Motorcycle helmet
Encyclopedia
A motorcycle helmet is a type of protective headgear
used by motorcycle
riders. The primary goal of a motorcycle helmet is motorcycle safety
- to protect the rider's head during impact, thus preventing or reducing head injury
or saving the rider's life. Some helmets provide additional conveniences, such as ventilation, face shields, ear protection, intercom
etc.
Motorcyclists are at high risk in traffic crashes. A 2008 systematic review
examined studies on motorcycle riders who had crashed and looked at helmet use as an intervention. The review concluded that helmets reduce the risk of head injury by around 69% and death by around 42%. Some studies have suggested that helmets may protect against facial injury but they have no effect on neck injury, more research is required for a conclusive answer.
T. E. Lawrence
(known as Lawrence of Arabia) had a crash on a Brough Superior SS100
on a narrow road near his cottage near Wareham
. The accident occurred because a dip in the road obstructed his view of two boys on bicycles. Swerving to avoid them, Lawrence lost control and was thrown over the handlebars. He was not wearing a helmet, and suffered serious head injuries which left him in a coma; he died after six days in hospital. One of the doctors attending him was Hugh Cairns
, a neurosurgeon, who after Lawrence's death began a long study of what he saw as the unnecessary loss of life by motorcycle despatch rider
s through head injuries. Cairns' research led to the use of crash helmets by both military and civilian motorcyclists.
, and their protective benefits are greatly reduced, if not eliminated, if the chin strap is not securely fastened so as to maintain a snug fit.
From most to least protective, as generally accepted by riders and manufacturers, the helmet types are:
, and a protective section over the front of the chin
. Such helmets have an open cutout in a band across the eyes and nose, and often include a clear or tinted transparent plastic face shield, known as a visor, that generally swivels up and down to allow access to the face. Many full face helmets include vents to increase the airflow to the rider.
The significant attraction of these helmets is their protectiveness. Some wearers dislike the increased heat, sense of isolation, lack of wind, and reduced hearing of such helmets. Full face helmets intended for off-road use sometimes omit the face shield, but extend the visor and chin portions to increase ventilation, since riding off-road is a very strenuous activity.
Studies have shown that full face helmets offer the most protection to motorcycle riders because 35% of all crashes showed major impact on the chin-bar area. Wearing a helmet with less coverage eliminates that protection — the less coverage the helmet offers, the less protection for the rider.
The motocross
and off-road helmet has clearly elongated chin and visor portions, a chin bar, and partially open face to give the rider extra protection while wearing goggles and to allow the unhindered flow of air during the physical exertion of this type of riding. The visor is to allow the rider to dip his head and provide further protection from flying debris during off road riding. It will also keep the sun out of the eyes of the rider during jumps.
Originally, off-road helmets did not include a chin bar, with riders using helmets very similar to modern open face street helmets, and using a face mask to fend off dirt and debris from the nose and mouth. Modern off-road helmets include a (typically angular, rather than round) chin bar to provide some facial impact protection in addition to protection from flying dirt and debris. When properly combined with goggles, the result provides most of the same protective features of full face street helmets.
A hybrid between full face and open face helmets for street use is the modular or "flip-up" helmet, also sometimes termed "convertible" or "flip-face". When fully assembled and closed, they resemble full face helmets by bearing a chin bar for absorbing face impacts. Its chin bar may be pivoted upwards (or, in some cases, may be removed) by a special lever to allow access to most of the face, as in an open face helmet. The rider may thus eat, drink or have a conversation without unfastening the chinstrap and removing the helmet, making them popular among motor officers
.
Many modular helmets are designed to be worn only in the closed position for riding, as the movable chin bar is designed as a convenience feature, useful while not actively riding. The curved shape of an open chin bar and face shield section can cause increased wind drag during riding, as air will not flow around an open modular helmet in the same way as a three-quarters helmet. Since the chin bar section also protrudes further from the forehead than a three-quarters visor, riding with the helmet in the open position may pose increased risk of neck injury in a crash. Some modular helmets are dual certified as full face and open face helmet. The chin bar of those helmets offer real protection and they can be used in the "open" position while riding. An example of such an helmet would be the Shark
Evoline.
As of 2008, there have not been wide scientific studies of modular helmets to assess how protective the pivoting or removable chin bars are. Observation and unofficial testing suggest that significantly greater protection exists beyond that for an open face helmet, and may be enough to pass full-face helmet standardized tests, but the extent of protection is not fully established by all standards bodies.
The DOT
standard does not require chin bar testing. The Snell Memorial Foundation recently certified a flip-up helmet for the first time. ECE 22.05 allows certification of modular helmets with or without chin bar tests, distinguished by -P (protective lower face cover) and -NP (non-protective) suffixes to the certification number, and additional warning text for non-certified chin bars.
