We all know that safety helmets (for any activity) are designed to reduce the effects of an impact and protect your brain from traumatic injury. How do they do that? Essentially, the materials are designed to break down to absorb and distribute the energy of the impact. In the most extreme cases, this will result in obvious deformations and cracks. When a helmet cracks as the result of an impact, it's not a sign that the helmet failed, it's a sign that it did its job. (And a pretty good indication of what might have happened to your head if you hadn't been wearing one.)
While it's obvious that you need a new helmet if it's split in two or smooshed on one side, the internal structure of the helmet can be compromised by *any* significant impact. Once it's compromised, the helmet's ability to protect your head from future accidents is greatly reduced. And there's no way to tell by looking at a helmet whether or not it's going to work the next time.
This is why manufacturers say that any helmet involved in an accident should be replaced immediately. In fact, motorcycle helmet manufacturers recommend replacing any helmet that has even been dropped on the ground! It might seem like an unnecessary expense, but let's put it in perspective. You've only got one brain. The human skull can be shattered by an impact of 4-6 mph. An average horse walks at about 4 mph, trots at 9 mph, canters at 15 mph, and can gallop at 30 mph. (Quarter horses have been clocked at 50 mph over short distances!)
So you might be patting yourself on the back thinking no sweat, I've had it for years but my helmet's never hit the dirt (or a jump standard, fence, tree, etc.). Not so fast...
How Long Have You Had Your Helmet?
Did you know your helmet has an expiration date? Recommendations vary by manufacturer, but in general you should replace your helmet at least every 5 years, no matter what. The materials break down over time, especially under extreme temperatures.
Do you keep your helmet in your car? You might want to think about replacing it every two or three years, as the high temperatures accelerate the deterioration of the materials that are supposed to protect the jello-like substance that's your brain.
But a New Helmet is Expensive!
Remember that bit about only having one brain? You can get a brand-new ASTM/SEI approved schooling helmet for $25. A super nice, comfy International ATH helmet will set you back about $150. If you really splurge, you can spend up to about $250 for a super-light, high-tech helmet. While it might be a bit more comfortable, there's really no functional difference between the $25 helmet and the $250 helmet. Any properly-fitted, approved helmet serves the same purpose. Which brings up another issue that's probably a topic for another post...
How Do I Know My Helmet Fits?
A good fit is essential--just having a helmet on your head isn't enough! To protect your head, your helmet needs to stay in the proper position even if you're being tossed around like a puppet. First off, you ALWAYS need to secure the harness, and it should be snug without restricting movement or being uncomfortable. However, the helmet should fit close enough around your head that it stays in place without the harness buckled. You should be able to give a sharp nod without the helmet slipping.
That said, you don't want it to be so tight that it gives you a headache! This is where the differences between helmets and manufacturers really stand out. Not everyone's head is the same shape! Many newer helmets are equipped with an adjustable harness system that give more flexibility in the fit. Some manufacturers offer helmets for different-shaped heads, such as round vs. oval. Other manufacturers aim for an "average" shape--which works for some, but more often seems to average out to a poor fit for the majority of riders.
Bottom line? Have your instructor check the fit of your new helmet before you ride in it. Or better yet, ask for their input before you go shopping.
A Few References...