Car Airbag Systems explained
An airbag is a vehicle safety device. It is an occupant restraint system consisting of a flexible fabric envelope or cushion designed to inflate rapidly during an automobile collision. Its purpose is to cushion occupants during a crash and provide protection to their bodies when they strike interior objects such as the steering wheel or a window. Modern vehicles may contain multiple airbag modules in various side and frontal locations of the passenger seating positions, and sensors may deploy one or more airbags in an impact zone at variable rates based on the type, angle and severity of impact; the airbag is designed to only inflate in moderate to severe frontal crashes. Airbags are normally designed with the intention of supplementing the protection of an occupant who is correctly restrained with a seatbelt. Most designs are inflated through pyrotechnic means and can only be operated once. Newer side-impact airbag modules consist of compressed air cylinders that are triggered in the event of a side impact vehicle impact.
The first commercial designs were introduced in passenger automobiles during the 1970s with limited success. Broad commercial adoption of airbags occurred in many markets during the late 1980s and early 1990s with a driver airbag, and a front passenger airbag as well on some cars; and many modern vehicles now include four or more units.
Various manufacturers have over time used different terms for airbags. General Motors' first airbag modules, in the 1970s, were marketed as the Air Cushion Restraint System (ACRS). Common terms in North America include nominal role as a supplement to active restraints, i.e., seat belts. Because no action by the vehicle occupant is required to activate or use the airbag, it is considered a passive device. This is in contrast to seat belts, which are considered active devices because the vehicle occupant must act to enable them. Note that this is not related to active and passive safety, which are, respectively, systems designed to prevent accidents in the first place and systems designed to minimize accidents once they occur. For example, the car's Anti-lock Braking System will qualify as an active-safety device while both its seatbelts and airbags will qualify as passive-safety devices. Further terminological confusion can arise from the fact that passive devices and systems — those requiring no input or action by the vehicle occupant — can themselves operate in an active manner; an airbag is one such device. Vehicle safety professionals are generally careful in their use of language to avoid this sort of confusion, though advertising principles sometimes prevent such syntactic caution in the consumer marketing of safety features. In contrast, the aviation safety community uses the terms active and passive in the opposite manner
The airbag specified for automobile use traces it origins to air-filled bladders as early as 1941
Reported in 1951, German engineer Walter Linderer designed an airbag. Linderer filed German patent #896,312 on October 6, 1951 which was issued on November 12, 1953, approximately three months after American John Hetrick was issued U.S. patent #2,649,311 earlier on August 18, 1953.Linderer's airbag was based on a compressed air system, either released by bumper contact or by the driver. Later research during the 1960s proved that compressed air could not blow Linderer's airbag up fast enough for maximum safety, thus making it an impractical system
John W. Hetrick, an industrial engineer and member of the United States Navy, designed the original safety cushion commonly referred to as an airbag. It was designed based on his experiences with compressed air from torpedoes during his service in the navy, as well as a need to provide protection for his family in their automobile during accidents. Hetrick worked with the major American automobile corporations at the time, but they chose not to invest in it.
In Japan, Yasuzaburou Kobori (小堀保三郎) invented an airbag in 1963, on which technology current airbags are based, for which he was awarded patents in 14 countries. He died in 1975 without seeing widespread adoption of airbag systems.
In 1967, a breakthrough occurred in the development of airbag crash sensors when Allen K. Breed invented a mechanically-based ball-in-tube component for crash detection, an electromechanical sensor with a steel ball attached to a tube by a magnet that would inflate an airbag under a 30 milli-second window. Sodium azide instead of compressed air was also used for the first time during inflation. Breed Corporation then marketed this innovation first to Chrysler. A similar "Auto-Ceptor" crash-restraint, developed by Eaton, Yale & Towne Inc. for Ford was soon offered as an automatic safety system in the USA, while the Italian Eaton-Livia company offered a variant with localized air cushions.
As a supplement to seat belts
Airbags for passenger cars were introduced in the United States in the mid-1970s, when seat belt usage rates in the country were quite low. Ford built an experimental fleet of cars with airbags in 1971, followed by General Motors in 1973 on Chevrolet vehicles. The early fleet of experimental GM vehicles equipped with airbags experienced seven fatalities, one of which was later suspected to have been caused by the airbag.
