March 2014

  1. What are airbags?

    Airbags are cushions built into a vehicle that protect occupants from hitting the vehicle interior or objects outside the vehicle (for example, other vehicles or trees) during a collision. The instant a crash begins, sensors start to measure impact severity. If the crash is severe enough, the sensors signal inflators to fill the bags with gas in a fraction of a second. The speed of a deploying airbag can reach up to 200 mph. Airbags are designed to offer the most protection when occupants are buckled up. and sitting properly in the seat. To determine the locations of airbags within a vehicle, look for the word "airbag" or "SRS" (supplemental restraint system) components of the vehicle interior. These labels may be stamped into plastic or stitched into fabric.

    Airbag marker tag
    Airbag marker stamp

    Frontal airbags: Most vehicles on the road today have airbags that deploy in frontal crashes to protect the heads and chests of front-seat occupants. The driver airbag is stowed in the steering wheel. The passenger airbag is stored in the instrument panel.

    Some manufacturers provide knee airbags, mounted in the lower instrument panel. Knee airbags distribute impact forces to reduce leg injuries. They also help reduce forces on an occupant's chest and abdomen by controlling movement of the occupant's lower body.

    Side airbags: Most recent models also have airbags that deploy in side-impact crashes. Side airbags deploy from the vehicle seatback, door or roof to protect front- and sometimes rear-seat occupants.

    Some side airbag systems protect only the head, and a few protect only the torso. Ideally, vehicles should have protection for both.

    Head-protecting airbags may extend into the rear seating area. Rear seats may also have head-protecting side airbags separate from those in the front seat or airbags that provide torso protection.

    Front dual airbag system

    Front dual airbag system


    Knee airbag

    Knee airbag


    Side head airbag
    Side head/torso airbag

    Side airbags to protect the head or head/torso


    Side head/torso airbag
    Side head/torso airbag
    Side head/torso airbag

    Side airbags to protect the head and torso


  2. Why do we need airbags?

    Frontal airbags: In serious frontal crashes, occupants don't stop immediately, but continue moving forward. Frontal airbags are designed to work with lap/shoulder belts to protect heads and chests from hitting the steering wheel, instrument panel, or windshield. If occupants strike these surfaces hard, they can sustain serious or fatal injuries.

    Side airbags: In side-impact crashes, the side structure of the struck vehicle or the structure of the striking vehicle can injure properly belted occupants. In some cases, occupants collide with nearby objects (like utility poles). Side airbags cushion and spread the load of these impacts to prevent any part of the body from sustaining concentrated impact forces. Side airbags that offer head protection are particularly important because they may be the only thing between an occupant's head and the front of a vehicle, a tree or other object, or the ground in the event of a rollover.

  3. Are airbags effective? Do they save lives and reduce injuries?

    Frontal airbags:  The National Highway Traffic Safety Administration (NHTSA) estimates that as of Jan. 1, 2009, more than 28,000 people were alive because of frontal airbags, which became common in the 1990s and have been required in new passenger vehicles since the 1999 model year. National Highway Traffic Safety Administration. 2009. Special Crash Investigations – Counts of frontal air bag related fatalities and seriously injured persons. Report no. DOT HS-811-104. Washington, DC: U.S. Department of Transportation. Eighty-two percent of the people whose lives were saved by airbags were drivers and 18 percent were front-seat passengers. Forty percent were belted and 60 percent were unbelted. 

    In frontal crashes, frontal airbags reduce driver fatalities by 29 percent and fatalities of front-seat passengers age 13 and older by 32 percent. Kahane, C.J. 2004. Lives saved by the federal motor vehicle safety standards and other vehicle safety technologies, 1960-2002: passenger and light trucks. Report no. DOT HS-809-833. Washington, DC: National Highway Traffic Safety Administration. The fatality reduction in frontal crashes is larger for unbelted drivers (34 percent) compared with belted drivers (21 percent). NHTSA estimates that the combination of an airbag plus a lap and shoulder belt reduces the risk of death by 61 percent compared with a 50 percent reduction for belts alone in frontal crashes. 

