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{{About|a car safety device}}

An '''airbag''' is a [[Automobile safety|vehicle safety]] device. It is an occupant restraint consisting of a flexible envelope designed to inflate rapidly during an automobile [[collision]], to prevent occupants from striking interior objects such as the steering wheel or a window.  Modern [[vehicle]]s may contain multiple airbags 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 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.

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.

==Terminology==
Various manufacturers have over time used different terms for airbags. [[General Motors Corporation|General Motors']] first bags, in the 1970s, were marketed as the ''Air Cushion Restraint System (ACRS)''. Common terms in North America include ''Supplemental Restraint System (SRS)'' and ''Supplemental Inflatable Restraint (SIR)''; these terms reflect the airbag system's 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 belt]]s, which are considered ''active'' devices because the vehicle occupant must act to enable them.<ref>{{cite web|url=http://jhppl.dukejournals.org/cgi/content/abstract/8/1/44 |title=Bags, Buckles, and Belts: The Debate over Mandatory Passive Restraints in Automobiles |doi=10.1215/03616878-8-1-44 |publisher=Jhppl.dukejournals.org |date= |accessdate=2010-10-17}}</ref><ref>{{cite web|url=http://www.motorvista.com/airhist.htm |title=U.S. air bag history |publisher=Motorvista.com |date= |accessdate=2010-10-17}}</ref><ref>{{cite web|url=http://www.patentstorm.us/patents/6272412/description.html |title=U.S. patent 6272412 - Passive restraint control system for vehicles |publisher=Patentstorm.us |date= |accessdate=2010-10-17}}</ref><ref>[http://www.consumerlawpage.com/article/seatbelt.shtml Passive Seatbelt Systems and the 65 MPH Speed Limit: A Cause for Concern]{{dead link|date=August 2011}}</ref><ref>{{cite web|url=http://www.ins.state.ny.us/circltr/1991/cl1991_10.htm |title=New York State memo re insurance discounts for passive restraints |publisher=Ins.state.ny.us |date=1991-04-12 |accessdate=2010-10-17}}{{dead link|date=October 2011}}</ref> Note that this is not related to [[Automobile safety#Active and passive safety|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 [[syntax|syntactic]] caution in the consumer marketing of safety features.

==History==
[[Image:Interior of 1975 Buick Electra.jpg|thumb|right|1975 [[Buick Electra]] with ACRS]]
[[Image:Ford airbag advertisement (1993.11).png|right|thumb|In 1994,
[[Ford Motor Company|Ford of Europe]] made airbags standard equipment in all the cars they built]]

===Invention===
Reported at the 1951 Munich Walter Linderer designed the airbag as a patent. The German Patent Office granted subsequently on 6 October 1951 a patent (Nr. 896312 DE "Einrichtung zum Schutze von in Fahrzeugen befindlichen Personen gegen Verletzungen bei Zusammenstößen"). Walter Linderer is therefore regarded as the inventor of the airbag.

An American inventor, John W. Hetrick, an industrial engineer and member of the U.S. Navy, designed (1952) and patented (1953) 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 U.S. Navy, as well as a need to provide protection for his family in their automobile during accidents.  Mr. Hetrick worked with the major American automobile corporations at the time, but they chose not to invest in it( in 1960s it was found out in studies that compressed air did not inflate airbags fast enough for occupant protection).<ref>[http://www.airbagsolutions.com/history2.aspx Airbag History |Airbag Components |Airbag Whitepapers – Airbag Solutions<!-- Bot generated title -->]</ref><ref>[http://inventors.about.com/od/astartinventions/a/air_bags.htm The History of Airbags<!-- Bot generated title -->]</ref>  Allen K. Breed invented and developed an alternative component for crash detection. Breed Corporation then marketed this innovation first in 1967 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,<ref>[http://blog.modernmechanix.com/category/transportation/automotive/page/34/ Popular Science] May, 1968</ref><ref>{{cite web|url=http://web.mit.edu/invent/iow/breed.html |title=Inventor of the Week: Archive |publisher=Web.mit.edu |date= |accessdate=2010-02-27}}</ref> while the Italian Eaton-Livia company offered a variant with localized air cushions.<ref name=thetimes>Safety Design, John Fenton, ''The Times'' [[Jan 24]] 1969hi :) </ref>

