Just took this off the Ulysses Website, thought it an interesting Read....
HELMETS a matter of life and death.How often do we see second hand helmets for sale, whether at Cash Converters, on Gumtree or occasionally at Ulysses Club Branch meetings? What is the condition of these helmets on the outside and more importantly, on the inside?
A helmet is a complicated piece of safety apparel which we often take for granted.
Helmets last forever right? Wrong! A helmet used virtually every day should be replaced every three years as a minimum and those used less frequently will see a replacement period of not more than five years. The outer shell is typically 3 to 5 mm thick and is either injection moulded thermoplastic or a pressure moulded thermoset reinforced with glass or Kevlar fibres.
The shell has at least six roles related to crash performance. It needs to absorb energy, distribute local forces from an impact, protect the face and temples, prevent the inner liner from fracturing, slide easily on the road surface and support other safety related components such as visors and chin straps.
Just as important is the inner foam liner. This is nearly always a polystyrene bead moulding with a regulated variable density. The foam cells are closed so the air inside is compressed in an impact. To provide a vital stopping distance for the head, this foam must compress by 90% during an impact and only partially recovers afterwards.
In other words, if your helmet is involved even in a low speed impact, it will have lost most of its resilience to protect your head in a subsequent impact.
If the helmet falls from your bike seat, how can you be sure that it retains its outer shell resilience?
You cant, and the helmet will always have a big question mark hanging over it.
Never, ever purchase a second hand helmet as one cannot be sure of its past history. Do you go to the wreckers to buy a second hand seat belt for the car? You cant anyway, as there is a legal requirement to destroy seat belts from a wrecked vehicle. One can purchase a decent new helmet for a measly $200 which will conform to AS1698, one of the most stringent helmet standards in the world. The $1000 helmet may be more comfortable and look a bit more spiffy, but will protect you to the same level a cheaper model will.
Just a casual look around at the commencement of a Club ride will reveal a few very suspect helmets of unknown condition. You will never know just how good they are until it is all too late.
That old helmet sitting in the garage for years that only comes out for the occasional pillion usage do everyone a favour, cut off the chin straps and chuck it in the bin, so no one else will ever be tempted to use it again. Even if your current in-date helmet has never suffered from any known damage, it will have deteriorated just by wearing it, as the polystyrene layer will be compressed when placed on the head and pulled down. So, have a good hard look at your helmet. How old is it and how many hours use has it had? If the answer is over five years and about a thousand hours use, it is good for only two things. Rip out the liner and use it as a planter pot or place it under the bed as the age of incontinence creeps up on us.
Dont forget the visor, as scratched visors produce problems at night, as the glare from oncoming headlights is increased by the light scattered from scratches.
OK, so youre off to buy a new helmet. Be sure to buy one that is a little on the tight side as the liner will soon settle in after a few hours use to produce a more comfortable and airtight fit which will give the added bonus of lessening the noise level somewhat. The helmet salesperson will know these things and be able to point you in the right direction. Make sure the chinstrap is done up tight as helmet loss in an impact is not uncommon. You wouldnt ride without a helmet, so why risk it coming off in an impact.
Direct Link:
http://www.ulyssesclub.org/News/tabid/83/articleType/ArticleView/articleId/4493/HELMETS-a-matter-of-life-and-death.aspx 
