Siliguri, Nov. 29: The decibel din is taking its toll on the town. Airhorns are the culprits and residents exposed to the shrill honking their hapless victims.

Cases of hearing impairment are on the rise, as are horn-happy drivers who break pollution norms and breach the sanctity of silence zones with equal impunity.

The annoying airhorns are banned by law and police book vehicles using the devices and fine the drivers. But that has done little to stem the menace.

A police survey has found that around 55 per cent of the trucks, lorries and military vehicles that ply on Siliguri roads flout airhorn norms. The details of a detection drive for vehicles with airhorns, conducted by Siliguri police on July 10, vindicate the findings of the survey.

Police collected Rs 1.35 lakh through spot fines, and booked 64 vehicles within six-hours. In another raid last month, they booked 33 buses and collected around Rs 80,000. This month, the police booked some 40 buses for flouting air horn norms.

?Of the 500 buses which connect Siliguri with Naxalbari, Kharibari and Phansidewa, more than 75 per cent use air horns. They don?t care about the laws laid down in the Motor Vehicles Act or the norms of the pollution control board,? said a senior traffic department official.

The ear-piercing noise of the horns, however, do a lot more damage than just irritating people on the street.

Doctors said cases of noise-induced hearing loss are on the rise in the town.

?On an average, we get around 13 cases related to hearing impairment every month. And the numbers are on the rise,? said T.K. Kar, an ENT surgeon attached to Siliguri Subdivisional Hospital.

The airhorn effect is also plainly visible from the long queues for audiometry tests outside places like North Bengal Clinic, arguably one of the best nursing homes in the town.

Proloy Chakravorty, a dealer in hearing aids, said: ?We sell around 10 to 12 hearing aids each month. The numbers have started rising in the past two years.?

Kar said sustained exposure to air horns affects the inner ear. ?It is the membrane of the cochlea which is damaged. Constant or prolonged exposure to noise levels above 70 decibels results in loss of hearing at ages beyond 55. Moreover, disorders of the cochlea can?t be cured,? he said.

?Instantaneous injury to the outer ear can rupture the tympanic membrane (located in the middle ear). Exposure to shrill noise, like those emitted by air horns, can rupture the ear?s membrane. Also, the ligaments inside the ear can be sprained,? Kar added.

What has frustrated the administration is that the drivers don?t even spare the no-horn zones of the city ? in front of the subdivisional hospital and at Pradhanagar (where there are four nursing homes).

?We had to come out of the hospital a few days ago and tell the drivers of an army truck and a bus, who were blowing their horns incessantly, to stop the noise as it was disturbing the patients,? said a doctor at S.D. Hospital.

As it is, being close to Hashmi Chowk, a major crossing with traffic congestion, the area is prone to the blowing of horns.

?The official silence zone signboard is flouted all the more with the use of airhorns,? said Mayor Bikash Ghosh.

Deputy superintendent of police (traffic) Farhat Abbas said: ?Heavy vehicles like trucks and lorries, which ply through Siliguri on their way to Calcutta on the one hand and the Northeast on the other, are often found to flout air horn norms. They bring in their highway psyche to the town. So do the drivers of the buses plying between Siliguri, Kharibari, Phansidewa and Naxalbari.?