Fig 1.
ABCD design and experimental apparatus.
(a) Schematic of aerosol bio-containment device (ABCD) and (b) photograph of ABCD in a simulated clinical patient scenario. The ABCD has a volume of 0.1 m3 and measures 0.52 m high, 0.58 m wide, and 0.34 m deep, and has multiple straps so it can be secured to a bed at different angles. (c) Schematic of 1 m3 stainless steel, environmental chamber system for aerosol evaluation testing, and (d) photograph of mannequin and ABCD within the chamber. Chamber system abbreviations; HF = HEPA filter; AT = atomizer; DR = diffusion drier; N = neutralizer; MFC = mass flow controller; FMPS = TSI Fast Mobility Particle Sizer 3091, which measures particles in range of 0.0056 to 0.56 μm in size-resolved basis over 32 bins at a time-resolution of 1 s.
Fig 2.
ABCD experimental conditions and summary.
(a) Description of experimental test conditions and fitted flow and emission rates; (b) time series of typical experimental measurements (using Exp. 6 as an example); (c) description of experimental phases corresponding to time series in (b); (d) average number and mass concentrations in major experimental phase groupings; average (e) size and (f) mass distributions in ABCD and 1 m3 environmental chamber during steady state phases; (g) estimate of percentage of aerosol lost to deposition in ABCD and environmental chamber during steady state phases.
Fig 3.
ABCD experimental performance.
(a) Performance of ABCD during steady state phases for metrics of number or mass containment fraction [amount in ABCD / (amount in ABCD + amount in environmental chamber)] and airflow-estimated removal efficiency [ABCD evacuation flow rate / (ABCD evacuation flow rate + ABCD escape flow rate)], and during cough phase for containment fraction; (b) demonstration that reduced performance is a more function of ABCD seal properties, rather than evacuation flow rate; experiments with low containment or efficiency are noted on the plot; (c) demonstration of theoretical, experimental, and fitted ABCD clearance times (time for 95% or 99% cleared) as a function of evacuation flow rate, using data from number and mass results for Experiments 1, 6, and 8.
Fig 4.
(a) Simulation 3D geometry of ABCD details a supine patient exhaling particles at average breathing rate of 10 L/min. Patient head and shoulders are contained within the device; evacuation flow located along the top of the device and there is a gap for make-up air to flow in through the bottom of the device. Also shown are (b) CFD mesh with 800,000 cells; and (c) representative results of simulation for 0.1 μm particle size emissions where green/blue color indicates short duration (age of particle) after emission and orange/red color indicates long duration (red shows particles trapped suspended in corner of ABCD). (d) Particle fate in ABCD, where CFD simulations demonstrate increasing percentage of suspended particles and decreased percentage of deposited particles in the device as particle size decreases.
Fig 5.
(a) Schematic of framework used to simulate impact of ABCD in a hypothetical clinical setting, using a two-zone well-mixed model. Patient emitted aerosols that escape the ABCD enter the near volume, in which exists a near proximity clinical worker, and then aerosols are transported from the near volume into the far volume, in which exists a far proximity clinical worker. (b) Table of nine simulated cases with different levels of protections, which started at a low protection base case and then increased protections to the highest simulated combination of protections. (c) Log10 protection according to inhaled dose of near and far proximity clinical workers for each protective case normalized by the base case (i.e., co-log10 of dose ratios).