In Japan, [[:ja:小堀保三郎|Yasuzaburou Kobori]] (小堀保三郎) invented an airbag at 1963, on which technology current  airbags are based, for which he was awarded patents in 14 countries. Unfortunately, he died in 1975 without seeing adoption of airbag systems.<ref>[http://www.jahfa.jp/jahfa6/pala/person5-1.htm "Achievements of Yasuzaburou Kobori"] Nonprofit Organization - [[Japan Automotive Hall of Fame]]</ref>

===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 Motor Company|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.<ref>{{cite web|url=http://www.airbagcrash.com/contactusetc.html |title=Gm'S Acrs |publisher=Airbagcrash.com |date=1993-02-07 |accessdate=2010-10-17}}</ref>

In 1974, GM made the ACRS or "Air Cushion Restraint System" available as a regular production option (RPO code AR3) in some full-size Buick, Cadillac<ref>[http://www.oldcarbrochures.com/static/NA/Cadillac/1975_Cadillac/1975_Cadillac_Brochure/1975%20Cadillac-25.html Directory Index: Cadillac/1975_Cadillac/1975_Cadillac_Brochure<!-- Bot generated title -->]</ref> and Oldsmobile models. The GM cars from the 1970s equipped with ACRS have a driver side airbag, a driver side knee restraint<ref name="oldcarbrochures1974">[http://www.oldcarbrochures.com/static/NA/Oldsmobile/1974_Oldsmobile/1974_Oldsmobile_Air_Cushion_Folder/1974%20Oldsmobile%20Air%20Cushion%20Folder-06-07.html Directory Index: Oldsmobile/1974_Oldsmobile/1974_Oldsmobile_Air_Cushion_Folder<!-- Bot generated title -->]</ref> (which consists of a padded lower dashboard) and a passenger side airbag. The passenger side airbag, protects both front passengers<ref name="oldcarbrochures1974"/> 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.<ref name=thetimes/>

An airbag is not, and cannot be an alternative to seatbelts.

===As a supplemental restraint===
====Frontal airbag====
{|align="right" colspan="4" |Airbag
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| &nbsp;
| [[file:Airbag1.jpg|center|150px|Phasenfoto1]]
| [[File:Airbag2.jpg|center|141px|Phasenfoto2]]
| [[File:Airbag3.jpg|center|150px|Phasenfoto3]]
|}
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 [[Mercedes-Benz W126|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 in the world 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]].<ref>{{cite web|url=http://www.jsae.or.jp/autotech/data_e/7-3e.html |title=240 Landmarks of Japanese Automotive Technology - Subaru Legend airbag system |publisher=Jsae.or.jp |date= |accessdate=2009-12-08}}</ref>

[[Audi]] was relatively late to offer airbag systems on a broader scale; until the 1994 model year, for example, the [[Audi Cabriolet|80/90]], by far Audi's 'bread-and-butter' model, as well as the [[Audi 100#Audi 100 (C4, 1991–1994)|100/200]], did not have airbags in their standard versions. Instead, the German automaker until then relied solely on its proprietary [[procon-ten]] restraint system.

In [[Europe]], airbags were almost entirely absent from family cars until the early 1990s. The first European [[Ford Motor Company|Ford]] to feature an airbag was the facelifted [[Ford Escort (Europe)|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 Motors|Vauxhall]]/[[Opel]], [[Rover Group|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]] was a classical example of how commonplace airbags became on mass market cars during the 1990s. On its launch in early 1993 most of the range did not even have driver airbags as an option. By 1999 however, side airbags were available on several variants.

