TNAG-1613-FCO40-2221-Executive-Council-of-Hong-Kong-memoranda-and-minutes-of-meet-1987 — Page 227

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2.10 Step 10

Corrections for the Effect of Barriers

In cases where the Authority considers that all items of PME to

totally screened by a

be used on the construction site will be

substantial barrier when viewed from the NSR, a negative correction of 10dB(A) shall be applied to the PNL obtained in Step 9.

Substantial barriers shall be taken to be large solid objects,

such as buildings or topographical features,

acoustic screens. Barries which are small,

which will act as effective

lightweight, incomplete or

are not to be considered.

temporary, such as site fences or hoardings,

The effects of purpose-built acoustic barriers may be taken into account

in accordance with Section 3.1.

In cases where the Authority considers that all items of PME to

be used on the onstruction site other than "quiet" items of PME will be

totally screened when viewed from the NSR, a negative correction of 5dB(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 15dB(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 5dB(A) shall be applied

to the PNL obtaianed in Step 9. Where the latter condition applies and the NSR is separated from the construction site by another building such

that none of the items of PME 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 totally screened.

2.11 Step 11 Corrections for Acoustic Reflections

In cases where the NSR is a building, a positive correction of 3dB(A) shall be applied to the PNL obtained in Step 9.