Seat belt

A three-point seat belt.
Lap seat belt (or "two points") in an aircraft
Three points seatbelt in a car. The three points belt is the standard seat belt for road cars.
Five points harness in a racing car.

A seat belt or seatbelt, sometimes called a safety belt, is a safety harness designed to secure the occupant of a vehicle against harmful movement that may result from a collision or a sudden stop. As part of an overall automobile passive safety system, seat belts are intended to reduce injuries by stopping the wearer from hitting hard interior elements of the vehicle, or other passengers (the so-called second impact), are in the correct position for the airbag to deploy and prevent the passenger from being thrown from the vehicle. Seat belts also absorb energy by being designed to stretch during any sudden deceleration, so that there is less speed differential between the passenger's body and their vehicle interior, and also to spread the loading of impact on the passengers body.

The final, so-called 'third impact' after a passenger's body hits the car interior, airbag or seat belts, is that of the internal organs hitting the ribcage or skull. The force of this impact is the mechanism through which car crashes cause disabling or life threatening injury. The sequence of energy dissipating and speed reducing technologies - crumple zone - seat belt - airbags - padded interior, are designed to work together as a system, to reduce the force of this final impact.

Contents

Lap

An adjustable strap that goes over the waist. This type of belt is frequently found in older cars, and has been used, until recently, on some newer vehicles in rear or rear middle seats. These types of belt are also found on some coaches. Passenger aircraft seats also use lap seat belts to help prevent injuries while still allowing passengers to adopt a brace position.

Sash

An adjustable strap that goes over the shoulder. Used mainly in vehicles during the 1960(1959), however they had limited benefit because it was very easy to slip out of them in a collision.

Three-point

Similar to the lap and sash belts, but has one single continuous length of belt. Both three-point and lap-and-sash belts help spread out the energy of the moving body in a collision over the chest, pelvis, and shoulders. Volvo introduced the first production three-point belt in 1959.[1] The first car with three point belt was a Volvo PV 544 that was delivered to a dealer in Kristianstad on August 13, 1959. The first car to feature the three point seat belt however was the 1959 Volvo 122 The three point belt was developed by Nils Bohlin who had earlier also worked on ejection seats at Saab.[2]

Until the 1980s, three-point belts were commonly available only in the front seats of cars; the back seats were only often fitted with lap or sash belts. Evidence of the potential of lap belts to cause separation of the lumbar vertebrae and the sometimes associated paralysis, or "seat belt syndrome", led to a revision of passenger safety regulations in nearly all developed countries, requiring that all seats in a vehicle have to be equipped with three-point belts. Since September 1, 2007, all new cars sold in the U.S. require a lap and shoulder belt in the center rear seat.[3]

Besides regulatory changes, "seat belt syndrome" has led to tremendous liability for vehicle manufacturers. One Los Angeles case resulted in a $45 million jury verdict against the Ford Motor Company; the resulting $30 million judgment (after deductions for another defendant who settled prior to trial) was affirmed on appeal in 2006.[4]

Harness

Belt-in-Seat (BIS)

The BIS is a three-point where the shoulder belt attachment is to the backrest, not to the b pillar.[5] The first car using this system in the United States was the 1990 Mercedes-Benz SL.[6] Some cars like the Renault Vel Satis use this system for the front seats. This system allegedly is safer in case of rollover, especially with 4–8 years old children,[7] though other sources dispute this claim.[8]

Experimental production car safety belts

Five-point harnesses

These restraints are safer but more restrictive than most other seat belt types. Five-point harnesses are typically found in child safety seats and in racing cars. The lap portion is connected to a belt between the legs and there are two shoulder belts, making a total of five points of attachment to the seat. (Strictly speaking, harnesses are never to be fastened to the seat—they should be fastened to the frame/sub-frame of the automobile.)

Six-point harnesses

These harnesses are similar to a five-point harness but include an extra belt between the legs, which is seen by some to be a weaker point than the other parts. These belts are used mainly in racing. In NASCAR, the six-point harness became popular after the death of Dale Earnhardt. Earnhardt was wearing a five-point harness when he suffered his fatal crash. As it was first thought that his belt had broken, some teams ordered a six-point harness in response.[12]

Seven-point harnesses (5+2)

Aerobatic aircraft frequently use a combination harness consisting of a five-point harness with a redundant lap-belt attached to a different part of the airframe. While providing redundancy for negative-g maneuvers (which lift the pilot out of the seat), they also require the pilot to un-latch two harnesses if it is necessary to parachute from a failed aircraft.