During the 2000s side airbags were commonplace on even budget cars, 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 a total of nine airbags. Although in some countries, such as [[Russia]], airbags are still not standard equipment on all cars, such as those from [[Lada]].

[[Airbag#Variable-force deployment|Variable force deployment]] front airbags were developed to help minimize injury from the airbag itself.

=====Shaped airbags=====
The [[Citroën C4]] provides the first "shaped" driver airbag, made possible by this car's unusual fixed hub steering wheel.<ref>{{cite news|url=http://www.theaustralian.news.com.au/story/0,20867,16128857-13232,00.html|title=Citroen C4|last=Wilson|first=Robert|date=3 August 2005|publisher=[[The Australian]]|accessdate=3 November 2009}}</ref>

====Side airbag====
[[Image:Seitenairbag Porsche.jpg|thumb|200px|Side airbag inflated permanently for display purposes]]
[[Image:Ford Mondeon curtain airbag deployed.jpg|thumb|200px|A deployed curtain airbag in a [[Opel Vectra]]]]

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]],<ref>{{cite web|url=http://www.iihs.org/ratings/ratingsbyseries.aspx?id=527 |title=IIHS-HLDI: Chevrolet Cobalt 4-door |publisher=Iihs.org |date= |accessdate=2010-02-27}}</ref> 2007-09 model [[Chevrolet Silverado|Chevrolet Silverado/GMC Sierra]], and 2009-10 [[Dodge Ram]]<ref>{{cite web|url=http://www.iihs.org/ratings/rating.aspx?id=1087 |title=IIHS-HLDI: Dodge Ram 1500 |publisher=Iihs.org |date=2009-11-18 |accessdate=2010-02-27}}</ref> 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|Autoliv AB]], was granted a patent on side 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.

=====Side tubular or curtain airbag=====
In late 1997 the 1998 model year [[BMW E38|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 is an industry's first in offering head protection in side impact collisions.<ref>{{cite web|url=http://www.theautochannel.com/news/press/date/19971030/press007605.html |title=BMW Head Protection System Sets New Standard in Side-Impact Protection in Latest IIHS Crash Test |publisher=Theautochannel.com |date= |accessdate=2010-10-17}}</ref> This airbag 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 for superior protection.

In May 1998 Toyota began offering a side curtain airbag deploying from the roof on the [[Toyota Progrès|Progrés]].<ref>{{cite web|url=http://www.theautochannel.com/news/2007/07/23/055878.html |title=Toyota to Make Side Airbags and Curtain Shield Airbags Standard on All New Passenger Vehicle Models in Japan |publisher=Theautochannel.com |date=2007-07-23 |accessdate=2009-12-08}}</ref> In 1998 the [[Volvo S80]] was given seat-mounted curtain airbags to protect both front and rear passengers. Curtain airbags were then made standard equipment on all new Volvo cars from 1998. Although initially seat-mounted, later versions deployed from the roof.

Roll-sensing side curtain airbags found on vehicles more prone to rollovers such as SUV's 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.<ref>{{cite web|author=USA |url=http://www.safercar.gov/portal/site/safercar/menuitem.13dd5c887c7e1358fefe0a2f35a67789/?vgnextoid=506769fd5ec14110VgnVCM1000002fd17898RCRD |title=NHTSA Side-Impact Airbags |publisher=Safercar.gov |date= |accessdate=2010-10-17}}{{dead link|date=October 2011}}</ref> Many recent [[Sport utility vehicle|SUVs]] and [[Multi-purpose vehicle|MPVs]] have a long inflatable curtain airbag that protects all 3 rows of seats.

