Bicycle helmet

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Bicycle helmet

A bicycle helmet is designed to provide protection for cyclists against minor injuries sustained in simple falls. Helmets are most suitable for preventing injury in straight falls, and for reducing friction related damage to the head. Modern bicycle helmets were first developed in the 1970s.

Helmet use has increased significantly in many, but not most, jurisdictions since the 1980s, primarily because of helmet promotion and compulsion laws. These laws were designed to improve bicycle safety but are controversial because none has resulted in a measurable reduction in cyclist head injury rates - indeed some studies have shown that helmet compulsion laws have decreased the overall safety of bicycle use and discouraged ridership.

Many believe that a helmet can save a cyclist's life, an idea which is repeatedly asserted in debate. There is no sound evidential basis for this claim and there are no known cases where mass helmet use has actually reduced the number of cyclists' deaths or serious head injuries (British Medical Journal 2006;332:722-5). Association with increased risk of death has been reported. It is likely that helmets could prevent a significant number of minor cycling injuries but the overall safety benefits are inconclusive; this is thought to be in part due to risk compensation behaviour.

Helmets can be one aspect of a cyclist's personal safety precautions, as a secondary safety measure, but primary safety measures such as maintenance, road conditions, the behaviour of motorised traffic, and training, are likely to be more important in overall cycling safety. In general, the value of bicycle helmets has been systematically overstated.

About helmets

How they work

There are two main types of helmet: hard shell and soft/micro shell (no-shell helmets are now rare). In both types impact energy is absorbed as a stiff foam liner is crushed, up to the point where the liner is crushed to its minimum thickness, or the helmet shatters, after which no further energy is absorbed. Collision energy varies with the square of impact speed: a typical helmet will absorb the energy of a fall from a stationary or slow-moving bicycle, an impact speed of around 12mph, but will reduce the energy of a 30mph impact to only 27.5mph, and even this will be compromised if the helmet fails. This energy calculation is based on the standards, which take no account of the weight of the rider's body.

As a subsidiary effect they also spread point impacts over a wider area of the skull. Hard shell helmets do this rather better, but they tend to be heavier and less well ventilated so are more common among stunt riders than road riders or mountain bikers. Additionally, the helmet (like any good hat) will reduce superficial injuries such as cuts and grazes to the scalp. Hard shell helmets can also reduce the likelihood of penetrating impacts although these are said to be very rare.

The key component of most modern bicycle helmets is a layer of expanded polystyrene (EPS), essentially the plastic foam material used to make inexpensive picnic coolers. This material is sacrificed in an accident, being crushed as it absorbs a major impact. Bicycle helmets should always be discarded after any accident.

Helmets are most effective in straight line, or linear, blows to the head at moderate speed. Helmets are not well designed to deal with high speed impacts or rotational stresses (crashes that are not centred, and involve rotation of the head) on the head. They are not designed to provide adequate protection for a collision involving another moving vehicle, (e.g. a car), though they do provide some protection. The reason for this is that nobody has been able to draw up a practical design providing such a protection.

A cycle helmet should not be too heavy and should provide adequate ventilation, because cycling can be an intense aerobic form of exercise which significantly raises body temperature and the head in particular needs to be able to regulate its temperature (a study of cricketers found that helmets reduced levels of concentration due to overheating [1]). Thus, most helmets are constructed from lightweight materials and have many ventilation holes.

History

Prior to the mid-1970s, the dominant form of helmet was the leather "hairnet" style. This offered minimal impact protection and acceptable protection from scrapes and cuts. 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 (EPS) 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, 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.

1985 saw the introduction of Snell B85, 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.

Some believe that helmet shells help reduce friction and reduce the tendency of the helmet to dig in to the surface on impact; there is evidence which contradicts this. The evidence regarding this effect mostly predates microshell helmets.

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. 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 UK the currently applicable standard is EN 1078:1997, which replaces BS 6863:1989.

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 (no current Bell brand helmet is Snell certified, some Specialized ones are - the Snell Memorial Foundation website includes a list of certified helmets).

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. 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.

