Guidelines for elevator design to mitigate the risk of spread of airborne diseases

Abstract

Airborne viral transmission in confined spaces, such as elevators, could lead to the spread of diseases such as COVID-19. A quantitative study of viral transmission in enclosed spaces, with a focus on assessing the efficacy of the present ventilation methods is hard to find. Additionally, there is a lack of guidelines for viral dispersion. The non-availability of such information reduces overall effectiveness in controlling the spread of the virus. A properly designed ventilation system for the elevator car will benefit in both pandemic situations as well as non-pandemic situations, especially for people using hospital elevators. For better control of the airborne viral transmission spread, it is essential to study the airflow in elevator cars. Exposure to high-emitter coughing for one minute by a SARS-CoV-2-infected person in an elevator can increase the risk of the virus reaching the lungs by generating a viral load that may remain airborne for a long time. There is little that has been considered for lessening the anticipated viral load in the elevator car. In this paper, we use a two-step approach. The first step is the risk assessment, and the second is risk mitigation. The risk is assessed by computing the probable viral load a healthy passenger will be subjected to during the typical travel in an elevator car contaminated by the ride of an infectious person. It is seen that the ventilation provided as per the minimum permissible requirements by various international codes is inadequate to maintain the viral load in the elevator car below the risky levels. To come up with the risk mitigation strategies, the required ventilation in the car was computed using a Computational Fluid Dynamics (CFD) model. Further, mathematical models are developed to enable quick calculations during the design of the elevator car ventilation system. Our CFD study shows that in the case of a 20-passenger capacity elevator car, with doors open, a 2000 Cubic Feet per Minute (CFM) airflow will disperse most of the viral load in less than one minute. In this paper, we give easy-to-follow design guidelines, and mathematical models to enable quick calculations during the design of the elevator car ventilation system. This study is useful for practicing engineers to achieve effective ventilation of the elevator car to curtail the spread of viral transmission.