Assessment of workplace air concentrations of indium dust in an indium-recycling plant

Objectives: Suspended indium dust in an indium-recycling plant was quantified, in order to improve the work environment and to reduce workers' exposure to the dust. Methods: Assessment of indium dust in the workplace air by multipoint area sampling and personal breathing zone sampling was conducted twice in 2004 and 2008. Results: In 2004, all recycling processes except for purity analysis were classified into control class III according to the 2004 Notification. Two out of 5 workers were exposed to total dust with indium concentrations exceeding the ACGIH's TLV-TWA of 0.1 mg In/m3. In 2008, the indium-contaminated workplace air was improved by local exhaust ventilation systems installed in some processes, resulting in control class I. According to the 2010 Technical Guideline, however, all the processes were classified into stage II or III, indicating that the first assessment value or Measurement B-based concentrations exceeded the acceptable exposure concentration limit of 0.0003 mg In/m³ of respirabe dust. Exposure of almost all the workers to indium dust was below the TLV-TWA. Conclusions: The first field survey showed that almost all workplaces were classified into control class III, and that some workers were exposed to dust with indium concentrations exceeding the TLV-TWA. It was found in the second survey that workplace air contamination was improved by the local exhaust ventilation system, but was not reduced sufficiently to a level that meets the new Guideline.