Occupational hygiene conditions were examined in a welding shop after repairing the air-handling unit. Good indoor air quality was achieved with the new replacement ventilation system. The airborne dust concentrations varied from the detection limit of 0.1 mg/m3 to 0.8 mg/m3 at the stationary sites. Even the breathing zone concentrations of the welders remained below or equal to 2.1 mg/m3. The concentrations of carbon monoxide did not exceed the level of 1 cm3/m3.