Virtual Isolator identifies product design issues before they occur

Chloé Guilmet and Jean-Luc Schneider, Getinge–La Calhène, describe airflow simulation in virtual reality to optimise isolator design 

The ‘Virtual Isolator’ was created as a result of a close partnership between Getinge-La Calhène and CEA LIST, part of the French Commissariat à l’Energie Atomique et aux Energies Alternatives. This virtual reality tool is mainly used to study issues related to the ergonomics of the isolator and accessibility inside its working area. It is employed in project design before any physical construction (mock-up or prototype) is produced.

Getinge-La Calhène wanted to go a step further by enhancing the Virtual Isolator with a new functionality - to perform numerical simulation of a bio-decontamination cycle with H₂O₂ inside a virtual isolator.

The bio-decontamination process is a complex, critical technique which creates and maintains the necessary aseptic conditions inside an isolator. The process is commonly based on the use of sporicidal gassing agent, such as H₂O₂ vapour which is injected inside the isolator during the bio-decontamination cycles.

A typical H₂O₂ bio-decontamination cycle consists of a series of phases:

1. Conditioning: injection of hot air to achieve the required conditions of humidity for bio-decontamination of the isolator chamber,
2. Injection: initial injection of H₂O₂ to reach the appropriate concentration in the chamber for the decontamination
3. Stabilisation: injection of small amounts of H₂O₂ at intervals to maintain the appropriate concentration
4. Aeration: a fresh airflow is injected in the chamber in order to reduce the concentration of H₂O₂ to the desired residual level.

A typical cycle may last for some tens of minutes during which time the isolator is not in production. The periodicity of these cycles varies from once a month to several times a day, depending on the applications for which the isolator is used.

The efficacy of the cycles and their optimization depend on a combination of interactions between several factors. One particularly critical factor is the airflow patterns. They are in fact caused by the ventilation system, the geometry of the isolator, the locations of pieces of equipment etc., which are defined during the Design Phase by designers, engineers and isolation experts, mainly according to their experience. The design of the isolator may be validated for flow behavior by smoke tests. As for the bio-decontamination process, the cycles are validated with tests using biological indicators.

Both of these tests are realised when the isolator is built and once its design is frozen. The tests cost time and money and are limited in terms of tested configurations / hypotheses.

Hence Getinge-La Calhène looked for a way to investigate the issues of airflow for bio-decontamination earlier in the project, during the Design Phase.