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ECTB 179-12a
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CONTROL TECHNOLOGY FOR AUTOBODY REPAIR
AND PAINTING SHOPS
at
Kay Parks/Dan Meyer Autorebuild
Tacoma, Washington
REPORT WRITTEN BY:
William A. Heitbrink
Marjorie A. Edmonds
Thomas J. Fischbach
REPORT DATE:
September 1992
REPORT NO.:
ECTB 179-12a
U.S. DEPARTMENT OF HEaltH AND HUMAN SERVICES
Public Health Service
Centers for Disease Control
National Institute for Occupational Safety and Health
4676 Columbia Parkway
Cincinnati, Ohio 45226
DISCLAIMER
Mention of company names or products does not constitute endorsement by the
National Institute for Occupational Safety and Health.
PLANT SURVEYED: |
Kay Parks/Dan Meyer Autorebuild
3102 South Twelfth Street
Tacoma, Washington 98405 |
SIC CODE: |
7531 |
SURVEY DATE: |
September 16-19, 1991 |
SURVEY CONDUCTED BY: |
William A. Heitbrink
Marjorie A. Edmonds |
EMPLOYER REPRESENTATIVES
CONTACTED: |
Dan and Sue Meyer, Owners |
EMPLOYEE REPRESENTATIVE: |
Ron Kinzel
International Machinists and Aerospace |
WORKERS UNION LOCAL LODGE 1152: |
Tacoma Mall Boulevard
Tacoma, Washington 98409 |
TABLE OF CONTENTS
-
INTRODUCTION
-
Shop Description
Description of Ventilated Sanders
Spray Painting Booth and Room
-
POTENTIAL HAZARDS
-
Diisocyanates and Their Oligomers
Organic Solvents
Metals
-
EXPOSURE EVALUATION CRITERIA
EVALUATION PROCEDURES
-
Air Contaminant Exposure Monitoring
Video Exposure Monitoring
Ventilation Measurements
-
RESULTS
-
Ventilation Measurements
Air Sampling Results
Video Exposure Monitoring
-
DISCUSSION
-
Airflow Recommendations for the Spray Painting Booths
-
CONCLUSIONS
REFERENCES
APPENDIX A
-
Particulate Concentrations During Sanding and Spray Painting
-
APPENDIX B
-
Concentration of Organic Vapors in Parts Per Million During Spray Painting
-
APPENDIX C
-
Computation of Limits of Detection and Quantitation
-
APPENDIX D
-
Statistical Analysis of the Real-time Data
SUMMARY
Orbital and in-line sanders (Hutchins, Pasadena CA) with
built-in high-velocity, low-volume exhaust hoods were studied in an autobody repair shop.
Measurements made with an aerosol photometer showed that the use of the in-line sander
reduced worker exposure to aerosols by approximately a factor of 8. When air samples were
collected in the worker's breathing zone, to measure worker exposure to total particulate,
a quantifiable mass of aerosol (limit of quantitation = 0.1 mg total particulate) was not
collected on the filter. Based upon a statistical treatment of the filters' weight changes
and the sample volume, the total particulate exposures during sanding were estimated to be
1.5 mg/m 3 when using a 6-inch diameter orbital sander and 0.3 mg/m 3
when using an in-line sander. In addition, the air samples were also analyzed for lead
(limit of detection (LOD) = 2 µg/filter), cadmium (LOD = 1 µg/filter), and chromium (LOD
= 1 µg/filter). These metals were not detected on any of the filters.
In addition, air samples for particulate and solvent
exposures were collected in the worker's breathing zone while he spray painted cars and
car parts outside of a spray painting booth. During such spray painting operations, less
than one pint of paint is used. Solvent and total particulate exposures were below
exposure limits promulgated by OSHA and recommended by NIOSH.
Keywords: SIC 75319, total particulate, autobody repair,
spray painting, toluene, xylene, acetone, ventilated sanders.
INTRODUCTION
The National Institute for Occupational Safety and Health
(NIOSH) is the primary federal organization engaged in occupational safety and health
research. Located in the Department of Health and Human Services, it was established by
the Occupational Safety and Health Act of 1970. This legislation mandated NIOSH to conduct
a number of research and education programs separate from the standard setting and
enforcement functions conducted by the Occupational Safety and Health Administration
(OSHA) in the Department of Labor. An important area of NIOSH research deals with methods
for controlling occupational exposure to potential chemical and physical hazards. The
Engineering Control Technology Branch (ECTB) of the Division of Physical Sciences and
Engineering has been given the lead within NIOSH to study the engineering aspects of
health hazards prevention and control.
Since 1976, ECTB has conducted several assessments of
health hazard control technology based on industry, common industrial process, or specific
control techniques. The objective of each of these studies has been to document and
evaluate effective techniques for the control of potential health hazards in the industry
or process of interest, and to create a more general awareness of the need for, or
availability of, effective hazard control measures.
A study of autobody repair is being undertaken by the
Engineering Control Technology Branch to provide control technology information for
preventing occupational disease in this industry. This project is part of a NIOSH special
initiative on small business and will be accomplished by developing and evaluating control
strategies and disseminating control technology information to a small business. Several
types of candidate small businesses with potential hazards were originally identified from
letters from OSHA 7(c)(1) state consultation programs. From these letters, contacts with
state consultation program representatives, discussions between DSHEFS and DRDS, and
review of the literature, small businesses with potential hazards were ranked as to the
best candidate for a control technology study. From the list of candidate small
businesses, autobody repair and painting shops were one of several potential industries
that were selected for study.
The objective of the overall study on autobody repair and
painting shops is to provide these shops information about practical, commercially
available, control methods that reduce worker exposure to air contaminants (e.g.,
isocyanates, refined petroleum solvents, spray paint mists, and airborne particles). To
develop this information, commercially available control methods need to be evaluated in
actual shops. Control measures to be studied include: ventilated sanders and welders,
vehicle preparation stations, and spray painting booths. The results of individual
plant/facility evaluations and information available from the literature will be used to
develop recommendations on controlling worker exposure to air contaminants in autobody
repair and painting shops. Then, this control technology information will be disseminated
to autobody workers, owners, and operators of autobody repair and painting shops, and
safety and health professionals.
The purpose of this specific site visit was to evaluate
orbital and in-line sanders with high-velocity, low-volume (HVLV) exhaust hoods. These
sanders exhaust a small volume of air through the sanding pad to capture the sanding dust
at its source. This control has application to all types of sanding operations. Also, air
contaminant exposures were measured while spray painting was done outside of a spray
painting booth. In addition, monitoring was conducted to evaluate whether this practice
caused excessive worker exposure to air contaminants.