    Side airbags: Side airbags with head protection reduce a car driver's risk of death in driver-side crashes by 37 percent and an SUV driver's risk by 52 percent, an Institute analysis of U.S. crashes showed. McCartt, A.T. and Kyrychenko S.Y. 2007. Efficacy of side airbags in reducing driver deaths in driver-side car and SUV collisions.Traffic Injury Prevention 8(2):162-70. Side airbags designed to protect only the torso reduce fatality risk by 26 percent for car drivers and by 30 percent for SUV drivers. A study of crashes in Australia found that side airbags with head and torso protection reduce a car driver's risk of death or injury in driver-side crashes by 41 percent. D'Elia, A.; Newstead, S.; and Scully, J. 2013. Evaluation of vehicle side airbag effectiveness in Victoria, Australia. Accident Analysis and Prevention 54:67-72. Similar trends were found in a NHTSA study focusing on the fatality risk to drivers and right-front-seat passenger vehicles involved in nearside crashes. Curtain and torso airbags reduce the risk of death by 31 percent, and combination head/torso airbags reduce the risk by 25 percent. Kahane, C.J. 2014. Updated estimates of fatality reduction by curtain and side air bag in side impacts and preliminary analyses of rollover curtains. Report no. DOT HS-811-882. Washington, DC: National Highway Traffic Safety Administration. The death reduction was lower in vehicles equipped only with a curtain airbag (16 percent) or only with a torso airbag (8 percent).

    The crucial role played by head-protecting side airbags is illustrated by the results of the Institute's side-impact crash tests, which measure how well passenger vehicles would protect occupants in a side crash. Since the program began in 2003, all the vehicles earning good ratings have been equipped with side airbags that protect the head. However, airbags alone aren't enough. Vehicles also need side structures that resist major intrusion into the occupant compartment.

  4. Are airbags required in all vehicles?

    Frontal airbags: Since the 1999 model year, the federal government has required automakers to install driver and passenger airbags for frontal impact protection in all cars, light trucks and vans. Most new vehicles had dual frontal airbags even before they were required safety equipment.

    Side airbags: The government doesn't mandate side airbags specifically but does require a certain level of head and torso protection for all occupants in side impact crashes. The vast majority of new passenger vehicles come with side airbags as standard equipment.

    Rollover airbags: These are side airbags that are designed to provide protection in a rollover crash. Although they aren't specifically required, automakers are expected to use them to comply with a new federal safety standard intended to prevent occupant ejection through side windows. Rollover airbags are larger than other side airbags, covering more of the window. They also are tauter, stay inflated longer and deploy during rollover crashes as well as side-impact crashes. The new standard to prevent ejection is being phased in beginning with model year 2014, and all passenger vehicles must comply by the 2018 model year.

  5. When do airbags deploy?

    Airbags are designed to deploy only when they might be needed to prevent serious injury. In order for airbags to be effective they must deploy early in a crash; this typically occurs within the first 50 milliseconds (0.05 seconds) in a frontal crash and within the first 20 milliseconds (0.02 seconds) in a side crash. A vehicle's airbag control module relies on feedback from sensors to predict whether a crash is severe enough to warrant airbag deployment.

    Frontal airbags: Frontal airbags are designed to inflate in moderate to severe frontal crashes. Among airbags with advanced features that include a safety belt sensor, there are different inflation thresholds depending on whether people are using safety belts. One threshold used by airbag designers is "must deploy," which includes a situation such as an impact into a rigid wall at 10-12 mph if occupants are unbelted. The "must deploy" threshold is slightly higher — about 16 mph — for belted occupants because the belts alone are likely to provide adequate protection up to these moderate speeds. Frontal airbags may deploy to help protect occupants in side impacts if there is sufficient forward deceleration during the crash. If a vehicle is moving forward at the time of a side impact, frontal airbags can help prevent serious injuries.

    Advanced airbags compliant with government crash performance standards have been required in all passenger vehicles since model year 2007. Advanced airbags are designed to suppress deployment or alter deployment characteristics to reduce the risk of injury by the airbag if weight sensors in the seat detect that a front-seat passenger is small or in a child safety seat. Advanced airbags also can deploy at a lower energy level or pressure when passengers are small or out of position, or if the crash is of very low severity.

    Side airbags: Because of the small space between an occupant and the side of the vehicle, side airbags must deploy very quickly to cushion occupants from intruding vehicles or objects. Some airbags typically deploy within the first 10-20 milliseconds of a side crash. "Must deploy" thresholds can be as low as 8 mph for narrow object crashes (e.g., trees and poles) and 18 mph for the more distributed side crashes (vehicle-to-vehicle crashes). Several auto manufacturers deploy the side airbags in frontal crashes to help control occupant movement.

