Emission determination, biological effects of pulsed exposure and protective components
A three-year research project of the Federal Institute for Occupational Safety and Health (BAuA) examined possible hazards posed by optical radiation during welding works, corresponding implications in terms of occupational safety according to the Occupational Safety and Health Ordinance on Artificial Optical Radiation (Arbeitsschutzverordnung zu künstlicher optischer Strahlung, OStrV) and the recommended protective measures.
Welding is the most frequently used technique for the thermal joining of two metals in industry. The development of welding technology is still constantly progressing; refined process variants emerge, and modern hybrid methods are used in everyday operations.
In a report commissioned by the German Welding Society (Deutscher Verband für Schweißen, DVS) in 2013 entitled "Macroeconomic and sectoral value added by the production and application of joining technology in Germany and Europe", the number of welders in Germany was estimated at about 260,000 in 2011. In Europe, this number is close to one million.
The national implementation of the EU Directive 2006/25/EC by the OStrV defines mandatory exposure limit values for workplaces exposed to optical radiation; their compliance with which must be assessed in the course of risk assessment, especially of welding workplaces.
© Marco Janßen (BAuA) ,
Considering the current state of the art, performing a risk assessment is often difficult, and conducting the necessary measurements may require a considerable effort. The emission of optical radiation from the arc can differ significantly for various welding techniques: in a mere fraction of a second, the emission from shielded metal arc welding can be very intense and exceed the UV exposure limit value; but it can also be significantly lower, for example, during oxy-fuel welding, where the UV exposure limit value for an 8-hour working day can be complied with. Moreover, the emitted radiation varies over time (intermittent).
In addition to protecting the welder, for whom a safe application of welding techniques can usually only be ensured when undertaking personal safety measures, other employees who might be in the vicinity of welding workplaces are also to be protected. These include, among others, crane operators, forklift operators, employees on traffic routes or at nearby workplaces, because intensive optical radiation can be hazardous at relatively long distances.
The overall objective of BAuA's three-part research project - carried out in the period between 2015 and 2018 - was to improve the protection of employees against hazards posed by optical radiation at and in the vicinity of welding workplaces.
The optical radiation emission of the most frequently used welding techniques in factories, including carbon dioxide welding and fibre laser welding, was recorded extensively under common process parameters. The focus of the studies was on the variation of the welding current. As a result of this first project, mathematical emission models have been developed. In order to make these models easier to handle for operational practice, the "Pocket Disc for Arc Welding" was created. After adjusting the welding technique as well as the welding current, the time until exceeding the UV exposure limit at a distance of 1 m (welding assistant) and 3 m (factory traffic route) can be read with this practical guide.
The exposure limit value for UV radiation can already be exceeded within milliseconds. With regard to blue light hazards, the exposure limit value can be reached within1 to 5 seconds. In comparison, infrared radiation poses a minor hazard; the time until exceeding the exposure limit value is in the range of 1 to 100 minutes, which is still not insignificant for an 8-hour working day.
Since the optical radiation emitted by the welding arc is strongly intermittent (varies over time), the question arises how to assess this incoherent radiation with regard to the hazards to employees. At the moment, regulations concerning laser radiation are used for this purpose; however, their transferability has not been scientifically examined. Within the second subproject, this problem was addressed and confirmed by a scientific report. Preliminary experimental tests on biological material showed that the disinfection rate of pulsed optical radiation is around 30% higher than its cw (continuous wave) analogue. In vitro UV irradiations of skin samples, however, showed no significant differences between the two types of radiation with regard to damage induction and repair capacity. Yet, the induction of apoptosis was highly dependent on various radiation parameters, including pulse duration and pulse repetition frequency.
The focus of the third subproject was on the investigation of the transmission and reflective properties of protective components at welding workplaces with regard to their effectiveness. In the context of this investigation, surfaces (wall coatings, floorings, side walls, etc.) that can lead to a significantly higher exposure at welding workplaces were identified. The investigation of transmission properties of protective clothing for welders showed a strong dependence on the grammage (areal density) of the fabric. A modified version of the Ultraviolet Protection Factor (UPF) was developed to allow an assessment of the protective properties of such clothing.
At the moment, tests are still being conducted as part of this still uncompleted third subproject. Specifications for protective components such as partition walls, wall paints or floorings for the reduction of UV reflection are to be derived from the final results. Recommendations for normative adaptations for protective clothing of welders will be made.