Bugs, dust, or even wind to the face and eyes can cause rider discomfort or injury. As a result, it is not uncommon (and in some U.S. states, is required by law) for riders to wear wrap-around sunglasses or goggles to supplement eye protection with these helmets. Alternatively, many open face helmets include, or can be fitted with, a face shield, which is more effective in stopping flying insects from entering the helmet.
The half helmet, also referred to as a "Shorty" in the USA and "Pudding Basin" or TT helmet in the UK and popular with Rockers
and road racers of the 1960s in the British Isles. It has essentially the same front design as an open face helmet but without a lowered rear in the shape of a bowl. The half helmet provides the minimum coverage generally allowed by law in the USA, and British Standards 2001:1956.
As with the open face, it is not uncommon to augment this helmet's eye protection through other means such as goggles
. Because of their inferiority compared to other helmet styles, some Motorcycle Safety Foundation
s prohibit the use of half helmets now. Notable UK manufacturers included Everoak, Chas Owens and, currently, Davida.
by allowing it to come to a gradual stop during an impact. A "novelty helmet" can protect the scalp against sunburn while riding and - if it stays on during a crash - might protect the scalp against abrasion, but it has no capability to protect the skull or brain from an impact.
However, the MAIDS report
did not back up the claims that helmet color makes any difference in accident frequency, and that in fact motorcycles painted white were actually over-represented in the accident sample compared to the exposure data. While recognizing how much riders need to be seen, the MAIDS report documented that riders' clothing usually fails to do so, saying that "in 65.3% of all cases, the clothing made no contribution to the conspicuity of the rider or the PTW [powered two-wheeler, i.e. motorcycle]. There were very few cases found in which the bright clothing of the PTW rider enhanced the PTW’s overall conspicuity (46 cases). There were more cases in which the use of dark clothing decreased the conspicuity of the rider and the PTW (120 cases)." The MAIDS report was unable to recommend specific items of clothing or colors to make riders better seen.
s. Premium price helmets are made with fiberglass reinforced with Kevlar
or carbon fiber
. They generally have fabric and foam interiors for both comfort and protection. Motorcycle helmets are generally designed to distort in a crash (thus expending the energy otherwise destined for the wearer's skull), so they provide little protection at the site of their first impact, but continued protection over the remainder of the helmet.
Helmets are constructed from an inner EPS “Expanded Polystyrene foam” and an outer shell to protect the EPS. The density and the thickness of the EPS is designed to cushion or crush on impact to help prevent head injuries. Some manufacturers even offer different densities to offer better protection. The outer shell can be made of plastics or fiber materials. Some of the plastics offer very good protection from penetration as in lexan (bulletproof glass) but will not crush on impact, so the outer shell will look undamaged but the inner EPS will be crushed. Fiberglass is less expensive than lexan but is heavy and very labor intensive. Fiberglass or fiber shells will crush on impact offering better protection. Some manufacturers will use Kevlar or carbon fiber to help reduce the amount of fiberglass but in the process it will make the helmet lighter and offer more protection from penetration but still crushing on impact. But this can be very expensive.
The conventional motorcycle helmet has two principal protective components: a thin, hard, outer shell typically made from polycarbonate
plastic, fiberglass
, or Kevlar and a soft, thick, inner liner usually made of expanded polystyrene
or polypropylene
"EPS" foam. The purpose of the hard outer shell is:
The purpose of the foam liner is to crush during an impact, thereby increasing the distance and period of time over which the head stops and reducing its deceleration.
To understand the action of a helmet, it is first necessary to understand the mechanism of head injury. The common perception that a helmet's purpose is to save the rider's head from splitting open is misleading. Skull fractures are usually not life threatening unless the fracture is depressed and impinges on the brain beneath and bone fractures usually heal over a relatively short period. Brain injuries are much more serious. They frequently result in death, permanent disability or personality change and, unlike bone, neurological tissue has very limited ability to recover after an injury. Therefore, the primary purpose of a helmet is to prevent traumatic brain injury
while skull and face injuries are a significant secondary concern.
The most common type of head injury in motorcycle accidents is closed head injury, meaning injury in which the skull is not broken as distinct from an open head injury like a bullet wound. Closed head injury results from violent acceleration of the head which causes the brain to move around inside the skull. During an impact to the front of the head, the brain lurches forwards inside the skull, squeezing the tissue near the impact site and stretching the tissue on the opposite side of the head. Then the brain rebounds in the opposite direction, stretching the tissue near the impact site and squeezing the tissue on the other side of the head. Blood vessels linking the brain to the inside of the skull may also break during this process, causing dangerous bleeding.
Another hazard, susceptibility of the brain to shearing forces, plays a role primarily in injuries which involve rapid and forceful movements of the head, such as in motor vehicle accidents. In these situations rotational forces such as might occur in whiplash-type injuries are particularly important. These forces, associated with the rapid acceleration and deceleration of the head, are smallest at the point of rotation of the brain near the lower end of the brain stem and successively increase at increasing distances from this point. The resulting shearing forces cause different levels in the brain to move relative to one another. This movement produces stretching and tearing of axons (diffuse axonal injury) and the insulating myelin sheath, injuries which are the major cause of loss of consciousness in a head trauma. Small blood vessels are also damaged causing bleeding (petechial hemorrhages) deep within the brain.