Standards are generally getting weaker, driven by the market's desire for lighter and more ventilated helmets, but efficacy against minor injuries, which is the design purpose of most helmets, is not dissimilar. Nonetheless, all other things being equal, a Snell certified helmet is probably objectively safer than a non-Snell one. However a recent comparison of motorcycle helmet standards, with regard to the amount of force passed through to the head, found that Snell's emphasis on a harder shell, lead to a higher level of G-force being transmitted to the head. The idea behind helmets is to absorb energy, not reusability. Failure to meet Snell standards may not be a bad thing.

All helmets sold today must meet basic safety standards. The difference between inexpensive and expensive helmets will more likely reflect ventilation, comfort and convenience issues rather than safety.

Proper fit

It is important that a helmet should fit the cyclist properly - according to research up to 96% of helmets have been found to be incorrectly fitted, and an incorrectly fitted helmet puts you at up to three times more risk.

First, the correct size must be purchased. Most manufacturers provide a range of sizes ranging from children's to adult with additional variations from small to medium to large.

Helmets are held on the head with nylon straps, which must be adjusted to fit the individual. The ease with which adjustments can be made can be one of the major differences between a cheap helmet and a better quality one.

A common mistake is to fit the helmet so that it sits high on the forehead. The helmet should sit level on the cyclists head with only a couple of finger-widths between eyebrow and the helmet brim. It should not be possible to insert more than one finger between the strap and the throat, or to move the helmet more than a centimetre or so in any direction. The strap should be well back under the chin, close to the throat.

The helmet debate

There is a long-running argument over the use, promotion and compulsion of cycle helmets. Most heated controversy surrounds laws making helmet use compulsory, particularly regarding the substantial disparity between claimed injury savings in small-scale prospective studies (e.g. Thompson, Rivara and Thompson, 1989) and later, more comprehensive studies, particularly from jurisdictions which have used compulsion to substantially raise helmet use over a very short period. Helmet use in New Zealand, for example, rose from 43% to over 95% in under three years, with no measurable change in head injury rates (Scuffham, 1997).

Controversy is fuelled by support given to the pro-compulsion movement by Bell Sports in particular, and by the fact that many of the most vocal proponents of helmets are not themselves cyclists.

Overall, most cycling groups are opposed to mandatory helmet use, partly on grounds of equitability (cyclists are more often the victims in crashes than the cause) but largely because of the deterrent effect of laws on levels of cycling. Cycling gets safer the more people who do it.

Do helmets reduce fatalities or serious injuries?

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Many areas with low helmet use have better bicycle safety.

It is often implied that wearing a helmet is the first, best thing a cyclist can do to ensure their safety. In general, analyses of the relative merits of different bike safety interventions put helmets last, because no helmet will reduce the probability of crashing (indeed there are credible suggestions that helmets may increase this likelihood). Proactive measures including bike maintenance and riding skills are far more important. Although the link is not directly causal it is noticeable that the countries with the best cycle safety records (Denmark and the Netherlands) have among the lowest levels of helmet use. Their bicycle safety record is attributable to improved education, separation from motor traffic (but see the entry on segregated facilities) and, most importantly, public awareness and understanding of cyclists.

The best scientific evidence on the effectiveness of helmets would be derived from randomized controlled trials, in which some cyclists were randomly assigned to wear helmets and others not. No such trials have been done. The available evidence comes from two main types of observational study. The first is case-control studies, in which cyclists who have injured their heads ("cases"), and cyclists who have not ("controls"), are asked whether they were wearing a helmet at the time of their crash. Several such [2] case-control studies have been done. They consistently find that cases report a lower rate of helmet-wearing than controls. This has been taken as strong evidence that cycle helmets are beneficial in a crash and that all cyclists should be compelled to wear them. These studies have a serious flaw; people exaggerate their use of cycle helmets, and this exaggeration may only apply to people who have not hit their heads [3]. If this is true, these studies would be valueless; they would incorrectly indicate benefit from helmet wearing. Other criticisms apply to some or all of the available case-control studies. For example, a study by Thompson, Rivara, and Thompson reported an 85% reduction in the risk of head injury by using a helmet. It used a control group which reported a voluntary helmet use rate almost 10 times higher than the general population. Voluntary helmet users are more cautious than the general bike riding population [4]. They would be expected to have different sorts of injury even without the use of helmets, and this particular study, the source of the most optimistic claims for helmet effectiveness, is weaker than most. Many more criticisms have also been levelled at the study. [5] [6]

