Seat belt
A seat belt or seatbelt, also known as a safety belt, is a vehicle safety device designed to secure the driver or a passenger of a vehicle against harmful movement that may result during a collision or a sudden stop. A seat belt reduces the likelihood of death or serious injury in a traffic collision by reducing the force of secondary impacts with interior strike hazards, by keeping occupants positioned correctly for maximum effectiveness of the airbag, and by preventing occupants being ejected from the vehicle in a crash or if the vehicle rolls over.
When in motion, the driver and passengers are traveling at the same speed as the vehicle. If the vehicle suddenly halts or crashes, the occupants continue at the same speed the vehicle was going before it stopped. A seat belt applies an opposing force to the driver and passengers to prevent them from falling out or making contact with the interior of the car. Seat belts are considered primary restraint systems, because of their vital role in occupant safety.
Effectiveness
An analysis conducted in the United States in 1984 compared a variety of seat belt types alone and in combination with air bags. The range of fatality reduction for front seat passengers was broad, from 20% to 55%, as was the range of major injury, from 25% to 60%. More recently, the Centers for Disease Control and Prevention has summarized these data by stating "seat belts reduce serious crash-related injuries and deaths by about half." Most malfunctions are a result of there being too much slack in the seat belt at the time of the accident.In case of vehicle rollover in a U.S. passenger car or SUV, from 1994 to 2004, wearing a seat belt reduced the risk of fatalities or incapacitating injuries and increased the probability of no injury:
- In case of vehicle rollover in a U.S. passenger car, there are % fatalities in 1994 and % in 2014 when user is restrained. There are % fatalities in 1994 and % in 2014 when the user is unrestrained.
- In case of vehicle rollover, there are % incapacitating injury in 1994 and % in 2014 when the user is restrained. There are % incapacitating injury in 1994 and % in 2014 when user is unrestrained.
- The probability of no injury is % in 1994 and % in 2014 when the user is restrained. There were % no injury in 1994 and % in 2014 when the user is unrestrained.
History
Seat belts were invented by English engineer George Cayley, to use on his glider, in the mid-19th century.By 1928, all aircraft were required to have them.
Nash was the first American car manufacturer to offer seat belts as a factory option, in its 1949 models. They were installed in 40,000 cars, but buyers did not want them and requested that dealers remove them. The feature was "met with insurmountable sales resistance" and Nash reported that after one year "only 1,000 had been used" by customers.
Ford offered seat belts as an option in 1955. These were not popular, with only 2% of Ford buyers choosing to pay for seat belts in 1956.
In the early 1950s C. Hunter Shelden, a neurologist working at the Huntington Memorial Hospital in Pasadena, California, studied the high number of head injuries he saw due to auto accidents. Based on his study of the early seat belts whose primitive designs were implicated in these injuries and deaths, in a 1955 paper he proposed retractable seat belts, as well as recessed steering wheels, reinforced roofs, roll bars, and passive restraints such as air bags.
Glenn W. Sheren, of Mason, Michigan, submitted a patent application on March 31, 1955, for an automotive seat belt and was awarded in 1958. This was a continuation of an earlier patent application that Sheren had filed on September 22, 1952.
The first modern three-point seat belt commonly used in consumer vehicles was patented in 1955 by the Americans Roger W. Griswold and Hugh DeHaven.
Saab introduced seat belts as standard equipment in 1958. 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.
Vattenfall, the Swedish national electric utility, did a study of all fatal, on-the-job accidents among their employees. The study revealed that the majority of fatalities occurred while the employees were on the road on company business. In response, two Vattenfall safety engineers, Bengt Odelgard and Per-Olof Weman, started to develop a seat belt. Their work was presented to Swedish manufacturer Volvo in the late 1950s, and set the standard for seat belts in Swedish cars. The three-point seat belt was developed to its modern form by Swedish inventor Nils Bohlin for Volvo, which introduced it in 1959 as standard equipment. In addition to designing an effective three-point belt, Bohlin demonstrated its effectiveness in a study of 28,000 accidents in Sweden. Unbelted occupants sustained fatal injuries throughout the whole speed scale, whereas none of the belted occupants was fatally injured at accident speeds below 60 mph. No belted occupant was fatally injured if the passenger compartment remained intact. Bohlin was granted for the device.
