Technical Memorandum on Noise from Construction Work Other Than Percussive Piling

2. ASSESSMENT OF NOISE FROM THE CONSTRUCTION WORK

2.8

Step 8 - Sound Power Levels for Items of Powered Mechanical Equipment (PME)

The sound power levels in dB(A) of each of the items of PME intended for use on the construction site (including lorries attending the construction site) shall be obtained from Table 3. If any item of PME intended for use on the construction site does not appear in Table 3 the Authority may make use of such sound power level as it considers appropriate.

2.9

Step 9 - Distance Attenuation and Summation of Noise Levels

2.9.1	General In determining the distance from the source position to the NSR blank facades shall not be considered and the distance shall be determined to the nearest NSR facade with windows, doors or other openings. The plan distance or, where appropriate, the slant distance shall be used.

2.9.2	Procedure for Use with a Single Notional Source Position If all items of PME are assumed to be located at a single notional source position, the sound power levels obtained in Step 8 shall be summed logarithmically in accordance with Table 4 to obtain a total sound power level. The distance between the notional source position and the NSR shall be determined and the appropriate correction factor shall be obtained from Table 5. This correction factor shall be subtracted from the total sound power level to give the Predicted Noise Level (PNL) at the NSR.

2.9.3	Procedure for Use with Actual Source Positions or a Combination of Actual and Notional Source Positions If in addition to a notional source position a number of actual source positions are being used, or if only actual source positions are being used, the distances between the actual source positions and the NSR shall be determined and the appropriate correction factors shall be obtained from Table 5. These factors shall be subtracted from the individual sound power levels for each item of PME to give the individual sound pressure levels for each item of PME at the NSR. Any combined sound pressure level from items of PME assumed to be located at a notional source position shall be determined in accordance with Section 2.9.2 and shall be added logarithmically to the individual sound pressure levels from items of PME assumed to be at actual source positions in accordance with Table 4, to give the PNL at the NSR.

2.10

Step 10 - Corrections for the Effect of Barriers

In cases where the Authority considers that all items of PME to be used on the construction site will be totally screened by a substantial barrier such that none will be visible when viewed from any window, door or other opening in any facade of the NSR, a negative correction of 10 dB(A) shall be applied to the PNL obtained in Step 9. In cases where the Authority considers a higher negative correction should be applied, the Authority shall use appropriate correction factors having regard to standard acoustical principles and practices.

Substantial barriers shall be taken to be large solid objects, such as buildings or topographical features, which will act as effective acoustic screens. Barriers which are small, lightweight, incomplete or temporary, such as site fences or hoardings, are not to be considered. The effects of purpose-built acoustic barriers may be taken into account in accordance with Section 3.l.

In cases where the Authority considers that all items of PME to be used on the construction site other than "quiet" items of PME will be totally screened when viewed from the NSR, a negative correction of 5 dB(A) shall be applied to the PNL obtained in Step 9. For the purpose of this section "quiet" items of PME shall be considered to be those whose sound power level is more than 15 dB(A) below the total sound power level being generated by all items of PME.

In cases where the NSR is a building directly adjacent to the construction site such that none of the items of PME to be used on the construction site will be visible when viewed from any window, door or other opening in any facade of the NSR, the NSR shall be considered to be partially screened and a negative correction of 5 dB(A) shall be applied to the PNL obtained in Step 9.