The fast option
Effective sterilization of freeze dryers

For more than 15 years, hydrogen peroxide has been of proven use in the sterilization of freeze dryers. Now the process has been optimized in such a manner that the cycle times for plant sterilization have been reduced significantly. Users now have the option of applying a sterilization procedure that is fast but gentle on the equipment as an alternative to traditional steam sterilization.
Ralph Groß
Constantly higher requirements from the health and supervisory authorities in terms of respecting sterile production conditions and avoiding contamination have led to the development of automated loading and unloading systems and the Vapovac sterilizer. Thanks to this automated production process, fewer staff are required for aseptic production, thereby reducing the risks of contamination. To that end, the feed lines are surrounded by insulation systems which are sterilized using hydrogen peroxide (HİüOİü). In contrast to most other chemical processes, this does not give rise to any carcinogenic or mutagenic by-products.

A new sterilization process now makes highly effective use of the existing vacuum technology of the respective freeze dryer. For this, the gaseous hydrogen peroxide penetrates the pipes. The sterilant is well-distributed even in dead ends of the pipe-work, meaning that no additional assistance is required to distribute the gas. The key difference between this and other procedures is that hydrogen peroxide gas sterilization is carried out at room temperature under vacuum conditions.

Step by step

The sterilization process comprises the drying phase, evacuation prior to injection, the injection of the hydrogen peroxide and the aeration phase. At the start of the process, as an option the freeze dryer is dried and then the degree of dryness for the unit is determined. A starting value of 20 mbar x liter/second is sufficient for hydrogen peroxide gas sterilization.

The freeze dryer and the connected pipe-work are evacuated to a vacuum rating of approx. 0.02 mbar, in order for the hydrogen peroxide then to be introduced condensation-free into the unit.

Very short process time

The pressure difference between the Vapovac sterilizer and the freeze dryer causes the hydrogen peroxide to be injected via a pulsed injection valve. Since the injection volumes of hydrogen peroxide are extremely low, the process time is significantly shorter. To sterilize an average-size production unit, around fifty milliliters of 35 per cent hydrogen peroxide is required.

On the path to the freeze dryer unit, the liquid hydrogen peroxide passes through a vaporizer. Injection is carried out, controlled by the vaporizer pressure, in a parameterized vacuum range, whilst the quantity of hydrogen peroxide injected is calculated using the freeze dryer chamber pressure. Accordingly, the hardware for the Vapovac sterilizer can be kept to a minimum. Furthermore, no regeneration cycles are required for the drying assemblies or to exchange desiccant cartridges.

Following the sterilization procedure, the residual hydrogen peroxide gas is reduced using vacuum pulses to below the statutory MAK (maximum workplace concentration) value of 1 ppm.

The residual gas value can be determinated either manually or automatically. To do this, a gas sample is taken from the freeze dryer chamber. If a gas concentration of below 1 ppm is confirmed, then the unit can be opened without adverse effect for the operator.

Well safeguarded

In principle, the process is safeguarded against inadvertent opening of the unit and any discharge of hydrogen peroxide gas under vacuum.

The retrofit option is intended for upgrading non-sterilizable freeze dryers
of any age, any size and any brand. In
such instances, the Vapovac sterilizer comes with its own PLC control unit, S7-300,
and its own display using WinCC flexible advanced 2005, along with pharma-appropriate batch documentation and Siemens Touch Panel 270. With this equipment, the sterilizers combine the required industry standard with a high level of process reliability.n