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Deafening Decibels

Published: 11th Nov 2015


Arne Berndt looks at how mitigating noise emissions and ensuring hearing protection is used can safeguard workers’ health and businesses’ reputations and legal positions.

From aircraft mechanics to welders and yard labourers, people working in a large number of occupations will be exposed to harmful levels of noise during the course of their working life at some point. With millions of people across the world affected by noise-related hearing loss at work, it is one of the most prevalent occupational health concerns.

Noisy workplaces

Excessive noise in work places is not just an environmental concern or annoyance. Nor is it limited to heavy manufacturing plants or mining operations – although it is certainly an issue there. Exposure to noise from machinery, traffic, entertainment equipment and the like can also cause significant health issues for workers and raise the possibility of litigation against any company not taking the necessary steps to protect those workers.

The USA’s National Institute for Occupational Safety and Health (NIOSH) has estimated that $242 million is spent compensating workers for hearing loss disability every year. The Association of British Insurers (ABI) has reported that British insurers have seen a significant rise in opportunistic claims for noise induced hearing loss (NIHL) in recent years, so it is not just workers who need protecting; making the workplace safer makes business sense, too.

Today we assume that the danger of hearing loss is a given if people are exposed to a noise level of more than 85 decibels (dB) for a sustained period. That’s about the volume of a household food blender. On average people’s pain threshold is around the 110 dB level (which is 16 times as loud as 70 dB) so long-term damage can occur long before pain is felt.

The risk of hearing loss increases with the magnitude and exposure time and the frequency of the noise, with higher frequencies doing more damage. Hearing loss makes up between 30% and 40% of occupation-related illnesses.

Effects of excessive noise

Occupational noise can cause both temporary and permanent hearing damage that has a severe impact on the affected employee. The hearing loss may occur gradually due to exposure to noise over time or can be caused by sudden, extremely loud noises.

As well as hearing loss, high levels of noise can result in sleep disturbance, cardiovascular disease and other physical disturbances in workers. This impacts on the individual and their family and friends, and can also affect a business’ financial results, either through lost working days, litigation or reputational damage; no-one wants to work or do business with somewhere that doesn’t look after its workers’ health and safety.

Loss of hearing has an enormously negative impact on the affected person and those around them. They are only able to hear if the sound levels are high enough and if the difference between the levels of what they are trying to listen to and the background noise is significant. In many cases this leads to the affected person suffering from social isolation, because proper acoustical communication is no longer possible.

There is also a risk that people cannot localise a noise source or cannot hear it at all. This can put them in greater danger than people with regular hearing, for example in urban traffic situations or when smoke alarms are activated.

Psychological impact of noise The psychological impact of noise is mainly related to the ability to work and concentrate and to psychological wellbeing. This describes the relationship between the personally experienced disturbance and the perceived noise level. Direct consequences of the noise impact in this content are:

  • Disturbance of communication
  • Reduced reactions
  • Reduction of the psychological wellbeing, resulting in nervousness

Impact of noise on human interaction High noise loads result in considerable social problems as people fail to interact normally. In workplaces where undisturbed communication is not possible people can become isolated and not take into account the environment around them. Affected people become more aggressive, their willingness to help others is reduced as is their sociability.

Noise laws and regulations

As well as health and safety regulations, many countries have specific noise rules, such as the USA’s Noise Control Act, Canada’s Occupational Exposure Limits, the UK’s Control of Noise at Work Regulations 2005 and the EU’s Environmental Noise Directive (Directive 2002/49/EC ). Employers should make themselves aware of the rules affecting their employees, but the general principles, depending on the level of risk, include:

  • Taking action to reduce the noise exposure
  • Providing employees with personal hearing protection
  • Making sure the legal limits on noise exposure are not exceeded
  • Maintaining and ensuring equipment provided to control noise risks is usedroviding employees with information, instruction and training •  Carrying out health surveillance, for example, monitoring workers’ hearing ability
  • Providing employees with information, instruction and training
  • Carrying out health surveillance, for example, monitoring workers’ hearing ability

Modelling noise

Occupational noise emissions come from a wide variety of sources. However, they cannot be categorised easily as every situation is different. This makes evaluation and mitigation much more difficult than for some noise sources, such as traffic.

Occupational sources also vary widely in sound power, emitted frequency spectra, directivity and also in their timings. The characteristics of the emitted noise in different occupational situations vary between irregularly distributed noise impulses, such as a coffee grinder, and almost continuous noise levels at a refinery.

The main problem in noisy locations is finding and documenting where the noise reaches 85 dB, known as the ‘noise contour line’. In areas where noise levels exceed 85 dB, workers must wear hearing protection. If the 85 dB line is not clearly marked companies may be liable to fines. Signs must make it clear to employees that hearing protection is required and supervisors should ensure it is always worn. It does not matter whether the high noise levels are inside or outside a building, the 85 dB contour line is enforced.

If a workplace has areas that may be close to or above 85 dB, it is wise to invest in a noise study to define all areas where hearing protection is required. An alternative solution is to provide workers with noise dosimeters that keep track of their daily dosage of noise. A well-studied and documented noise policy is better than paying for lawsuits from workers with hearing problems and paying for disability because of tinnitus and hearing loss.

Noise simulations

Before computers were fast enough to carry out effective simulations, and simulation software had reached its current level of proficiency, noise control engineers had to measure noise levels and then use their best judgment to control it. For the past 30 years, researchers have measured noise and developed different interpretations of cause and effect, so the equations are becoming more complex to better represent the complex nature of sound propagation in the environment. The calculations have become so complicated and time consuming that the use of computers is paramount. Hand calculations and rough estimates with spread sheets are a thing of the past.