History

Seat belts were invented by Dorothy Richardson's husband in the late 1800s, though Edward J. Claghorn of New York, New York was granted the first patent (U.S. Patent 312,085, on February 10, 1885 for a safety belt).[13] Claghorn was granted United States Patent #312,085 for a Safety-Belt for tourists, described in the patent as "designed to be applied to the person, and provided with hooks and other attachments for securing the person to a fixed object."

In 1911, Benjamin Foulois had the cavalry saddle shop fashion a belt for the seat of Wright Flyer Signal Corps 1. He wanted it to hold him firmly in his seat so he could better control his aircraft as he bounded along the rough field used for takeoff and landing. C-130 aircraft in South Vietnam also bounded on runways to the extent that a tight seat belt improved the pilot's ability to control the aircraft. It was not until World War II that seat belts were fully adopted in military aircraft, and even then, it was mainly for safety reasons, not improved aircraft control.

In 1946 Dr. C. Hunter Shelden had opened a neurological practice at Huntington Memorial Hospital in Pasadena, California. In the early 1950s Dr. Shelden had made a major contribution to the automotive industry with his idea of retractable seat belts. This came about greatly in part from the high number of head injuries coming through the emergency rooms.[14] He investigated the early seat belts whose primitive designs were implicated in these injuries and deaths. His findings were published in the November 5, 1955 Journal of the American Medical Association (JAMA) in which he proposed not only the retractable seat belt, but also recessed steering wheels, reinforced roofs, roll bars, door locks and passive restraints such as the now-and-ever-popular air bag. Subsequently in 1959 Congress passed legislation requiring all automobiles to comply with certain safety standards.[15]

American car manufacturers Nash (in 1949) and Ford (in 1955) offered seat belts as options, while Swedish Saab first introduced seat belts as standard in 1958.[16] After the Saab GT 750 was introduced at the New York motor show in 1958 with safety belts fitted as standard, the practice became commonplace.[17]

However, the first modern three point seat belt (the so-called CIR-Griswold restraint) used in most consumer vehicles today was patented in 1951 by the Americans Roger W. Griswold and Hugh De Haven,[18] and developed to its modern form by Nils Bohlin for Swedish manufacturer Volvo—who introduced it in 1959 as standard equipment. Bohlin was granted U.S. Patent 3,043,625 for the device.[16] Bohlin's lap-and-shoulder belt was introduced by Volvo in 1959, in Sweden.

In 1970, the state of Victoria, Australia, passed the first law worldwide making seat belt wearing compulsory for drivers and front-seat passengers.[19] [20]

Technologies

Seat Belt uncovered Inertial Reel

Most seat belts are equipped with locking mechanisms (or inertia reels) that tighten the belt when pulled fast (e.g. by the quick force of a passenger's body during a crash) but do not tighten when pulled slowly. This is implemented with a centrifugal clutch, which engages as the reel spins quickly. Alternatively, this function may be secured by a weighted pendulum or ball bearing: when these are deflected by deceleration or roll-over they lock into pawls on the reel.

Types of inertia reel type seatbelts:

NLR (no locking retractor): Commonly used in recoiling lap belts

ELR V (emergency locking retractor - vehicle sensitive): Single sensitive mechanism, composed of a locking mechanism activated in an emergency by deceleration or rollover of the vehicle. Thus, the seatbelt is sensitive to the vehicle's motion.

ELR VW (emergency locking retractor - vehicle and webbing sensitive): Dual sensitive means a seatbelt retractor that, during normal driving conditions, allows freedom of movement by the wearer of the seatbelt by means of length-adjusting components that automatically adjust the strap to the wearer, with a locking mechanism that is activated by two or more of the following:

A recent study by McCoy & Chou (2007) from the Ford Motor Company (Safety Test Methodology, SP-2123) demonstrated that the standard inertia reel seatbelt does not stop the head from making contact with the interior of the roof on a standard rollover test in their dynamic Rollover Component test System (ROCS). Even with modern pre-tensioning devices the head contacts the interior of the roof and the neck suffers 'visible' compression.

