On January 3, 2010, Donna Lynn Hopkins was a front-seat passenger in a 2008 Hyundai Accent, with her husband, Tom, at the wheel. As they approached an intersection on Highway 181 in Bexar County, Texas, another driver failed to yield the right of way. The Hyundai T-boned the other vehicle with sufficient force to deploy the airbags. But only the driver’s airbag inflated. The occupant seat sensor mat in the front passenger seat determined that, Donna Hopkins, a 165-pound woman, was actually a child, and turned off the airbag. Worse, Hyundai’s sensor strategy also turned off the seat belt pretensioner. Like some other manufacturers, Hyundai’s occupant sensor is designed so that the front passenger seat belt pretensioner fires only if the airbag is deployed. Mrs. Hopkins had none of the advanced safety features needed to adequately protect her in that crash, even though she was belted, and weighed 55 pounds more than the regulated cut-off for smart airbag deployment. Her husband, Tom, walked away from the crash; Donna Hopkins died.

Attorney Stephen Van Gaasbeck, who represented the Hopkins family, says that his research revealed many airbag non-deployment complaints for the Accent and its model twins. In fact, in May 2008, then-Senator Elizabeth Dole (R-NC) wrote to NHTSA on behalf of a constituent who complained about his 2006 Kia Rio. Kia is a Hyundai owned company. In his letter to Dole, the Mint Hill, NC owner wrote:

“There is an airbag sensor on the passenger side that is supposed to keep the passenger airbags disabled when only the driver is in the front seat. There is a dashboard light connected to this sensor that illuminates when this airbag is deactivated. However, very often when my wife, who weighs approximately 220 lbs. is seated in the front passenger seat, the passenger airbag sensor light is still on, indicating that the front passenger seat airbags are not activated. This means that should there be an accident with this vehicle when she is riding as a passenger in it, the airbags on her side may not activate. This is a very dangerous situation…The service department at Folger Automotive would tell me that they had never seen or heard of a similar problem. They said on many occasions that the reason the problem was occurring was probably because of the way my wife was ‘sitting in the seat’. They stated to me that they had discussed this situation with KIA technical personnel and that that nobody there had ever heard of a problem like ours. We were made to feel that something we were doing was causing this problem.”

Hyundai occupant sensor system also presents many opportunities for failure, because it does not directly measure weight, rather, it measures the depth of suppression of cells within the mat. Designed by supplier company International Electronic Engineering (IEE), this mechanism can be affected by seat manufacturing differences, moisture, temperature – even body shape.

“The sensor strategy Hyundai uses is so fragile, it’s going to fail somewhere along the line,” Van Gassbeck says. “The degradation can be at any level – even the stitching on the seat cover becoming looser or the fabric becoming looser.”

So-called “smart” airbags came into being in 2000s, when the National Highway Traffic Safety Administration mandated that vehicles include technologies that minimize risk for  children and small adults by either automatically turning off the airbag in the presence of young children or deploying the airbag in a manner much less likely to cause serious or fatal injury to out-of-position occupants. The weight-based cut-off between small-statured adults and children was 110 pounds – the weight of the fifth-percentile female dummy used in the tests.

This rule capped a four-year debate following that recognition that airbags could not only prevent injury, but cause injury and fatality by inflating with too much force. In 1996, the agency opened the discussion by requesting comments about the undesired side effects of the then-current air bag designs. NHTSA pointed to injuries that were occurring during pre‑impact braking as unrestrained occupants moved forward relative to the seat and into close proximity of the deploying air bag. The agency went on to note that certain technological enhancements such as occupant sensing and phased deployment could minimize these side effects.  In 1998, NHTSA issued a notice of proposed rulemaking to require advanced air bag technology. The proposal would have required air bag improvements to protect occupants of different sizes (both belted and unbelted) and require systems that are designed to minimize risks to infants, children, small adults and out-of-position occupants, with air bag deployment suppression strategies or less aggressive deployment strategies. The rule was finalized two years later.

Because of the high potential for misclassification, the supplier must implement a rigorous testing regime to identify sensor performance with a wide range of body shapes – not just weights.  For example, some suppliers will place many occupants of the same weight, but with different body types in the seat to ensure that the sensor is registering the occupant accurately.

Andrew Varga, a former seating engineer who worked on developing sensor systems, says that multiple factors can affect a sensor’s performance. At the unit level, there can be bugs in the analysis algorithms, wide variations in each sensor cell arrayed in the occupant sensing mat and in how the seat is constructed. For example, knit fabric seats have greater compliance than leather seats. The curing of the foam can affect the resilience of the seat, dictating how well the sensors detect occupant weight.

“In the early days, there could be variation as much as 20 to 30 percent,” Varga says. “Improved cells and the use of sensor arrays for better pressure mapping, have reduced errors.”

