booths 1 and 3. Painting time varies with
ship size and the complexity of the individual color scheme. The ships are
then moved to the South Bay Area where seats and upholstery are installed and
general clean-up is performed.

Coatings

A variety of coating systems are available for the helicopters. The selection
of a particular system is based primarily upon the end use of the ship and upon
the customer's preference.

All ships receive a primer coat for corrosion protection. This coating system
can be described as a two-component, epoxy-polyamide resin system that contains
strontium chromate pigment. One component consists of a pigmented epoxy resin
based on bisphenol A and epichlorohydrin. The other component is a clear poly-
amide resin, containing a small quantity of the aromatic amine 2,4,6-tris
(dimethylaminomethy1) phenol. The two components are manually mixed before
application by slowly pouring the polyamide resin solution into the pigmented
epoxy component until a one-to-one volumetric ratio has been attained. Compo-
sition of the epoxy primer is described in Table 7-1.

Table 7-1. Composition of epoxy-polyamide primer.*

Component A Component B
Non-volatiles Volatiles Non-volatiles Volatiles

30% Epoxy resin 35% 2-Butanone 20% Polyamide resin 30% Ethanol

20% Strontium chromate -- 5% Aromatic amide 25% Isopropanol

15% Tale and diato- -- 20% Toluene
maceous silica

* Component A and component B are combined in a 1:1 volumetric ratio 30
minutes before use. Composition stated is approximate percentage by weight.

7-2


Table 7-4, Airborne levels of paint mist, strontium, and chromium
in light aircraft finishing: primer application.

Sample
Ship duration Total mist Strontium Chromium
number Operation (min) (mg/m3) (mg/m3) (mg/m3)
1 Prime 25 7.9 1.7 1.2
2 Prime 40 40.6 4.4 2.7
2 Prime 41 17.5 1.9 1.3
GM (GSD) 23.3(1.6) 2.4(1.7) 1.6(1.6)
OSHA PEL* 15 -- 1.0
ACGIH TLV (1979)* 10 -- 0.05
NIOSH* -- -- 0.001

GM: Geometric mean
GSD: Geometric standard deviation
*For full shift exposures.

The exposures to organic solvents reported in Table 7-5 are well below any
existing or proposed standards for the materials used.

7-10


cost of the paint consumed is so small when it is compared to the total labor
involved that paint savings from the improved techniques would not justify the
expenditure.

Many components of the coatings in use have not been evaluated for chronic
toxicity, or serious questions have been raised about the adequacy of current
legal maximums, Unfortunately, suitable substitutes have not been found for
all of these materials, and even improved ventilation controls may be incap-
able of reducing these hazards to an acceptable level. Until solutions are
found, a good program of protective equipment and medical supervision is
essential. Because the greatest hazard is associated with the inhalation of
the paint aerosol, respiratory protection is the foundation of such a program.
Because of the improved fit and the better protection against eye irritation,
a full face piece respirator is recommended. A supplied-air respirator is
preferable not only for its high degree of protection, but for its increased
comfort in hot weather.


paint. The basic objective in spraying is to apply the finish with a minimum
of fog and overspray loss. The correct balance of air and fluid supply to the
gun is crucial; the painter must use the lowest possible air pressure that will
give the necessary degree of atomization. Muirhead?! notes that excessively
high air pressure is a prime factor contributing to poor quality work,

Because spray booths function by directing clean air past the worker towards
the process, the operator must not position himself between the object being
painted and the point of exhaust. Some typical examples of situations where
this occurs are illustrated in Figure 4.

In Figure 4-a, four sides of an object are sprayed in a side draft booth. By
incorporating a turntable, all four sides can be painted without the operator
being covered with his own overspray. A similar situation occurs when internal
cavities are sprayed as in Figure 4-b. The painter's breathing zone can be
removed from the area of active mist generation if an extension or pole gun is
used. Airless spray equipment is useful for such cases because of its inherent
low mist generation and its superior coverage of deep recesses. In the last
illustration (Figure 4-c), an operator is spraying a tall object in a downdraft
booth. Stepladders, platforms, or manlifts can be employed to avoid exposure
to the spray backwash.

4)


SECTION I. INTRODUCTION

The National Institute for Occupational Safety and Health (NIOSH) is charged
with the responsibility of conducting research and developing criteria for the
advancement of health and safety in the workplace. In order to expand the
knowledge of available options for the solution of occupational health prob-
lems and the constraints that influence the selection of these options, NIOSH
has sponsored a series of industry-wide control technology evaluations. The
goals of these evaluations or assessments are to stimulate private industry to
prevent hazardous exposures of workers, and to establish a catalog of solutions
by documenting successful application of control measures. These studies seek
to identify the best control techniques practiced by different companies, en-
courage the dissemination of this knowledge across industries, and outline con-
trol technology research needs; this is all done to aid in the voluntary appli-
cation of demonstrated control technologies.

This report presents the findings of a state-of-the-art study of available
technology associated with the spray application of industrial finishes.
Manual rather than automatic application was emphasized in this study because
of its greater potential for worker exposure. Spray finishing operations were
selected for study for several reasons. First, industrial finishes employ many
substances long recognized as health hazards. Spray booths have been widely
used to control these hazards, but no systematic study of their effectiveness
had been undertaken. Second, coatings technology has changed rapidly with the
introduction of many new materials, some of which represent toxic hazards.
Last, parallel developments in paint application methods promised new ways of
reducing worker exposure in spray finishing operations.

The study began with a review of available data on industrial finishing pro-
cesses and equipment, and any hazards associated with their use. Based upon
this information, five Standard Industrial Classification (SIC) groups directly
associated with spray finishing were identified for inclusion in the study. !
These industries are:

@ Automobile refinishing (SIC major group 75--automotive
re- pair, services, and garages)

@ Wood and metal furniture finishing (SIC major group 25--
furniture and fixtures)

@ Appliance finishing (SIC group 363--household appliances)

e@ Non-automotive transportation equipment (SIC major group
37--transportation equipment, excluding subgroup 3711--
motor vehicles and passenger car bodies)



tion of the required protection. Generally, a respiratory protection program
should be viewed as only an interim measure, not as a substitute for suitable
engineering controls. Where respiratory protection is required, a full face-
piece style is recommended because of increased wearing comfort, higher degree
of protection, and the added eye protection.

Distance

Automation of the paint application process is one means of isolating the
worker from the hazard. There are two fundamentally different methods of auto-
mating spray finishing operations. The first method involves mounting the
spray guns in fixed positions or on a reciprocating assembly. The product
items are painted as they pass by the assembly on a conveyor. The parts may be
rotated as they are painted. This type of automation is designed and built for
the requirements of a limited product line, where the size and shape of the
objects finished are easily definable. Manual paint sprayers are often re-
quired for touch-up. The second method of automation involves the use of pro-
grammed robots. These machines can accommodate production runs of various
sizes and shapes. Since they can duplicate virtually all of the movements of
a manual spray painter, the use of robots allows for the removal of workers
from potentially hazardous areas or unhealthful working conditions.

GENERAL VENTILATION

Ventilation systems can be either local or general in nature. A general venti-
lation system supplies and exhausts large volumes of air in an attempt to
dilute air contaminants. General ventilation can successfully control the
build up of explosive vapors in enclosed spaces.

The practice of placing a fan in a manhole, doorway, or window is not satisfac-
tory because the air is circulated only at the opening; the fan does not move
or dilute the air in other portions of the enclosed area. Munger43 recom-
mends that clean air be drawn into the enclosed space from an opening at the
top by exhausting air from the lowest portion of the enclosed area as shown in
Figure 1.

Reichenbach44 describes a similar procedure for ventilating the spray
painting of ship holds and tanks. He recommends that painters in enclosed
areas should wear supplied-air type respirators. The fan capacity required
for dilution ventilation can be calculated from the lower explosive limits for
the solvents employed and the paint application rate, using the formulas in
Industrial Ventilation: A Manual of Recommended Practice.4°

LOCAL VENTILATION-SPRAY BOOTHS

Excessive quantities of air need to be handled to protect the breathing zone
of a spray finisher solely by the use of general ventilation. Hence, indoor
spray finishing operations are usually controlled by ventilated spray booths.
They function by directing relatively uncontaminated air past the worker
towards the process, and into a collection point or exhaust hood. The source
of the uncontaminated air may be a tempered fresh air supply or simply general
workroom air.

35


polymerization. This oxidation is catalyzed by the presence of a lead soap
drier. Several ounces of a baking converter additive are sometimes added by
the painter; this material is a mixture of acrylic and urea resins and a
wrinkle inhibitor, mixed in a solvent. This additive confers some thermoset-
ting qualities to the finish. Despite the use of the bake converter, the basic
function of the oven is to promote rapid evaporation of the solvent rather than
providing a true baked finish. The finish continues to cure over several
months.

Enamel finishes are used for total body repainting because with them, no hand
rubbing is necessary to gain a high gloss surface film; lacquer finishes, on
the other hand require hand rubbing. The rapid cure of lacquer finishes per-
mits the painter to blend spot repairs into undamaged areas, which makes this
type of finish more popular in body repair shops.

The alkyd resin that is used in the enamel topcoat is modified by the addition
of an acrylic resin with hydroxyl groups. This resin not only improves the
durability of the finish, but allows the use of a polyisocyanate cross linking
agent in order to provide a chemically-cured, urethane paint film. This iso-
cyanate hardener consists of prepolymers of hexamethylene diisocyanate (HDI),
mixed in a solution of ethyl acetate, 2-ethoxy ethyl acetate, and xylene.
Free isocyanate comprises less than 0.7 percent of the resin fraction at manu-
facture, but may increase to 1.6 percent with age. Eight to sixteen ounces of
this optional isocyanate hardener are added to each gailon of enamel (at extra
cost to the customer). Approximately 10 percent of the customers of this fa-
cility choose the isocyanate-modified urethane finish. The composition of the
finishing materials is listed in Table 5-1.

HAZARD ANALYSIS

The organic solvents employed in these formulations all exhibit similar physio-
logical effects. In general they are irritants to the conjunctiva and to the
mucous membranes of the upper respiratory tract. They all produce depression
of the central nervous system and, at high concentrations, produce symptoms of
headache, nausea, and drowsiness, followed by unconsciousness.

