The major findings of the study are based on the following recommendations:

Transcription

1 SIEBEIN ASSOCIATES, INC. Consultants in Architectural & Environmental Acoustics 625 NW 60 th Street, Suite C Gainesville, Florida Telephone: (352) Facsimile: (352) Website: August 28, 2014 Mr. Barry Burdick AIA, PMP, LEED AP BD+C Clark Nexsen 213 South Jefferson, Suite 1011 Roanoke, Virginia Dear Barry: Enclosed please find one bound and one loose copy of our Acoustical Analysis of the Building Envelope System for the Proposed Regional Firearms Training Range for Albemarle County, Virginia. The acoustical analysis is based on drawings downloaded from the Clark Nexsen Server on July 22, 2014; a description of the construction assemblies received from the Architect during telephone conversations; and acoustical analysis conducted in our office. The report contains an executive summary of the results, background information relevant to the acoustical analysis, a review of the applicable noise ordinances, a description of the method used to conduct the analysis, and an aerial map showing the analysis results. The major findings of the study are based on the following recommendations: 1. The results of the analysis indicate that the proposed firing range constructed with a 6" thick precast concrete roof with a ballistic steel ceiling below it incorporating 2 layers of 5/8" gypsum board closing the spaces between the metal ballistic panels, 6" thick glass fiber batt insulation covering the top of the baffles and gypsum board, and the proposed wall assembly, which consists of 3½ concrete 3 insulation 3 ½ concrete, reduce gunfire sounds to levels that meet the night time noise ordinance sound level limit of 55 dba. 2. The findings assume noise mitigation is provided for the ventilation and HVAC systems, and acoustical doors of sufficient STC rating are provided at exterior range doors. These items will be designed and specified once the architectural and mechanical systems for the building are developed. Please do not hesitate to contact us if you have any questions regarding the findings of our analysis or if we can be of additional assistance in this regard. Sincerely, SIEBEIN ASSOCIATES, INC. Marylin Roa Consultant Members of the Acoustical Society of America, National Council of Acoustical Consultants, Institute for Noise Control Engineers, American Society for Testing and Materials, and the American Society for Heating, Refrigerating, and Air-Conditioning Engineers.

2 ACOUSTICAL ANALYSIS OF THE BUILDING ENVELOPE SYSTEM for a PROPOSED REGIONAL FIREARMS TRAINING RANGE Albemarle County, Virginia for CLARK NEXSEN Clark Nexsen 213 South Jefferson, Suite 1011 Roanoke, Virginia by SIEBEIN ASSOCIATES, INC. Consultants in Architectural Acoustics 625 NW 60 th Street, Suite C Gainesville, Florida Telephone: (352) Facsimile: (352) Electronic mail: office@siebeinacoustic.com August 28, 2014

3 ACOUSTICAL ANALYSIS OF THE BUILDING ENVELOPE SYSTEM for a PROPOSED REGIONAL FIREARMS TRAINING RANGE Albemarle County, Virginia for CLARK NEXSEN Clark Nexsen 213 South Jefferson, Suite 1011 Roanoke, Virginia by SIEBEIN ASSOCIATES, INC. Consultants in Architectural Acoustics 625 NW 60 th Street, Suite C Gainesville, Florida Telephone: (352) Facsimile: (352) Electronic mail: office@siebeinacoustic.com August 28, 2014 INTRODUCTION This report contains the results of an acoustical analysis of the exterior envelope systems for the proposed 50-yard indoor Firearms Range for the Albemarle County Police Department located on Milton Road in Albemarle County, Virginia. The acoustical analysis is based on drawings downloaded from the Clark Nexsen Server on July 22, 2014; a description of the construction assemblies provided by the Architect during telephone conversations; and acoustical analysis conducted in our office.

4 Clark Nexsen August 28, 2014 EXECUTIVE SUMMARY 1. The results of the analysis indicate that the proposed firing range constructed with a 6" thick precast concrete roof with a ballistic steel ceiling below it incorporating 2 layers of 5/8" gypsum board closing the spaces between the metal ballistic panels, 6" thick glass fiber batt insulation covering the top of the baffles and gypsum board, and the proposed wall assembly, which consists of 3½ concrete 3 insulation 3 ½ concrete, reduce gunfire sounds to levels that meet the night time noise ordinance sound level limit of 55 dba. 2. The findings assume noise mitigation is provided for the ventilation and HVAC systems, and acoustical doors of sufficient STC rating are provided at exterior range doors. These items will be designed and specified once the architectural and mechanical systems for the building are developed. BACKGROUND Siebein Associates, Inc., performed an acoustical analysis of the exterior envelope (walls and roof) for the proposed Firearms Range on Milton Road in Albemarle County, Virginia. The purpose of the analysis was to estimate the resulting sound levels propagated through the exterior envelope of the building at nearby receiver locations, with the intent that sound levels that comply with the Albemarle County Noise Ordinance's nighttime sound level limit of 55 dba (Lmax) should be reached. Albemarle County Noise Ordinances Item 4.18, Noise, of the Albemarle County Code, establishes a maximum permissible sound level of 60 dba during the day and 55 dba at night when measured on the receiving property of land zoned as rural areas, residential, public space, or institutional. The sound level meter is to be set to measure the sound using the fast response setting, and set to record the maximum (Lmax) sound level during the measurement period when measuring impulse sounds. Since the range is intended to operate at night, and gunfire sounds are impulsive type sounds, a design sound level limit of Lmax = 55 dba was used in the analysis. Section 7-104, General Prohibitions, of Article I, Noise, of Chapter 7, Health and Safety, of the Albemarle County Code states that "It shall be unlawful for any person to produce sound that causes at least a fifteen (15) dba increase in the sound level above the ambient sound level". Acoustical measurements of ambient sound levels at the site has not been made, so comparisons of estimated sound levels to ambient sound levels are not included in this report. It is possible that even at the lower sound levels estimated, gunfire sounds may be audible in the presence of the ambient. We would be pleased to conduct ambient sound level measurements at locations around the site if this type of evaluation is desired. S A S i e b e i n A s s o c i a t e s, I n c. P a g e 3