Once in use, the way people sit in the seats can affect the sensors’ performance. Most mats are designed to measure weight when the occupant is sitting erect in the center of the seat. If, for example, the occupant shifts his weight to accommodate a package on the seat beside him, a lateral shift of two or three inches off-center can place the heaviest load point in a dead-zone, where there are no sensors. Passengers sometimes put their feet on the dashboard, or out of the window. All of these variations can affect sensor performance.

“A good development program with properly executed FMEAs would catch all that.  Still intrinsic variations in those sensors must be taken into consideration” he says.

Nonetheless, this issue of occupant sensor detection reliability is widespread and has led to many manufacturer recalls. For example, in 2002, General Motors recalled some 2000 Chevrolet and GMC C/K models, because the air bag sensing diagnostic module (SDM), contained “an anomaly that could result in the driver and passenger’s air bag failing to deploy during certain frontal collisions.”  In February 2010, Hyundai recalled some 2010 Tucson vehicles, because “properly seated adult right front seat passengers weighing over approximately 240 pounds cause the passive occupant detection system (pods) module program to illuminate the air bag warning lamp.”  In 2011, Kia recalled some 2007-2008 Sorento passenger cars because “the occupant sensor might misclassify an adult and turn off the front passenger air bag.” In 2010, Nissan recalled some 2005 through 2007 Infiniti G35 sedans because the wire harness connecting the belt tension sensor and the occupant detection sensor control unit under the front passenger seat “can experience relative movement which can cause wear and oxidization of the terminals and may cause interruption of the signal,” causing a non-deployment in a crash.

The rule establishes a new Federal Motor Vehicle Safety Standard 226 Ejection Mitigation. FMVSS 226 applies to the side windows next to the first three rows of seats in motor vehicles with a gross vehicle weight rating of 10,000 pounds or less. The performance-based standard would institute a compliance test in which an impactor would be propelled from inside a test vehicle toward the windows. The ejection mitigation system would have to prevent the impactor – based on the mass imposed by a 50th percentile male’s upper torso on the window opening – from moving more than a specified distance beyond the plane of the window.  Each side window would be impacted at up to four locations around its perimeter at two time intervals following deployment, to ensure that the airbags remain deployed for the beginning and end stages of a rollover.

The ejection mitigation rulemaking was mandated under the Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users, the massive transportation bill of 2005. NHTSA was to have issued a final ejection mitigation rule by September 1, 2009, when SAFETEA-LU’s funding expired.

The proposed rulemaking, published in December 2009, made a stronger push for laminated side glass as a partner with side airbags in keeping occupants contained:

“Advanced glazing could have a role in complementing ejection mitigation curtain systems. NHTSA tested several vehicles’ ejection mitigation side curtain air bags both with and without laminated glazing to the 18 kg impactor performance test proposed in this NPRM. In the tests, the glazing was pre-broken to simulate the likely condition of the glazing in a rollover. Tests of vehicles with advanced glazing resulted in an average 51 mm reduction in impactor displacement across target locations. That is, optimum (least) displacement of the headform resulted from use of both an ejection mitigation window curtain and advanced glazing. To encourage manufacturers to enhance ejection mitigation curtains with advanced glazing, this NPRM proposes to allow windows of advanced laminated glazing to be in position, but pre-broken to reproduce the state of glazing in an actual rollover crash. Although the glazing is pre-broken, the laminate in combination with the remaining integrity of the glazing acts as a barrier to ejection.”

To encourage manufacturers to enhance ejection mitigation curtains with advanced glazing, the NPRM proposed to allow advanced laminated glazing to be in position, but pre-broken to reproduce the state of glazing in an actual rollover crash.

But the agency made it clear that it was not married to this aspect of the proposal. It debated the merits of testing with movable laminated glass windows up or down or pre-broken, and put the question out to automakers. But, the agency also noted that it was loathe to completely disembowel the incentives for laminated glass:

“The agency is contemplating alternatives to the approach of allowing windows to be in place and pre-broken. One option would be to test with all movable windows removed or rolled down, regardless of whether the window is laminated. Fixed laminated windows would continue to be kept in place, but pre-broken. This would assure that the ejection mitigation performance of vehicles with laminated windows is equal to those without laminated windows, when the windows happen to be rolled down. However, this would not provide an incentive to vehicle manufacturers to install advanced glazing in movable windows.”

In response to the NPRM, Automakers – notably Honda and Ford – argued that in real-world rollovers, advanced glazing is often detached from the frame and pre-breaking it for a test configuration didn’t simulate what happens in a rollover. This prompted the agency to take a split-the-baby-in-half approach.

