Sound advice on noise pollution

Regulations that came into force last year place the onus of ensuring aural wellbeing firmly with employers. Jane Dawson explains how Wakefield Acoustic has helped the water industry comply with the law and protect employees.

Cleaning water can be a noisy business. The decanter centrifuges used to separate solids from liquid during the treatment process run at speeds of around 3,000rpm. Untreated noise levels can typically exceed 80dBA.

Worldwide, increasingly stringent regulations are coming into force in order to limit worker's exposure to industrial noise. More than one million employees in Britain are exposed to levels of noise at work that puts their hearing at risk. And 170,000 suffer from deafness, tinnitus - ringing, humming or buzzing in the ears - or other ear conditions as a result.

By law, employers must assess and identify measures to eliminate or reduce risks from exposure to noise.

Where the risks are low, the actions taken may be simple and inexpensive. But, where they are high, they should be managed with a prioritised noise-control action plan.

Sound rules
Today's employers must be aware of the stringent new rules introduced under the Control of Noise at Work Regulations, which came into force in April 2006. The directive is designed to ensure all workers are protected from the effects of noise and the risk of damage to hearing.

Employers have to ensure that, where required, hearing protection is provided and used, any other controls are correctly applied, and information, training and health surveillance is provided.

Factors that contribute to hearing damage are:
  • Noise levels (given in decibels - dBA)
  • How long people are exposed to the noise, daily and over a number of years
>The focus of the new legislation is on:
  • A reduction of 5dBA in the exposure levels at which action has to be taken - from 90dBA and 85dBA in the previous directive to 85dBA and 80dBA in the new one
  • Implementing good practice noise control and risk-management procedures, such as reducing noise exposure and providing employees with hearing protection, information and training
  • Controlling noise at source by technical or organisational means, such as introducing quieter processes and equipment and a low-noise purchasing policy
The new legislation moves away from an over-reliance on assessment, quantification of exposure levels and consequent hearing protection. The new agenda is one of proactive and active control and management of noise issues.
Noise control
In the water treatment process, particles, sediment and solids fall to the bottom of the settling tank due to gravity. The centrifuge is then rotated rapidly, replacing gravity with controllable centrifugal forces that can be up to 3,000 times greater than gravity. This can create quite a racket.

In order to comply with both industrial and environmental noise legislation, a UK water utility was looking for a solution that involved a degree of noise attenuation. On this particular application the specification was to reduce emitted noise levels at a distance of 1m to no more than 74dBA.

The company supplying the centrifuges, Alfa Laval, called in industrial noise control specialist Wakefield Acoustics. Wakefield has provided noise and acoustic control products and solutions for industrial, commercial and environmental applications worldwide since 1980.

Alfa chose to use Wakefield because of this experience, and specifically its track record of working within the wastewater sector throughout the UK. It has worked closely with original-equipment manufacturers, contractors and directly with water authorities. Wakefield has provided noise-control solutions for applications such as sludge dewatering, aeration, filtration and odour control.

Tailor-made solution
Wakefield Acoustics' solution was to supply bespoke designed and purpose-built enclosures for several decanter centrifuges in the dewatering plant of the water utility's wastewater treatment works.

The decanter required a detailed maintenance programme. With this in mind, the enclosures were designed to achieve the required noise reduction while providing access for installation and ongoing regular upkeep.

A one-piece lift-off roof and side panels were provided to allow for easy installation and removal of centrifuge components. Quick-release catches were also included in the design, along with fan-assisted ventilation.

All Wakefield Acoustics' enclosures are application engineered to customer requirements, and are suitable for heavy-duty applications. They can incorporate acoustic doors, windows and access panels. Enclosures range from modular panel-to-panel bolted constructions to one-piece drop-over units.

Following installation, the water utility commissioned an independent noise report. It recorded noise levels at 72dBA, lower than the original specification of 74dBA and well below the limits set under the 2005 Control of Noise at Work Regulations.
All parties - the utility, Alfa Laval and Wakefield Acoustics - reported they were satisfied with the solution.

"Thanks to Wakefield Acoustics' engineering expertise, we have reduced the noise levels," says Alfa's Steve Twinn. "This was an area with a particular noise problem. Wakefield Acoustics have provided a cost-effective solution, and have worked with the project team to reduce the noise issues to comply with environmental and legal requirements."

Wakefield Acoustics specialises in providing practical and cost-effective bespoke engineered industrial noise-control solutions. Its acoustic design software is backed up with more than 27 years experience. The company says this allows it to accurately diagnose noise problems, and to provide effective acoustic products which optimise noise control requirements, airflow, cooling, access and maintenance issues, as well as overall cost.

Wakefield Acoustics' Noise At Risk Assessment service starts with a free consultation, where any specific noise factors can be taken into account.

Jane Dawson is managing director of Wakefield Acoustics.
T: 01274 872 277

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