Prepared by:
Rebecca A. Niedzielski
Minnesota Pollution Control Agency
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MPCA Impulse Noise Study: FINAL REPORT, MAY 1991
The State of Minnesota has had an active noise control program since 1976. The current one hour standard has statistical L 10 and L 50 limits for three receiving land use types. An impulse noise event, loud enough to disrupt normal activities and usually lasting less than one second, is not effectively controlled due to the 6 minute duration needed to violate the current L 10 level.
During the 1989 session of the Minnesota Legislature, a bill was proposed that would have required the Minnesota Pollution Control Agency (MPCA) to amend the current Noise Pollution Control Rule, parts 7010.0010 through 7010.0080, to adopt an impulse noise standard. Although the bill did not pass, the MPCA conducted an extensive survey of current state regulations and reviewed impulsive noise literature during the summer of 1990.
Thirteen states other than Minnesota have noise regulations of some kind. Six of these are non-active offices providing only assistance to local communities in drafting noise ordinances or offering minimal technical support. Seven states have noise programs similar to Minnesota's and have some manner of .addressing impulse noise: Connecticut, Hawaii, Illinois, Maine, Maryland, New Jersey, and Oregon. Further follow-up with noise personnel in these states found sporadic application of established impulse regulations which were most effective with stationary sources.
Determining what impulse noise sources can or should be regulated is a critical issue. Enforcement of irregular or unpredictable events not associated with a source's normal operating procedure is difficult and very labor intensive. Sources such as sirens or back-up alarms created for safety reasons might fail to serve their purpose if regulated. Federal pre-emption in inter-state commerce laws prevent local governments and states from placing stricter controls on airways, highways and railways.
In conclusion, an "impulse" standard that exempts pre-empted or other specific sources could be written as an extension of the existing MPCA L 10 and L 50 standards. Since there is a lack of clear consensus among the state programs, as well as the literature, as to the appropriate measurement method, the MPCA staff intends to conduct further field study. For the next two years, the maximum level (L max), "A-weighted" peak level (L APK), equivalent level (L eq),and shorter hourly statistical level (L 1) will be collected while responding to complaints surveying the required L 10 and L 50 levels. Based upon this information, a decision can be made regarding the need for and form of an impulse noise addition to the MPCA Noise Rule.
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MPCA Impulse Noise Study: FINAL REPORT, MAY 1991
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APPENDIX: A - REFERENCES
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NPC Editor's note: Appendix C is not included here.
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MPCA Impulse Noise Study: FINAL REPORT, MAY 1991
The State of Minnesota has had an active noise control program since 1974. The current one hour standard has statistical L 10 and L 50 limits for three receiving land use types. These limiting levels apply to outdoor sources and are 10 decibels quieter at night for residential receivers.
During the 1989 Minnesota Congressional session, a bill was proposed that would have required the Minnesota Pollution Control Agency (MPCA) to amend the noise pollution control rules:
A BILL FOR AN ACT
relating to the environment; requiring the pollution control agency
to amend noise pollution rules.
"Section 1. [Noise Pollution Rules] By July 1, 1990 the pollution control agency shall amend rules relating to noise pollution to provide for noise control requirements based on impulsive noise that preserve the public health and welfare. The agency shall use the equivalent A-weighted sound level for determining the noise control requirements. The rules shall be consistent with existing rules and provide noise control requirements based on noise area classification. The agency shall provide an exemption from the rules on impulsive noise for airports under the control and direction of the metropolitan airports commission."
An impulse noise event, loud enough to disrupt normal activities and usually lasting less than one second, is not effectively controlled due to the six minute duration needed to violate the current L 10 level.
Although the bill did not pass, MPCA noise staff felt an in depth study would provide a practical baseline for evaluating any future consideration of changes in the noise rule. A student intern was added to the MPCA Noise Program staff during the summer of 1990 dedicated solely to researching the impulse noise issue.
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MPCA Impulse Noise Study: FINAL REPORT, MAY 1991
The current Noise Pollution Control Rule, parts 7010.0010 through 7010.0080, effectively control sources that emit loud noise levels more than fifty percent of an hour (L 50), or more than ten percent of an hour (L 10). There are occasions when very loud and disruptive levels of noise are present, but do not last long enough to violate the L 10 (shorter) limit during an hour. These events may be referred to as short term, or impulse noise events. Some examples include: back-up alarms, whistles, horns, bells, sirens, fireworks, qunfire, blasting, pile-driving, riveting, hammering, stamping, rail car coupling, sonic booms, aircraft flyovers, and dogs barking.
The study was set up in the following manner:
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MPCA Impulse Noise Study: FINAL REPORT, MAY 1991
This report is assembled from literature research notes and phone conversations. Due to the range of opinion and number of the references used, the staff used discretion in summarizing the findings and did not reference specific quotes. The references are listed in Appendix "A".
Over one hundred letters were sent to state environmental agencies in the United States, foreign environmental offices in Canada, western Europe, Japan, and Australia, and various academic institutions in the United States and abroad. Because recent survey information concerning noise regulations could not be found elsewhere, staff took this opportunity to request not only information regarding impulse noise regulations, but also airport and/or aircraft noise regulations and general community noise regulation information. The current Minnesota Noise Rule is contained in Appendix "B". Those surveyed, sample letters, and the resulting responses are contained in Appendix "C".
Of the fifty states, thirteen other than Minnesota have noise regulations of some kind. Six of these thirteen states (California, Colorado, Kentucky, Massachusetts, Rhode Island, Washington) provide assistance to local communities in drafting noise ordinances but currently have no active state regulations or state noise office. The declining role of states in noise regulation is a direct result of the demise of the federal Office of Noise Abatement and Control (ONAC) in the early 1980s and subsequent lack of federal funding to the states.
Of the seven remaining states with noise programs similar to Minnesota's (Connecticut, Hawaii, Illinois, Maine, Maryland, New Jersey, and Oregon), most specifically exempt airports/aircraft, railroads or highways from regulation due to federal pre-emption. Maryland and Oregon retain separate aircraft/airport noise "regulations", but these deal with non-operational (non-flying) noise and promote the adoption of airport plans for improving land use compatibility.
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MPCA Impulse Noise Study: FINAL REPORT, MAY 1991
Following is a short summary of the impulse noise section(s) of each state's regulations; the complete noise regulations sent in response to the survey are included in Appendix "C":
(a) No person shall cause or allow the emission of impulse noise in excess of 80 dB (unwght) peak sound pressure level during the nighttime to any Class A Noise Zone (residential/sleep areas).
