TOP Noise Survey

Conducting boundary TOP (Temporary Occupational Permit) Noise survey for exhaust and ventilation

Ensscom conduct Boundary TOP Noise survey for exhaust and ventilation as per NEA guidelines on Boundary Noise Limit For Centralised Air Conditioning and Ventilation System in Non-Industrial Buildings.(2nd Edition 2018) 

Legal requirement of TOP noise survey

While submitting the application for Temporary Occupational Permit(TOP), Noise emission levels for air conditioning and mechanical ventilation have to be measured and and to be submitted along as well.

Please refer to the NEA technical Guideline On Boundary Noise Limits For Air Conditioning And Mechanical Ventilation Systems In Non-Industrial Buildings (2nd Edition 2018), Document Link

Type of affected premises

Boundary noise limit (reckoned as the equivalent continuous noise level over 15minutes) in decibels (dBA)


7 am to 7 pm


7 pm to 11 pm


11 pm to 7 am

(a) Noise Sensitive Premises such as hospital, home for the aged sick, library, etc




(b) Residential Premises




(c) Other premises

(Other than those in (a) and (b)




*Table 1

Noise measurement Requirement

Initial mandatory noise assessment shall be done and to be submitted along (TOP) application for non-industrial building. 

For equipment that is installed above ground level e.g. at roof-top, the noise measurements should be taken at least 1m from the noise source and at the same height as the equipment. The noise level shall be computed for a point that is at the site boundary and at the same height as the equipment.

The owner of the premises shall measure the noise levels at specific distance, duration and time as shown on the table above (table 1) and submit the measured noise level readings along with extrapolations at required locations including all the relevant facts that may influence the noise level measured (such as background noise).