The research instruments consisted of four types: (1) interview forms; (2) air sampling tools; (3) gas chromatography; and (4) high performance liquid chromatography (HPLC). First, the researcher instructed and explained the objectives, tech- niques, methods, process, and procedure of research to the research assistant to ensure consistency in data collection. After that, the researcher explained the research objectives and necessary information to the volunteers and asked them to sign consent forms to participate in the research.