Assessing Operator Exposure to Brush Cutter Engine Exhaust Using Computational Fluid Dynamics

This study examined the extent of gasoline engine exhaust exposure during brush cutting, using Computational Fluid Dynamics (CFD) simulations to quantify carbon monoxide (CO) exposure. We validated the model (RANS and SST k-ω) against experimental bench test data for CO concentrations across seven validation points (MAE = 51 ppm). The simulation tracked exhaust dispersion under stagnant ambient air and under incoming wind at 10 and 20 kph, testing multiple angles of attack and assuming a forward operating speed of 1.8 kph. In stagnant air, the fan-like airflow from the cutting blade lifted exhaust gases directly into the operator's breathing zone, producing an average CO concentration of 45 ppm. This warrants attention: sustained operation at this level could exceed the 8-hour time-weighted average limits recommended by health organizations (including the WHO). When incoming wind and forward movement were introduced, however, the exhaust plume was diverted away from the operator, dropping breathing-zone CO concentrations below 1 ppm across all tested wind angles. These results suggest that brush cutter emissions can present a genuine health hazard in poorly ventilated settings, but that the risk is substantially reduced during typical open-field work, where natural wind keeps the exhaust away from the operator. The findings point to ventilation and airflow as key factors in operator safety and offer a practical basis for guidance on safe use.