Potential airborne transmission between two isolation cubicles through a shared anteroom.

Full-scale experiments and CFD simulations were performed to study potential inter-cubicle airborne transmissions through a shared anteroom due to the hinged door opening. When doors are closed, current negative pressure designs are effective for the containment of airborne pathogens in the 'dirty' cubicle with an index patient. When the 'dirty' cubicle door is open, airborne agents can move into the other 'clean' cubicle via the shared anteroom. As the door being opened or closed, the door sweeping effect is the main source of the two-way airflow and contaminant exchange through the doorway. When the dirty cubicle door remains fully open, temperature difference and concentration gradient across the doorway induce the two-way buoyancy-driven flow and transport of airborne agents across the doorway. The longer the dirty cubicle door remains fully open (10 s, 30 s or 60 s) or the smaller the air change rate (34-8.5 ACH for each cubicle), the more airborne pathogens are being transported into the 'clean' cubicle and the longer time it takes to remove them after the door is closed. Keeping the door completely open is potentially responsible for the majority of inter-cubicle transmissions if its duration is much longer than the duration of door motion (only 3 s). Our analyses suggest a potential inter-cubicle infection risk if the shared anteroom is used for multiple isolation cubicles. Decreasing the duration of door opening, raising air change rate or using a curtain at the doorway are recommended to reduce inter-cubicle exposure hazards.

The influence of human walking on the flow and airborne transmission in a six-bed isolation room: Tracer gas simulation.

By performing unsteady CFD simulations using RNG k-ɛ model and dynamic mesh technique, this paper investigates how the walking motion of health care worker (HCW) influences gaseous dispersion in a six-bed isolation room with nine downward supplies and six ceiling-level or floor-level exhausts. The flow near and behind HCW is easily affected by HCW motion. The flow disturbance induced by HCW walking with swinging arms and legs is a mixing process. The walking HCW displaces air in front of it and carries air in the wake forwardly, meanwhile pressure difference drives air from two lateral sides into the wake. HCW motion (0-5.4 s) indeed induces a little gaseous dispersion, but the residual flow disturbance after HCW stops (5.4 s-25.4 s) induces more gaseous agent spread and it requires more than 30-60 s to approximately recover to the initial state after HCW stops. Although HCW motion indeed affects airborne transmission, but its effect is less important than ventilation design. No matter with or without HCW motion, the ceiling-level exhausts perform much better in controlling airborne transmission than the floor-level exhausts with the same air change rate (12.9 ACH). Smaller air change rate of 6 ACH experiences higher concentration and more gaseous spread than 12.9 ACH. In contrast to the realistic human walking, the simplified motion of a rectangular block produces stronger flow disturbance. Finally surface heating of HCW produces a stronger thermal body plume and enhances turbulence near HCW, thus slightly strengthens airborne transmission.