(b) No person shall cause or allow the emission of impulse noise in excess of 100 dB (unwght) peak sound pressure level at any time to any Noise Zone.
(h) daytime means 7:00 a.m. to 10:00 p.m. local time.
(k) impulse noise means noise of short duration (generally less than one second), especially of high intensity, abrupt onset and rapid decay, and often rapidly changing spectral composition.
Residential limit:
night: 80 dB (unwght) peak; day: 100 dB (unwght) peak. Phone follow-up: regs measured at property line of source; apply to stationary sources only; exemptions include: natural phenomena, humans, animals, religious bells/chimes, emergency vehicles, back-up alarms, farm equipment, lawn/snow removal equipment, construction, and blasting.
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MPCA Impulse Noise Study: FINAL REPORT, MAY 1991
(d) the allowable noise levels for impulsive noise shall be ten dBA above the allowable noise levels in the above table. [night: 45 dBA, day: 55 dBA - L 10 limit per 20 minute period]
"daytime" means the time period from 7:00 a.m. to 10:00 p.m. of the same day;
"impulsive noise" or "impact noise" means any sound with a rapid rise and decay of sound pressure level, lasting less than one second, caused by sudden contact between two or more surfaces, or caused by a sudden release of pressure, including but not limited to any hammering, pile driving, explosion, and gunfire. "Fast" meter response shall be used to measure these types of noises.
Residential limit:
night: 55 dBA "fast"; day: 65 dBA "fast".
Property line standard; exemptions include: emergency vehicles, civil defense sirens, emergency repair or maintenance of highways-parks-public utilities, boat whistles-horns, Hovercrafts, back-up alarms, fireworks.
Except as elsewhere in this Part provided, no person shall cause or allow the emission of impulsive sound from any property-line-noise-source located on any Class A, B, or C land to any receiving Class A or B land which exceeds the allowable A-weighted sound levels, specified in the following table, when measured at any point within such receiving Class A or B land, provided measurement be at least 25 feet from the property-line-noise-source.
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MPCA Impulse Noise Study: FINAL REPORT, MAY 1991
Illinois - continued:
"Daytime hours": 7:00 a.m. to l0:00 p.m., local time.
"Impulsive sound": either a single pressure peak or a single burst (multiple pressure peaks) for a duration usually less than one second. Examples of impulsive sound sources are a drop forge hammer and explosive blasting.
Residential limit:
night: 45 dBA fast maximum; day: 50 dBA fast maximum. Phone contact: impulse section rarely used, focus is on separate forging and blasting regs; one person office serves primarily as reference and court witness. Property line standard; exemptions include: sound emitted from residential land uses, emergency warning devices, lawn and agricultural equipment used in daytime, construction, blasting.
This regulation applies only to proposed developments and/or new expansions or new modifications of developments with further conditions detailed. It does not apply to existing conditions.
(1.e) When routine operation of a development produces short duration repetitive sound, the following limits shall apply: (1.e.i) ... 5 dBA shall be added to the observed levels of the short duration repetitive sounds that result from routine operation of the development...
(1.e.ii) For short duration repetitive sounds resulting from scrap metal, drop forge and metal fabrication operations or developments... 5 dBA shall be added to the observed levels... maximum sound levels shall not exceed the following limits:
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MPCA Impulse Noise Study: FINAL REPORT, MAY 1991
Maine - continued:
a) At any protected location... not predominantly commercial, transportation, or industrial: 65 dBA - 7:00 a.m. to 7:00 p.m. and 55 dBA - 7:00 p.m. to 7:00 a.m.
(b) At any protected location... predominantly commercial, transportation, or industrial: 75 dBA - 7:00 a.m. to 7:00 p.m. and 65 dBA - 7:OO p.m. to 7:OO a.m.
"Short Duration Repetitive Sounds" a sequence of repetitive sounds which occur more than once in an hour, each clearly discernible as an event and causing an increase in the sound level of at least 6 dBA on the fast meter response above the sound level observed immediately before and after the event, each typically less than ten seconds in duration, and which are inherent to the process or operation of the development and are foreseeable.
"Daytime" is 7:00 a.m. to 7:00 p.m.
Residential limit:
5 dBA penalty added to 1 hour L eq, niqht=50; day=60 dBA; Phone follow-up: new rules mandated by legislature mainly to address scrap metal loading yards; regs apply only to new developments or additions.
... residential: 55 dBA Ldn...
A person may not cause or permit noise levels which exceed those specified in Table 2... Maximum allowable for receiving land use... residential: night= 55 dBA, day = 65 dBA...
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MPCA Impulse Noise Study: FINAL REPORT, MAY 1991
Maryland - continued:
A person may not cause or permit the emission of prominent discrete tones and periodic noises which exceed a level which is 5 dBA lower than the applicable level listed in Table 2. .
"Daytime hours" means 7 a.m. to l0 p.m., local time.
"Periodic noise" means noise possessing a repetitive on and off characteristic.
"Prominent discrete tone" means any sound which can be distinctly heard as a single pitch or set of single pitches...
Residential limit:
night: 55 dBA fast maximum; day: 65 dBA fast maximum. Measured at/within property line of receiver; exemptions include: emergency warnings, household tools, lawn/snow equipment, agricultural equipment, blasting, daytime pile driving.
(a) No person shall cause, suffer, allow, or permit sound from any industrial, commercial, public service, or community service facility that, when measured at any residential property line, is in excess of any of the following:
(a.1) From 7:00 a.m. to 10:00 p.m.:
(a.1.iii) Impulsive sound in air which has a peak pressure level in excess of 80 decibels.
(a.2) From 10:00 p.m. to 7:00 a.m.:
(a.2.iii) Impulsive sound in air which has a peak pressure level in excess of 80 decibels.
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MPCA Impulse Noise Study: FINAL REPORT, MAY 1991
New Jersey - continued:
7:29-1.I Definitions
"impulsive sound" means either a single pressure
peak or a single burst (multiple pressure peaks) having a duration of less
than one second.
Residential limit:
night: 80 dBA peak; day: 80 dBA peak. Phone follow-up: regs
generally apply to stationary sources, measured at or within property line
of receiver; use octave band levels more often; exemptions include:
agriculture, emergency work, religious bells/chimes, warning systems,
aircraft operations public celebrations, human voice, explosives.
(1.d) ...no person owning or controlling an industrial or commercial source shall cause or permit the operation of that noise source if an impulsive sound is emitted in air by that source which exceeds the sound pressure levels specified below... (3.b.B) All other impulse sounds - day:100 dB pk, night:80 dB pk.