It is important that the liner in a motorcycle helmet is soft and thick so the head decelerates at a gentle rate as it sinks into it. Unfortunately, there is a limit to how thick the helmet can be for the simple reason that the helmet quickly becomes impractical if the liner is more than 1–2 in (2.5–5.1 cm) thick. This implies a limit to how soft the liner can be. If the liner is too soft, the head will crush it completely upon impact without coming to a stop. Outside the liner is a hard plastic shell and beyond that is whatever the helmet is hitting, which is usually an unyielding surface, like concrete pavement. Consequently, the head cannot move any further, so after crushing the liner it comes suddenly to an abrupt stop, causing high accelerations that injure the brain.
Therefore, an ideal helmet liner is stiff enough to decelerate the impacting head to an abrupt stop in a smooth uniform manner just before it completely crushes the liner and no stiffer. The required stiffness depends on the impact speed of the head, which is unknown at the time of manufacture of the helmet. The result is that the manufacturer must choose a likely speed of impact and optimize the helmet for that impact speed. If the helmet is in a real impact that is slower than the one for which it was designed, it will still help but the head will be decelerated a little more violently than was actually necessary given the available space between the inside and outside of the helmet, although that deceleration will still be much less than what it would have been in the absence of the helmet. If the impact is faster than the one the helmet was designed for, the head will completely crush the liner and slow down but not stop in the process. When the crush space of the liner runs out, the head will stop suddenly which is not ideal. However, in the absence of the helmet, the head would have been brought to a sudden stop from a higher speed causing more injury. Still, a helmet with a stiffer foam that stopped the head before the liner crush space ran out would have done a better job. So helmets help most in impacts at the speeds they were designed for, and continue to help but not as much in impacts that are at different speeds. In practice, motorcycle helmet manufacturers choose the impact speed they will design for based on the speed used in standard helmet tests. Most standard helmet tests use speeds between 4 m/s (8.9 mph; 14.4 km/h).
s and other small-displacement bikes. In some countries, most notably the USA and India, there is some opposition to compulsory helmet use (see Helmet Law Defense League
); not all USA states have a compulsory helmet law.
Worldwide, many countries have defined their own sets of standards that are used to judge the effectiveness of a motorcycle helmet in an accident, and define the minimal acceptable standard thereof. Among them are:
The Snell Memorial Foundation has developed stricter requirements and testing procedures for motorcycle helmets with racing in mind, as well as helmets for other activities (e.g. drag racing, bicycling, horseback riding), and many riders in North America consider Snell certification a benefit when considering buying a helmet while others note that its standards allow for more force (g's) to be transferred to a rider's head than the U.S. Department of Transportation (DOT) standard. However, the DOT standard does not test the chin bar of helmets with them, while the Snell (and ECE) standards do.
In the United Kingdom, many riders choose helmets bearing an Auto-Cycle Union (ACU) Gold sticker as it defines a stricter standard than the legal minimum ECE 22.05 specification. Helmets with an ACU Gold sticker are the only ones allowed to be worn in competition, or at track days.
s higher than 20 m/s (45 mph), the perpendicular impact speed of the helmet is usually not the same as the road speed of the motorcycle, and the severity of the impact is determined not only by the speed of the head but also by the surface it hits and the angle of impact. Since the surface of the road is almost parallel to the direction a motorcyclist moves while driving, only a small component of their velocity is directed perpendicularly (though other surfaces may be perpendicular to the motorcyclist's velocity, such as trees, walls, and the sides of other vehicles). The severity of an impact is also influenced by the nature of the surface struck. The sheet metal wall of a car door may bend inwards to a depth of 7.5 –ch) during a helmeted-head impact, allowing more stopping distance for the rider's head than the helmet itself. A perpendicular impact against a flat steel anvil
at 5 m/s (11 mph) may be of approximate severity to an oblique impact against a concrete surface at 30 m/s (67 mph) or a perpendicular impact against a sheet metal car door or windscreen at 30 m/s. Since there is a wide range of severity in the impacts that could happen in a motorcycle accident, some will be more severe than the impacts used in the standard tests and some will be less.
Helmet
A helmet is a form of protective gear worn on the head to protect it from injuries.Ceremonial or symbolic helmets without protective function are sometimes used. The oldest known use of helmets was by Assyrian soldiers in 900BC, who wore thick leather or bronze helmets to protect the head from...
used by motorcycle
Motorcycle
A motorcycle is a single-track, two-wheeled motor vehicle. Motorcycles vary considerably depending on the task for which they are designed, such as long distance travel, navigating congested urban traffic, cruising, sport and racing, or off-road conditions.Motorcycles are one of the most...
riders. The primary goal of a motorcycle helmet is motorcycle safety
Motorcycle safety
Motorcycle safety concerns many aspects of vehicle and equipment design as well as operator skill and training that are unique to motorcycle riding.-Accident rates:...
