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REPORT AS6570.110616.R1
NOISE IMPACT ASSESSMENT OF INDOOR SHOOTING RANGE
Prepared: 16th June 2011
The Building Consultancy Group 44 Canal Street Bootle Liverpool L20 8QU
4.1 Method of Assessment 2 4.2 Calculation Parameters 3
5.1 Noise Control Via External Wall, Excluding Glazing 4 5.2 Noise Control Via External Glazing 5 5.3 Noise Control Via Roof, Excluding Ventilation Duct 5 5.4 Noise Control Via Ventilation Duct 6 5.5 Noise Control Via External Door 6
Appendix A Acoustic Terminology
It is proposed to construct a building for multi-purpose sports use on land off Ramsey Road, Laxey. One of the activities proposed to be undertaken within the building is live round pistol shooting.
Alan Saunders Associates has been appointed by The Building Consultancy Group to undertake an assessment of the required noise control measures in order to mitigate the impact to the closest residents.
Calculations have been undertaken and predictions compared to current Standards and guidance documents to determine any mitigation measures considered necessary to satisfy the requirements of an imposed planning condition.
Please refer to Appendix A for full details of acoustic terminology used throughout this report.
The proposed multi-purpose sport building is to be built into a hillside on land adjacent to Rockwood, Ramsey Road.
The building is surrounded by residential properties and is bounded by Ramsey Road to the north and a rail line to the south.
The grounds of the nearest residential property to the north is Kia-Ora at approximately 60 metres from the north façade. The grounds of the nearest residential property to the east is South Court at approximately 20 metres from the east façade. The grounds of the nearest residential property to the west is Spring House at approximately 45 metres from the west façade.
The design is still in the outline phases. In general, the building is proposed to be constructed from a cavity masonry external wall, double glazed windows with internal safety shutters and a 'green' roof laid onto a concrete composite structure. The main hall is accessed via an internal lobby.
The shooting range is proposed to be used privately by the developer for approximately two hours, once a week.
Planning permission for the development has been granted subject to conditions, one of which relates to noise control as repeated below.
Condition No. 4: Prior to the commencement of development a scheme prepared by a suitably qualified acoustic engineer, or satisfactory equivalent, detailing and identifying any sound proofing requirements, must be submitted to and agreed by the Planning Authority. Thereafter any sound proofing measures contained within the agreed scheme must be installed prior to the commencement of use of the building and thereafter maintained for the life span of the building.
There is no current standard or guidance document that specifically details the assessment of noise from an indoor shooting range. Through liaison with Simon Renton, Environmental Protection Officer for the Isle of Man’s Department of Environment, Food and Agriculture (DEFA), an assessment following the guidance outlined in Clay Target Shooting: Guidance on the Control of Noise published by the Chartered Institute of Environmental Health (CIEH) in January 2003 has been deemed appropriate by the Local Authority.
A limit on noise emissions has been proposed by DEFA, repeated as follows:
Noise from shooting shall not exceed a mean Shooting Noise Level (SNL*) of 50 dB(A) measured at any neighbouring noise sensitive premises.
There have been a number of research investigations into what levels of gunshot noise cause annoyance to residential occupants, notably by Sørensen S & Magnusson J, G F Smoorenburg and Hoffman. The current thinking on their impact has been set out in Clay Target Shooting: Guidance on the Control of Noise published by the Chartered Institute of Environmental Health (CIEH) in January 2003. Measurement and social survey work carried out by the Building Research Establishment during 1996/1997, provides the basis for applying limits at noise sensitive premises.
The research by the BRE suggests that there is no fixed level for annoyance to occur. The BRE criterion is quoted in terms of a Shooting Noise Level (SNL). The SNL is the average of the loudest 25 shots, measured as a maximum noise level ($L_{Amax}$) at the noise sensitive location, in a 30 minute period. The research concludes:
“...For a given exposure level, community annoyance was found to vary significantly between shoots, but no particular shoot characteristics or socio-demographic variables were seen to be associated with the degree of annoyance. There is some suggestion that different sensitivities exist in different communities and that this affects annoyance, but the causes of differing sensitivities are not clear.
