Crackers can legally hit 125 decibels. How loud is too loud for your ears?

It begins with a hiss. A spark races along the fuse, someone steps back, and the night splits open with a bang. For a moment, the whole street flinches.Deep inside every ear on that street, something far more delicate flinches too.In India, a cracker is allowed to be as loud as 125 decibels. But a legal limit is not the same as a safe one."The limit is a regulatory ceiling for products, not a guarantee of safety for the ear," Dr Niraj Kumar Singh, Associate Professor and Head of the Department of Audiology, the science of hearing, at the All India Institute of Speech and Hearing (AIISH) in Mysuru, told India Today Digital. With Diwali on November 8, and the Supreme Court allowing green crackers in Delhi-NCR on November 7 and 8, millions of ears are about to meet that number. So how loud is 125 decibels, and how loud is too loud?HOW LOUD IS 125 DECIBELS?A decibel is the unit used to measure loudness. But its scale is deceptive. Every 10 decibels added means ten times more sound energy. An ordinary conversation is about 60 decibels. Heavy traffic is about 85. A cracker at 125 decibels sits only 40 numbers above traffic, yet it carries about 10,000 times more sound energy.And that legal limit is measured 4 metres from where the cracker bursts. On Diwali night, few of us keep that distance.HOW LOUD IS TOO LOUD FOR YOUR EARS?For a sudden bang, what matters most is its peak, the single loudest instant of the sound.The World Health Organization's Guidelines for Community Noise say that peak should never exceed 140 decibels for adults. For children, whose ears are more vulnerable, the ceiling is 120 decibels. A 125-decibel cracker carries about 10,000 times more sound energy than heavy traffic. (Representative image: Unsplash) Now comes the catch. In open air, every time you halve your distance from a sound, it grows about 6 decibels louder. So a cracker that measures 125 decibels at 4 metres reaches about 131 at 2 metres, 137 at 1 metre and 143 at 50 centimetres."That is the distance of a cracker held in the hand, or a child crouching over one," Dr Singh said.A perfectly legal cracker, held in the hand, can therefore cross the safe limit even for an adult. For a child bending low to light a fuse, the margin vanishes altogether.WHAT DOES A CRACKER DO TO YOUR EARS?A cracker sends out a sudden wave of air pressure that travels straight into the ear.It first strikes the eardrum, a thin skin stretched across the ear canal that vibrates with sound. The vibration passes through three tiny bones into the cochlea, a snail-shaped chamber filled with fluid. Inside it sit about 15,000 hair cells, the tiny sensors that turn sound into signals for the brain."You can imagine a field of tiny wheat stalks swaying in a breeze," Dr Singh said. "A typical conversation-level sound can be equated to the breeze, whereas a cracker at close range is like a storm."A strong blast close by can tear the eardrum and, in rare cases, dislocate the joints between the tiny bones, which may need surgery. Small tears in the eardrum often heal within weeks.The hair cells are not so fortunate. "A blast overloads the hair cells in the inner ear. They can be physically bent or torn, run out of energy, or be damaged by a chemical flood," Dr Singh said. That flood occurs when the thin walls separating different fluids inside the cochlea tear, and the fluids mix."Humans cannot regrow hair cells, so this loss is usually permanent," he said.WHY IS A CRACKER MORE DANGEROUS THAN OTHER LOUD NOISE?The ear is not defenceless. When a sound grows loud, tiny muscles in the middle ear tighten, reducing how much vibration reaches the inner ear. This is called the acoustic reflex.But this guard is slow to wake. "The reflex needs time, roughly a tenth of a second at moderate levels," Dr Singh said. "A cracker's peak arrives in a fraction of a millisecond and is over before the muscle acts. The bang is also unexpected, so there is no chance to brace." The WHO says peak sound should never exceed 140 decibels for adults and 120 decibels for children. (Representative image: Unsplash/Pexels) By the time the ear raises its shield, the blow has already landed.Steady noise is different. It gives the reflex time to help, and it wears hearing down slowly, over years. A cracker, a gunshot or a hammer breaking concrete produces what scientists call impulse noise, a sudden, sharp burst of sound. "An impulse noise is judged by its peak, and studies find it more damaging than steady noise of equal energy," he said.HOW IS CRACKER NOISE MEASURED?Every cracker's voice is tested in an open space, with nothing that could reflect sound for 15 metres around. A sound level meter, an instrument that measures loudness, stands on a tripod 4 metres away and records the bang.It records two numbers. The first, dB(AI), shows how loud the bang seems to the human ear. The second, dB(C)pk, captures the peak, the raw force with which the pressure wave strikes. The legal limits are 125 dB(AI) or 145 dB(C)pk."Both are needed because the ear can be mechanically hurt by a peak even when the perceived loudness looks acceptable," Dr Singh said.WHY DO CRACKERS SOUND LOUDER IN NARROW LANES?A cracker that passes its test in an open field may behave very differently in the lane outside your home."In a lane lined with buildings, sound bounces back and adds to the original, often by several decibels, and it lingers longer," Dr Singh said. Crackers bursting together add even more. Two equal bangs add about 3 decibels, and ten add about 10.IS RINGING IN THE EARS AFTER DIWALI NORMAL?Many people wake after Diwali to a faint ringing, called tinnitus, or muffled hearing. Usually, this is a temporary threshold shift, a short-term dip in hearing."The hair cells are stunned, like your legs after a long run," Dr Singh said. Hearing often returns within hours or a few days.But permanent damage is more likely if the symptoms last beyond 24 to 48 hours, if there was pain, bleeding, discharge or severe dizziness, or if one ear hears less than the other. "Sudden hearing loss is treated as urgent, and treatment works best when started early," he said.HOW TO PROTECT YOUR EARS FROM CRACKERS?Dr Singh’s first piece of advice is distance. Stand at least 4 to 5 metres from where a cracker will burst, and never hold one in your hand.Children need extra care. Give them foam earplugs or earmuffs, because properly inserted foam plugs can cut noise by 20 to 30 decibels. Cotton wool, a common household fix, helps very little. Infants and the elderly are safest indoors, with doors and windows shut. It is also wise to avoid crowded streets and rooftops, where many crackers burst at once.If your ears ring, bleed or hurt after the celebration, resist the urge to pour oil or drops into them. Instead, see an audiologist, a hearing specialist, or an ENT (ear, nose and throat) doctor.A cracker's bang lasts less than a blink. What it takes from the ear can last a lifetime. This Diwali, keep your distance, and let the lamps speak a little louder than the crackers.- Ends