mx medical - Head case!
By TMX Archives on 13th May 05
As we're constantly reminded when we enter a race circuit or practice track - 'motorsports are dangerous'. As we're constantly reminded when we enter a race circuit or practice track - 'motorsports are dangerous'. It's something that we are all aware of although it's probably one - perhaps unconscious - reason why many participate as this element of danger is what makes this sport so exhilarating.Nobody likes to dwell on injury or try to point out the many danger aspects of racing bikes - these are normally obvious and for a rider if you spent all day thinking of what might happen out on the track you'd never get out of first gear.Having said this, keeping safe and sensibly protected is important and one piece of kit we all rely heavily on for safety and comfort is a helmet. With this in mind I hope to help explain what a helmet must go through to get certified as 'safe' and how helmets on the dealers' shelves differ.Most people will first look at graphics, design and price when choosing a helmet. This is why riders get paid to endorse products and some teams don't like their riders to have custom-painted helmets - they want the public to see the helmet that they can buy in the shops out front on the track.This is the marketing 'packaging' of the helmet and the designers will try to combine a good looking shape and 'cool' graphics with a safe and advanced product.A helmet has numerous components to it - these include an outer shell, a protective inner liner, internal padding to fit the rider's head and a retention system (aka 'strap') to keep it on your head securely.The outer shell of the helmet goes a long way to giving the helmet its strength properties and is the biggest contributing factor to the weight of the helmet. The materials used are either a thermoplastic or a composite of resin reinforced with glass, Kevlar or carbon fibres.A low-end or budget helmet will usually be made of a plastic polymer such as polycarbonate which is cheap and easy to form into shape and has good performance properties including a high strength to impact and fracture ratios. However, as it's required to give very high strength it must be made relatively thick - so this adds weight to the helmet.Higher specification helmets go for composite construction and are often carbon or Kevlar fibre reinforced polymers. This composite material gives very high strength to weight ratios and the fibres can be laid specifically (in different directions or thicker in one area) to give certain properties and extra strength where required. The same strength can be achieved with a much lighter and thinner shell compared to a simple polycarbonate helmet shell.However, due to the material costs and the manufacturing processes it is more expensive. If you were to hold two finished helmets of different constructions you would not necessarily notice the difference in looks - but the weight difference would be marked and out on the track this would be noticeable.The liner of the helmet is a very functional component and is designed to absorb and disperse an impact so it's not all directly transmitted to your skull. The shell will absorb a certain amount and this is the reason that it's not necessarily a bad thing to crack a helmet in a crash. If the helmet was completely bomb-proof you'd have no fear of anything piercing through but all the impact would be transferred to your head.The liner is often made from expanded polystyrene and different manufacturing techniques are used by different companies to get the greatest possible dispersion of impact forces. If you crash and hit your head the outer shell may look fine but the liner may have had to absorb the impact and by doing so the polystyrene may have been greatly compressed.If there is a subsequent impact the liner will not be able to absorb or compress to the same degree and if the polystyrene is completely compressed it will offer no benefit and the forces will be transferred to the rider's head which may result in serious concussion.There's a company in the United States that's now pioneering a sticker that's placed on the helmet and changes colour if the lid is subjected to a significant shock ('The Shock Spotter'). This informs the rider that although it may look fine, its integrity is not and it should be replaced for safety.The padding and retention straps are vital to ensure a good fit to the rider. An ill-fitting helmet - or one that won't stay on in a crash - will cause more danger and offer little protection to the rider. And if there is any twisting on the helmet it will be increased and passed on to the rider's head or neck.Due to the importance of a helmet's performance on the track, safety standards are employed to prove a helmet meets certain requirements. There are numerous standards and they do differ in many ways in their actual testing criteria.All helmets sold within the EU must possess helmet safety standard ECE 22/05. This is regardless of cost or brand of helmet. On top of this, for all ACU competitions a rider must have