The non-volatile components of the coating formulations are for the most part
physiologically inert. Exceptions are lead and chromium, which are present as
chrome yellow and molybdate orange pigments that are used in many yellow and
red colors, and the lead soaps that are used as driers. According to the
coating formulator, lead can account for up to 15 percent of the total paint
weight in certain shades of red. Lead is a cumulative poison that affects the
red blood cells and produces damaging effects on the tissues it contacts. Lead
chromate (chrome yellow) has been implicated as a lung carcinogen in workers
who produce chromate pigments.

The isocyanate hardener, used to a limited extent for premium body repainting
Jobs, is a prepolymer of hexamethylene diisocyanate (HDI), and contains small
quantities of residual monomer. The monomeric material is a lacrimator and
irritant, and produces respiratory sensitization in certain individuals. The
prepolymer and the monomer have an acute inhalation toxicity that is of the
same order of magnitude as the monomer, but the prepolymer's capability for

5-3


SECTION III. SPRAY APPLICATION METHODS

Industrial finishes are commonly applied by spraying because of the excellent
finish that can be obtained and the speed at which the coating material can be
applied. The spray can be generated by compressed air, by hydraulic pressure,
or by electrostatic forces. This section briefly describes these three meth-
ods. Section IV describes the industries in which spray painting was studied
for this report. The hazards associated with these methods and their relative
advantages in terms of worker protection are discussed in Sections V and VI.

COMPRESSED AIR METHOD

The compressed air spray gun is the most widely used because of its versa-
tility, its low cost, and because it creates a high quality finish. In this
method, compressed air provides the energy to atomize the finish. The atomi-
zation is produced by an air nozzle. Two types of nozzles are used: external
mix and internal mix nozzles. In the external mix nozzle, the coating and the
compressed air exit from separate orifices and are mixed outside the nozzle.
The air jet atomizes and shapes the spray fan. Internal mix nozzles combine
the compressed air and finishing materials in a chamber inside the nozzle.
The atomized mixture is shaped by the geometry of the chamber opening.

Finishing materials can be delivered to the spray gun under pressure, or by the
siphoning action of a siphon-fed, external mix nozzle. Siphon-type guns re-
quire small paint containers attached directly to the spray gun, thus they are
limited to low volume applications. Because siphon-fed guns require more com-
pressed air than pressure-fed equipment, they produce more stray mist.

Heated paint can be applied by air-atomized equipment. Heating the paint low-
ers the viscosity, which reduces the amount of solvent required. The finish
cools rapidly after it is sprayed, which creates an applied coat that is much
more viscous than a coat that is sprayed unheated. This process permits appli-
cation of heavier films; applications also dry more rapidly. Finishes can be
applied at lower air pressures, which reduces the amount of stray mist
generated.

AIRLESS METHOD

Airless spray equipment atomizes paint by forcing it through a very small ori-
fice at a very high pressure. The airless spray gun consists simply of a de-
vice to hold the orifice and a valve for shutting off the flow. The size and
shape of the nozzle determine the volume of material sprayed and the geometry
of the spray pattern. The hydraulic pressure necessary for atomization is pro-
vided by a high pressure pump that is operated by compressed air or an electric
motor.

Like air-atomized equipment, airless systems can be used to spray heated paint

14


used isocyanate, followed by the so-called prepolymers. They are adducts of
polyols with isocyanates, in which either of the components is in considerable
excess of the other. The resulting intermediate is a medium molecular weight
polymer that has reactive isocyanate groups. In addition to toluene diiso-
cyanate, dipheny] methane diisocyanate is another aromatic isocyanate of com-
mercial importance. Aliphatic isocyanates are used for coatings with superior
light fastness and gloss retention. Important aliphatic isocyanates include
hexamethylene diisocyanate, methylene dicyclohexy] diisocyanate and isophorone
diisocyanate.

Urethane coatings can be classified according to curing mechanisms as: oil-
modified, moisture-cured, blocked, prepolymer plus catalyst, prepolymer/polyol,
and lacquers, !0

Oil-modified urethane coatings are made by reacting a drying oi] with an iso-
cyanate to form an urethane-oil resin. The ratio of isocyanate to hydroxyl is
adjusted in order to leave no reactive isocyanate groups in the finished resin.
Oil modified urethane coatings are one-package systems that cure by the oxida-
tion of the unsaturated oil portion of the polymer. Driers, such as cobalt
naphthenate, catalyze air drying.

Moisture-cured urethane coatings are one-package prepolymer systems that are
characterized by the presence of terminal isocyanate groups. These systems
cure into useful films by reacting the free isocyanate groups with ambient
moisture.

Blocked urethane coatings are one-package systems. They are relatively inert
at room temperature because the isocyanate has been reacted with a "blocking
agent." Phenol, caprolactam, cresol, and methyl] ethyl] ketoxime are typical
blocking agents that volatilize or break down when heated to 160°C or higher.
When this occurs, the isocyanate radicals are released and readily react with ©
substances, such as polyesters, that have active hydrogen groups. This reac-
tion is normally catalyzed with dibutyltin dilaurate.

Prepolymer-plus-catalyst urethane coatings are two-package systems that cure
by reacting an isocyanate prepolymer with a relatively small amount of cata-
lyst, such as a monomeric polyol or polyamine contained in a second package.
This coating system is essentially the same as the moisture-cured system, ex-
cept that the catalyst is provided in a separate package to allow an acce-
lerated cure. Methyl diethanolamine is a common catalyst.

Prepolymer/polyol urethane coatings are two-package systems that cure by
reacting a prepolymer with a substantial quantity of a second package con-
taining a polyol or polyamine and a small amount of catalyst. Polyols typi-
cally found include: polyethers, polyesters, polycaprolactone polyols, and
castor oi] derivatives. Dibutyltin dilaurate and zinc octoate are a typical
catalysts.

Urethane lacquers are one-package coating systems that dry by simple solvent
evaporation. In these lacquers, prereacted urethane polymers are combined
with nitrocellulose or thermoplastic acrylics to produce a durable finish.




SUPPLY AIR
PLENUM a

bid
Aq

SG wh

20°

Figure 6-3. Cross-section of automatic
electrostatic spray room.

PROTECTIVE EQUIPMENT

At the start of each workshift, painters and system operators don clean cover-
alls. Respirator usage is limited to liner painting operations. The respi-
rators used in that operation are of the supplied air variety (NIOSH approved),
with a replaceable plastic viewing window, cloth cap, and loose-fitting, plas-
tic coated, cloth hood.

EVALUATION

Eight employees are potentially exposed to paint solvents or spray mist in this
operation. This number includes 5 spray painters, 2 operators for the auto-
mated equipment, and a mix room attendant. Potential sources of exposure
include spray mist and solvent vapors from spraying, solvent vapors evaporating
from finished cabinets, and (for the mix room attendant) solvent vapors from
paint thinning operations.

As an index of control, the 8-hour time-weighted average (TWA) concentrations
of total spray mist, lead, toluene, and xylene were determined for the hand
sprayers. Four hand sprayers spend their entire workshift in the spray booth
except for scheduled breaks and a 30 minute lunch period. The fifth painter
serves as a relief and as an additional sprayer for embossed doors. Because
of the extended periods spent outside the booth, the exposure of this worker
was not evaluated. The 8-hour TWA concentrations were calculated from separate
Morning and afternoon samples.

Total mist and lead samples were collected using closed-face cassettes with
preweighed 37 mm polyvinyl] chloride membrane filters and personal pumps

6-5


DEAD AIR SPACE

A—Y <-~VVCH

D-P <rvVCW

EXHAUST

Figure 4-5. Side view of airflow patterns in a semi-downdraft booth.

neck and wrists. A full-facepiece, supplied air respirator, and rubber gloves
are worn during painting, so no skin is exposed.

The facepiece of the respirator is kept clear by stretching clear plastic food
wrap over the viewing window. Up to 10 sheets of wrap are applied, leaving
tabs around the circumference of the facepiece. The tabs allow the sheets to
be removed singly, as they are contaminated by overspray. A contaminated sheet
is shown alongside a freshly wrapped respirator in Figure 4-6.

The full-facepiece respirator offers maximum protection against air contami-
nants, with little inconvenience to the painter. The full-facepiece is more
comfortable than a half-mask because the pressure of the attaching strips is
distributed over a larger facial area. In addition, for the full-facepiece, no
goggles are required to protect the eyes from the potentially irritating compo-
nents of the overspray. The respirator airline does not hinder operations,
because the painter must drag the paint line along anyway.

WORK PRACTICES

The painters are careful to work on opposite sides of the railcar, thus minimi-
Zing direct contact with the each other's overspray. However, the painters are
careless about their own overspray, often painting the upper half of the car
from floor level. Access platforms that would permit proper orientation of the
painter with respect to the downdraft airflow are provided.

EVALUATION

Two painters are required to finish a railroad car. A third painter rotates
assignments with the others. In addition to painting, the painters are respon-
sible for moving the cars in and out of the booth, applying decals, mixing
paint, maintaining spray guns, and general housekeeping in the paint area. To
determine control effectiveness, breathing zone concentrations (outside respi-
rator) of total spray mist, lead, chromium, and organic solvents were deter-
mined by personal air samples taken during the time required to paint each hop-
per car. Total mist, lead, and chromium were collected using closed-face
cassettes with 0.8 u polyvinyl chloride/acrylonitrile membrane filters at a
sampling rate of 2.0 lpm. After weighing, the filters were ashed and analyzed

4-7


In the first’ section of the powder booth, the spray operator applies powder to
the panel edges that are not accessible to the automatic equipment. In the
next section, three reciprocating guns apply a 2-mil coat to the appearance
side, the panel rotates, and two guns attached to the same reciprocating
assembly apply a 0.5-mil coat to the back half. All guns are electrostatic
and operate at 90 kV. Powder delivery to the three guns that coat the
appearance side is 22 lb/hr. Each of the two guns Coating the opposite side
is supplied at 11 lb/hr. All guns are rated at a maximum of 40 lb/hr.

TO OUST COLLECTOR

PAINT

PAINT.

EXPLOSION VENT
(TO ROOF )

2" VENT TO
DUST COLLECTOR
(HIEFF FILTER)

PAINT,

y

Ay

PAINT x

[ ‘eo
PAINT FLUID FLUID

‘RUM BED No.1 BED No.2
(VIRGIN: :
TANK)

PAINT

Figure 1-2. Schematic of powder flow.

