Under Singapore's Environmental Protection and Management (Control of Noise at Construction Sites) Regulations, Second Schedule, the 12 hours equivalent continuous noise level(LEQ12hrs) maximum permissible noise level for construction sites are set based on a start time of 7am and end time of 7pm for the DAY period. And from 7pm to 7am for the NIGHT period. 

In order to know the 12hr Leq, a 12-hr measurement time would have to performed.

The "Current ongoing 12hr Leq" for DAY period, attempts to provide reader or user with a Leq value that is started since 7am, and is updated to the most current Leq5 minutes. (Maybe a more appropriate description would be "Leq since 7am" or "Leq since 7pm" depending on whether it is during the day or night 12-hr period. Edited on 13 Mar 2024)

Example 1: If the "current ongoing 12hr Leq" value is being read at 3:04pm, then the Leq value is for measurement duration from 7:00am to 3:00pm.

This value provide a gauge on 'how much' noise has been measured since 7am, so as to estimate if the maximum permissible noise level for LEQ12hrs would be met.

Common question:

Q1. Can the Leq12P(%) fluctuate up and down?

A1. Leq12P(%) is calculated from the "current ongoing 12hr Leq" (or more accurately the "Leq since 7am"). As time passes, the duration increases, and "current ongoing 12hr Leq" continues to reflect the current equivalent sound pressure level, started since 7am. If the sound pressure levels drops, the Leq since 7am will drop, as the duration increases. Hence it is possible for Leq12P(%) to fluctuate up and down as time passes.

To illustrate:

If noise levels at a site next to residential premises maintains a sound pressure level at 75 dBA for 12 hrs. The Leq12P(%) will be 100%.

At 1pm, six (6) hours after 7am, if the "ongoing Leq" is 78 dBA, Leq12P(%) will be at 100%.

At 7pm, twelve (12) hours after 7am, if the "ongoing Leq" drops to 75 dBA, Leq12P(%) will still be 100%.

If the 12hrs Leq at 7pm is less than 75 dBA, then Leq12P(%) will be lower than 100%.

Our system referenced the following table provided by NEA, and has also gone through stringent verification by NEA.

T(hrs) : Maximum duration for noise level.

L (dB) : Equivalent sound pressure level.

For more details on NEA"s EPM regulations, kindly visit http://statutes.agc.gov.sg/ and search for control of noise at construction sites.