Pretensioners and webclamps

Pyrotechnic pretensioner diagram

Seatbelts in many newer vehicles are also equipped with "pretensioners" and/or "Webclamps".

Inflatable Seatbelts

The Inflatabelt Seatbelt utilizes tubular inflatable bladders contained within an outer cover. When a crash occurs the bladder inflates with a gas to increase the area of the restraint contacting the occupant and also shortening the length of the restraint to tighten the belt around the occupant, improving the protection. The inflatable sections may be shoulder only or lap and shoulder. The system supports the head during the crash better than a web only belt. It also provides side impact protection. The inflatable seatbelt was invented by Donald Lewis and tested at the Automotive Products Division of Allied Chemical Corp.

Automatic seat belts

Main article: Automatic seat belt

Some vehicles have shoulder belts that automatically move in reverse to secure the passenger when the vehicle is started. A separate lap belt is usually included, and the lap belt must be fastened manually. Automatic seat belts have fallen out of favor recently, since the airbag became mandatory in many countries.

Use of seat belts by child occupants

As with adult drivers and passengers, the advent of seat belts was accompanied by calls for their use by child occupants, including legislation requiring such use. It has been claimed that children in adult restraints suffer lower injury risk than unrestrained children.

The UK extended compulsory seatbelt wearing to child passengers under the age of 14 in 1989. It was observed that this measure was accompanied by a 10% increase in fatalities and a 12% increase in injuries among the target population.[21] In crashes, small children who wear adult seatbelts can suffer "seat-belt syndrome" injuries including severed intestines, ruptured diaphragms and spinal damage. There is also research suggesting that children in inappropriate restraints are at significantly increased risk of head injury,[22] one of the authors of this research has been quoted as claiming that "The early graduation of kids into adult lap and shoulder belts is a leading cause of child-occupant injuries and deaths."[23] As a result of such findings, many jurisdictions now advocate or require child passengers to use specially designed child restraints. Such systems include separate child-sized seats with their own restraints and booster cushions for children using adult restraints. In some jurisdictions children below a certain size are forbidden to travel in front car seats."[24]

In rear seats

In 1955 (as a 1956 package) Ford offered lap only seat belts in the rear seats as an option within the Lifeguard safety package. In 1967 Volvo started to install lap belts in the rear seats. In 1972 Volvo upgraded the rear seat belts to a three point belt.[25]

In crashes, unbelted rear passengers increase the risk of belted front seat occupants' death by nearly five times.[26][27]

Reminder chime and light

11 ceintures.jpg

In North America, cars sold since the early 1970s have included an audiovisual reminder system consisting of a light on the dashboard and a buzzer or chime reminding the driver and passengers to fasten their belts. Originally, these lights were accompanied by a warning buzzer whenever the transmission was in any position except park if either the driver was not buckled up or, as determined by a pressure sensor in the passenger's seat, if there was a passenger there not buckled up. However, this was considered by many to be a major annoyance, as the light would be on and the buzzer would sound continuously if front-seat passengers were not buckled up. Therefore, people who did not wish to buckle up would defeat this system by fastening the seatbelts with the seat empty and leaving them that way.

By the mid-1970s, auto manufacturers modified the system so that a warning buzzer would sound for several seconds before turning off (with the warning light), regardless of whether the car was started. However, if the driver was buckled up, the light would appear, but with no buzzer. New cars sold in the United States in 1974 and the first part of the 1975 model year were sold with a special "ignition interlock", whereby the driver could not start the car until the seat belt was fastened; however, this system was short-lived.

Today, the belt warning light may stay on for several minutes after the car is started if the driver's seat belt is not fastened.

In Europe and some other parts of the world, most modern cars include a seat-belt reminder light for the driver and some also include a reminder for the passenger, when present, activated by a pressure sensor under the passenger seat. A Swedish study showed that of the cars with seat belt reminder 8 of 10 drivers not using the seat belts were driving an Audi.[28]

Some cars will intermittently flash the reminder light and sound the chime until the driver (and sometimes the front passenger, if present) fasten their seatbelts, and they sometimes even lock the speed to 10 km/h or less.