The excess powder (powder overspray) collected in the powder booth is sepa-
rated from the air stream by a cartridge-filter-type dust collector. Powder
from the dust collector hopper is returned to the sieve via an aspirator, and
then discharged to the powder reservoir (second fluidized bed) for reuse.

After receiving the coat of powder, panels are conveyed from the powder
painting unit to a baking oven. A temperature of 360°F, maintained for 12
minutes, fuses the powder and activates the cross-linking agent.

Coatings

Both colors are pigmented acrylic resin powders. Approximately 50 percent, by
weight, of the powder is a hydroxyl modified acrylic resin. The hydroxy]
groups are incorporated into the acrylic polymer during manufacture to provide
reaction sites for an isocyanate cross-linking agent. This cross-linking agent
is a polymeric isocyanate whose active isocyanate groups are chemically blocked
by caprolactam. At baking temperatures, the caprolactam is released and the
active isocyanate is regenerated.


Both liquid paint and powder coating lines are highly automated, but hand-held
conventional and airless spray guns are still used in reinforcement operations,
It is common for defective coatings to be manually reworked. The commonly used
resins, solvents, and pigments are shown in Table 7.

Table 7. Metal furniture (and fixtures).
(resins, solvents, and pigments as percent of total consumption)4

Per- Per- Per-

Resins cent Solvents cent Pigments cent
Alkyd 39 Aliphatic 36 Titanium 60

hydrocarbons dioxide
Amino 12 Xylene 18 Iron 9
Acrylic iW Toluene 10 Barytes 7

MEK 10 Talc 6
Vinyl VW Other 9 Calcium 6

aromatics carbonate
Polyester 6 n-Butanol 5 Chromium 3
Other 16 Other 12 Other 9
Cellulosic 5

MAJOR APPLIANCES

This industry is a part of SIC major group 34 (Fabricated Metal Products,
except Machinery and Transportation Equipment) and 36 (Electrical and
Electronic Machinery, Equipment, and Supplies). These establishments are pri-
marily engaged in the manufacture of household ovens, ranges, grills, freezers,
refrigerators, and laundry machinery. They also include different types of
heaters, gas-oil burners, domestic furnaces, air conditioners, and different
types of refrigeration equipment.

Before coating, the metal surfaces are prepared in order to remove rust, oil,
and other unwanted material, and to passivate the surface. Treatment generally
involves eight automated stages, consisting of alkali cleaning, double water
rinsing, and a zinc-phosphate bath, followed by water, chromic acid, and deion-
ized water rinsing.

Primers are generally applied by electrocoating in a water bath that contains
8 to 10 percent paint material. As alternatives to this method, dip and flow

19


The interior dimensions of each booth are 24 feet wide by 70 feet long by 20
feet high. Both ends of the booth are equipped with full height, roll-up doors
with access doors at the side. The top of the booth consists of a supply air
plenum containing polyester filters. The plenum chamber measures 3-1/2 feet
high by 15 feet wide and runs the length of the booth. Air is supplied to the
plenum through 4 supply air ducts. The floor of the booth contains 2 parallel
exhaust grates, each 2-1/2 feet wide and running the length of the booth. A
pit, covered by removable plates, is available to facilitate painting of heli-
copter underbodies, but is not used. An under the floor exhaust plenum aids
in air distribution and houses the overspray filters. These filters consist
of a non fire-supporting paper folded into accordian style pleats with stag-
gered air holes. The filter media is arranged in 3 rows along the wall of the
plenum.

Both inlet and exhaust filters are changed at 5 week intervals. Five ducts per
booth route exhaust to roof-mounted, vane axial fans. Exhaust fans are rated
at 34,000 cfm each, for a booth exhaust rate of 170,000 cfm. This exhaust rate
corresponds to a nominal downdraft velocity of 100 fpm within the booth. Four-
teen make-up air heaters with evaporative coolers, can supply a total of
588,000 cfm of tempered air to the spray booths. The make-up air that is
available limits the total number of booths in use at one time. Five of the
make-up air heaters are capable of producing a 120°F temperature rise,
allowing the booths to serve as curing chambers. During the curing cycle, the
booth airflow is reduced to 56,000 cfm.

Airflow Measurements

Ventilation measurements were performed in 2 of the spray booths and reported
in Table 7-3. Total exhaust was within + 10 percent of the design rate for
both booths. Air velocities at the exhaust grates showed little variation as
a result of good air distribution by the exhaust plenum (grate velocity was
twice the theoretical plenum velocity). Air velocity within the booths varied
considerably with both time and position, from a low of 10 fpm near the walls
to 300 fpm near the fresh air plenum. Figure 7-4 illustrates booth airflow

patterns.
Table 7-3. Ventilation mesurements for
light aircraft finishing.
Booth No. 1 Booth No. 2
Exhaust: Exhaust:
West grate 92,000 cfm West grate 92,000 cfm
East grate _ 88,000 cfm East grate 67,000 cfm

Total 80,000 cfm

Control velocity:
Average 110 fpm

Range 50 to 300 fpm

Total 759,000 cfm

Control velocity:
Average 95 fpm

Range 10 to 250 fpm



Water emulsions of thermoplastic materials form films by coalescence. In latex
coatings, the dispersed solids are coated with an emulsifier to prevent floccu-
lation; typically the dispersed solids have a particle size of less than one
micron. The formulation of those products utilizes a coalescing agent that
permits film formation by the contact and fusion of adjacent resin solids upon
evaporation of the water.

Film Formation by Convertible Binders

Convertible binders form paint films by irreversible transformations brought
about through oxidation, heat conversion, catalytic action, chemical cross-
linking, or moisture activation.

Coatings that contain drying oils produce films by oxygen conversion. These
oils absorb oxygen from the air, forming oil-peroxides, which subsequently de-
compose, cross-linking the polymer by covalent bonding. Lead and cobalt soaps
are commonly used in the formulation in order to accelerate drying. water
soluble binders can be produced by the reaction of an amine with an acidic
resin/oil, resulting in an amine salt.

Heat can be applied to oxygen-convertible coatings in order to accelerate the
reactions; however, there are true heat convertible, or thermosetting, resins
that require the application of heat to initiate the reaction. This reaction
can be accomplished by the use of a single resin or the combination of two
resins that interact to form insoluble polymers. These resins are often com-
bined with thermoplastic or oxygen-convertible resins in order to promote
specific desirable properties.

Certain resins can be made to cure at room temperature by using a catalyst.
However, coatings made from these resin systems have the disadvantage that they
are normally two-component systems.

Resins can form paint films by the action of a cross-linking agent. This
method of film formation is often confused with catalytic conversion, because
both are two-package systems. Polymerization by means of a cross-linking agent
is initiated at ambient temperatures by the reaction of a polymer and a mono-
mer, or by the reaction of two polymers, rather than the catalyzed reaction of
a single constituent. An insoluble, three dimensional molecular structure
results from the cross-linking of the molecules of two materials.

Certain urethane resins form films by the reaction between isocyanate groups
and airborne moisture.

COMPOSITION

The major constituents in industrial finishes can be grouped into four general
categories: 1) binders, or film formers; 2) pigments; 3) volatile solvents; and
4) additives.

Binders

Binders, or film formers, are the non-volatile portion of the liquid components
of a coating. They bind, or cement, the pigments and the paint film to the

5


coatings have been reported to cause asthma-like symptoms and urticaria when
applied under conditions of poor ventilation, The use of the polyamide resin
should preclude these manifestations. The aromatic amine 2,4,6-tris (dimethyl-
aminomethy1) phenol is a minor constitutent of the curing agent. It has been
evaluated for acute toxicity, and, like phenol, is corrosive. It possesses
the same order of dermal toxicity as phenol. The long-term effects of exposure
are unknown; however, several of the aromatic amines have been shown to be car-
cinogenic in humans or animals or both.

The pigment portion of the primer contains substantial quantities of the cor-
rosion-resistant pigment, strontium chromate and the extender and filler pig-
ments, talc and diatomaceous silica. Strontium chromate has been determined
to induce cancer in animals at the site of implantation and has been implicated
as a lung carcinogen in workers who manufacture chromate pigments.

Talc and diatomaceous silica can cause fibrosis of the lung. These materials
are at least partially encapsulated in a paint resin matrix, which may act to
limit their biological availability. However, in no case would a hazard exist
from the extender pigments at paint mist levels of 15 mg/m3 or less, based
on the fraction of the paint solids represented by these materials.

The solvents that are used in the primer pose no unusual hazards that are not
associated with other paints.

Topcoat

The polyester resin component of the urethane topcoat is similar to resin
systems used in conventional coatings. This resin presents no known toxic
hazards. The isocyanate activator, a prepolymer of HDI, contains a small
quantity of residual monomer. The level of free monomer may increase during
storage. The monomeric material is an irritant to the eyes and respiratory
tract, and produces respiratory sensitization in certain individuals.

The prepolymer is of the same acute inhalation toxicity as the monomeric
material. Its capability of producing sensitization has not been demonstrated;
however, the fact that the monomeric materials have produced sensitization
should not be ignored when discussing the polyisocyanates. Because both mono-
mer and polymer are materials of low vapor pressure, the principal isocyanate
hazard is associated with the inhalation of the paint aerosol. The polyiso-
cyanate represents about 15 percent of the paint solids in this formulation.
If the polymeric material does pose the same sensitization potential as the
monomer, then a safe limit for total paint mist would be about 1 mg/m3, No
instances of sensitization have been reported by this plant in five years of
use; however, all painters wear respirators.

Pigment hazards vary with the topcoat color. Inorganic pigments are weak
colors and require considerable pigment to produce the depth of color desired.
The principle hazards are associated with yellow, orange, and red. Lead con-
tent ranges from 8 to 20 percent of the dried film.

Current standards for organotin compounds are based on analogy with mercury,
thallium, and selenium compounds. Indications are that the dialkyl tin com-
pounds are Jess toxic than the tri- and tetra-alky] compounds.

7-4


CASE STUDY 10
PAINT STORAGE AND MIXING

Work practices and equipment that minimize solvent evaporation are employed
together with dilution ventilation in order to limit the exposure of paint
room attendants to organic solvent vapors.

PROCESS
Operations

Approximately 750 gallons of paint are mixed and delivered each shift to the
paint booths in this plant, which produces components for metal office furni-
ture. The paint mixing and storage room is manned by two attendants. The
senior attendant is responsible for inventory control, and for mixing and thin-
ning raw paint to application viscosity. The other attendant assists him in
these duties and, in addition, is responsible for clean-up details.