At shooting noise levels below the mid 50’s dB(A) there is little evidence of significant annoyance at any site, whereas for levels in the mid to high 60’s, significant annoyance is engendered in a majority of sites. For levels in between however, the extent of the annoyance varies considerably from site to site. Thus a level of, say, 60dB(A) may be deemed acceptable at one site, but not at another”
This current guidance supports the original findings by the above researchers who found that an absolute noise level from the firing of guns was a good indicator of annoyance, rather than a comparison with the background noise in the area.
The CIEH document goes on to say that noise annoyance as discussed by the BRE research is not the same as noise ‘nuisance’ since this will depend on other factors. It concludes, however, that “...the level of noise experienced will usually be an important factor in any assessment of nuisance from clay target shooting.”
The limit proposed by DEFA is consistent with ensuring shooting noise remains below the mid 50’s dB(A) as referred to in the CIEH document.
The methodology set out in the CIEH: ‘Guidance on the Control of Noise’, requires that the logarithmic mean value of the loudest twenty five shots in 30 minutes be taken as the Shooting Noise Level.
The shooting range is proposed to be used for the firing of 9mm pistols. ASA library data for a pistol shot at 250 feet has been used as the source noise level, as presented in the table below:
Table I – Pistol Shot Sound Pressure Level at 250 feet
The above library data represents the free-field sound pressure level at 250 feet. The data has been converted to an equivalent sound power level for the purpose of calculating an indoor reverberant sound pressure level inside the shooting range.
For the purposes of deriving an internal reverberant sound pressure level, it has been assumed that the inside surface of the shooting range is acoustically hard, e.g. concrete or blockwork.
Building dimensions and the proposed outline design have been provided by Ashley Pettit Architects, including drawing references PA 100 to PA 105, dated January 2011.
Calculations are based on the distances between the proposed building and the grounds of the identified noise sensitive properties.
Based on the above input parameters, the outline design proposals and the agreed external noise limits, sound insulation requirements for each of the external building fabric elements have been calculated.
The external wall is proposed to comprise a cavity masonry construction.
In order to provide sufficient sound insulation, a block wall comprising two leaves of 100mm thick lightweight aggregate block (minimum density 1350 kg/m³) separated by 100mm cavity is required.
| Frequency (Hz) | 63 | 125 | 250 | 500 | 1k | 2k | 4k | 8k | dB(A) |
|---|---|---|---|---|---|---|---|---|---|
| Pistol Shot Sound Pressure Level at 250 feet (dB) | 90 | 88 | 93 | 83 | 91 | 99 | 102 | 106 | 108 |
Required sound reduction indices for the above construction are presented in the table below. {{table:2507}} Table 2 – External Wall SRI Any wall that meets or exceeds the above sound insulation or mass and thickness requirements should provide sufficient sound insulation.
Thermal double glazed units are proposed on the northern façade of the building. In order to protect the glazing from live firing rounds, internal shutters may also be required.
Any such glazing unit will need to comprise three individual glass panes. The required sound reduction indices for the glazing are presented in the table below. {{table:2508}} Table 4 – Required SRI for External Glazing Without Shuttering
A glazed unit comprising 4mm glass / 16mm air cavity / 4mm glass primary unit, 100mm air cavity and 6mm glass secondary unit, would typically be expected to provide the above sound insulation performance.
In addition, it may be necessary to incorporate a roller shutter system for safety purposes to protect the glazing from bullet ricochets. Providing the above sound insulation performance is achieved by the glazed unit, there would be no acoustic requirements for the roller shutter system.
The roof construction is proposed to comprise beam and block with a ‘green’ (grass) topping.
In order to provide sufficient sound insulation performance, a 375mm thick construction is required of approximately $690\mathrm{kg} / \mathrm{m}^2$. Typically, this would be provided by a 225mm thick beam with 100mm thick high density aggregate blocks and a 150mm thick concrete compound screed to finish.
Alternatively, a 300mm thick solid concrete slab (approximate mass per unit area 690 kg/m²) or a composite 100mm solid concrete / neoprene rubber (e.g. Regupol) / 150mm solid concrete construction would also be expected to provide sufficient sound insulation.
Required sound reduction indices for the proposed roof are presented in the table below. Table 4 – Required SRI for Roof
There are four roof mounted fans proposed for ventilation purposes, two for supply of fresh air and two for extraction of internal air. Shooting noise can transmit via the ventilation duct and fans to outdoor areas.
Calculations have been undertaken, accounting for any attenuation afforded by an in-line fan.
