Unilever Foods, Dublin
Over a period of several years ADC Acoustics worked with Unilever Foods in Dublin to assess and resolve a range of environmental noise issues, as well as a comprehensive internal occupational noise (noise at work) assessment and control programme which we report on separately.
The project began with our being advised that there was a requirement by the local authority to restrict boundary noise levels to 35 dB LAeq at any time and the client's concern that a new pair of dust plants might exceed it. Our first recommendation was to query the criterion with the local authority. Firstly it needed identifying which boundaries it applied to. The nearest boundary to the main sources was only 30m away whereas the nearest houses were 130m away. Secondly, a level of 35 dB LAeq is very stringent in these circumstances. Not only was the housing not particularly close but the area not particularly quiet, being less than 4km from the centre of Dublin and fronting onto a busy road.
In the end the criterion was renegotiated to be relative to background noise - the industrial noise could be no more than background noise by night and no more than 10 dB above background noise by day. This amounted to a relaxation of criteria of 5 to 21 dB, for night time and daytime respectively.
The next stage was to identify which sources exceed these criteria. Under the renegotiated criteria the factory was well within daytime criteria and at night only the larger of the two new dust plants and the compressor house required noise control.
The larger dust plant had a lot of noise breaking out from the ductwork and the in-line silencers which were supplied with the dust plants were not working properly. In fact the silencers were fitted "upstream" of the bag filters and were clogged with dust. Straight forward duct lagging was specified for the noisy ductwork and properly specified silencers were designed for the main bag filter vents and to the explosion vents.
For the compressor house, the 300mm deep acoustic louvre doors were not adequate either for airflow or as effective silencers and exhaust fans were all rigidly fixed to the building fabric and transmitting vibration the form of structure-borne noise. We specified solid (ie. non-louvred) acoustic doors and a separate silenced ventilation system to provide adequate airflow. All fans were reused but specified with anti-vibration hangers and flexible connectors.
"Thanks a million for this work, it's excellent. I think we will make your trip to Dublin an annual event as I like your approach and your practical solutions."