Look at the numbers.
In 1997, 52 people died when air bags deployed at speeds upwards of 200 m.p.h.
After carmakers were allowed to reduce the force of air bags by about 15 percent, 37 were killed in 1998, 19 died in 1999 and 11 died in 2000 as a result of air bag deployment.
Since air bags began showing up in significant numbers in cars in the early 1990s, they have been credited with saving an estimated 7,224 lives through June of 2001, according to the National Highway Traffic Safety Administration. But those injuries and deaths, particularly of small women and children, remain vexing.
To address this, the National Highway Traffic Safety Administration in the mid-1990s re-wrote the federal motor vehicle safety standards to depower the bags, which had been designed to protect an unbelted man of median size: 5 feet, 8 inches tall and weighed 172 pounds.
“We knew we had to have less aggressive bags,” said Joel MacWilliams of the University of Michigan Transportation Research bio-sciences division. “NHTSA told the industry to de-power the air bags, but it didn’t say by how much. The result is they have generally been de-powered by 15 percent.”
Designers and producers of air bags, such as Autoliv and TRW, did this by creating bags that would inflate based on crash severity. Sensors in these second-generation systems determine the magnitude of impact to inflate the bags at maximum speed, the rate needed to protect the 50th percentile man, in a major collision, or less aggressively in a minor impact.
So some of today’s new cars and trucks feature de-powered air bags, some have two-stage front air bags and some have standard air bags, which the makers consider safe and effective.
Dual-stage air bags are the successors to the de-powered, single-stage air bags, according to Jim Khoury, advanced safety engineer for General Motors North America.
Air-bag system sensors now constantly ask, “Should I deploy?” even if you go over a pothole, MacWilliams said. “They are also capable of asking, `who is on the seat and is that person belted?'”
Air-bag deployment speed is based on the deceleration of a vehicle, Khoury said.
Using technology borrowed from the aerospace industry, a silicon chip is laser-machined to bend in deceleration, he said. A microprocessor measures the forces and strain of that chip and determines whether the bag will inflate and with what force.
In the 1980s, the automakers used ball and tube sensors, said GM’s Khoury. In a crash, a ball rolled through a tube, triggering a sensor that determined deployment.
Khoury said GM typically does 35 crash tests and 60 computer simulations to calibrate the body structure of each model and obtain its crash signature. The crash signature is the individual characteristic of a vehicle, how its structure deforms in a crash to protect the occupants. For example, it took 11 months to prepare (from design to manufacture) dual-stage front air bags for the current Impala, he said.
Air bag suppliers also must address the issue of depowered and multi-stage bags.
“Our responsibility as a supplier runs the gamut,” said Patrick Jarboe, director of communications for Autoliv North America, a supplier of air bags, inflators, safety belts, sensors and seat subsystems in Auburn Hills, Mich.
“Some customers tell us specifically what they want, down to the brackets and bag material. Others give us more of a role in the design and manufacture.” So, in some cases, Jarboe said, the automakers specify exactly what they want in the air bag system and its deployment.
Ford Motor Co. put dual-stage front air bags in its Taurus beginning with the 2000 model year. Taurus also is equipped with seat positioning and safety belt sensors.
Customers at Tyson Ford Lincoln-Mercury take them for granted, said Jeff Robinson, a salesman at the Gary dealership. “People don’t ask about the second-generation air bags,” Robinson said.
But today’s depowered and dual-stage bags are just the first step. The government has required “smart air bags.”
According to Khoury, the term “smart air bags” has become a catch-all that can include dual-stage bags and more advanced bags in the works.
Their sensors will measure such things as weight and position of passengers, crash severity and seat-belt use.
Susan Ferguson, senior vice president for research at the Insurance Institute for Highway Safety, an insurance industry research and lobbying group, said the latest update of the federal rule for front-impact crashes requires bags that protect small women and young children in a 25 m.p.h. crash.
Dual-stage air bags are required in all vehicles beginning Sept. 1, 2005, according to Terry Rhadigan, GM public relations spokesman.
Newer generations of bags will be more adaptable to additional input, for example, whether driver and passenger are buckled in or not.
A smart buckle switch ties into the diagnostics of a computer. A good sensor can tell if it’s only a coin or piece of paper in the buckle, he said.
“We needed a standard that protects more people, including kids,” Ferguson said.
“Manufacturers are having trouble with air-bag suppression technology,” she said. A “smart air bag” system, for example may suppress the air bag if it senses a child is in the front passenger seat.
But it will be designed to deploy if it detects the passenger is the size of a small female, she said.
But less aggressive or benign bags may not offer enough protection in some instances, she said.
All do not see this as a problem, Ferguson continued. NHTSA says depowered air bags have not dimished protection.
To ensure that air bags do not harm children in crashes, manufacturers are considering technology that will detect the presence of a child in the passenger seat and suppress the air bag. This technology has not been shown to be foolproof, Ferguson said.
Doug Campbell, vice president of engineering for occupant safety systems at TRW in Washington Township, Mich., added that an advanced vision system for detection might be available by 2004 or 2005.
That technology tries to track the occupant in rapid movement, so vision sensing could relate to how quickly and at what level the air bag deploys.
7,585 lives saved
The federal government estimates how many lives air bags have saved since they became common in cars in 1990. The National Highway Traffic Safety Administration does this by counting the number of traffic crashes and the number of people killed in those crashes, and then examines seat-belt and air-bag use in fatal and non-fatal crashes, says Tim Hurd, a NHTSA spokesman. When seat belts and air bags are both used, credit for lives saved often goes to the seat belt, Hurd says. NHTSA periodically updates the estimate; the most recent number is 7,585 lives saved as of Oct. 1, up from 7,224 July 1. %%
BELTED UNBELTED
Drivers 6,360 1,781 4,579
Front passengers 1,225 343 882
Total 7,585 2,124 5,461
Source: National Highway Traffic Safety Administration
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