In 1974, GM made the ACRS or "Air Cushion Restraint System" available as a regular production option (RPO code AR3) in full-size Cadillac, Buick and Oldsmobile models. The GM cars from the 1970s equipped with ACRS have a driver side airbag, a driver side knee restraint (which consists of a padded lower dashboard) and a passenger side airbag. The passenger side airbag, protects both front passengers and unlike most newer ones, it integrates a knee cushion, a torso cushion and it also has dual stage deployment which varies depending on the force of the impact. The cars equipped with ACRS have lap belts for all seating positions but they do not have shoulder belts. These were already mandatory equipment in the United States on closed cars without airbags for the driver and outer front passenger seating positions.
The development of airbags coincided with an international interest in automobile safety legislation. Some safety experts advocated a performance-based occupant protection standard rather than a standard mandating a particular technical solution, which could rapidly become outdated and might not be a cost-effective approach. As countries successively mandated seat belt restraints, there was less emphasis placed on other designs for several decades.
As a supplemental restraint (SRS)
The auto industry and research and regulatory communities have moved away from their initial view of the airbag as a seat belt replacement, and the bags are now nominally designated as Supplemental Restraint System (SRS) or Supplemental Inflatable Restraints.
In 1981, Mercedes-Benz introduced the airbag in Germany as an option on its high-end S-Class (W126). In the Mercedes system, the sensors would automatically pre-tension the seat belts to reduce occupant's motion on impact (now a common feature), and then deploy the airbag on impact. This integrated the seat belts and airbag into a restraint system, rather than the airbag being considered an alternative to the seat belt.
In 1987, the Porsche 944 turbo became the first car to have driver and passenger airbags as standard equipment. The Porsche 944 and 944S had this as an available option. The same year also saw the first airbag in a Japanese car, the Honda Legend.
In 1988, Chrysler was the first U.S. company to install standard driver's side air bags They came in six lines of its volume production passenger cars.The following year, Chrysler became the first U.S. auto manufacturer to install driver-side air bags in all its domestic-built automobiles. All versions of the Chrysler minivans came with airbags starting January 1991. In 1992, the Jeep Grand Cherokee became the first SUV with airbags in the market place. Driver and passenger air bags became standard equipment in all Dodge Intrepid, Eagle Vision, and Chrysler Concorde sedans ahead of any regulations.Early 1993 saw the 4-millionth air bag-equipped Chrysler vehicle roll off the assembly line In October 1993, the Dodge Rams became the first pickup trucks with airbags.
In Europe, airbags were almost entirely absent from family cars until the early 1990s. The first European Ford to feature an airbag was the facelifted Escort MK5b in 1992; within a year, the entire Ford range had at least one airbag as standard. By the mid-1990s, European market leaders such as Vauxhall/Opel, Rover, Peugeot, Renault and Fiat had included airbags as at least optional equipment across their model ranges. By the end of the decade, it was very rare to find a mass market car without an airbag, and some late 1990s products, such as the Volkswagen Golf Mk4 also featured side airbags. The Peugeot 306 is one example of European mass market cars evolution starting from early 1993 when most of these new models did not even have a driver's airbag as an option, but by 1999, even side airbags were available on several variants. On the other hand, Audi was late to offer airbag systems on a broader scale, as even to the 1994 model year its popular models did not offer airbags. Instead, the German automaker until then relied solely on its proprietary procon-ten restraint system.
During the 2000s side impact airbags became commonplace on even low to mid-range vehicles, such as the smaller-engined versions of the Ford Fiesta and Peugeot 206, and curtain airbags were also becoming regular features on mass market cars. The Toyota Avensis, launched in 1998, was the first mass market car to be sold in Europe with nine airbags. Although in some countries, such as Russia, airbags are still not standard equipment on all cars, such as those from Lada.
Variable force deployment front airbags were developed to help minimize injury from the airbag itself.
The Citroën C4 provides the first "shaped" driver airbag, made possible by this car's unusual fixed hub steering wheel.
There are essentially two types of side airbags commonly used today, the side torso airbag and the side curtain airbag.
Most vehicles equipped with side curtain airbags also include side torso airbags. However some exceptions such as the Chevrolet Cobalt, 2007-09 model Chevrolet Silverado/GMC Sierra, and 2009-12 Dodge Ram do not feature the side torso airbag.