Under the new standard, movable advanced glazing can not be the sole means of meeting the displacement limit, and the 16 km/h-6 second test must be performed without it. The agency argued

“This approach will assure a reasonable level of safety when side glazing is rolled down or when the severity of the rollover damages or destroys the effectiveness of the glazing, and still encourages the use of advanced glazing as a countermeasure to supplement the vehicle’s performance in meeting the 20 km/h-1.5 second test.”

So, will this really encourage the installation of laminated side glass? Or does it delay it?

Part Ardis, a Memphis attorney who has litigated ejection cases and a long-time advocate for laminated glazing, has argued that laminated glass should be used in conjunction with side airbags to complete the occupant protection system.

“Seat belts restrain, they do not retain,” he says.

Over a three-year period, GM had offered fleet buyers as a cost savings the option of deleting the standard side airbags in 2006-2008 Chevrolet Impalas and MY 2008-2009 Chevrolet Cobalt and Buick LaCrosse models. Last month, investigations by SRS and the Kansas City Star revealed that the troubled automaker and Enterprise, its biggest fleet customer and the nation’s largest used car seller, were re-selling these altered fleet vehicles – mostly the Impalas –  to retail consumers and advertised them as having the important safety feature.

After the story received national attention, Enterprise, which ordered 66,000 Impalas without the standard side air bag, offered to buy back 750 of them sold under false pretenses for $750 over the Kelly Blue Book value. GM offered a desultory defense of the practice, saying that it did not violate NHTSA’s minimum standards for side impact protection and that the discount was an important selling point for its fleet customers.

NHTSA, however, has taken the matter more seriously. On September 2, SRS president Sean Kane wrote to NHTSA Acting Administrator Ronald Medford asking the agency to amend its side-impact NCAP information for the affected models. Medford responded two days later, with a thank-you note to Kane and a commitment to quick action.

“In light of this information, the agency reviewed side airbag data provided by GM for the models in question and found the information provided is misleading,” Medford wrote. “Accordingly, the agency has revised the safercar.gov website to indicate that side curtain airbags are optional equipment for Model Years (MY) 2006-2008 Chevrolet Impalas and MY 2008-2009 Chevrolet Cobalt and Buick LaCrosse models. The agency also amended the crash test ratings information to reflect that the models tested for side impact crash protection were equipped with the optional side curtain airbags.”

Further, Medford said, beginning with MY 2011, the agency would request that vehicle manufacturers specifically state whether fleet models have different safety equipment from those models sold at dealerships and any differences will be noted in the ratings information provided.

The Impala, for example, won a five-star side-impact crash rating for the front driver’s seat and the four-star rating for the rear were earned with the aid of the side curtain air bag. The vehicle would have likely received a lower rating without it.

“NHTSA clearly recognized that this is an important issue to consumers – and not just in this immediate instance with GM vehicles,” Kane said. “By taking the extra step and requesting manufacturers disclose differences in fleet safety equipment, the agency is sending a clear signal that it won’t be party to the obfuscation of what is really ‘standard.’”

Kane also wrote to GM CEO Fritz Henderson in early September, suggesting that GM ought to be an active participant in undoing the damage. While GM did remove the erroneous information from its Certified GM website, many GM dealers continued to advertise the Impalas as having the standard feature. Kane asked GM to re-brand the altered vehicles “to alert all future purchasers and dealers that this safety equipment was not included.” SRS’s request also called on GM to immediately “change its advertising and marketing materials to reflect that the feature is not standard, and that you alert all dealers and car buyer’s guide organizations of this anomaly on the 2006 through 2008 Impala, 2008 through 2009 Cobalt and any other vehicles that GM has marketed with “standard” side curtain airbags that were offered to fleet buyers without the feature.”

GM replied the following day, denying that the status of safety feature was ever hidden from buyers:

“When modifications or deletes are made to a GM vehicle for fleet purchase, the deleted equipment is clearly marked on the original window sticker as well as on the invoice. In GM-sponsored closed auctions, the content of each GM vehicle is fully disclosed,” said Brian Latouf, GM’s Director Global Structure & Safety Integration Center in a letter to SRS.

Otherwise, Latouf said, the information on how to tell if the vehicle actually contained the standard side airbag was tucked away in the owner’s manual. In the case of auctions outside of GM’s control, buyer beware, he added.

In addition, GM said that it had taken steps to prevent further misunderstandings, including: modifying its GM Certified website so that when a dealer printed the window sticker, the side airbag feature would no longer be automatically listed; contacted internet seller sites, such as AutoTrader.com, to inform them about the deletion for fleet vehicles; asked eBay to change its advertisements for all certified GM used vehicles. The manufacturer also asked dealers with GM certified used vehicles and third party providers to correct their window stickers for the affected vehicles.

SRS estimates that approximately 200,000 fleet vehicles have the deleted side curtain airbags despite GM’s assertion that the feature was standard.

More on SRS investigation into deleted side curtain airbags