INTRODUCTION
The indoor air quality of air-conditioned offices is a subject of public health importance because we spend a substantial amount of time in these premises. Good indoor air quality can lead to improved productivity at the workplace. On the other hand, poor indoor air quality will cause productivity to drop because of comfort problems, ill health and sicknessabsenteeism.
Our city's tropical climate, highly built environment, and energy conservation requirements pose special constraints and challenges to the building industry in ensuring that indoor air quality remains acceptable. In 1995, my Ministry appointed a Technical Advisory Committee on Indoor Air Quality comprising members from both private and public sectors to advise on the guidelines for good air quality. This document represents a very important first step towards interdisciplinary consensus on the issue of indoor air quality.
The objective of this document is to provide general guidance on improving the indoor air quality of air-conditioned office premises and acceptable values for selected parameters. It also provides information on the potential health effects of indoor contaminants, and an action plan to achieve good indoor air quality. The contents are intended to complement the engineering specifications set out in the Singapore Standard Code of Practicefor Mechanical Ventilation and Air-conditioning in Buildings (SS CP13), and should be useful to building owners/management corporations, those involved in servicing the ventilation and air-conditioning systems, and all others responsible for designing, operating and maintaining the building environment. As research continues, amendments may be made from time to time in subsequent editions.
Purpose
The purpose of this document is to provide guidelines for good indoor air quality.
Scope and application
This document applies to all buildings, new and existing, which are air-conditioned and used as office premises in Singapore.
The indoor air quality parameters addressed are carbon dioxide, carbon monoxide, formaldehyde, ozone, volatile organic chemicals, total bacterial counts, total fungal counts, suspended particulate matter, air temperature, relative humidity, and air movement.
Guideline maximum concentrations for acceptable indoor air quality are specified for carbon dioxide, carbon monoxide, formaldehyde, and ozone based on their known health effects.
Recommended maximum concentrations for acceptable indoor air quality are specified for suspended particulate matter, volatile organic chemicals, bacteria and fungi based on their potential health effects.
Because human health and comfort are complex issues responsive to the interaction of multiple factors, guideline acceptable values are specified for indoor air temperature, relative humidity, and air movement.
IDENTIFYING INDOOR AIR QUALITY PROBLEMS
1 Assessment of indoor air quality problems
14.1 It should be the responsibility of the owner of the building to:
(a) assess the risks to health arising from the indoor air quality;
(b) set up a programme to ensure acceptable indoor air quality, implement the programme, and monitor the effectiveness of the programme; and
(c) keep records of all activities implemented.
1.2 The owner should ensure that the building inclusive of its installations is designed, constructed, operated and maintained in such a way that acceptable indoor air quality is achieved.
1.3 Those engaged by the building owner to carry out the assessment of any indoor air quality problems should be competent persons who are adequately qualified and experienced, and provide supervision for the management of the indoor air quality programme.
2 Indoor air quality and health
2.1 Good indoor air quality improves productivity at the workplace. On the other hand, poor indoor air quality could lead to losses in productivity as a result of comfort problems, ill health and sickness-absenteeism.
2.2 Building-related illness is said to occur when occupant exposure to indoor contaminants results in a clinically defined illness, disease or infirmity. Some common indoor air contaminants and their sources are listed in Appendix A. Those affected usually require prolonged recovery after leaving the building.
2.3 Sick building syndrome is said to occur when a substantial proportion of the occupants of a building experience symptoms associated with acute discomfort that are relieved upon leaving the premises. The mechanisms are still not fully understood, but indoor air quality is thought to be contributory. Those affected typically recover completely soon after leaving the building.
2.4 Factors affecting indoor air which can give rise to poor air quality are: the presence of indoor pollution sources; poorly designed, maintained or operated ACMV systems; and uses of the building that were unplanned for when the building was designed or renovated.
3 Action plan to achieve good indoor air quality
3.1 In the event or on the suspicion that the indoor air quality is not good, the following should be made available for inspection during an investigation:
(a) building plans showing the details of all the floors, and location of the cooling towers and fresh air inlets to the building;
(b) ACMV system layout plans or schematics; and
(c) ACMV system operating schedule and maintenance records.
