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A Bicycle helmet is specifically designed to provide head protection for cyclists. An increasing number of jurisdictions are enacting legislation requiring cyclists to wear these helmets as well as other items of safety equipment. This legislation is controversial, with commercial interest groups in the US lobbying in favor but other substantial bodies and cycle groups opposed to such legislation on grounds that more deaths are caused by introducing such legislation (by decreasing cycle use and increasing long term under-exercise) than are saved by it.
How they work
Cycle helmets protect the head when the cyclist falls off the bike and hits the ground. 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 be not too heavy and provide adequate ventilation, because cycling can be an intense aerobic form of exercise which significantly raises body temperature. Thus, most helmets are constructed from lightweight materials pierced by strategically placed ventilation holes.
The key component of most modern bicycle helmets is a layer of expanded polystyrene (E.P.S.), 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 major accident.
Controversy
There is a long-running argument over the use, promotion and compulsion of cycle helmets. The main source of controversy stems from the substantial disparity between claimed injury savings in small-scale prospective studies (Thompson, Rivara and Thompson, 1989), and real-world experience, 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).
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:
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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.
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Poor fitting: 96% of helmets not fitted correctly and incorrectly fitted helmets reportedly increase risk by a factor of 3.
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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 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.
There is good evidence to suggest that helmets prevent many, probably most, minor injuries. Solid evidence for their preventing any serious or fatal injuries is much harder to come by; it would be most unwise to take risks relying on a cycle helmet to prevent serious injury.
History
Prior to the mid-1970s, the dominant form of helmet was the leather "hairnet" style. This offered minimal protection. Two of the first modern bicycle helmets were made by MSR, a manufacturer of mountaineering equipment, and Bell, a manufacturer of helmets for auto racing and motorcycles. These helmets had EPS foam liners and, additionally, had hard polycarbonate plastic shells.
It was soon decided that a hard shell added minimally to the safety of a helmet. For a time many helmets simply covered the foam with a stretch nylon cover. Most current helmets have an outer shell of vacuum formed plastic; this protects the helmet from minor scrapes and probably prevents the helmet from 'digging-in' in a sliding impact.
Standards
In America 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 BS 6863:1989. This is in the process of being replaced by the European BS EN 1078:1997 standard.
The EN1078 standard is lower than the Snell B95 (and B90) standard; the Snell Memorial Foundation website includes a list of manufacturers whose helmets meet these higher standards. Many of the well-known, branded cycle helmets do not meet the tough Snell standards.
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. (It may be noted at this point that 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.)
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.
Safe Cycling vs Helmet Use
It is often suggested that wearing a helmet is the first, best thing a cyclist can do to ensure their safety. However, no helmet will reduce your probability of crashing. Make sure that your bike is in good order, that you are riding skilfully and legally.
The former UK Minister for Road Safety, Mr David Jamieson MP, acknowledged that he knows of no evidence linking increasing helmet use with reduced severity, or risk, of head injury to the cyclist population.
Research (http://www.officeofroadsafety.wa.gov.au/facts/papers/bicycle_helmet_legislation.html) by the University of Western Australia Public Health Department in the late 1990s could not reveal noticeable reduction in head injuries to Western Australian cyclists between 1973 and 1998, despite the take-up of helmet use from zero to around 85%, following legislation in 1992. The study compared cyclist and pedestrian head injuries in road traffic accidents. There was only a single year (out of the entire 25 year time line) in which there was a marked advantage for cyclists, 1991; the year before the law came into effect. Despite this, the authors concluded helmet use had reduced serious head injuries by 11-18%. The slight reduction detected by the study may well have been due to fewer child cyclists (some having been put off by having to wear a helmet) than more helmet use. A similar study was conducted in New Zealand by the Otago Injury Prevention Unit.
A major consequence of any helmet law is the sharp decline in cycle use. Arguably, even helmet promotion or high levels of helmet use by utility cyclists will deter non-cyclists by reinforcing the misconception that road riding is a lot more dangerous than walking or driving, which it is not. 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.
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