Over 98% of the world's industrial laser processing machines use high power CO2 or Nd:YAG lasers. Both lasers produce invisible infrared laser beams, but at quite different wavelengths. High power beams of any wavelength can cause a severe injury, but wavelength does become important in the context of guarding to protect against relatively low levels of scattered laser light.

Current best guarding practice is quite different for CO2 and Nd:YAG laser machines

At low levels of CO2 laser exposure, the long laser wavelength means that it is the outer surface of the cornea of the eye that is primarily at risk. Such injuries can be painful, but victims often recover completely within a few days. By contrast, exposure to low levels of the shorter wavelength light from the Nd:YAG laser can cause a retinal injury resulting in permanent partial loss of sight.

Not surprisingly, a risk assessment can lead to quite different acceptable guarding solutions for equivalent CO2 and Nd:YAG laser machines. For example, commercial flatbed CO2 laser profiling machines are generally provided with peripheral guarding up to a height of about 2.5 m from the floor, but often have small gaps between sections of the perimeter guard and/or larger clearance gaps to facilitate automatic loading of the cutting table. Most are open topped. An equivalent Nd:YAG profiling machine would almost certainly have a complete Class 1 enclosure.

To take another example, CO2 laser marking systems integrated onto product conveyor lines are often fitted with no more than short 'tunnels' to reduce line-of-sight angles through the entrance and exit apertures in the enclosure whereas the Nd:YAG equivalent might have a labyrinth entrance and exit, brush seals or guillotine doors to block stray reflections.

There is much confusion over what constitutes Class 1 in the laser machine context

Laser machines with gaps in the guarding are almost certainly Class 4 if any gaps in the guarding offer a direct line of sight to an unenclosed portion of the Class 4 laser beam, regardless of how low the actual levels of laser light emerging through these gaps. Strictly, a hazard distance (ENOHD) calculation must be performed, but for high power lasers the distance generally exceeds the dimensions of the machine.

These examples illustrate a limitation in the classification scheme that is far from resolved, and users may be understandably confused as to how to interpret international laser safety user guidance (as given is the primary laser safety standard, EN60825-1) in this context. Manufacturers often side-step the issue by placing a Class 4 label on the laser source (only), while others correctly refer to the product in user manuals and brochures as 'a Class 4 laser product with full perimeter guarding'.

The laser standard to support conformity to the Machinery Directive is in need of improvement

At the present time the only standard available to support the Machinery Directive for laser processing machines is EN12626 'Safety of machinery - laser processing machines - safety requirements'. This standard requires, among other things, for the machine to be a Class 1 laser product. Proposals are being made to extend EN12626 to include open-topped machines where operators and others are not exposed to laser light in excess of the Class 1 MPE, but at the present time this particular standard cannot be used in its entirety to support a claim of conformity to the Machinery Directive for the CO2 laser machine examples given above.

For high power laser activity, more than any other, safety standards must be risk based

Laser radiation is only one of many hazards encountered in the industrial workplace, and only by adopting a risk-based approach can it be treated in the same way as other hazards to be guarded. More recent standards in the EN60825 series, but not yet EN60825-1, embrace the risk assessment approach. As a result, there is a conflict between the 'worst single fault' condition for Class 1 in EN60825-1, and the requirements of other machine safety standards for assessment under 'reasonably foreseeable fault conditions'.

EN60825-4 'Laser Guards' is risk-based. This allows great flexibility in the design of guards for laser processing machines. A forthcoming informative annex to EN60825-4 will deal with the arrangement and installation of laser guards for CO2 or Nd:YAG lasers. Such guarding is often built to contain only relatively weak reflections and scattered laser light, implicitly relying on a high degree of structural integrity in the beam forming components to maintain the beam path from laser to workpiece. The implications of this, together with requirements for guarding free space and optical-fibre beam-delivery lines, will be addressed

Pro Laser undertakes guard design and specialises in product conformity to laser safety standards.