bike - Bicycle helmet
Photograph by Noah Scalinon Flickr.
Most of the literature that mentions helmets refers back to a small number of these studies, rather than itself providing primary evidence. The most common standard in the US, CPSC, is self-certified by the manufacturers.
A bicycle helmet is a helmet intended to be worn while riding a bicycle. 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.
EN 1078 is also externally validated, but lacks Snell s traceability. 44,000 cyclists were reported injured in traffic crashes in 2006. Overall, cycling is beneficial to health – the benefits outweigh the risks by up to 20:1. No randomized controlled trials have been done on the subject.
The head tries to dampen these forces using a combination of built-in defences: the scalp, the hard skull and the cerebrospinal fluid beneath it. This means that if the number of cyclists on the road doubles, then the average individual cyclist can ride for an additional 50% of the time without increasing the probability of being struck.
In general, the more skull coverage a helmet provides, the more effectively it can be fitted to the head and hence the better it will remain on the head in an accident. The helmet should sit level on the cyclist s head with only a couple of finger-widths between eyebrow and the helmet brim. The same report estimated that, at most, universal helmet use would save the lives of three children aged 0 to 15 each year.
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. 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).
I collected damaged infant/toddler helmets for several months in 1995. In 1984 Bell produced the Li l Bell Shell, a no-shell children s helmet.
An attempt to enforce the rule at the 1991 Paris–Nice race resulted in a riders strike, forcing the UCI to abandon the idea. While voluntary helmet use in professional ranks rose somewhat in the 1990s, the turning point in helmet policy was the March 2003 death of Kazakh Andrei Kivilev. The majority of professional cyclists chose not to wear helmets, citing discomfort and claiming that helmet weight would put them in a disadvantage during uphill sections of the race. The first serious attempt by the UCI to introduce mandatory helmet use in 1991 was met with strong opposition from the riders.
This trend to lower standards has been noted in some of the studies 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 correct size is important.
This type of helmet is mainly dedicated to Time Trial racing as they lack significant ventilation, making them uncomfortable for long races. 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. Proponents of helmet compulsion may tend to quote figures for the (large) total number of head injuries or injuries of any kind; opponents may be more likely to produce estimates for the (low) risk of serious injury per cyclist.
drink-drive campaigns); inaccuracy of exposure estimates (numbers cycling, distance cycled etc.), changes in the definitions of the data collected, failure to analyse control groups, failure to analyse long-term trends, and the ecological fallacy. Robinson s review of cyclists and control groups in jurisdictions where helmet use increased by 40 % or more following compulsion concluded that enforced helmet laws discourage cycling but produce no obvious response in percentage of head injuries . There are many other studies. “Another source of field experience is our experience with damaged helmets returned to customer service.
This offered minimal impact protection and acceptable protection from scrapes and cuts. All of their helmets are Snell certified.) Although helmet standards have weakened over time there are no data on which to base an assessment of how this has affected the design goal of mitigating minor injuries.
These provide no protection, only fit, so helmets with this type of adjustment are unsuitable for roller skating, stunts, skateboarding and unicycling. The evidence comes from two main types of observational study.
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. 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.
A range of theories have been proposed to explain why helmet use might indirectly translate into more or worse accidents. Potential weaknesses of this type of study include: simultaneous changes in the road environment (e. g.
Helmets are held on the head with nylon straps, which must be adjusted to fit the individual. Standards require the use of headforms heavier and more rigid than the human head; these are more capable of crushing foam than is the human head. In real accidents, while broken helmets are common, it is extremely unusual to see any helmet that has compressed foam and thus may have performed as intended.
In short, the analysis of helmet effectiveness is confounded by changes in human behaviour apparently induced by the presence of protective headgear. Under the risk compensation theory, helmeted cyclists may be expected to ride less carefully; this is supported by evidence for other road safety interventions such as seat belts and anti-lock braking systems. Motorists may also alter their behavior towards helmeted cyclists. They are designed to attenuate impacts to the skull of a cyclist in falls while minimizing side effects such as interference with peripheral vision. 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.
Additionally, the helmet should reduce superficial injuries to the scalp. It should not be possible to insert more than one finger s thickness between the strap and the throat. Newer helmets for toddlers and children feature flat backs that prevent the helmet from tilting too far forward when worn while riding in a trailer or child seat with a headrest. The Snell Memorial Foundation recommends that any helmet that has sustained a substantial blow should be discarded and replaced, including any helmet involved in a crash in which the head has hit a hard surface or in which a fall has resulted in marks on the shell.
