Noise is basically an unwanted sound. And ambient noise, also known as background noise, is all of the noise from the environment around you, work/ occupational noises, or noise from a large city and traffic. Sound is measured in decibels which works on a logarithmic scale. The range of human hearing ranges from a little bit above zero decibels to around 140 decibels when it is so loud that it hurts your ears. Some common noises and their decibel levels are: a whisper is about 30 decibels, a normal conversation at a distance of three feet is around sixty decibels, a lawnmower is approximately 90 decibels, and a chain saw is about 110 decibels. An ambulance is even louder, around 120 decibels. The pitch of a sound is measured in the Frequency of Hertz. Human speech is in the range of 500 to 4000 Hertz. Regulation of noise in work environments is by OSHA. OSHA has noise standards. The OSHA permissible exposure limit is 90 decibels as a time-weighted average over eight hours. That means a worker is permitted to work in an environment with up to 90 decibels of ambient noise for up to eight hours a day. If the work environment is louder, say 95 decibels, then the worker can only work in that environment for up to 4 hours per day. And the same for the next 5 decibels louder. At 100 decibels, the worker is only allowed to work in that environment for up to 2 hours per day. Every 5 decibels over 90 decibels results in a halving of the time. So for 110 decibels, the worker is only allowed to work in that environment for one hour. Alterations to the work environment should be made when employees are exposed to noise above the permissible exposure limits. Suppose changes to the work environment are not possible or ineffective. In that case, the employee should be provided with adequate personal protective equipment to decrease the sound level to fall within the permissible exposure limits. It's important to understand that people can still experience noise-induced hearing loss within the boundaries of OSHA's permissible exposure limits. In fact, around 25 percent of people will develop noise-induced hearing loss if exposed to a 40-year lifetime exposure of the 90-decibel permissible exposure limit of eight hours per day. OSHA also sets the noise action level at 85 decibels. If the work environment is 85 decibels or louder, the employer must participate in an occupational hearing conservation program. Components of an occupational hearing conservation program must include: noise exposure monitoring, engineering and administrative controls to decrease the noise the workers are exposed to, a baseline and annual hearing test (audiometric evaluation) for employees, personal protective equipment to protect against hearing loss such as earplugs if engineering and administrative controls were not possible or not effective, employee education and training regarding noise exposure and hearing loss, record keeping of the hearing conservation program, and the employer must conduct evaluations of the hearing protection adequacy. Occupational noise-induced hearing loss is associated with a signature feature of the audiogram of a high-frequency notch around four thousand Hertz to six thousand Hertz in both ears or one ear. For public noise issues, state and local governments are responsible for addressing public noise issues. Noise exposure was traditionally considered an occupational health concern that was monitored as mentioned. Excessive occupational noise is associated with cardiovascular disease. And cigarette smoking may have a synergistic effect with noise on cardiovascular disease. Additionally, studies done to determine the impact of noise on populations living near airports found similar harms as seen among workers exposed to loud noise. Studies have also been done to determine the effects of traffic noise. Outside of noisy work environments, one of the most problematic noise exposures is due to traffic noises in busy cities. Traffic noises in cities may cause a substantial amount of hearing loss from noise but are challenging to study due to the many variables and possible sources of confounding involved. The health effects of excessive noise exposure, in addition to hearing loss, are: increased risk of cardiovascular disease, psychological stress, and mental health disorders, impaired cognition in children, and sleep problems. Noise is associated with increased catecholamines, increased sympathetic tone, activation of the adrenal cortex by the hypothalamus, with the release of cortisol as well as adrenaline and noradrenaline. There are two main types of hearing loss: sensorineural hearing loss and conductive hearing loss. Sensorineural hearing loss is caused by damage to the inner ear, which may be irreversible. Conductive hearing loss is from a mechanical obstruction to transmitting energy from sound waves from the tympanic membrane, such as cerumen impaction. Common causes of conductive hearing loss besides cerumen impaction are sequelae of otitis media and eustachian tube dysfunction. And there can be mixed sensorineural and conductive hearing loss. Excessive noise exposure causes sensorineural hearing loss. The most common causing of sensorineural hearing loss are noise-induced hearing loss and hearing loss associated with aging called presbycusis. There can be a delay of over ten years until the onset of noise-induced hearing loss following noise exposure. There are also toxicants known as ototoxins that can cause hearing loss or make noise-induced hearing loss worse through synergistic sensorineural effects. An example of a potentially ototoxic substance is the antibiotic, gentamicin, and aminoglycoside, among others. Some other chemicals with ototoxicity are benzene, lead, carbon monoxide, and organomercury. Other chemicals and medications that are ototoxins are some organic solvents such as toluene and other medications such as loop diuretics and chemotherapeutic medications with the catalyst platinum. Sometimes hearing loss is not the only problem; there also may be impairment of understanding what people are saying (decreased speech acuity). Patients may be at risk for or have already sustained noise-induced hearing loss if they experience tinnitus (ringing of the ears) after leaving work, if they need to raise their voice to be heard by a coworker within a few feet (an indication that the noise level may be above 85 decibels, and if they notice temporary hearing loss after leaving work. Most noise at work is from short-duration loud intensity noise exposures.

Reference:

Linares C, de la Osa J, Díaz J. Diseases Due to Physical Factors: Noise. In: Boulton ML, Wallace RB. eds. Maxcy-Rosenau-Last Public Health & Preventive Medicine, 16e. McGraw Hill; 2022.