    Rollover airbags: Side airbags that provide rollover protection deploy in response to sensors that measure a vehicle's sideways moving and tilting. They typically inflate within the first 10-20 milliseconds of a side or rollover crash and can remain inflated for 10 or more seconds to protect during multiple-roll crashes.

  6. Do frontal airbags ever fail to deploy when they're needed?

    An Institute study reviewed airbag deployment status for fatal frontal crashes contained in the National Automotive Sampling System/Crashworthiness Data System, a sample of tow-away crashes with detailed data from crash investigators. Braver, E.R.; McCartt, A.T.; Sherwood, C.P.; Zuby, D.S.; Blanar, L.; and Scerbo, M. 2010. Front air bag nondeployments in frontal crashes fatal to drivers or right-front passengers. Traffic Injury Prevention 11(2):178-87. Institute researchers estimated that 1-2 percent of frontal occupant deaths represented potential airbag system failures where deployments would have been expected. However, there are inherent uncertainties about whether or not airbags would be expected to deploy in some crashes. 

  7. Can airbags injure people?

    Occasionally, the energy required to quickly inflate airbags can cause injury. This was a serious concern with older generations of frontal airbags, but, thanks to new government requirements, airbag injuries are becoming a thing of the past. Fortunately, even with older airbags, most of the injuries that occur are minor scrapes and abrasions, and serious injuries and deaths are relatively rare.

    NHTSA estimates that during 1990-2008, more than 290 deaths were caused by frontal airbag inflation in low-speed crashes. National Highway Traffic Safety Administration. 2009. Special Crash Investigations – Counts of frontal air bag related fatalities and seriously injured persons. Report no. DOT HS-811-104. Washington, DC: U.S. Department of Transportation. Nearly 90 percent of the deaths occurred in vehicles manufactured before 1998, and more than 80 percent of people killed were unbelted or improperly restrained. Unbelted occupants are likely to move forward if, for example, there is hard braking or swerving before a frontal crash. These occupants can end up on top of, or extremely close to, the airbags as they begin to inflate.

    Most of the deaths identified by NHTSA were passengers, and more than 90 percent of those were children and infants, most of whom were unbelted or in rear-facing child safety seats that placed their heads close to the deploying airbag.  Short and elderly drivers can also be vulnerable to inflation injuries from frontal airbags because they tend to sit close to the steering wheel.

    Side airbags also have the potential to cause injury, although they typically are smaller and deploy with less energy than frontal airbags. Injuries from contact with side airbag inflations in crashes have been documented, Hallman, J.J.; Brasel, K.J.; Yoganandan, N.; and Pintar, F.A. 2009. Splenic trauma as an adverse effect of torso-protecting side airbags: biomechanical and case evidence. Ann Adv Automot Med. 53: 13-24. but there is no indication that such injuries are common. A field study of children in side crashes found no increased risk of injury to children age 15 and younger associated with side airbag deployment. Arbogast, K.B. and Kallan, M.J. 2007. The exposure of children to deploying side airbags: an initial field assessment. Proceedings of the 51th Annual Conference of the Association for the Advancement of Automotive Medicine, 245-59. Barrington, IL: Association for the Advancement of Automotive Medicine.

  8. What can drivers and passengers do to prevent injuries from airbags?
    Vehicles provide optimal protection when occupants are belted and sitting in the proper position. Drivers and front-seat passengers should sit in the center of the seat upright against the seatback with feet on the floor. Arms and legs should never be resting against an airbag because the forces of a deploying airbag and the hot gases exhausted by the airbag may cause injury.
    Areas on or around airbags should be free of objects that can either alter the proper deployment of airbags or become dangerous projectiles within the vehicle. Aftermarket dash covers may block a frontal airbag and seat covers may block a seat-mounted side airbag from proper deployment or redirect the airbag in a way that is dangerous.

    Drivers: Drivers should sit with their chests at least 10 inches away from the center of the steering wheel. For shorter drivers with the seat positioned further forward, this can often be achieved by slightly reclining the seatback. Many newer airbags take into account seating position and deploy with less force if an occupant is sitting close. For drivers of older vehicles who cannot get far enough away from the steering wheel, pedal extenders or an airbag on/off switch may be an option. The government is allowing installation of switches on vehicles manufactured before Sept. 1, 2015.

