Safety concept for test benches: from risk assessment to emergency stop

Where every safety concept starts: the risk assessment

Before anyone talks about guards or relays, there is the systematic question: what on this bench can injure whom, and how? EN ISO 12100 prescribes the procedure: identify hazards (rotating shafts and couplings, parts flying off when a specimen fails, electrical energy, hot surfaces, batteries), rate risks by severity and probability, and derive measures. The result is documented; it is the basis for everything else and part of the CE target picture.

Important for self-builders: even someone building a bench only for internal use legally becomes a manufacturer with the corresponding obligations. This article gives a technical overview and is not legal advice.

The hierarchy of protective measures

The standard prescribes a clear order. First, design inherently safe: limit energies, avoid pinch points, do not size speeds and torques larger than necessary. Then technical protective measures: guards such as a polycarbonate hood over the rotating line, with monitored interlocking where needed, plus emergency stop devices per EN ISO 13850 within reach of the operator station. Only last come organizational measures such as markings, signal lights and work instructions; they complement technical measures but never replace them.

Functional safety: the safety PLC

Emergency stop, hood monitoring and safe shutdown are safety functions in the sense of EN ISO 13849 and need provable reliability (performance level). Configurable safety PLCs such as the Pilz PNOZmulti exist for this: dual-channel acquisition, monitored shutdown paths to the inverters, defined reaction to wire breakage.

The most important rule: safety functions never belong in the regular test bench software. The automation may stop the bench conveniently, but safety must not depend on a PC program running flawlessly. Safety chain and control remain separate worlds; the software merely learns that the emergency stop was triggered.

What this looks like on a real bench

Taking a drivetrain test bench as an example: the rotating line runs under a bolted polycarbonate hood with warning markings, the emergency stop button sits right at the operator station, a signal tower shows the system state from afar, and the drive enable goes through the safety PLC. This keeps the bench controllable even when a specimen fails or an operator makes a mistake, which is exactly what the concept is for.