Exposure to wood dust and its particle size distribution in a rubberwood sawmill in Thailand.

A cross-sectional study on wood dust exposure and respiratory health effects was conducted at one of the largest rubberwood sawmills in Thailand. All workers (N = 340) from all jobs on a day shift were recruited for personal sampling. Overall, the personal inhalable dust (n = 742) and respirable dust (n = 241) of full-shift samples were collected from 27 job titles. These data were used to classify workers into high, moderate, and low exposure groups based on the concentrations found in each job. Static samples were also collected to determine the particle size distribution. Geometric means (GM) are used to present the concentrations of the rubber wood dust. Inhalable dust concentrations were clearly high, ranging between 0.2 to 59.4 mg/m3 and with GM of 4.7 mg/m3. The GM of inhalable dust in each job title enabled classification of the workers into three exposure groups: (1) high exposure; >5 mg/m3, (2) moderate exposure; 2.0-5.0 mg/m3, and (3) low exposure; 0.18-1.9 mg/m3. Among the high exposure group, the highest GM inhalable dust concentrations were found in sawing green lumber (12.8 mg/m3) and cutting dry lumber (7.3 mg/m3). The respirable dust concentrations were generally low, in the range of 0.1 to 6.0 mg/m3 with a GM of 0.5 mg/m3. The largest percentage of dust in major operations belonged to the thoracic fraction; 50% cutoff diameter was smaller than 9 mum. The size distribution of wood dust indicated a high proportion in the large particle sizes.