Monthly Round Up of Important Ideas and Standards in
Industrial Hygiene and Safety
IN THIS ISSUE: Hexavalent Chromium in Painting Operations
The use of chromate-based paints is a significant contributor to employee exposure to hexavalent chromium Cr(VI). Chromate (Cr2O3) is one of the molecules where each chromium atom has a plus two charge. In 2007, the Occupational Safety & Health Administration (OSHA) established the Hexavalent Chromium Standards, 1910.1026 for general industry 1926.1126 for construction, and lowered the Permissible Exposure Limit to 5 micrograms per cubic meter. In addition to lung cancer, high levels of this metal may irritate or damage the nose, throat, and lungs, the eyes and skin are at risk if hexavalent chromium contacts these organs in high concentrations or for a prolonged period of time. Employees may become allergic to Cr(VI) so that inhaling chromate compounds can cause wheezing and shortness of breath. They may also develop skin allergies that cause swelling and a red, itchy rash that is long lasting and becomes more severe with repeated contact.
In spray painting, the coating consists of a carrier component that can generate vapors and the pigment, which is in the form of a mist. Most spray paint booths and rooms are designed to capture vapors but not mists. Spray booths are designed to comply with OSHA 1910.107 and have an average face velocity of 100 feet per minute (fpm). This may not have a sufficient velocity to capture chromate mist. Velocities as much as 200 fpm or higher may be needed. This can be difficult to achieve since there has to be a balance between what is needed to control the hazard and what is needed to deposit the paint on the surface. Controlling Cr(VI) exposure can be challenging and requires careful planning to protect workers and the enclosure may need to be specially engineered. Spray-painting parts can be done in a spray booth or room with a downdraft or cross-draft exhaust ventilation system to keep exposures below the OSHA PEL of 5 μg/m3. In addition, fixtures should be designed so the painter never has to place his face between the part and ventilation intake that may cause the mist to pass through his/her breathing zone and actually increase exposure.
Prepping of parts for chromate painting may require sanding and grinding. Without proper controls, these operations create a significant employee exposure to Cr(VI). Use of handheld powered sanding, cutting, and grinding equipment with attached local exhaust ventilation connected to high efficiency particulate air (HEPA) filtered exhaust may be needed. Instead of using compressed air to blow dust off parts, the use of HEPA filtered vacuums or wet methods (spray mist) will reduce dust. Ventilated, fully enclosed glove box abrasive blasting units for small objects will also reduce employee exposures.
Respiratory protection is often used to supplement controls that are in place to minimize exposure to hexavalent chromium in painting operations. However, like most personal protective equipment, respiratory respirators have limitations with their usage and effectiveness. Management should most importantly have in place feasible engineering controls to protect their employees from the health hazards of hexavalent chromium.
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