Subsequently, in 1966, Congress passed the National Traffic and Motor Vehicle Safety Act, requiring all automobiles to comply with certain safety standards.
The first compulsory seat belt law was put in place in 1970, in the state of Victoria, Australia, requiring their use by drivers and front-seat passengers. This legislation was enacted after trialing Hemco seat belts, designed by Desmond Hemphill, in the front seats of police vehicles, lowering the incidence of officer injury and death. Mandatory seat belt laws in the United States began to be introduced in the 1980s and faced opposition, with some consumers going to court to challenge the laws. Some cut seat belts out of their cars.
Material
The 'belt' part of the typical seatbelt seen in vehicles worldwide is referred to as the 'webbing'. Modern seat belt webbing has a high tensile strength, about, to resist tearing at high loads such as during high-speed collisions or while restraining larger passengers.While nylon was used in some early seat belts, it was replaced by 100% polyester due to its better UV resistance, lower extensibility and higher stiffness. Nylon was also prone to stretching much more than polyester, and was prone to wear and tear, with tiny abrasions drastically reducing tensile strength, causing a lack of reliability in one of the most important safety measures in a vehicle. Seat belts are commonly 46 or 48 mm wide with a 2/2 herringbone twill weaving pattern to maximize the thread density. Modern seatbelt weaves also feature snag-proof selvedges reinforced with strong polyester threads to prevent the wear and tear, while remaining flexible. The weave features about 300 warp threads for every 46mm wide webbing, leading to around 150 ends per inch of webbing.
Accident investigators often examine the webbing of a seatbelt to determine if an occupant of a vehicle was wearing their seatbelt during a collision. The material of the webbing may contain traces of the occupant's clothing. Certain materials such as nylons may become permanently affixed or melted onto the fabric as a result of heat produced by friction, whereas fiber-based clothing leaves no remains on modern webbing.
Types
Two-point airplane seat belts
An airplane seat belt is designed to protect from up and down movement and to keep passengers in their seats during turbulence or collisions on the runway. A simple strap was first used March 12, 1910, by pilot Benjamin Foulois, a pioneering aviator with the Aeronautical Division, U.S. Signal Corps, so he might remain at the controls during turbulence.While lap belts are exceedingly rare to spot in modern cars, they are the standard in commercial airliners. The lift-lever style of commercial aircraft buckles allows for the seatbelt to be easily clasped and unclasped, accessible quickly in case of an emergency where a passenger must evacuate, and fulfills the minimum safety requirements provided by the FAA while remaining low-cost to produce. Furthermore, in case of any collision, a passenger in economy class has only around 9 inches for their head to travel forward, meaning restraining the torso and head is relatively unnecessary as the head has little room to accelerate before collision.
Two-point land seat belts
A two-point belt attaches at its two endpoints, land vehicles move typically in a forward or backward or sideways motion, because they generally stay on the ground, and need a shoulder belt. The Irvin Air Chute Company made the seat belt for use by professional race car driver Barney Oldfield when his team decided the daredevil should have a "safety harness" for the 1923 Indianapolis 500.Lap belt
A lap belt is a strap that goes over the waist. This was the most common type of belt prior to legislation requiring three-point belts and is found in older cars. Coaches are equipped with lap belts, as are passenger aircraft seats.University of Minnesota professor James J. "Crash" Ryan was the inventor of, and held the patent for, the automatic retractable lap safety belt. Ralph Nader cited Ryan's work in Unsafe at Any Speed and, following hearings led by Senator Abraham Ribicoff, President Lyndon Johnson signed two bills in 1966 requiring safety belts in all passenger vehicles starting in 1968.
Until the 1980s, three-point belts were commonly available only in the front outboard seats of cars; the back seats were often only fitted with lap 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 the progressive revision of passenger safety regulations in nearly all developed countries to require three-point belts, first in all outboard seating positions, and eventually in all seating positions in passenger vehicles. Since September 1, 2007, all new cars sold in the U.S. require a lap and shoulder belt in the center rear seat. In addition to regulatory changes, "seat belt syndrome" has led to a liability for vehicle manufacturers. One Los Angeles case resulted in a $45 million jury verdict against Ford; the resulting $30 million judgment was affirmed on appeal in 2006.