Ageing of safety net materials

Status:

completed 02/1995

Aims:

Safety nets are used for construction and mounting work as fall arrest systems or protection against falls from a height. In most cases, safety nets are used outdoors where they are exposed to different climatic factors such as UV-radiation, heat, humidity, rain and air pollution for a long time. The nets must therefore be made of highly weathering-resistant materials to ensure a sufficient mechanical load capacity. Some investigations have so far been carried out with regard to the weathering resistance of materials used for safety nets. The results, however, were partly inconsistent. The project which was initiated by the expert committee for personal protective equipment was therefore aimed to gain detailed knowledge on the weathering-resistance of safety nets.

Activities/Methods:

The tested nets were made of polyamide, polypropylene and polyester. These materials were subjected to a five-years-period of weathering both in moderate Central European climate and in Mediterranean climate. Yarn and knot tensile tests served to analyse the effects of weathering in the course of the project with the breaking force and breaking elongation as characteristic values.

Results:

The investigations showed that the mechanical properties of the safety net materials changed generally more in the first year of weathering than in the following years. Especially the yarn tensile test revealed the large effect which the climatic conditions have on the ageing speed. As a rule, net materials age more quickly in Mediterranean climate than they do in the moderate Central European climate. The ageing behaviour also depends on the coloration and on the type of and content in ageing protecting agents. As long as the material is carefully chosen, ageing of safety nets is of little importance. Ageing effects as a result of climatic conditions can be counterbalanced by considering increased safety factors in the dimensioning of the nets. Very often mechanical damage, which is difficult to avoid under the extreme conditions of building sites, puts an end to the lifetime of safety nets long before ageing effects occur. Nevertheless, it is useful to insert test yarns which could be used to check the mechanical properties in yarn tensile tests and thus decide on the further use of a net.

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