Real-time monitoring and controlling strategies of indoor environment in the frontline hospitals during COVID-19 pandemic

Many emergent measures on mitigating and controlling the COVID-19 pandemic have been unprecedented in China, one of which is the urgent construction of isolation wards in Huoshenshan Hospital and Leishenshan Hospital, as well as in sixteen Fangcang shelter hospitals. These hospitals, built or reconstructed within a remarkably short period, have treated a large number of COVID-19 patients in time and successfully mitigated disease spread in population. One of the many challenges during the hospitals' functioning period is the precaution of potential airborne transmission. Airborne transmission could occur during medical procedures including tracheotomy, intubation, extubation, etc., and several surveillance studies have detected SARS-CoV-2 virus in air by polymerase chain reaction (PCR), but direct methods on monitoring airborne SARS-CoV-2 in real-time have not been developed so far. Though it is yet to know whether these airborne viruses are viable and able to cause person-to-person infection, airborne precautions such as negative-pressure wards and N95 respirators have already been recommended and implemented in China. In order to protect the healthcare workers (HCWs) and reduce the demand of high-level protection gear, this study proposed an indirect method to identify and alert the airborne infection risk. We deployed numerous sensors to monitor CO₂ concentration, PM_2.5 mass concentration, air temperature and relative humidity, and illumination at ICUs (intensive care units), general wards, nurse stations, buffer rooms, etc. in real-time. Online CO₂ concentration reflects the dilution of occupants' exhalation substances by the ventilation and air distribution system. High CO₂ concentrations indicate either the fresh air supply fails or the room is overcrowded at the moment. The readings of CO₂ concentration across adjacent zones with known functions can also help identify whether the airflow direction is consistent with the designed requirement. PM_2.5 mass concentration indicates the air cleanness of the measured zones, which could be crucial for patient recovery and reduction of symptom complication. Air temperature and relative humidity are key parameters that influence the evaporation of expiratory droplets and the thermal comfort of patients, while illumination indicates the intake of ultraviolet from outdoor. The sensors could keep quiet during the sampling process, so they would not disturb the HCWs and patients. Moreover, they are integrated with 3G SIM cards and powered just by a DC 5V/3A power adapter with a USB Type-C line, so they could be easily installed at target locations, and adapt for multi-scene, multi-demand, and long-term online and offline monitoring. When integrated with online meta-analysis and computer fluid dynamics (CFD) simulation, this method can send alarms to the HCWs about the locations where the ventilation against potential pathogen-laden aerosols fails. This study introduces the principle of the method in detail as well as its application at Huoshenshan Hospital, Leishenshan Hospital and Jiangxia Dahuashan Fangcang shelter hospital, etc., in Wuhan, China, during February and March of 2020. As the society gradually steps into post-pandemic phase, the proposed method could help optimize the ventilation and filtration strategies in public buildings and transportations.