    Pregnant women: Women in the late stages of pregnancy may not be able to get their abdomens far away enough from the steering wheel to be safe. There can be a risk of fetal injury from a frontal airbag if it inflates. However, without the airbag, there is a risk of fetal injury from hitting the steering wheel. Women in the late stages of pregnancy should avoid driving whenever possible. If they must drive, the combination of properly positioned safety belts and airbags offers the best protection.

    Infants and children: How and where infants and children are restrained in a vehicle are critical factors in avoiding airbag-related injuries. Infants, particularly those in rear-facing safety seats, should never sit in the front because this puts an infant's head too close to the frontal airbag. Rear seats are always safest for infants and children. Seventeen states have provisions requiring children of various ages to be seated in the rear. Even if your state's law does not require children to sit in the rear, children 12 and younger should always sit restrained in rear seats.

    If an adult is transporting too many children for them all to sit safely and comfortably in the back, the youngest children should ride in the back. When a child does need to ride in the front seat, the seat should be as far back as possible and the child should be securely buckled in a lap/shoulder belt and sitting against the seatback. If a driver routinely has to put a child in the front seat of an older vehicle, an airbag on/off switch may be considered.

    Nearly all older children killed by frontal airbags were either unbelted or improperly belted. But even belted children can be at risk if they wiggle out of position or sit on the edge of the seat, putting the head too close to the airbag.

    Children should not lean against the door area where the airbag is stored because the initial deployment force may be harmful. With or without an airbag, children who lean against doors or lie down with their heads near the doors or sides of vehicles are at higher risk of injury in the event of a side impact. All vehicle manufacturers have committed to following a test protocol for designing side airbag systems that assures that the inflation injury risk is low even for small children who might lie down or assume other positions against a deploying side airbag.

  9. What steps has the government taken to minimize the risk of injury from airbags?

    In 1997, the federal government modified safety rules to encourage automakers to take energy out of frontal airbags. Depowering began with 1998 models. Manufacturers were allowed to use sled tests with unbelted dummies to certify that their vehicles met crash performance rules. The maximum sled accelerations NHTSA prescribed under this option were lower than typically occur in crash tests so airbags didn't need to deploy as quickly or forcefully to catch and cushion unbelted dummies. Airbags meeting this standard are called sled-certified.

    At the same time, a large-scale public education campaign encouraged parents to restrain children, especially infants in rear-facing restraints, in the back seat, where they're safest. Legislators in many states enacted laws requiring children to sit in the rear. Today most children ride restrained in back seats. National Highway Traffic Safety Administration. 2010. The 2009 National Survey of the Use of Booster Seats. Report no. DOT HS-811-377. Washington, DC: U.S. Department of Transportation.

    Institute researchers found an overall reduction in fatal crash risk associated with sled-certified, depowered airbags compared with earlier designs. Braver, E. R.; Kyrychenko, S.Y.; and Ferguson, S.A. 2005. Driver mortality in frontal crashes: comparison of newer and older airbag designs. Traffic Injury Prevention 6(1):24-30. A 2006 NHTSA study reported that redesigned airbags reduced fatality risk to child passengers by 45 percent compared with pre-1998 airbags – without reducing the benefits for adults. Kahane, C.J. 2006. An evaluation of the 1998-1999 redesign of frontal air bags. Report no. DOT HS-810-685. Washington, DC: National Highway Traffic Safety Administration.

    In 2001, NHTSA issued a certified-advanced airbag rule that required more sophisticated airbags in all passenger vehicles by the 2007 model year. Advanced airbags modify deployment patterns if weight sensors detect a small driver or front-seat passenger or a child safety seat. These airbags can be suppressed altogether or deploy with less force when passengers are small or out of position, or if a crash isn't severe. They also can determine if occupants' safety belts are buckled and generally deploy at lower thresholds for people who aren't using belts.

    The new rule changed the way auto manufacturers test vehicles for compliance. It introduced a range of crash tests using different-size dummies and different crash test speeds. Different tests still are performed for unbelted and belted dummies.

  10. How is the latest generation of advanced airbags performing?

    Airbags continue to save lives, but Institute research suggests that the newest ones aren't working as well as the ones they replaced for some vehicle occupants.

