BACKGROUND NOISE SURVEY - ...
 
 
 Scope of Report
To present the background noise levels at the site of the building at ... and to suggest suitable noise emission limits for the site.
1. INTRODUCTION
1.1 ... have purchased a warehouse/office unit at ..., near ....
1.2 The building will be used as an internet hosting facility. There will be potentially noisy equipment installed on the site, such as diesel generators, air cooled chillers, and boiler plant.
1.3 Civil Engineering Dynamics were instructed by ... to perform an acoustic survey of the background noise present at the site in order to set suitable noise emission limits for the site.


2. THE SITE

2.1 Figure 1 shows a plan of the site.
2.2 The site and surrounding land is essentially flat.
2.3 Traffic on Wharfedale Road (to the south of the site) is fairly heavy, particularly between 08:00 and 09:00 and 17:00 - 19:00. There is a Parcelforce depot to the south west of the site that is visited by large lorries 24 hours a day at frequencies of at least every 20 minutes.
2.4 The north of the site is bounded by another warehouse/office unit. There are few windows in this façade of the building. Across Wharfedale Road, to the south east of the site, is the Efdex building. This building is set back from the road by an access road, car park, and semi-circular grass verge.


3. MEASUREMENT PROCEDURE

3.1 The survey was undertaken from 13:00 4th November 99 to 11:00 5th November 99. The weather was dry until 11:00 5th November 99, when the survey was terminated due to rain. The wind was breezy during the day, with occasional gusts, and calm at night.
3.2 Two sound level meters were used for the survey - a Bruel & Kjaer 2236 and a Bruel & Kjaer 2260.
3.3 Figure 1 shows the measurement locations used for the survey. The measurements were made on tripods with a microphone height of approximately 1.5m. All measurements were at 'free-field' loactions.
3.4 The 2236 was fitted with a Bruel & Kjaer UA1404 Outdoor Microphone Protection Kit and set up at Location M throughout the entire survey period. The 2260 was used to take measurements at six locations around the perimeter (A - F) and on location at the perimeter of the site of the nearest acoustically sensitive location - the efdex building, Location G. The samples taken with the 2260 were timed to coincide with measurements taken by the 2236. One hour LAeq and LA90 measurements were taken during the period 07:00 to 23:00. Five minute LAeq and LA90 measurements were taken during the period 23:00 to 07:00. The night-time period was arbitrarily chosen as there are no residential areas local to the site.


4. RESULTS

4.1 Tables A and B list the logged results of the survey.
4.2 Figures 2 and 3 show the LAeq and LA90 for the day and night periods measured at Location M. The results are summarised in Table C.
TABLE C: Results Summary
Position
Background Noise Level LA90 dB(A)
07:00 to 19:00
24 hours
M
54
44.5
A
53
43.5
B
52
42.5
C
54
44.5
D
51
41.5
E
56
46.5
F
53
43.5
G
52.5
44.5
     
4.3 Background noise levels are relatively constant along the southern and western perimeters of the site. Background noise levels are typically lower along the northern perimeter, particularly at Location D, due to the shielding of the road by the building and the increased distance.
4.4 The nearest acoustically sensitive building is the 'Efdex' offices across the road from the site. The nearest corner of the efdex site perimeter is Location G. Background noise levels at Location G are slightly higher than those measured at M, due to increased proximity to the road.


5. CONCLUSIONS
5.1 Two standards are considered to establish a range of noise control that may be needed for equipment such as chillers and electrical generators. These standards are based upon BS 4142 with (a) the new noise sources controlled to 5 dB less than the current background noise and (b) controlled to 5 dB over the current background noise. This would result in noise emission limits given in Table D.
TABLE D: Noise Emission Limits
Position
5 dB Above Background

Noise Emission Limits, LA90 dB(A)
5 dB Below Background

Noise Emission Limits, LA90 dB(A)
07:00 – 19:00
24 hours
07:00 – 19:00
24 hours
M
59
49.5
49
39.5
A
58
48.5
48
38.5
B
57
47.5
47
37.5
C
59
49.5
49
39.5
D
56
46.5
46
36.5
E
61
51.5
51
41.5
F
58
48.5
48
38.5
G
57.5
47.5
47.5
39.5
 
5.2 These limits are proposed for normally operating equipment. It may be appropriate to argue that the limits should be 5 dB above the current background at boundaries facing commercial properties and 5 dB below the current background at boundaries facing residential properties.


6. REFERENCES

BS4142:1995 'Method for Rating Industrial Noise Affecting Mixed Residential and Industrial Areas'