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DOUBLE-REDUNDANT AND FAIL-SAFE DESIGN


Double-redundant and fail-safe design reduce dependence on operator vigilance.

To address these concerns about undetected faults, double-redundant and fail-safe design is becoming a requirement in the area of medical device processing machinery. In this process, manufacturers carefully examine the risks of undetected errors occurring to ensure that systems are modified so that either the mistakes cannot occur or there is zero risk of them going undetected. But many medical manufacturers and their machinery suppliers have thus far failed to realize the need for or consequences of not embracing double-redundant and fail-safe design in their packaging machinery and processes.

The need for these design criteria in medical manufacturing emerged as a result of two basic factors in industry as a whole: the limitations of statistical analysis and machine complexity.

STATISTICAL ANALYSIS


If a fault is discovered, the machine rejects the product or stops the process.

Sample inspection or statistical controls cannot detect spurious machine events or aberrations in a process. A well-recognized and legitimate method of controlling a machine or process is to apply statistical tools that will predict the standard deviation of a batch. Using such tools on a reasonable sample, it is possible to predict to a high probability whether the entire batch is going to be within the specification. Of course, these statistical tools must be applied with care—the incorrect use of statistical tools in applications where there are multiple variables can be dangerous and should only be approached with absolute care. But statistical analysis is essential and valuable in the field of validation, and a sound mathematical basis for ensuring process stability and capability.