Side torso airbag
Side-impact airbags or side torso airbags (side thorax/abdomen airbags) are a category of airbag usually located in the seat, and inflate between the seat occupant and the door. These airbags are designed to reduce the risk of injury to the pelvic and lower abdomen regions. Some vehicles are now being equipped with different types of designs, to help reduce injury and ejection from the vehicle in rollover crashes. More recent side airbag designs include a two chamber system; a firmer lower chamber for the pelvic region and softer upper chamber for the ribcage.
The Swedish company Autoliv AB, was granted a patent on side impact airbags, and they were first offered as an option in 1994 on the 1995 model year Volvo 850, and as standard equipment on all Volvo cars made after 1995.
Some cars, such as the 2010 Volkswagen Polo Mk.5 have combined head and torso side airbags. These are fitted in the backrest of the front seats, and protect the head as well as the torso. Side tubular or curtain airbag
In late 1997 the 1998 model year BMW 7-series and E39 5-series were fitted with a tubular shaped head side airbags, the "Head Protection System (HPS)" as standard equipment. This airbag was designed to offer head protection in side impact collisions and also maintained inflation for up to seven seconds for rollover protection. However, this tubular shaped airbag design has been quickly replaced by an inflatable 'curtain' airbag.
In May 1998 Toyota began offering a side curtain airbag deploying from the roof on the Progrés. In 1998 the Volvo S80 was given roof-mounted curtain airbags to protect both front and rear passengers. Curtain airbags were then made standard equipment on all new Volvo cars from 2001 except for the C70. The 2006 model C70 convertible received the world's first door-mounted side-curtain airbags that deployed upwards.
Roll-sensing side curtain airbags found on vehicles more prone to rollovers such as SUVs and pickups will deploy when a rollover is detected instead of just when an actual collision takes place. Often there is a switch to disable the feature in case the driver wants to take the vehicle offroad.
Curtain airbags have been said to reduce brain injury or fatalities by up to 45% in a side impact with an SUV. These airbags come in various forms (e.g., tubular, curtain, door-mounted) depending on the needs of the application. Many recent SUVs and MPVs have a long inflatable curtain airbag that protects all 3 rows of seats.
The second driver's side and separate knee airbag was used in the 1996 model Kia Sportage vehicle and has been standard equipment since then. The airbag is located beneath the steering wheel. The Toyota Avensis became the first vehicle sold in Europe equipped with a driver's knee airbag. The EuroNCAP reported on the 2003 Avensis, "There has been much effort to protect the driver's knees and legs and a knee airbag worked well." Since then certain models have also included front passenger knee airbags, which deploy near or over the glove compartment in a crash. Knee airbags are designed to reduce leg injury. The knee airbag has become increasingly common from 2000.
Rear curtain airbag
In 2008, the Toyota iQ launched featuring the first production rear curtain shield airbag to protect the rear occupants' heads in the event of a rear end impact.
In 2008 the Toyota iQ added a seat cushion airbag in the passenger seat. This is to prevent the pelvis from diving below the lap belt during a frontal impact or submarining . Later Toyota models such as the Yaris added the feature to the driver's seat as well.
In 2009, Toyota developed the first production rear-seat center airbag designed to reduce the severity of secondary injuries to rear passengers in a side collision. This system deploys from the rear center seat first appearing in on the redesigned Crown Majesta.In late 2012 General Motors with supplier Takata introduced a front center airbag, it deploys from the driver's seat.
In 2009, the S-class ESF safety concept car showcased seatbelt airbags. They were included in the 2010 Lexus LFA. Starting in 2011, Ford Explorer had optional rear seatbelt airbags, as well as available at at extra cost on the 2013 Ford Flex and they were standard on the 2013 Lincoln MKT. Cessna Aircraft also introduced seatbelt airbags. They are now standard on the 172, 182, and 206.
Introduced in 2012 the Volvo V40 included the first pedestrian airbag, the V40 ranked highest (88%) in the EuroNCAP's pedestrian tests
Types of airbags were tested on motorcycles by the UK Transport Research Laboratory in the mid-1970s. In 2006 Honda introduced the first production motorcycle airbag safety system on its Gold Wing motorcycle. Honda claims that sensors in the front forks can detect a severe frontal collision and decide when to deploy the airbag, absorbing some of the forward energy of the rider and reducing the velocity at which the rider may be thrown from the motorcycle.
