A bicycle helmet is a helmet intended to be worn while riding a bicycle. They are designed to attenuate impacts to the cranium of a cyclist in falls while minimizing side effects such as interference with peripheral vision. There is an active scientific debate, with no consensus, on whether helmets are useful for cyclists, and on whether any benefits are outweighed by their disadvantages. The debate on whether helmet use should be compulsory is intense and occasionally bitter, often based not only on differing interpretations of the academic literature, but also on differing assumptions and interests on the two sides.
About helmets
History of designs
A cycle helmet should be light in weight and should provide adequate ventilation, because cycling can be an intense aerobic activity which significantly raises body temperature, and the head in particular needs to be able to regulate its temperature. The dominant form of helmet up to the 1970s was the leather "hairnet" style, mainly used by racing cyclists. This offered minimal impact protection and acceptable protection from scrapes and cuts. In countries with long traditions of utility cycling, very few cyclists wear helmets. The use of helmets by non-racing cyclists began in the U.S. in the 1970s. After many decades when bicycles were regarded as children's toys only, many American adults took up cycling during and after the bike boom of the 1970s. Two of the first modern bicycle helmets were made by MSR, a manufacturer of mountaineering equipment, and Bell Sports, a manufacturer of helmets for auto racing and motorcycles. These helmets were a spinoff from the development of expanded polystyrene foam liners for motorcycling and motorsport helmets, and had hard polycarbonate plastic shells. The bicycle helmet arm of Bell was split off in 1991 as Bell Sports Inc., having completely overtaken the motorcycle and motor sports helmet business.
The first commercially successful purpose-designed bicycle helmet was the Bell Biker, a polystyrene-lined hard shell released in 1975. At the time there was no appropriate standard; the only applicable one, from Snell, would be passed only by a light open-face motorcycle helmet. Over time the design was refined and by 1983 Bell were making the V1-Pro, the first polystyrene helmet intended for racing use. In 1984 Bell produced the Li'l Bell Shell, a no-shell children's helmet. These early helmets had little ventilation.
In 1985, Snell B85 was introduced, the first widely adopted standard for bicycle helmets; this has subsequently been refined into B90 and B95 (see Standards below). At this time helmets were almost all either hard-shell or no-shell (perhaps with a vacuum-formed plastic cover). Ventilation was still minimal due mainly to technical limitations of the foams and shells in use.
Around 1990 a new construction technique was invented: in-mould microshell. A very thin shell was incorporated during the moulding process. This rapidly became the dominant technology, allowing for larger vents and more complex shapes than hard shells.
Hard shells declined rapidly among the general cyclist population during the 1990s, almost disappearing by the end of the decade, but remain popular with BMX riders as well as inline skaters and skateboarders.
The late 1990s and early 2000s saw advances in retention and fitting systems, replacing the old system of varying thickness pads with cradles which adjust quite precisely to the rider's head. This has also resulted in the back of the head being less covered by the helmet; impacts to this region are rare, but it does make a modern bike helmet much less suitable for activities such as unicycling, skateboarding and inline skating, where falling over backwards is relatively common. Other helmets will be more suitable for these activities.
Since more advanced helmets began being used in the Tour de France, Carbon Fiber inserts have started to be used to increase strength and protection of the helmet. The Giro Atmos and the Bell Alchera are among the first to use carbon fiber.
Some modern racing bicycle helmets have a long tapering back end for streamlining.
History of standards
In the United States the Snell Memorial Foundation, an organization initially established to create standards for motorcycle and auto-racing helmets, implemented one of the first standards, since updated. Snell's standard includes testing of random samples. In 1990 the Consumers' Association (UK) market survey showed that around 90 % of helmets on sale were Snell B90 certified. By their 1998 survey the number of Snell certified helmets was around zero. There are two main types of helmet: hard shell and soft/micro shell (no-shell helmets are now rare). Hard shells declined rapidly among the general cyclist population over this period, almost disappearing by the end of the decade, but remained more popular with BMX riders as well as inline skaters and skateboarders.
The American National Standards Institute (ANSI) created a standard called ANSI Z80.4 in 1984. Later, the United States Consumer Product Safety Commission (CPSC) created its own mandatory standard for all bicycle helmets sold in the United States, which took effect in March 1999.
In the European Union (EU) the currently applicable standard is EN 1078:1997.
In the UK the current standard is BS EN 1078:1997, which is identical to the EU standard, and which replaced BS 6863:1989 in 1997.
In Australia and New Zealand, the current official standard is AS/NZS 2063. The performance requirements of this standard are slightly less strict than the Snell B95 standard but incorporate a quality assurance requirement. As a result, the AS/NZS can be argued to be safer. SAI Global run a marketing program based on the AS/NZS 2063 standard, in which manufacturers pay royalties and fees to affix a "5 ticks" sticker on helmets.
The CPSC and EN1078 standards are lower than the Snell B95 (and B90) standard; Snell helmet standards are externally verified, with each helmet traceable by unique serial number. EN 1078 is also externally validated, but lacks Snell's traceability. The most common standard in the US, CPSC, is self-certified by the manufacturers. It is generally true to say that Snell standards are more exacting than other standards, and most helmets on sale these days will not meet them (currently, Specialized is the only bicycle helmet brand in the world to meet the Snell standard. All of their helmets are Snell certified.)
Although helmet standards have weakened over time there is no data on which to base an assessment of how this has affected the design goal of mitigating minor injuries. Minor injuries are substantially under-reported and it is difficult to measure such injuries validly in any large population.
A helmet's ability to absorb energy could be improved by increasing the volume of expanded polystyrene, but this would make it thicker, heavier, and hotter to wear. Another concern is that a thicker helmet increases the risk of rotational-type brain injuries (discussed in more detail below). Ultimately, every helmet design represents some sort of compromise.
The trend is towards thinner helmets with many large vents. This trend to lower standards has been noted in some of the studies It is relatively common for helmets to fail on test, and some helmets on sale are not certified to any accepted standard.
Design intentions and standards
Both are intended to reduce acceleration to the head due to impact, as a stiff liner made of expanded polystyrene liner is crushed against the head.
Standards involve the use of an instrumented headform which is dropped, wearing a helmet, onto various anvils. The speed of impact is designed to simulate the effect of a rider's head falling from approximately usual riding height, without rotational energy and without impact from another vehicle.
As noted earlier, collision energy varies with the square of impact speed. A typical helmet is designed to absorb the energy of a head falling from a bicycle, hence an impact speed of around 12 mph or 20 km/h. This will only reduce the energy of a 30 mph or 50 km/h impact to the equivalent of 27.5 mph or 45 km/h, and even this will be compromised if the helmet fails. As a subsidiary effect, they should also spread point impacts over a wider area of the skull. Hard shell helmets may do this better, but are heavier and less well ventilated. They are more common among stunt riders than road riders or mountain bikers. Additionally, the helmet should reduce superficial injuries to the scalp. Hard shell helmets may also reduce the likelihood of penetrating impacts, although these are very rare.
Criticism of current standards; new designs
Helmet liners may be too stiff to be effective. Standards require the use of headforms heavier and more rigid than the human head; these are
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