The laser safety standard BS EN 60825-1 requires Class 3B and Class 4 laser systems to incorporate a beam stop or attenuator (Clause 4.7) and outlines the general requirements for tests to claim compliance (Clause 9.1). How then is it that some commercial lasers are delivered with beam stops/attenuators that are totally unsuitable or inadequate?

The fact is that 60825-1 does not even hint at the form of the beam stop/attenuator. It could be a metal cap that fits over the laser output aperture and secured with a chain to comply with the “permanently attached” requirement; it could be a manually-operated flap that moves to cover the laser aperture. It need not even be a physical beam shutter: software that inhibits the fire signal also satisfies 60825-1. Whilst these solutions may meet the laser standard requirements they may be impractical and totally useless if, for example, the laser is to be used within a laser processing machine.

However, under the Machinery Directive we would demand that where, for instance, embedded Class 3B and 4 lasers are required to remain on during access to the processing zone by the machine operator for piece part loading or unloading, the beam stop (often called a shutter in this context) must provide the same level of protection and integrity as does the process zone guard during laser processing. That is, the shutter must tolerate the full laser beam radiation without deterioration or damage and have an adequate lifetime. This may involve monitoring the beam shutter for damage, monitoring that the shutter is closed when it is intended or commanded to be closed and controlling its operation by safety-related control circuits. Many laser suppliers to the industrial market do indeed provide their sources with shutters that can be remotely operated, are fail safe and incorporate a range of safety features that give heightened confidence in the security of operation of the device. Nevertheless, a surprisingly high number of laser processing machines incorporating lower power (but nevertheless Class 4) lasers appear to have totally inadequate shutter systems.

In general, the laser user will need to consider how the laser is to be used and assess the risks that may be presented by inadequate shutter provision or a shutter failure. Ideally, this should be done before ordering the laser, but it may well be that an additional safety shutter will be required.