Airbag suits have also been developed for use by Motorcycle Grand Prix riders. In their earlier form, they were connected to the motorcycle by a cable and deployed when the cable became detached from its mounting clip, inflating to protect the back of the rider. The French manufacturer, Helite, specializes exclusively in developing airbag jackets for motorcyclists, snowmobile riders and horseback riders. Further developments were conducted by Dainese and led to an autonomous system on board the leathers, without a cable connected to the bike. Instead, an electronic system detects a fall and triggers the inflation of the nitrogen airbags to protect the rider's upper body.
How airbags work
The design is conceptually simple; a central "Airbag control unit" (ACU) (a specific type of ECU) monitors a number of related sensors within the vehicle, including accelerometers, impact sensors, side (door) pressure sensors, wheel speed sensors, gyroscopes, brake pressure sensors, and seat occupancy sensors. When the requisite 'threshold' has been reached or exceeded, the airbag control unit will trigger the ignition of a gas generator propellant to rapidly inflate a fabric bag. As the vehicle occupant collides with and squeezes the bag, the gas escapes in a controlled manner through small vent holes. The airbag's volume and the size of the vents in the bag are tailored to each vehicle type, to spread out the deceleration of (and thus force experienced by) the occupant over time and over the occupant's body, compared to a seat belt alone.
The signals from the various sensors are fed into the Airbag control unit, which determines from them the angle of impact, the severity, or force of the crash, along with other variables. Depending on the result of these calculations, the ACU may also deploy various additional restraint devices, such as seat belt pre-tensioners, and/or airbags (including frontal bags for driver and front passenger, along with seat-mounted side bags, and "curtain" airbags which cover the side glass). Each restraint device is typically activated with one or more pyrotechnic devices, commonly called an initiator or electric match. The electric match, which consists of an electrical conductor wrapped in a combustible material, activates with a current pulse between 1 to 3 amperes in less than 2 milliseconds. When the conductor becomes hot enough, it ignites the combustible material, which initiates the gas generator. In a seat belt pre-tensioner, this hot gas is used to drive a piston that pulls the slack out of the seat belt. In an airbag, the initiator is used to ignite solid propellant inside the airbag inflator. The burning propellant generates inert gas which rapidly inflates the airbag in approximately 20 to 30 milliseconds. An airbag must inflate quickly in order to be fully inflated by the time the forward-traveling occupant reaches its outer surface. Typically, the decision to deploy an airbag in a frontal crash is made within 15 to 30 milliseconds after the onset of the crash, and both the driver and passenger airbags are fully inflated within approximately 60-80 milliseconds after the first moment of vehicle contact. If an airbag deploys too late or too slowly, the risk of occupant injury from contact with the inflating airbag may increase. Since more distance typically exists between the passenger and the instrument panel, the passenger airbag is larger and requires more gas to fill it.
Older airbag systems contained a mixture of sodium azide (NaN3), KNO3, and SiO2. A typical driver-side airbag contains approximately 50-80 g of NaN3, with the larger passenger-side airbag containing about 250 g. Within about 40 milliseconds of impact, all these components react in three separate reactions that produce nitrogen gas. The reactions, in order, are as follows.
(1) 2 NaN3 → 2 Na + 3 N2 (g)
(2) 10 Na + 2 KNO3 → K2O + 5 Na2O + N2 (g)
(3) K2O + Na2O + 2 SiO2 → K2O3Si + Na2O3Si (silicate glass)
The first reaction is the decomposition of NaN3 under high temperature conditions using an electric impulse. This impulse generates to 300°C temperatures required for the decomposition of the NaN3 which produces Na metal and N2 gas. Since Na metal is highly reactive, the KNO3 and SiO2 react and remove it, in turn producing more N2 gas. The second reaction shows just that. The reason that KNO3 is used rather than something like NaNO3 is because it is less hygroscopic. It is very important that the materials used in this reaction are not hygroscopic because absorbed moisture can de-sensitize the system and cause the reaction to fail. The final reaction is used to eliminate the K2O and Na2O produced in the previous reactions because the first-period metal oxides are highly reactive. These products react with SiO2 to produce a silicate glass which is a harmless and stable compound.
According to a patent, the particle size of the sodium azide, potassium nitrate, and silicon dioxide are important. The NaN3 and KNO3 must be between 10 and 20 microns, while the SiO2 must be between 5 and 10 microns.
