Metals smelting and processing has been associated with exposure to airborne inorganic arsenic and an increased risk of health effects. Biological monitoring on a metals processing site identified urinary arsenic concentrations exceeding corporate and ACGIH guidelines at levels associated with increased risks of health effects. Plant operators considered the inhalation of arsenic trioxide powder (As2O3), used in the process, as the source of their exposure. This study's initial objective was to determine operator exposures to airborne inorganic arsenic. Two groups of plant operators participated in full shift personal air monitoring and biological monitoring over their working weeks. In parallel, wipe samples were taken from control rooms and grab sampling for arsine was carried out to capture a wider range of potential exposure routes. Air monitoring results did not approach exposure standards, with many below the limit of detection. In contrast, biological monitoring results exceeded corporate and the ACGIH guidelines indicating exposure via routes other than inhalation. This demonstrates that relying on air monitoring alone for exposure assessment is inadequate. The findings informed management and workers of practical measures required to adequately control process emissions, secondary exposure due to contaminated surfaces, and poor personal hygiene, prior to the closure of the plant and cessation of all associated processes in early 2015. Assessment of occupational exposure to substances with multiple exposure routes should not rely on air monitoring alone; but integrate other evaluative techniques such as biological monitoring (where available) to ensure exposure risk via all routes is adequately evaluated.