More and more machinery requires safety systems with flexible functionalities. Essential for this are safety controllers or drives powered by embedded software. But ultimately the individual safety application is often realised with application programming by end users. Each device comes along with a different tool. This variety is often engineered either by programmers experienced with standard PLCs or electricians familiar with hard-wired safety circuits. An analysis of our accident statistics has revealed the remarkable fact that more than 60% of accidents at stationary machines occur during the operation of evidently faultless machines. Might software error also contribute to accidents in a large number of unreported cases? What are the appropriate countermeasures and activities? An obvious approach would be for application software developers to emphasize the specification and design phases in order to avoid human mistakes.
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