====Knee airbag====
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.<ref>{{cite web|url=http://cms.firehouse.com/web/online/University-of-Extrication/Kia-Motors-Knee-Airbag-System/19$708 |title=Kia Motors' Knee Airbag System &#124; Firehouse.com |publisher=Cms.firehouse.com |date= |accessdate=2009-12-08}}{{dead link|date=October 2011}}</ref> The [[Toyota Avensis]] became the first vehicle sold in Europe equipped with a driver's knee airbag.<ref>[http://www.toyota.eu/06_Safety/04_implementing_passive_safety/02_airbags.aspx ]{{Dead link|date=December 2009}}</ref><ref>{{cite web|url=http://www.toyoda-gosei.com/news/2003/030630.html |title=Toyoda Gosei |publisher=Toyoda Gosei |date=2003-06-30 |accessdate=2009-12-08}}</ref> 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."<ref>{{cite web|url=http://www.euroncap.com/tests/toyota_avensis_2003/172.aspx |title=For safer cars &#124; Toyota Avensis |publisher=Euro NCAP |date= |accessdate=2009-12-08}}</ref>  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 in the 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.<ref>{{cite web|last=Abuelsamid |first=Sam |url=http://www.autobloggreen.com/2008/09/30/toyota-develops-rear-curtain-airbag-for-tiny-iq/ |title=Toyota develops rear curtain airbag for tiny iQ — Autoblog Green |publisher=Autobloggreen.com |date=2009-03-23 |accessdate=2009-12-08}}</ref>

====Center airbag====
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 console first appearing in on the redesigned [[Toyota Crown Majesta|Crown Majesta]].<ref>{{cite web|last=Hellwig |first=Ed |url=http://blogs.edmunds.com/straightline/2009/03/toyota-unveils-first-rear-seat-center-airbag.html |title=Toyota Unveils First Rear Seat Center Airbag |publisher=Blogs.edmunds.com |date=2009-03-11 |accessdate=2009-12-08}}</ref>

====Seat belt airbag====
In 2009, the S-class ESF safety concept car showcased seatbelt airbags.  They will be included standard on the production [[Lexus LFA]] in late 2010, and the 2011 [[Ford Explorer]] will offer rear seatbelt airbags as an option. Ford claims it will eventually introduce inflatable seat belts on other Ford models globally. Cessna Aircraft also now feature seatbelt airbags. They are now standard on the 172, 182, and 206.

===On motorcycles===
[[File:Motorradairbag.JPG|thumb|Airbag on a motorcycle]]
Various 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.<ref>[http://www.motorcyclenews.com/MCN/News/newsresults/archive/86493/86922/86926/86935/?&R=EPI-86935 Motorcycle News] '06 Wing gets airbag 2 September 2005</ref>

Airbag suits have also been developed for use by [[Motorcycle Grand Prix]] riders. They are connected to the motorcycle by a cable and deploy when the cable becomes detached from its mounting clip, inflating to protect the back.<ref>[http://www.motorcyclenews.com/MCN/News/newsresults/mcn/2007/November/november12-18/nov1207gpriderstestdaineseairbag/?&R=EPI-96969 Motorcycle News] Dainese airbag suit in action 21 November 2007</ref>

==How airbags work==
[[Image:2008-04-14 Airbag control unit.jpg|thumb|An ACU from a [[Geo Storm]].]]
The design is conceptually simple; a central "Airbag control unit"<ref>[http://www.audi.com/audi/com/en2/tools/glossary/safety/airbag_control_unit.html Airbag control unit]{{dead link|date=October 2011}} at Audi.com Glossary</ref> (ACU) (a specific type of [[Electronic control unit|ECU]]) monitors a number of related sensors within the vehicle, including [[accelerometers]], impact sensors, side (door) pressure sensors,<ref>[http://mediacenter.conti-online.com/internet/generator/MAM/index,templateId=Folder_2FrenderDefault.jsp.html?method=show&action=/details.do&oid=2109316 Media Center] at Continental.com</ref> [[wheel speed sensor]]s, [[gyroscope]]s, [[pressure sensor|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 [[nylon]] 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.