Shop Description
This autobody shop employs 14 workers; 10 workers repair
cars and 4 workers paint cars. It has been in operation for 20 years and repairs an
average of 5.5 cars per day. The layout of the shop is schematically illustrated in Figure
1. In the autobody repair area, the cars' structural damage is repaired. This involves the
repair and replacement of damaged parts. During these activities, the workers may be
exposed to aerosols from sanding, grinding, and welding. After the cars are repaired, they
are prepared for painting in the vehicle preparation area. This involves some sanding to
remove old paint and to provide a smooth surface for the
paint. According to shop rules, spray painting outside of a spray painting booth in the
vehicle preparation area is permitted when these two conditions are both satisfied:
- Less than a pint of paint is used; and,
- The paint does not contain isocyanates.
If more than a pint of paint is needed, or if the paint
contains isocyanates, the painting is done in a spray painting booth.
Ventilated sanders and spray painting booths are used to
control worker exposure to air contaminants. Ventilated sanders are used to control air
contaminants generated during sanding. A ventilated spray painting booth and a small parts
spray painting booth are used for spray painting jobs involving either isocyanates or more
than one pint of paint. The booths are used for spray painting cars and the small parts
spray painting booth is used for spray painting autobody parts. Air-supplied respirators
are worn by workers in the spray painting booth and the small parts spray painting booth.
When spray painting is conducted outside of a spray painting booth, workers wear half-face
piece air purifying respirators.
Description of Ventilated Sanders
Three types of sanders (Hutchins Manufacturing Company,
Pasadena, CA) are used in this autobody shop: 6-inch and 8-inch diameter orbital sanders
and a straight-line sander. These sanders were designed for use with a central vacuum
system. Air is exhausted through holes in the sander pads. The sand paper contains
prepunched holes which match the holes in the pad. Some details of these Hutchins sanders
are described in Table 1.
The exhaust from these sanders is attached to a vacuum
hose. At this connection, the static pressure in the vacuum line is 6 inches of Hg. The
flexible vacuum hose and compressed air lines are supported by retractors shown in Figure
2. Throughout this shop, 22 work stations have these vacuum hoses. After flowing through
the vacuum tubing, the air flows through piping into a bag house where it is filtered. The
airflow is provided by a 15 horse power turbine. The total installed cost for this system
was $38,000 in 1987.
Spray Painting Booth and Room
although the spray painting booth and spray painting room
were not the focus of this field investigation, some data was taken in the two spray
painting booths at this autobody shop. Cars entering or leaving the cross draft spray
painting booth had to pass through the small parts spray painting room. The small parts
spray painting room was 14 feet wide, 12.6 feet high, and 19 feet long. When the doors to
this room were closed, this room lacked makeup air. Air is exhausted from this room
through a plenum which is located next to the wall separating the spray painting room from
the cross draft spray painting booth. According to the owner, the spray painting booth was
12 feet high and 14 feet wide. The internal configuration of this spray painting booth was
not documented.
Table 1
Description of Sander Study
Type of Sander |
Hutchins Model
Number |
Action |
Description of Pad |
6-inch |
4500va |
random orbit |
A 6-inch diameter
pad. The sand paper has 6, 0.4 inch-diameter holes on a circle 1.5 inches from the
edge of the sand paper. |
8-inch |
4001ba |
random orbit |
A 8-inch diameter
pad. The sand paper has 12, 0.45-inch diameter holes on a circle 0.375 inches from
the edge of the sand paper. |
in-linesander |
2000 (Hustler) |
straight -
line |
The abrasive pad is
2.75 inches wide and 17.5 inches long. Along the length of the sand paper, two rows of
nine equally spaced holes are located 0.5 inches from the edge of the sandpaper. The holes
are 0.45 inches in diameter. |
POTENTIAL HAZARDS
Workers involved in autobody repair can potentially be
exposed to a multitude of air contaminants. During structural repair, activities such as
sanding, grinding, and welding generate aerosols which are released into the worker's
breathing zone. If the surface of the car being repaired contains toxic metals such as
lead, cadmium, or chromium, exposure to these metals is possible. Workers who paint cars
can be exposed to organic solvents, hardeners, which may contain isocyanate resins, and
pigments, which may contain toxic components.
The International Agency for Research on Cancer (IARC) has
reviewed the health effects associated with being a painter. 1 In the IARC
publication, the term "painters" included workers who apply paint to surfaces
during construction, furniture manufacturing, automobile manufacturing, metal products
manufacturing, and autobody refinishing. After reviewing a wide range of publications,
they concluded: "There is sufficient evidence for the carcinogenicity of occupational
exposure as a painter." In addition, they noted that painters suffer from allergic
and nonallergic contact dermatitis, chronic bronchitis, asthma, and adverse effects on the
central nervous system. Some of the health effects for specific air contaminants are
briefly summarized in the following paragraphs.
Diisocyanatesand Their Oligomers
The unique feature of all diisocyanate-based compounds is
that they contain two -N=C=O functional groups, which readily react with compounds
containing active hydrogen atoms to form urethanes. The chemical reactivity of
diisocyanates, and their ability to cross-link, makes them ideal for use in surface
coatings, polyurethane foams, adhesives, resins, and sealants. Diisocyanates are usually
referred to by their specific acronym; e.g., TDI for toluene diisocyanate or HDI for
hexamethylene diisocyanate. 2 To reduce the inhalation exposure to monomers due
to vaporization, the isocyanate monomers are prepolymerized into oligomers. These
prepolymers are believed to be trimers of the monomer. In commercial spray painting
operations, the monomer is usually less than 2 percent paint by weight. However, the
oligomers still pose an inhalation hazard to the workers as an aerosol.
Experience has shown that diisocyanates cause irritation to
the skin, mucous membranes, eyes, and respiratory tract. Worker exposure to high
concentrations may result in chemical bronchitis, chest tightness, nocturnal dyspnea
(shortness of breath), pulmonary edema (fluid in the lungs), and reduced lung function. 3,4
The most important and most debilitating health effect from exposure to diisocyanates is
respiratory and dermal sensitization. After sensitization, any exposure, even to levels
below any occupational exposure limit or standard, will produce an allergic response that
may be life threatening. 5,6 The only effective treatment for the
sensitized worker is cessation of all diisocyanate exposure. 7
Organic Solvents
Occupational exposure to organic solvents can cause
neurotoxic effects that can include dizziness, headache, an alcohol-like intoxication,
narcosis, and death from respiratory failure. 8 Automotive spray painters
exposed to organic solvents are reported to have decreases in motor and nerve conduction
velocities. 9 In addition, organic solvents such as acetone, toluene, and
xylene can cause eye, nose, and throat irritation. 10 Dermal exposure to
organic solvents can defat the skin and, thereby, increase the uptake of these solvents by
the body. In addition, dermal exposure can cause dermatitis. Some health effects
attributed to specific organic solvents are briefly summarized:
-
Acetone
Few adverse health effects have been attributed to acetone
despite widespread use for many years. Awareness of mild eye irritation occurs at airborne
concentrations of about 1000 ppm. Very high concentrations (12000 ppm) depress the central
nervous system, causing headache, drowsiness, weakness, and nausea. Repeated direct skin
contact with the liquid may cause redness and dryness of the skin.11
Exposures over 1000 ppm cause respiratory irritation, coughing, and headache.
n-Butyl Acetate
At concentrations exceeding 150 ppm, significant irritation
of the eyes and respiratory tract are reported in the literature.12
n-Butyl Alcohol
n-Butyl alcohol is an irritant to the eyes and the mucous
membranes of nose and throat. Exposures over 200 ppm can cause keratitis.10
Eye irritation and headaches have been reported at concentrations in excess of 50 ppm.12
Exposure to n-butyl alcohol is reported to increase hearing losses for workers who
are also exposed to noise.
