The impacts of production units on their surrounding areas are assessed from many perspectives, and the requirements of their environmental permits cover nearly all of the senses. Noise is one of the most challenging environmental impacts of industrial operations, as its spread and disturbance depend on many factors, such as the weather conditions. In addition, the experience of noise is subjective: not everyone perceives the same level of noise to be intrusive, and all interpretations are equally right.
Controlling based on modelling
In environmental permits noise is usually defined with certain limit values, for night time and daytime separately. Some production units have stricter requirements because they are located close to recreational areas or holiday homes, for example. The limits set in environmental permits are always controlled by measuring the nearest site affected by the noise, which is usually a permanent residential building. Noise levels are monitored by means of modelling based on calculations and through physical measurements. The modelling is based on noise levels measured at a distance of around one metre from the equipment causing the noise. The spread of the noise and the noise levels in the surrounding areas are modelled based on these measurements. The accuracy of the modelling is verified with noise measurements carried out using physical meters.
Hums are only mildly disturbing; impact noises increase
the measured value
In terms of noise, wood processing is probably the most challenging production phase for Metsä Group, as it generates clanks and noises from the vehicles moving the wood. For historical reasons, wood processing areas are usually located close to the shore, and noises can carry long distances over water. The noise generated by wood processing can be managed by using electric wood processing equipment and by processing as much of the wood as possible during the daytime.
Noise is also caused by various alarm sounds in special situations, and their use is based on the occupational health and safety legislation. In some cases, it has been possible to lower the volume of these noise levels or to replace the sounds with alarm lights. Noise is also taken into account when purchasing equipment, as certain noise criteria are typically specified for new devices.
The noise caused by production units is usually a steady hum caused by blowers, and this type of noise is generally perceived as only slightly intrusive. It has been reduced by means of various casing and sound insulation solutions. Impact noises and narrow-frequency noises are perceived as considerably more disturbing and also increase the measured values.
Metsä Board's Tako paperboard mill carrying out improvements in line with the noise reduction plan
Metsä Board's Tako paperboard mill, in the heart of Tampere in Southern Finland, has been operating since 1865. Due to its central location, the mill pays special attention to the noise from its operations.
The main source of noise at Metsä Board's Tako mill is the hum from blowers. The mill has prepared a noise reduction plan, and the implementation of the plan is being monitored in cooperation with the local authorities. "Last year, we reduced the noise level of a noisy blower by installing a new ducted silencer and increasing the length of the duct and the insulation. In the autumn, we will increase the dampening in the inlet ducts of the Tako power plant. During 2019, we will update the dampening of the paperboard machine blowers. These measures will significantly reduce the extent of daytime and night-time noise areas," says Tuomas Lammi, Environmental and Quality Manager of Metsä Board's Tako and Kyro mills. Noise generated by occasional interruptions in the operation of equipment is addressed immediately at the mill. Noise reduction increases well-being at the mill, as well as in its surrounding areas.