For discussion
on 8 January 1999

Legislative Council
Panel on Environmental Affairs

Control of Indoor Air Pollution


At the meeting held on 11 December 1998, Members requested the Administration to provide the following information on the issue of indoor air pollution:

  1. an analysis of the summary table of the indoor air pollutant levels recorded in public places, and to provide an analysis of the problem of radon and asbestos;

  2. the draft Code of Practice on indoor air quality; and

  3. the prosecution statistics in respect of the ban on smoking in public places such as shopping arcades since it has been come into force.

Analysis on Indoor Air Pollutant Levels recorded in Public Places

2. The summary table of indoor air pollutant levels recorded at public places during the Summer survey is at Annex I. All readings higher than the level of indoor air quality objectives proposed by the consultant are highlighted. In general, the following observations can be made:

  • High concentration of carbon dioxide is the most widespread issue;

  • Other pollutants with measured concentrations higher than the proposed indoor air quality objectives are formaldehyde, nitrogen dioxide, ozone, respirable suspended particulates, nicotine, benzene, and counts of bacteria and fungi; and

  • Restaurants have more pollutants with an elevated level than cinemas and shopping malls.

3. Carbon dioxide per se is not an important pollutant in terms of its adverse health effect. Its concentration in an indoor environment is, however, a good indicator of the effectiveness of ventilation systems and adequacy of fresh air. The survey results indicate that poorly performing or inadequate ventilation systems are the most common cause of indoor air pollution. Particularly high level of carbon dioxide was recorded at restaurants and cinemas. This phenomenon is not uncommon for enclosed places containing many people. Prolonged exposure to this or higher level may make people tired and sleepy but poses no significant health risks.

4. People exposed to elevated bacteria and fungi counts will have an increased chance of being affected. Bacteria and fungi counts are usually indicators of the cleanliness of ventilation systems, particularly the filters, and sometimes indicators of the cleanliness of carpets. Therefore the survey results show that, in addition to fresh air volume, cleanliness of ventilation systems and carpets is also an important issue which needs to be addressed.

5. For other indoor air pollutants which were found to have exceeded the proposed indoor air quality objectives, formaldehyde comes mainly from new furniture or materials used in renovation work. Nicotine, and often respirable suspended particulates, are indicators of level of cigarette smoking. Nitrogen dioxide usually comes from cooking stoves. Ozone comes from photocopiers or other devices that may emit ultra violet light. Benzene can come from petrol vapour or other solvents. The measured concentrations should not cause any immediate adverse health effects to a normal healthy person although some nuisance effects such as mild irritation of eyes may result at the highest concentrations measured. In the longer term, however, exposure to these indoor air pollutants at high levels may impair lung function, cause respiratory disease, and enhance the probability of contracting cancer.

6. It is expected that with properly designed, maintained and operated ventilation systems, most, if not all, of the elevated levels of these other pollutants will be reduced to within the air quality objective values proposed. The survey results do, however, point out that cigarette smoking, new furniture, renovation materials, cooking stoves, paints and solvents as well as ultra violet light emitting sources are the common sources of indoor air pollution in Hong Kong. These findings match many similar findings in overseas studies.

7. Survey findings also indicate that the indoor air quality of restaurants is of more concern than cinemas and shopping malls. Due to the presence of oily cooking fumes, ventilation systems of restaurants demand more maintenance effort than cinemas and shopping malls. Moreover, the findings also show that cigarette smoking in restaurants and the use of new furniture and renovation materials are more important issues than in other places.

Radon and Asbestos

8. The Environmental Protection Department (EPD) conducted an indoor radon survey in 1992/93. The findings were that, out of 619 premises surveyed, 10% exceeded the recommended level of 200 Bq/m3, with the maximum being 300 Bq/m3. Again, lack of proper ventilation was identified to be the principal cause of elevated radon levels. Subsequently, the EPD has issued a publicity pamphlet on radon and how to reduce its level. In 1995/96, the EPD conducted a follow-up survey on these premises. Of the 172 premises surveyed, only 2 exceeded the recommended level of 200 Bq/m3, with the maximum being 205 Bq/m3. This shows that radon level can be effectively reduced through simple measures.

9. Asbestos is a completely different issue. Asbestos materials are safe when they are in good condition. They are hazardous only when damaged or in poor physical condition and the asbestos fibres could be emitted into the air. Therefore, the control of asbestos is not by specifying a concentration limit in air. Its control is to ensure the proper use and handling of asbestos and any materials containing asbestos. Under the Air Pollution Control Ordinance, any works that may involve the use or removal of asbestos materials must be carried out by registered people who are properly trained and equipped. The registration system covers contractors, supervisors, consultants and laboratories. The EPD also conducts compliance check of the asbestos abatement work to ensure sufficient precautionary measures have been taken to avoid asbestos fibre emissions.

