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Choosing a bicycle helmet
http://www.cycling-inform.com/articles/169/1/Choosing-a-bicycle-helmet/Page1.html
Jodie Batchelor
Jodie is the current Victorian Vets Criterium and Road champion in her age group. She has been racing for several years now and likes any event that involves sprinting and not too many hills. She initially used cycling as an important part of her rehabilitation from a mountaineering accident in New Zealand. She then got into racing as a replacement for martial arts in which she represented Australia and won Gold, Silver & Bronze medals in the Martial Arts World Games in 2000.  
By Jodie Batchelor
Published on 12-Aug-08
 
In Australia and other countries it is mandatory to wear a bicycle helmet, with the retention straps fastened, while riding on roads or paths. It is also highly recommended when using mountain bike trails. This rule applies not only to the rider, but also to children sitting on a carrier seat or being towed in a trailer. Riding with the helmet on the handlebars or attached to your backpack does not do your head any good in an accident, neither does an ill-fitting helmet!

A helmet primarily should fit your head and meet Australian Standard 2063 (the helmet must have a valid sticker inside stating it meets this standard). Additionally you can select a helmet that is lightweight and has plenty of ventilation holes to allow airflow.

When trying on a helmet try many styles, brands etc, and choose a helmet with an internal shape that closely matches your dimensions. Don't rely on the adhesive pads to take up the slack - they should only be used to achieve a fractional fit. If there is a gap and you can fit your fingers between the helmet and your head then either choose a different helmet or adjust the tension at the back of the helmet. Your helmet should not be able to slide from front to back or side to side once fastened on your head.

Once you have chosen your helmet, don't wear it resting too high on the forehead. As a guide, the front rim should be about the width of two fingers above the eyebrows. Getting the right strap position takes practice - the side toggles on the straps should be adjusted so that they sit just under the ears.

Don't skimp on a cheap helmet, this piece of equipment could save your life or quality of life if in an accident. I am sure that your local bike shop they will have some unfortunate riders smashed up helmet behind the counter to show you. Remember, your helmet is an investment in your safety.

A bicycle helmet should be replaced at least every five years because the foam can deteriorate over time. Also after any impact as the foam may have weakened.

Helmet wearing exemption
A cyclist can apply for an exemption from wearing a helmet on medical grounds, contact you r local cycling body for details. If approval is granted, the cyclist will receive written confirmation and this must be kept on hand at all times while riding.