Noise control in the offshore industry introduces novel problems to the oil industry. The major differences between offshore and onshore noise control are discussed, and the concepts of noise control in terms of direct sound from the equipment, the reverberant noise introduced when the equipment is enclosed in a module, and problems of structure-borne noise are developed and illustrated with examples.
In recent years the oil industry has been concerned with the problems of hazardous noise levels on process plants and the effects of the noisy plant on its neighbors. This has resulted in considerable advance in design for noise control in the industry, and plants are now in operation in which noise levels are acceptable both on and in the neighborhood of the plant. However, the installation of fixed production platforms to develop the oil and gas fields in the North Sea has introduced novel noise control problems to the oil industry.
It has become apparent that the personnel manning these platforms are not prepared to accept the high noise levels associated with this type of operation, and appear to be more concerned with this than the personnel engaged on mobile drilling installations.
Following on from work in the onshore industry, Acoustic Technology has undertaken and is currently carrying out several design studies in the noise and vibration aspects of offshore platforms, and the concepts involved are outlined in this paper.
The major differences between onshore petrochemical plants and offshore platforms that affect noise levels are summarized below.(Available in full paper)
These differences mean that a totally different approach to offshore noise control is required, and this approach must encompass path air- and structure-borne noise. While structure borne noise is ultimately perceived as an airborne signal, and consequently may not be subjectively distinguished from air-borne noise, its quantification is more easily dealt with separately - notwithstanding, of course, the fact that ultimately the sources will add together and must not jointly exceed the preset criterion for air-borne noise.
In Europe there are no universal statutory limits for workers exposed to high noise levels. However, in Britain the Dept. of Employment has issued a Code of Practice recommending a maximum noise level to which workers should be exposed. This level is 90 dBA, or roughly Noise Rating curve 85 (NR 85), for a 40-hour week exposure. Furthermore, it is likely that this level will be incorporated into the Factories Act, and therefore it will become a statutory undertaking for employers to "take all reasonable means" to ensure that the noise levels are not exceeded. It is also likely that a similar regulation will apply to fixed production platforms in the near future.
This level, of course, relates only to a maximum permissible noise level in order to reduce the risk of hearing damage. It does not purport to exclude it, or indeed create an acceptable environment for any specific task.