3.2 A walk-through inspection of the premises and the ACMV system should be conducted by the competent persons to identify possible irregularities. A sample checklist for building inspection is provided in Appendix B.
3.3 Feedback from occupants on the conditions in the building and the operation of the ACMV system should be obtained by the competent persons. A sample confidential questionnaire which can be administered to obtain information is provided in Appendix C.
3.4 Indoor air analysis, and any environmental or biological sampling, should be conducted by the competent persons if deemed necessary for the investigation so that adjustments or alterations can be made.
3.5 Based on the findings of (6.1)-(6.4), building remedial measures should be formulated, implemented and evaluated so that good indoor air quality can be achieved and does not deteriorate again in future.
IMPROVING INDOOR AIR
QUALITY
4 Design
4.1 A new or retrofitted building should be designed with regard to the pollution which may arise within the building. Unless a space has adequate openable windows that can meet natural ventilation requirements, the building should be provided with a mechanical ventilation system that can be operated when required to purge the indoor air from the space, in addition to the air-conditioning system.
4.2 The ACMV system should be designed so that the potential spread of contaminants in the building is kept low. Materials used should not include those that emit chemicals, bacteria or fungi to the supply air. Pollution sources, or pollutive activities of frequent occurrence, should be provided with such process ventilation of the encapsulation, hood or local extraction type so that the spread of contaminants is prevented.
4.3 Building materials and surface finishes should not contain any substances that emit chemicals, bacteria or fungi. They should be able to stand up to the intended use and not cause any emission of contaminants to the indoor air.
4.4 Water supply, drainage, sewerage and other installations should be planned for construction in such a way that the risk of leaks and consequential damage caused by leaks is prevented.
4.5 Outdoor air intakes should be placed where the air admitted is likely to be cleanest, taking into consideration the outdoor air quality standards specified in Appendix D, the position of the building, the exhaust opening position, traffic routes, carparks, unloading bays, refuse chutes and other nearby sources of pollution. Intakes should not be located below ground level or close to evaporative cooling towers. Outdoor air filters should be placed as close as possible to the intake points.
4.6 The building should be designed so that cleaning of windows, doors, floors and other surfaces in contact with supply air or room air is possible. Such surfaces should be cleaned before the building is taken into use. Surfaces which are likely to become heavily soiled should be readily accessible and easily cleanable.
Construction
5.1 At all stages of the construction of the building and its ACMV system, inspections should be made by the competent persons so that acceptable indoor air quality can be secured when the system is put into operation.
5.2 The building structure should be constructed in such a way that harmful spread of contaminants from the outside, the ground, or some other separate part of the building does not occur.
5.3 In the construction of the ACMV system, the supply and return air ducts should be made accessible for inspection and cleaning. Components should be made of materials which stand up to the intended use and maintenance. Those which require attendance and maintenance should be sited so that they are readily accessible and replaceable, and mounted so that work can be carried out easily and safely. To reduce dust accumulation, the inner surfaces of the ducts for supply and return air should be smooth and resistant to abrasion.
5.4 Outdoor air for ventilation and indoor air that is to be recirculated should be filtered for particulates. A filter should be placed for outdoor air that is to be introduced into an air handling unit room. The filter should be protected from being wetted by sprays, rain, etc. In placing the filters, there should be an adequate seal between the air filters and the walls of the surroundings ducts or units.
5.5 Installations unrelated to the ACMV system should not be located in the air-handling unit rooms
6 Commissioning and operation
6.1 Before a new or retrofitted building is commissioned into service, it should be demonstrated that the ACMV system has been constructed and is able to function in the way intended. The entire ACMV system should be cleared of any construction debris and dirt, and cleaned before operation starts.
6.2 The specifications and operations of the ACMV system should be in accordance with all provisions of the Singapore Standard Code of Practice for Mechanical Ventilation and Air-conditioning in Buildings (SS CP13).
6.3 Unless there are strong pollutants sources, in which case corrective action should be taken, the ventilation rate should be sufficient to dilute or remove any airborne contaminants to levels which comply with the indoor air quality guideline values specified in Appendix E. Where this is not possible, an air-purging system should be activated to enable purging of the contaminated air, routinely or as and when required.