- to protect the rider's head during impact, thus preventing or reducing head injury
Head injury
Head injury refers to trauma of the head. This may or may not include injury to the brain. However, the terms traumatic brain injury and head injury are often used interchangeably in medical literature....
or saving the rider's life. Some helmets provide additional conveniences, such as ventilation, face shields, ear protection, intercom
Intercom
An intercom , talkback or doorphone is a stand-alone voice communications system for use within a building or small collection of buildings, functioning independently of the public telephone network. Intercoms are generally mounted permanently in buildings and vehicles...
etc.
Motorcyclists are at high risk in traffic crashes. A 2008 systematic review
Systematic review
A systematic review is a literature review focused on a research question that tries to identify, appraise, select and synthesize all high quality research evidence relevant to that question. Systematic reviews of high-quality randomized controlled trials are crucial to evidence-based medicine...
examined studies on motorcycle riders who had crashed and looked at helmet use as an intervention. The review concluded that helmets reduce the risk of head injury by around 69% and death by around 42%. Some studies have suggested that helmets may protect against facial injury but they have no effect on neck injury, more research is required for a conclusive answer.
Origins
T. E. Lawrence
Lieutenant Colonel Thomas Edward Lawrence, CB, DSO , known professionally as T. E. Lawrence, was a British Army officer renowned especially for his liaison role during the Arab Revolt against Ottoman Turkish rule of 1916–18...
(known as Lawrence of Arabia) had a crash on a Brough Superior SS100
Brough Superior SS100
The Brough Superior SS 100 was designed and built by George Brough in Nottingham, England in 1924. Although every bike was designed to meet specific customer requirements—even the handlebars were individually shaped—sixty-nine SS100s were produced in 1925 and at £170 were advertised by Brough as...
on a narrow road near his cottage near Wareham
Wareham, Dorset
Wareham is an historic market town and, under the name Wareham Town, a civil parish, in the English county of Dorset. The town is situated on the River Frome eight miles southwest of Poole.-Situation and geography:...
. The accident occurred because a dip in the road obstructed his view of two boys on bicycles. Swerving to avoid them, Lawrence lost control and was thrown over the handlebars. He was not wearing a helmet, and suffered serious head injuries which left him in a coma; he died after six days in hospital. One of the doctors attending him was Hugh Cairns
Hugh Cairns (surgeon)
Sir Hugh William Bell Cairns was a British neurosurgeon.Hugh Cairns was born in Port Pirie, but came to Adelaide for his secondary education at Adelaide High School and tertiary education at the University of Adelaide...
, a neurosurgeon, who after Lawrence's death began a long study of what he saw as the unnecessary loss of life by motorcycle despatch rider
Despatch rider
A despatch rider is a military messenger, mounted on horse or motorcycle.Despatch riders were used by armed forces to deliver urgent orders and messages between headquarters and military units...
s through head injuries. Cairns' research led to the use of crash helmets by both military and civilian motorcyclists.
Basic types
There are five basic types of helmets intended for motorcycling, and others not intended for motorcycling but which are used by some riders. All of these types of helmets are secured by a chin strapStrap
A strap, sometimes also called strop, is an elongated flap or ribbon, usually of fabric or leather.Thin straps are used as part of clothing or baggage, or bedding such as a sleeping bag. See for example spaghetti strap, shoulder strap...
, and their protective benefits are greatly reduced, if not eliminated, if the chin strap is not securely fastened so as to maintain a snug fit.
From most to least protective, as generally accepted by riders and manufacturers, the helmet types are:
Full face
A full face helmet covers the entire head, with a rear that covers the base of the skullHuman skull
The human skull is a bony structure, skeleton, that is in the human head and which supports the structures of the face and forms a cavity for the brain.In humans, the adult skull is normally made up of 22 bones...
, and a protective section over the front of the chin
Chin
In the human anatomy, the chin is the lowermost part of the face.It is formed by the lower front of the mandible.People show a wide variety of chin structures. See Cleft chin....
. Such helmets have an open cutout in a band across the eyes and nose, and often include a clear or tinted transparent plastic face shield, known as a visor, that generally swivels up and down to allow access to the face. Many full face helmets include vents to increase the airflow to the rider.
The significant attraction of these helmets is their protectiveness. Some wearers dislike the increased heat, sense of isolation, lack of wind, and reduced hearing of such helmets. Full face helmets intended for off-road use sometimes omit the face shield, but extend the visor and chin portions to increase ventilation, since riding off-road is a very strenuous activity.
Studies have shown that full face helmets offer the most protection to motorcycle riders because 35% of all crashes showed major impact on the chin-bar area. Wearing a helmet with less coverage eliminates that protection — the less coverage the helmet offers, the less protection for the rider.