Front airbags normally do not protect the occupants during side, rear, or rollover accidents.<ref>{{cite web|author=USA |url=http://www.safercar.gov/portal/site/safercar/menuitem.13dd5c887c7e1358fefe0a2f35a67789/?vgnextoid=ba4769fd5ec14110VgnVCM1000002fd17898RCRD |title=Safercar.gov |publisher=Safercar.gov |date= |accessdate=2010-10-17}}{{dead link|date=October 2011}}</ref> 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 airbag|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.

===Triggering conditions===
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&nbsp;km/h (14&nbsp;mph) barrier collision, or similarly, striking a parked car of similar size across the full front of each vehicle at about twice the speed.<ref>{{cite web|url=http://www.nhtsa.gov/people/injury/airbags/airbags03/page3.html |title=What You Need to Know About Air Bags, DOT HS 809 575 |publisher=Nhtsa.gov |date= |accessdate=2010-10-17}}</ref> International regulations are performance based, rather than technology-based, so airbag deployment threshold is a function of overall vehicle design.

Unlike [[crash test]]s 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 [[Microelectromechanical systems|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 switch]]es 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).<ref>{{cite web|url=http://www.nhtsa.dot.gov/people/injury/airbags/airbags03/page3.html |title=What You Need to Know About Air Bags, DOT HS 809 575 |publisher=Nhtsa.dot.gov |date= |accessdate=2009-12-08}}</ref>  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.

====Inflation====
When the frontal airbags are to deploy, a signal is sent to the [[gas generator|inflator unit]] within the airbag control unit. An igniter starts a rapid [[chemical reaction]] generating primarily [[nitrogen]] gas (N<sub>2</sub>) 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 [[propellant]]s. Propellants containing the highly toxic [[sodium azide]] (NaN<sub>3</sub>) were common in early inflator designs.

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&nbsp;grams of sodium azide.<ref>{{cite web|url=http://www.sdearthtimes.com/et0800/et0800s9.html |title=ET 08/00: Sodium azide in car airbags poses a growing environmental hazard |publisher=Sdearthtimes.com |date= |accessdate=2010-10-17}}</ref>

The alternative propellants may incorporate, for example, a combination of [[nitroguanidine]], phase-stabilized [[ammonium nitrate]] (NH<sub>4</sub>NO<sub>3</sub>) or other nonmetallic oxidizer, and a nitrogen-rich fuel different than azide (e.g. [[tetrazole]]s, [[triazole]]s, and their salts). The burn rate modifiers in the mixture may be an alkaline metal [[nitrate]] (NO<sub>3</sub>-) or [[nitrite]] (NO<sub>2</sub>-), [[dicyanamide]] or its salts, [[sodium borohydride]] (NaBH<sub>4</sub>), etc. The coolants and [[slag]] formers may be e.g. [[clay]], [[silica]], [[alumina]], glass, etc.<ref>{{cite web|url=http://www.freepatentsonline.com/6306232.html |title=Thermally stable nonazide automotive airbag propellants - Patent 6306232 |publisher=Freepatentsonline.com |date= |accessdate=2010-10-17}}</ref> 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 tri[[carboxylic acid]]s with [[chlorate]]s (ClO<sub>3</sub>-) or [[perchlorate]]s (HClO<sub>4</sub>) and eventually metallic oxides; the nitrogen-free formulation avoids formation of toxic [[nitrogen oxide]]s).

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.

=====Variable-force deployment=====
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 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.

[[Image:Airbag SEAT Ibiza.jpg|right|thumb|Post-deployment view of a [[SEAT Ibiza]] airbag]]

====Post-deployment====
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 NaN<sub>3</sub>), 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]] (often used as a table salt substitute) 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.