Other studies have looked at the results of laws compelling cyclists to wear helmets. Many such laws have been passed in various areas. Only four such areas have both enforced these laws and produced good quality data on the results [7]. These data, from areas where helmet wearing increased by at least 40%, show no obvious effect on the proportion of head injuries. These studies are based on observations of helmet wearing by third parties, and are more likely to be valid than the case-control studies. They have in turn been attacked[8].

Other researchers [9] in the University of Western Australia Public Health Department in the late 1990s have suggested that there had been a small, but statistically significant reduction in head injuries to Western Australian cyclists between 1973 and 1998, during which period helmet use rose from zero to around 85%. Cycle helmets were made compulsory in 1992. The study compared the percentage of head injuries recorded among cyclists and pedestrians in road traffic accidents. After the law, there were fewer cyclists in any age group. Child cyclists are more likely to bump their heads, and their numbers declined more than adults. A reduced proportion of cyclists in the age group most likely to bump their heads could account for all the apparent, small, protective effect of helmets in this study. A similar study was conducted in Otago, New Zealand. (Scuffham, Alsop, Cryer, Langley 2003)

The conflicting evidence has led to widespread and longstanding controversy. Various organizations have taken up definite positions on the issue, not always based on a full review of the evidence. For example, the British Medical Association used to be against helmet compulsion, following an extensive review of the evidence in 1999. In late 2004 the BMA's Board of Science and Education adopted a 'position' calling on the UK government to introduce cycle helmet legislation, and this was confirmed at the 2005 Annual Representative Meeting following fifteen minutes of debate(transcript). The BMA's new position may use statistics provided by the British political lobby group, the Bicycle Helmet Initiative Trust. Several provably wrong figures were removed after initial publication, but the supposed review of evidence is still distorted, excluding not only references included in the 1999 BMA study, but the 1999 study itself.

However, the former UK Minister for Road Safety, Mr David Jamieson MP, has acknowledged that he knows of no evidence linking increasing helmet use with reduced severity, or risk, of head injury to the cyclist population. This contrasts with jurisdictions which have made bicycle helmets compulsory, where the utility of helmets and helmet laws has been vigorously asserted.

Reduction in bicycle participation

Mandatory bicycle helmet laws may lead to a reduction in the number of cyclists. The reduction in the number of cyclists may have a more negative impact on the health of a population than would have arisen from the head injuries that would have resulted from not using helmets since the reduction in injuries is apparently so small. The long term health benefits of bicycle use are well established so any reduction in bicycle activity will likely have a negative impact on the overall health of a population.

Arguably, even helmet promotion or high levels of helmet use by utility cyclists will deter non-cyclists by reinforcing the misconception that bicycling is a lot more dangerous than walking or driving. This reduction of cycle use directly imposes increased risk on cyclists that continue to ride, due to the now well established "safety in numbers" effect. However, by statistics, cycling in general is safe compared to almost any other form of transportation. Only airline travel is safer per million exposure hours according to one American study. [10]

Helmets and increased risk of injury

Some studies have even suggested that helmets increase risk. Although the head injury rate in the US rose by 40% as helmet use rose from 18% to 50%, this does not necessarily mean that helmets themselves increase risk. In fact, a range of theories exist to explain the observed disparity, including:

• Risk compensation: helmeted cyclists may ride less carefully; this is well supported by evidence for other road safety interventions such as seat belts and antilock brakes.
• Poor fitting: 96% of helmets not fitted correctly and incorrectly fitted helmets reportedly increase risk by a factor of 3.
• Sampling bias in prospective studies: voluntary wearers may be more risk averse, skewing the results.

