Case series: from ventilation failure to substitution success in occupational lead poisoning at a Korean indoor firing range.

Background: Indoor firing ranges are globally recognized as high-risk settings for occupational and recreational lead exposure due to the use of lead-based ammunition and frequently inadequate ventilation systems. In Korea, however, public health surveillance and regulatory oversight have remained limited. This case series empirically demonstrates that in high-emission settings like indoor firing ranges, ventilation upgrades are insufficient. Source substitution with lead-free primer ammunition proved to be the only definitive intervention. Case presentation: In late 2023, an index case presenting with abdominal pain was found to have a blood lead level (BLL) of 55 μg/dL, prompting a government-mandated investigation. Nine male shooting instructors (tenure: 4-65 months) were subsequently identified with BLLs ranging from 38.2-73.2 μg/dL, while airborne lead concentrations (ALC) reached 0.51 mg/m³-10 times the occupational exposure limit (OEL: 0.05 mg/m³). During a 3-month closure to upgrade ventilation, workers received chelation therapy (CaNa₂EDTA and D-penicillamine), which reduced their BLLs to 3.2-25.7 μg/dL. However, 2 months after reopening, post-intervention ALC remained elevated at 0.0797 mg/m³, still exceeding the OEL, and BLLs rebounded to 16.2-53.3 μg/dL. A substitution strategy was then implemented, replacing lead-based ammunition with copper-clad, lead-free primer rounds. This intervention decreased ALC to <0.003 mg/m³ and lowered BLLs to 4.9-23.1 μg/dL. Despite the reduced airborne concentrations, several workers continued to exhibit BLLs around 20 μg/dL, suggesting subtle ongoing exposure and mobilization of bone-stored lead. Conclusions: This cluster demonstrates that in environments where hazardous agents are continuously generated, such as indoor firing ranges, engineering controls alone, such as improved ventilation, may not provide adequate protection. Substitution-the most effective intervention within the hierarchy of controls-was essential for eliminating exposure. Furthermore, the toxicokinetics of bone lead in chronically exposed adults highlight the need for ongoing monitoring and cautious decision-making regarding treatment and return-to-work planning.