The 5,000 square foot room is organized into storage areas for paint and empty
drums, solvents, and paint mixing tanks as shown in Figure 10-1. Because not

Figure 10-1. Paint mixing and storage room.

10-1


Coating application is generally by airless or electrostatic-airless spray
technology; however, dipping and flow coating are also used. Despite some
automatization, most top coating is done by hand-spray equipment. As a curing
method, air-dry and force-dry techniques are’ mainly used. The most common
resins, solvents, and pigments can be found in Table 12.

Table 12. Machinery and equipment (resins, solvents, and
pigments as percent of total consumption) .4

Per- Per- Per-
Resins cent Solvents cent Pigments cent
Alkyd 48 Aliphatic 51 Titanium 54
hydrocarbons dioxide
Acrylic 13 Other 9 Talc 9
aromatics
Amino 0] Xylene 6 Chromium 6
Other 6 Lead 2
ketones
Epoxy 5 Other 28 Clay 6
Other 23
Urethane 5
Other 18

24


CASE STUDY 9

METAL FURNITURE:
CONVENTIONAL AND HIGH SOLIDS COATINGS

File cabinets and office partitions are finished with high-solids polyester or
acrylic baking enamels in two separate plants. Both plants apply identical
coatings in similar processes. Differences in product shape require different
degrees of manual reinforcement and slight variations in application equipment.
The appropriate selection of application equipment and spray booths result in
low levels of paint spray mist and organic solvents with both product lines.
Airless equipment was selected for painting the interiors of filing cabinets
in a succesful attempt to reduce the bounce-back of paint overspray in that
operation.


Figure 10-3. Paint mixing drum with loose fitting
lid and clamp-on agitator.

HAZARD ANALYSIS

The principal hazard to which the paint room attendants are exposed is from the
inhalation of organic solvents. The solvents come from two sources: rapid
evaporation during filling and pouring, and slow evaporation from paint con-
tainers, spills, and leaks. Xylene and an aromatic petroleum distillate are
the main constituents of the short exposures during pouring operations. These
materials, together with other solvents in the raw paint formulations, n-bu-
tanol and butyl acetate, contribute to the background concentration. All of
these solvents exhibit similar physiological effects. They are irritants to
the conjunctiva and to the mucous membranes of the upper respiratory tract.
They all produce depression of the central nervous system and, at high concen-
trations, produce symptoms of headache, nausea, and drowsiness, followed by
unconsciousness.

VENTILATION
A dilution ventilation system introduces fresh air through registers located in

10-3


Table 3-1. Spray booth airflow rates.

Supply (cfm)

Exhaust Behind Control velocity
Booth (cfm) Total painter Vestibules (f pm)
Prime A 9,000 33,000 16,000 17,000 60
Prime B 14,000 25,000 10,000 15,000 50
Finish A 44,000 32,000 14,000 18,000 140
Finish B 25,000 27,000 13,000 14,000 80
Special 20,000 35,000 11,000 24,000 60
Design 27,800 31,600 NA NA 118

The heavy paint buildup on the exhaust filters in both prime booths caused the
exhaust flow to drop off considerably. The exhaust flow for Prime Booth A was
only one-third the design value. The heavy paint buildup in this booth could
be attributed to the operation of reciprocator-mounted spray guns. Exhaust
filters on both this booth and the others were replaced every three to six
workshifts. Based on the low exhaust flow, this service period is considered
too long. Measured total supply rates presented in Table 3-1 were within + 10
percent of design specifications. ~

The proportioning of make-up air between the vestibules and booth supply air
inlets varied considerably. Increased quantities of fresh air supplied to the
vestibules resulted in a net decrease in air movement in the painters’ breath-
ing zone, as shown in Table 3-1 and Figure 3-3. Spray mist was observed
escaping from booths which had a severe imbalance of supply and exhaust air.

PROTECTIVE EQUIPMENT

At the start of each workshift, painters don clean coveralls and either rubber
or cloth gloves (at their option). During the painting operations, they wear
a supplied-air respirator (not NIOSH-approved) that has a replaceable plastic
viewing window, cloth cap, and loose fitting cloth hood. In an earlier survey
by the company's insurance carrier, reported solvent levels inside the hood
were slightly higher than in the breathing zone outside the hood. This was
probably because the respirator hood fabric was permeated by liquid paint or
solvent. The respirator did appear to offer protection from the paint over
spray. Volumes and pressures of the respirator supply air were regulated,
within certain limits, by the individual painters.

3-5


Polyurethane enamels are the standard exterior finish and constitute over 80
percent of the topcoats that are applied. Acrylic lacquers are also available
on a special order basis. Epoxy enamels used for cockpit and cabin interiors
comprise the balance of paint usage. The polyurethane enamel topcoat system
is a two-component, air dry, aliphatic type material. One component of this
system consists of a pigmented, hydroxylated, acrylic polyester resin solution,
containing a small quantity of an organotin catalyst (dibutyltin dilaurate).
The second component, or activator, is a clear isocyanate prepolymer based on
hexamethylene diisocyanate (HDI) in a solvent solution. The prepolymer is a
mixture of the biuret compound of HDI and other trimers. The two components
are mixed before application in a 3 to 1 volumetric ratio. In order to speed
the curing time, approximately 4 ounces of a solution containing dibutyltin
dilaurate are added to each gallon of the mixture.

The heavy metal content in the exterior finishes varies widely with their
color. Lead content of the dried film can range from 8 to 20 percent in
oranges, yellows, and reds while other colors are essentially lead-free.
There are no cadmium-containing pigments formulated by the manufacturer of
this coating system. Composition of the polyurethane enamel is described in
Table 7-2.

Table 7-2. Composition of polyurethane enamel.*

Component A

Component B (activator)

Non-volatiles Volatiles

Non-voTatiles Volatiles

53% Pigment** in 29%-Ethoxyethy]

modified poly- acetate
ester resin
16%-Ethy]
acetate

2%-Al iphatic
hydrocarbons

39% Polyisocyanate 5%-Ethoxyethy]

acetate

56%-Ethy]
acetate

Accelerator:
dibutyltin
dilaurate ina
solvent

* Component A and component B are combined in a 3:1 volumetric ratio. the
accelerator is added at a rate of 4 ounces per gallon. Composition stated

is approximate percentage by weight.

**Pigment primarily titanium dioxide; orange, yellow, and red colors may
contain from 8 to 20 percent lead in dried film.

HAZARD ANALYSIS

Primer

Solid, uncured epoxy resins found in solvent-based epoxy primers seldom cause

any dermal irritation or sensitization.
major component of the curing agent is also relatively harmless.

The polyamide resin, present as the
Amine-cured

7-3


Table 2-6. Airborne solvent levels in lacquer operations.

8-hour time-weighted average (mg/m3)

Booth Date (a) (by (ey (dy (ey UF) Ca) Ch) Cer
6 9/10 2 6 10 6 <12 2 2 12 0.12
6 9/11 2 6 7 6 <7 3 1 9 0.10
7 9/12 2 5 <6 4 <8 3 1 9 0.08
7 9/13 <l 3 5 4 <7 4 3 27 0.09
14 9/12 8 24 15 14 VW 5 4 23 0.21
14 9/13 10 25 18 15 in) 7 5 27 0.23

Back ground(GM)** 1 2 <3 1 4 1 1 <4 --

OSHA PEL* 980 700 300 750 240 150+ 950 2950 1.0

ACGIH TLV (1979) 980 700 150 375 120 - 950 - 1.0

NIOSH - - - 375 - - - 350 -

(a) Isopropanol; (b)~ IsobutyT acetate; (c) n-ButanoT; (d) Toluene; (e)
Ethylene glycol monobuty] ether; (f) Isobutyl jisobutyrate; (g) Isopropyl
acetate; (h) Petroleum distillates.

*Combined exposure: Ce = Gy oP Soe cee 1

Gi le Ly
where C is the concentration of the individual contaminant, and
L is the exposure limit.

**Geometric mean

*No OSHA standard for isobutyl] isobutyrate exists; 150 mg/m3 is used by
analogy with n-butanol; see text.

2-14


material to which it is applied. Synthetic resins, natural resins, and drying
oils are the three categories of binders used in paint; synthetic resins repre-
sent over 90 percent of binder usage. The consumption of various resins by the
coatings industry is listed in Table 2.

Table 2. Estimated consumption of important
resins in paints and coatings.4

Millions of pounds
Resins 973 «1974 975 976 97

Alkyd 760 750 695 705 715
Acrylic 361 383 348 395 408
Viny] 413 395 367 389 406
Epoxy 94 109 83 112 126
Urethane 69 67 60 83 90
Amino 74 74 63 81 85
Cellulosic 63 56 50 55 57
Phenolic 29 27 24 25 25
Chlorinated rubber 13 13 14 13 13
Styrene-butadiene > 30 25 24 21 20
Polyester 26 27 25 34 39
Natural 22 21 19 7 16
Linseed Oil 84 58 45 42 40
Other 183 194 184 185 187

Some of the more important resins are discussed in the following sections.

Acrylic Resins--

The term “acrylic resin" applies to the polymers and copolymers of the esters
of acrylic and methacrylic acids. Acrylic resins can be classified into ther-
moplastic and thermosetting types.°

Thermoplastic acrylic resins are used in lacquer-type finishes for automobiles.
Heat after application causes these resins to flow, resulting in a high gloss
finish. The physical properties of these resins are highly dependent on the
alcohol that is used to prepare the acrylate or methacrylate ester. Methanol,
ethanol, butanol, and 2-ethy] hexanol are commonly used alcohols.

Thermosetting acrylic resins incorporate carboxyl or hydroxyl groups to provide
reaction sites for cross-linking agents. Resins with pendent carboxy] groups
usually employ an epoxy resin as the cross-linking agent; those with hydroxy]
groups employ an amino resin. Isocyanates are used to cross-link acrylic
resins that are hydroxyl modified in two-package, air drying, paint systems.
Acrylonitrile, acrylamide, styrene, and vinyl toluene are often used in thermo-
setting acrylic resins.

Both thermoplastic and thermosetting acrylic resins are also used in emulsion
coatings. The thermoplastic emulsions are used primarily in trade sales

6


up air was to be supplied to the vestibules, in effect sealing out dust and
dirt from the spray booth.