One pro-helmet website gives its own pick of Basic Numbers from many sources : 773 bicyclists died on US roads in 2006, down just 11 from the year before. A helmet s ability to manage linear deceleration of the skull could be improved by providing a greater thickness of expanded polystyrene foam and also by making this foam softer, but this would make the entire helmet bulkier, heavier, and hotter to wear.
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. These helmets were a spinoff from the development of expanded polystyrene foam liners for motorcycling and motorsport helmets, and had hard polycarbonate plastic shells.
Because some helmet materials deteriorate with age (in particular sunlight exposure), the Snell Memorial Foundation recommends that a helmet be replaced at least every 5 years, or sooner if the manufacturer recommends it. Historically, road cycling regulations set by the sport s ruling body, Union Cycliste Internationale (UCI), did not require helmet use, leaving the matter to individual preferences and local traffic laws. The dominant form of helmet up to the 1970s was the leather hairnet style, mainly used by racing cyclists.
Not only did I not see bottomed out helmets, I didn’t see any helmet showing signs of crushing on the inside.” Most helmets provide no protection against rotational injury and may make it worse. Another concern is that a thicker helmet increases the risk of rotational-type brain injuries (discussed in more detail below).
In Victoria, Australia, during 1977-1980, bicyclist casualties, then unhelmeted, sustained head injuries including severe head injuries, more than twice as frequently as the helmeted motorcyclist casualties. It may be assumed that a broken helmet has prevented some serious injury. It is therefore almost impossible to hit it without causing it to rotate.
Hard shell helmets may do this better, but are heavier and less well ventilated. This absorbs energy from the impact. It is important that a helmet should fit the cyclist properly – in one study 96 % . Most manufacturers provide a range of sizes ranging from children s to adult with additional variations from small to medium to large.
The strap should sit at the back of the lower jaw, against the throat, and be sufficiently tight that the helmet does not move on the head. 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.
Bicycle helmets cost money and may make cycling less convenient; they are bulky and often cannot be stored securely with bikes. Bicycle helmets are seen as incompatible with some hairstyles, forcing bicycle users to recreate their hairstyle after each journey. He says almost all head injuries involve not just a direct blow to the skull but also damage to blood vessels caused by the brain rotating within the skull. In mechanical terms, the head is an elliptical spheroid with a single universal joint, the neck.
One small study from England found that vehicles passed a helmeted cyclist with measurably less clearance (8.5 cm) than that given to the same cyclist unhelmeted (out of an average total passing distance of 1.2 to 1.3 metres). It has been suggested that the major causes of permanent intellectual disablement and death after head injury may be torsional forces leading to diffuse axonal injury (DAI), a form of injury which usual helmets cannot mitigate and may make worse. There are a few documented cases of young children, playing on bunkbeds, trees, jungle gyms, and so on, suffering death or severe brain damage as a result of strangulation by the straps of their bicycle helmets. The World Health Organisation promote the use of helmets as a strategy for preventing head injuries caused by bicycle crashes or falls. Significant helmet promotion preceded epidemiological studies evaluating the effectiveness of bicycle helmets in bicycle crashes. Robinson reviewed data from jurisdictions where helmet use increased following legislation, and concluded that helmet use did not demonstrably reduce cyclists head injuries. In 1998 the European Cyclists Federation adopted a position paper rejecting compulsory helmet laws as being likely to have greater negative rather than positive health effects. It is thought that the increased frequency of motorist-cyclist interaction creates more aware motorists. Several mechanisms by which cycle helmet promotion or compulsion may deter cycling have been suggested.
About 540,000 bicyclists visit emergency rooms with injuries every year. So much so, that my helmet broke in two (as it is designed to do).
Minor injuries are substantially under-reported, and it is difficult to measure such injuries validly in any large population. In brief, the primary design goal of a helmet is to decelerate the skull (and by implication, the brain inside it) more gently than would be the case if no helmet were worn. They are more common among stunt riders than road riders or mountain bikers.
The new rules were introduced on May 5, 2003 subsequent revisions made helmet use mandatory at all times. No studies have been published yet into whether injuries to racers have reduced as a result. There is no one agreed way of presenting risk. Snell s standard includes testing of random samples.