    A 2013 Institute study examined death rates in frontal crashes among front-seat occupants in vehicles with sled-certified airbags with and without advanced features and in vehicles with certified-advanced airbags. Braver, E.R.; McCartt, A.T.; Sherwood, C.P.; Zuby, D.S.; Blanar, L.; and Scerbo, M. 2010. Front air bag nondeployments in frontal crashes fatal to drivers or right-front passengers. Traffic Injury Prevention 11(2):178-87. Teoh, E.R. 2013. How have changes in front airbag design affected frontal crash death rates? An update. Traffic Injury Prevention, in press. Death rates were 10 percent lower for drivers of vehicles with sled-certified airbags with advanced features compared with sled-certified airbags without advanced features; the benefit was 16 percent for adults riding in front passenger seats.

    Results for the newest airbags – certified-advanced – didn't follow the same pattern. Certified-advanced airbags were associated with slightly elevated nonsignificant frontal crash death rates for both drivers and right-front passengers overall, compared with sled-certified airbags with advanced features. However, when looking separately at belted and unbleted drivers, certified-advanced airbags were associated with a significant 12 percent increase in the belted driver death rate and a comparable but nonsignificant decrease in unbelted driver death rate compared with sled-certified airbags with advanced features.

    A 2013 NHTSA study found that certified-advanced airbags were associated with a slightly lower nonsignificant fatality rate for front seat occupants in frontal crashes when compared with sled-certified airbags. Greenwell, N.K. 2013. Evaluation of the certified-advanced air bags. Report no. DOT HS-811-834. Washington, DC: National Highway Traffic Safety Administration. However, the study also reported that certified-advanced airbags were associated with a 6 percent nonsignificant increased death rate for belted drivers and a 7 percent nonsignificant decrease for unbelted drivers, trends similar to those observed by IIHS.

    These findings suggest potential problems with the way manufacturers are required to certify airbags as advanced. It may be that the new rule didn't strike the right balance in protecting belted and unbelted occupants. 

  11. What maintenance do airbags require? When do they need to be replaced?

    Airbag systems do not typically require regular maintenance. A properly functioning airbag can last the lifetime of the car unless it deploys in a crash. A demonstration test conducted by the Institute showed that the original frontal airbags in a 1973 Chevrolet Impala deployed properly more than 20 years after the car was built.

    To check that the airbags in a vehicle are working properly, observe the airbag warning light on the instrument panel. If the airbags are working properly, the warning light illuminates for a few seconds when the ignition is switched on. The airbag requires maintenance and should be taken to service center if the airbag warning light is flashing, remains illuminated with or without a warning beep or doesn't illuminate during the ignition on cycle.

    Airbags must be replaced after deployment in a crash. Airbags should be replaced at a repair shop that uses original equipment manufacturer (OEM) replacement parts to ensure that the new airbag is not counterfeit.

  12. Is there new airbag technology?

    Yes. Airbag technology is continuously developing. For example, in 2012 Ford rolled out an inflatable safety belt aimed at reducing rear-seat injuries. In a crash, the torso portion of the belt softly inflates, distributing crash forces across the torso and chest. The inflatable belts are currently available as optional equipment in the outboard second-row seating positions of the Ford Flex, Ford Explorer, Lincoln MKT and Lincoln MKZ.

    Ford inflatable safety belt
    Ford press website

    Ford inflatable safety belt


    Beginning with the 2012 model year, the Scion iQ microcar has a rear window curtain airbag as a standard feature. The airbag is intended to prevent direct contact of the back seat occupants with vehicle parts and broken glass in the event of a rear crash. The airbag deploys in front of the rear windshield and around the rear seat head restraints.

    Rear curtain airbag

    Rear curtain airbag


    Beginning with the 2012 model year, the Scion iQ and Toyota Yaris have seat cushion airbags for the driver and front passenger as standard features. The front of the seat cushion inflates in a frontal crash. The seat cushion inflates, lifting the occupant’s knees upward, to make the safety belt fit better and to reduce submarining of the occupant’s pelvis below the safety belt by supporting the occupant’s knees.