One common fault of filter type spray booths that is shared by these booths is
that the air velocity in the immediate vicinity of the painter is often the
lowest in the booth. This is because the heaviest accumulation of paint on
the filters is in this area. In general, there is only one painter stationed
in each spray booth (but this can vary with the size and shape of a particular
product run during any given workshift). Stationing a single painter per
booth eliminates the possibility of the painter being exposed to another
painter's overspray.

There are certain product runs where the painter is stationed in the booth
with reciprocator-mounted equipment. The increased overspray generated by
this type of equipment can create excessive solids buildup on the exhaust
filter, reducing the exhaust air volume of the booth, and causing the entire
booth to fill with spray mist.

In order to stay ahead of the conveyor line, most painters prefer to work near
the conveyor entrance to the booth, as opposed to working near the center of
the spraying section. However, spraying from the end of the booth may cause
spray mist to escape through the entrance vestibule into the plant.

<8
Conver

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FILTERS

Figure 3-2. Spray booth configuration.
Airflow Measurements
A hot wire anemometer was used to measure air velocities within the spray

booth, and the total volume of supply and exhaust air. Results of these
measurements are reported in Table 3-1.

3-4


a plenum that runs directly below the ceiling. Six exhaust grilles are located
along the opposite wall at floor level, providing an effective sweep of fresh
air across the room.

PROTECTIVE EQUIPMENT

The protective equipment used includes uniforms, safety glasses, and rubber
gloves. Half-facepiece respirators, with organic vapor cartridges, were avail-
able. Respirator use was limited to the mop-up operation, using methy] chloro-
form.

WORK PRACTICES

Because many sources of potential solvent evaporation are present, the mix room
attendents have considerable responsibility for the maintenance of low back-
ground concentrations of organic solvents. Safety cans are used below solvent
spigots as shown in Figure 10-4 to catch any paint drippage and lessen the sub-
sequent evaporation. Paint spills are quickly cleaned up and the smooth con-

Figure 10-4. Solvent dispensing area.

10-4


Table 3-4. Airborne levels of lead in metal furniture finishing

Sample duration Lead
Painter (minutes) (ug/m3)
U 152 1050
W 156 660
x 150 30
Y 154 250

3-9


DEPARTMENT OF HEALTH AND HUMAN SERVICES
PUBLIC HEALTH SERVICE
CENTERS FOR DISEASE CONTROL
NATIONAL INSTITUTE FOR OCCUPATIONAL SAFETY AND HEALTH
ROBERT A. TAFT LABORATORIES
4676 COLUMBIA PARKWAY, CINCINNATI, OHIO 45226

OFFICIAL BUSINESS
PENALTY FOR PRIVATE USE. $300

DHHS (NIOSH) Puplication No. 81-121

Special Fourth Class -Book

POSTAGE AND FEES PAID
U.S. DEPARTMENT OF HHS.
HHS 398


CASE STUDY 5
AUTO REFINISHING

Automobiles and light trucks are refinished in this modern repaint shop. Com-
plete body repainting comprises over 90 percent of this paint shop's output;
the remainder consists of spot painting. Conventional air-atomized spray
equipment is used, fed by pressure pots. All complete body repainting and spot
repainting of areas over two-square feet are performed in a conventional
"drive-through" spray booth with an integral oven. Airborne concentrations of
lead, hexamethylene diisocyanate (HDI), and organic solvents were within recom-
mended levels. Spraying certain yellow and red colors (not used during this
survey) represents a potential for over exposure to lead.

PROCESS
Operations

Unlike shops that specialize in body work, over 90 percent of the painting in
this shop is complete body repainting. Although spot painting of body work is
also performed, a large percentage of the vehicles that require body work will
be completely repainted. Figure 5-1 is a layout of the shop.

Complete body repainting begins with masking and cleaning of the old painted
surfaces. First, two technicians wash the vehicle to remove water soluble
dirt. Then, painted surfaces are lightly, but carefully, sanded to remove im-
perfections and provide a smooth surface; they are also solvent-wiped to remove
traces of old wax or road gum. Chrome trim and glass areas are masked, and the
car is driven into the spray booth.

One painter performs essentially all the paint work, completing 6 to 8 cars per
shift. The painter is responsible for mixing all paint, and for matching the
finish color to the original for spot repainting. The paint mixture is based
on a formula card that specifies the required proportions of 30 stock color
paints that are combined with a paint drier, bake converter, and optional iso-
cyanate hardener. Mixing generally takes 5-10 minutes, but additional tinting
required to match faded or odd colors will require longer mixing times.

After closing the booth doors and starting the fan, the painter removes any
body shop dust from the vehicle with an air nozzle and wipes the vehicle with
a tack rag. Next, he applies a light coat of a gray primer/sealer (about 1
quart), starting at the hood and working around the car. Finally, he applies
two coats (about 1 gallon) of the enamel finish, starting again with the hood
and working back around the vehicle. Both finishes are applied with conven-
tional air-atomizing spray guns fed from pressure pots. Atomizing-air pressure
wasobserved to range from 50 to 65 psig. Air pressure on the paint delivery
pot was 15 psig. Overall painting application time was 40 to 45 minutes.

Coatings

Both the primer/sealer and the enamel topcoats are alkyd enamels, which form a
cured paint film by the oxidation of double bonds in the resin and subsequent

5-1




Figure 1-3. Powder coating booth.

DUST COLLECTOR AND FINAL FILTERS

Powder-laden air from each of the powder booths is routed to a combination
powder-recovery/air-recirculation system. A cartridge-type dust collector
separates the powder from the air stream. Each dust collector contains 16
pleated paper elements, cleaned by a pulse of compressed air. A 10-hp centri-
fugal fan is located on the clean air side of the collector. The final dis-
charge is at an elevation of 12 feet, through a set of three high efficiency
final filters mounted in parallel. Each filter is rated at an efficiency of
90 percent, (as determined by American Society of Heating, Refrigeration, and
Air Conditioning Engineers (ASHRAE) test procedures). Outlet filters are
periodically removed and cleaned by compressed air. Clean filter resistance
is 0.75 inch water gauge at 1700 cfm. Both dust-collector and final-filter
resistance are monitored. Observations of final-filter pressure losses (2 to
3 inches wg) and light dusting from the filter indicate less than complete
powder removal. Noise from the fan outlet is reduced by an acoustical silencer
located on the fan outlet.


Common extender pigments include barium sulfate; calcium carbonate, silicate,
and sulfate; silica (quartz, synthetic and diatomaceous silica); and the sili-
cates: clay, talc, and mica.

Table 3. Estimated consumption of important
pigments in paints and coatings.4

Millions of pounds

Pigments 1973 9741975" 19761977
Titanium dioxide 864 791 71 787 796
Calcium carbonate 415 420 400 410 421
Tale 357 316 300 345 331
Clay 280 290 290 294 305
Silica 125 140 130 145 154
Iron oxide 115 105 95 104 115
Chromium 94 80 65 80 85
Barytes (barium 95 85 76 78 81

sulfate)

Zinc dust 58 55 52 69 75
Other extenders

and fillers 53 50 45 50 55
Zinc oxide 52 34 25 30 31
Aluminum 28 24 23 28 26
Lead (corrosion 26 26 23 22 22

inhibiting)

Carbon black 22 19 18 19 20
Other colored

inorganic) 15 14 14 W7 19
Other organic 7 7 15 W7 18
Other white opaque 10 9 8 9 9
Cuprous oxide 6 6 5 6 8
Phthalocyanine 5 5 4 5 6
Other 4 4 3 4 4

Colored pigments reflect only a certain part of the visible spectrum. The
colored pigments can be divided into two basic groups--inorganic and organic.
Many of the organic pigments are dyestuff-based; the dyestuff is combined with
an inorganic compound to render it insoluble.

Metallic powders of aluminum or zinc may be used as pigments. These powders
may be incorporated to produce a metallic effect, or may be included to provide
corrosion protection by galvanic action.

Solvents

The primary function of solvents is to dissolve the binders and to provide a
consistency suitable for application. Because the solvent evaporates, the

1


Airflow Measurements

Total exhaust air was measured by a pitot tube traverse of the stacks of each
of the 6 exhaust fans. Total supply air, and pit and vestibule supply air were
also determined, and the ceiling air was determined from the difference. Air-
flow measurements are summarized in Table 8-1. Control velocity was deter-
mined with a hot wire anemometer held approximately 5 feet above the grate
area, with the wagon in the booth, and repeated with the wagon absent. These
measurements are shown in Figure 8-6. Air velocity was relatively uniform over
the grate area, dropping slightly near the booth exits. A drop in air velocity
was also noted above the pit area, and was exacerbated by the presence of the
tall wagon.

Table 8-1. Booth airflow summary.

Exhaust:
northeast fan 21,000 cfm (A11 fans 25,000 cfm
north fan 25,000 cfm design volume)
northwest fan 23,000 cfm
southeast fan 29,000 cfm
south fan 27,000 cfm
southwest fan 24,000 cfm
Total exhaust 149,000 cfm

Make-up Air:
west unit 91,000 cfm (Both units 90,000 cfm
east unit 80,000 cfm design volume)

make-up air distribution:

overhead plenum 133,000 cfm
west air seal 18,000 cfm
east air seal 16,000 cfm
booth pit 4,000 cfm
Air velocity:
wagon absent from booth (Measured 5 feet
mean 110 fpm (39 SD) above floor)

wagon in booth
mean 140 fpm (65 SD)



EXHAUST PLENUM

EXIT ENTRANCE
Kw J YX we

/_\ CONVEYOR
PX CY BREATHING ZONES

t + t 4

SUPPLY PLENUM

Figure 3-3. Booth airflow.
WORK PRACTICES

The opposed painting sections of the in-line booths eliminate the need to turn
the workpiece during the painting process. However, painters often spray both
sides of a workpiece on short production runs. The worker paints the back side
of each workpiece by positioning himself between the object being painted and
the exhaust filter. This practice caused the painter to be engulfed in his own
spray mist. With longer production runs, the painters were stationed in op-
posing booths, which obviated the need for this practice.

EVALUATION

Up to 12 employees are potentially exposed to paint solvents or spray mists at
this facility. The employees are identified as one paint vault attendant, one
relief painter, and up to 10 spray painters/workshift. Potential sources of
exposure include spray mist and solvent vapors from spraying, solvent vapors
evaporating from finished pieces, and paint system cutting or mixing opera-
tions.