In order to sufficiently control shooting noise via the ventilation duct, a rectangular splitter silencer complying with the specifications below should be installed on the atmospheric side of each of the fan ducts.
Table 5 – Required SIL for each ventilation fan
The atmospheric side ductwork opening for the selected in-line fans should face towards the hillside (south-west) in order to assist in mitigating noise emissions.
Noise transmission via the external door has been considered. The specific door type is unknown. It is therefore assumed that the door comprises solid core timber. It is presumed that a standard 40mm panel door will be installed internally between the lobby area and the main room.
| Frequency (Hz) | 63 | 125 | 250 | 500 | 1k | 2k | 4k | 8k |
|---|---|---|---|---|---|---|---|---|
| Roof SRI (dB) | 37 | 40 | 45 | 52 | 59 | 63 | 67 | 70 |
| Minimum Dimensions (mm) | Volume duty m³/s | Pressure drop Pa | Static Insertion Loss, SIL (dB) at Octave Band Mid Frequency (Hz) | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| W | H | L | 63 | 125 | 250 | 500 | 1k | 2k | 4k | 8k | |
| Face velocity not to exceed 2.5m/s | 1200 | - | 50 | 11 | 21 | 31 | 49 | 50 | 50 | 50 | 44 |
An external timber door set (comprising door blank, framing and acoustic seals) achieving $R_{\mathrm{w}}$ 35dB would be expected to provide sufficient sound insulation performance. Typically, an $R_{\mathrm{w}}$ 35dB door would comprise 54mm solid core timber door blank in a hardwood frame, with acoustic seals to the head, jamb and threshold.
It is likely that an armour plated internal steel door is required. In which case, the actual sound insulation between the main room and the outdoor areas is likely to be in excess of that assumed.
It is proposed to construct a building for multi-purpose sports use on land off Ramsey Road, Laxey. One of the activities proposed to be undertaken within the building is live round pistol shooting.
Alan Saunders Associates has undertaken an assessment of the required noise control measures in order to mitigate the impact to the closest residents.
Alan Saunders Associates has contacted the Isle of Man’s Department of Environment, Food and Agriculture (DEFA), who have specified that noise from shooting shall not exceed a mean Shooting Noise Level (SNL, as outlined in the Chartered Institute of Environmental Health document Clay Target Shooting: Guidance on the Control of Noise) of 50dB(A) measured at any neighbouring noise sensitive premises. Simon Renton.
A review of the proposed building design in the context of the proposed location and stipulated noise limits has been undertaken.
Outline requirements for noise control have been identified in order to achieve the stipulated noise limits.
As a result of the proposed noise control requirements and the stipulated limits, which are based on the research summarised in the CIEH document, it is considered reasonable to conclude that significant annoyance from occupants within the grounds of the surrounding residential properties as a result of noise from the shooting range will be avoided.
Furthermore, considering the proposed private usage (two hours, once a week), the noise impact over the course of a normal week following incorporation of the specified noise control measures can be regarded as insignificant to the average person.
James Healey
ALAN SAUNDERS ASSOCIATES
The annoyance produced by noise is dependent upon many complex interrelated factors such as 'loudness', its frequency (or pitch) and any variations in its level. In order to have some objective measure of the annoyance, scales have been derived to allow for these subjective factors.
The human ear is more susceptible to mid-frequency noise than the high and low frequencies. To take account of this when measuring noise, the 'A' weighting scale is used so that the measured noise corresponds roughly to the overall level of noise that is discerned by the average human. It is also possible to calculate the 'A' weighted noise level by applying certain corrections to an un-weighted spectrum. The measured or calculated 'A' weighted noise level is known as the dB(A) level.
$L_{10}$ & $L_{90}$: If a non-steady noise is to be described it is necessary to know both its level and the degree of fluctuation. The $L_n$ indices are used for this purpose, and the term refers to the level exceeded for $n\%$ of the time, hence $L_{10}$ is the level exceeded for $10\%$ of the time and as such can be regarded as the 'average maximum level'. Similarly, $L_{90}$ is the average minimum level and is often used to describe the background noise.
It is common practice to use the $L_{10}$ index to describe traffic noise, as being a high average, it takes into account the increased annoyance that results from the non-steady nature of traffic noise.
