This article on buying a helmet by James Freeman was published in 1999 – more than 20 years later and its message is just as pertinent: protect your head.
Almost all paraglider and hang glider pilots will crash eventually. Even a low-speed crash can scramble your brains. Gravel rash and broken bones heal – brains do not. Exact figures are not available for hang gliding or paragliding, however research shows that around 90% of cyclists’ brain injuries can be prevented by a properly fitted helmet.
The physics of how a helmet works
Head injuries are caused by the sudden stop when our head hits a hard surface. The way to prevent the injury is to bring the head (and the brain) to a more gradual stop. A helmet reduces the peak force applied to the head in a sharp impact.
The force in a deceleration is inversely proportional to the time taken for that deceleration to occur. The only variable in a crash situation is the time the change in velocity occurs over, as this determines the deceleration and hence the force applied to the head.
If we can increase this time by a factor of 2 the deceleration (and thus the force) is halved; If we can increase this time by a factor of 4 the force is reduced to 25% of what it would have been without a helmet. A human brain can withstand around 400 G without ill effect. 400-700 G causes concussion with a variable period of loss of consciousness. 700G+ results in permanent brain damage.
To increase the critical time over which deceleration occurs requires a material that brings our head to a safe stop by gradually crushing under load: it should have a very slow recovery rate when squeezed. It also needs to be thick enough and stiff enough to not totally collapse (bottom out) before our head comes to a stop.
A material which can do this was developed in the 50s and today nearly all helmets do this with expanded polystyrene (EPS), the same foam used for packing electronics. Once crushed, the foam does not recover. Spongy foam is added inside for comfort and fit.
But we’re not finished. What if the surface we hit is not flat? Rounded surfaces concentrate the force of the blow in a smaller area. The smaller the radius, the greater the concentration. To compensate, we add a hard outer shell to spread the force over a wider area and reduce the concentration.
What type of helmet do I need?
A helmet consists of an outer shell, crushable foam, a comfort liner, and a retention strap system. There are at least four critical elements that effect a helmet’s protective properties:
1. Impact management: how well the helmet protects against collisions with large objects.
2. Helmet stability: whether the helmet will be in place, and stay in place, when it’s needed.
3. Retention system strength: whether the chinstraps are sufficiently strong to hold the helmet on throughout an impact.
4. Extent of Protection: the area of the head protected by the helmet.
The EPS foam layer is absolutely critical to impact management as explained above. The thicker the layer of foam the greater its ability to absorb impact forces. The firm rubber found in some helmets is a very poor substitute and not recommended.
The shell also plays an important role in impact management in that it firstly it holds the EPS together during an impact, secondly it helps prevent objects penetrating the helmet and spreads the load to the foam and thirdly it helps the helmet skid easily on rough surfaces to avoid twisting your neck.
Obviously a helmet must stay on even if your head hits more than once so it needs a strong strap and an equally strong fastener that cannot be accidentally opened. The comfort liner and straps help hold the helmet in correct position.
With the strap fastened you should not be able to get the helmet off your head by any combination of pulling or twisting. If it comes off or slips enough to leave large areas of your head unprotected, adjust the straps again, add some padding or try another helmet. Keep the strap comfortably snug when flying.
Open face helmets generally represent an acceptable level of protection for your brain but provide less protection for your face. Full face helmets offer some extra facial protection at the expense of extra weight, decreased peripheral vision and perhaps decreased hearing and tactile sensation. It is also very important that they fit firmly.
I was unfortunate enough to have to attend a recent hang glider lock-out incident in which the pilot impacted face first. The impact on the chin guard led to the helmet rotating downward causing the pilots sunglasses to shear his nasal bridge off, later repaired with plastic surgery. Of concern is the extra leverage of the chin guard on the neck, especially some designs in which the chin guard is an excessive distance in front of the chin.
Bicycle style helmet vents mean less foam in contact with your head in a crash, which could concentrate force on one point of your skull. These vents are designed to dissipate heat which is not always optimal for hang gliding where staying warm is often the main concern. They also tend to have very thin shells.
“Aero” helmets are not noticeably faster unless you fly at competition speeds, and the “tail” could snag in a fall twisting your neck.
Comfort requirements should be considered. Fit, weight, and temperature/sweat control are the most critical comfort needs. A snug fit with no pressure points ensures comfort and correct position on the head if you crash. It may take a half hour of wearing to feel pressure points.
Weight is a big issue for long flights. Airflow over the head determines warmth. Vented bicycle style helmets are designed to facilitate heat loss – OK on the coast but less use at cloudbase. Sweat control can require a brow pad or separate sweatband.
When do I need to replace a helmet?
Immediately replace a helmet after you crash and hit your head. Impact crushes some of the foam. The helmet is less protective but the damage may not be visible. Helmets soften impact, so you may not even know your head hit unless you examine the helmet for marks or dents.
If you can see marks on the shell or notice any foam crush at all, replace the helmet. You may be reluctant to replace a helmet that looks almost as good as new, but if you did hit, you don’t want to take chances. If the foam of a bicycle helmet is cracked under the thin shell, it will be more likely to fly apart in your next crash. Replace the buckle if it cracks or a piece breaks off.
If you still have a helmet from the 1970s without an EPS liner, replace it immediately. They just do not have the protection of modern helmets.
Finally, the protective capability may diminish over time. Some helmets are made of materials which deteriorate with age and therefore have a limited life span. Most manufacturers recommend helmet replacement after five years.
Realistically that depends on usage, and most helmets given reasonable care should be good for longer than that. Please note that experience indicates there will be a noticeable improvement in the protective characteristic of helmets over a five year period. Thus, the recommendation for five year helmet replacement has some merit.
What about helmet standards?
The applicable standard for air sports helmets is EN966.
What to look for when buying a helmet
– Look for a standards sticker such as EN966
– Check that it has a thick layer of EPS foam
– Check that it has a sturdy shell
– Put it on, adjust the straps and then try hard to tear it off
– Look at the buckle for long-term durability
– Make sure it is comfortable
– Compare the price to the cost of a prolonged hospital stay
– Consider the nightmare of being a vegetable
– You will never regret buying and wearing a quality helmet
– Remember, your brain is priceless!