Effectiveness of engineering interventions in decreasing worker exposure to metalworking fluid aerosols

Machine industry accounts for the highest proportion of primary industry in Taiwan. Long-term exposure to metalworking fluid aerosols may pose significant threats to the health of workers. The aims of this study were to verify the efficacy of intervention methods in reducing airborne bacterial concentrations as well as effects on aerosol particle size distribution. This study evaluated airborne bacterial concentrations in a large precision machinery factory in Taichung, Taiwan, before and after the implementation of intervention methods. The installation of local exhaust systems and improvement of the operation mode were used as intervention methods. Concentration and size distribution of bacteria in the metal working environment were assessed using Andersen one-stage and six-stage viable impactors, respectively. The analytical results indicate that most bacterial concentrations were less than the recommended concentrations in the indoor air quality standards (500 CFU/m³) proposed by the United States Association of Advancing Occupational and Environmental Health (US ACGIH) before the installation of local exhaust systems. There was no significant difference in bacterial concentrations before and after the installation of the local exhaust and the intervention effect on reducing bacterial exposure was not as expected. The bacterial concentrations were significantly lowered in the Z region after improving the operation mode. The particle size of bioaerosols <7.0 μm was also substantially reduced. Improper operation modes are likely to expose employees to higher concentrations of bacteria within a short time period. It recommends adjusting the metal processing methods and proper use of air spray guns for decreasing high airborne bacterial concentrations exposure.