An interesting example of the application of risk assessment in product safety compliance is provided by the laser that is supplied with an optical fibre for flexible beam delivery. The optical fibre both directs the laser radiation and provides enclosure of the beam, but at the same time it presents a number of challenges including the design of fibre couplings and control of access at the possibly remote) fibre output. Take for example a Class 4 laser product comprising a laser source plus an optical fibre beam delivery system. In this case the body of the fibre becomes part of the protective housing of the laser product, for which EN60825-1 requires of manufacturers that removable covers (which include fibre couplings) be fixed so that tools are required in order to access to the laser radiation. Alternatively, if they are for user access, such items must in general be interlocked.
EN60825-1 manufacturers requirements also imply that if the distal end of the fibre (the laser aperture) can be more than 2m from the laser source, then an extension or duplication of certain features is needed:

1. a warning device to indicate the potential for emission from the fibre end;
2. a beam attenuator that can be operated from the vicinity of the fibre end.

EN60825-1 is a harmonised standard under the Low Voltage Directive and the above-mentioned requirements of the standard provide a means of complying with the more general risk assessment approach of the directive.From a risk assessment viewpoint the flexibility that fibre optic delivery offers, including and simplicity of remote operation (e.g. laser in one area, where it presents no hazard in normal operation and fibre output in another area) presents the sort of potentially hazardous situations that the manufacturers requirements highlighted above are designed to address. In addition to the above requirements, we would advise the supplier to state what assumptions have been made concerning the environment in which the equipment is to be used, and indeed whether the fibre is supplied as one component of a kit of parts or as an integral part of the laser product. For example, many state-of-the-art fibre delivered laser products are sold to research laboratories, where users may be expected to replace and realign the optical fibre. If this is indeed the expectation, then the supplier should make the user aware of the safety measures that must be taken in such circumstances.

Also, the safety documentation should describe any basic engineering and administrative controls (including the establishment of a controlled area) to be implemented, emphasising the need for laser safety eyewear in open-beam activities. The supplier should also make clear the level of competence that is required of the person responsible for implementing these controls.

Many models of optical fibre test equipment previously designated Class 3B can now be downgraded to Class 1M.

To illustrate the point, the calculation that follows concerns the near-IR CW laser output limits for emission from a simple plane-ended single mode optical fibre. The single mode beam diameter d63 a distance x from the fibre end is:

d63 = 2x . NA/1.7 where NA = Numerical aperture

The limiting condition for Class 1M is ‘safe for naked eye viewing’, specified in 60825-1 to mean that the 100s MPE (in this case assessed under point source conditions, C6 = 1) is not exceeded at a distance of 100 mm from the fibre end.

The MPE has associated with it a measurement aperture, either 7 mm (for wavelength in the range 700-1400 nm) or 3.5 mm (for wavelength > 1400 nm) and at 100 mm only a small fraction of the fibre output is collected, which is why Class 1M fibre output can be so much greater than the Class 1 AEL.

The fraction of the output collected, f, is: f = 1 – exp(-[(collection diameter)/d63]2)

Values are typically around 0.1. Some results for the Class 1M CW output limit from single mode fibres are: