Hearing loss is irreversible, isolating, and life changing. If your hearing is damaged in your own time – perhaps from listening to music too loudly in headphones or at concerts – that’s bad enough, but for the life changing injury to take place at work is completely unacceptable and makes the reality of impaired hearing sting that bit more knowing it was caused when all you were trying to do was keep a roof over your family’s head.
We’ve all been there. You’ve not heard something in a conversation, so you ask the person to repeat themselves, but then still can’t hear the reply. You might ask again, but on the third repetition it’s sometimes just easier to pretend you’ve heard. With this in mind, not only is hearing loss itself devastating, but it could then lead a worker to miss crucial information in safety briefings. This in itself could lead to fatal accidents impacting not just that particular individual, but the wider workforce and environment potentially nationally – just consider the impact of a chemical plant leak or an offshore oil and gas platform.
Despite being irreversible and totally avoidable, noise-related hearing loss is still one of the most common occupational health issues, affecting thousands of workers each year. As already mentioned, the damage is always permanent and cannot be corrected by surgery. Even in the short term, exposure to loud noise can cause a temporary change in hearing. These short-term effects include temporary ringing in the ears or a feeling like your ears are blocked. Repeated exposure to noise hazards can lead to permanent tinnitus or hearing loss. As well as hearing damage, noise hazards can also:
- Reduce productivity
- Interfere with communication and concentration
- Contribute to workplace accidents and injuries by making it difficult to hear warning signals
- Create physical and psychological stress
According to International Labour Organization C148 – Working Environment (Air Pollution, Noise and Vibration) Convention, 1977 Article 7 1 an employer has to undertake, and employees have to comply with, the prevention and control of – and protection against – occupational hazards due to noise in the working environment.
Workplace noise sources
Industrial machinery and processes are composed of various noise sources such as rotors, stators, gears, fans, vibrating panels, turbulent fluid flow, impact processes, electrical machines, internal combustion engines etc. The mechanisms of noise generation depend on the particularly noisy operations and equipment including crushing, riveting, blasting (quarries and mines), shake-out (foundries), punch presses, drop forges, drilling, lathes, pneumatic equipment (e.g. jack hammers, chipping hammers, etc.), tumbling barrels, plasma jets, cutting torches, sandblasting, electric furnaces, boiler making, machine tools for forming, dividing and metal cutting, such as punching, pressing and shearing, lathes, milling machines and grinders, as well as textile machines, beverage filling machines and print machines, pumps and compressors, drive units, handguided machines, self-propelled working machines, in-plant conveying systems and transport vehicles.
Following impact and material handling, industrial jet noise ranks incredibly highly as a major cause of hearing damage. Air jets are used extensively for applications including: cleaning, drying and ejecting parts, blowing off compressed air, steam valves, pneumatic discharge vents, and gas and oil burners.
The basic noise sources from compressors are caused by trapping a definite volume of fluid and carrying it around the case to the outlet with higher pressure. The pressure pulses from compressors are quite severe, and equivalent sound pressure levels can exceed 105 dB (A).
There are three basic sources involved in the noise generated by electric motors:
- Broad-band aerodynamic noise generated from the end flow at the inlet/outlet of the cooling fan.
- The cooling fan is usually the dominant noise source, due to discrete frequency components caused by the blade passing frequencies of the fan.
- Mechanical noise caused by bearing, casing vibration, motor balancing shaft misalignment, and/or motor mounting. For large motors in the range of 1000 kW, 3600 RPM, a sound pressure level of as high as 106 dB(A) occurs.
When using woodworking machines, the basic noise sources encountered are:
- Structure vibration and noise radiation – this comes from the work piece or cutting tool - such as a circular saw blade - and machine frame, especially at the mechanical resonance frequencies.
- Aerodynamic noise – this is caused by turbulence, generated by tool rotation and the workplace in the air flow field. Fan dust and chip removal air carrying systems.
- Pneumatic tools like compressed air-powered, hand-held tools such as drills, grinders, riveting guns, chipping, hammers, impact guns, pavement breakers, etc. also contribute to high industrial noise.
Effects on health
In addition to the well-known consequence of noise, which is of course the damage to delicate hearing mechanisms we humans possess, unwanted damaging sound can cause a plethora of other health effects, including hypersensitivity to noise, stress, compromising communications at work, and increases to both heart rate and blood pressure. Sadly, exposure to very loud noise can cause the hair cells of the inner ear to collapse and flatten temporarily, resulting in deafness. Depending on the noise level and length of exposure this may be either temporary or permanent. To compound the damage, even if hearing loss is only temporary it may be accompanied by tinnitus – the sensation of a ringing, buzzing, roaring, clicking or hissing noise in the ears, which is heard when no external sound is present. This is symptomatic of an underlying condition such as ear injury or a circulatory system disorder.