"impulse sound" means either a single pressure peak or single burst (multiple pressure peaks) for a duration of less than one second as measured using unweighted peak dB, or dBC slow. "daytime" means 7:00 a.m. to 10:00 p.m.
Residential limit:
night: 80 dB peak; day: l00 dB peak. Phone follow-up; comprehensive rules, impulse section used little; exemptions include: religious bells or chimes, emergency equipment, agricultural equipment, warning devices, construction, lawn care and snow removal equipment.
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MPCA Impulse Noise Study: FINAL REPORT, MAY 1991
A literature search was conducted using in-house reference materials and the MPCA library's outside network capabilities. Much of the research regarding impulse noise deals with highly technical and scientifically detailed definitions beyond the intended scope of this study. The literature on effects of impulse noise focuses mainly on threshold levels above which hearing damage or sleep disruption occurs. There were many opinions regarding the prediction of community response and the best unit of measurement of environmental impulse noise, but conclusions Were few and far from uniform. Sonic booms, explosive blasts, and gunfire were the sources most commonly referred to in the literature. Each of these subjects will be reviewed in further detail below:
Impulse noise has several defining characteristics:
- the duration, or length, of an impulsive event which is a combination of rise time, peak amplitude, and decay time. The length of time an event lasts in order to be "impulsive" varies widely among the experts ranging from microseconds (one millionth of a second) to anything less than two seconds;
- the intensity, or loudness, of an impulsive event is driven by the crest factor, or the maximum amount, in dB, that the sound increases above the threshold level for noisiness (estimated as 45 dBA indoors and 55 dBA outdoors). Generally a rate of increase greater than about l0 dB per second is needed for a sound to be judged impulsive;
- the types of impulsive sounds may be classified into three
main categories according to repetition rate:
(1) occasional widely-separated impulses with repetition rates less
than 1 impact per second, typified by gunfire and other very intermittent
explosive noise sources;
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MPCA Impulse Noise Study: FINAL REPORT, MAY 1991
(2) repetitive impulses with impact rates in the range of 1 to 10 per
second, typified by manual hammering;
(3) highly repetitive, semicontinuous, impulses with a repetition
rate greater than l0 impacts per second; the most common impulse noise
type found in industry, typified by pneumatic chippers and hammers, or
riveting.
- the waveform shape of an impulsive sound may be defined with
one of three configurations:
(1) shock-impulse: a sharp, high positive pressure peak followed by
a long, low negative peak, example: gunshot;
(2) single sinusoidal: near the source, the sound pressure curve has
a sharp rise followed by a slower decaying rate of the pressure to just as
large a negative value which then dies out abruptly; often referred to as
an N curve; Similar to the idealized shock impulse;
(3) decaying sinusoid: characterized with many cycles, or wave
motions, and considerable resonance amplification takes place, example: a
typical hammer blow.
Some authors distinguish reverberant impulse noise as "impact"
noise (typically produced by metal to metal impact as in industrial
forging), to distinguish it from simple one cycle impulses (typified by a
gunshot in the open air).
Impulsive noise is defined under current MPCA Noise Rules (Appendix "B") as: "...either a single sound pressure peak (with either a rise time less than 200 milliseconds or total duration less than 200 milliseconds) or multiple sound pressure peaks (with either rise times less than 200 milliseconds or total duration less than 200 milliseconds) spaced at least by 200 millisecond pauses."
The other states define impulse noise as single or multiple noise events lasting one second or less. This definition has a more tangible meaning for individuals impacted as well as regulatory personnel providing enforcement.
"Ambient", or background noise may influence the accuracy of a noise measurement. Ideally, the background noise must not "drown out" the sound of interest. This means that the level of interest must be at least 3 dB higher than the ambient noise. If the difference is between 3 dB and 10 dB, a correction to the measurement is needed. No correction is
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MPCA Impulse Noise Study: FINAL REPORT, MAY 1991
necessary if the difference is greater than 10 dB and current Minnesota test procedures include this documentation.
Most of the literature focuses on hearing loss and threshold limitations for impulse noise in the work place. The damaging characteristics of continuous sounds are well known, but damage-risk in impulse sounds has been considerably more difficult to determine. Review of data leads to the conclusion that the impulse noise limit requisite to prevent more than a 5 dB permanent hearing loss, at 4000 Hz after years of daily exposure, is a peak sound pressure level (SPL) Of 145 dB. Workplace criteria for impulse noise proposed by the Committee on Hearing and Bioacoustics and Biomechanics of the National Research Council (CHABA) establishes a maximum allowable peak pressure level of 164 dB. This maximum value is applied to the short-duration impulses - 25 microseconds Or less. Exceeding a level of 165 SPL is likely to lead to permanent damage in 50 percent of ears.
Noise below the levels usually associated with hearing damage can also cause regular and predictable changes in the body. Our bodies react automatically to sudden or loud sounds - blood pressure rises, heart rate and breathing speed up, muscles tense, hormones are released into the bloodstream, and perspiration appears - preparing us physically for this "fight or flight" response. These changes can occur even during sleep and some studies conclude that continuous exposures during the night, degrading the quality of sleep, may effect one's general health producing irritability and fatigue.
Most people can usually become habituated or accustomed to this alerting-type reflex response to sudden changes in the sound environment when awake more than when asleep. A high degree of habituation, even to intense impulse noises such as gunfire, is normally seen in animals, and man, when the exposure is repeated, provided that the noise character or type is not changed.
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MPCA Impulse Noise Study: FINAL REPORT, MAY 1991
Short duration, high intensity, intermittent noises are judged by most people to be more annoying than steady noises having the same overall energy content. Even when impulses are regular and expected, their sharpness and startle effects contribute to increased annoyance. Impulsive noise events are more likely to cause deeper annoyance during the night than during the day and increase the overall sensitivity to the noise. Therefore, some impulsive noises can be disturbing to some individuals if heard at all - classically, the dropping of a pin, or dripping of a faucet - even though they may be lower than the normal ambient or background noise levels.
Environmental noise surveys across the nation indicate that the interruption of rest, relaxation, and sleep is the main cause of many people's complaints. Noise can interfere with sleep by increasing sleep latency (the amount of time required to fall asleep), by waking a person, or by causing shifts from deeper to lighter sleep stages. It has been shown that the intensity of an event has to be louder to disrupt the deeper stages of sleep. Unfortunately, the elderly and the sick, particularly sensitive to disruptive noise, are more easily awakened by noise and, once awake, have more difficulty returning to sleep.
