designing an air-conditioning system to control isocyanates and dust in woodwork industries

spreading wood particles and attached colored materials in work places can cause many problems for woodwork industry workers. the aim of this study is to design and implement a local exhaust ventilation system to control wood dust and isocyanates simultaneously. the study was conducted on 18 workers in the paint workroom of a wood door industry. at first, an overview of the workplace indoor air was done in 18 workstations. the national institute for occupational safety and health (niosh) method was used to measure the concentration of wood dust and tdi(2,4-toluenediisocyanate). in order to control the worker exposure to the pollutants, a semi-downdraft spray chamber was chosen and implemented on the basis of american conference of government industrial hygienists (acgih) control air pollution method. orifice scrubber was used to avoid entry of pollutants into the environment. finally, after the establishment of a new ventilation system, the emissions were remeasured and the results were evaluated. before design and implementation of local exhaust ventilation system, the emissions in workstations were measured as 0.0015 ± 0.0074 ppm for tdi and 0.01 ± 0.42 mg/m 3 for total dust. then, the pollution concentrations were measured after implementing the local exhaust ventilation system. the concentration of tdi and total dust were measured respectively as 0.007 ± 0.003 ppm and0.07 ± 0.15 which had a significant (p˂0.05) lower concentration than before the implementation. also, the measured concentrations after the implementation had met the national institute of occupational safety and health limits: (tlv twa = 0.005ppm for tdi and tlw twa = 0.5 mg/m 3 for total dust). the result shows that the current ventilation system (before implementing and spray chamber) was suitable for dusts, but not for the tdi. so, the workers were exposed to non-standard levels of isocyanate. after design and implementation of the spray chamber, the pollutants were clearly decreased (p<0.05). in conclusion, the system efficiency for wood dust and tdi were 64% and 60% respectively.