There has been a recent effort to find alternative compounds that can be used in airbags which have less toxic byproducts. In a journal article by Akiyoshi et. Al., it was found that for the reaction of the Sr complex nitrate, (Sr(NH2NHCONHNH2)∙(NO3)2 of carbohydrazide (SrCDH) with various oxidizing agents resulted in the evolution of N2 and CO2 gases. Using KBrO3 as the oxidizing agent resulted in the most vigorous reaction as well as the lowest initial temperature of reaction. The N2 and CO2 gases evolved made up 99% of all gases evolved. Nearly all the starting materials won’t decompose until reaching temperatures of 500°C or higher so this could be a viable option as an air bag gas generator. In a patent containing another plausible alternative to NaN3 driven airbags, the gas generating materials involved the use of guanidine nitrate, 5-amino tetrazole, bitetrazole dehydrate, nitroimidazole, and basic copper nitrate. It was found that these non-azide reagents allowed for a less toxic, lower combustion temperature reaction and more easily disposable air bag inflation system
Front airbags normally do not protect the occupants during side, rear, or rollover accidents.Since airbags deploy only once and deflate quickly after the initial impact, they will not be beneficial during a subsequent collision. Safety belts help reduce the risk of injury in many types of crashes. They help to properly position occupants to maximize the airbag's benefits and they help restrain occupants during the initial and any following collisions.
In vehicles equipped with a rollover sensing system, accelerometers and gyroscopes are used to sense the onset of a rollover event. If a rollover event is determined to be imminent, side-curtain airbags are deployed to help protect the occupant from contact with the side of the vehicle interior, and also to help prevent occupant ejection as the vehicle rolls over.
Airbags are designed to deploy in frontal and near-frontal collisions more severe than a threshold defined by the regulations governing vehicle construction in whatever particular market the vehicle is intended for: U.S. regulations require deployment in crashes at least equivalent in deceleration to a 23 km/h (14 mph) barrier collision, or similarly, striking a parked car of similar size across the full front of each vehicle at about twice the speed. International regulations are performance based, rather than technology-based, so airbag deployment threshold is a function of overall vehicle design.
Unlike crash tests into barriers, real-world crashes typically occur at angles other than directly into the front of the vehicle, and the crash forces usually are not evenly distributed across the front of the vehicle. Consequently, the relative speed between a striking and struck vehicle required to deploy the airbag in a real-world crash can be much higher than an equivalent barrier crash. Because airbag sensors measure deceleration, vehicle speed is not a good indicator of whether an airbag should have deployed. Airbags can deploy due to the vehicle's undercarriage striking a low object protruding above the roadway due to the resulting deceleration.
The airbag sensor is a MEMS accelerometer, which is a small integrated circuit with integrated micro mechanical elements. The microscopic mechanical element moves in response to rapid deceleration, and this motion causes a change in capacitance, which is detected by the electronics on the chip that then sends a signal to fire the airbag. The most common MEMS accelerometer in use is the ADXL-50 by Analog Devices, but there are other MEMS manufacturers as well.
Initial attempts using mercury switches did not work well. Before MEMS, the primary system used to deploy airbags was called a "rolamite". A rolamite is a mechanical device, consisting of a roller suspended within a tensioned band. As a result of the particular geometry and material properties used, the roller is free to translate with little friction or hysteresis. This device was developed at Sandia National Laboratories. The rolamite, and similar macro-mechanical devices were used in airbags until the mid-1990s when they were universally replaced with MEMS.
Nearly all airbags are designed to automatically deploy in the event of a vehicle fire when temperatures reach 150-200 °C (300-400 °F). This safety feature, often termed auto-ignition, helps to ensure that such temperatures do not cause an explosion of the entire airbag module.
Today, airbag triggering algorithms are becoming much more complex. They try to reduce unnecessary deployments and to adapt the deployment speed to the crash conditions. The algorithms are considered valuable intellectual property. Experimental algorithms may take into account such factors as the weight of the occupant, the seat location, seatbelt use, and even attempt to determine if a baby seat is present.
When the frontal airbags are to deploy, a signal is sent to the inflator unit within the airbag control unit. An igniter starts a rapid chemical reaction generating primarily nitrogen gas (N2) to fill the airbag making it deploy through the module cover. Some airbag technologies use compressed nitrogen or argon gas with a pyrotechnic operated valve ("hybrid gas generator"), while other technologies use various energetic propellants. Propellants containing the highly toxic sodium azide (NaN3) were common in early inflator designs, little to no toxic sodium azide has been found on used airbags.