Other studies conducted to determine adaptability to a threshold noise over a number of successive nights revealed only slight adaptation, however, adaptation to new sleep environments did occur more readily. Sounds which are familiar and which do not require anything to be done about them, are less liable to awaken. Still other studies suggest that adaptation to noise is constant, for example, cessation of aircraft landing operations between 11 p.m. and 6 a.m. at an international airport had no appreciable effect on subjects' reports of sleep interference.
On a federal level the recommended interior noise levels for sleeping in hospitals is between 34 and 47 dB, and for other sleeping environments, the maximum acceptable intrusive noise level is 55 dB. Threshold environmental noise levels which can cause sleep disturbance cover a range of 35 dBA to 70 dBA depending on the difference from the ambient, or total background noise in a given environment. Researchers disagree widely on the intrusive effects of environmental
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MPCA Impulse Noise Study: FINAL REPORT, MAY 1991
impulse noise ranging from: "no level for impulse noise is too low to be ignored" to: "lack of an impulse standard does not place the public's hearing in jeopardy".
Impulsive noise requires special noise measurement equipment and measurement techniques. The literature provides little guidance in the area of predicting community annoyance or for measuring impulse noise because the studies contradict each other as to the "best" method. Experiments comparing impulsive . sounds to steady sounds indicate a greater variability of human response to impulsive sounds, thus making the choice of a criterion level more difficult.
A standard sound level meter usually has the choice of "slow" or "fast" exponential-time-averaging response, as well as a choice of "A" or "C" frequency weighting. These meters are designed for and best used with steady-state noise conditions. They do not respond fast enough to the very rapid rise times of impulsive sounds, and will generally underestimate the noise. More elaborate meters may be equipped with an "impulse" time response, a "peak" detector with a "hold" option, or a "flat" or "linear" weighting response. They capture the impulsive nature of the sound better, but are less available for general use because of the higher cost and a need for increased operator skill.
Significant points regarding the various time response features and weightings are as follows:
"slow" measurement response: the exponential-time-averaging done in a sound level meter every 1000 milliseconds. "Slow" time response has been used in conjunction with "C-weighting" when measuring blast noise or other low frequency impulse sources and is available in most types of sound level meters.
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MPCA Impulse Noise Study: FINAL REPORT, MAY 1991
"fast" measurement response: the exponential-time-averaging done in a sound level meter every 125 milliseconds, responding eight times faster than for the "slow" time weighting. "Fast" time response is best used to measure intermittent and fluctuating sounds and is available in most types of sound level meters.
"impulse" measurement response: the exponential-time-averaging done in a sound level meter every 35 milliseconds, responding four times faster than for the "fast" time weighting. Some experts claim the "impulse" time weighting simulates the loudness response of the human ear to impulsive sounds, while others feel that 35 milliseconds is not long enough to be perceived by the human auditory system and that it is not the most appropriate way to measure impulsive sounds. This option is available in some of the better sound level meters.
"A-weighting": closely imitates the response of the human ear by filtering out some lower and higher frequencies (not normally heard) and allowing better efficiency at the speech-range frequencies. A-weighting is most commonly used in environmental noise control work when dealing with community annoyance.
"C-weighting": reflects a uniform response to all frequencies in the meter range providing the closest approach to a "flat" or equal frequency weighting. The use of C- weighting is a reasonable measure of low-frequency, high energy impulses such as sonic booms, mortar fire, and blasting which produce sound-induced vibrations in buildings, and also of high frequency sounds above 8,000 Hz that are louder than 85 decibels.
A "hold" option is sometimes available on specialized meters with a peak or maximum feature. The digital display or needle moves to and remains at the peak or maximum level the sound pressure has reached and continues to hold at this level until either the sound reaches a higher level or a manual reseat button is pushed.
In addition, "octave band" spectral frequency analysis can be accomplished using an integrating sound level meter equipped
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MPCA Impulse Noise Study: FINAL REPORT, MAY 1991
with filters, a real-time analyzer with the entire impulse contained in memory, or digitization and finite discrete Fourier transform of the entire impulse. This procedure has much more value as an engineering and design tool than as an enforcement method. The equipment needed is generally expensive, not very "field friendly", and requires a more sophisticated level of training to operate and analyze. It is not considered a desirable option to pursue at this time.
In addition to the time responses and weighting functions, a standard method of measurement, or metric, for a potential impulse rule needed review. Briefly, a specific measurement time period must be set for averaging and statistical methods, while maximum and penalty addition methods require a defined difference from any other noise sources. Ldn, Leq, SEL, L1, Lmax, Lpk, and penalties are detailed further:
"Ldn": day/night level, is the 24 hour average of continuous "A-weighted" sound energy having a 10 decibel penalty added to the nighttime hours of 10 p.m. to 7 a.m. The Environmental Protection Agency (EPA) developed health and welfare guidelines using Ldn, and it is the metric most often used to define noise contours around airports. A "C"- weighted Ldn has been used for some studies regarding blast noise and sonic booms because of the low frequencies emitted. It is not a good indicator for a variety of source types and generally would average out the effects of a few seconds of impulsive noise.
"Leq": equivalent continuous A-weighted sound level, has the same acoustic energy for a constant sound level as for a fluctuating or intermittent level in the same period of time. Leq is more sensitive to short duration, spurious noise events than the current statistical LID level. The Leq can be measured directly by suitable instrumentation for some impulse and impact noises, and can be used with any time response for any time period.
"SEL": sound exposure level, or single event level, is that level which, lasting for one second, has the same acoustic energy as a given noise event lasting for a period
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MPCA Impulse Noise Study: FINAL REPORT, MAY 1991
of time; it is a measure of acoustic energy and can compare unrelated noise events because the time is normalized to one second. This method is sometimes used in aircraft flyover analysis. Little information is available relating to impulse noise applications.
"L1": a statistical measure of sound, the highest one percent of the time period surveyed. The current Minnesota L10 limit reflects the highest six minutes for one hour, an L1 would reflect the highest 36 seconds of the hour . This metric can be used with any weighting or time response.
"Lmax ": maximum sound level, the greatest sound pressure level for a specific exponential-time-averaging constant during a given time period. This metric can be used with any weighting or time response for any time period.
"Lpk": peak sound level, is the greatest absolute sound pressure level during the time of observation, and it can be the same as the maximum. This metric can be used with any time response for any time period using weighting or not.
The literature states that maximum and peak measurements must be treated with caution, since some impulsive sources have extremely short rise times and even some better meters may not respond fast enough to accurately reflect the absolute greatest levels. They also can be unwieldy when a succession of impulses, sometimes overlapping, must be evaluated individually. For outdoor, environmental applications this degree of accuracy is not required provided a suitable limiting level can be found.