    Seat cushion airbag
    Toyota press site

    Seat cushion airbag


    General Motors has developed a front center airbag intended to prevent front passengers from colliding with each other during side-impact crashes and to maintain occupant position in far-side or rollover crashes. Starting with the 2013 model year, the airbag is available in the Buick Enclave, GMC Acadia and Chevrolet Traverse. Toyota has developed a rear center airbag that deploys from the center console. It’s meant to do the same thing as the GM front center bag, only in the back seat. Toyota is launching this airbag in a new model available in Japan.

    GM front center airbag
    GM press release

    GM front center airbag



    Volvo has developed the first hood airbag designed for pedestrian protection. When a pedestrian is detected, an external airbag deploys from under the hood and covers the hard parts of the windshield and the A-pillar, locations on vehicles that pedestrians frequently strike. The pedestrian hood airbag is standard on the Volvo V40 available in Europe only, starting with the 2013 model year.

    Hood airbag
    Volvo press site

    Volvo hood airbag


     
  13. Is it OK to use airbags from salvaged vehicles to repair other vehicles?

    A new replacement airbag module from the original manufacturer of the vehicle should be used for vehicles that require an airbag replacement. However, when it’s not possible to buy a new airbag module, the Institute recommends that care be taken to identify a salvaged airbag module that has been inspected and certified. Certification documentation should include the vehicle identification number of the vehicle from which the airbag was removed, the airbag salvage date, storage location and shipment details. Buyers should check the NHTSA recall database for any recalls that may apply to the salvaged airbag.

  14. What are the risks associated with using salvaged airbag modules to repair other vehicles?

    Processing salvaged airbag modules can present a number of difficulties.

    The designs of the airbag systems in most cars have been improved in recent years (sometimes several times). Therefore, there's a significant possibility of a mismatch between the salvaged airbag module and the vehicle being repaired.

    Another issue involves the possibility of water damage. There is a risk that salvaged airbag modules will be from vehicles that have been in floods, or that the airbag module was exposed to precipitation while at the salvage facility. Water damage can adversely affect the way an airbag inflates. There is no standard method to test the functionality of salvaged airbags.

    Using salvaged airbags could also encourage airbag theft, which is already a significant problem. In recent years thieves have developed a black market for airbags, which they sell at a low price to unethical repair-shop owners, who then charge customers the standard price for a replacement airbag.

  15. What is a counterfeit airbag?

    Unlike salvaged airbags, counterfeit airbags were never certified by the vehicle manufacturer as meeting the same standards as the vehicle’s original airbag. National Highway Traffic Safety Administration. 2012. Safety Advisory: NHTSA Alerting Consumers to Dangers of Counterfit Airbags. Report no. NHTSA 42-12. Washington, DC: U.S. Department of Transportation. They may look almost identical to airbags certified to federal standards, but they often do not perform the same. Investigations conducted by NHTSA have shown that counterfeit airbags consistently malfunction. In some cases they simply fail to deploy; in other cases, metal shrapnel is released during deployment. NHTSA estimates that only 0.1 percent of the U.S. vehicle fleet has counterfeit airbags, and no serious injuries or deaths have been associated with them.

  16. Which vehicles are at risk for a counterfeit airbag?

    NHTSA advises that a vehicle is at risk of having counterfeit airbag if it has an unknown repair history; a salvage, rebuilt or reconstructed title; or airbags replaced after 2009 at an independent repair shop that cannot be verified as OEM replacement stock. National Highway Traffic Safety Administration. 2012. Safety Advisory: NHTSA Alerting Consumers to Dangers of Counterfit Airbags. Report no. NHTSA 42-12. Washington, DC: U.S. Department of Transportation. Consumers who have purchased low-cost replacement airbags online are also at risk.

    Vehicles that have never had an airbag replaced and vehicles in which airbags have been replaced at a repair shop associated with a new car dealership are not at risk.

    Information about how to determine if a vehicle has a counterfeit airbag, along with a list of models for which counterfeit airbags are known to be available, can be found at safercar.gov.

  17. Do motorcycles have airbags?

    A frontal airbag is offered as an option on 2006 and later models of Honda's Gold Wing touring motorcycle. Honda's airbag is designed to deploy in severe frontal impacts and absorb some of the forward energy of the driver. No studies have been conducted on the real-world effectiveness of motorcycle airbags.

    Motorcycle airbag
    Honda media

    Honda Gold Wing touring motorcycle
    with frontal airbag