Retrofitting Reciprocating Compressors For Noise Control
Authors: Frank Leslie D. , Quaife L. Ronald 
Published: March 2010

Abstract
Industrial noise has caused environmental noise pollution from many oil and gas facilities. The Alberta Energy Resources Conservation Board (ERCB) has enacted legislation to control excessive noise, which has caused facilities to mitigate their operations. This paper presents a descriptive case study of how an Alberta gas processing facility reduced the amount of environmental noise it generated, by first assessing which plant equipment was responsible for the louder noise generation, and then by designing a balanced acoustical silencer retrofit program. The result was a significant noise reduction that met the ERCB requirements.

Introduction
Noise has been recognized as a workplace issue for several decades. Initial concerns focused primarily on worker's safety as addressed by generalized Occupational Health & Safety regulations. More specific noise related regulations were invoked in Alberta in 1981, via a separate set of Occupational Health & Safely regulations. Then in 1988, the ERCB enacted their Noise Control Directive ID 88–1. This legislation is not aimed at worker's safety, but at reconciliation of environmental noise concerns between the public and oil and gas operators. Since its inception, this regulation has undergone substantial government and industry review and has been reissued in 1992 as ID 92–2.
Notwithstanding changes to the original directive, the challenges it represents to industry are substantial. As it stands, ID 92–2 is the most stringent environmental noise guideline in North America. Although determination of compliance to the directiveinvolves complex technical assessments, it in essence requires that energy related industrial facilities meet a night-time sound level of 40dBA Leq or any nearby local residence. A single number descriptor commonly used for environmental sound level measurements is the energy equivalent sound level ‘Leq’. The Leq value is an energy average accumulated over the measurement ime period. It is often described as the steady sound level over a specific period of time, that has the same acoustic energy as the actual fluctuating sound levels that occurred during the same period. Leq values are based on a measurement of the A-weighted sound levels expressed in units of ‘dBA’. The dBA value takes into account the frequency content of the measured sound, and assesses it with a frequency response similar to that of the human ear. As a result two sounds having different frequency components.but judged to be equivalent in loudness would have the same A-weighted sound level. This stringent night-time sound level compares with 55 dBA Ldn as allowed by other regulatory agencies such as the United States Environmental Protection Agency "levels document", the United States Federal Energy Regulatory Commission's requirements and the Ontario Ministry of the Environment "Model Municipal Noise Control Bylaw."The ‘Ldn’ value is similar to the previously discussed Leq value, yet it also includes a 10 dBA penalty for noises that occur during defined night-time hours. Because sound levels are measured on a logarithmic scale, this 15 decibel difference represents a considerable departure in allowable noise, and has created ramifications for many facilities, which may now be found to be in a position of non-compliance.