Legislation

Observational studies of car crash morbidity and mortality,[29][30][31] experiments using both crash test dummies and human cadavers indicate that wearing seat belts greatly reduces the risk of death and injury in the majority of car crashes.

This has led many countries to adopt mandatory seat belt wearing laws. It is generally accepted that, in comparing like-for-like accidents, a vehicle occupant not wearing a properly fitted seat belt has a significantly and substantially higher chance of death and serious injury. One large observation studying using US data showed that the odds ratio of crash death is 0.46 with a three-point belt, when compared with no belt.[32] In another study that examined injuries presenting to the ER pre- and post-seat belt law introduction, it was found that 40% more escaped injury and 35% more escaped mild and moderate injuries.[33]

The effects of seat belt laws are disputed by those who observe that their passage did not reduce road fatalities. There was also concern that instead of legislating for a general protection standard for vehicle occupants, laws that required a particular technical approach would rapidly become dated as motor manufacturers would tool up for a particular standard which could not easily be changed. For example, in 1969 there were competing designs for lap and 3-point seat belts, rapidly-tilting seats, and air bags being developed. But as countries started to mandate seat belt restraints the global auto industry invested in the tooling and standardized exclusively on seat belts, and ignored other restraint designs such as air bags for several decades[34]

Risk compensation

Some have proposed that the number of deaths was influenced by the development of risk compensation, which says that drivers adjust their behavior in response to the increased sense of personal safety wearing a seat belt provides.

In one trial subjects were asked to drive go-karts around a track under various conditions. It was found that subjects who started driving unbelted drove consistently faster when subsequently belted.[35] Similarly, a study of habitual non-seatbelt wearers driving in freeway conditions found evidence that they had adapted to seatbelt use by adopting higher driving speeds and closer following distances.[36] Similar responses have been shown in respect of anti-lock braking system, airbags, and, more recently, the electronic stability control system.

A 2001 analysis of US crash data aimed to establish the effects of seatbelt legislation on driving fatalities[37] and found that previous estimates of seatbelts effectiveness had been significantly overstated. According to the analysis used, seatbelts were claimed to have decreased fatalities by 1.35% for each 10% increase in seatbelt use. The study controlled for endogenous motivations of seat belt use, which it is claimed creates an artificial correlation between seat belt use and fatalities, leading to the conclusion that seatbelts cause fatalities. For example, drivers in high risk areas are more likely to use seat belts, and are more likely to be in accidents, creating a non-causal correlation between seatbelt use and mortality. After accounting for the endogeneity of seatbelt usage, Cohen and Einav found no evidence that the risk compensation effect makes seatbelt wearing drivers more dangerous, a finding at variance with other research.

Increased traffic

Other statistical analyses have included adjustments for factors such as increased traffic, and other factors such as age, and based on these adjustments, a reduction of morbidity and mortality due to seat belt use has been claimed.[29] However, Smeed's law predicts a fall in accident rate with increasing car ownership and has been demonstrated independently of seat belt legislation.

Use in vehicles other than cars

Buses

Pros[38][39] and cons[40][41][42][43] had been alleged about the use of seatbelts in school buses. See also Seat belts in school buses.

In the European Union, all new long distance buses and coaches must be fitted with seat belts.[44]

Trains

Use of seatbelts in trains has been investigated. Concerns about survival space intrusion in train crashes and increase of injuries to unrestrained or incorrectly restrained passengers led the researches to discourage the use of seat belts in trains.

It has been shown that there is no net safety benefit for passengers who choose to wear 3-point restraints on passenger carrying rail vehicles. Generally passengers who choose not to wear restraints in a vehicle modified to accept 3-point restraints receive marginally more severe injuries.[45]

Airplanes

The "Father of Crash Survivability", Hugh De Haven, was a plane pilot. His interest in crash survivability was sparked by his surviving a plane crash during the First World War.

