Chlorine gas and ultrafine particle emissions from bleach disinfection: exposure risk characterization

Background: Chlorine-based disinfectants, such as bleach, are widely used in healthcare settings. However, their use has been linked to occupational respiratory risks. During disinfection, both chlorine gas and ultrafine particles (UFPs) can be generated, yet their exposure dynamics and health impacts remain poorly understood. This study aimed to characterize the emissions of chlorine gas and UFPs during disinfection under varying environmental and surface conditions to better understand exposure dynamics and inform risk mitigation strategies. Methods: Controlled experiments were conducted in a sealed chamber to simulate typical healthcare disinfection scenarios. Bleach was tested under different conditions of temperature, light exposure, and in the presence of organic contaminants, including simulated vomit, urine, and blood. Chlorine gas was quantified using electrochemical sensors, while UFP emissions were measured using a condensation particle counter and mobility particle sizers. Additional validation experiments were performed in real-world office settings before and after cleaning. Results: Chlorine gas was primarily emitted when bleach interacted with organic contaminants, particularly acidic substances such as simulated vomit, with an emission factor of 9.4 × 106 µg/min/m2. In contrast, UFP emissions were highest on clean surfaces under elevated temperature and light exposure, reaching up to 1.0 × 1011 particles/min/m2. Real-world validation confirmed that cleaning prior to disinfection significantly reduced chlorine gas emissions but led to increased UFP formation. Chlorine gas and UFP emissions were rarely observed simultaneously, indicating distinct and independent emission pathways. Conclusions: Bleach-based disinfection generates airborne hazards through separate mechanisms: chlorine gas via reactions with organic residues and UFPs through secondary processes influenced by environmental conditions. These findings support enhanced cleaning protocols, improved ventilation, and the need for regulatory attention to UFP exposure in occupational settings.