As an index of control, the 8-hour time-weighted average (TWA) concentrations
of total spray mist, lead, and organic solvents were determined for the paint
sprayers. All sprayers spend their entire workshift in the finishing depart-
Ment, excluding scheduled breaks and lunch. Conventional solvent-reduced
paints were in use during the first day of the survey. An acrylic emulsion
paint was used exclusively during the second day of the survey. On the last
day of the survey, both solvent and emulsion paints were used,

The 8-hour TWA concentrations were calculated from separate morning and after-
noon samples collected outside the respirator. Samples of total spray mist
were collected using closed-face cassettes with preweighed 37 mm polyviny]
chloride/acrylonitrile copolymer membrane filters and personal pumps operated
at 2.0 lpm. Because of the variety of paints used and the lack of material

3-6


SECTION IV. INDUSTRIAL FINISHING PRACTICES

This section describes the industries in which spray finishing operations were
studied. Included in this summary are the SIC codes of the subject industry,
the application process, and the commonly used resin systems, solvents, and
pigments.

AUTOMOBILE REFINISHING

This industry is classified under SIC major group 75 (Automotive Repairs,
Services, and Garages). It includes the following categories: SIC 7535
(Paint Shops) and SIC 7531 (Automotive Repair Shops). These are establishments
primarily engaged in automotive painting and refinishing, and car body re-
pairing.

The automotive refinishing industry was considered separately from the automo-~
bile producing industry because of the nature of the establishments performing
this work. Many of these shops can be characterized as being small, poorly
ventilated, with few or no controls. Only modern, larger automobile paint
shops use auto refinishing booths.

The surface that is to be painted is normally cleaned, sealed, and sanded
before paint application. These operations are usually performed by hand.
Coatings are normally applied by hand-held air atomizing equipment. The
coating material is generally cured by air drying.

Alkyd enamels are used for total body repainting because, unlike the case with
lacquer finishes, no hand rubbing is needed to gain a high gloss surface film.
The rapid cure of lacquer finishes permits blending of spot repairs into un-
damaged areas, which makes this type of finish more popular in body repair
shops. The air drying alkyds are more typically applied in spray booths be-
cause of their susceptibility to contamination by airborne dust. The commonly
used resins, solvents, and pigments are shown in Table 5.

WOOD FURNITURE

This section includes industrial products described in the SIC major group 25
(Furniture and Fixtures). These establishments are primarily engaged in the
manufacture of wooden household and office furniture; upholstered furniture on
wooden frames; television, radio, and sewing machine cabinets; furniture for
schools, churches, libraries, and assembly halls. Also included are establish-
ments engaged in manufacturing wooden shelving, lockers, store fixtures; pre-
pabricated partitions; plastic laminated fixture tops and related fabricated
products.

Before coating, the wood surface is prepared and pretreated in several steps,
such as sealing, glazing, sanding, and polishing. These techniques are used

16


Table 14.

Chromatographic conditions for

various solvent mixtures.

Solvent mixture

Gas chromatograph conditions

MEK, toluene, ethanol,
isopropanol*

Ethyl acetate, ethoxyethy]
acetate, aliphatic hydrocarbons

Toluene, xylene, other aromatics,
aliphatic hydrocarbons

Toluene, xylene, butyl acetate,
diisobutyl ketone, ethoxyethy]
acetate, aliphatic hydrocarbons

Xylene, toluene, n-butanol,
isobutyl acetate, isopropanol
ethanol, aliphatic hydrocarbons

Isophorone, isobuty]
acetate, n-butanol,
toluene, xylene, EGME,
ethanol, MEK, petroleum

MEK, isopropyl acetate, xylene,
isopropanol, MIBK, toluene,
isobutyl isobutyrate, petroleum
distillates

Xylene, toluene

Toluene, xylene, butyl acetate,
MEK, MIBK, ethyl acetate,
ethoxyethyl acetate, petroleum
distillates

9'x 1/8" SS column with 80/100 mesh
Chromosorb 108; temperature programmed
from 130 to 160°C; flame ionization
detector

20' x 1/8" nickel alloy column with 10%
SP-1000 on 80/100 mesh Supelcoport; temp-
erature programmed from 100 to 160°C

at 8°C/min; flame ionization detector

20' x 1/8" nickel alloy column with 10%
SP-1000 on 80/100 mesh Supelcoport; temp-
erature programmed from 80 to 170°C

at 8°C/min; flame ionization detector

20' x 1/8" nickel alloy column with 10%
SP-1000 on 80/100 mesh Supelcoport; temp-
erature programmed from 85 to 160°C

at 8°C/min; flame ionization detector

20' x 1/8" nickel alloy column with 10%
SP-1000 on 80/100 mesh Supelcoport; temp-
erature programmed from 85 to 150°C

at 8°C/min and 150°C for 4 min

20' x 1/8" nickel alloy column with 10%
SP-1000 on 80/100 mesh Supelcoport ;
temperature programmed 85°C, 8 min;
8°C/min; finally 190°C, 8 min

20' x 1/8" SS column with 20% SP-2100/
0.1% Carbowax 1500 on 100/120 mesh
Supelcoport; temperature programmed
110°C, 8 min; 32°C/min; finally

170°C, 16 min

20' x 1/8" SS column with 10% SP-1000
80/100 mesh Supelcoport; 130°C; flame
jonization detector

20' x 1/8" nickel alloy column with 10%
SP-1000 on 80/100 mesh Supelcoport;
temperature programmed from 100 to
160°C at 8°C/min

*Desorbed by CSo with 1% sec-butanol

45


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Figure 3-1. Process layout - metal furniture finishing.

Coatings

Coating formulations are specified by customer order. These orders can gener-
ate runs of as few as several pieces to runs that require several shifts. The
largest single type of paint consumed at the facility is an alkyd baking enam-
el. This conventional solvent-type paint is supplied by several vendors, in
an array of formulations that conform to customer requirements. These coatings
cure when they are baked in an oven for approximately 25 minutes at 300°F.

The second most significant type of paint consumed is a waterborne acrylic
emulsion, which comprises 30 to 40 percent of the total paint consumption at
this facility. A move to substantially increase this percentage is antici-
pated. This shift in the type of paint consumed was initiated principally to
Meet environmental regulations. Other advantages of this waterborne paint
cited by plant personnel are excellent adhesion to the metal substrate and
reduced solvent exposure to the paint sprayer. The increased adhesion proper-
ties present special problems in stripping this material from defective parts;
the cost of stripping can often exceed the cost of the part itself. This type
of coating system requires baking for approximately 25 minutes at 350°F.

A central paint supply system delivers and recirculates a total of 25 colors*
to the booths. With this system, color changes can be accomplished in less

3-2


losic resins contain substantial quantities of modifying resins or plasti-
cizers. These plasticizers include castor oi], dibutyl phthalate, tributy]
phosphate, tricresyl phosphate, dioctyl phthalate, and others. The toxicity
of these materials is discussed under "Plasticizers".

Epoxy Resins--

Epoxides are alkylating agents of moderate reactivity. In biological systems,
epoxies react with amino acids, nucleic acids, and with phosphate groups. Re-
action with proteins will give rise to antigens probably responsible for aller-
genic activity; the alkylation of membrane constituents is involved in irrita-
tion; and reactions with DNA are associated with gene mutation and cancer.9

Epoxy resins used in coatings are most commonly based on epichlorohydrin and
bisphenol-A. In his comprehensive review of epoxy resins used in surface
coatings, Lemon2! reports that extensive testing of these resins indicated no
significant toxicity following regular ingestion or exposure to their vapors.
No skin cancer was produced by Jong term percutaneous exposure. Skin irrita-
tion was produced only by the liquid resin grades. .

Liquid epoxy resins are primarily used in solvent-free and waterborne two-com-
ponent epoxy paints. These liquid resins are modified by the addition of re-
active diluents (glycidyl ethers). These reactive diluents are themselves
irritants to the skin, the eyes, and the respiratory tract.

Aliphatic and aromatic polyamines, polyamine adducts, and polyamides are used
as curing agents in two component. epoxy coating systems. The aliphatic amines
are potent irritants and sensitizers; the aromatic amines are somewhat less
potent. The polyamide resins are relatively harmless. Acid anhydrides and
formaldehyde resins are used as cross-linking agents in powder coatings and
baking enamels. The acid anhydrides are irritants and sensitizers.

Epoxy resins are commonly reacted with fatty acids to produce epoxy esters.
Because coatings produced with these resins contain no unreacted epoxy groups,
no hazard exists.

Urethane Resins--

Organic isocyanates are the principle hazard associated with urethane coatings.
Isocyanates can cause severe irritation to the conjunctiva, and respiratory
distress. They react with various protein functional groups and should be
capable of forming ant igens. 23 A typical response to isocyanate inhalation,
either as a vapor or an aerosol, is the manifestation of an asthma-like syn-
drome, characterized by a feeling of chest constriction and difficult breath-
ing, sometimes accompanied by a dry, irritant cough. A small percentage of the
population may become sensitized to isocyanates, whereupon the above symptoms
are produced on exposure to even low airborne concentrations. 24

The degree of isocyanate hazard varies with the type of urethane coating. 0i1
urethanes and urethane lacquers contain no unreacted isocyanate and thus re-
present little or no hazard. Moisture-cured urethane varnishes and two package
urethane coatings contain reactive isocyanate groups. Most contain polymeric
isocyanates to minimize the hazards of vapor inhalation. Hardy and Devine

attribute adverse respiratory effects to the inhalation of isocyanate-con-
taining aerosols. They state that inhalation of any species with multiple un-

28


interior paint on black exterior surfaces, the interiors for black cases are
coated with black exterior paint. In this instance both finishes are applied
with conventional air-atomizing equipment, however, air-atomizing pressure is
reduced to 40 psi to lessen overspray.

Application of the first coat is completed in two successive sidedraft booths
positioned on opposite sides of the conveyor. Each booth houses four electro-
static spray guns, mounted on reciprocators, applying the paint in a vertical
plane. The first of these booths contains an additional reciprocator to coat
(in a horizontal plane) the backs of the cabinets, while the second contains
similar equipment to coat the top of each workpiece. The spray guns are oper-
ated with an air-atomizing pressure of 25 psi, a paint delivery pressure of 15
psi, and a voltage of 100,000 volts. An array of electronic eyes and associ-
ated logic circuitry identifies parts and schedules the painting sequence to
minimize paint waste. A solvent purge system allows a 15 second color change.

Following a two minute flash-off period, the second finish coat is applied with
automated equipment similar to that applying the first coat. One operator/
mechanic is responsible for both sets of automated systems.

Two manual spray operators are stationed in a downdraft booth (similar to the
first booth) to reinforce workpiece edges and touch up light areas. This is
accomplished with conventional air-atomized equipment, operated at air pres-
sures that are generally higher than the first stage of the process. Air
pressures in this booth range from 65 psi for solid colors up to 80 psi for
metallics.

The workpieces are then transported to roof-mounted curing ovens (for 8 to 9
minutes) operating at 375°F,

Coatings

In order to meet environmental regulations, coating formulations are currently
being switched from conventional thermosetting acrylic enamels to medium high-
solids polyester baking finishes. Presently, the polyester finishes are being
used in the three most common colors, and represent approximately 55 percent of
the total paint applied on this line. These materials are 53 percent by weight
paint solids, and are formulated from hydroxyl functional, saturated polyester
resins, which are cross-linked with a melamine resin. The amount of cross-
linking agent is not increased over that which is used in a conventional acry-
lic baking enamel, though relatively low molecular weight polyester resins are
used to achieve fluidity at the high-solids content.

The conventional thermosetting acrylic enamels are formulated from hydroxy]
functional acrylic resins, which are modified by the addition of alkyd resins,
and cross-linked by urea and melamine resins.

Both finishes are pigmented with the same types of pigment materials; titanium
dioxide, yellow and red iron oxides, and lamp and furnace blacks, are the most
common. Both types employ the same solvents--n-butanol, xylene, an aromatic
petroleum distillate, and butyl] acetate--although the high-solids material

9-3


operated at 2.0 Ipm. After weighing, the filters were wet-ashed and the re-
sulting solution analyzed for lead by atomic absorption. Organic solvents were
collected on 150 mg charcoal tubes with personal pumps operated at 50 cc/min.
Tubes were subsequently desorbed and analyzed for toluene and xylene by gas
chromatography. Toluene and xylene were selected based on qualitative analysis
of selected charcoal tube samples by mass spectroscopy. Methyl ethyl ketone,
1,1,1-trichloroethane, and n-butanol were also indicated by the qualitative
analysis, but at low concentrations.

It was observed that the liner painting operation engulfed the painter in mist
as shown in Figure 6-4. Although it comprised only 10 percent of the painting
time ( 5 minutes each hour), it probably contributed significantly to the aver-
age mist concentration. To determine this contribution, solvent levels were
compared during cabinet and liner painting with a combustible gas indicator.
In addition, 5 short term samples for total mist were taken during the liner
painting (outside the respirator). Results of these measurements are reported
in Table 6-3.

Figure 6-4. Liner painting operations.

6-6


least expensive combination of solvents is used, as long as the solvent will
dissolve the binders and give the desired viscosity.

Solvency and volatility are the prime factors in determining the usefulness of
solvents. Solvency is largely a function of the kind of binder. Polar resins
require polar solvents; non-polar resins require non-polar solvents. The vo-
latility of the solvents affects the evaporation rate, which in turn influences
the behavior of the coating during application and drying. The optimum eva-
poration rate is dependent upon the method of application.

Solvent use in paint and coatings is reported in Table 4,

Table 4. Estimated consumption of important
solvents in paints and coat ings.4

Millions of pounds

Pigments 6

Aliphatic hydro- 1603. 1375-1280 TT85”—s‘7*720
carbons

Methyl ethyl ketone 380 342 319 345 357
Xylenes 544 435 363 325 300
Other aromatics 421 399 326 305 290
Toluene 326 250 268 260 255
Ethanol 200 210 200 200 200
Acetone 200 184 175 190 196
Glycol ethers and 180 194 176 190 195
ether esters

n-Butanol 140 155 135 145 151
Isopropano] 121 125 115 120 125
Ethyl acetate 120 103 91 110 110
Methyl isobuty] 122 125 103 105 105
ketone

Buty] acetates 93 86 80 84 86
Other ketones and 70 75 70 74 75
esters

Ethylene glycol 57 52 48 54 56
Propy] acetates 60 55 50 53 54
Other alcohols 40 42 40 41 41
Other solvents 40 40 36 38 38
Propylene glycol 30 32 29 33 34
Methylene chloride 15 15 14 15 15
Other glycols 1 1 1 1 1

Additives

Many items in a paint formulation are used in relatively small quantitites for
the purposes of manufacturing ease, package stability, application ease, and
final appearance or performance. These items are collectively referred to as

12


7.

10.

i.

12.

13.

REFERENCES

Office of Management and Budget. 1972. Standard Industrial Classification
Manual.

Federation of Societies for Coatings Technology. 1978. Paint/Coatings
Dictionary. Philadelphia, PA.

Fuller, W.R. 1965. Formation and Structure of Paint Films. Federation
Series on Coating Technology, Philadelphia. Federation of Societies for
Coatings Technology, Unit 2.

National Paint and Coating Association, 1978. NPCA Data Bank.

Allyn, G. 1971. Acrylic Resins. Federation Series on Coatings Techno-
logy, Philadelphia. Federation of Societies for Coating Technology. Unit
17, 36 pp.

Martens, C.R. 1974. Technology of Paints, Varnishes, and Lacquers.
R. Krieger Publishing Co.

Armstrong, R.S. 1974. Paint, Chemical and Process Technology Encyclope-
dia. McGraw-Hill.

Hamilton, E.C., and L.W. Early. 1972. Cellulosic Resins. Federation
Series on Coatings Technology, Philadelphia. Federation of Societies for
Coatings Technology, Unit 21, 47 pp.

Ehrner, H., and 0. Sjoholm. 1974. Health Hazards from Epoxy. Compiled
from Lecturers' Manuscripts. Stockholm.

Lasovick, D. 1970. Urethane Coatings. Federation Series on Coatings
Technology, Philadelphia. Federation of Societies for Coatings Techno-
logy, Unit 15, 31 pp.

Powell, G.M. 1972. Vinyl Resins. Federation Series on Coatings Techno-
logy, Philadelphia. Federation of Societies for Coatings Technology,
Unit 19, 55 pp.

Stewart, W.J. 1969. Paint Driers and Additives. Federation Series on
Coatings Technology, Philadelphia. Federation of Societies for Coatings
Technology, Unit 11, 64 pp.

Hama, G.H. and K.J. Bonkowski. 1970. Ventilation Requirements for Air-
less Spray Paintings. Heating, Piping, and Air Conditioning. pp 80-2.

56


HAZARD ANALYSIS

The principal hazard that is associated with the coatings used is a result of
the volatile organic materials, chiefly toluene and xylene, employed as sol-
vents. Both these materials can produce irritation of the skin, the conjunc-
tiva, and the mucous membranes of the upper respiratory tract. At high concen-
trations, they can produce the symptoms of headache, nausea, and drowsiness,
followed by loss of consciousness. Dermal contact with these finishes should
be avoided because toluene can be absorbed through the skin, producing systemic
poisoning. Dermal contact should also be avoided because coatings are not
easily removed from the skin, and workers tend to use these solvents in per-
sonal cleaning.

Lead is a potential hazard in all colors. Even in white paints, traces may be
present in raw materials or as contaminants introduced in manufacture. The
other pigment materials are essentially physiologically inert. To date, no
evidence of harm has been demonstrated by the thermosetting acrylic resins
used. As a minimum, however, these non-volatile materials should be controlled
to below the maximum levels recommended for nuisance materials.

SPRAY BOOTHS
Manual Spray Operations

The paint booths for the manual spray application of the prime and finish coats
are shown in Figure 6-2. Fresh air is supplied from behind the painters
through seventy 20 in x 20 in filters located on the front wall of the booth,
and removed at the rear of the booth through a water curtain. The water cur-
tain consists of a water header located above four rows of asbestos-cement
board; each sheet is about 2 feet high, forming overlapping sheets of water and
providing four horizontal exhaust slots. An additional water header cleans
paint mist from the exhaust air stream. A series of metal baffles in the ex-
haust plenum reduce water carryover into the exhaust fans. Parts enter and
exit the booth through short vestibules supplied with make-up air.

Make-up and exhaust airflows were measured in both the prime and finish booths.
Control velocity was measured with a hot wire anemometer at 24 points in the
vertical plane occupied by the paint sprayer and the measurements were aver-
aged. Results of these measurements are presented in Table 6-1. The average
control velocity for the finish booth was double that of the prime booth, in
spite of an exhaust rate that was only 20 percent greater. This was because
of a lower volume of air supplied behind the painter in the prime booth, re-
sulting in air from outside the booth being short circuited through the vesti-
bules into the waterfall.


Table 4-4, Airborne levels of spray mist, lead, and
chromium in railroad car finishing.

Sample Total
Car time mist Lead Chromium
type Painter Paint (min) (mg/m3) (ug/m3) (ug/m3)

Pulp Xx A 50 27.0 120 120
Pulp Xx A 57 42.1 210 180
Y A 60 35.0 170 140
Pulp X A 24 57.7 250 250
Zz A 24 33.9 140 160
Coal Zz B,C 40 66.3 620 910
Y B,C 49 47.3 510 750
Gravel Y O,E 23 71.9 280 540
(partial)
Zz O,E 22 69.3 270 420
Gravel Zz E 15 28.3 170 100
(sides
only) Y E 16 41.3 160 130
Gravel X* E 38 33.2 120 100
(partial)
E 7 41.4 140 110
Painter X (geometric mean) 38.4 (1.4)** -- --
Painter Y (geometric mean) 47.1 (1.4) -- --
Painter Z (geometric mean) 44.9 (1.5) -- --
Grand Mean 43.3 (1.4) 211(1.7) 220 (2.2)
OSHA PEL*** 15 50 1000****
ACGIH TLV (1979)*** 10 150 50
NIOSH*** -- -- 1

* Painter used heated electrostatic spray gun

** Number in parentheses are geometric standard deviations
*kk For full shift exposures

**x**Chromium metal and insoluble salts

4-11


DISCUSSION

In many paint shops, coating formulations are continually changing to meet the
specifications of different customers. The nature and degree of the hazards
associated with these coatings varies, and the material safety data sheet, if
available, may not be complete. In these shops a full-facepiece, supplied-air
respirator, or an air-supplied hood, is a logical choice for a Paint spray res-
pirator. They not only afford a high degree of protection, but protect the
eyes from the irritating effect of many of the paint constitutents. The full
facepiece respirator is more comfortable to the wearer than a cartridge-style
half-mask because of the lower breathing resistance and the distribution of the
headband pressure over a larger facial area. The major drawback of the full-
facepiece respirator for paint spraying is that the viewing window fogs with
stray mist; the problem is overcome in this operation by covering the viewing
window with food wrap. However, the painter's vision may be impaired by the
food wrap, limiting this technique to rough painting operations.