The azide-containing pyrotechnic gas generators contain a substantial amount of the propellant. The driver-side airbag would contain a canister containing about 50 grams of sodium azide. The passenger side container holds about 200 grams of sodium azide.
The alternative propellants may incorporate, for example, a combination of nitroguanidine, phase-stabilized ammonium nitrate (NH4NO3) or other nonmetallic oxidizer, and a nitrogen-rich fuel different than azide (e.g. tetrazoles, triazoles, and their salts). The burn rate modifiers in the mixture may be an alkaline metal nitrate (NO3-) or nitrite (NO2-), dicyanamide or its salts, sodium borohydride (NaBH4), etc. The coolants and slag formers may be e.g. clay, silica, alumina, glass, etc. Other alternatives are e.g. nitrocellulose based propellants (which have high gas yield but bad storage stability, and their oxygen balance requires secondary oxidation of the reaction products to avoid buildup of carbon monoxide), or high-oxygen nitrogen-free organic compounds with inorganic oxidizers (e.g., di or tricarboxylic acids with chlorates (ClO3-) or perchlorates (ClO4-) and eventually metallic oxides; the nitrogen-free formulation avoids formation of toxic nitrogen oxides).
From the onset of the crash, the entire deployment and inflation process is about 0.04 seconds. Because vehicles change speed so quickly in a crash, airbags must inflate rapidly to reduce the risk of the occupant hitting the vehicle's interior.
Advanced airbag technologies are being developed to tailor airbag deployment to the severity of the crash, the size and posture of the vehicle occupant, belt usage, and how close that person is to the actual airbag. Many of these systems use multi-stage inflators that deploy less forcefully in stages in moderate crashes than in very severe crashes. Occupant sensing devices let the airbag control unit know if someone is occupying a seat adjacent to an airbag, the mass/weight of the person, whether a seat belt or child restraint is being used, and whether the person is forward in the seat and close to the airbag. Based on this information and crash severity information, the airbag is deployed at either at a high force level, a less forceful level, or not at all.
Adaptive airbag systems may utilize multi-stage airbags to adjust the pressure within the airbag. The greater the pressure within the airbag, the more force the airbag will exert on the occupants as they come in contact with it. These adjustments allow the system to deploy the airbag with a moderate force for most collisions; reserving the maximum force airbag only for the severest of collisions. Additional sensors to determine the location, weight or relative size of the occupants may also be used. Information regarding the occupants and the severity of the crash are used by the airbag control unit, to determine whether airbags should be suppressed or deployed, and if so, at various output levels.
A chemical reaction produces a burst of nitrogen to inflate the bag. Once an airbag deploys, deflation begins immediately as the gas escapes through vent(s) in the fabric (or, as it's sometimes called, the cushion) and cools. Deployment is frequently accompanied by the release of dust-like particles, and gases in the vehicle's interior (called effluent). Most of this dust consists of cornstarch, french chalk, or talcum powder, which are used to lubricate the airbag during deployment.
Newer designs produce effluent primarily consisting of harmless talcum powder/cornstarch and nitrogen gas. In older designs using an azide-based propellant (usually NaN3), varying amounts of sodium hydroxide nearly always are initially present. In small amounts this chemical can cause minor irritation to the eyes and/or open wounds; however, with exposure to air, it quickly turns into sodium bicarbonate (baking soda). However, this transformation is not 100% complete, and invariably leaves residual amounts of hydroxide ion from NaOH. Depending on the type of airbag system, potassium chloride may also be present.
For most people, the only effect the dust may produce is some minor irritation of the throat and eyes. Generally, minor irritations only occur when the occupant remains in the vehicle for many minutes with the windows closed and no ventilation. However, some people with asthma may develop a potentially lethal asthmatic attack from inhaling the dust.
The dust-like particles and gases can cause irreparable cosmetic damage to the dashboard and upholstery, so minor collisions which result in the deployment of airbags can be costly accidents, even if there are no injuries and there is only minor damage to the vehicle exterior.
On 11 July 1984, the U.S. government amended Federal Motor Vehicle Safety Standard 208 (FMVSS 208) to require cars produced after 1 April 1989 to be equipped with a passive restraint for the driver. An airbag or a seat belt would meet the requirements of the standard. Airbag introduction was stimulated by the U.S. National Highway Traffic Safety Administration. However, airbags were not mandatory on light trucks until 1997.