Additionally, some helmets have adjustable cradles which fit the helmet to the occipital region of the skull. Of those, about 67,000 have head injuries, and 27,000 have injuries serious enough to be hospitalized.
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. Most helmets will have multiple adjustment points on the strap to allow both strap and helmet to be correctly positioned.
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. This can be difficult to achieve, depending on the design.
Hard shell helmets may also reduce the likelihood of penetrating impacts, although these are very rare. Helmet liners may be too stiff to be effective. In 1990 the Consumers Association (UK) market survey showed that around 90 % of helmets on sale were Snell B90 certified.
As a subsidiary effect, they should also spread point impacts over a wider area of the skull. Finally, bicycle helmets and other safety equipment have, in the past, occasionally been seen as vexatious and ridiculous. Rodgers re-analysed data which supposedly showed helmets to be effective; he found data errors and methodological weaknesses so serious that in fact the data showed bicycle-related fatalities are positively and significantly associated with increased helmet use .
The major discovery is that the skull plays an important role in protecting against rotational acceleration, says Phillips. These assumptions are most unlikely to be correct in the real world. The following countries have mandatory helmet laws, in at least one jurisdiction, for either minors only, or for all riders: Australia, Canada, Czech Republic, Finland, Iceland, Israel, A study of cycling in major streets of Boston, Paris and Amsterdam illustrates the variation in cycling culture: Boston had far higher rates of helmet-wearing (32% of cyclists, versus 2.4% in Paris and 0.1% in Amsterdam), Amsterdam had far more cyclists (242 passing bicycles per hour, versus 74 in Paris and 55 in Boston). .
Helmets and their promotion may reinforce the misconception that bicycling is more dangerous than traveling by passenger car. A very thin shell was incorporated during the moulding process.
At this time helmets were almost all either hard-shell or no-shell (perhaps with a vacuum-formed plastic cover). in the 1970s.
By their 1998 survey the number of Snell certified helmets was around zero. Bicycle crashes and injuries are under-reported, since the majority are not serious enough for emergency room visits.
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. Some adjustment can usually be made using different thickness foam pads.
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. In countries with long traditions of utility cycling, very few cyclists wear helmets.
There are two main types of helmet: hard shell and soft/micro shell (no-shell helmets are now rare). 92% (720) of them died in crashes with motor vehicles.
That figure assumes universal and correct use of helmets, it assumes that risk compensation does not occur and it assumes that no children die as a result of strangulation or other injuries caused by helmet use. 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.
Without the helmet, it would have been my head that was broken and I wouldn’t be writing this blog entry! I’d be dead. To prevent overt fragmentation, the foam in most helmets is reinforced inside with plastic netting to keep the foam together even after cracking. Concerns have been raised that mandatory bicycle helmet laws lead to a reduction in the number of cyclists When mandatory bicycle helmet laws were enacted in Australia, slightly more than one third of bare-headed cyclists ceased to ride their bicycles frequently. Bicycle use has large long-term health benefits. A reduction in cycling may lead to an increased risk for the cyclists remaining on the road, due to a safety in numbers effect. the main impact was to my head.
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. During an impact, the scalp acts as rotational shock absorber by both compressing and sliding over the skull.
The Giro Atmos and Ionos, as well as the Bell Alchera are among the first to use carbon fiber. Some modern racing bicycle helmets have a long tapering back end for streamlining. The largest, covering eight million cyclist injuries over 15 years, showed no effect on serious injuries and a small but significant increase in risk of fatality. Known potential problems with this type of study design include confounding (attributing benefits from unmeasured differences in behavior to differences in helmet choice), and recall bias (people incorrectly reporting helmet use). Such studies consistently find that cases of head injury report a lower rate of helmet-wearing than controls who have injured other parts of the body. Other case-control studies exist, all showing similar results.
Over time the design was refined and by 1983 Bell were making the V1-Pro, the first polystyrene helmet intended for racing use. Overall, according to CTC, the UK s national cyclists organisation, the evidence currently available is complex and full of contradictions, providing at least as much support for those who are sceptical as for those who swear by them. Time-trend analyses compare changes in helmet use and injury rates in populations over time, most validly where helmet laws have resulted in large changes in a short time.
Ultimately, every helmet design represents some sort of compromise. The trend is towards thinner helmets with many large vents. 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.