The two kinds of tinnitus are subjective and objective tinnitus.
Subjective tinnitus is caused by ear problems in the outer, middle or inner ear. It also can be caused by problems with the hearing (auditory) nerves or the part of your brain that interprets nerve signals as sound (auditory pathways).
Objective tinnitus is a rare type of tinnitus that may be caused by a blood vessel problem, a middle ear bone condition or muscle contractions. If high noise exposure is repeated over many years, the hair cells in the inner ear may also become permanently damaged resulting in permanent hearing loss. Immediate permanent hearing loss can also occur if someone is exposed to very intense or explosive sounds, e.g. a gunshot or explosion. This type of damage is known as acoustic trauma. In some cases, a very intense sound can actually perforate the eardrum.
The harmful effects of noise may be cumulative and not necessarily confined to the workplace. For instance, the use of personal stereo units and frequenting nightclubs may result in young people having some early damage to their hearing before they even join the workforce. As people respond differently to noise, the exact level at which noise will cause damage is not certain for each person. However, the amount of damage caused by noise depends on the total amount of energy received over time and each person's susceptibility to hearing loss. The degree of hearing loss that occurs is dependent on how loud the noise is, how long someone is exposed to it and, to some extent, individual susceptibility. The frequency or pitch can also have some effect on hearing loss, since highpitched sounds are more damaging than low-pitched ones.
Exposure to a number of common industrial chemicals and some medications can also cause hearing loss or exacerbate the effects of noise on hearing. These substances are called ototoxic substances. Ototoxic substances absorbed into the bloodstream may damage the cochlea in the inner ear and/or the auditory pathways to the brain, leading to hearing loss and tinnitus. Hearing loss is more likely if exposure is to a combination of substances or a combination of the substance and noise.
There is also some evidence that exposure to hand transmitted vibrations can exacerbate the effects of noise on hearing. Most people are protected from long-term damage in a working day (8 hours) by keeping exposure around the 85 decibel (dB)(A) level. But if noise exposure becomes more intense, damage may occur in a shorter time. The acceptable noise exposure standard in the workplace is 85 dB (A) averaged over an eight-hour period. This is not to imply that a safe condition exists at below 85 dB (A). It simply means that an eight-hour exposure of 85 dB (A) is considered to represent an acceptable level of risk to hearing health in the workplace. Impulse or sudden noise levels in excess of the peak exposure standard of 140 dB(C) are considered to be hazardous and capable of causing immediate hearing damage. The above table demonstrates the length of time a person without hearing protectors can be exposed before the standard is exceeded.
Selection of equipment and the duration of noise monitoring are based on the type of ambient noise.
Continuous noise is produced by machinery that operates without interruption in the same mode, for example, blowers, pumps and processing equipment. Measuring for just a few minutes with hand-held equipment is sufficient to determine the noise level.
When machinery operates in cycles, or when single vehicle or aeroplane pass by, the noise level increases and decreases rapidly. A single passing vehicle or aircraft is called an event.
The noise from impacts or explosions, e.g., punch press or gunshot, is called impulsive noise.
Annoying tones are created in two ways: Machinery with rotating parts such as motors, gearboxes, fans and pumps often create tones. Unbalance or repeated impacts cause vibration that, transmitted through surfaces into the air, can be heard as tones. Pulsating flows of liquids or gases can also create tones, caused by combustion processes or flow restrictions.
Low frequency noise has significant acoustic energy in the frequency range 8 to 100 Hz. Noise of this kind is typical for large diesel engines in trains, ships, and power plants and, since the noise is hard to muffle and spreads easily in all directions, it can be heard for miles.
Sound level meters
The Sound Level Meter (SLM) consists of a microphone, electronic circuits and a readout display. The microphone detects the small air pressure variations associated with sound and changes them into electrical signals. These signals are then processed by the electronic circuitry of the instrument. The readout displays the sound level in decibels. The SLM takes the sound pressure level at one instant in a particular location. To take measurements, the SLM is held at arm’s length at the ear height for those exposed to the noise. With most SLMs it does not matter exactly how the microphone is pointed at the noise source. The instrument’s instruction manual explains how to hold the microphone. The SLM must be calibrated before and after each use. The manual also gives the calibration procedure. With most SLMs, the readings can be taken on either SLOW or FAST response. The response rate is the time period over which the instrument averages the sound level before displaying it on the readout. Workplace noise level measurements should be taken on SLOW response. A Type 2 SLM is sufficiently accurate for industrial field evaluations. The more accurate and much more expensive Type 1 SLMs are primarily used in engineering, laboratory and research work. Any SLM that is less accurate than a Type 2 should not be used for workplace noise measurement.
