Curbing Air Bags'
New smarts, new sensors, and
variable inflation could reduce
injury and death
By PETER WEISS
and costly equipment, he argues, people should be better taught to use seat belts and to put children and small adults in the back seat. "The solution is education. It's not technology," he says.
Automakers have already introduced some changes to air bag equipment to reduce air bag-induced injuries, but these alterations are considered only stopgaps until more sophisticated solutions are ready. Foremost among the changes is so-called air bag depowering, which means installing air bags that inflate more slowly and to a lesser volume than the original designs. Most 1998 American vehicle models contain air bags depowered by 20 to 35 percent compared to 1997, says Felrice.
Engineers have also incorporated an air bag disabling switch for the passenger side of new vehicles with only a single row of seats, such as pickup trucks. Under limited circumstances, the federal government is also allowing vehicle owners to install on-off switches or disconnect air bags in older models.
Companies keep tight wraps on many details. "It's a competitive issue for manufacturers," explains Felrice. "They all want to be first with safety improvements. Whether it's night vision or antilock brakes, safety sells these days."
Earlier this month, the U.S. government reconfirmed its commitment to technology as a necessary part of preventing crash fatalities and injuries. In a Sept. 14 preliminary ruling, NHTSA unveiled plans to order vehicle makers to install smarter restraints in 25 percent of new passenger cars and light trucks by Sept. 1, 2002, and in all new models by Sept. 1, 2005. Instead of mandating specific technologies, the agency will require vehicles to pass a battery of tests.
These plans demonstrate that NHTSA officials, as well as industry designers, regard better crash prediction as a high priority
"The challenge is to predict this event with very little up-front information," Phen says.
In a typical crash, the air bag-control microprocessor must decide within 20 milliseconds whether or not to fire the air bag. Otherwise, the bag won't be fully deployed before the occupant strikes it. During that time, the controller examines voltage readings from a tiny accelerometer mounted at the front of the passenger compartment, typically just behind the firewall.
To interpret the often wildly fluctuating deceleration and acceleration of a car during an accident, the computer employs problem-solving pathways, or algorithms. They either compare the accelerometer's signal to a library of known crashes or extrapolate forces and other crash parameters from accelerometer readings.
&nnbsp; Accelerometer readings vary greatly
Air bags punch out of their dash- board cocoons at more than 140 miles per hour. Because of their speed, they both save lives and occasionally squander them.
The rapidly inflating nylon sacks have prevented nearly 3,500 auto collision deaths since the late 1980s, according to the National Highway Traffic Safety Administration (NHTSA). From 1991, when the first air bag-induced death was reported until Sept. 1, 1998, the agency has tallied 113 people, mostly children and small adults, killed by the bags during minor accidents when their lives weren't otherwise at risk.
"Anyone who gets too close to [an inflating] bag, whether a young child or a 300pound football player, is in big trouble," says Barry Felrice, director of regulatory affairs for the American Automobile Manufacturers Association. Air bags, which are inflated by gas from a rapidly burning propellant and sometimes also from a pressurized cartridge, have caused nonfatal injuries including broken bones, burns, and eye damage, although the damage may have been worse in many cases had the air bag not deployed.
Today's automobiles carry only one-sizefits-all air bags. Nonetheless, these bags, by federal decree, pack a wallop intended to immobilize an average-size man. So, by design, they unleash too much energy for people at the smaller end of the scale.
As this dark side of air bags gained wide attention over the past few years, automobile manufacturers and the companies that build safety restraints for them stepped up efforts to develop a safer technology.
"It's a difficult problem, in my opinion, but that doesn't mean it's not achievable," says Robert L. Phen, program manager for energy and surface transportation at the Jet Propulsion Laboratory (JPL) in Pasadena, Calif. Phen led a year-long JPL study of advanced air bag technology for the National Aeronautics and Space Administration and NHTSA. The study, released in April, concluded that in model
year 2003 "systems should be able to remove most of the risk of injury from deploying air bags."
To achieve this goal, the auto industry must boost the ability of airbag-control computers to predict within an instant of onset a crash's severity. Too often today, restraint engineers say, the computers that control air bag firing misjudge the severity of a crash.
Safety improvement also relies on developing sensor arrays that can feed the air bag controller up-to-the-millisecond details about vehicle occupants, such as their weight, position, and whether or not they are wearing seat belts.
At the same time, the air bags themselves must also become more talented-for instance, by being able to inflate at several different rates and pressures. Engineers must coordinate all new air bag technology with the advanced seat belt features that are also under development, such as automatic tightening at the start of a crash.
Air bag technology is a highly controversial issue. James Walker is the air bag specialist for the National Motorists Association, a motorists' advocacy group based in Waunakee, Wis., and a vocal critic of mandatory air bags. He says it is folly to make air bag systems more complex. "There are just too many points of failure, and we can't make the simple systems work now," he argues.
Walker notes that millions of air bag-equipped cars have been recalled, many of them because bags have fired at random, when no accident was taking place, sometimes causing injuries.
The high-tech approach is "backwards," says Morris Kindig, president of TIER ONE, an automotive electronics market research firm in Mountain View, Calif. The firm has just completed a study of sensors that would provide information about the occupants of a car to the air bag controller. Rather than installing complex