Ethyl Acetate
Ethyl acetate vapor is irritating to the eyes and
respiratory passages of humans at concentrations above 400 ppm.(12) In animals it has a
narcotic effect at concentrations of over 5000 ppm.
Isopropyl Alcohol
At exposures above 400 ppm, irritation to the eyes, nose,
and throat are reported. Above 800 ppm, the symptoms intensified.12
Trimethyl Benzene
Trimethyl benzene has been reported to cause nervousness,
anxiety, and asthmatic bronchitis.12
Toluene
Toluene can cause irritation of the eyes and respiratory
tract, dermatitis, and central nervous system depression.10 At concentrations
of 200 ppm or less, complaints of headaches, lassitude, and nausea have been reported. At
concentrations of 200-500 ppm, loss of memory, anorexia, and motor impairment are
reported.12 In addition, muscle impairment and increased reaction time can
occur at exposures of greater than 100 ppm.
Xylene
Xylene vapor may cause irritation of the eyes, nose, and
throat. Repeated or prolonged skin contact with xylene may cause drying and defatting of
the skin which may lead to dermatitis. Liquid xylene is irritating to the eyes and mucous
membranes, and aspiration of a few milliliters may cause chemical pneumonitis, pulmonary
edema, and hemorrhaging. Repeated exposure of the eyes to high concentrations of xylene
vapor may cause reversible eye damage.13 At concentrations between 90 and
200 ppm, impairment of body balance, manual coordination, and reaction times can occur.
Acute exposure to xylene vapor may cause central nervous system depression and minor
reversible effects upon liver and kidneys.1 Workers exposed to concentrations
above 200 ppm complain of loss of appetite, nausea, vomiting, and abdominal pain.
Brief exposure of humans to 200 ppm has caused irritation of the eyes, nose, and throat.14
Metals
Toxic metals such as lead, chromium, and cadmium may be
used as pigments in some paints. As a result, welding and sanding on these surfaces may
involve occupational exposure to toxic metals. In addition, autobody welding will involve
exposure to welding fumes. Health effects attributed to specific metals are discussed below:
-
Cadmium
Cadmium is a toxic heavy metal which may enter the body
either by ingestion (swallowing) or by inhalation (breathing) of cadmium metal or oxide.
Once absorbed into the body, cadmium accumulates in organs throughout the body, but major
depositions occur in the liver and kidneys.15 Acute inhalation exposure
to high levels of cadmium can cause respiratory irritation and pulmonary edema. In
addition, cadmium exposure causes kidney damage.16 Chronic exposure may
lead to emphysema of the lungs and kidney disease which may be associated with
hypertension.17 After finding that exposure to cadmium has been
associated with excess respiratory cancer deaths among cadmium production workers, NIOSH
has concluded that cadmium is a potential occupational carcinogen.18
Chromium
Some paints may contain chromates hexavalent chromium as a
pigment. These compounds can produce health effects such as contact dermatitis, irritation
and ulceration of the nasal mucosa, and perforation of the nasal septum.16 Certain
insoluble hexavalent chromium compounds are suspect carcinogens.19
Lead
Lead adversely affects several organs and systems. The four
major target organs and systems are the central nervous system, the peripheral nervous
system, kidney, and hematopoietic (blood-forming) system.20 Inhalation or
ingestion of inorganic lead can cause loss of appetite, metallic taste in the mouth,
constipation, nausea, pallor, blue line on the gum, malaise, weakness, insomnia, headache,
muscle and joint pains, nervous irritability, fine tremors, encephalopathy, and colic.16
Lead exposure can result in a weakness in the wrist muscles known as "wrist
drop," anemia (due to lower red blood cell life and interference with heme
synthesis), proximal kidney tubule damage, and chronic kidney disease.21,22
Lead exposure is associated with fetal damage in pregnant women.16 Lastly, elevated
blood pressure has been positively related to blood lead levels.23,24
EXPOSURE EVALUATION CRITERIA
As a guide to the evaluation of the hazards posed by
workplace exposures, NIOSH field staff employ environmental evaluation criteria for
assessment of a number of chemical and physical agents. These criteria are intended to
suggest levels of exposure to which most workers may be exposed up to 10 hours per day, 40
hours per week, for a working lifetime without experiencing adverse health effects. Table
2 summarizes exposure limits for air contaminants which may be present in autobody shops.
It is, however, important to note that not all workers will be protected from adverse
health effects if their exposures are maintained below these levels. A small percentage
may experience adverse health effects because of individual susceptibility, a preexisting
medical condition, and/or a hypersensitivity (allergy).
In addition, some hazardous substances may act in
combination with other workplace exposures, the general environment, or with medications
or personal habits of the worker to produce health effects even if the occupational
exposures are controlled at the level set by the evaluation criterion. These combined
effects are often not considered in the evaluation criteria. Also, some substances are
absorbed by direct contact with the skin and mucous membranes and thus, potentially
increase the overall exposure. Finally, evaluation criteria may change over the years as
new information on the toxic effects of an agent become available.
The primary sources of environmental evaluation criteria in
the United States that are used for the workplace are: 1) NIOSH Recommended Exposure
Limits (RELs); 2) the American Conference of Governmental Industrial Hygienists' (ACGIH)
Threshold Limit Values (TLVs); and 3) the U.S. Department of Labor (OSHA) Permissible
Exposure Limits (PELs). The OSHA PELs are required to consider the feasibility of
controlling exposures in various industries where the agents are used; the NIOSH RELs, by
contrast, are based primarily on concerns relating to the prevention of occupational
disease. ACGIH Threshold Limit Values (TLVs) refer to airborne concentrations of
substances and represent conditions under which it is believed that nearly all workers may
be repeatedly exposed day after day without adverse health effects. ACGIH states that the
TLVs are guidelines. The ACGIH is a private, professional society. It should be noted that
industry is legally required to meet only those levels specified by OSHA PELs.
