Researchers Address Airborne Transfer of Particulates Via Thermal Convection Flows in Burn Units

Controlling 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, French researcher Christian Beauchene and colleagues studied a computational fluid dynamic methodology (CFD).

The study was carried out in four steps: patient room design; CFD simulations of patient room design to model air flows throughout the patient room, adjacent anterooms and the corridor; construction of a prototype room and subsequent experimental studies to characterize its performance; and qualitative comparison of the tendencies between CFD prediction and experimental results. Electricite De France (EDF) open-source software Code_Saturne(R) 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.

The researchers 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 degrees Celsius, a significant contamination transfer was observed to enter into the positive pressure room when the access door was opened, while 2 degrees Celsius had little effect. Based on these findings the researchers say the constructed burn unit was outfitted with supplemental air exhaust ducts over the doors to compensate for the thermal convective flows.

Beauchene, et al. conclude that CFD simulations proved to be a particularly useful tool for the design and optimization of a burn unit treatment room. They say their 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. Their research was published in BMC Infectious Diseases. 

Reference: Beauchene C, Laudinet N, Choukri F, et al. Accumulation and transport of microbial-size particles in a pressure protected model burn unit: CFD simulations and experimental evidence. BMC Infectious Diseases 2011, 11:58doi:10.1186/1471-2334-11-58.