Off-Road/Motocross
Motocross
Motocross is a form of motorcycle sport or all-terrain vehicle racing held on enclosed off road circuits. It evolved from trials, and was called scrambles, and later motocross, combining the French moto with cross-country...
and off-road helmet has clearly elongated chin and visor portions, a chin bar, and partially open face to give the rider extra protection while wearing goggles and to allow the unhindered flow of air during the physical exertion of this type of riding. The visor is to allow the rider to dip his head and provide further protection from flying debris during off road riding. It will also keep the sun out of the eyes of the rider during jumps.
Originally, off-road helmets did not include a chin bar, with riders using helmets very similar to modern open face street helmets, and using a face mask to fend off dirt and debris from the nose and mouth. Modern off-road helmets include a (typically angular, rather than round) chin bar to provide some facial impact protection in addition to protection from flying dirt and debris. When properly combined with goggles, the result provides most of the same protective features of full face street helmets.
Modular or "Flip-up"
Police motorcycle
A police motorcycle is a motorcycle used by various police forces and departments. They may be custom designed to meet the requirements unique of a particular use. A police motorcycle is often called a "motor" by police officers in the United States...
.
Many modular helmets are designed to be worn only in the closed position for riding, as the movable chin bar is designed as a convenience feature, useful while not actively riding. The curved shape of an open chin bar and face shield section can cause increased wind drag during riding, as air will not flow around an open modular helmet in the same way as a three-quarters helmet. Since the chin bar section also protrudes further from the forehead than a three-quarters visor, riding with the helmet in the open position may pose increased risk of neck injury in a crash. Some modular helmets are dual certified as full face and open face helmet. The chin bar of those helmets offer real protection and they can be used in the "open" position while riding. An example of such an helmet would be the Shark
Shark (helmet manufacturer)
Shark is a French company that produces motorcycle helmets, which was founded in 1929 in Marseille, France.-Helmets:Shark places a strong emphasis on safety and quality in their helmets. Their designs concentrate on the dispersion of impact force away from the wearer's head, while utilizing...
Evoline.
As of 2008, there have not been wide scientific studies of modular helmets to assess how protective the pivoting or removable chin bars are. Observation and unofficial testing suggest that significantly greater protection exists beyond that for an open face helmet, and may be enough to pass full-face helmet standardized tests, but the extent of protection is not fully established by all standards bodies.
The DOT
Department of Transportation
The Department of Transportation is the most common name for a government agency in North America devoted to transportation. The largest is the United States Department of Transportation, which oversees interstate travel. All U.S. states, Canadian provinces, and many local agencies also have...
standard does not require chin bar testing. The Snell Memorial Foundation recently certified a flip-up helmet for the first time. ECE 22.05 allows certification of modular helmets with or without chin bar tests, distinguished by -P (protective lower face cover) and -NP (non-protective) suffixes to the certification number, and additional warning text for non-certified chin bars.
Open face or 3/4 helmet
The open face, or "three-quarters", helmet covers the ears, cheeks, and back of the head, but lacks the lower chin bar of the full face helmet. Many offer snap-on visors that may be used by the rider to reduce sunlight glare. An open face helmet provides the same rear protection as a full face helmet, but little protection to the face, even from non-crash events.Bugs, dust, or even wind to the face and eyes can cause rider discomfort or injury. As a result, it is not uncommon (and in some U.S. states, is required by law) for riders to wear wrap-around sunglasses or goggles to supplement eye protection with these helmets. Alternatively, many open face helmets include, or can be fitted with, a face shield, which is more effective in stopping flying insects from entering the helmet.
Half helmet
Rocker (subculture)
Rockers, leather boys or ton-up boys are a biker subculture that originated in the United Kingdom during the 1950s. It was mainly centered around British cafe racer motorcycles and rock and roll music....
and road racers of the 1960s in the British Isles. It has essentially the same front design as an open face helmet but without a lowered rear in the shape of a bowl. The half helmet provides the minimum coverage generally allowed by law in the USA, and British Standards 2001:1956.
As with the open face, it is not uncommon to augment this helmet's eye protection through other means such as goggles
Goggles
Goggles or safety glasses are forms of protective eyewear that usually enclose or protect the area surrounding the eye in order to prevent particulates, water or chemicals from striking the eyes. They are used in chemistry laboratories and in woodworking. They are often used in snow sports as well,...
. Because of their inferiority compared to other helmet styles, some Motorcycle Safety Foundation
Motorcycle Safety Foundation
The Motorcycle Safety Foundation is a United States national, not-for-profit organization, founded in 1973, and sponsored by the U.S. manufacturers and distributors of BMW, Ducati, Harley-Davidson, Honda, Kawasaki, KTM, Piaggio/Vespa, Suzuki, Triumph, Victory and Yamaha motorcycles...
s prohibit the use of half helmets now. Notable UK manufacturers included Everoak, Chas Owens and, currently, Davida.