5 Clark Nexsen August 28, 2014 The Site The site for the proposed range is located at 2300 Milton Road in Charlottesville, Virginia. It is bordered on the west by Milton Road and on the east by a creek. There are residential properties immediately to the north, east, south, and west of the site, with the closest residential property line located on the west side of Milton Road, approximately 200 ft. to the west of the rear of the range. An aerial photograph of the site with the proposed location of the firearms range and the property lines is included in Figure 1. The direction of fire (D.O.F.) in the range is included in the figure. Range Envelope The exterior envelope of the Firearms Range consists of walls made of 3½ concrete 3 insulation 3 ½ concrete on all four sides of the range and a 6 pre-cast concrete roof deck with a sound isolating ceiling suspended below. The interior steel ceiling baffles are spaced as required with gaps between the baffles covered with 2 layers of gypsum board on metal framing sealed to the steel baffles with glass fiber insulation in the framing above the ceiling. The top of the baffles and gypsum board elements are covered with 6" thick glass fiber batt insulation. In addition to the wall and roof/ceiling described above, the following are also required. 1. Acoustically rated doors with a Sound Transmission Class (STC) rating of approximately 50 must be used at all openings to the exterior: A Sound Transmission Class (STC) rating of approximately 22 is required for the roll-up doors exposed to the exterior on the east and west sides of the building; and a Sound Transmission Class (STC) rating of approximately 35 is required for the roll-up doors leading into the firing range. 2. Noise control for HVAC and lead exhaust systems to meet the property line sound level limits will be required. This has to be analyzed based on the specific sound power levels of the equipment. Strategically locating the equipment on the sides or roof of the building away from the nearest sensitive receivers, and providing sound attenuators in the ductwork will be required. 3. Gunfire noise breaking out of the supply and exhaust ductwork must also be controlled. This is done through a combination of sound attenuators and duct enclosures to reduce breakout sound levels. Assumptions Applied to the Acoustical Analysis of the Range Siebein Associates, Inc., was provided with drawings of the firearms range. The dimensions used for the firing range are 68 ft. x 182 ft. The height of the interior of the range is estimated 21-6 measuring from the finished floor to the underside of the roof since the suspended ceiling will have gaps between the ballistic panels. The range will be used as a tactical range, with a "saw tooth" design ballistic steel ceiling. All of the ballistic steel ceiling and the walls below the ceiling will be covered in sound absorbing ballistic tiles. The trap is rubber granular medium covering a steel bed; sidewall bullet proof trap is provided along the perimeter of the west wall from the 0 yard line up to the 25 yard line. The floor will be concrete. S A S i e b e i n A s s o c i a t e s, I n c. P a g e 4

6 ANALYSIS METHOD Clark Nexsen August 28, The analysis assumed the most intense use of 16 shooters firing.223 caliber rifles at the same time. The.223 caliber rifles are generally as loud as.308 rifles, and louder than shotguns and handguns. According to Regional Firearm Training Range staff, the most common.223 caliber rifle used is a Colt AR-15. This is equivalent to an M-16 rifle of the same caliber. Octave band sound data for the.223 caliber rifle were obtained from a report entitled "Field Measurement of Sound Pressure Levels of Various Firearms," published by the Architectural Acoustics Research Group at the University of Florida in 1993 for the National Rifle Association, which includes data for an M-16 rifle with.223 Remington 55 grain power-locked hollow point ammunition. A summary of the octave band sound exposure level data for the.223 caliber rifles used in the analysis is included in Appendix A. The data were converted to maximum sound levels (Lmax) by adding 4 db to the sound level based on hundreds of acoustical measurements made of gunfire sounds that showed a 3 to 4 db difference between the Lmax and SEL sound levels. 2. A three dimensional computer model was constructed using AutoCAD software from a threedimensional topographical drawing showing the ground elevations of the firing range and the land area that extends approximately 1.5 miles from the approximate center of the firing range provided by Clark Nexsen. Buildings within the 1.5 mile radius from the approximate center of the firing range were constructed also. The average heights of buildings were 16 ft. The AutoCAD model was imported into Cadna-A software which is a state-of-the-art noise propagation modeling software. The octave band sound pressure level data for the.223 rifles described above was used as the sound source. The computer sound propagation model was used to estimate the Lmax sound levels from the gunfire at the nearest receiving property lines on all four sides of the range. The octave band sound pressure levels for the.223 caliber rifles described above were used as the source, with the following conditions taken into account. A. Number of shooters (16 total) B. Direction of fire relative to the receiver (front, front/side, side). C. Distance to the wall and roof from the average shooter position. D. Sound absorbing characteristics of the interior of the range. E. Sound transmission loss provided by the wall and roof assemblies based on laboratory test data available in the technical acoustical literature. F. Distance between the wall/roof and the receiving location outside the range. G. Molecular sound absorption for a standard day (77 F, 70%RH) H. Anomalous excess attenuation (from small scale differences in wind, temperature, and humidity in the air). I. Cadna-A assumes a downwind condition with wind velocity of 1 11 mph J. Vegetation (trees) was not included in the analysis. S A S i e b e i n A s s o c i a t e s, I n c. P a g e 5