Table 2
Occupational Exposure Limits
Substance |
NIOSH Recommended Exposure Limit Limit26 |
OSHA Permissible Exposure Limit26 |
b27 |
|
TWAa |
TWAb |
STELc |
TWAa |
STELc |
Acetone |
250 ppm |
750 ppm |
1000 ppm |
750 ppm |
1000 ppm |
n-Butyl acetate |
150 ppm |
150 ppm |
200 ppm |
150 ppm |
200 ppm |
Cadmium |
Lowest feasible concentration (0.01 mg/m3 Limit of quantitation) |
0.2 mg/m3
as an 8 hour time weighted-average 0.6 mg/m3 as a ceiling |
|
a 0.05 mg/m3 |
|
Chromium compounds with a valence of 2 or 3 |
0.5 mg/m3 |
0.5 mg/m3 |
|
0.5 mg/m3 |
|
Hexavalent Chromium |
0.001 mg/m3 |
1 mg/10 m3 as a ceiling |
|
0.05 mg/m3 |
|
Ethyl acetate |
400 ppm |
400 ppm |
|
400 ppm |
|
IsopropyL alcohol |
400 ppm twa 800 ppm Ceiling |
400 ppm |
500 ppm |
400 ppm |
500 ppm |
HexamethyLene diisocyanate
(HDI monomer) |
5 ppb twa28
20 ppb Ceiling |
|
|
5 ppb |
|
Lead |
Less than 0.1
mg/m3
so that blood Lead Levels remain below 0.06 mg of lead per 100 grams of whole blood. |
50 µg/m3
for an 8-hour day29 |
|
0.15 mg/m3 |
|
Particulate (not
otherwise regulated) total respirable |
|
15 mg/m3
5 mg/m3 |
|
10 mg/m3
5 mg/m3 |
|
Toluene |
100 ppm TWA
200 ppm Ceiling |
100 ppm |
150 ppm |
100 ppm |
150 ppm |
Trimethyl benzene |
|
25 ppm |
|
25 ppm |
|
XyLene |
100 ppmTWA
200 ppm Ce i l i ng |
100 ppm |
150 ppm |
100 ppm |
150 ppm |
a TWA - Time-Weighted Average based upon a 10 hour day, 40 hour work week for NIOSH Recommended Exposure Limit.
b TWA - 8-hour Time-Weighted Average.
c STEL - Short-Term Exposure Limit.
A time-weighted average (TWA) exposure refers to the
average airborne concentration of a substance during a normal eight to ten hour workday.
Some substances have recommended short-term exposure limits or ceiling values that are
intended to supplement the TWA where there are recognized toxic effects from high
short-term exposures.
Generally, spray painters are exposed to multiple solvents.
To evaluate whether the total solvent exposure is excessive, a combined exposure, CE,
is computed:
C1
C2 Cn
CE = -- + -- +.... + --
L1 L2
Ln
Where:
C = Exposure to an individual contaminant, and;
L = The lowest exposure limit for the corresponding contaminant listed in
Table 1.
When the value of C E is less than 1, the
combined exposure is believed to be acceptable.
EVALUATION PROCEDURES
The objective of this site visit was to obtain an
appreciation of the ventilated sanders' ability to control worker exposure to sanding
dust. To evaluate the effectiveness of the Hutchins sanders' ventilation, worker air
contaminant exposures were measured. The exhaust airflow volume of the Hutchins sanders
were measured.
At this autobody shop, autobody spray painting is done
outside of a spray painting booth when less than a pint of paint is used. Air sampling was
done to evaluate whether this restriction keeps worker air contaminant exposures below the
limits specified in Table 2.
Air Contaminant Exposure Monitoring
The worker's total particulate exposure was measured using
NIOSH Method 0500. 30 In this method, a known
volume of air is drawn through a preweighed PVC filter at a flow rate of 3.5 liters per
minute using a personal sampling pump (Aircheck Sampler, Model 224 -- PCXR7, SKC Inc,
Eighty Four, PA). The weight gain of the filter is used to compute the milligrams of
particulate per cubic meter of air. After weighing, the filters were analyzed for lead,
cadmium, and chromium. The filters were digested using NIOSH Method 7300 and were diluted
to 25 mL. Then a simultaneous scanning inductively coupled plasma emission spectrometer
was used to analyze the samples for lead, cadmium, and chromium.
Material safety data sheets were used to identify the major
organic solvents which may be present during spray painting. Exposures to these solvents
were measured: acetone, n-butyl acetate, ethyl acetate, isopropyl alcohol, n-butyl
alcohol, toluene, and xylene. Exposure measurements were made by placing charcoal tubes
(SKC lot 120) in a charcoal tube holder and mounting the charcoal tube holder on the
worker. Tubing connects the outlet of the charcoal tube holder to a personal sampler pump
(Model 200, Dupont Inc.) that draws air through the charcoal tube at 200 cm 3/min. The collected solvents are desorbed from the
charcoal using carbon disulfide and the solvents are quantitated using a gas chromatograph
equipped with a flame ionization detector. NIOSH Methods 1300, 1400, 1450, 1401, and 1501
were used with some modifications. 31 The
modifications are listed below:
Desorption Process: |
Thirty minutes in 1.0 milliliter
of carbon disulfide with 0.5 microliter ethyl benzene/ml CS2 as an internal
standard and 1 percent n-propyl alcohol as a desorbing aid. |
Gas Chromatograph: |
Hewlett-Packard Model 5890
equipped with a flame ionization detector. |
Column: |
30m x 0.32mm fused silica
capillary coated, internally with 0.5 µm of DB-EAD. |
Oven Conditions: |
35 °C for five minutes,
temperature increase at a rate 5 ° C/minute until a temperature of 75 ° C is reached.The
latter temperature is held for two minutes. |
In addition to collecting personal samples for metals,
particulates, and organic solvents, area samples were collected away from the operation of
interest. When sampling was done in the autobody repair area, area samples were collected
5-10 feet away from the worker. In the autobody preparation area, the area samples were
collected at the location noted in Figure 1.
Video Exposure Monitoring
Video exposure monitoring was used to study in greater
detail how specific tasks affect the workers' exposure to air contaminants. 32,33 Worker exposures were monitored with a direct
reading instrument, and its analog output was recorded with a data logger. Workplace
activities were simultaneously recorded on videotape. The analog output of the real-time
instruments was connected to a data logger (Rustrak Ranger, Gulton, Inc., East Greenwich,
RI). When the data collection was completed, the data logger was downloaded to a portable
computer (Compaq Portable III, Compaq Computer Corporation, Houston, TX) for analysis.