There is also a "penalty" method of assessing impulse noise. Five or ten decibels can be added to the statistical or Leq limit if a sound is judged impulsive. This more subjective way of addressing short term noise should include a statement as to how much the maximum level of the sound would have to exceed the ambient sound just before and after the event to be legally classified as impulsive.
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MPCA Impulse Noise Study: FINAL REPORT, MAY 1991
Determining what impulse noise sources can or should be regulated is probably the most critical and sensitive issue. Every state with an active noise regulation exempts air, rail, or road operations engaged in interstate commerce. In current practice, Minnesota noise rules are not exercised over such sources as aircraft flyovers, sonic booms, rail car coupling, or highways when in conflict with federal preemption.
Trying to regulate irregular or unpredictable events not associated with a source's normal operating procedure is difficult. Tracking of such events is very time-intensive and may not ultimately be within the control of the facility.
Enforcement activities regarding construction type events such as use of power tools, riveting, hammering, and pile driving, are best handled at the local level in addition to dog barking and other animal control. Back-up alarms, train whistles, horns, bells, or sirens all serve meaningful safety functions and should not be unduly regulated.
Sources that are not to be regulated need to be specifically exempted. Gun clubs and shooting ranges are currently exempted from Minnesota's noise rules as are racing facilities in existence prior to July 1, 1983.
Impulse noise should be defined as single or multiple noise events lasting one second or less. A further distinction should be made as to the difference from the ambient sound level immediately before or after the event.
Researchers disagree widely on the intrusive effects of environmental impulse noise. There is no clear evidence of any permanent physical effect on the public's health from environmental impulse noise at this time. Sleep disturbance
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MPCA Impulse Noise Study: FINAL REPORT, MAY 1991
is the most important adverse effect of environmental impulse noise. Threshold noise levels which can cause sleep disturbance cover a range of 35 dBA to 70 dBA depending on the difference from the ambient noise in a given environment. Therefore, no limiting level can be readily identified at this time.
The literature also provides little guidance for measuring impulse noise because the studies contradict each other as to the "best" method. By using Minnesota's current "A- weighting" and "fast" response options, implementation of an additional Leq, L1, Lmax, or "A"-weighted Lpk limit could be done with minimal disturbance to current enforcement methods.
Practical considerations, providing the most efficient use of personnel, should allow for simultaneous monitoring of L10, L50, and "impulse" levels, with a single sound level meter. While requiring a modified survey duration and monitoring procedure, the Lmax, Lpk, or Leq options would work best with a shorter duration time period, such as one second or one minute, to better ensure capturing a specific source. Any of these alternatives would effectively capture high intensity sounds not currently addressed by the L10 limit.
A new rule must be simple and define a tangible reality to be most effective. It is unknown at this time if the number of impulsive sources which could realistically be regulated would warrant a change in the noise rules. Further field study will be undertaken in order to establish a need, and to determine a reasonable and enforceable impulse noise level. By summarizing enforcement episodes where a State impulse standard would be both helpful and enforceable, the most appropriate noise metric can be chosen. Current MPCA measurement procedures enable the simultaneous collection of hourly Leq, Lmax, L1, and Lpk (A-weighted) while surveying the required L10 and L50 levels. Future monitoring in response to noise complaints will be documented in this manner for the next several years as a consideration for any future efforts regarding a change to Minnesota's noise rule.
Page 19
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MPCA Impulse Noise Study: FINAL REPORT, MAY 1991
American National Standard - Quantities and Procedures for Description and Measurement of Environmental Sound - Part 1. ANSI S12.9-1988.
American National Standard - Method for Assessment of High-Energy Impulsive Sounds with Respect to Residential Communities. ANSI S12.4-1986.
American National Standard - Methods for the Measurement of Impulsive Noise. ANSI S12.7-1986.
American National Standard - Specification for Sound Level Meters. ANSI S1.4-1983 (revision of S1.4-1971).
American National Standard - Methods for the Measurement of Sound Pressure Levels. ANSI S1.13-1971 (R1976).
Berry, B.F. - The Evaluation of Impulsive Noise. National Physical Laboratory Report Ac111, United Kingdom, Sept 1987.
Berry, B.F., Wallis, A.D., Rozwadowski, A. - The Use of Short Term LAEQ in the Assessment of Implulsive Noise. Institute of Acoustics Autumn Conference, Windmere, November 1989.
Brambilla, G., Carretti, M., and Corbino, O.M. - Evaulation of Annoyance Due to Impulsive Sound. Noise-Con 90, October 1990.
Brambilla, G., Carretti, M., and Corbino, O.M. - Assessment of Annoyance and Impulsivity of Environmental Noises. 13th International Congress on Acoustics, Yugoslavia, 1989.
Brambilla, G., Carretti, M., and Santoboni, S. - Noise as a Public Health Problem: Laboratory Subjective Evaluation of Environmental Impulsive Sounds. Swedish Council for Building Research, 1988.
British Acoustical Society - Impulsive Noise. Papers 72.34-72.38, Proceedings of the B.A.S. Vol, 1, No. 3. April 1972.
British Standards Institution - Method of Rating Industrial Noise Affecting Mixed Residential and Industrial Areas. BS.4142 , 1967.
Bruel, Per V. - Measurement of Impulsive Signals. Bruel & Kjaer Instruments, Inc., Technical Paper: Inter-Noise 87, Marlborough, MA, 1987.
Bruel & Kjaer Instruments, Inc. - Sound Intensity. Bruel & Kjaer Instruments, Inc., Marlborough, MHA, July 1986.
Bruel & Kjaer Instruments, Inc. - Industrial Noise Control and Hearing Testing. Bruel & Kjaer Instruments, Inc., Marlborough, MA, 1985.
Bruel & Kjaer Instruments, Inc. - Measuring Sound. Bruel & Kjaer Instruments, Inc., Marlborough, MA, revised: 1984.
Burns, William - Noise and Man. Second Edition. J.B. Lippincott Co., Philadelphia, PA, 1973.
Appendix A: References page A 1
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MPCA Impulse Noise Study: FINAL REPORT, MAY 1991
Coles, R. and Rice, C. - Towards a Criterion for Impulse Noise in Industry. Annals of Occupational Hygiene, Vol. 13, 1970.
Coles, R., Garinther, G.R., Hodge, D., and Rice, C. - Hazardous Exposure to Impulse Noise. Journal of the Acoustical Society of America, February 1968.
Coles, R, and Rice, C. - Hazards from Impulsive Noise. Annals of Occupational Hygiene, Vol. 10, 1967.
