How Airfence Works
David Swarts, Roadracing World & Motorcycle Technology
Published: April 24, 2002
The most dangerous aspect of an accident for motorcycle road racers is not the speed at which the accident occurs, but how the rider decelerates. Racers who can bleed off potential energy through a long slide into a grassy field are often able to continue with no more damage than grass-stained leathers. However, if that same slide is cut short by a steel or concrete barrier the rider will almost always be injured to some degree.
Although most new racetracks constructed in the U.S. are being built with proper barrier- free run-off areas for motorcycles, many older tracks have dangerous concrete walls, steel barriers or other unyielding obstacles in the impact zones. Traditionally in the U.S., riders have been protected from these impediments by haybales, or worse, nothing at all. Haybales, for such a low tech device, work admirably well but often the effort, expense and sheer volume of haybales required to properly protect a wall result in less-than-adequate protection, sometime with fatal results. Haybales do not do such a good job with multiple impacts, cannot be installed against a wall on the top of an oval (like at Daytona) and can create a traction hazard on the track if an impact explodes hay across the racing line.
Inflatable barriers, commonly known as Air Fence although that’s actually a trademark owned by Airfence Safety Systems (it’s sort of like calling “tissue” – “Kleenex” or “cola” –“Coke” even though those are trademarks) provide a far superior solution to haybales. Air Fence takes its name from the Australian-based Airfence Safety Systems, the latest incarnation of the company that developed the first inflatable barrier specifically for motorsports in 1991. Austria-based Alpina Safety Systems, once allied with Airfence Safety Systems’ predecessor, has its own version of inflatable air barriers, called Air Modules. Both companies' safety barriers are nearly identical, work in a very similar manner and are used by the world's leading motorcycle racing sanctioning bodies.
Air barriers are made from a heavy-duty, tear-resistant, fire-retardant, repairable PVC fabric that is designed to withstand multiple crash impacts and years of exposure to the elements. Front, back and interior wall sections in each module are inflated to slightly above ambient air pressure to give each air module shape, roughly 27 feet long, four feet high and four feet deep. The hollow space between these wall sections, the majority of the modules' volume, remains at ambient air pressure. The modules dovetail together so that a series of air barriers can be deployed to cover a long expanse of wall. Straps, similar to automobile seat belts, located at each end, tie multiple modules together end-to-end.
Like a permanent air bag for concrete walls, the air barriers are designed to gradually absorb the energy of a crashed rider. The rider’s deceleration is controlled by the release of air through control valves. The goal is to slow the rider to a stop gradually before the rider can make contact with the hard objects behind the module. After an impact the air barrier will recover its original shape and its impact-absorbing ability automatically. The re-inflation process is gradual and gentle so as not to eject a rider from the barrier.
Air barriers are tied securely, top and bottom, in order to keep the barrier from being displaced on impact. A skirt or flap, made from the same fabric as the module, is deployed from the lower front portion of the barrier and staked down to the ground to prevent crashed riders from sliding underneath the soft barrier. If the modules are deployed on a hard surface that prevents staking the skirt down, small-diameter, cylindrical sandbags are used to keep the skirt in place. Properly securing the air barrier prevents the air barrier from uncovering the wall if a motorcycle precedes the rider in the crash and helps prevent the barrier from moving into the racing line where it could create a hazard.
Airfence Safety Systems of Australia and Alpina Safety Systems of Austria make other soft barrier systems that can be used for motorcycle racing applications. Most of the other systems are designed for semi-permanent placement in one spot on one track. Inflatable air barriers, on the other hand, can be deflated, rolled up into a relatively small bundle, shipped from racetrack to racetrack or moved from location to location at a track as needed.
While it is not possible to eliminate risk from motorcycle racing, it is everyone’s responsibility to reduce risk wherever possible. If it is not possible to remove hard walls from impact zones, those hard walls should be insulated with the best possible protection. Currently, that is inflatable air barrier.
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