During vehicle preparation operations, the Hand-held
Aerosol Monitor (HAM, PPM Inc., Knoxville, KY) was used to measure relative air
contaminant concentrations during sanding operations. The aerosol scatters the light
emitted from a light emitting diode. The scattered light is detected by a photomultiplier
tube. The analog output of the HAM is proportional to the quantity of the scattered light
detected by a photomultiplier tube. Because the calibration of the HAM varies with aerosol
properties such as refractive index and particle size, the analog output of the HAM is
viewed as a measure of relative concentration. An Aircheck personal sampling pump
(Aircheck, SKC Inc, Eighty Four, PA) was used to draw air through the HAMs sensing chamber
at a rate of 3.5 lpm.
During spray painting, a Microtip HL200 (PHOTOVAC Inc,
Thornhill, Ontario) was used to monitor worker solvent exposure. The analog output of the
Microtip is proportional to the concentration of ionizable compounds in the air. Because
the instrument's response varies with the composition of the organic solvents in the air,
this instrument also is used as a measure of relative concentration. Because of fire
safety considerations, this instrument was located outside of the spray painting area.
Teflon tubing (0.125 inside diameter, 45 feet long, Alltech Associates, Deerfield, IL) was
attached to the worker in his breathing zone. A personal sampler pump drew air through
this tubing at 3.5 liters per minute and exhausted the sampled air into a glass tee. The
Microtip then sampled the air in this glass tee.
Ventilation Measurements
The exhaust flow rates from the ventilated sanders were
measured in the apparatus illustrated in Figure 3. The exhaust flow rate was measured when
the sanders were off, when they were on (but not sanding), and when they were sanding
metal on the bottom of the apparatus. The air velocity in the exhaust duct was measured
using a hot wire anemometer (Model 1040 Digital Air Velocity Meter, Kurz, Carmel Valley,
CA). The exhaust flow rate was calculated as the product of the duct's cross sectional
area and 0.9 times the air velocity at the duct's centerline.
Figure 3. Apparatus for measuring the exhaust airflow of ventilated tools.
Exhaust fans for the spray painting booth and the small
parts spray painting booth were located on the roof of the autobody shop. The area through
which the fan discharges the air and the exhaust velocity were measured. From this data,
the exhaust volume of each fan was estimated as the product of the area and exhaust
velocity.
RESULTS
Ventilation Measurements
Tables 3 and 4 summarize the ventilation measurements. The
sanders ventilation rates are summarized in Table 3. Turning the compressed air on for the
6-inch sander and the in-line sander decreased the exhaust flow rates because the
compressed air is discharged into the vacuum hose. The flow rates during sanding appeared
to decrease about 20 percent pending the force applied to the sander.
The small parts spray painting booth has no provisions for
makeup air. As a result, its exhaust flow rate decreased dramatically when the doors to
this booth room were closed. This booth is exhausted by two fans which move about 650 cfm.
However, one fan also exhausts air from a paint mixing area near the small parts spray
painting booth. When this booth's door is closed, the air will follow the path of least
resistance to the fan, which is apparently through the exhaust grates in the paint mixing
area. Closing this door increases the paint mixing area flow rate from 130 to 630 cfm and
decreases the exhaust flow from the small parts spray painting booth from 1200 to 400 cfm.
Table 3
Sander Ventilation Rates
Type of Sander |
Exhaust Flow Rate(cfm) |
Compressed Air Off
On |
Sanding on Sheet Metal |
6-inch sanding pad |
67 |
47 |
35 |
9-inch sanding pad |
68 |
68 |
45 |
in-line sander |
18 |
14 |
15 |
Table 4
Exhaust Ventilation Rates Measured on the Roof
Exhaust Flow Measurement |
Exhaust Flow Rate (cfm) |
Measured |
Recommended |
Central vacuum system |
310 |
NA |
Cross draft spray painting booth.
The recommended flow rate is based on the booths cross sectional area (14 feet wide and a
height of 12.6 feet). For such booths, ACGIH recommends an exhaust volume of 50
cfm/ft2 of cross sectional area. |
11800 |
17500 (OSHA)34
8750 (ACGIH)35 |
Car repair area, east side |
6880 |
NA |
Car repair area, west side |
2650 |
NA |
Paint preparation area, local
exhaust ventilation at paint mixing area. The exhaust volume is affected by the
small parts spray painting booth doors:
open
closed |
130
630 |
NA |
Small parts spray painting booth;
doors open
doors closed |
1200
425 |
17500 (OSHA)
8750 (ACGIH)
1600 (Oregon)36 |
Area for autobody preparation and
painting of small areas on the car. The recommended exhaust rate is based upon the
assumption that one pint of toluene is evaporating in a ten minute period. In actual
practice, the paints used are a mixture of organic solvents, and these paints contain
solid materials which do not evaporate. |
3950 |
3800
(ACGIH)37 |
Air Sampling Results
The results of individual air samples are presented in
Appendices A and B. The concentration of particles in the air was computed by
subtracting the average weight change of blank filters from the weight change of the
sample filters and dividing this difference by the sample volume. For some samples, the
individual filters actually lost more weight than the average of the blank filters; so,
these concentrations are labelled with an "n" to indicate that the computed
concentration is less than zero. although individual sampling results did not provide
insight into the exposures encountered during sanding and spray painting operations, the
sum filters weight changes and sample volumes were used along with the blank correction to
compute a time-weighted average concentration. As described in Appendix C, the standard
deviation of the blank filters was used to estimate a limit of detection (LOD) and a limit
of quantitation (LOQ) for these time-weighted average concentrations listed in Table 5.
Table 5
Summary of Particulate Air Sampling Results
Operations for Which Particulate Exposures were Monitored |
Number of Samples |
Concentration+ (mg/m3) |
Spraying parts in large spray painting area |
4 |
6.9 |
Spray painting small area on a car in the large spray painting area |
3 |
2.1 |
Spray painting parts in small parts spray painting booth |
1 |
25.0 |
Spray painting a car in a booth |
1 |
4.6 |
Sanding with a ventilated 6-inch sander |
3 |
1.5 |
Sanding with a ventilated in-line sander |
4 |
0.3* |
Sanding with an unventilated in-line sander |
1 |
2.1* |
+ - These are short-term, time-weighted average concentrations.
* - The result is between the estimated limits of qualitation and quantitation. See Appendix C for details.
Most of the short-term exposures listed in Table 5 were
below the exposure limits listed in Table 2. However, in Table 5, one short-term air
sample for particulates revealed a concentration of 24 mg/m 3
for a 17 minute period. Because the OSHA PEL for an eight hour time-weighted average
exposure is 15 mg/m 3 and the worker had other
duties which involve particulate exposures which were well below 15 mg/m 3, this worker's particulate exposure over the an eight
hour period is probably less than 15 mg/m 3. This
study was not conducted specially to evaluate compliance with OSHA PELs and eight hour
time-weighted average samples were not collected. However, this single sample indicates a
need to improve ventilation in the small parts spray painting booth. Recommendations for
improving the ventilation in this booth are discussed later.