Committee on Hearing, Bioacoustics and Biomechanics, Guidelines for Preparing Environmental Impact Statements on Noise. National Academy of Science, Washington D.C., 1977.
Dietrich, Eldred, Berman - Comments in Response to the Notice of Intent to Solicit Outside 0pinion on MPCA Rules NPC-1 and NPC-2. Bolt Beranek and Newman Inc, Cambridge, MA, April 1980.
Dym, C. - Sources of Industrial Impact and Impulsive Noise. Noise Control. Engineering Vol. 8, No. 2, March-April 1977.
Erdreich, John - Problems and Solutions in Impulsive Noise Dosimetry. Journal of Sound and Vibration, March 1984.
Fiddel, S., Pearsons, K., Grignetti, M., and Green, D. - The Noisiness of Impulsive Sounds. Journal of the Acoustical Society of America, Vol. 48, No, 6, 1970.
Harris, Cyril H, - Handbook of Noise Control. 2nd Edition. McGraw-Hill, Inc., New York, NY, 1979.
International 0rganization for Standardization - Acoustics-Guide to International Standards on the Measurement of Airborne Acoustical Noise and Evaluation of Its Effects on Human Beings. #2204, 1979.
Johnston, Clifton James - Assessment of Annoyance Due to Varying Noise Levels. University of Natal, Pretoria, Republic of South Africa, January 1979.
Kryter, Karl D. - The Effects of Noise on Man- 2nd Edition. Academic Press, Inc., Orlando, FL, 1985.
Kryter, Karl D. - Evaluation of Exposure to Impulse Noise. Archives of Environmental Health, May 1970.
Lipscomb, David H. - Noise: The Unwanted Sounds. Nelson-Hall Publishers, Chicago, IL, 1974.
Lowey, Brian and Associates - A Review of Minnesota's Environmental Noise Control Regulations. Executive Summary. Technical Paper, Lowey and Assoc., St, Paul, MN, March 1983.
McRobert, H, and Ward, Q. - Damage-Risk Criteria: The Trading Relation Between Intensity and the Number of Non-Reverberant Impulses. Journal of the Acoustical Society of America, Vol. 53, No. 5, 1973.
Peterson, Arnold and Gross, Ervin E. Jr. - Handbook of Noise Measurement. 7th Edition. General Radio Company, 1972.
Appendix A: References page A 2
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MPCA Impulse Noise Study: FINAL REPORT, MAY 1991
Schomer, P, and Neathammer, R. - Community Reaction to Impulsive Noise: A Ten Year Research Summary. U.S. Army Corps of Engineers, Champaign, IL, Feb 1984.
Solaini, A. - Impulsive Noise- A Brief Review. Transport and Road Research Laboratory, Supplementary Report 85 UC, 1974.
South African Bureau of Standards - The Measurement and Rating of Environmental Noise With Respect to Annoyance and Speech Communication. Council of south African Bureau of Standards, SABS 0103-1983, Pretoria, Republic of South Africa, March 1983.
Sulkowski, Wieslaw J., M.D., Ph.D. - Industrial Noise Pollution and Hearing Impairment Foreign Scientific Publication; Department of National Center for Scientific, Technical, and Economic Information, Warsaw, Poland, 1980.
Swing, J.W. and Pies, D.B. - Assessment of Noise Environments Around Railroad 0perations. Report WCR 73-5, Wyle Laboratories, July 1973.
Tempest, William - The Noise Handbook. Academic Press Inc., London, 1985.
Thiessen, G. - Disturbance of Sleep by Noise. Journal of the Acoustical Society of America, Vol. 64, No, 1, 1978.
United States Environmental Protection Agency: Study for Westover AFB -Sound Exposure Level Analysis (Sleep Interference). Env Protect Agency, Washington DC, April 1987.
United States Environmental Protection Agency - Noise Emission Standards for Transportation Equipment: Interstate Rail Carriers. Final Rule. Rules and Regs, 40 CFR Part 201 [FRL 1361-3], Washington DC; Federal Register, Vol 45 #3, Jan 1980.
United States Environmental Protection Agency, Office of Noise Abatement and Control - Noise: A Health Problem. EPA, Aug 1978.
United States Environmental Protection Agency, Office of Noise Abatement and Control - Information on Levels of Environmental Noise Requisite to Protect Public Health and Welfare with an Adequate Margin of Safety. Appendix G EPA 550/9-74-004, Washington D.C., March 1974.
United States General Accounting Office; Resources, Community, and Economic Development Division - Transportation Noise. Federal Control and Abatement Responsibilities May Need to Be Revised. GAO/RCED-90-11, Washington, D.C., October 1989.
Vernet, H. - Effect of Train Noise on Sleep for People Living in Houses Bordering the Railway Line. Journal of Sound and Vibration, Vol. 66, No.3, 1979.
Von Gierke, H.E., Robinson, D.W., and Karmy, S.J. - Results of the Workshop on Impulse Noise and Auditory Hazard. Institute for sound and Vibration Research, Memorandum 618, 1981.
Wallis, A.D., and Berry, B.F. - Using Short LEQ in the Measurement of Impulsive Noise. Inter-Noise, CA, Dec 1989.
Yerges, Lyle F. - The Uses and Abuses of Codes and Standards. Journal of Sound and Vibration, April 1974.
Appendix A: References page A 3
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MPCA Impulse Noise Study: FINAL REPORT, MAY 1991
07/15/86
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INCORPORATION BY REFERENCE |
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DEFINITIONS |
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NOISE CONTROL REQUIREMENT |
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NOISE STANDARDS |
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NOISE AREA CLASSIFICATION |
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MEASUREMENT METHODOLOGY |
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SOUND ATTENUATION MEASUREMENT METHODOLOGY |
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VARIANCE |
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For the purpose of chapter 7010, American National Standards Institute, Specification for Sound Level Meters, S1.4-1983 is incorporated by reference. This publication is available from the American National Standards Institute, 1430 Broadway, New York, New York 10018 and can be found at: the offices of the Minnesota Pollution Control Agency, 520 Lafayette Road North, Saint Paul, Minnesota 55155; the Government Documents Section, Room 409, Wilson Library, University of Minnesota, 309 19th Avenue South, Minneapolis, Minnesota 55454; and the State of Minnesota Law Library, Ford Building, 117 University Avenue, Saint Paul, Minnesota 55155. This document is not subject to frequent change.
