Measurement of the strength of UV radiation in reflections on different surfaces

Status:

completed 02/2015

Aims:

The radiation exposure of welders and their assistants depends essentially on the radiation emitted by the welding arc. Considerable exposure may however arise from reflections, as well as from direct radiation. Pilot measurements conducted at the IFA have shown that reflections may typically account for 0.1 to 1% of direct radiation, and in some cases more. The exposure limit for protection against UV radiation stated in EU Directive 2006/25/EC and in the German Ordinance on optical radiation is reached in as little as one to two seconds with some welding methods. It can therefore be surmised that this exposure limit will be attained during exposure to reflected radiation alone after as little as 100 to 200 seconds. It is therefore not sufficient for protection to be provided against direct radiation alone during welding work. Welders' assistants in particular are frequently less well protected than the actual welders.

The aim of the project was to study the reflection of UV radiation on a range of surfaces. The order of magnitude of the reflected radiation component was to be determined. The project was also to reveal the feasibility of a larger study into the reflection properties of surfaces (material, roughness, colour).

Activities/Methods:

A test arrangement for measurement of the irradiance was set up at the SLV welding testing and training institute in Duisburg in co-operation with the German Social Accident Insurance Institution for the woodworking and metalworking industries (BGHM).

Results:

The measurements at the SLV in Duisburg were conducted under expert supervision to ensure that they reflected real-case conditions. Particular attention was paid to the measurement of direct and reflected radiation, and also to measurements inside welders' helmets.

Substantial variation in the measurement results, even under identical test conditions, was observed immediately in the first series of measurements (pilot tests). The irradiance also varied as a function of several factors, including the welding current, the distance between the source and the detector, and the distance between the electrode and the workpiece. The welding method selected also had a major influence upon the irradiance: during MAG welding, an effective irradiance in the UV range of 37.2 W/m² was observed at a distance of 50 cm (limit value of Directive 2006/25/EC reached in less than 1 second), whereas an effective irradiance in the UV range of 1.5 W/m² was attained during pulsed TIG welding (limit reached after 20 seconds).

A relationship was also established between the magnitude of the reflected radiation component and the reflecting surface. The material of the surface was a factor here, as was its colour. For example, it was found that the welding curtains used did not necessarily exhibit the lowest reflection. The different materials also responded differently depending upon the wavelength. Some surfaces (such as a fire blanket and highly reflective Silverice plates) exhibited increasing reflection with rising wavelength, whereas no relationship between wavelength and reflection was observed for the standard welding curtains. The pattern of the spectrum absorbed directly from the source was evident in all reflection spectra, however. Altogether, it was confirmed that reflection is in the order of 0.2 to 1.2%.

From the measurements conducted inside the welders' helmets, it was concluded that UV radiation components do not penetrate the helmet and that protection of the welder's eyes and facial skin is assured provided the helmet is fitted tightly against the face. Where a gap exists between a welder's helmet and the face, reflected radiation components are able to reach the eyes and the face. The project constitutes the successful preparation and feasibility analysis of a further project in which the most common welding methods and workplaces are to be studied systematically.

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