The laser damage shown opposite occurred in the 8mm thick polycarbonate panel of a large 5-axis laser cell in which a 1.8 kW CO2 laser trims pressed panels. At the time of the incident the beam focus was some 2m from the panel and despite the fact that the machine was under operator control, action was not taken for several tens of seconds. If the machine had been left unattended the beam would certainly have penetrated the panel.

“The whole incident has been a real eye opener,” said the LSO. “The fact that untrained operators were running the machine at the time of the incident has brought home to me the need to be vigilant in implementing administrative controls, including operator training and procedures for restricting laser use inside the cell,” he added.

Whereas a risk assessment would generally indicate that the probability of generating a powerful errant laser beam is very low during operation of a flatbed laser cutting machine, the same cannot be said for a 5-axis machine, especially one that is used for process development. Yet as this example illustrates, simple panelling is widely used for guarding such machines, even when the laser is multi-kW. This incident supports Pro Laser’s recommendation not to use simple panels for guarding 5-axis machines unless it can be demonstrated that they provide protection for a sufficient (burnthrough) time under worst-case errant beam exposure. We would argue that ‘active’ guards, based on the ‘double layer’ designs described in EN 60825-4, provide a practical alternative for use in vulnerable areas.

EN 60825-4 ‘Safety of laser products - Part 4: Laser Guards’ requires that a risk assessment be undertaken to assess the Foreseeable Exposure Limit (FEL) for the laser guarding. The forthcoming amendment to the standard will recommend exposure durations for the testing of proprietary guards of 30,000s for automated machine applications, 100s for machines with short cycle operation and intermittent inspection, and 10s for machines operating under continuous observation. This incident clearly underlines the unreliability of human monitoring and justifies the general approach of 60825-4 not to permit human monitoring as an acceptable means of meeting the requirements for Class 1 operation.

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