Armed with a noise-measuring app, Nairobi-based teacher Alice Wawira was determined to prove that a bus she boarded on August 31 was playing music at volumes at least 21 units louder than acceptable.
She started the app and let the technology do the analysis. The results shocked her. The bus was playing music at an average of 106 decibels (dB), well above the 85-decibel threshold for safe volume levels. It detected a maximum of 114 decibels and a minimum of 94.9.
“It is the most hazardous noise level I have ever encountered,” Ms Wawira told BDLife.
She raised the matter with the conductor, but nothing came of it. She then took the drastic step of alighting midway through her journey. She had been heading to Juja from Nairobi and had to leave the bus at Githurai.
Experts, including the United States’ National Institute for Occupational Safety and Health (NIOSH), advise that at 106 decibels, the level Ms Wawira detected, one should not be exposed for more than three minutes and 48 seconds at a time.
“This is a serious health issue for the people immediately affected-the conductor, the driver and their families,” Ms Wawira said. “After some years, these people will need hearing aids.”
Hearing loss
Ear, nose and throat surgeon, Dr Kennedy Kipkoech, who works with Equity Afya, advises Kenyans to use Wawira’s approach to check whether they are in environments detrimental to their ears.
“If you want to really understand your exposure, just download those apps,” said Dr Kipkoech. “We call them sound level meters. They average the total noise you are exposed to in a particular place.”
Explaining how prolonged exposure to loud volumes can damage the ears, he notes that hair cells inside the ear can snap and fail to recover.
“Sound energy is transmitted into electrical energy for the brain to interpret,” he says, adding that this transformation happens in the inner ear, about four centimetres from the visible outer ear, with the hair cells playing a key role.
These hairs can bend and recover after a while, but if noise is too loud for too long, they die.
“There are times when the damage is irreversable. If the sound is too loud for too long, it causes serious stress until the hair cell dies. The more persistently you expose yourself, the more cells die. Unlike hair cells in birds or amphibians, human hair cells, once dead, stay dead,” he says.
Noting that normal human speech ranges from 60 to 70 dB, Dr Kipkoech says people should not dismiss loud music in open spaces or through earphones as a mere nuisance.
“The higher the decibel level, the higher the risk,” he says. “There is also a time factor-how long you are exposed. Both play a critical role in the risk of hearing loss.”
In occupational health, 85 decibels over an eight-hour period is commonly used as the threshold at which repeated exposure becomes hazardous. NIOSH states that workplace noise becomes hazardous with repeated exposure at or above 85 dB, and that noise-induced hearing loss is preventable. At higher volumes, safe exposure time drops sharply.
“At 85 dB, you should not be exposed for more than eight hours continuously. At 90 dB, the allowable exposure drops to four hours. At 95 dB, you must halve that to two hours,” explained Dr Kipkoech.
This is why personal listening devices require special caution, he says. Earbuds and in-ear headphones deliver sound directly into the ear canal, encouraging long listening sessions without anyone noticing the volume.
“Long ago, we had what I call communal hearing,” he says. “There’s a TV, we’re all listening, and a parent says, ‘Turn that down.’ That was a form of self-regulation. Now everyone is on their earphones, in the streets, and we don’t know how loud it is. Sometimes, sitting next to someone in a matatu, you can hear their music more than they can.”
The World Health Organization advises keeping personal-device volume low, using well-fitting noise-cancelling headphones, limiting time in noisy environments, taking listening breaks and monitoring sound levels. It warns that loud sound exposure can cause temporary hearing loss or tinnitus, while regular or prolonged exposure can permanently damage sensory cells.
For those working in noisy settings-factories, workshops, bus termini or venues with heavy machinery-Dr Kipkoech says prevention shouldn’t rely on willpower alone. Employers and regulators can reduce risk through engineering controls, shorter exposure periods, rest breaks, monitoring and protective gear such as earplugs or earmuffs.
He also cautions against assuming the ear will always recover after a loud event. Muffled hearing or ringing after a concert may fade, but that doesn’t mean no harm was done.
“You might be lucky, but you don’t know the resilience of your inner hair cells. Chronic exposure will wear them out, even if you’re banking on recovery.”
A single extremely loud event-above 120 dB, up to 160 dB, such as in minefields or war zones-can rupture the eardrum, dislocate the tiny middle-ear bones, or damage inner hair cells directly.
Warning signs include needing people to repeat themselves, missing words on the phone, struggling in noisy conversations, and hearing persistent ringing or buzzing. Dr Kipkoech recommends at least one hearing check-up a year, and more frequent reviews for those regularly exposed to high noise.
Hearing aids can help those with hearing loss but are not cosmetic devices, he stresses. “This is something you can prevent. But if you don’t, noise-induced hearing loss is permanent.”