Apart from the laser wavelength, the hazardous potential of hand-held laser devices or automated non-closed laser machines is strongly dependent on the distance of the potentially irradiated part of the human skin to the processing zone. The reason is that the intensity of focused laser radiation increases with the square of the decreasing distance to the processing zone. A typical situation which occurs to the operators standing next to the processing zone during HLD use, and the corresponding distances from the processing zone to the different parts of the human body are shown in Figure 1. According to this illustration, the most endangered body parts are the hands that operate the HLD.
Figure 1: Typical distances between process zone and body parts during hand-held laser-processing
(the distance of the body part regarded to the process zone mainly affects the hazardous potential),
left. Possible scenario during e.g. maintenance (unintended reflection), right.
In principle, three types of laser irradiation can be distinguished: irradiation by a diffusely reflected beam, irradiation by a directly reflected beam, and direct irradiation. According to this listing, the safety level required with respect to skin protection increases form left to right in Figure 2.
With respect to the dimensioning of laser PPE and curtains, the worst case has to be taken into account. Mostly, HLDs are equipped with safety systems, e.g. two-hand control buttons or contact pins, which should avoid direct irradiation by a focused laser beam.
Figure 2: Typical laser irradiation cases and corresponding qualitative
safety levels required (qualitative consideration).