Noise from Oil & Gas Facilities Acoustics 101 and Best Practices for Noise Control Rob Stevens, HGC Engineering
Noise From Oil & Gas Facilities Acoustics 101 and Best Practices for Noise Control Rob Stevens HGC Engineering
Environmental Noise From Oil and Gas Facilities 1. Acoustics 101 2. Best Practices for Noise Control
Acoustics 101 for Oil & Gas Plants Why Care About Noise? The Science of Sound Measures for Time-varying Sound Frequency and Pitch Octave Bands & A-weighting Environmental Sound Level Limits (Sound Pressure versus Sound Power) If time allows
Why care about noise?
Why care about noise? Outdoors ( Environmental ) LEGAL REQUIREMENTS. Avoid adverse impact: disturbance, annoyance, loss of enjoyment of property, interference with sleep Workplace Noise Exposure LEGAL REQUIREMENTS. Avoid risk of hearing loss Indoors (Lab, Office, Control Room): Communications, comfort & productivity, avoiding fatigue
Environmental (Offsite) Noise Impact There are legislative noise limits in many jurisdictions, sometimes with reporting/permitting requirements: Federal/State Environmental Protect Act(s) Municipal codes, ordinances, bylaws Requirements of financiers World Bank, International Finance Corporation, International Development Corporation, sovereign development banks
A Bit about the Science of Sound
Sound = Air pressure fluctuations (in the range of 20 to 20,000 per second)
The Ear is Essentially a Microphone
Sound = Air pressure fluctuations (in the range of 20 to 20,000 per second) Amplitude of fluctuations => Loudness Sound Pressure Time
Sound = Air pressure fluctuations (in the range of 20 to 20,000 per second) Sound Pressure Level, Lp Sound Pressure Instantaneous Pressure Fluctuations Time
Sound Pressure Level, Decibels Audible range of loudness is immense more than a factor of one million, from 20 micro-pascals (µpa) to more than 20,000,000 µpa So, we use a logarithmic scale, in units of decibels
Sound Pressure Level, Decibels Sound pressure level L P in decibels is defined as: L P = 20log(p/p 0 ) p 0 = 20 micro-pascals = 0 db Threshold of Hearing
2.0 Pa 1,000,000 x 0.2 Pa 10,000 x 0.002 Pa 100 x 0.00002 Pa 1 x
Time-varying Sound
Steady sound, the level is obvious... Sound Pressure Sound Pressure Level, Lp Steady Sound Time
What is the level of this sound?
Most Common Descriptor for Time-varying sound: L EQ L EQ = Energy equivalent sound exposure level (over a given time period) Like an average, but a logarithmic average Definition: L EQ is the hypothetical steady sound level that would contain the same energy in a given period of time as the actual time-varying sound
Another Important Descriptor for Time-varying sound: L 90 L 90 = Ninetieth percentile exceedance sound level The sound level that is exceeded 90% of the time in a given period Useful for capturing the steady component of the sound, and rejecting short term transient sounds
Sound Pressure Sound Pressure Level, Lp Leq L90 Instantaneous Pressure Fluctuations Time
Sound Pressure Spurious Noise Leq L90 Steady Sound Time
The Use of L EQ and L 90 L EQ correlates well with potential of a sound to disturb residents L EQ is the basis of most environmental noise legislation L 90 is useful to isolate the sound of a steady industry from transient background sounds e.g., traffic, birds, voices
The Weighted Day/Night Equivalent Level: L DN Used in some jurisdictions: L DN is a 24 hour LEQ with the nighttime-average levels penalized by +10 dba Usually for L DN, daytime is defined as 07:00 to 22:00 and nighttime as 22:00 to 07:00 L DN is an alternative to having separate daytime and nighttime limits (usually with nighttime being more restrictive)
Acoustic Frequency
Frequency In addition to differences in level of sound (loudness), the ear can detect differences in frequency (tone, pitch) Frequency = rate of pressure oscillations Measured in Hz Hz = cycles per second
Frequency Sound Pressure Low Frequency Time
Frequency Sound Pressure High Frequency Time
Frequency Sound Pressure Multiple Frequencies Time
Frequency Many noises contain an irregular mixture of multiple frequencies (Whereas (most) music contains a harmonious mixture of multiple frequencies) How to handle the multitude of frequencies contained in a sound or noise, when measuring?
Frequency Octave Bands
Frequency Octave frequency bands can be inconvenient a spectrum of levels Also, a spectrum does not intuitively describe how loud the combined sound is To make simpler and more intuitive, we use the A- weighted sum (single number) particularly for environmental noise (outdoors)
Frequency A-weighting Human ear is not equally sensitive to sounds (or components of a sound) having different frequencies Frequency response of the human ear is referred to as the A curve We apply the A curve weightings to the levels at each frequency and sum the result into a single number
Frequency A-weighting 10 Weighting [db] 0-10 -20-30 -40-50 31 63 125 250 500 1k 2k 4k 8k 16 k Frequency [Hz]
Frequency A-weighting An A-weighted sum (dba) is a good single-number descriptor of the loudness of a sound Levels measured in dba correlate well with the potential of a sound to cause disturbance or annoyance in a community So, environmental noise limits are quoted in units of dba However, for the more detailed purpose of acoustical modeling, analysis and noise control, spectral levels (e.g., octave bands) are necessary
Environmental Noise Limits
Environmental Noise Limits Usually legally mandated Federal/ State/Municipal In US, usually Municipal Resource of links to noise laws by jurisdiction: www.noise-ordinances.com
Environmental Noise Limits How They Vary Location at which the limits apply? Point of reception e.g., neighboring residence, or Property line, or Point of emission e.g., 25 from equipment
Environmental Noise Limits Quantitative or Qualitative e.g., not clearly audible versus L EQ 45 dba Time period of limits? Worst case 1 hour L EQ day/night Full day/full night Leq 15 hour / 9 hour 24 hour period using L DN Fixed Limits (e.g., 45 dba) or relative to background sound?
Environmental Noise Limits E.g., New Jersey State Noise Limits: Point of reception neighbouring property line Daytime/Nighttime: 07:00 to 22:00 & 22:00 to 07:00 Duration Unclear! L EQ? L P? 1 hour? Full period? Fixed Limits: Residential 65 dba day; 50 dba night
Best Practices for Noise Control
Best Practices for Noise Control Assess noise when contemplating: New facility Addition or modification to an existing facility Periodically, if required by regulator or from time to time as a best practice Complaint received
Best Practices for Noise Control In most cases, assessing noise requires an Engineering Noise Study by a qualified practitioner Except when a contemplated undertaking involves direct replacement of existing equipment or new equipment/activities that are acoustically negligible Qualified practitioner could be internal, or an outside consultant
Best Practices for Noise Control An Engineering Noise Study entails: Identifying governing laws, codes, guidelines Establishing the applicable sound level limits Preparing a sound source inventory Quantifying the facility-total sound levels Evaluating the facility-total sound levels against limits If needed, developing noise control recommendations Creating a report, perhaps for submission to regulator
Best Practices for Noise Control The Equity Engineering Group (E 2 G) is a firm specializing in outsourcing of technical specifications and Best Practices. E 2 G has a published Noise Control Best Practice document for Oil & Gas and Petrochemical facilities See: www.equityeng.com
Optional (Time Permitting): Sound Power vs Sound Pressure
Sound Power vs Sound Pressure Sound pressure level represents the magnitude of resulting air pressure fluctuations at some defined point in space (the effect). Sound power level is the total rate at which a source emits sound energy into the surrounding environment (the cause).
Sound Power vs Sound Pressure Thermal Analogy Thermal Power (Watts) Temperature (degrees)
Sound Power vs Sound Pressure Sound Power Level (db re 10-12 W) Sound Pressure Level (db re 20 µpa)
Sound Power vs Sound Pressure Sound pressure level depends upon: Source sound power level Source-receiver distance Reverberation/Reflections Background Sound Sound power level is a fundamental quantity, independent of these environmental factors.
Sound Power vs Sound Pressure Because sound power is a fundamental quantity, it is preferred for specifying the maximum sound output of equipment (or comparing one item to another) A calculation is needed to determine sound pressure from sound power, or vice versa (depends on room, distance, orientation, etc.)
Can Estimate Sound Power by Measuring Sound Pressure Fine if there is no background sound or room reverberation Sound Level Meter
Or Measure True Sound Power Using Sound Intensity Instrumentation & Methods Sound Intensity Probe
Sound Power vs Sound Pressure More information about sound power measurement using sound intensity methods at: www.soundintensity.com
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