In addition to analyzing the filters for total amount of
particulate in the air, the filters were analyzed for lead, cadmium, and chromium. The
amount of these metals on the filters was less than the detection limit. The limits of
detection for cadmium, chromium, and lead were respectively 1, 1, and 2 µg per sample.
Solvent exposure during spray painting operations were
generally low and exposures to individual solvents are presented in Appendix B. Table 6
shows the results of computing the combined exposure, C E. This computation
assumes that the exposures take place over an eight hour day. In reality, the workers only
spend a fraction of each day spray painting. The results in Table 6 indicate that, under
the conditions present during testing, exposures are within permissible limits.
Because the composition of paints varies, one cannot tell
whether the use of a high velocity, low pressure (HVLP) spray gun actually reduces worker
solvent exposure. However, one of the highest and one of the lowest combined solvent
exposures occurred with a conventional spray painting gun.
Video Exposure Monitoring
The results presented in Figures 4 and 5 show the output of
HAMs while the worker was using the in-line sander to smooth body filler which had been
applied to a door. The effectiveness of the ventilated sanders was demonstrated by
comparing dust exposures while using an unventilated in- line sander. As shown in Figure
4, the worker's exposure increased dramatically when the nonventilated sander was in use.
Based upon the HAMs response, the use of the ventilated sander apparently decreased the
worker's particulate exposure by a factor of about 8. The statistical analysis presented
in Appendix D shows that decrease was statistically significant.
Table 6
Combined Solvent Exposures
Operation |
Spray Painting Gun |
Date |
Sample Start Time |
Sample Stop Time |
CE |
Spray painting small area on car outside of a booth |
HVLP |
9/16 |
11:00 |
11:25 |
0.18 |
Spray painting small area on car outside of a booth |
HVLP |
9/16 |
13:10 |
13:35 |
0.69 |
Spraying parts within small parts spray painting booth |
HVLP |
9/17 |
9:25 |
9:42 |
0.31 |
Spray painting car in large booth |
HVLP |
9/17 |
14:42 |
15:45 |
0.05 |
Spray painting parts ouside of a booth |
HVLP |
9/17 |
10:56 |
11:05 |
0.07 |
Spray painting small area on car outside of a booth |
HVLP |
9/18 |
9:07 |
9:35 |
0.16 |
Spray painting parts outside of a booth with conventional gun |
Conventional |
9/18 |
11:21 |
11:27 |
0.49 |
Spray painting parts outside of a booth with a conventional spray painting gun |
Conventional |
9/19 |
Sampling times obtained from pump's built-in timer |
0.10 |
Spray painting parts outside of booth |
HVLP |
9/19 |
Sampling times obtained from pump's built-in timer |
0.14 |
Figure 4. Sanding with a ventilated and unventilated in-line sander.
Figure 5. Background concentrations measured while data in Figure 4 was taken
While a worker was sanding quarter panels with
a 6-inch sander, HAMs wereused to monitor the worker's particulate exposure and the
background concentration. This result is presented in Figure 6. This sander was
ventilated. The fact that the background measurement is higher than the measurement on the
worker is probably due to a slight difference between instruments. |
|
|
Figure 6. output of a HAM while worker was sanding auto parts using a 6-inch ventilated sander. |
|
While a worker spray painted two body panels using an HVLP spray painting gun, his exposure to solvent vapors was monitored with a
Microtip. Its output was recorded using a data logger, and the worker's activities were
videotaped. Figure 7 shows the response of the Microtip to organic vapors. Viewing of the
videotape reveals that spray painting outside of a booth disperses the overspray
throughout the work area. While spray painting, the worker moved around the panel and
periodically returned to his bench which was 5-10 feet from where the spray painting was
being done. A statistical analysis presented in Appendix D found that the worker's
exposure did not vary with his location. The worker's exposure was observed to increase
with spraying time and decrease with length of time after spraying had ceased. |
Figure 7. Response of Microtip to
solvent vapors generated by spray painting autobody parts in large painting area. |
DISCUSSION
The video exposure monitoring data suggests that the
ventilated sanders control much of the aerosol generated during sanding. Based upon the
limits of detection in Table 5, the total dust samples indicate that the worker's
particulate exposure is less than 1-2 mg/m 3. The
HAM readings taken when the 6-inch sander and the in-line sander were used suggest that
the worker's respirable particulate exposure during sanding may actually be less than 0.2
to 0.1 mg/m 3. Typically, the concentration of
particles smaller than 10 µm in the ambient environment is generally less than
0.1 mg/m 3 and is typically between 0.02 and 0.06
mg/m 3. 38
Because aerosol photometers are relatively insensitive to particles larger than 10 µm,
aerosol photometer measurements do not provide much insight as to whether the sanders are
capturing the larger particles which have most of an aerosol's mass. although the
available data indicates that these sanders apparently do provide a degree of dust
control, the data does not provide a complete understanding of the abilities and
limitations of devices to control worker dust exposure during sanding. Thus, there is a
need for further evaluation.
The workers liked the installation of the ventilated
sanders. The retractors kept the exhaust hoses and compressed air lines at a convenient
location. Because of this convenience, these sanders were always used with the exhaust
hose. In other shops visited by the survey team, the hoses were stored separately from the
tools. As a result, workers had to take time to find the exhaust hoses, and this lack of
convenience results in some sanding without ventilation.
Airflow Recommendations for the Spray Painting Booths
Table 4 lists exhaust volume recommendations for different
sources for the spray painting booth and the small parts spray painting room. In the spray
painting booth, the worker's particulate exposure and solvent exposure were below the
exposure limits listed in Table 2. although the spray painting booth's flow rates are
below the flow rates specified in OSHA standard 29 CFR 1910.94(c), ventilation standards
are enforced only when there is a violation of the OSHA PELs specified in Table 2. The
flow rate is well above that recommended by ACGIH. Furthermore, the state of Washington's
Division of Safety and Health considers these standards to be recommendations to
employers. 39 As stated in this manual:
"Ventilation within this category (Health-Related Ventilation Standards)" will
be considered adequate when the concentration of air contaminants to which employees are
exposed does not exceed recognized hazardous levels." Based on the limited sampling
and evaluation, there is no urgency, at present, to change the spray painting booth's flow
rate.
