Accumulation and transport of microbial-size particles in a pressure protected model burn unit: CFD simulations and experimental evidence

Abstract

BackgroundControlling airborne contamination is of major importance in burn units because of the high susceptibility of burned patients to infections and the unique environmental conditions that can accentuate the infection risk. In particular the required elevated temperatures in the patient room can create thermal convection flows which can transport airborne contaminates throughout the unit. In order to estimate this risk and optimize the design of an intensive care room intended to host severely burned patients, we have relied on a computational fluid dynamic methodology (CFD).MethodsThe study was carried out in 4 steps: i) patient room design, ii) CFD simulations of patient room design to model air flows throughout the patient room, adjacent anterooms and the corridor, iii) construction of a prototype room and subsequent experimental studies to characterize its performance iv) qualitative comparison of the tendencies between CFD prediction and experimental results. The Electricité De France (EDF) open-source software Code_Saturne® (http://www.code-saturne.org) was used and CFD simulations were conducted with an hexahedral mesh containing about 300 000 computational cells. The computational domain included the treatment room and two anterooms including equipment, staff and patient. Experiments with inert aerosol particles followed by time-resolved particle counting were conducted in the prototype room for comparison with the CFD observations.ResultsWe found that thermal convection can create contaminated zones near the ceiling of the room, which can subsequently lead to contaminate transfer in adjacent rooms. Experimental confirmation of these phenomena agreed well with CFD predictions and showed that particles greater than one micron (i.e. bacterial or fungal spore sizes) can be influenced by these thermally induced flows. When the temperature difference between rooms was 7°C, a significant contamination transfer was observed to enter into the positive pressure room when the access door was opened, while 2°C had little effect. Based on these findings the constructed burn unit was outfitted with supplemental air exhaust ducts over the doors to compensate for the thermal convective flows.ConclusionsCFD simulations proved to be a particularly useful tool for the design and optimization of a burn unit treatment room. Our results, which have been confirmed qualitatively by experimental investigation, stressed that airborne transfer of microbial size particles via thermal convection flows are able to bypass the protective overpressure in the patient room, which can represent a potential risk of cross contamination between rooms in protected environments.

Different Types of Door-Opening Motions as Contributing Factors to Containment Failures in Hospital Isolation Rooms

“…Further experiments are required to investigate the effects of various ventilation modes, though the scaling issues for thermal buoyancy and pressure effects may make this difficult in a small-scale, water-tank model like the one used here. Computational fluid dynamical (CFD) modeling of the airflows across doorways has been performed recently [24], but this is difficult to compare directly to these experimental results as they also take into account pressure and thermal differences across the doorway, which are both equal on either side of the doorway in the baseline experiments presented here. However, one interesting finding from the CFD modeling, the phenomenon of the back-flow of potentially contaminated air when a hinged-door is opened, has been observed in our qualitative experimental findings here, and demonstrated in the case report by Tang et al [23].…”

An Effective Surrogate Tracer Technique for S. aureus Bioaerosols in a Mechanically Ventilated Hospital Room Replica Using Dilute Aqueous Lithium Chloride

“…This study has shown that a substantial quantity of the deposited particles may have been in the micron or submicron size range, which has also been reported in modern literature [22,64]. As a result, certain infection inducing microorganisms that were thought to be predominantly airborne such as influenza or varicella, could deposit onto surfaces many meters way from the infectious source.…”

The Effectiveness of the Anteroom (Vestibule) Area on Hospital Infection Control and Health Staff Safety: A Systematic Review

“…The 2°C temperature difference between the anteroom and isolation room significantly affected the air transfer, especially in the rooms which had sliding doors. When the difference between the two rooms' temperatures is more than 2°C, the risk of transporting contaminated sources to the next room is higher due to thermal convective flows ( 24 , 28 ).…”