Several opportunities exist to reduce exposure to spray mist without major
design changes. Improved application equipment might reduce the overspray,
but probably not without an attendent increase in application time. However,
the use of a pole-type spray gun could decrease exposure during under carriage
painting without slowing the painter by increasing the distance from the spray.
Booth design could be markedly improved at minimal cost by relocating the make-
up air inlets to above the car sides as shown in Figure 4-3. Lastly, mist con-
centrations could be reduced while painting car sides, if Painters are required
to use the access platforms while painting the car sides.


ACKNOWLEDGMENT

We gratefully acknowledge the cooperation of the management and workers at the
plants participating in the field studies. Their willingness to contribute
their experience for the benefit of others made this study possible.

We want to especially thank Patrick Hurd of the National Paint and Coatings
Association for access to the NPCA Data Bank and use of the NPCA library. The
help of Francis Flitner of the DeVilbiss Company, Don Scarbrough of the Nordson
Corporation and Rod Wolford of the International Brotherhood of Painters and
Allied Trades in the early phases of the study is also appreciated.

A number of people and groups had direct input to this evaluation; their help
was invaluable and should also be recognized. The authors were assisted in the
field evaluations by John W. Sheehy, Harold D. Van Wagenen, John C. Frede,
Daniel Kemme, Michael Green, and others. Qualitative analyses of bulk air
samples were performed by Mark Millson, Ardith Grote, and others in the
Measurements Support Branch. Field samples were analyzed by Thomas M. Murray,
Rodney F. Kirk, David G. Daniels, Denise Cook, and other staff of the Utah
Biomedical Test Laboratory. Illustrations were provided by August Lauman.

The manuscript was patiently and very ably typed by Ruby Watson.

The authors also wish to recognize Richard E. Kupel and Charles L. Geraci,

PhD., for their help in coordinating the analytical services, and Robert Hughes,
for his encouragement and guidance throughout the project.

vil




solvent component in NAD systems, although they are poorer solvents for common
resins.

Powder coatings represent the ultimate step in the removal of solvent hazards
from paint spraying. Powder coating requires not only special application
equipment (electrostatic or flame spray guns) but special powder recovery
booths. Other limitations include difficulties with frequent color changes,
metallic finishes, and wood and plastic substrates. Advantages of powder
coatings include the lack of solvent emissions, low energy consumption, and the
ability to produce a heavy coating in a single pass.38 This coating techni-
que has been most successful in the appliance industry, which is the largest
industrial user of powder coatings.

Isocyanates--

The monomeric isocyanates are well known irritants and sensitizers. The use
of heat-cured, blocked isocyanate prepolymers eliminates the hazard. during
spray application. In these coating systems, phenol, caprolactam, cresol, or
methyl] ethyl ketoxime may be used as blocking agents that will volatilize or
breakdown upon heating at temperatures above 160°C. 40

Epoxy Curing Agents--

Amine-cured epoxy coatings have a dermatitis potential; asthma-like symptoms
and urticaria have been reported. Key4 discusses polyamides used as curing
agents. These products are non-toxic, non-irritating, and provide a longer
pot-life, but they possess somewhat lower resistance to chemical attack and do
not cure as rapidly as polyamine systems. Key also suggests the use of
Cardura(R)E ester in place of the more irritating and sensitizing glycidyl
ethers as reactive diluents.

Substitution of Equipment

The use of airless atomization, heated paint, and electrostatic attraction in
place of conventional, compressed air spray equipment can significantly reduce
the amount of stray mist or fog produced. Compressed air spraying atomizes
liquid paint by directing a high velocity air jet at the paint stream as it
exits from a nozzle. The flow of air conveys the finely atomized droplets to
the object being painted. This stream of air is deflected when it strikes the
object. The paint particles of sufficient mass are not deflected and deposit
themselves on the object. Hama and Bonkowski!3 note that droplets less than
approximately 12 microns are of insufficient mass to deposit on the object
being painted and are deflected with the "bounce-back" air stream. They note
that approximately 20 percent of the droplets in conventional paint spraying
are smaller than 12 microns. Additional paint mist is lost when the spray
pattern does not completely contact the object. Total paint losses of 50 per-
cent are not uncommon.

In airless spraying, the paint is atomized by forcing it through a small ori-
fice under very high pressure. This method produces less fog than compressed
air spraying because not as many fine droplets are produced. Hama and
Bonkowski note that only 2 percent of the spray droplets in airless painting
are less than 12 microns. The phenomena of "“bounce-back" is largely reduced
because the paint droplets are conveyed to the object being painted by their

33


ROOF LINE

MAKE UP AIR
PLENUM

PERFORATED
DISTRIBUTION PLATE

FILTER BANK

UNDERBODY
PAINT PIT FRESH AIR

PLENUM

Figure 8-4. Spray booth cross-section.

8-5

FLOOR LINE


Table 5-2. Airborne levels of paint mist, lead, and
chromium in automobile refinishing.

Sample

duration Total mist Lead Chromium
car size Color (min) (mg/m3)— (ug/m3)—(ug/m3)
Subcompact. White 42 8.0 <36 72
Standard Brown 44 11.3 57 <34
Compact Green 40 16.1 63 <38
Subcompact. Blue 45 8.8 34 <34
Subcompact Blue 40 12.4 76 <38
Fender only Brown 15 6.1 <97 <97
Compact Blue 43 4.0 <34 <34
Geometric mean 8.7 52 --
Geometric standard deviation 1.6 1.5 oO
Estimated 8-hour TWA* 5.0 30 --
OSHA PEL 15 50 100
ACGIH TLV (1979) 10 150 50
NIOSH -- - 1

*8-hour time-weighted average, based on 7 cars per shift and 40 min per car.


safety data sheets for specific coatings, all filters were subsequently ashed
and analyzed for lead by atomic absorption spectroscopy. Solvents for analyses
were selected based on a limited number of available material safety data
sheets and on the qualitative analysis of selected charcoal tube samples by
mass spectroscopy. Major compounds on these samples were toluene, xylene,
aliphatic hydrocarbons in the C8-11 range, n-butyl acetate, diisobuty] ketone,
and 2-ethoxyethyl acetate. Other compounds that were identified but present
in lesser quantities included methyl amyl ketone, isobutyl alcohol, isobuty]
acetate, isopropanol, and trimethyl-and tetramethyl benzenes.

RESULTS

Airborne concentrations of organic solvents are reported in Table 3-2. In all
cases the concentration to organic solvents was less than 50 percent of allow-
able levels. Airborne concentrations of paint mist are reported in Table 3-3.
One-half of the samples exceeded the 15 mg/m3 limit set by OSHA for total
dust. This can be attributed to high atomizing-air pressures, the presence of
a second painter in the booth, or low spray booth airflow. Painters U and Y
showed the highest mist levels. Both these painters sprayed using an atom-
izing-air pressure of approximately 80 psi and frequently shared the same
booth. The mist levels of painter W were somewhat lower, even though air
pressure exceeded 90 psi. This painter most frequently worked alone.
Painters X and Z showed the lowest mist levels. Both these painters worked
alone and consistently sprayed at an air pressure of 60 psi or less.

The majority of the samples that were analyzed for lead were below detectable
limits, corresponding to airborne lead concentrations less than 7 ug/m3,
However, all samples that were taken on the afternoon shift of the first day
of the survey showed hygienically significant amounts of lead. The specific
paint and the exact percentage of lead in the paint that was responsible for
these levels were not identified. These lead concentrations are reported in
Table 3-4. The range of colors used and the variety of workpieces painted did
not allow an accurate estimate of the time-weighted average concentration of
lead.

DISCUSSION

The use of excessively high air pressure is a prime contributing factor to
poor quality work, excess spray mist, and paint waste. Improved supervision
of spraying practices, with a goal of reducing-atomizing air pressures, could
reduce paint mist levels substantially while improving paint mileage.

Paint mist levels could also be reduced by assigning only one painter to each
booth whenever that is possible. In no case should a spray painter occupy the
same booth with automatic, reciprocator-mounted equipment.

Spray booth efficiency could be markedly improved by replacing exhaust filters
at the end of every shift, or by monitoring the pressure drop across the filter
bank and changing filters when a given pressure drop is exceeded. Equally
large gains in booth efficiency could be achieved by properly proportioning
the fresh air supplied to the booth and the vestibules, reducing vestibule air
to no more than one third of the total quantity of makeup air.

3-7


EXHAUST

ff

NOTE: AIR SUPPLIED RESPIRATOR
MUST BE WORN

Figure 1. Ventilation of enclosed spaces.

For practical purposes, spray booths can be classified into two basic designs
based on the direction of airflow. Booths with a horizontal airflow are termed
"sidedraft booths." These booths take advantage of the momentum of the spray
mist and can successfully be used when painting small- to medium-sized
articles. With larger articles, it may not be possible to maintain adequate
airflow on all sides of the object being painted, and rotating the workpiece
may not be practical. In these situations, a downdraft spray booth permits
greater protection, while allowing more freedom of movement for the painter.

Both sidedraft and downdraft booths will vary in size, in the degree of enclo-
sure, in the method of air makeup, in air velocity, and in overspray control.
These variations are illustrated in Figures 2 and 3, and discussed in the
following sections.

Size

Spray booths range in size from small bench type models that are designed for
spraying small objects to huge chambers that are capable of holding a large
airplane. The basic consideration in determining the size of a spray paint
booth is the size of the object being painted; adequate space around the top
and sides of the object are needed to permit the painter easy access to these
areas. The booth should be deep enough to allow the operator to work within
the booth. If the object is transported by a conveyor, the booth must be
sufficiently long to permit coating within the time the object remains inside
the confines of the booth at the maximum line speed.

36