Employees of a metal furniture manufacturer asked the National Institute for Occupational Safety and Health (NIOSH) to evaluate health hazards at their workplace. They were concerned about exposures to welding fumes and dust from powder painting and grinding operations. Some employees reported breathing problems, excessive tiredness and dust in their noses at the end of their work shifts.
The company had 146 employees and was located in a 110,000-square foot building. Employees’ work included cutting, bending and welding sheet metal to form end tables, lockers and beds. Most employees spoke Spanish as their primary language, and most were members of a union. The company had a safety committee, which met every 3 months.
Employees bent metal furniture parts to the desired shapes and spot-welded the corners. Parts that could not be joined using a spot welder were welded by tacking the corners using a metal inert gas (MIG) welder. The total welding time per part was minimal.
MIG welders used welding wire that contained 1.4 percent to 1.8 percent manganese by weight. Some parts, such as bed frames, were made by cutting metal tubing with a saw and welding the pieces together. The welding area did not have its own ventilation system; however, one fume extractor was used while welding bed frames (Figure 1). Fourteen employees worked as MIG welders and 13 as spot welders.
After welding, employees in the grinding area used hand-held grinders to smooth the welds and remove sharp edges. Completed parts traveled on an overhead conveyor through a degreasing booth, where they were rinsed with phosphoric acid. As the parts exited the booth, an employee used a rag dipped in toluene for touch-up cleaning.
Metal parts were grounded with an electrostatic charge to attract paint particles to the part. The parts traveled on a conveyor through a powder paint spray booth in which permanently mounted spray guns coated the parts as they passed through. Painters stood at openings in the booth or sometimes stepped into the booth and manually powder painted any areas on the parts missed by the spray guns (Figure 2). Painted parts continued on the conveyor to a gas oven for curing, then to the packing and shipping departments. Painters regularly entered the spray booth and used a squeegee to remove paint overspray that had settled onto the floors and walls of the booth. The company had 15 painters.
What NIOSH Evaluated
During our site visit, we met with management and employee representatives and toured the facility. We observed the manufacturing processes, use of personal protective equipment (PPE) such as respirators and protective clothing and engineering controls (such as ventilation). We also interviewed 10 employees about their work.
We took personal air samples to measure levels of air contaminants the employees might be breathing. For welders and grinders, we tested for metal fumes or particles and for carbon monoxide. We also tested welders for exposure to nitrogen dioxide. Spray painters’ personal air samples were tested for 1,3,5-triglycidyl isocyanurate (TGIC), respirable dust and total dust. TGIC, a chemical in powder paint, can cause skin sensitization, allergic contact dermatitis and occupational asthma. Respirable dust is made of extremely fine particles that can be inhaled deeply into the lungs, and total dust is a measure of dust of all particle sizes.
We measured how much air was flowing into the spray paint booth through the door openings and how well welding fumes were being removed by the welding fume extractor. We also measured noise levels throughout the facility. We interviewed nine painters and gave them devices to check their breathing so we could see if their breathing was affected by TGIC in powder paint.
NIOSH Puts Health Hazards to Bed at Metal Furniture Manufacturer