Evaluation of Drying Methods for Humidity Control During Real-Time Respirator Fit Monitoring

Respiratory protective devices are widely used to reduce occupational exposure to hazardous airborne particles. However, the protective performance of respirators can deteriorate during real-world use due to poor fit, even if they were initially well-fitted. The Exposure Protection Integrated Communicator (EPIC) is a recently developed portable system that is equipped with dual optical particle counters (OPCs) to measure aerosol concentrations inside and outside a respirator, enabling real-time fit monitoring in a real-world workplace. Since OPC performance is sensitive to humidity, this study evaluated two drying methods, Nafion tubing and a desiccant membrane (DM) dryer, for their effectiveness in reducing relative humidity and minimizing particle loss within the EPIC device. Experiments were conducted to characterize the efficiency of relative humidity (RH) reduction and particle transmission across a range of particle sizes (0.3-10 µm). Nafion tubing showed ~25% desiccant efficiency at ambient RH ≤ 40%, whereas the DM dryer achieved >50% efficiency at higher RH levels. However, both dryer units exhibited particle losses, particularly of larger micron-sized particles, with the DM dryer exhibiting >90% loss for particles >5 µm. These findings highlight the trade-offs between RH control and particle preservation in a field-deployable aerosol monitoring system. Nafion tubing has the potential for applications requiring real-time respirator monitoring under moderate RH environmental conditions. This study provides critical design insights for optimizing OPC-based systems like EPIC, where maintaining both sensor accuracy and particle transmission is essential.