Week 6 - People
5. Noise
5.4. Hearing Risks from Construction
- The risk of damage to hearing is dependent on the total energy reaching the ear in a given period
- LA,eq is the basis of safe exposure to noise during an 8 hour working day.
- Current Noise Dose Limit in NZ:
LAeq,8hr = 85 dB
The equivalent continuous sound level compares a varying sound level to a theoretical constant sound which gives an equivalent amount of sound energy.
Equivalent continuous sound level, LAeq,T is that constant sound level which, over the same period of time T, provides the same total sound energy as the varying sound.
Unit: dB(A)
Although human hearing does not judge loudness in terms of energy, the LAeq measurement of accumulated sound energy is found to correlate well to – the annoyance caused by noise and also to damage to hearing.
Energy Equivalents- 3 dB increase corresponds to double the energy.
- By reducing time to half = equivalent ‘dose’ of energy over an 8 hour period.
- Assumptions include a continuous noise output from machinery.
- In situations where noise varies – use integrating sound level meters which sample regularly.
Permissible Noise Levels and Times
Construction work within residential areas:
Where * L10 refers to a noise level which can only be exceeded for 10 percent of the time. E.g. L1075 dBA means that over a 30 minute period, the noise may only go above 75 dBA for three minutes.