$L_{eq}$: The concept of $L_{eq}$ (equivalent continuous sound level) has up to recently been primarily used in assessing noise in industry but seems now to be finding use in defining many other types of noise, such as aircraft noise, environmental noise and construction noise.
$L_{eq}$ is defined as a notional steady sound level which, over a stated period of time, would contain the same amount of acoustical energy as the actual, fluctuating sound measured over that period (e.g. 8 hour, 1 hour, etc).
The use of digital technology in sound level meters now makes the measurement of $L_{eq}$ very straightforward.
Because $L_{eq}$ is effectively a summation of a number of noise events, it does not in itself limit the magnitude of any individual event, and this is frequently used in conjunction with an absolute noise limit.
$L_{max}$: $L_{max}$ is the maximum sound pressure level recorded over the period stated. $L_{max}$ is sometimes used in assessing environmental noise where occasional loud noises occur, which may have little effect on the $L_{eq}$ noise level.
$D$: The sound insulation performance of a construction is a function of the difference in noise level either side of the construction in the presence of a loud noise source in one of the pair of rooms under test. $D$, is therefore simply the level difference in decibels between the two rooms in different frequency bands.
$D_w$: $D_w$ is the Weighted Level Difference. The level difference is determined as above, but weighted in accordance with the procedures laid down in BS EN ISO 717-1.
$D_{nT,w}$: $D_{nT,w}$ is the Weighted Standardised Level Difference as defined in BS EN ISO 717-1 and represents the weighted level difference, as described above, corrected for room reverberant characteristics.
$C_{tr}$: $C_{tr}$ is a spectrum adaptation term to be added to a single number quantity such as $D_{nT,w}$, to take account of characteristics of a particular sound.
$L'_{nT,w}$: $L'_{nT,w}$ is the Weighted Standardised Impact Sound Pressure Level as defined in BS EN ISO 717-2 and represents the level of sound pressure when measured within room where the floor above is under excitation from a calibrated tapping machine, corrected for the receive room reverberant characteristics.
| Change in Sound Level dB(A) | Subjective Impression | Human Response |
|---|---|---|
| 0 to 2 | Imperceptible change in loudness | Marginal |
| 3 to 5 | Perceptible change in loudness | Noticeable |
| 6 to 10 | Up to a doubling or halving of loudness | Significant |
| 11 to 15 | More than a doubling or halving of loudness | Substantial |
| 16 to 20 | Up to a quadrupling or quartering of loudness | Substantial |
| 21 or more | More than a quadrupling or quartering of loudness | Very Substantial |
In order to determine the way in which the energy of sound is distributed across the frequency range, the International Standards Organisation have agreed on "preferred" bands of frequency for sound measurement and analysis. The widest and most commonly used band for frequency measurement and analysis is the Octave Band. In these bands, the upper frequency limit is twice the lower frequency limit, with the band being described by its "centre frequency" which is the average (geometric mean) of the upper and lower limits, eg. 250 Hz octave band runs from 176 Hz to 353 Hz. The most commonly used bands are:
Octave Band Centre Frequency Hz 63 125 250 500 1000 2000 4000 8000
Because of the logarithmic nature of the decibel scale, it should be borne in mind that noise levels in dB(A) do not have a simple linear relationship. For example, 100dB(A) is not twice as loud as 50 dB(A) sound level. It has been found experimentally that changes in the average level of fluctuating sound, such as traffic noise, need to be of the order of 3 dB(A) before becoming definitely perceptible to the human ear. Data from other experiments have indicated that a change in sound level of 10 dB(A) is perceived by the average listener as a doubling or halving of loudness. Using this information, a guide to the subjective interpretation of changes in traffic noise level can be given.
When considering the reduction in noise level of a source provided by a barrier, it is necessary to establish the "effective screen height". For example if a 3 metre high barrier exists between a noise source and a listener, with the barrier close to the listener, the listener will perceive the noise source is louder, if he climbs up a ladder (and is closer to the top of the barrier) than if he were standing at ground level. Equally if he sat on the ground the noise source would seem quieter than it was if he were standing. This may be explained by the fact that the "effective screen height" is changing with the three cases above, the greater the effective screen height, in general, the greater the reduction in noise level.
Where the noise sources are various roads, the attenuation provided by a fixed barrier at a specific property will be greater for roads close to the barrier than for roads further away.
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