In the heart of Japan, at Kyushu University, a groundbreaking study is reshaping our understanding of how airborne particles behave in indoor environments. Led by Onkangi Ruth from the Interdisciplinary Graduate School of Engineering Sciences, this research delves into the intricacies of droplet dispersion, inhalation exposure, and dermal deposition, offering crucial insights for industries grappling with airborne transmission risks.
Imagine a bustling office or a crowded factory floor. The air is stagnant, and workers are in close proximity, engaging in conversations or performing tasks that require close contact. What happens when an infected individual coughs or speaks? How do the droplets they exhale behave, and what are the implications for those around them?
Ruth and her team set out to answer these questions using a realistic human model equipped with a respiratory tract. They simulated various interpersonal distances (IPDs), close-contact postures, and face orientations under stagnant indoor airflow conditions. Their findings, published in the journal ‘Indoor Air’ (translated from ‘Indoor Environments’), provide a nuanced understanding of inhalation and dermal exposure risks.
One of the most striking findings is the dominance of short-range inhalation exposure at distances greater than 0.3 meters. “Short-range inhalation is the primary mode of exposure at these distances,” Ruth explains. This has significant implications for industries where workers are in close proximity, such as manufacturing, construction, and energy sectors.
The study also revealed that the risk of inhalation exposure is higher during coughing than speaking, particularly in the standing-standing posture. Interestingly, orienting the face to the side (cheek) reduced inhalation exposure during speaking but not during coughing. This suggests that simple adjustments in posture and orientation could potentially mitigate exposure risks in indoor work environments.
The research also highlighted the inverse relationship between inhalation and deposition fractions with increasing IPD. In other words, the closer the contact, the higher the risk of inhalation exposure. Moreover, the standing-standing posture posed a higher risk than the standing-sitting posture at the same IPD due to higher velocity magnitude at the nose.
For the energy sector, these findings are particularly relevant. Workplaces in this industry often involve close contact and stagnant indoor airflow conditions. Understanding the dynamics of droplet dispersion and inhalation exposure can inform the development of safer work protocols, ventilation systems, and personal protective equipment (PPE).
Ruth’s study also sheds light on the deposition of inhaled particles. During speaking, a higher fraction of particles with a wider diameter (≥15 µm) were deposited in the nasal cavity. For coughing, most inhaled droplets of pre-evaporation sizes (<10 µm) passed through the pharyngeal end, with minimal deposition in the nasal cavity. This underscores the need for targeted protective measures based on the nature of the task and the type of exposure. The timing of the inhalation period and droplet concentration in the breathing zone also play a crucial role in aspiration efficiency. This highlights the importance of real-time monitoring and adaptive control measures in indoor environments. As we look to the future, this research paves the way for innovative solutions in infection control. From smart ventilation systems that adapt to real-time droplet concentrations to PPE designed to protect against specific types of exposure, the possibilities are vast. Industries can leverage these insights to create safer, healthier work environments, ultimately boosting productivity and reducing healthcare costs. Ruth's work is a testament to the power of interdisciplinary research in addressing complex real-world problems. As we continue to grapple with airborne transmission risks, studies like these will be instrumental in shaping a safer, healthier future.
