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Airbags are meant to protect drivers and front-seat passengers involved in car crashes, but new research has found that the device actually places people who are either very short or extremely tall at greater risk of injury or death.

"Our findings may be explained in part by the fact that airbags were developed for the 'average' size person, yet may not biomechanically function the same way for occupants outside of the typical height range," said Dr. Craig Newgard, an assistant professor of emergency and preventative medicine at Oregon Health & Science University, who has spent years studying the dangers of airbags.

His latest research, presented this week in Chicago to the annual meeting of the Society for Academic Emergency Medicine, analyzed more than 67,000 people in the United States - 52,552 drivers and 14,732 front-seat passengers - who were in car accidents between 1995 and 2005.

He found that 5 per cent of those were seriously injured. Although this study did not looked at specific types of injuries, it did conclude that people who are shorter than 4-foot-11 (1.5 metres) or taller than 6-foot-3 (1.9 metres) are worse off during a collision than those of medium height, about 5-foot-3 to 5-foot-11 ( 1.6 to 1.8 metres).

Injuries were more pronounced among front-seat passengers who didn't fit into that average height category than for drivers who didn't.

Airbags seemed to present neither a benefit nor a risk to patients in the transition ranges, and height and body weight did not seem to alter the effect of the airbags in those ranges, Dr. Newgard said.

Airbags are designed to deploy when a vehicle hits something or if there is a sudden deceleration. A sensor sends a signal to ignite a chemical propellant, usually a toxic compound known as sodium azide, which produces nitrogen and inflates the pouch.

(The U.S. Centers for Disease Control and Prevention says it has received no reports of injury from sodium azide exposure related to airbags.)

The bags are meant to cushion occupants or prevent them from striking the dashboard or windshield, but they don't eliminate injury.

A bag deploys in less than a 20th of a second and at speeds up to 320 kilometres an hour with a force of 900 kilograms. That can result in cuts or bruises. But more serious harm such as broken bones, head and chest injuries, even death, including decapitations, have occurred.

According to Transport Canada, 15 people have died - eight adults and seven children - over the past 14 years as a result of airbag deployment. However, the department does not count injuries related to airbags.

At greater risk for airbag injuries are people who sit close to the steering wheel and small children, the government notes. Ottawa advises that children aged 12 and younger sit in the back seats and requires that air bag warning labels be placed inside vehicles. In the United States, the federal government mandates similar stickers, but also warns of specific dangers to children under the age of 12.

Dr. Newgard's latest study, which has yet to go through the peer-review process before publication, builds on previous airbag safety research.

In a 2005 report published in the American Academy of Pediatrics' journal Pediatrics, Dr. Newgard and his co-author found that it's not just kids under 12 who are at risk if they sit in the front passenger seat.

Children as old as 14 are also vulnerable according to the study, which involved 3,790 accident reports of children aged one month to 18 years. The report concluded that height and weight among children may not be a good way to assess risk.

Changes during puberty to muscle mass, bone density and bone-mineral content may help explain why air bags pose greater risks to younger teens, yet they seem to protect teens aged 15 to 18, the researchers concluded.

For Denise Desrosiers, neither her middle age nor her average height saved her from serious airbag injuries she says she suffered during a collision two years ago.

Ms. Desrosiers, 46, was a front-seat passenger in a 1997 Hyundai Sonata when her driver rear-ended another vehicle on an Edmonton street.

"I remember a bright, bright flash of light; a really, really loud bang and then it felt like my teeth were being shoved down my throat," Ms. Desrosiers recalled.

She wound up with chemical burns to her face, loss of vision in her right eye, severe hearing loss in her left ear, five operations on her right wrist, which is now fused, limiting her hand movement, and two dental operations (she requires further work) in addition to a host of other unexplained ailments.

And the driver?

"He got out without a scratch," she said.

Dr. Newgard said he hopes his research will help people make informed decisions when travelling in the front seat based on his findings.

"This may be choosing to sit in the back for passengers, or using the air bag on-off switch when available," he said.

He also wants to see vehicle safety agencies include his findings in future guidelines and order airbag on-off switches in all vehicles.

Meanwhile, Ms. Desrosiers has run into road blocks trying to find people who have experienced airbag injuries, since no agencies keep track, and now wants others to know about the hazards. She is hoping for new regulations and new technology to curb the dangers.

"I just want people to make an educated choice," Ms. Desrosiers said. "I had no idea."