No research has yet been published which adequately addresses the reasons for the disparity, so while the disparity itself is solid fact based on robust data collected and published by governments, the above reasons are speculative and undoubtedly not exhaustive.

Recent research on brain injury adds further confusion, suggesting that the major causes of permanent intellectual disablement and death may well be torsional forces leading to diffuse axonal injury, a form of injury which helmets cannot mitigate. Helmets can increase the rotational force acting on the head by virtue of the longer distance between the extremities of the helmet and the centre of the cervical spine, compared to the head without a helmet. In addition, the hardness of the typical helmet may accentuate this problem. For example, if a person is sliding and the helmet strikes an object, the linear movement may be converted into rotational force about the spine.

Inadequate design

Some argue that the helmets that are currently on the market are not designed suitably to make a large reduction in fatalities for the types of injuries they are supposed to protect against. However, measures required to improve helmets would make the helmets commercial failures. Helmets designed to a higher standard have not sold well, while helmets designed to even lower standards have sold well. [11] Some helmets on the market do not even meet basic requirements.

Use, promotion, compulsion

Due to the "safety in numbers" effect, decreased cycling has a directly negative effect of bicycle safety.

It is plausible that if a rider chooses to use a helmet, and maintains their safe cycling habits, they should be moderately safer than if they chose not to wear a helmet, although risk compensation theory states that an intervention as obtrusive as a helmet will very likely affect riding practice at the subconscious level. Wearing and non-wearing are both, therefore, sound choices, supportable from the available evidence. A person refusing to ride without one probably overestimates either the risks of cycling or the protective effect of helmets.

Promotion of helmets is somewhat more problematic. Helmet promoters routinely make claims which manufacturers cannot, due to advertising restrictions. Promotion campaigns are often supported and/or funded by manufacturers. Bell, one major helmet manufacturer, supports both helmet promotion and, through its Legislative Assistance Programme, laws. The major problem with helmet promotion, from the point of view of cycle activists, is that in order to present the idea of a "problem" to match the solution they present, promoters tend to overstate the dangers of cycling. Cycling is, according to the evidence, no more dangerous than being a pedestrian. In fact, helmet compulsion in cars would be far more effective at reducing injuries than on bicycles. [12]

Some bicycle activists complain that focus on helmets diverts attention from other issues which are much more important for improving bicycle safety, such as training, roadcraft, and bicycle maintenance. Of 28 publicly funded cycle safety interventions listed in a report in 2002, 24 were helmet promotions. For context, one evaluation of the relative merits of different cycle safety interventions estimated that 27% of cyclist casualties could be prevented by various measures, of which just 1% could be achieved through a combination of bicycle engineering and helmet use.

Data from around the world shows that despite the optimistic claims for injury reduction made by their proponents, no helmet law currently in force has led to a measurable reduction in cyclist head injury rates. There are a number of plausible explanations for this:

• the studies on which the laws are founded mainly compare those who choose to wear helmets with those who do not; forcing a cyclist to wear a helmet will not make them behave like the kind of cyclist who wears one by choice

• helmets are not designed to withstand motor vehicle impacts, but these account for most serious and almost all fatal cyclist injuries

• governments do not tend to measure minor injury rates; any protective device would be expected to be much more effective against minor injuries, rapidly tailing off with severity - although a few studies do claim that cycle helmets are more effective against serious than against minor injuries, it is more likely that the efficacy figures cited in advance are against a type of injury which subsequent statistics will not measure

• helmet laws tend to deter cycling; there is good evidence that cycling becomes safer the more people who do it.

Overall, cycling is beneficial to health - the benefits outweigh the risks by up to 20:1. Anything which jeopardises that benefit must be carefully weighed to ensure it is likely to achieve some meaningful benefit in turn. Thus far, no helmet law has been shown to do that.

Cycling as a dangerous activity

A further source of contention is the apparent arbitrariness of cycle helmet promotion and/or compulsion. Ordinary cycling is not demonstrably more dangerous than walking or driving, yet no country promotes helmets for either of these modes. Cycle helmet use correlates inversely with the level of cycling in a given country. Official zeal for cycle helmets is greatest where cycling is a minority activity.