Headwear not intended for motorcycling
There are other types of headwear - often called "beanies," "brain buckets", or "novelty helmets", a term which arose since they cannot legally be called motorcycle helmets. These helmets are not certified and are generally only used to provide the illusion of compliance with mandatory helmet laws. Such items are often smaller and lighter than helmets made to DOT standards, and are unsuitable for crash protection because they lack the energy-absorbing foam that protects the brainBrain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
by allowing it to come to a gradual stop during an impact. A "novelty helmet" can protect the scalp against sunburn while riding and - if it stays on during a crash - might protect the scalp against abrasion, but it has no capability to protect the skull or brain from an impact.
Conflicting findings on color visibility
Although black helmets are popular among motorcyclists, one study determined they offer the least visibility to motorists. Riders wearing a plain white helmet rather than a black one were associated with a 24% lower risk of suffering a motorcycle accident injury or death. This study also notes "Riders wearing high visibility clothing and white helmets are likely to be more safety conscious than other riders."However, the MAIDS report
MAIDS report
The MAIDS report is a large-scale, comprehensive study of Powered Two Wheelers accidents carried out across five European countries, using both accident and exposure cases, as was done in the Hurt Report, and following the standards of OECD...
did not back up the claims that helmet color makes any difference in accident frequency, and that in fact motorcycles painted white were actually over-represented in the accident sample compared to the exposure data. While recognizing how much riders need to be seen, the MAIDS report documented that riders' clothing usually fails to do so, saying that "in 65.3% of all cases, the clothing made no contribution to the conspicuity of the rider or the PTW [powered two-wheeler, i.e. motorcycle]. There were very few cases found in which the bright clothing of the PTW rider enhanced the PTW’s overall conspicuity (46 cases). There were more cases in which the use of dark clothing decreased the conspicuity of the rider and the PTW (120 cases)." The MAIDS report was unable to recommend specific items of clothing or colors to make riders better seen.
Construction
Modern helmets are constructed from plasticPlastic
A plastic material is any of a wide range of synthetic or semi-synthetic organic solids used in the manufacture of industrial products. Plastics are typically polymers of high molecular mass, and may contain other substances to improve performance and/or reduce production costs...
s. Premium price helmets are made with fiberglass reinforced with Kevlar
Kevlar
Kevlar is the registered trademark for a para-aramid synthetic fiber, related to other aramids such as Nomex and Technora. Developed at DuPont in 1965, this high strength material was first commercially used in the early 1970s as a replacement for steel in racing tires...
or carbon fiber
Carbon fiber
Carbon fiber, alternatively graphite fiber, carbon graphite or CF, is a material consisting of fibers about 5–10 μm in diameter and composed mostly of carbon atoms. The carbon atoms are bonded together in crystals that are more or less aligned parallel to the long axis of the fiber...
. They generally have fabric and foam interiors for both comfort and protection. Motorcycle helmets are generally designed to distort in a crash (thus expending the energy otherwise destined for the wearer's skull), so they provide little protection at the site of their first impact, but continued protection over the remainder of the helmet.
Helmets are constructed from an inner EPS “Expanded Polystyrene foam” and an outer shell to protect the EPS. The density and the thickness of the EPS is designed to cushion or crush on impact to help prevent head injuries. Some manufacturers even offer different densities to offer better protection. The outer shell can be made of plastics or fiber materials. Some of the plastics offer very good protection from penetration as in lexan (bulletproof glass) but will not crush on impact, so the outer shell will look undamaged but the inner EPS will be crushed. Fiberglass is less expensive than lexan but is heavy and very labor intensive. Fiberglass or fiber shells will crush on impact offering better protection. Some manufacturers will use Kevlar or carbon fiber to help reduce the amount of fiberglass but in the process it will make the helmet lighter and offer more protection from penetration but still crushing on impact. But this can be very expensive.
Function
Polycarbonate
PolycarbonatePhysical PropertiesDensity 1.20–1.22 g/cm3Abbe number 34.0Refractive index 1.584–1.586FlammabilityV0-V2Limiting oxygen index25–27%Water absorption – Equilibrium0.16–0.35%Water absorption – over 24 hours0.1%...
plastic, fiberglass
Fiberglass
Glass fiber is a material consisting of numerous extremely fine fibers of glass.Glassmakers throughout history have experimented with glass fibers, but mass manufacture of glass fiber was only made possible with the invention of finer machine tooling...
, or Kevlar and a soft, thick, inner liner usually made of expanded polystyrene
Polystyrene
Polystyrene ) also known as Thermocole, abbreviated following ISO Standard PS, is an aromatic polymer made from the monomer styrene, a liquid hydrocarbon that is manufactured from petroleum by the chemical industry...
or polypropylene
Polypropylene
Polypropylene , also known as polypropene, is a thermoplastic polymer used in a wide variety of applications including packaging, textiles , stationery, plastic parts and reusable containers of various types, laboratory equipment, loudspeakers, automotive components, and polymer banknotes...