In the small parts spray painting booth, the worker's
particulate exposure was 24 mg/m 3 indicating that
the ventilation in this room needs to be improved. At the time of the study, closing the
doors caused the airflow out of this room to drop from 1200 cfm to 400 cfm. Clearly, the
worker's exposure to total particulate could be reduced by introducing makeup air into
this room. The state of Oregon specifies at least 30 air changes per hour for spray
painting rooms. 36 This results in a recommended
air flow of 1600 cfm of air flow for spraying rooms. At a ventilation rate of 1600 cfm,
applying less than a pint of paint to autobody parts in a ten minute period would result
in exposures below 100 ppm (the REL for solvents such as xylene). This assumes that half
of the paint is a volatile organic solvent such as xylene. Furthermore, restricting the
amount of paint used should also result in lower particulate exposures. If this
recommendation is followed, air sampling should be done to document the exposures which
result.
Generally, a face velocity of 100 fpm is specified to
control the paint overspray at spray painting booths and hood. 34
However, the American Conference of Governmental Industrial Hygienist's ventilation manual
specifies 50 fpm air velocity in an automotive spray painting booth when the cross
sectional area is greater than 150 square feet and 100 fpm when the cross sectional area
is less than 150 square feet. 35 When a cross draft
automotive spray painting booth with a face velocity of
100 fpm was used to spray paint an entire car, worker total particulate exposures ranged
between 4 and 16 mg/m 3, and solvent exposures were
below NIOSH recommended exposure limits. 40 This
suggests that if the cross draft spray painting booth were used for spray painting small
parts instead of the small parts spray painting booth, the worker's particulate exposure
should be reduced. Because this shop already has a cross draft spray painting booth, it
probably does not make sense to convert the small parts spray painting booth to a shorter
version of a cross draft spray painting booth.
CONCLUSIONS
The ventilated Hutchins sanders studied at this autobody
shop appear to be useful for controlling worker exposure to aerosols generated during
sanding. The available data indicate that the workers' particulate exposures are less than
1-2 mg/m 3 when the ventilated sanders are in use.
For the conditions observed in this study, spray painting
outside of a spray painting booth or the small parts spray painting booth did not cause
excessive solvent or particulate exposures when less than a pint of paint was used.
However, spray painting in the small parts spray painting booth did result in a short-term
exposure to a spray painting mist of 24 mg/m 3 for
a 17 minute period. This single sampling result does indicate that the ventilation in the
small parts spray painting booth is inadequate. This exposure could be minimized by
providing makeup air for the small parts spray painting room.
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In Appendix A, the weight change of many of the filters is
actually negative. However, after correcting for the weight change of the field blanks
(unused filters), positive values of concentrations were computed. In Appendix A,
four of the seven personal samples for sanding operations resulted in filters which lost
less weight than the average of the blank filters. After correction for the weight change
of the blank filters, individual values of concentrations are computed to have positive
values. Because the uncertainty in these individual concentration values is greater
than ±20%, the individual values of concentration are not very meaningful. In order to
obtain some information about the exposures during the operations listed in Table 5,
individual sampling results can be combined to compute a single time-weighted average
concentration for each operation listed in Table 5. This is done dividing the sum of the
individual filter weight gains (after correction for the blank) by the sum of the
individual sample volumes. From the sums, a single value of concentration is computed.
From the standard deviation of the field blanks (sb),
the uncertainty in the time-weighted average concentration can be evaluated. The
development of the formulas for estimating the standard deviation sum of the filter weight
gains is presented below.
In order to compute a time-weighted average concentration,
the sum of the filter weight gains, mtotal, is computed:
Where:
k = number of samples which are being summed, and;
b = mean weight change of field blanks.
Since the members of sample of filter weights, {mi}, are
assumed to have equal variances, ,
and are statistically independent of each other and
of b, the variance of m total is given by:
Where:
= the variance assumed for any blank filter, and;
n = number of blank filters used to estimate the mean weight change of the blank filters.
-
Note: the result in equation 2 follows from the general
formula for the variance of a linear combination of random variables, e.g., u = ar + ds
where a and d are constants and r and s are random variables:
These expressions were generalized to the sum of the k
terms mi, as i ranges from 1 to k, and k times the average blank filter weight
corrections when equation 1 is expanded. These k+1 terms are statistically independent
and, therefore, all pairwise correlations are zero. The term involving k2 in
equation 2 occurs because the average blank weight is multiplied by the constant k in
equation 1 when it is expanded.
The term is the variance of the filter weighing process which is
assumed to be the same for any filter whether blank or not. Thus, it is assumed that
Using this assumption, equation 2 may be simplified as follows:
Since is used to estimate
, the estimated variance for the
total weight gain, is
computed by substituting in equation 4 to obtain:
Thus, the required estimator for standard deviation for the sum of the filter weight gains is given as:
Then the limits of detection and quantitation can be computed:
limit of detection = |
3 S tot
|
total volume of air sampled |
limit of quantitation = |
10 S tot
|
total volume of air sampled |
The limits of detection (LOD) and quantitation (LOQ) are
used to evaluate the quality of environmental data.41 When the LOD is exceeded,
there is a 99 percent probability that an analyte has been measured. When the summed mass
does not exceed the LOD, one is uncertain whether these computed concentrations reflect
the actual particle collection or the experimental noise in the measurement process. When
the LOQ is exceeded, the uncertainty in the measured concentration is less than 30 percent
at the 99 percent level of confidence. When the measured concentration is between the LOD
and the LOQ, the results are reported although they are known to be imprecise.
The real-time data collected during the use of the in-line sander and during
spray painting was analyzed by regression analysis using the SAS General
Linear Models Procedure to determine whether events in the workplace affected relative
concentrations, which were literally the analog output of the instruments in volts. After
down loading and file conversion, the analog output was imported into a spreadsheet. Each
row in the spreadsheet contained the relative concentration at the end of a one second
sampling period. A videotape of the worker's activity was viewed and variables were added
to describe events in the workplace. For the data taken with the in-line sander, a column
was added to describe whether the worker was sanding with a ventilated sander, sanding
with an unventilated sander, or not sanding. For the data taken while the worker was spray
painting with an HVLP spray painting gun, two columns of explanatory variables were added.
One column was coded to describe whether the worker was actually spraying paint. A second
column was added to describe the location of the worker relative to the object being
sprayed. As schematically illustrated in Figure D1, the worker had five possible
locations, away from the object, in front of it, behind it, right side, and left side.
After assembling all of the data on a spread sheet, the data was analyzed using the
Statistical Analysis System's general linear models procedure. 42
Figure D1. Schematic illustrating the worker's locations during spray painting.
Before conducting the statistical analysis, the logarithm
of the relative concentration was computed and this value was termed C in the regression
models. Real-time data generally involves autocorrelation which is caused by the
dependency of the present value of concentration measurements upon past values of
concentration. This causes an understatement of the data's variability and an
overstatement of the conclusions which are obtained from the analysis. To minimize these
complications, the regression models included prior values of C in the preceding time
intervals.
