Although it seems obvious that the most detected heavy metals and crystalline silica have additive or even synergistic health effects, multiple exposures to Al, As, Pb, Cd, and Mn have not consistently been taken into account in exposure assessments. The purpose of this study was to measure workers’ multiple exposure to inhalable dust, metals, and crystalline silica during maintenance and ash removal tasks in eight biomass-fired power plants, and to evaluate the possible exposure-associated additive and synergistic health effects of the exposing agents.