7 RESULTS/CONCLUSIONS Clark Nexsen August 28, The resulting sound levels for the proposed envelope is plotted on a scaled map/aerial for the site in Figure The results of the analysis indicate that the proposed firing range is constructed with a 6" thick pre-cast concrete roof with a ballistic steel ceiling below it incorporating 2 layers of 5/8" gypsum board closing the spaces between the metal ballistic panel and the proposed wall assembly, which consists of 3½ concrete 3 insulation 3 ½ concrete, reduce gunfire sounds to levels that meet the night time noise ordinance sound level limit of 55 dba. 3. A sound level of 45 dba or less from gunfire noise is estimated at the nearest residences to the north, east, west and south. A sound level of 45 dba is roughly equivalent to the ambient sound level in a residential neighborhood with some moderate, distant automotive traffic taking place or wind rustling leaves in nearby trees. LIMITATIONS OF THE STUDY Octave band sound level data for specific firearms and ammunition combinations used by the ACPD are not available in the technical acoustical literature. The best available sound data for guns and ammunition similar to the worst case conditions were therefore used. Generally, most guns of similar type and with similar ammunition are within several db of each other in terms of the overall sound level, although their sound levels vary more significantly with direction. For sound level estimates at distances over 500 ft., there will be variability in the sound level measured at any point in time due to atmospheric conditions (temperature inversions, wind). Therefore, the estimated sound levels at these distances should be used with some caution, particularly if comparing them to field measurements of gunfire noise in the future. Also, as stated earlier in the report, acoustical measurements of ambient sound levels at the site were not made, so comparisons of estimated sound levels to ambient sound levels are not included in this report. It is possible that even at the lower sound levels estimated (below 55 dba Lmax), gunfire sounds may still be audible in the presence of the ambient sounds. S A S i e b e i n A s s o c i a t e s, I n c. P a g e 6

8 Clark Nexsen August 28, 2014 Figure 1. Aerial map of the project site showing sound contour map overlaid with the location of the firearms range, property lines, the receiver locations analyzed, and the results of the analysis. S A S i e b e i n A s s o c i a t e s, I n c. P a g e 7

9 Clark Nexsen August 28, 2014 APPENDIX A: SUMMARY OF WEAPONS DATA Weapons to be used on Proposed 50-yard Ranges (per ACPD) a. Glock caliber b. H&K UMP Submachine Gun.40 caliber (not full-automatic) c. Colt AR caliber (A small number are full-automatic. SWAT) d. Remington gauge shotgun e. Remington Sniper rifle (SWAT) f. 40MM gas grenade launcher (4 to 4 times per year. SWAT) g. Ruger 10/22 Rifles.22 caliber (animal control) Ammunition to be used on Proposed 50-yard Ranges (per ACPD) a..40 Federal 165 grain full metal jacket b..223 Fiocchi 62 grain full metal jacket c. 12 gauge Federal slug and Tactical 9 shot 00buck d..308 Winchester 168 grain boat tail hollow point e. 40MM gas or smoke rounds f..22 long rifle Octave Band Sound Exposure Level Data for M-16 with.223 Rem. 55gr. Power-locked hollow point rounds at a distance of 13 ft (4 meters) Receiver Direction Relative to Direction of Gunfire Octave Band Sound Exposure Level in db Hz 250 Hz 500 Hz 1000 Hz 2000 Hz 4000 Hz Front Front/Side Side Rear/Side Rear Notes: 1. Taken from Field Measurements of Sound Pressure Levels of Various Firearms, a research report to the National Rifle Association published by the Architectural Acoustics Research Group at the University of Florida, Sound levels were interpolated between the Front and Side conditions. 3. Sound levels were interpolated between the Rear and Side conditions. 4. Sound levels were estimated from an M-16 with a 16" barrel - data from same report referenced in Note 1 S A S i e b e i n A s s o c i a t e s, I n c. A p p e n d i x A