Down to the wire! Using wireless dataloggers for autoclave validation
In this article, Chris Maughan — managing director and Autoclave Validation SME at Thermal Compliance— investigates the use of wireless dataloggers for autoclave validation, looking into the how they can help and issues with their use.
If you have ever been involved in the process of autoclave validation you’re probably aware of how frustrating and time consuming it can be. Working validation slots into production schedules, failures in test equipment, machine failures and test failures all lead to a challenging project. But is there anything we can do to streamline the validation process?
Wireless dataloggers have been around for several years now and are regularly used for temperature mapping of controlled temperature units (CTUs), where they offer substantial time savings in the validation process. So, can they be used for autoclave validation and if so what benefits and pitfalls do they offer?
Benefits
The most significant benefit of using wireless dataloggers as opposed to a wired system is time saving. Table 1shows a time line of a typical validation exercise for both a thermocouple-based system and a wireless datalogger.
The main time saving benefits arise due to the following reasons:
- Setting up a thermocouple-based system requires leak rate tests. Using wireless dataloggers does not break the integrity of the autoclave chamber so leak rate tests are not required.
- Thermocouple-based systems require pre- and post-test calibrations (typically every three to six cycles). This is due to the short-term drift of thermocouples. Wireless dataloggers often use PT sensors with minimal drift which require annual calibration. Calibration verifications can be performed as well, however, this would not impact autoclave downtime.
- When using wireless dataloggers, thermocouple and biological indicator setup and removal can be performed offline whilst the autoclave is in production use.
Wireless dataloggers also provide flexibility to work around production requirements. The autoclave can remain in use until the load is fully prepared with thermocouples and biological indicators. It can then be returned immediately to production use after the validation cycle. This works very well during requalification of loads, although for performance qualification triplicate runs should be performed consecutively.
Wireless sensors are available in many different shapes and sizes. Manufacturers are keen to provide solutions for all applications from ultra-low freezers to depyrogenation tunnels. With autoclave validation, flexible sensors can be used in long tubing, bendable sensors for repeatable placement in filters or smaller sensors to be placed in sealed items or packaging well before the validation takes place. Wireless sensors also mean pressure can be monitored within load items, for example in terminally sterilised bottles or within vessels.
Manufacturers are also increasingly assisting with sensor placement not only by developing sensors suitable for specific applications but also by offering the accessories to repeatedly place sensors. Solutions are available for repeatable sensor location in vials, bottles, IV Bags, syringes and so on.
Software improvements also allow for significant time savings with validated software processing complex calculations in a repeatable and robust manner. Data analysis and processing times can therefore be significantly reduced, and the subjectivity of individual engineers can be removed. Reports can be generated within minutes of test completion providing clear pass/fail 21 CFR compliant data that is easy to review from a technical and quality perspective. Software packages therefore have the ability to produce fast, accurate and detailed test results.
Limitations
Whilst using wireless dataloggers brings some benefits to the table it also brings particular issues which are certainly worth some consideration. The main issues we have found when using wireless dataloggers or discussing projects with our clients are live data, sensor cost, sensor failure, battery life and specifications.
During the validation process engineers who are used to seeing live temperature and pressure data within the autoclave may find using dataloggers a challenge. There are options available to allow for live data, with transmitting loggers, for example. However, receiving a signal from outside a jacketed stainless-steel vessel can be a challenge. We have been able to receive a signal from dataloggers for autoclave validation, but it is not always possible without the addition of an aerial. Live data can therefore be an issue, however with suitable software a wireless datalogging system can produce clear pass/fail reports very soon after completion of the validation cycle.
Suitable wireless dataloggers are expensive and for a good system this is significantly more expensive than a standard wired system. Switching from thermocouples to PT sensors is going to be an expensive option and replacing damaged sensors can also be costly. Although a damaged thermocouple can be frustrating they are simple and fast to replace. Wireless dataloggers are more robust than thermocouples but sensor failures do happen. It is worth considering the return on investment of wireless dataloggers and the benefits they bring to validation, production and quality departments. An important question to ask is how many days production can you save and what is that worth to the business?
Thermocouple based systems are typically powered by mains power and battery life is not a significant problem. Battery management is however an important concern for wireless dataloggers and should be considered as part of the system use. If the battery life is managed correctly then the only consideration regarding batteries in the ongoing cost.
Equipment specification is possibly the most important and under considered issue with wireless dataloggers. There are now a significant number of manufacturers producing dataloggers that are marketed as suitable for autoclave validation. Not all loggers meet the required standards, however, and it is important to ensure the accuracy and the sensor are compliant to the relevant standards such as EN285:2015 and HTM 0101 Part B.
Conclusion
In conclusion, wireless loggers are highly likely to become the standard approach for autoclave validation. The time-saving and flexible nature of the systems work well with the increasing demands of production and validation departments. A robust URS for the specifications of the system should be in place to ensure they meet regulatory standards for response time and accuracy. Consideration should also be given to the flexibility of the software.