In 1998, FMVSS 208 was amended to require dual front airbags, and de-powered, or second-generation airbags were also mandated. This was due to the injuries caused by first-generation airbags, though FMVSS 208 continues to require that bags be engineered and calibrated to be able to "save" the life of an unbelted 50th-percentile size and weight "male" crash test dummy.
Outside the U.S.A.
Some countries outside North America adhere to internationalized European ECE vehicle and equipment regulations rather than the U.S. Federal Motor Vehicle Safety Standards. ECE airbags are generally smaller and inflate less forcefully than U.S. airbags, because the ECE specifications are based on belted crash test dummies. In the United Kingdom, and most other developed countries there is no direct legal requirement for new cars to feature airbags. Instead, the Euro NCAP vehicle safety rating encourages manufacturers to take a comprehensive approach to occupant safety; a good rating can only be achieved by combining airbags with other safety features. Thus almost all new cars now come with at least two airbags as standard.
Inadvertent airbag deployment while the vehicle is being serviced can result in severe injury, and an improperly installed or defective airbag unit may not operate or perform as intended. Some countries impose restrictions on the sale, transport, handling, and service of airbags and system components. In Germany, airbags are regulated as harmful explosives; only mechanics with special training are allowed to service airbag systems.
Some automakers (such as Mercedes-Benz) call for the replacement of undeployed airbags after a certain period of time to ensure their reliability in an accident. One example is the 1992 S500 which has an expiry date sticker attached to the door pillar. Some Škoda vehicles say 14 years from the date of manufacture. In this case replacement would be uneconomic as the car would have negligible value at 14 years old, far less than the cost of fitting new airbags. Volvo, on the other hand, has stated "airbags do not require replacement during the lifetime of the vehicle," though this cannot be taken as a guarantee on the device.
Injuries and fatalities
Under some rare conditions, airbags can injure and in some very rare instances kill vehicle occupants. To provide crash protection for occupants not wearing seat belts, U.S. airbag designs trigger much more forcefully than airbags designed to the international ECE standards used in most other countries. Recent airbag controllers can recognize if a belt is used, and alter the airbag cushion deployment parameters accordingly.
In 1990, the first automotive fatality attributed to an airbag was reported. TRW produced the first gas-inflated airbag in 1994, with sensors and low-inflation-force bags becoming common soon afterwards. Dual-depth (also known as dual-stage) airbags appeared on passenger cars in 1998. By 2005, deaths related to airbags had declined, with no adult deaths and two child deaths attributed to airbags that year. Injuries remain fairly common in accidents with an airbag deployment.
Serious injuries are less common, but severe or fatal injuries can occur to vehicle occupants very near an airbag or in direct contact when it deploys. Such injuries may be sustained by unconscious drivers slumped over the steering wheel, unrestrained or improperly restrained occupants who slide forward in the seat during pre-crash braking, and properly belted drivers sitting very close to the steering wheel. A good reason for the driver not to cross hands on the steering wheel, a rule taught to most learner drivers but quickly forgotten by most, is that an airbag deployment while negotiating a turn may result in the driver's hand(s) being driven forcefully into his or her face, exacerbating any injuries from the airbag alone.
Improvements in sensing and gas generator technology have allowed the development of third generation airbag systems that can adjust their deployment parameters to size, weight, position and restraint status of the occupant. These improvements have demonstrated a reduced injury risk factor for small adults and children who had an increased risk of injury with first generation airbag systems.
Airbag fatality statistics
From 1990 to 2000, the U.S. National Highway Traffic Safety Administration identified 175 fatalities caused by air bags. Most of these (104) have been children, while the rest are adults. About 3.3 million air bag deployments have occurred and the agency estimates more than 6,377 lives saved and countless injuries prevented.
A rear-facing infant restraint put in the front seat of a vehicle places an infant's head close to the airbag, which can cause severe head injuries, or death if the airbag deploys. Some modern cars include a switch to disable the front passenger airbag (although not in Australia, where rear-facing child seats are prohibited in the front where an airbag is fitted), in case a child-supporting seat is used there.
In vehicles with side airbags, it is dangerous for occupants to lean against the windows, doors, and pillars, or to place objects between themselves and the side of the vehicle. Articles hung from a vehicle's clothes hanger hooks can be hazardous if the vehicle's side curtain airbags deploy. A seat-mounted airbag may also cause internal injury if the occupant leans against the door.