The integrating sound level meter (ISLM) is similar to the dosimeter. It determines equivalent sound levels over a measurement period. The major difference is that an ISLM does not provide personal exposures because it is hand-held like the SLM, and not worn. A noise dosimeter is a small, light device that clips to a person's belt with a small microphone that fastens to the person's collar, close to an ear. The dosimeter stores the noise level information and carries out an averaging process. It is useful in industry where noise usually varies in duration and intensity, and where the person changes locations.
Assessment and control
A walk-through inspection will help determine: sources of excessive noise, workers likely to be exposed to excessive noise, work practices that are noisy and ways of reducing noise levels. This type of preliminary assessment should assist in establishing a list of most activities in the workplace that may pose a risk to a worker's hearing. A noise assessment may not always need measurement. For example, if only one activity at the workplace (e.g. the use of a single machine) involves noise level above 85 dB(A) and the manufacturer has provided information about the machine's noise levels when it is operated in particular ways, then a sufficient assessment can be made without measurement. More complex situations may require measurement to accurately determine a worker's exposure. A number of factors determine the best noise control measure. They are Financial and technical feasibilities, Safety, Maintenance accessibility, Minimum allowable disruption time for a particular production operation or process As previously discussed, the source, path, or receiver can be treated.
Noise radiates from a source. For projects in the design stage, try to specify the quietest operating equipment you can. This may not eliminate all potential for a noise problem, but it will make the noise control project easier and less expensive to implement. Buyers should be aware of and consider the noise level when making new equipment purchases. When a noise problem already exists, it is unusual that the mechanisms or processes that generate the noise can be quieted. In these situations, adding acoustical materials to the noise-radiating surfaces may help reduce the noise strength at the source, either eliminating the noise problem or partially controlling the problem. The materials that are added in these situations may provide sound absorbing, sound blocking, or damping properties (or any combination of these three properties). Particularly in industrial noise problems, compressed air discharge noises are easily treatable with the addition of pneumatic silencers.
Noise is transmitted via sound waves through the space that separates the source from the receiver. Altering the path of this transmission to reduce the amount of acoustical energy that will reach a receiver is an effective approach to industrial noise control. Usually, this involves impeding the sound transmission by interfering with its reflected and direct paths. Reflected noise paths can be reduced by adding sound-absorbing panels to walls and by hanging sound-absorbing devices (unit absorbers) from ceilings. Direct noise paths can be disrupted by using enclosures or acoustical barrier walls between the source and receiver. These barriers are most effective when used in combination with materials designed to treat reflected sounds.
Ear plugs or ear muffs are considered highly economical methods for reasonably effective receiver noise control. However, employees are often uncomfortable having to constantly wear these devices. They also note their inability to detect changes in the sound of equipment and problems in communicating with other employees.
Maximum noise control is provided by quality sound enclosures because they normally include materials and design features that provide sound absorption, transmission loss, sealing, and ventilation in one system. Noise is blocked from either leaving or entering the enclosure. This provides the option of enclosing either the noise source or the noise receiver. Proper sealing is required for an enclosure to maintain its acoustical integrity. Access doors, windows, and ventilation systems can pose special problems. Doors, windows, and structural joints must be properly sealed and caulked to ensure no sound leakage, in or out, occurs to degrade an enclosure's performance. In cases where a manufacturing process requires materials to be constantly moved in and out of an enclosure, acoustic tunnels or shields must be incorporated into the design to ensure acoustical integrity. The enclosure's ventilation system also may require adequate silencing of the inlet and outlet paths.
Along with the active monitoring techniques like noise assessment and implementing noise control measures, health surveillance to be executed. Audiometric testing must be provided within three months of the worker commencing work. Starting the audiometric testing before people are exposed to hazardous noise (such as new starters or those changing jobs) provides a baseline as a reference for future audiometric test results. Regular follow-up tests must be carried out at least every two years. These should be undertaken well into the work shift so that any temporary hearing loss can be picked up. By taking training from the competent Therapeutic trainer, the muscles around the head and neck, and this helps to reduce the noise issues caused by the condition especially the tinnitus. The following two poses would act as better solution for hearing issues.
Triangle Pose - instantly sends a gush of fresh blood to head and neck as your head hangs on one side. The muscles in that area are relaxed, and it is possible that you will instantly feel your ears pop and open up. This reduces or completely halts the ringing sounds.
Camel Pose - increases the flow of blood in the head, neck and resolve the tinnitus issue.
Worker exposure to industrial and workplace noise is unavoidable one as they have to involve in production, maintenance activities along with the machines and equipment. By doing proper noise risk assessment like Identifying noise hazard sources in the work place, measuring the noise level in the work place, noise risk can be determined. After risk assessment proactive control measures to be implemented. Along with the control measures regular health surveillance, involving the workers in Hearing improving Therapeutic Training will maintain the hearing mechanism of the workers. This commitment from the management will groom the staff morale, chronic hearing illness as well as increases the business reputation of the organisation