Detailed analysis of hospital admissions data also fails to support the idea that cycling is unusually dangerous: a study in the UK found that the proportion of cyclist injuries which are head injuries is lower than the proportion for pedestrians.

References

Case studies/risk

• Thompson, R., Rivara, F. and Thompson, D. (1989), A Case-Control Study of the Effectiveness of Bicycle Safety Helmets, New England Journal of Medicine, 25 May, 320:21, 1361-67 Abstract — The most widely cited pro-helmet study (commentary).
• Scuffham Trends in cycle injury in New Zealand under voluntary helmet use, Langley. Accident Analysis and Prevention, Vol 29:1, 1997 — Showed no benefit from large-scale increases in helmet use.
• John Adams, 1995, Risk, Routledge, ISBN 1857280687 — Authoritative reference on risk compensation theory.

Helmet Fit

• Parkinson, Gregory and Hike, Kelly E. (2003), Bicycle Helmet Assessment During Well Visits Reveals Severe Shortcomings in Condition and Fit, [13] Pediatrics, 2 August 2003 Vol. 112 No. 2, pp. 320-323 — Showed that correct fitting is an exception.

Do helmets reduce fatalities or serious injuries?

Thompson DC, Rivara FP, Thompson R. Helmets for preventing head and facial injuries in bicyclists. The Cochrane Database of Systematic Reviews 1999, Issue 4. Art. No.: CD001855. DOI: 10.1002/14651858.CD001855

http://bmj.bmjjournals.com/cgi/eletters/332/7543/722-a#133697

Farris, Spaite, Criss, Valenzuela, Meislin. Observational evaluation of compliance with traffic regulations among helmeted and nonhelmeted bicyclists, Ann Emerg Med 1997 May;29(5):625-9

http://www.bikebiz.co.uk/daily-news/article.php?id=5495, accessed 21st June 2006

Hagel, Macpherson, Rivara, Pless. Br med J 2006;332:725-726 (25 March), doi:10.1136/bmj.332.7543.725

An economic evaluation of the mandatory bicycle helmet legislation in Western Australia. D Hendrie, M Legge, D Rosman, C Kirov. Road Accident Prevention Research Unit, Department of Public Health, The University of Western Australia.

http://www.bikebiz.co.uk/daily-news/article.php?id=5728, accessed 21st June 2006

Scuffham, Alsop, Cryer, Langley. Head Injuries to Cyclists and the New Zealand Cycle Helmet Law. Accident Analysis and Prevention, 2000, 32: 565-573

BMA position, accessed 21st June 2006

Helmet Laws Tend to Reduce Cycling

• Merton, R.K., "The Unanticipated Consequences of Purposive Social Action", American Sociological Review, Vol.1, No.6, (December 1936), pp.894-904. (see Unintended consequence)
• Vulcan, A.P., Cameron, M.H. & Heiman, L., "Evaluation of mandatory bicycle helmet use in Victoria, Australia", 36th Annual Conference Proceedings, Association for the Advancement of Automotive Medicine, Oct 5-7, 1992.
• Vulcan, A.P., Cameron, M.H. & Watson, W.L., "Mandatory Bicycle Helmet Use: Experience in Victoria, Australia", World Journal of Surgery, Vol.16, No.3, (May/June 1992), pp.389-397.

Safe cycling

• John Forester, 1992, Effective Cycling, ISBN 0262560704
• John Franklin, 1999, Cyclecraft, ISBN 0117020516

External links

• Bicycle Helmet Research Foundation (sceptical)
• How to Fit a Bicycle Helmet from BHSI website
• BikeBiz (industry journal) list of 40+ articles on helmets and compulsion
• CPSC publication announcing new US helmet standard
• cycle-helmets.com List of cycle helmet research links
• John Forester, author of Effective Cycling.
• John Franklin's page on cycle helmets
• Ontario Coalition for Better Cycling Helmet FAQ
• Snell Memorial Foundation, list of certified helmets
• helmets.org rebuttal of anti compulsion arguments (pro-helmet)
• Bicycle Helmet Safety Institute - (pro-helmet)