Engineering Controls Database
Autobody Repair - Painting
|After structural damage to a car has been repaired, spray painting is used to refinish the car. A spray-painting gun atomizes the paint into droplets, some of which impact on the car and form a surface coating. Those droplets that do not impact on the surface being painted are called paint overspray. The painter is exposed to this overspray and solvent vapors that evaporate from the overspray and the painted surface.|
Paint overspray can expose workers to lead, chromium, polyisocyanates and liquid organic solvents. Chromium is a known human carcinogen. It can cause bronchial asthma and perforations of the nasal septum, and prolonged skin contact can lead to dermatitis and ulceration. Lead can damage the nervous and reproductive systems, cause kidney malfunction, and lead to digestive disorders.
Some organic solvents, notably benzene, carbon tetrachloride and trichloroethylene, are widely recognized as carcinogenic; while others, such as methylene chloride, are considered reproductive hazards. Exposure to organic solvents can also create neurotoxic disorders such as emotional and behavioral disturbances, impaired psychomotor function, and fatigue.
Polyisocyanates such as toluene and 4,4’-diphenylmethane are found in paints and other automotive coatings. These are toxic to the nervous system and are also skin and eye irritants.
Three controls are commonly used to control worker exposure to paint overspray: (1) high volume low pressure (HVLP) spray painting guns, (2) paint ventilation boots, (3) respiratory protection.
Spray Painting Guns
In auto body repainting operations, spray painting guns can be classified as either conventional or High Volume, Low Pressure (HVLP) guns. In conventional spray painting guns, compressed air is forced through a nozzle where a reduction in pressure occurs. The reduced pressure causes the paint to flow from a cup into an orifice where the atomization occurs. In HVLP spray painting guns, this atomization pressure is less than 10 psig. HVLP guns are believed to have a transfer efficiency of at least twice that of conventional spray painting guns (therefore, reduces the particulate overspray concentration by half). Thus, using an HVLP spray painting gun can reduce both paint usage and overspray production, resulting in noticeably lower work exposure to particulate overspray.
Paint Booth Ventilation
Downdraft Ventilation spray painting booths are recommended instead of Crossdraft or Semi-Downdraft Ventilation spray painting booths. Properly operated Downdraft booths produce lower concentrations of paint overspray compared to the other two types of booths. Downdraft booths produce a cleaner paint job that requires less buffing.
In a downdraft booth air flows around the car into the exhaust opening located below the car. Downdraft booths allow the energy of the spray painting gun’s jet to be dissipated so that the overspray moved away from the worker and was exhausted from the booth before it could be mixed into the incoming fresh air. In order for downdraft booths to work effectively and efficiently, proper maintenance is necessary.
Properly used and maintained HVLP spray painting guns and downdraft booths will greatly reduce paint overspray concentrations, but they will not completely eliminate overspray from the air workers breathe. Therefore, Personal Respiratory Protective Equipment is also recommended. Follow the Occupational Safety and Health Administration (OSHA) Respiratory Standard [29 CFR 1910.134] (www.osha.gov/SLTC/etools/respiratory/index.html). The provisions of the program include procedures for selection, medical evaluation, fit testing, training, use, and care of respirators.
|179-11-A; 179-12-A; 179-13-A; 179-14-A; 179-15-A; 179-16-A; 179-17-A; 179-18-A; 179-21-A;|
Particulate overspray concentrations in the NIOSH study were 15 times lower when using a downdraft booth than with crossdraft or semi-downdraft booths.
HVLP guns are believed to have a transfer efficiency of at least 65%, while conventional spray-painting guns are commonly reported to have a transfer efficiency of 20 to 40%.