When workers are exposed to high noise levels in the workplace, they can suffer from various adverse health effects. These can be caused by a single exposure to a very loud noise or by exposures to raised levels.
The effects of noise on hearing depend on:
- noise intensity or sound pressure (dB)
- frequency or pitch of sound (Hz)
- exposure time
- distance from source
- individual susceptibility (age, disease, genetics etc)
- nature of the sound (reverberation, impact noise etc)
- other factors (lifestyle, hobbies).
The most well-known effect of occupational noise is loss of hearing. However, it can also aggravate other health conditions. Some individuals are more sensitive to the effects of noise than others and will suffer harm more readily through noise exposure.
Physiological effects of noise
The effects of noise on the psyche are dependent on the individual and what they consider to be acceptable. Different sounds affect people differently. Noise may startle, annoy, and disrupt concentration. Even nuisance noise can lead to issues with concentration, productivity, irritability, and stress, and must not be confused with excessive or prolonged exposure to noise. Technically nuisance noise is ambient noise levels between 50dB(A) to 60dB(A), which are below the levels that could damage a worker hearing but cause annoyance e.g., dripping tap. They affect individuals in different ways depending on several factors, such as the volume of the noise, how long it occurs, and how long it occurs (continuous or intermittent). Excessive noise can influence occupational accidents rates by affecting the accuracy of movements and perception of auditory signals. For industry loss of attention, work efficiency and productivity are extremely important outcomes of noise exposure.
Loss of hearing or hearing impairments
Common symptoms of noise induced hearing loss (NIHL)
It’s important to spot hearing loss as early as possible because early symptoms can help to identify the problem quickly and prevent permanent hearing losses.
Early warnings can include:
- ringing in the ears (tinnitus)
- inability to hear soft and high-pitched sounds
- muffling of speech and other sounds
- trouble understanding conversation at a distance or in a crowd
- listening to music or watching television with the volume higher than other people need
- difficulty hearing the telephone or doorbell
- finding it difficult to tell which direction noise is coming from
- regularly feeling tired or stressed, from having to concentrate while listening
- answering or responding inappropriately in conversations
- reading lips or more intently watching people’s faces during conversations
- feeling annoyed at other people because of not understanding them
- withdrawal from social interaction and,
- feeling nervous about trying to hear and understand others.
Research suggests it can take 10 years from the time someone notices they have hearing loss before they do anything about it.
Many of the early warning symptoms of NIHL are subtle often causing a worker to ignore them until the damage is done. For this reason, it is important to use audiometry testing as a screening test for hearing losses in the occupational setting. This simple quantitative hearing test can be used to identify early losses or TTS. Once identified this should prompt improved controls to prevent any further or permanent hearing losses.
Temporary hearing loss
Known as a temporary threshold sift (TTS) this loss of hearing is due to exposure to noise above the 85dB level but below approximately 100dB or highly hazardous noise. It is in essence an intrinsic form of protection as sensitivity of the Organ of Corti is reduced during TTS, providing a transitory auditory fatigue or temporary hearing loss from which the ear will recover however long it takes. Originally it was the loss which resulted from a day’s exposure to noise and from which the ear recovered overnight. In most people recovery occurs in the first hour or two after exposure depending on the level of noise. The extent of the TTS depends on the type of noise responsible. Usually with this type of impairment no physical signs appear, the ears appear normal and there is no pain or dizziness. Early signs and symptoms may be tinnitus or ringing in the ears and a slight muffling sound.
Permanent hearing loss or noise induced hearing loss
This occurs because excessive and prolonged exposure to noise damages the delicate hearing mechanism of the inner ear (Organ of Corti). Loss in acuity occurs first in 3000-6000Hz band but characteristically at 4000Hz, and with time and continued exposure these frequency losses increase, and the lower frequencies begin to be affected. The losses are subtle and are often unnoticed until the damage is severe and impacts the workers communication skills. Generally, permanent hearing loss tends to be highest after 10 years of exposure and it is known that TTS and permanent hearing loss run parallel. It is the most common preventable occupational health condition across the world. The level of noise that is likely to damage hearing varies depending on the individuals’ characteristics and the duration of exposure to noise. The exposure limits established by countries is deemed to be that level at which unprotected exposure will not cause adverse health outcomes.
Noise induced hearing loss does not only occur at work. Environmental exposures through activities such as carpentry, metal work and attending night clubs are known to expose individuals to noise levels above 95dB causing hearing loss which may exacerbate any occupational exposure to noise.
Noise induced hearing loss is caused by chronic exposure to noise above or more than the upper exposure values. This differs from acoustic trauma which can cause damage from a one-off exposure.
Acoustic trauma or acoustic shock
This is caused by short bursts of extremely loud noise in a sudden single exposure such as an explosion or gun shots. It is often associated with a rupture of the ear drum due to the force of the trauma. The hearing loss experienced can be temporary returning to normal or near normal within three months.
Other effects of noise
Noise can influence other systems of the body i.e the cardiovascular system, resulting in an increase in blood pressure and the release of catecholamines in the blood (catecholamines are hormones which help the body respond to stress or fright and prepare the body for fight-or-flight reactions8). An increased level of catecholamines in the blood is associated with stress, making people breath faster, raise blood pressure and send more blood to organs such as brain, heart and kidneys. It may also cause ear pain, nausea, reduce muscle control and diminished visual fields both for colour and form. Prolonged exposure over a period may well cause occupational stress in an individual.
Excessive noise can also increase the likelihood of undesired events or incidents by:
- distracting workers, such as drivers
- making it harder for workers to hear and understand instructions correctly
- masking the sound of approaching danger and warning signals
- contributing to irritation and annoyance that may lead to human error.
Exposure of high noise in pregnant workers can affect an unborn child. Research suggests that prolonged exposure of the unborn child to high noise levels during pregnancy may influence a child’s hearing later in life with the low frequencies have a greater potential for harm.
Many chemicals in the workplace are Ototoxic too and exposure to these chemicals even in areas where noise levels are controlled may cause exacerbated hearing loss in workers.