==Regulatory specifications==
===United States===
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 an [[automatic seat belt]] would meet the requirements of the standard. Airbag introduction was stimulated by the U.S. [[National Highway Traffic Safety Administration]].<ref>http://www-nrd.nhtsa.dot.gov/pdf/nrd-01/Esv/esv16/98S8P12.PDF</ref> However, airbags were not mandatory on light trucks until 1997.<ref>{{cite web|url=http://www.nhtsa.gov/cars/rules/import/fmvss/index.html#SN208 |title=Federal Motor Vehicle Safety Standards and Regulations |publisher=Nhtsa.gov |date= |accessdate=2011-08-10}}</ref>

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.===
Most countries {{Who|date=April 2009}} outside North America adhere to internationalized European [[ECE regulations|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 [[Automobile safety|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.<ref name=ncap>[http://www.euroncap.com/tests/frontimpact.aspx Frontal impact test description] Euro NCAP website</ref> Thus almost all new cars now come with at least two airbags as standard.

==Maintenance==
{{Globalize|section|date=September 2008}}
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 [[Auto mechanic|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 Auto|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.<ref name=BohrAAA>{{Citation
 | last = Bohr | first = Peter | date = July/August 2010 | title = Air Time | periodical = [[AAA World]] | volume = 12 | issue = 4 | page = 24
 | url = | archiveurl = | archivedate = | accessdate = 26 June 2010}}</ref>

==Injuries and fatalities==
{{cleanup|section|date=May 2008}}
[[File:Lives Saved by Safety Belts and Air Bags, NHTSA, DOT.jpg|thumb|right|240px|Lives saved by [[seat belt]]s and airbags]]

Airbags can injure or 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 bag deployment parameters accordingly.<ref>{{cite web|url=http://www.nhtsa.gov/cars/rules/rulings/AAirBagSNPRM/#snprm7 |title=NHTSA 49 CFR Parts 552, 571, 585, and 595, Docket Notice |publisher=Nhtsa.gov |date= |accessdate=2010-10-17}}</ref>

In 1990, the first automotive fatality attributed to an airbag was reported.<ref name="NHTSAAirBag">{{cite web|url=http://www.nsc.org/partners/status3.htm |archiveurl=http://web.archive.org/web/20080226234316/http://www.nsc.org/partners/status3.htm |archivedate=2008-02-26 |title=National Highway Traffic Safety Administration Air Bag Fatalities |publisher=Web.archive.org |date= |accessdate=2010-10-17}}</ref> [[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.

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.<ref>{{cite web|url=http://aje.oxfordjournals.org/cgi/reprint/164/2/161.pdf |title=American Journal of Epidemiology, '&#39;Association of First- and Second-Generation Airbags with Front Occupant Death in Car Crashes: A Matched Cohort Study'&#39;, October 4, 2005. |format=PDF |date= |accessdate=2010-10-17}}</ref>

===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.<ref name="NHTSAAirBag" /><ref name=BohrAAA2>The statement "...they've saved some 26,000 lives, according to estimates from the ... (NHTSA)" has been published. {{Citation
 | last = Bohr | first = Peter | date = July/August 2010 | title = Air Time | periodical = [[AAA World]] | volume = 12 | issue = 4 | page = 24
 | url = | archiveurl = | archivedate = | accessdate = 26 June 2010}}</ref>

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 injury|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.<ref>Toyota Aurion: User Manual 2006 model - Australia</ref>  A seat-mounted airbag may also cause internal injury if the occupant leans against the door.<ref>Hallman et al., 2009, http://www.ncbi.nlm.nih.gov/pubmed/20184829</ref><ref>Hallman et al., 2010, http://www.ncbi.nlm.nih.gov/pubmed/21512911</ref>

==Aerospace and military applications==
[[Image:Pathfinder Air Bags - GPN-2000-000484.jpg|thumb|left|NASA engineers test the [[Mars Pathfinder]] airbag [[landing]] system on simulated Martian terrain]]
The [[aerospace]] industry and the [[Federal government of the United States|US Government]] have applied airbag technologies for many years. [[NASA]], and [[United States Department of Defense|US DoD]] have incorporated airbag systems in various aircraft and spacecraft applications as early as the 1960s.
[[Image:OH-58D Cockpit Air Bag System (CABS).jpg|thumb|OH-58D CABS test]]

===Airbag landing systems===
The first use of airbags for [[landing]] were [[Luna 9]] and [[Luna 13]], which landed on the [[Moon]] in 1966 and returned panoramic images. The [[Mars Pathfinder]] lander employed an innovative airbag landing system, supplemented with [[aerobraking]], [[parachute]], and [[solid rocket]] landing thrusters. This prototype successfully tested the concept, and the two [[Mars Exploration Rover Mission]] landers employed similar landing systems. The [[Beagle 2]] Mars lander also tried to use airbags for landing, but the landing was unsuccessful for reasons which are not entirely known.