The Federal Highway Administration publication, Sound Procedures for Measuring Highway Noise: Final Report, FHWA-DP-45-1R (August 1981) is incorporated by reference. This publication is available from the United States Department of Transportation, Federal Highway Administration, 1000 North Globe Road, Arlington, Virginia 22201 and can be found at: the offices of the Minnesota Pollution Control Agency, 520 Lafayette Road North, Saint Paul, Minnesota 55155; the Government Documents Section, Room 409, Wilson Library, University of Minnesota, 309 19th Avenue South, Minneapolis, Minnesota 55454; and the State of Minnesota Law Library, Ford Building, 117 University Avenue, Saint Paul, Minnesota 55155. This document is not subject to frequent change.
Statutory Authority, Ms s 116.07 subds 2,4
Appendix B: Minnesota Noise Rule page B 1
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MPCA Impulse Noise Study: FINAL REPORT, MAY 1991
page 2 - NOISE POLLUTION CONTROL RULES
Subpart 1. Application. The terms used in chapter 7010 have the meanings given them in this part.
Subp. 2. A-Weighted. "A-Weighted" means a specific weighting of the sound pressure level for the purpose of determining the human response to sound. The specific weighting characteristics and tolerances are those given in American National Standards Institute Sl.4-1983, section 5.I.
Subp. 3. Daytime. "Daytime" means those hours from 7:00 a.m. to 10:00 p.m.
Subp. 4. dB(A). "dB(A)" means a unit of sound level expressed in decibels (dB) and A-weighted.
Subp. 5. Decibel. "Decibel" means a unit of sound pressure level, abbreviated as dB.
Subp. 6. Impulsive noise. "Impulsive noise" means either a single sound pressure peak (with either a rise time less than 200 milliseconds or total duration less than 200 milliseconds) or multiple sound pressure peaks (with either rise times less than 200 milliseconds or total duration less than 200 milliseconds) spaced at least by 200 millisecond pauses.
Subp. 7. L 10 . "L 10" means the sound level, expressed in dB(A), which is exceeded ten percent of the time for a one hour survey, as measured by test procedures approved by the director.
Subp. 8. L 50. "L 50 " means the sound level, expressed in dB(A), which is exceeded fifty percent of the time for a one hour survey, as measured by test procedures approved by the director.
Subp. 9. Municipality. "Municipality" means a county; a city; a town; a regional planning and development commission established under Minnesota Statutes, chapter 473; the metropolitan council; or other governmental subdivision of the state responsible by law for controlling or restricting land use within its jurisdiction.
Subp. 10. Nighttime. "Nighttime" means those hours from 10:00 p.m. to 7:00 a.m.
Subp. 11. Person. "Person" means any human being, any municipality or other governmental or political subdivision or other public department or agency, any public or private corporation, any partnership, firm, association, or other organization, any receiver, trustee, assignee, agency, legal entity, other than a court of law, or any legal representative of the foregoing, but does not include the agency.
Subp. 12. Sound pressure level. "Sound pressure level", in decibels, means 20 times the logarithm to the base 10 of the ratio of the pressure to the reference pressure. The reference pressure shall be 20 micronewtons per square meter.
Statutory Authority: MS s l16.07 subds 2,4
Appendix B: Minnesota Noise Rule page B 2
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MPCA Impulse Noise Study: FINAL REPORT, MAY 1991
page 3 - NOISE POLLUTION CONTROL RULES
No person may violate the standards established in part 7010.0040, unless exempted by Minnesota Statutes, section l16.07, subdivision 2a. Any municipality having authority to regulate land use shall take all reasonable measures within its jurisdiction to prevent the establishment of land use activities listed in noise area classification (NAC) 1, 2, or 3 in any location where the standards established in part 7010.0040 will be violated immediately upon establishment of the land use.
Statutory Authority: MS s l16.07 subds 2,4
Subpart 1. Scope. These standards describe the limiting levels of sound established on the basis of present knowledge for the preservation of public health and welfare. These standards are consistent with speech, sleep, annoyance, and hearing conservation requirements for receivers within areas grouped according to land activities by the noise area classification (NAC) system established in part 7010.0050. However, these standards do not, by themselves, identify the limiting levels of impulsive noise needed for the preservation of public health and welfare. Noise standards in subpart 2 apply to all sources.
Subp. 2. Noise standards.
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Noise Area
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Daytime
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Daytime
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Nighttime
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Nighttime
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L50 |
L10 |
L50 |
L10 |
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1 |
60 |
65 |
50 |
55 |
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2 |
65 |
70 |
65 |
70 |
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3 |
75 |
80 |
75 |
80 |
Statutory Authority, MS s l16.07 subds 2,4
Subpart I. Applicability. The noise area classification is based on the land use activity at the location of the receiver and determines the noise standards applicable to that land use activity unless an exemption is applied under subpart 3.