"EPS" foam. The purpose of the hard outer shell is:
- to prevent penetration of the helmet by a pointed object that might otherwise puncture the skull, and
- to provide structure to the inner liner so it does not disintegrate upon abrasive contact with pavement. This is important because the foams used have very little resistance to penetration and abrasion.
The purpose of the foam liner is to crush during an impact, thereby increasing the distance and period of time over which the head stops and reducing its deceleration.
To understand the action of a helmet, it is first necessary to understand the mechanism of head injury. The common perception that a helmet's purpose is to save the rider's head from splitting open is misleading. Skull fractures are usually not life threatening unless the fracture is depressed and impinges on the brain beneath and bone fractures usually heal over a relatively short period. Brain injuries are much more serious. They frequently result in death, permanent disability or personality change and, unlike bone, neurological tissue has very limited ability to recover after an injury. Therefore, the primary purpose of a helmet is to prevent traumatic brain injury
Traumatic brain injury
Traumatic brain injury , also known as intracranial injury, occurs when an external force traumatically injures the brain. TBI can be classified based on severity, mechanism , or other features...
while skull and face injuries are a significant secondary concern.
The most common type of head injury in motorcycle accidents is closed head injury, meaning injury in which the skull is not broken as distinct from an open head injury like a bullet wound. Closed head injury results from violent acceleration of the head which causes the brain to move around inside the skull. During an impact to the front of the head, the brain lurches forwards inside the skull, squeezing the tissue near the impact site and stretching the tissue on the opposite side of the head. Then the brain rebounds in the opposite direction, stretching the tissue near the impact site and squeezing the tissue on the other side of the head. Blood vessels linking the brain to the inside of the skull may also break during this process, causing dangerous bleeding.
Another hazard, susceptibility of the brain to shearing forces, plays a role primarily in injuries which involve rapid and forceful movements of the head, such as in motor vehicle accidents. In these situations rotational forces such as might occur in whiplash-type injuries are particularly important. These forces, associated with the rapid acceleration and deceleration of the head, are smallest at the point of rotation of the brain near the lower end of the brain stem and successively increase at increasing distances from this point. The resulting shearing forces cause different levels in the brain to move relative to one another. This movement produces stretching and tearing of axons (diffuse axonal injury) and the insulating myelin sheath, injuries which are the major cause of loss of consciousness in a head trauma. Small blood vessels are also damaged causing bleeding (petechial hemorrhages) deep within the brain.
It is important that the liner in a motorcycle helmet is soft and thick so the head decelerates at a gentle rate as it sinks into it. Unfortunately, there is a limit to how thick the helmet can be for the simple reason that the helmet quickly becomes impractical if the liner is more than 1–2 in (2.5–5.1 cm) thick. This implies a limit to how soft the liner can be. If the liner is too soft, the head will crush it completely upon impact without coming to a stop. Outside the liner is a hard plastic shell and beyond that is whatever the helmet is hitting, which is usually an unyielding surface, like concrete pavement. Consequently, the head cannot move any further, so after crushing the liner it comes suddenly to an abrupt stop, causing high accelerations that injure the brain.
Therefore, an ideal helmet liner is stiff enough to decelerate the impacting head to an abrupt stop in a smooth uniform manner just before it completely crushes the liner and no stiffer. The required stiffness depends on the impact speed of the head, which is unknown at the time of manufacture of the helmet. The result is that the manufacturer must choose a likely speed of impact and optimize the helmet for that impact speed. If the helmet is in a real impact that is slower than the one for which it was designed, it will still help but the head will be decelerated a little more violently than was actually necessary given the available space between the inside and outside of the helmet, although that deceleration will still be much less than what it would have been in the absence of the helmet. If the impact is faster than the one the helmet was designed for, the head will completely crush the liner and slow down but not stop in the process. When the crush space of the liner runs out, the head will stop suddenly which is not ideal. However, in the absence of the helmet, the head would have been brought to a sudden stop from a higher speed causing more injury. Still, a helmet with a stiffer foam that stopped the head before the liner crush space ran out would have done a better job. So helmets help most in impacts at the speeds they were designed for, and continue to help but not as much in impacts that are at different speeds. In practice, motorcycle helmet manufacturers choose the impact speed they will design for based on the speed used in standard helmet tests. Most standard helmet tests use speeds between 4 m/s (8.9 mph; 14.4 km/h).
Laws and standards
Motorcycle helmets greatly reduce injuries and fatalities in motorcycle accidents, thus many countries have laws requiring acceptable helmets to be worn by motorcycle riders. These laws vary considerably, often exempting mopedMoped
Mopeds are a type of low-powered motorcycle designed to provide economical and relatively safe transport with minimal licensing requirements.Mopeds were once all equipped with bicycle-like pedals , but moped has been increasingly applied by governments to vehicles without pedals, based on their...
s and other small-displacement bikes. In some countries, most notably the USA and India, there is some opposition to compulsory helmet use (see Helmet Law Defense League
Helmet Law Defense League
The Helmet Law Defense League is a group founded in 1993 that opposes the laws in states which mandate motorcycle helmets. The group contends that mandatory motorcycle helmet laws enacted at the state, county, and municipal levels of government against consumers and users are unconstitutional due...
