STORY :
WHY :
With the increase of people contaminated by the COVID-19 who need healthcare at the hospital, the question about separating COVID area with the other rooms will become critical.
After some discussion with hospital workers, it seems that in some situation, there are not completely sure that the risk of virus propagation between contaminated and COVID free rooms are secured.
HOW : Based on our experience with the Wuhan hospital, CFD simulation doen with our SIMULIA tools could bring a quick overview of the current statuts the hospital will have and in some cases, maybe help to improve the separation.
Of course, it will only be simulations, we will have probably huge hypothesis to take (there will have no CAD of the hospital, no CAD of the HVAC system) but in some cases, basic aerodynamics consideration could be sufficient to give an advice. We can for sure do the same for temporary hospital (New York or Mulhouse in France) and bring an overview of the virus propagation inside but more interesting outside the hospital.
WHO :
- Emmanuel Vanoli, Boris Fechner, Sylviane Famibelle, Lucas Chambaud, Grace Lau & Nicolas Arsenijevic from SIMULIA
- Nathalie, Zuliani, Sebastien Laurent - directors of the hospital of Marange Silvange
Marange Silvange Hospital simulation , near Metz in France
1. Start with a floor plan
2. Get the 3D Modeling - Wall
3. Hypothesis and assumptions
It is very difficult to have accurate boundary conditions for such a simulation. Some assumptions and uncertainties had lead us to make some modelization hypothesis. The contaminated sectors are located in the South & West areas.
Based on the information provided by the hospital, the simulation was set with :
- All rooms have a ventilation system, extracting air from the hospital floor (massflow outlet). In a first approach, all system will work the same way.
- Fresh external is brought to the hospital through natural leakages of the windows. A simplified pressure inlet set as the external ambiant level has been set for each windows. This choice will probably overestimate the amount of fresh air provided by the leakages
- 32 sick people "rough" during 1s at different time of the simulation. This approach of rejecting 100% of contaminated air will probably overestimate the amount of COVID particules inside the simulation.The virus is considered as a perfect aerosol (following the air flow field)
4. CFD Simulations "as is"
As a first analysis, we had a look at the contaminated particles concentration (between 0% to 10% of the air on the animation below).
We can clearly see that the natural pattern of the air is from the COVID area to the safe one. As results, at some point, some contamination can happen in the safe area.
By looking at the air velocity animation, we can observe that the corridor is the main propagation vectors. It can be explained by the contamination coming from the rooms and pushed on the corridor by the windows leakages.
The overall flow circulation is coming from the COVID area to the safe one because of the pressure gradient observed in the floor. We have indeed a low pressure area in the safe place, attracting naturally the air coming from the contimated area. The concentration of many ventilation systems in small rooms is explaining the low pressure level.
5. CFD Simulations "optimization"
As a first iteration, we decided to find an easy way to counter the low pressure area in the safe sector. A simple way to do that is to reduce by 50% the ventilation compared to the COVID one, still at 100%. It can easily be done if you can control each sectors ventilation or by masking part of them.
The animation of particles concentration shows that the contimation is strongly reduced with this configuration. Most of the contaminated air remains localized in a short proximity of the COVID area.
A pressure equilibrium seems to be reached now between the two sectors. It will naturally limit any flow transfer.
Another easy way to counter the propagation is to use strategic open windows to break the flow field in the corridor. 2 windows will be opened in the stairs location as showed below. The idea is to use the fresh air coming from the outside to break the flow pattern and the pressure gradient.
As observed in the air velocity animation below, the fresh air from the windows are spliting the flow in the contaminated corridor in two separated ways, limiting the amount of air from the rooms.
In the sector between the COVID and the safe areas, the flow is directed very close the separation door. It will naturally avoid the flow coming the contaminated sector to penetrate in the safe area.
The particles concentration is validating this hypothesis by showing a strong blockage at the separation door. The virus propagation is then limited but the rooms next to the stairs could still be contaminated.
To conclude, we had a very positive and interesting feedback from the hospital directors. It will help them to better understand how their hospital is aerodynamically behaving. It also brings simple solution to reduce propagation risks.
We are currently in contact with local companies with measurement materials to validate our pressure repartition prediction.
To be continued...