The real-time data collected with the in-line sander was used to fit a model of this form:
Where:
C j = The logarithm of the relative concentration
in the j-th interval preceding the measurement. These are called lagged values of C j.
A1 = 1 if the worker is sanding with the ventilated sander, otherwise the value is 0.
A2 = 1 if the worker is not sanding, otherwise the value is 0.
ß = regression coefficients.
In this model, the regression coefficient for A 1
is an estimate of the concentration difference between the ventilated and the
nonventilated sander. The value of this regression coefficient and the other regression
coefficients are shown in Figure D2 under the column labelled "Estimate."
The physical magnitude of this estimate is low because of the inclusion of lagged values
of C j. The column labelled "Pr > |T|" is the probability that
chance could have caused the observed regression coefficient to differ from zero. The
probabilities for the regression coefficients for C j indicate that
autocorrelation is occurring. The probability for A 1's regression coefficient
is 0.0003. This indicates that it is unlikely that the observed difference is due to
chance, and one can conclude that the ventilated sander does reduce the aerosol
concentration.
The real-time data collected during the spray painting
operation was used to fit a model of this form:
Where:
-
L1 = | 1 if worker is away from the object being
spray painted, otherwise the value is 0. |
L2 = | 1 if the worker is behind the object being
spray painted, otherwise the value is 0. |
L3 = | 1 if worker is in front of the object being
spray painted, otherwise the value is 0. |
L4 = | 1 if the worker is on the left hand side of
the object being spray painted, otherwise the value is 0. |
Ts = | Cumulative time spent spraying since last
break in spraying (seconds). |
TNS = | Cumulative time spent with spray gun off
since the last episode of spraying. |
Source |
DF |
Sum of Squares |
Mean Square |
F Value |
Pr > F |
|
|
|
|
|
|
Model |
11 |
1053.445321 |
95.767756 |
2684.10 |
0.0 |
|
|
|
|
|
|
Error |
959 |
34.216744 |
0.035680 |
|
|
|
|
|
|
|
|
Corrected Total |
970 |
1087.662065 |
|
|
|
|
|
|
|
|
|
|
R-Square |
C.V. |
Root MSE |
|
LOGC Mean |
|
0.968541 |
-6.720999 |
0.188890 |
|
-2.8104522 |
|
|
|
|
|
|
Dependent Variable: C |
|
|
|
|
|
|
T for HO: |
Pr > |T| |
Std Error of |
|
Parameter |
Estimate |
Parameter = 0 |
|
Estimate |
|
INTERCEPT |
-0.040594737 B |
-2.27 |
0.0233 |
0.01786977 |
|
C1 |
1.040180383 |
32.22 |
0.0001 |
0.03228142 |
|
C2 |
-0.080487968 |
-1.73 |
0.0843 |
0.04658461 |
|
C3 |
-0.045055881 |
-0.97 |
0.3344 |
0.04664895 |
|
C4 |
0.025904838 |
0.56 |
0.5781 |
0.04656780 |
|
C5 |
-0.041088151 |
-0.88 |
0.3770 |
0.04648488 |
|
C6 |
0.046441989 |
1.00 |
0.3182 |
0.04650026 |
|
C7 |
-0.024902833 |
-0.54 |
0.5924 |
0.04650167 |
|
C8 |
-0.014503289 |
0.31 |
0.7547 |
0.04640520 |
|
C9 |
0.022963210 |
0.71 |
0.4752 |
0.03214755 |
|
ACTIVITY
1 (A1) |
-0.096387608 B |
-3.62 |
0.0003 |
0.02662823 |
|
2 (A2) |
-0.074639294 B |
-2.62 |
0.0089 |
0.02846210 |
|
3
|
0.000000000 B |
|
|
|
|
Figure D2. Selected output from SAS for the analysis of the
real-time data collected when the ventilated sander was in use. The terms C1-C9 is the
value of C in the preceding 1 through 9 time intervals respectively.
The terms TS and TNS were included
because concentration increases when spraying occurs and decreases when spraying ceases.
As a source of variability, an analysis of variance, conducted as part of the SAS General
Linear Models procedure, showed that the worker's location did not significantly affect
worker exposure (probability of a larger F = 0.2373).
General Linear Models Procedure
Dependent Variable: C |
|
|
|
|
|
|
Sum of |
Mean |
|
|
Source |
DF |
Squares |
Square |
F Value |
Pr > F |
Model |
17 |
155.1365311 |
9.1256783 |
653.51 |
0.0 |
Error |
478 |
6.6748442 |
0.0139641 |
|
|
Corrected Total |
495 |
161.8113754 |
|
|
|
|
R-Square |
C.V. |
Root MSE |
|
LV Mean |
|
0.958749 |
-15.35271 |
0.118170 |
|
-.76969999 |
|
|
|
|
|
|
|
General Linear Models Procedure |
|
Dependent Variable: C |
|
|
|
|
|
|
|
T for HO: |
Pr > |T| |
Std Error of |
Parameter |
Estimate |
Parameter=0 |
|
Estimate |
INTERCEPT |
-0.023031644 B |
-1.01 |
0.3121 |
0.02277085 |
C1 |
1.286321990 |
28.32 |
0.0001 |
0.04542764 |
C2 |
-0.373120006 |
-5.03 |
0.0001 |
0.07414134 |
C3 |
-0.140338485 |
-1.85 |
0.0650 |
0.07587944 |
C4 |
0.097912175 |
1.28 |
0.2017 |
0.07587399 |
C5 |
0.021303748 |
0.28 |
0.7797 |
0.07612342 |
C6 |
0.048775851 |
0.64 |
0.5214 |
0.07600726 |
C7 |
0.027800068 |
0.37 |
0.7152 |
0.07613752 |
C8 |
-0.137610616 |
-1.81 |
0.0708 |
0.07599124 |
C9 |
0.116037701 |
1.53 |
0.1273 |
0.07595812 |
C10 |
0.087445420 |
1.18 |
0.2397 |
0.07429013 |
C11 |
-0.081027847 |
-1.78 |
0.0761 |
0.04557663 |
LOC
away (L1) |
0.011965781 B |
0.49 |
0.6245 |
0.02442893 |
behind (L2) |
-0.015378830 B |
-0.65 |
0.5171 |
0.02372164 |
front (L3) |
-0.015400296 B |
-0.69 |
0.4895 |
0.02226424 |
left (L4) |
-0.039941736 B |
-1.45 |
0.1469 |
0.02749389 |
right
|
0.000000000 B |
|
|
|
TNS (time not sanding) |
-0.000440506 |
-2.53 |
0.0118 |
0.00017433 |
TS (time sanding) |
0.001122704 |
2.41 |
0.0164 |
0.00046633 |
Figure D3. Selected SAS output from the analysis of real-time data collected during spray painting with an HVLP spray painting gun.
|