); not all USA states have a compulsory helmet law.
Worldwide, many countries have defined their own sets of standards that are used to judge the effectiveness of a motorcycle helmet in an accident, and define the minimal acceptable standard thereof. Among them are:
- ACU (Auto-Cycle Union) Gold or Silver badge
- AS/NZS 1698:2006 (Australia and New Zealand)
- BSI (British Standards Institute) 6658
- CSA CAN3-D230-M85 (Canada. they no longer certify motorcycle helmets)
- DOTDepartment of TransportationThe Department of Transportation is the most common name for a government agency in North America devoted to transportation. The largest is the United States Department of Transportation, which oversees interstate travel. All U.S. states, Canadian provinces, and many local agencies also have...
FMVSS 218 (USA) - GOSTGOSTGOST refers to a set of technical standards maintained by the Euro-Asian Council for Standardization, Metrology and Certification , a regional standards organization operating under the auspices of the Commonwealth of Independent States .All sorts of regulated standards are included, with examples...
R 41.22-2001 (ГОСТ Р 41.22-2001) (Russia) - NBR 7471 (Brazil)
- IS 4151 (India)
- JIS T 8133:2000 (Japan)
- SnellSnell Memorial FoundationThe Snell Memorial Foundation is a not-for-profit organization created to provide a high quality standard of safety for helmets. Founded in 1957, SMF is named after William "Pete" Snell, a popular sports car racer who died in 1956 of head injuries he received when the racing helmet he wore failed...
M 2005 "2005 Helmet Standard For Use in Motorcycling" - SNI (Indonesia)
- SHARP (UK) - Star Rating
- ECEUnited Nations Economic Commission for EuropeThe United Nations Economic Commission for Europe was established in 1947 to encourage economic cooperation among its member states. It is one of five regional commissions under the administrative direction of United Nations headquarters. It has 56 member states, and reports to the UN Economic and...
22.05 (Europe) - TCVN 5756:2001 (test and certify by QUATEST 3) (VietnamVietnamVietnam – sometimes spelled Viet Nam , officially the Socialist Republic of Vietnam – is the easternmost country on the Indochina Peninsula in Southeast Asia. It is bordered by China to the north, Laos to the northwest, Cambodia to the southwest, and the South China Sea –...
)
The Snell Memorial Foundation has developed stricter requirements and testing procedures for motorcycle helmets with racing in mind, as well as helmets for other activities (e.g. drag racing, bicycling, horseback riding), and many riders in North America consider Snell certification a benefit when considering buying a helmet while others note that its standards allow for more force (g's) to be transferred to a rider's head than the U.S. Department of Transportation (DOT) standard. However, the DOT standard does not test the chin bar of helmets with them, while the Snell (and ECE) standards do.
In the United Kingdom, many riders choose helmets bearing an Auto-Cycle Union (ACU) Gold sticker as it defines a stricter standard than the legal minimum ECE 22.05 specification. Helmets with an ACU Gold sticker are the only ones allowed to be worn in competition, or at track days.
Standards testing
Most motorcycle helmet standards use impacts at speeds between 4–7 m/s (9–16 mph). While motorcyclists frequently ride at speedSpeed
In kinematics, the speed of an object is the magnitude of its velocity ; it is thus a scalar quantity. The average speed of an object in an interval of time is the distance traveled by the object divided by the duration of the interval; the instantaneous speed is the limit of the average speed as...
s higher than 20 m/s (45 mph), the perpendicular impact speed of the helmet is usually not the same as the road speed of the motorcycle, and the severity of the impact is determined not only by the speed of the head but also by the surface it hits and the angle of impact. Since the surface of the road is almost parallel to the direction a motorcyclist moves while driving, only a small component of their velocity is directed perpendicularly (though other surfaces may be perpendicular to the motorcyclist's velocity, such as trees, walls, and the sides of other vehicles). The severity of an impact is also influenced by the nature of the surface struck. The sheet metal wall of a car door may bend inwards to a depth of 7.5 –ch) during a helmeted-head impact, allowing more stopping distance for the rider's head than the helmet itself. A perpendicular impact against a flat steel anvil
Anvil
An anvil is a basic tool, a block with a hard surface on which another object is struck. The inertia of the anvil allows the energy of the striking tool to be transferred to the work piece. In most cases the anvil is used as a forging tool...
at 5 m/s (11 mph) may be of approximate severity to an oblique impact against a concrete surface at 30 m/s (67 mph) or a perpendicular impact against a sheet metal car door or windscreen at 30 m/s. Since there is a wide range of severity in the impacts that could happen in a motorcycle accident, some will be more severe than the impacts used in the standard tests and some will be less.