Keeping the peace
July 1st 2008

Getting an accurate noise assessment based on true readings is vital when there is any question of the legal thresholds being breached says Tim Turney, product manager, Casella

Ears are clever things. When subjected to constant noise for a short period of time the hearing adjusts, and the perceived level of noise reduces considerably. As a result a person might barely notice a 3dB increase in volume, even though a 3dB change doubles the sound energy being produced. Two pieces of machinery which each produce 85dB will produce 88dB when running together, and although perceived as only a small increase in volume this will double its propensity to damage hearing.

Advice from the HSE on assessing workplace noise levels is that if you have to shout to be understood by someone two metres away, the ambient noise levels are at around 85dB. It advises that if the noise is intrusive but normal conversation possible, the level is likely to be 80dB.

What is clear is that casual noise assessments are fraught with difficulty, not least of which being the body's own is accommodating mechanisms. Less accommodating are the new Control of Noise at Work Regulations 2005, which came into effect in 2006 and brought the Lower Exposure Action Value (LEAV) down to 80 dB.

The LEAV set at an 8-hour average noise exposure level (or daily personal noise exposure level, LAEP,d) of 80dB. At this level the employer has to provide information and training for their staff and make hearing protection available. The Upper Exposure Action Value (UEAV) is set at a LAEP,d of 85dB and above this the employer is required to take reasonable, practicable measures to reduce noise exposure such as engineering controls or other technical measures, and the use of hearing protection is mandatory if noise cannot be mitigated by these measures.

Small errors in noise level estimates can lead to large errors in exposure calculations. These in turn can lead to hearing damage for workers and the risk of prosecution for the employers, or the expense of noise reduction or exposure limiting measures being incurred unnecessarily on the basis of inaccurate guesses.

Getting an accurate noise assessment based on true readings is vital when there is any question of the legal thresholds being breached. And if measuring continuous noise levels is hard, it is harder still to estimate the exposures of workers when work patterns or machine noise levels are variable.

Two pieces of equipment can be used for this; a sound level meter is primarily designed as a hand held device used by an operator, while the noise dosimeter is worn by the staff member for his or her working shift. The preferred method of measurement for noise surveys is a sound level meter, which takes a representative measurement for each task and enables an 8 hour exposure to be calculated. The more complex the work pattern or variable the noise the more complex is the individual dose calculation, and a noise dosimeter such as the CEL-350 dBadge is required.

Whatever equipment is selected needs to be simple to operate and reliable. Expectations for electronic devices have been driven by products like the iPod and mobile phones, and consumers are most comfortable with products that are small, simple to use and with clear colour displays. Casella's new CEL-600 range of sound level meters fits the description, and the range of three all have an intuitive user interface which offers colour coded measurement parameters and displays. Simple icons replace a complex menu system and allow users to pick up the unit without using a manual.

The product demonstrates that using a sound level meter need not be a specialist task.

The CEL-600 series is based on digital signal processing technology and fully compliant with all the national and international accuracy standards. Digital technology has allowed for a single measurement range up to 140dB, while the older analogue instruments have a fixed range that must be selected and are therefore vulnerable to operator errors. The CEL-620 allows the measurements required for the selection of hearing protection to be obtained by either the HML method or by the HSE preferred octave band method.

Acoustic terminology can be confusing to people new to the Control of Noise at Work regulations and picking the correct weightings on the equipment can lead to mistakes. The CEL-620 measures all weightings parameters simultaneously, and the user simply picks which 'view' is most appropriate for the local workplace noise legislation, eliminating the possibility of measurement errors. All parameters required by the legislation are measured simultaneously without the need to change setups or make separate measurements.

Using the HSE guidelines as a quick way of deciding whether you have a noise problem is where everyone starts. But if there is any question of non-compliance then the selection of an accurate noise level meter and the conducting an initial noise assessment is essential. Choosing equipment that is durable, easy to use by most members of staff and one which simplifies the whole noise assessment process is a good first step towards keeping the peace when the shouting starts.

More articles from Casella Measurement: