Dry heat sterilization (or Depyrogenation) is a process aimed at the reduction in the level of pyrogens with the use of hot air in temperature ranging from 160°C up to 400°C. The temperature used depends on the duration of the process. Gravity or mechanical heat convection can be used for this process. The former uses the natural interaction between air and different temperatures, and the latter produces a specific flow of air with the help of a blower.
Depyrogenation is mainly used in the sterilization of vials for aseptic filling. The process is also useful to sterilize assembled and packaged materials, since heat conduction does not require the contact of the product with steam or water.
However, not all products can withstand the high temperatures required for this kind of process (e.g. metal goods, heat sensitive solutions, etc.).Batch and dynamic are the two main techniques for depyrogenation. Batch production is usually done in static ovens where the product is placed in metal crates and exposed to high temperatures. Dynamic involves the use of a depyrogenation tunnel, where goods are transported over a continuous band through different heating zones of the tunnel.
The depyrogenation process varies depending on the technique used, the load type and the product being sterilized. No matter the specifics of your application, Ellab has a flexible solution.
Ellab offers custom made mineral insulated semi-flexible metal sensors. Ellab high temperature sensors withstand exposure to temperatures up to 400°C and can be delivered in custom lengths. Their small diameter and ductile characteristics makes them perfect for measurements inside empty vials and exact positioning in the cold spot. If there are space constraints inside the vessel, double sensors are available.
When monitoring depyrogenation processes, all wireless data loggers need to be protected from the extreme temperatures. Ellab’s thermal barriers offer different levels of protection, depending on the length and temperature of your process so you can optimize space and resources.
Our flat-pack thermal barrier is specially designed to provide high protection in tunnels with little gate headspace, making your study easy to set-up.
For real-time data collection during depyrogenation processes, it is no longer required to use cables. Ellab’s TrackSense® Pro SKY system allows for wireless radio transmission of data directly to your PC for documentation and process control.
Thermal processes above 150°C may damage the electronics and sensors of monitoring equipment, resulting in the loss of valuable process data. Ellab’s high quality materials provides a reliable validation system. The sterilization of empty glass vials can be a fragile process during the set-up; the vials can be tipped over/broken easily by the movement of thermocouples.
During dry heat sterilization, air is the heat transmitter, which poses specific concerns for correct sensor positioning if a worst-case scenario approach is to be taken. The use of high temperature semi-flex metal sensors minimizes inaccuracies in sensor positioning by keeping the desired shape during the complete process.
Depyrogenation tunnels offer limited gate headspace to optimize the sterilization process, making it difficult to introduce monitoring equipment. By using thermal barriers of different sizes, it is possible to find the best fit for the application. When the depyrogenation of small ampoules is being performed in a tunnel, the flat-pack offers a compact solution that is easily introduced with the load.
The PDA Technical Report No. 3 and ISO 20857:2010 offers useful guidelines for the qualification of Dry heat sterilization processes.
The number and positioning of measuring points varies depending on the technique used. In a dynamic technique (tunnel), temperature sensors are placed in three horizontal lines throughout the entire load; one line at the beginning, one in the middle and the last one at the end of the batch. The number of sensors per line depends on the width of the tunnel, but five sensors are commonly used as a rule of thumb. In a static technique, temperature sensors are placed in different levels of each crate and the number of points can be as high as five per crate.
When creating the thermal profile for a dry heat sterilization process, the main tests performed are heat penetration and heat distribution. The former is concerned with the heat generation inside the vessel and its homogeneity and the latter is focused on the heat transmitting from the vessel to the product and its effectiveness. This is normally measured in terms of lethality. The worst-case scenario is a recommended perspective as an acceptance criterion.
Independent of the technique used for depyrogenation, static or dynamic, it is important to record simultaneous temperature data from a relevant number of points. Creating and documenting sensor positions is an important part of the documentation for the process control. Using the Unit tool within the ValSuite™ software with the option of multiple pictures makes it possible to have a documented map of sensor placement that will facilitate repeatable and comparable studies.
Once the position of the sensors in the chamber or tunnel have been documented, it is necessary to observe sensor placement inside the product. Using semi-flex metal sensors makes it possible to accurately position the sensing element in the cold spot. It is important to take into account the kind of heat convection used in the vessel and the shape of the product for the correct assessment of the cold spot. ValSuite™ software facilitates the documentation of sensor placement in the cold spot by allowing users to include descriptive pictures per every channel used.
When all data is collected, the homogeneity, stability and heat generation of the vessel is observed in order to create a good assessment of the heat distribution during all the phases of the process. ValSuite™ provides tools to analyze the performance of the vessel in all phases of the process. The use of time-markers helps generate graphical and analytical reference points in the data collected. Statistics such as min., max., delta and Lethality FH (Tref =160°C, Z =20°C) are also available in the software. ValSuite™ integrates all calculations into self-generated reports without the need to export data into other software. Reports can also include logger placement inside the vessel and descriptive pictures of sensor positioning. Generating ValSuite™ reports provides the highest data security for the results due to the software being compliant with FDA 21 CFR Part 11.