Today’s technology means more realistic simulations are possible, allowing users to predict future levels of noise and work with ‘what-if scenarios’ prior to building.

Through software it is also possible to create a noise map. Noise mapping is mostly an exercise of tapping into existing data sources and compiling a simulation model from the data representing the infrastructure and the buildings involved. Each noise map is unique according to project size, the geography and the objective, but most of all, on what data is available and can be readily acquired to be imported and used for the noise map.

The noise levels can be measured or calculated, opening up the possibility of introducing theoretical noise reduction measures and evaluating possible improvements.

Controlling noise

A reduction of just a few decibels means the risk of hearing loss and its many consequences are lessened. An important way to help safeguard workers’ hearing is to modify or replace the noisiest equipment or to adapt the environment around them. Using low noise and well-maintained equipment or placing a barrier between the worker and noise source are relatively simple steps, but they can have a huge impact on people’s lives.

Whether you’re planning a new workplace or looking to improve an existing one, workers need to be protected from noise.

Protecting with PPE

Even with effective modelling and mitigation in place, it is not always possible to reduce noise at the source in a workplace, either for technological reasons or due to the type of workplace; for example, construction sites will always be noisy. In locations where the noise can’t be mitigated, workers should wear hearing protectors to reduce the amount of noise reaching the ears.

Although there are a many types and brands of hearing protectors available, they will only be effective if workers actually use them. Ear sizes and shapes can vary greatly, so what is comfortable for one person won’t be for another. Employers need to ensure that they make sufficient options available so that workers can find a solution that suits them, although there may be reasons why some protectors are not suitable for safety or hygienic reasons. While earplugs may be the preferred choice they are not suitable for excessively high noise and are not appropriate in settings where workers remove and reinsert them throughout the day as they risk causing ear infections, because they introduce dirt and bacteria into the ears.

Aside from user preference, the type of protector to be used can vary according to the volume of the problem noise and whether there are any circumstances that make one form or other inappropriate.

There are two main types of hearing protectors: earplugs and earmuffs.

Earplugs may be:

  • Pre-moulded – mainly made from either polyvinyl chloride (PVC) or polyurethane (PU) (memory foam), which are compressed and put into the ear canal, where they expand to plug it
  • Individually mouldable – made of silicone rolled into a ball and carefully moulded to fit over the external portion of the ear canal

The plugs are available in disposable, reusable and custom moulded forms. They are less expensive than alternatives and are usually more comfortable to use in work areas that are hot or damp. A concern when considering using earplugs is that they usually offer less protection than earmuffs, so it is recommended that they are not used in areas with noise levels reaching over 105 dB.

Earmuffs, on the other hand, have soft cushions that fit over the ear and hard outer shells, held together by a headband. The headband must fit tightly enough to maintain a proper seal, yet not be too tight for comfort. Earmuffs generally provide greater protection than plugs, with deeper and heavier domes offering more protection than shallow, lighter ones. Earmuffs are also very visible so supervisors can easily see that workers are following safety procedures. They are, however, more expensive and often less comfortable than plugs, especially in hot work areas.

For very noisy areas it may be necessary to wear both types of protection.

Unintended consequences

Ear protection and other mitigation factors could have the unintended consequence of workers not being able to hear emergency alarms. For this reason loudspeakers at any given point in a plant must be at least 10 dB above the ambient noise. For verbal messages the requirements are even more stringent. Protectors that reduce the level at the ear to below 70 dB should be avoided, since this over-protection may cause difficulties with communication and hearing warning signals.

Like all PPE it is important to follow the manufacturer’s instructions and check the hearing protection equipment regularly for wear and tear. Ear cushions and plugs should be supple and must be replaced when this is no longer the case. The headband should keep ear cushions snugly against the head and be replaced if they become loose.

Levels of protection

Manufacturers provide information about the noise reducing capability of hearing protectors to help users select the right level of protection. The ratings are expressed in dBs and used as a guide for comparing the potential noise reduction capability of different hearing protection devices.

Different rating systems are used across the world:

  1. Single Number Rating (SNR) is used by the European Union and associated countries. In addition to an overall rating, the SNR rates protectors in terms of the particular noise environments in which they will be used.
  2. Noise Reduction Rating (NRR) is primarily used in the United States, but can be found in a number of other countries. The NRR labelling requirement is a standardised format for all hearing protectors distributed in the United States.Sound Level Conversion (SLC80) is used in Australia and New Zealand. It is an estimate of the amount of protection attained by 80% of users, based upon laboratory testing.
  3. Sound Level Conversion (SLC80) is used in Australia and New Zealand. It is an estimate of the amount of protection attained by 80% of users, based upon laboratory testing.

Using these numbers can help guide your purchasing decision, but the real test is in the workplace.

Planning, mitigation and protection

Wherever you are in the world, the message is clear: by following good practice, planning for noise, mitigating it wherever possible and providing protective equipment – plus ensuring its use – workers exposed to unavoidable excessive noise can be sheltered from its worst impacts. In turn businesses can meet their responsibilities to their workers and avoid reputational damage and costly legal proceedings.

Published: 11th Nov 2015 in Health and Safety International

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Arne Berndt, owner / adviser at SoundPLAN GmbH and SoundPLAN International LLC – a market leader in sound and air pollution mapping software.