Airbags have also been used on military fixed wing aircraft such at the [[Escape crew capsule#Design and development|Escape Crew Capsule]] of the [[F-111 Aardvark]].

===Occupant protection===
The [[United States Army|US Army]] has incorporated airbags in its [[UH-60 Black Hawk|UH-60A/L]]<ref>{{cite web|url=http://www.defenselink.mil/contracts/contract.aspx?contractid=1462 |title=Defenselink article |publisher=Defenselink.mil |date= |accessdate=2010-10-17}}</ref><ref>[http://www.helis.com/news/1999/h60abag.htm US Army Demonstrates Simula's Cockpit Air Bag System] at Helios.com</ref> Black Hawk and [[OH-58 Kiowa|OH-58D]] Kiowa Warrior<ref>{{cite web|url=http://www.fas.org/man/dod-101/sys/ac/oh-58.htm |title=FAS OH-58D article |publisher=Fas.org |date=1995-06-17 |accessdate=2010-10-17}}</ref> helicopter fleets. The Cockpit Air Bag System (CABS)<ref>{{cite web|url=http://www.tslaerospace.com/product/simula/PDF/CABS%20Sunset%20Brochure.pdf |title=Microsoft Word - Sunset Brochure.doc |format=PDF |date= |accessdate=2010-10-17}}</ref> consists of forward and lateral airbags, and an inflatable tubular structure (on the OH-58D only) with an Electronic Crash Sensor Unit (ECSU).  The CABS system was developed by the US Army [[Aviation Applied Technology Directorate]], [[Fort Eustis]], [[Virginia|Va]] through a contract with Simula Safety Systems (now [[BAE Systems]]).<ref>{{cite web|url=http://csat.au.af.mil/2025/concepts/900312.HTM |title=Air Defense concept papers |publisher=Csat.au.af.mil |date= |accessdate=2010-10-17}}</ref> It is the first conventional airbag system for occupant injury prevention (worldwide) designed and developed and placed in service for an aircraft, and the first specifically for helicopter applications.<ref>{{cite web|url=http://findarticles.com/p/articles/mi_m0EIN/is_2002_June_13/ai_87142543 |title=BNET News Release on AHS Annual Forum award |publisher=Findarticles.com |date=2002-06-13 |accessdate=2010-10-17|archiveurl=http://archive.is/I3XJ|archivedate=2012-07-12}}</ref><ref>[http://www.allbusiness.com/government/government-bodies-offices-government/5706607-1.html Simula Receives Orders for its Cockpit Air Bag Systems] at All Business.com</ref>

== See also ==
* [[Airbag dermatitis]]
* [[Airplane airbags]]
* [[Automobile safety]]
* [[Precrash system]]
* [[Safety standards]]
* [[Glossary Index]]

== References / sources ==

{{Reflist|colwidth=30em}}

==External links==
{{Commons category|Air bags|Airbags}}
* [http://www.autoliv.com.au/airbag.html Airbag Information and Airbag Deployment video in slow motion]
* [http://www.chemistry.wustl.edu/~edudev/LabTutorials/Airbags/airbags.html Chemistry behind airbags]
* [http://www.cardomain.com/ride/770691/3 Pictures and details about the 1970s GM Air Cushion Restraint System]

{{CarDesign nav}}
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[[Category:Automotive safety technologies]]
[[Category:American inventions]]
[[Category:1973 introductions]]
[[Category:Aerospace]]