Three ear specialists say they have treated people who have developed hearing loss after being involved in collisions when driving at low speed.

They believe the problems were caused by the high-decibel level when the airbag inflates.

The doctors think there could be a big increase in injuries in the future since car manufacturers are planning to install more airbags.

Long-term effects

Writing in the British Medical Journal (BMJ), they describe two cases in which people driving at speeds of between 15 and 20mph had collisions that resulted in hearing loss.

Neither of the two suffered any other injuries.

A 38-year-old woman, with no known history of hearing problems, suffered tinnitus and hearing loss in both ears, after the airbag struck her on the right side of the face.

The hearing in her left ear gradually improved, but the problems in her right ear continued.

The other person was a 68-year-old man, who had suffered hearing loss before the crash. However, this worsened substantially after the collision.

Rifle crack

Airbag noise levels tend to be in the range of 150 to 170 decibels, but the level depends on the size of the car, the number of occupants and other factors.

Noise levels have been tested on squirrel monkeys as it is difficult to find human volunteers. No permanent hearing loss was noted.

But Mr Graham Buckley, a co-author of the BMJ article and a head and neck surgeon at Leeds General Infirmary, said it was difficult to test the impact of short-term high-frequency noise on monkeys.

He said: "People tend to imagine an airbag like a billowing cushion, but it is more like an explosion. When it inflates, it is like a rifle crack to the ear. It lasts for a tenth of a second."

The article in the BMJ is an attempt to test the waters to see if other doctors have noted similar cases.

Mr Buckley says there may be a case for manufacturers to attempt to lower the decibel levels.

Doctors have noted other types of injury related to airbags, including face, eye and chest problems, but there is little research into hearing damage.

The BMJ article says this could be because people may put any problems down to other factors related to the collision.

Saving lives

Mr Buckley believes there could be more hearing damage in the future because car manufacturers are starting to install more airbags to protect passengers, including side airbags.

He says these would have to be installed very near the driver's and passenger's ears and could cause more damage.

Mr Buckley is also worried about the level of noise caused by using multiple airbags.

Airbag manufacturers Autoliv said the impact depended on car design.

The Society for Motor Manufacturers and Traders says concerns about airbags need to be balanced against their role in saving lives.

"Airbags have proven to be very effective in saving lives," said a spokeswoman.

"But if there was seen to be a significant cause for concern, we would look at it."

Over 3,500 people a year die in road accidents in the UK. A large proportion of deaths are due to frontal impact.