10. Copy of publicity pamphlets on radon and asbestos are at Annex II and Annex III respectively.

Draft Code of Practice for the Management of Indoor Air Quality

11. A comprehensive Code of Practice has been drafted under the "Consultancy Study on Indoor Air Pollution in Offices and Public Places in Hong Kong" to define and specify the procedures, measures and methodologies to follow to evaluate indoor air quality and to achieve the proposed Indoor Air Quality Objectives. The draft document which is only available in English (with Chinese translation under preparation) is at Annex IV.

12. This Code of Practice is intended to act as a guide for the public and as the reference document for public and private professionals. This draft will be used as the main basis for consultation with the professional bodies, relevant organisations, as well as the general public in the first quarter of 1999.

Prosecution statistics on the ban on smoking in public places

13. The Smoking (Public Health) Ordinance designates no smoking areas in public places, regulates the sale of tobacco products and prohibits activities like selling cigarettes to minors. Under the Ordinance, all indoor areas open to the public in shopping malls, department stores, supermarkets and banks have been designated as no smoking areas with effect from 1 July 1998.

14. Enforcement of the relevant provisions in the Smoking (Public Health) Ordinance in respect of public places, such as shopping malls, rests primarily with the management of those premises through persuasion and verbal warning. The police will offer assistance when offenders refuse to co-operate and when the assistance from the police is sought by the managers. So far, no prosecution action has been instituted by the police under the new provisions.

15. The Government will continue to work closely with the Hong Kong Council on Smoking and Health to enhance the publicity and education for the general public on the potential hazard of smoking.

Planning, Environment and Lands Bureau
January 1999

Annex I

Summary of Indoor Pollutant Levels Recorded from the Public Places
During the Summer Survey

Restaurant Cinema Shopping Mall
Pollutant IAQ-O (1 hr) Unit High Low Mean High Low Mean High Low Mean
CO 30,000 /m36739.34 905.34 3344.87 3487.93 938.61 1695.87 3180.70 766.56 1659.50
CO21,000appm 1921.71 754.41 1271.63 2369.00 546.26 1362.12 1371.00 716.06 1002.60
HCHO 100b/m3975.18 20.86 161.73 463.95 20.86 139.36 57.15 23.98 38.84
NO2200 /m3279.42 29.78 133.16 134.11 22.87 66.10 98.29 38.03 63.64
O3240 /m3367.25 27.48 54.36 27.48 27.48 27.48 93.32 27.48 38.46
RSP 180a/m31070.06 53.14 323.0 64.74 43.16 54.97 110.66 38.40 77.89
Nicotine 6.8a/m356.23 0.95 7.40 0.95 0.95 0.95 3.18 0.95 1.95
Benzene 16.1 /m331.9 0.32 12.23 2.87 0.32 1.85 10.21 2.08 5.78
Carbon Tetrachloride 103 /m31.26 0.63 0.69 2.52 0.63 1.26 0.79 0.63 0.65
Chloroform 163 /m310.74 0.21 1.86 1.24 0.21 0.66 0.83 0.21 0.47
o-Dichlorobenzene 1,830 /m36.61 0.60 1.26 6.61 0.60 2.04 5.56 0.60 1.69
m-Dichlorobenzene 1,830 /m33.61 0.60 0.87 6.01 0.60 1.80 3.31 0.60 1.54
p-Dichlorobenzene 1,100 /m337.88 1.80 11.60 42.09 1.80 12.14 36.98 1.65 13.88
Ethylbenzene 10,000 /m329.05 0.43 7.74 11.27 1.30 3.81 20.48 1.19 8.29
Tetrachloroethylene 250 /m331.23 0.68 5.60 5.43 0.68 1.63 7.47 0.68 1.89
Toluene 1,092 /m3451.53 4.14 104.08 8.65 6.02 7.60 232.35 9.79 85.88
Trichloroethylene 770 /m33.23 0.54 1.02 1.08 0.54 0.65 13.85 0.54 2.74
o-xylene 4,850 /m341.62 0.43 8.63 25.58 0.43 6.42 16.69 1.63 7.55
m,p-xylene 4,850 /m382.37 2.6 22.85 69.37 1.73 17.86 54.09 3.25 18.75
Bacteria 1,000acfu/m32275.00 125.00 1002.78 856.00 69.00 430.00 4891.00 465.33 2140.06
Fungi 500acfu/m3200.00 6.00 77.11 44.00 6.00 26.20 1161.00 77.00 376.54


a 8 hours IAQ-objective

b 30-minute average