Ageing of industrial helmets

Status:

completed 08/1997

Aims:

Safety helmets are mostly made of 100 percent plastics whose mechanical properties suffer from material ageing caused by environmental factors. The problem is to know whether the protection level of a used helmet is still sufficient, and whether there is a simple method to identify when a safety helmet must be replaced.

Activities/Methods:

The ageing behaviour of industrial safety helmets made of different plastic materials was analysed in a three-step- approach: identification of damage and analysis of the causes of damage observed at different helmets and for different times of use, literature research into the ageing behaviour of plastic materials and safety helmets, open-air weathering of 1320 helmets for up to ten years. In addition, some of the helmets were aged artificially using UV radiation. The helmets were then tested in view of their shock absorption behaviour and their penetration resistance,

Results:

The ageing behaviour and thus the lifetime of safety helmets depend primarily on the material and the used UV-stabilisers. Design and colour have little influence. The following recommendations for the lifetime of helmet materials were elaborated:

polyethylene (PE): 4 years; polycarbonate, also glass fibre reinforced (PC): 10 years; acrylonitrile butadiene styrene (ABS): 4 years; fibre reinforced phenol formaldehyde resins (PF-SF): 5 years; glass fibre reinforced polypropylene (PP-GF): 10 years; unsatisfied polyester resin, glass fibre reinforced (UP-GF): 10 years.

A practical way of checking a helmet's state of wear is the so-called "crackling test", where the peak is slightly moved up and down. If this causes a crackling sound, the helmet should be replaced.

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