Safety of machinery: three decades of impact testing of machine guards led to significant improvements

The year 2026 marks three decades of VDW-research on impact testing on machine guard windows and enclosures. The pressure to act was very high in the 1990s due to a significant number of accidents involving machine tools. This urgency led to a pragmatic approach in the initial investigations in order to bring about safe design conventions. This worked well, because all stakeholders contributed effectively. The design recommendations were established in product safety standards for machine tools, to start with, in CEN standards and subsequently in ISO standards. These standard provisions have been tried and tested over a long period of time and they proved to be very successful, because the number of accidents decreased significantly. However, there was sometimes a lack of scientific professionalism in the early pragmatic approach, for example with regard to the statistical evaluation of the test data. In recent years, this deficit has been overcome by establishing significantly improved testing techniques in the research laboratories, which have also been supplemented with improved models for evaluating the test results: For example, the Recht-Ipson method for determining the so-called "ballistic limit" or the application of a "logistic regression" to derive confidence intervals for the evaluation of results from the interval halving method. The incremental steps to more professional procedures have been documented in great detail every year at ESREL during the last decade by experts from Italy and Germany. However, there have not yet been incorporated in the relevant safety standards.

Keywords: Machine tool guard, impact resistance, Recht-Ipson method, logistic regression, proven-in-use.