the Gold ACU standard sticker on the helmet as well.In the States all helmets must reach 'DOT' certification but the British Kite Mark test BS 6658 Type A and the SNELL test M2000 are two voluntary standards aimed to provide additional certification and are often found on helmets to re-assure the American market.With British Engineering Standards being one thing we can be proud of (along with the booze culture and Jordan's breasts) manufacturers such as Suomy are using the fact that their helmets reach this 'premier' British Kite Mark Standard as their major marketing tool.Some helmets will possess numerous stickers on the back of them and this may be confusing or hint to the fact that they are 'more qualified' than others. So what tests must these helmets go through to get these stickers or are they just given away?The unified standard of safety and the requirement for helmets sold in Europe is the ECE 22/05. The test is performed pre-release for any new helmet and samples are tested as follows...The Impact Absorption Test: The helmet is fitted to a dummy head and dropped onto a steel anvil from a height of 287cm in order to get an impact speed of 27km/h. Four points on the helmet are each tested once and the anvils are both flat and rounded (to simulate a kerbstone).The helmet is then dropped chinguard first onto a flat anvil from a height of 155cm. The velocity and duration of impact are both measured by sensors on the dummy head and when analysed, the acceleration of the head due to gravity must not exceed 275g.The Head Injury Criteria (HIC) factor which is a measurement of the total impact energy onto the head is calculated by multiplying the velocity with the duration of impact. The maximum permissible figure for this is 2,400. Reducing the total peak g and also the duration of impact will provide the rider with the best protection and is therefore a main aim of designers.The chin strap is also tested by hanging a mass from it (a static load) and then dropping a proportion of this mass (a dynamic load) from a height of 75cm. This must not displace the chin strap by more than 35mm (from the dynamic load) and the static load must not displace the chin strap by more than 25mm.A 'roll off' test is also performed by attaching a mass to the rear of the helmet and dropping the mass in front of the helmet to test if it shifts forward. It must not move forward by more than 30mm.The ECE 22/05 standard has the most stringent 'peak g' rating which on face value is the most re-assuring. However, while the other standards (SNELL, BSI and DOT) all employ a hemispherical anvil which increases the concentration of loading and challenges the shell to withstand puncturing, the ECE does not and the nearest equivalent is the kerbstone.This is an interesting point for off-road riders as - unlike the flat, smooth Tarmac that road riders' helmets will impact - stones, rocks or similar objects found off-road will greatly concentrate the impact force. Also the HIC value is brought into question as this is based largely on skull fractures observed in bare-headed cadaveric subjects struck with a shaped impacter (yep, dead people's heads hit with metal objects - pretty gruesome).According to some research, the actual value for injury is 1000 rather than the seemingly high ceiling require of 2400 by the ECE test. Another couple of points to mention are that only one drop is performed for each test in the ECE certification and this only at a speed of 27 km/h.If you think about the number of knocks you may have taken in your current helmet you'll realise that there will have been no evaluation of performance of the helmet for subsequent impacts. I also think 27 km/h seems very low and with average speeds on motocross tracks above 30 mph (48 km/h) it isn't as high as it could be to test 'real life' situations.So as you can see there's a lot more goes into the production of a helmet than putting on a big peak and some air vents. There is a very wide variety out there and one of the main things you pay for is the quality of materials and workmanship to give a lightweight but strong product.What is re-assuring though is that regardless of the depth of your pockets or the brand that you favour, if they possess the various necessary stickers on the back they have been tested and are deemed as safe as any other helmet on the shelves. However, there are some short-comings of the tests performed and it should be noted that there has been no development for an off-road specific test by these testing bodies.So the next time you're looking for a lid you'll have a good idea of what goes into making them, how construction varies and what they must have been through before they are deemed to be safe enough for general release.Medical MilwayAlan Milway is a qualified Sports Scientist who works as a fitness trainer specialising in training motocross and enduro riders. For more information on how Alan can help you train - or just to give him some abuse - check out his website www.mxfitness.co.uk or call him on 07810 827427.Words and photos by Alan Milway