Is the Support for Air Bags Overblown? : Safety: While deployment sometimes causes injuries, experts say the risk of death from an unprotected frontal crash is far greater.

The air bag, now in at least 10 million vehicles nationwide, has been credited with saving more than 300 lives and preventing thousands of serious injuries during motor vehicle accidents.

But the bags, which use an explosive charge to inflate nearly instantaneously, present some hazards, as a growing number of cases have shown.

The New England Journal of Medicine reported that an air bag struck a 27-year-old Danbury, Conn., woman in the chest, creating a pressure wave that tore a hole in her heart.

That unusual injury and others, including burns, eye damage and broken bones, are being watched carefully by federal safety officials and the insurance industry.

Yet safety experts say these incidents should not discourage public support for air bags. They say the risks posed by the bags are far outweighed by any risks occupants face during a high-speed frontal crash in a vehicle without one.

“In a few cases we are aware of, it appears the air bag itself has caused injuries, and we are concerned about that,” said Charles A. Hurley, a senior vice president for the Insurance Institute for Highway Safety. “But we are not alarmed by what we see. In fact we are very impressed with overall performance of air bags.”

Safety experts say studies show that in major frontal collisions, drivers in vehicles equipped with air bags had a 29% lower death rate than those riding in the same make and model without an air bag. Still, the institute is conducting a study of air-bag-related injuries to determine how the bags can be made to operate more safely.

Hurley and other experts say the injuries also underscore the need for motorists to follow safety precautions in vehicles equipped with the bags.

The most common misconception, they say, is that an air bag is a substitute for a seat belt and shoulder harness.

Air bags, which date back to some 1973 vehicles, protect the occupants of a vehicle mainly during a frontal collision at speeds above 12 m.p.h. During side and rear impacts, rollovers and frontal crashes at slower speeds, the air bag generally will not inflate. Without a seat belt and shoulder harness, an occupant would be free to hit the steering wheel, dashboard or other part of the vehicle or be thrown out.

But even in a high-speed, head-on crash that causes the bag to inflate, seat belts are needed to ensure that occupants are properly positioned so that the air bag works correctly. And an inflated air bag will do little to hold an occupant inside a vehicle during a collision.

In the Danbury accident, doctors at Danbury Hospital concluded that the driver’s heart injury was caused by her failure to wear a shoulder belt.

But there may also have been another factor. There is growing evidence that air bags pose a danger to drivers who are too near the wheel when the bag deploys and consequently come in contact with the air bag too soon--as it inflates. The protective cushion comes in to play only when the bag begins to deflate.

Because of patient confidentiality, few details are known about the incident in Danbury. But safety experts who read about the case theorize that the driver may have been sitting or leaning very close to the steering wheel when her vehicle struck a parked vehicle at about 15 m.p.h. last September.

During a high-speed accident, sensors in the front of the vehicle cause sodium azide to ignite. That produces nitrogen, the gas that inflates the bag. The inflation time, about 1/25th of a second, is so quick that the air bag usually is fully deployed by the time a vehicle occupant, thrown forward by the collision, strikes it or even the seat belt safety harness. By the time the person hits the bag, it should be deflating.

This timing is so critical that air bags have to be specially “tuned” for each vehicle, taking into account the vehicle’s so-called crash pulse--how long it takes for the force of the crash to be felt in the passenger compartment.

Occupants near the wheel when the bag deploys risk being struck by a force propelled as fast as 211 m.p.h. Safety experts say that would explain what happened in the Danbury case and several others.

In one case, an air bag is believed to have contributed to the fatal chest injuries suffered by a Windsor, Conn., man whom witnesses said had passed out and was leaning against the wheel moments before his car struck a tree. Air bags also were implicated in fatal injuries of two elderly women in separate accidents. Safety experts believe that they, too, may have been too close to the wheel when the air bag deployed.

The incidents demonstrate that drivers need to sit as far from the steering wheel as possible, said Philip W. Haseltine, president of the American Coalition for Traffic Safety, a Virginia-based educational organization funded by the automotive industry.

While short people may be at greater risk of injury because they generally sit closer to the wheel, said Hurley, there is enough clearance between the wheel and even the shortest drivers to provide reasonable safety. A General Motors’ study showed that the risk of injury declines greatly when the driver is more than 2 inches from the wheel when the bag inflates, he said.

Such advice also is recommended for drivers of vehicles that are not air-bag equipped. In frontal collisions, which account for about half of all occupant fatalities on the roadway, the steering wheel often causes the major injuries to the driver.

Chest injuries from air bags are additional evidence for wearing a seat belt and shoulder harness. Without such restraints, any hard braking before the actual collision could propel a driver forward against the wheel, setting the person up for serious injury when the bag deploys.

Air-bag-related injuries may be corrected by design changes. Some already have been made.

For example, there have been several reports of drivers and passengers being burned by hot air-bag gasses. As a result, the vent holes on the back of the bag have been relocated so they are farther from where a driver’s hands are likely to be on the steering wheel.

Experts recommend that if an air bag deploys, vehicle occupants and rescue workers rinse off as soon as possible. A caustic byproduct of the combustion, sodium hydroxide, or lye, is produced in small quantities.

Manufacturers also are studying different bag configurations to determine how the initial force works best during deployment.

Although it’s safest never to use a child seat in the front seat of a vehicle, safety experts say it’s particularly true if the seat is a rear-facing model and the vehicle is equipped with a passenger side air bag. The bag striking the back of the seat could injure a child.

Because of the nature of the rapidly deploying air bag, there simply may be no way to prevent all air bag injuries. But safety officials say that in most cases injuries caused by air bags are far fewer than those occurring in vehicles without them.