Noise: the requirements and the measures taken to comply with them
Authors: Donovan Kevin A. 
Published: October 2008

Abstract
This paper describes the parameters for the acoustic engineering for Troll Phase 1 such as, noise requirements, contractual guarantees, organisation, resources and work structure. Traditional acoustic engineering in a project relies heavily on experience data on equipment and facilities in order to complete simulations. This has been difficult due to the fact that some of the equipment is the largest of its kind and reliable acoustic data has not been available. This has been a particular challenge for the Kollsnes onshore plant engineering where noise limitations are most stringent. If applied at an early stage in project design, acoustic engineering input will help to obviate expensive rework later on such as piping insulation and noise overruns for key equipment. The requirements are laid down in the regulations concerning the workplace and the working environment. In addition, noise pollution is regulated by the State Pollution Control Authority. Contractual requirements on noise have been specified in contracts, and have included noise guarantees.

Introduction
Proper management of acoustic engineering in development projects ensures product compliance with regulations and specifications. Correct resource management may have the added bonus of major savings on investment.
Troll project experience indicates that there are external factors such as contractual requirements and the planning of activities that influence acoustic engineering. Too stringent noise requirements may lead to unnecessarily high cost for the measures taken to comply with them. If noise requirements are established and applied early in the design phase of a project, acoustic engineering will help to reduce the risk of expensive redesign and remedial work later on. The total cost of the noise control measures for the onshore plant have been estimated to $35 000 000.
The Troll Onshore Plant at Kollsnes was completed through an EPCM (Engineering, Procurement, Construction and Management) contract where the noise requirements were specified in a guarantee clause. The requirement laid down by the SPCA (State Pollution Control Authority) was a community noise sound pressure level limit of 40dBA. In order to meet a 95% risk confidence margin the design noise level target was set to 34dBA. This limit led to comprehensive noise control measures, including for example an option for inline silencers on the inlet and discharge sides of the 40MW gas export compressors. Initially, only one of the five compressor trains was supplied with silencers. Following a series of field tests it became clear that the effect of transmitted noise from compressors to inlet separators and aftercoolers had been overestimated, and thus concluded that the silencers could be deleted. The experience from compressor and pipe noise attenuation on the onshore plant is of significant importance and can be utilized in process and utility areas on offshore installations.

Regulations and Requirements

Community noise level limit.
The Authority requirements for noise emission from the production plant to the surroundings are covered by SPCA report TA-506 entitled "Requirement Limitations for Noise". These requirements are summarised in table 1.
The "limiting value" for design is the requirement of 40dBA between 2200 and 0600 hours, since the local communities contain no hospitals or recreation areas and the nearest house is approximately 1600 metres from the centre of the onshore plant.