Sub . 2. Noise area classification. The noise area classifications and the activities included in each classification are listed below:
Appendix B: Minnesota Noise Rule page B 3
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MPCA Impulse Noise Study: FINAL REPORT, MAY 1991
page 4 - NOISE POLLUTION CONTROL RULES
Noise Area Classification I - Land Use Activities
Household Units (includes farm houses)
Group quarters
Residential hotels
Mobile home parks or courts
Transient lodging
Other residential
Motion picture production
Correctional institutions
Educational services
Medical/other health services
Religious activities
Cultural activities and nature exhibitions
Entertainment assembly
Camping and picnicking areas (designated)
Resorts and group camps
Other cultural, entertainment, recreational activities
Noise Area Classification 2 - Land Use Activities
Railroad terminals (passenger)
Railroad terminals (passenger and freight)
Rapid rail transit and street railway passenger terminals
Bus passenger terminals (intercity)
Bus passenger terminals (local)
Bus passenger terminals (intercity and local)
Other motor vehicle transportation
Airport and flying field terminals (passenger)
Airport and flying field terminals (passenger and freight)
Marine terminals (passenger)
Marine terminals (passenger and freight)
Telegraph message centers
Transportation services and arrangements
Wholesale trade
Public assembly (except race tracks and entertainment assembly)
Recreational activities (except designated camping and picnicking
areas)
Retail trade -
building materials
hardware
farm equipment
general merchandise
food
automotive & accessories
marine craft & accessories
aircraft & accessories
apparel & accessories
furniture, home furnishings and equipment
eating and drinking
Other retail trade
Finance, insurance, and real estate services
Personal services
Business services
Repair services
Legal services
Other professional services
Contract construction services
Governmental services (except correctional institutions)
Miscellaneous services (except religious activities)
Amusements (except fairgrounds and amusement parks)
Parks
Automobile parking
Appendix B: Minnesota Noise Rule page B 4
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MPCA Impulse Noise Study: FINAL REPORT, MAY 1991
page 5 - NOISE POLLUTION CONTROL RULES
Noise Area Classification 3 - Land Use Activities
Food and kindred products - manufacturing
Textile mill products - manufacturing
Apparel and other finished products made from fabrics, leather &
similar materials - manufacturing
Lumber and wood products (except furniture) - manufacturing
Furniture and fixtures - manufacturing
Paper and allied products- manufacturing
Printing, publishing, and allied industries
Chemicals and allied products - manufacturing
Petroleum refining and related industries
Rubber and miscellaneous plastic products - manufacturing
Stone, clay, & glass products - manufacturing
Primary metal industries
Fabricated metal products - manufacturing
Professional, scientific, and controlling instruments; photographic &
optical goods; watches and clocks - manufacturing
Miscellaneous manufacturing (except motion picture production)
Railroad, rapid transit, and street railway transportation (except
passenger terminals)
Motor vehicle transportation(except passenger terminals)
Aircraft transportation (except passenger terminals)
Marine craft transportation (except passenger and freight terminals)
Highway and street right-of-way Communication (except telegragh
message centers)
Utilities
Other transportation, communication & utilities (except
transportation services and arrangements)
Race tracks
Fairgrounds and amusement parks
Agricultural
Agricultural and related activities
Forestry activities and related services (including commercial
forest land, timber production, and other related activities)
Fishing activities and related services
Mining activities and related services
Other resource production and extraction
All other activities not otherwise listed
Appendix B: Minnesota Noise Rule page B 5
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MPCA Impulse Noise Study: FINAL REPORT, MAY 1991
page 6 - NOISE POLLUTION CONTROL RULES
Noise Area Classification 4 - Land Use Activities
Undeveloped and unused land area (excluding noncommercial forest
development)
Noncommercial forest development
Water areas
Vacant floor area
Under construction
Other undeveloped land and water areas
Subp. 3. Exceptions. The noise area classification for a land use may be changed in the following ways if the applicable conditions are met.
A. The daytime standards for NAC-1 shall be applied to NAC-1 during the nighttime if the land use activity does not include overnight lodging.
B. The standards for a building in a NAC-2 shall be applied to a
building in a NAC-I if the following conditions are met:
1) the building is constructed in such a way that the exterior to
interior sound level attenuation is at least 30 dB(A); and
2) the building has year-round climate control; and
3) the building has no areas or accommodations that are intended for
outdoor activities.
C. The standards for a building in a NAC-3 shall be applied to a
building in a NAC-1 if the following conditions are met:
1) the building is constructed in such a way that the exterior to
interior sound level attenuation is at least 40 dB(A); and
2) the building has year-round climate control; and
3) the building has no areas or accommodations that are intended for
outdoor activities.
D. The standards for a building in a NAC-3 shall be applied to a
building in a NAC-2 if the following conditions are met:
1) the building is constructed in such a way that the exterior to
interior sound level attenuation is at least 30 dB(A); and
2) the building has year-round climate control; and
3) the building has no areas or accommodations that are intended for
outdoor activities.
Statutory Authority: MS s l16.07 subds 2,4
Appendix B: Minnesota Noise Rule page B 6
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MPCA Impulse Noise Study: FINAL REPORT, MAY 1991
page 7 - NOISE POLLUTION CONTROL RULES
Subpart 1. Measurement location. Measurement of sound must be made at or within the applicable NAC at the point of human activity which is nearest to the noise source. All measurements shall be made outdoors.
Subp. 2. Equipment specifications. All sound level measuring devices must meet Type 0, I, II, or S specifications under American National Standards Institute S1.4-1983.
Subp. 3. Calibration. All sound level measuring devices must, at a minimum, be externally field calibrated before and after monitoring using a calibration device of known frequency and sound pressure level.
Sub. 4. Measurement procedures. The following procedures must be used to obtain representative sound level measurements:
A. Measurements must be made at least three feet off the ground or surface and away from natural or manmade structures which would prevent an accurate measurement.
B. Measurements must be made using the A-weighting and fast response characteristics of the sound measuring device as specified in American National Standards Institute S1.4-1983.
C. Measurements must not be made in sustained winds or in precipitation which results in a difference of less than ten decibels between the background noise level and the noise source being measured.
D. Measurements must be made using a microphone which is protected from ambient conditions which would prevent an accurate measurement.
Subp. 5. Data documentation. A summary sheet for all sound level measurements shall be completed and signed by the person making the measurements. At a minimum, the summary sheet shall include:
A. date;
B. time;
C. location;
D. noise source;
E. wind speed and direction;
F. temperature; .
G. humidity;
H. make, model, and serial number of measuring equipment;
I. field calibration results;
J. monitored levels; and
K. site sketch indicating noise source, measurement location,
directions, distances, and obstructions.
Statutory Authority: MS s 116.07 subds 2,4
Appendix B: Minnesota Noise Rule page B 7
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MPCA Impulse Noise Study: FINAL REPORT, MAY 1991
page 8 - NOISFE POLLUTION CONTROL RULES
Subpart 1. Purpose. Sound level measurements made for assesing sound attenuation as specified in part 7010.0050, subpart 3, item B, C, or D, shall be made according to the requirements of this part.
Subp. 2. Equipment. The equipment shall meet the requirements specified in part 7010.0060, subpart 2.
Subp. 3. Calibration. The equipment must meet the calibration requirements specified in part 7010.0060, subpart 3.
Subp. 4. Measurement procedure. The measurement procedure described in FHWA-DP-45-lR, section 8 must be used for determination of the sound attenuation.
Subp. 5. Equivalent methods. Methods equivalent to those described in subpart 4 may be used provided they are approved by the director of the Minnesota Pollution Control Agency. The director shall approve an alternative method if the director finds that the method will produce representative data and results which are as reliable as the methods specified in subp 4.
Statutory Authority: MS s l16.07 subds 2,4
If, upon written application of the responsible person, the agency finds that by reason of exceptional circumstances strict conformity with any provisions of any noise rule would cause undue hardship,. would be unreasonable, impractical, or not feasible under the circumstances, the agency may permit a variance upon the conditions and within the time limitations as it may prescribe for the prevention, control, or abatement of noise pollution in harmony with the intent of the state and any applicable federal laws.
Statutory Authority: MS s l16.07 subds 2,4
Minnesota Rules, parts 7010.0100, 7010.0200, 7010.0300,
7010.0400, 7010.0500, 7010.0600, 7010.0700 are repealed.
Appendix B: Minnesota Noise Rule page B 8