See also

References

  1. ↑ "Volvo Cars airbag celebrates 20 years". Volvoclub.org.uk. 2007-05-26. http://www.volvoclub.org.uk/press/releases/2007/20_years_air_bags.shtml. Retrieved 2009-08-29. 
  2. ↑ Allt om Motor: Trepunktsbältet 50 år
  3. ↑ Federal Motor Vehicle Safety Standards; Occupant Crash Protection. Final Rule
  4. ↑ Karlsson v. Ford Motor Co., 140 Cal. App. 4th 1202 (2006).
  5. ↑ Autoliv Inc - What we do - Seatbelts
  6. ↑ The first seat offered in the U.S. that incorporated a three-point belt—on the 1990 Mercedes-Benz SL—
  7. ↑ It's a seat belt praised in several internal GM memos obtained by the 11 News Defenders that say this different belt system "improves safety performance", "occupant retention", "rollover protection" and works "for all size occupants in all seat positions". This lap and shoulder belt system looks just like the old one, but for one obvious difference -- this lap and shoulder belt attaches not to the frame of the vehicle but to the seat.
  8. ↑ Bob Lange, executive director of safety integration for General Motors Corp...concurred that such seats cost more to build but, interestingly, don't boost safety ratings. "We were hoping to record a [safety] performance improvement, but it didn't happen," Lange said. "We found we could provide the same level of protection with a body-mounted belt."
  9. ↑ default - Concept Cars - Volvo Models - www.volvocars.com/intl
  10. ↑ 3+2 Point Seatbelt and Side-Support Airbag, from Autoliv
  11. ↑ 11.0 11.1 Ford researches possible next-generation safety belt technology
  12. ↑ TIME magazine article on issue about Earnhardt
  13. ↑ Andréasson, Rune; Claes-Göran Bäckström (2000.). The Seat Belt : Swedish Research and Development for Global Automotive Safety. Stockholm: Kulturvårdskommittén Vattenfall AB. p. 12. ISBN 91-630-9389-8. 
  14. ↑ HMRI News
  15. ↑ PREVENTION, THE ONLY CURE FOR HEAD INJURIES RESULTING FROM AUTOMOBILE ACCIDENTS, C. Hunter Shelden, M.D., Journal of the American Medical Association, Nov. 5, 1955;159(10):981-986.
  16. ↑ 16.0 16.1 "The man who saved a million lives: Nils Bohlin - inventor of the seat belt - Features, Gadgets & Tech". The Independent. 2009-08-19. http://www.independent.co.uk/life-style/gadgets-and-tech/features/the-man-who-saved-a-million-lives-nils-bohlin--inventor-of-the-seatbelt-1773844.html. Retrieved 2009-12-08. 
  17. ↑ Trollhattan Saab — Saab 9-1, 9-3, 9-4x, 9-5, 9-7x News
  18. ↑ Andréasson, Rune; Claes-Göran Bäckström (2000.). The Seat Belt : Swedish Research and Development for Global Automotive Safety. Stockholm: Kulturvårdskommittén Vattenfall AB. pp. 15–16. ISBN 91-630-9389-8. 
  19. ↑ "A Potted Seat Belt History". Drivers Technology. http://www.driverstechnology.co.uk/seatbelts.htm. 
  20. ↑ "Seat Belt History of the World". God. http://home.vicnet.net.au/~donkeysh/. 
  21. ↑ Adams, John (1995). Risk. London: UCL Press Ltd. University College. ISBN 1857280687. 
  22. ↑ Winston FK, Durbin DR, Kallan MJ, Moll EK (June 2000). "The danger of premature graduation to seat belts for young children". Pediatrics 105 (6): 1179–83. doi:10.1542/peds.105.6.1179. PMID 10835054. http://pediatrics.aappublications.org/cgi/pmidlookup?view=long&pmid=10835054. 
  23. ↑ "Kids at Risk: When Seatbelts are NOT Enough", by Karp H, Reader's Digest (US Edition), November 1999.
  24. ↑ Road Amendment (Isabelle Broadhead Child Restraint Measures) Rules 2010. No. 46. Rule 1. New South Wales Government on NSW legislation website (http://www.legislation.nsw.gov.au), NSW Government.
  25. ↑ Volvocars corporate website
