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Good indoor air quality (IAQ) is essential for safeguarding people’s health. A system of setting IAQ standards, implementing IAQ improvement measures, performing periodic assessments of IAQ against standards, and reporting and publishing of the assessment results will help improve IAQ and enhance public accountability.

The Environment Bureau and the Environmental Protection Department (EPD) are responsible for formulating and implementing environmental policies, including those on indoor and outdoor air quality.

In 2003, the EPD established the IAQ Objectives for Office Buildings and Public Places (IAQ Objectives — see Table 3). The IAQ Objectives, comprising 12 parameters, are to be used for evaluating and assessing IAQ in offices and public places served by mechanical ventilation and air-conditioning (MVAC) systems for human HVAC comfort. Two classes of achievement are provided under the IAQ Objectives, namely:

(a) Excellent Class: representing an excellent level of IAQ that a high-class and comfortable building should have; and

(b) Good Class: representing the level of IAQ that provides protection to the public at large including the young and the aged.

IAQ Objectives
Item Parameter Unit Excellent Class Good Class
1 Room temperature °C 20 to 25.5 < 25.5
2 Relative humidity % 40 to 70 < 70
3 Air movement Meters/second < 0.2 < 0.3
4 Carbon dioxide Parts-per-million (ppm) < 800 < 1000
5 Carbon monoxide microgram/m3 < 2000 < 10000
6 Respirable suspended particulates microgram/m3 < 20 < 180
7 Nitrogen dioxide microgram/m3 < 40 < 150
8 Ozone microgram/m3 < 50 < 120
9 Formaldehyde microgram/m3 < 30 < 100
10 Total VOC microgram/m3 < 200 < 600
11 Radon Becquerel/m3 < 150 < 200
12 Airborne bacteria Colony-forming-units/m3 < 500 < 1000
Note: Measurements are to be taken on an eight-hour average basis.

In its guidance notes, the EPD has set out the minimum number of sampling points for different ranges of floor areas served by MVAC systems for IAQ assessments.

Minimum number of sampling points
Total floor area served by MVAC system (m2) Minimum number of sampling points (No.)
< 3000 1-6 (500m2 per point)
3000 to < 5000 8
5000 to < 10000 12
10000 to < 15000 15
15000 to < 20000 18
20000 to < 30000 21
≥ 30000 ≥ 25 (1200m2 per point)
Notes: 1. At least 80% of the sampling points for each of the parameters should comply with the relevant IAQ Objectives. 2. For each of the parameters on room temperature relative humidity and air movement. None of the measured values of the sampling points should exceed 10% of the relevant IAQ Objectives or fall outside 10% of the upper or lower limit of a range. 3. For each of the chemical and biological parameters (see Items 4-12 in Table IAQ Objectives) none of the measured values of the sampling points should exceed 50% of the relevant IAQ Objectives.

Since January 2011, the EPD has taken up the leading role in handling IAQ complaints received by its Pollution Complaint Hotline and by the Government’s centralised “1823” Hotline, and will forward complaints to the responsible government bureaux and departments for action, where necessary.

The above professional practice notes are extracted from Report No. 56 of the Director of Audit, Hong Kong Government which is published in 2011.