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Motorcycle stone shields
Motorsport riders risk being hit by stones and other flying debris
Image © www.iStockphoto.com/grahamheywood
In addition to the risks associated with road riding, participation in motor sports can introduce further hazards. One such hazard prevalent in off-road motorsports such as Motocross is that of stones and other debris thrown up from the riding surface impacting the rider. In these circumstances, stone shields can provide impact protection.
Stone shields typically come in the form of complete assemblies which include rigid shields intended to cover specific areas of the body, as well as straps or textile fittings intended to hold the shield(s) in the correct places. They include (as a minimum) a shield to cover the chest, but can also include protection for shoulders, biceps or the back.
The specification for motorcycle stone shields sold in the EU is defined in EN 14021:2003. This standard defines a number of design and performance requirements and test methods.
Stone shields are intended to protect the wearer by ensuring that the full force of the impact of the flying stone or piece of debris is not transmitted to the wearer’s body. EN 14021:2003 requires that the transmitted force through the stone shield and padding does not exceed 27kN in the specified impact test and that the shield provides this level of protection without cracking or shattering.
EN 1621 demands high-impact testing
EN 1621 parts 1 and 2, cover 'motorcyclists' protective clothing against mechanical impact', but the impact test specified in EN 14021:2003 differs from the impact tests called up in EN 1621 in several important respects. For example, the impact energy and the impactor are both much smaller in the stone shield test than in the protective clothing tests. These differences are because the EN 14021 test is intended to simulate a smaller-scale event than that simulated in the tests for protective clothing. The mass of the impactor in the stone shield test is 1kg and the impact energy is 10J – a fifth of that specified for the corresponding tests on protective clothing for motorcyclists.
The apparatus for the stone shield test, unlike the apparatus for the clothing tests, incorporates a means of ensuring that no force is registered until the shield is distorted by at least 10mm. This means that if a shield is sufficiently rigid, for example one that distorts by only 5mm in the test, a peak force value of zero will be recorded. This may seem strange to those used to seeing the results of impact tests on protective clothing for motorcyclists.
Vital body protection
Stone shields are required to cover a specified minimum area of the wearer's body, particularly in important zones (such as across the chest). The stone shield must incorporate a breast guard and this must cover the anterior (front) portion of the rib cage, including the sternum. Shoulder, bicep and back guards must also cover specific areas of the body if included in the garment. The guards are checked for significant gaps in the protective areas covered using a 15mm diameter tapered probe. When inserted in any direction, the probe should not be capable under its own weight (500g +/- 10g), of passing through any holes, gaps or slots present in the stone shield components – thus effectively limiting the size of the allowable ventilation holes.
Shields are subjected to an ergonomic assessment, in which they are checked for any significant hindrance to freedom of movement when worn, as well as checks for any potentially dangerous projections or causes of discomfort. In addition, any restraints used for holding the shields in place, or holding additional components (for example, shoulder guards), are subjected to tensile strength tests to ensure the shield is unlikely to detach from the garment in use.
SATRA can offer both a testing and EC type-approval (where applicable) service for motorcycle clothing to a number of European standards, covering body, hand and foot protection.
Further information on SATRA's PPE certification and testing services is available at www.satra.com/ppe
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