  26. ↑ Ichikawa M, Nakahara S, Wakai S (January 2002). "Mortality of front-seat occupants attributable to unbelted rear-seat passengers in car crashes". Lancet 359 (9300): 43–4. doi:10.1016/S0140-6736(02)07279-3. PMID 11809187. 
  27. ↑ "Unbelted rear passengers 'biggest danger in crash"
  28. ↑ Allt om motor: Åtta av tio utan bälte kör Audi
  29. ↑ 29.0 29.1 Nakahara S, Ichikawa M, Wakai S (2003). "Seatbelt legislation in Japan: high risk driver mortality and seatbelt use". Inj. Prev. 9 (1): 29–32. doi:10.1136/ip.9.1.29. PMID 12642555. 
  30. ↑ Allen S, Zhu S, Sauter C, Layde P, Hargarten S (2006). "A comprehensive statewide analysis of seatbelt non-use with injury and hospital admissions: new data, old problem". Academic emergency medicine : official journal of the Society for Academic Emergency Medicine 13 (4): 427–34. doi:10.1197/j.aem.2005.11.003. PMID 16531597. 
  31. ↑ Bourbeau R, Desjardins D, Maag U, Laberge-Nadeau C (1993). "Neck injuries among belted and unbelted occupants of the front seat of cars". The Journal of trauma 35 (5): 794–9. doi:10.1097/00005373-199311000-00024. PMID 8230348. 
  32. ↑ Bédard M, Guyatt GH, Stones MJ, Hirdes JP (2002). "The independent contribution of driver, crash, and vehicle characteristics to driver fatalities". Accident; analysis and prevention 34 (6): 717–27. doi:10.1016/S0001-4575(01)00072-0. PMID 12371777. 
  33. ↑ Thomas J (1990). "Road traffic accidents before and after seatbelt legislation--study in a district general hospital". Journal of the Royal Society of Medicine 83 (2): 79–81. PMID 2319551. 
  34. ↑ Fenton, John (1969-01024). "Safety Design". The Times. 
  35. ↑ Streff FM, Geller ES (1988). "An experimental test of risk compensation: between-subject versus within-subject analyses". Accident; analysis and prevention 20 (4): 277–87. doi:10.1016/0001-4575(88)90055-3. PMID 3415759. 
  36. ↑ Janssen W (1994). "Seat-belt wearing and driving behavior: an instrumented-vehicle study". Accident; analysis and prevention 26 (2): 249–61. doi:10.1016/0001-4575(94)90095-7. PMID 8198694. 
  37. ↑ 'The Effects of Mandatory Seat Belt Laws on Driving Behavior and Traffic Fatalities' by Alma Cohen and Liran Einav at Harvard Law School
  38. ↑ Spital M, Spital A, Spital R (November 1986). "The compelling case for seat belts on school busses". Pediatrics 78 (5): 928–32. PMID 3763306. 
  39. ↑ Albers AC (2001). "Should there be laws mandating seatbelts in all school busses? Writing for the pro position". MCN Am J Matern Child Nurs 26 (1): 8. doi:10.1097/00005721-200101000-00002. PMID 11198463. http://meta.wkhealth.com/pt/pt-core/template-journal/lwwgateway/media/landingpage.htm?issn=0361-929X&volume=26&issue=1&spage=8. 
  40. ↑ Begley CE, Biddle AK (1988). "Cost-benefit analysis of safety belts in Texas school buses". Public Health Rep 103 (5): 479–85. PMID 3140273. 
  41. ↑ Seat-belts in School Buses?
  42. ↑ Pros, Cons of School Bus Seatbelts
  43. ↑ Garzon DL (2001). "Should there be laws mandating seatbelts in all school buses? Writing for the con position". MCN Am J Matern Child Nurs 26 (1): 9. doi:10.1097/00005721-200101000-00003. PMID 11198464. http://meta.wkhealth.com/pt/pt-core/template-journal/lwwgateway/media/landingpage.htm?issn=0361-929X&volume=26&issue=1&spage=9. 
  44. ↑ "EU law makes seat belts obligatory in long distance buses and coaches". European Public Health Alliance. 2006-07-19. http://www.epha.org/a/1765. Retrieved 6 January 2010. 
  45. ↑ Assessment of three-point passenger restraints (seatbelts) fitted to seats on rail vehicles PDF, page 33

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