6.4 It should be possible to assess at any time the condition of the filter, including the pressure drop, the contamination and the installation. The minimum arrestance efficiency for the air filters for cleaning outdoor and indoor air should be 60% and 80%, respectively.
6.5 Instructions for the operation of the building and its ACMV system should be drawn up in direct cooperation with the operations and maintenance staff, including all necessary information for satisfactory ventilation of the rooms served. The instructions manual for each ACMV system should include: (a) a schematic plan of the system; (b) its operation; and (c) the precautions to be taken specifying checks and their frequency, and steps to be taken to remedy defects and deficiencies.
6.6 Rooms where air handling units are situated should not be used as passage ways or for storage. Where they open to a source of contamination, the doors of the rooms should remain air-tight. The inner surfaces of the units and equipment should be easy to clean and abrasion-resistant. Sufficient space for cleaning and for access to the units should be provided.
6.7 Air distribution should be efficient, effective and uniform to ensure no stagnation of air in dead spaces.
7 Renovation
7.1 Major renovation works should be undertaken in such a way that a satisfactory indoor environment is secured. Where relevant to the renovation works, consideration should be given to (7.1)-(7.6) and (8.1)-(8.5) in the stages of design and construction, respectively.
7.2 Processes and activities should be selected so that they have the lowest possible emission. Where processes and activities which pollute the air cannot be avoided, they should as far as possible be encapsulated, provided with local extraction, carried out in areas with direct exhaust to the exterior, or limited to times when few people are exposed.
7.3 The building materials should not contain any toxic substances which could pose a hazard to health when used in the occupied building. Fittings, fixtures, furnishings and furniture should be manufactured, selected, handled, stored and used so that emission to the room air is the least possible.
7.4 For occupied buildings undergoing partial renovation, spaces to be renovated should be effectively isolated from the occupied zones. If necessary, supply air should be separated so that acceptable indoor air quality for the occupants is maintained. Concentrations of formaldehyde, volatile organic compounds, suspended particulate matter and other contaminants in room air should be within the limits specified in Appendix E.
7.5 After any major renovation to the building where the airconditioning system has been affected (eg. by partitioning of office space), rebalancing of the air distribution should be required
8 Maintenance
8.1 Competent persons should be employed specifically to ensure that regular maintenance of the building inclusive of the ACMV system is carried out on a routine basis. Maintenance staff should be familiar with the prevention of any hazard arising from the building.
8.2 The schedule of maintenance for the ACMV system should be in accordance with the manufacturer's recommendation to ensure that the equipment operate efficiently. If this is not specified for any component, the frequencies listed in (11.3)- (11.7) should constitute the minimum requirements.
8.3 The building and its ACMV system should be inspected at least every six months with regard to functions which are significant for the indoor air quality. Normal operation of the system should be monitored so that it continues to operate at maximum efficiency and breakdowns are avoided.
8.4 The ACMV system and the air handling unit room should be cleaned and maintained in such a way that the indoor air quality is not adversely affected by the cleaning and maintenance. The components of air-handling units such as fans and dampers should be cleaned at least every six months, depending on the condition of the incoming air and use of the system. Filters should be cleaned or replaced so that they are performing properly at all times and do not become clogged.
8.5 Cooling coils, condensate pipes and water trays should be checked regularly for signs of sludge, algae or rust build-up, chokage and leaks where water could enter the airstream. Coils and condensate pipes should be cleaned at least every six months. The trays should be cleaned at least every one month to ensure that contaminants do not build up. Any ferrous metal surface should be treated with an anticorrosion coating. Re-circulating water should also be treated to prevent rust but that treated water must not be allowed to enter the airstream.
8.6 Cooling towers should be cleaned and treated in accordance with guidelines specified in the Code of Practice for the control oflegionella bacteria in air-conditioning cooling towers in Singapore (Ministryof the Environment, August 1992).
8.7 The ACMV system should be checked and adjusted to ensure correct air flow, temperature and humidity after the first year of operation and at least every two years thereafter. It should also be checked and adjusted after any renovations or changes in floor layout that might affect air distribution.
8.8 Records should be kept of all maintenance work - when and what was done.
9 Quality control
9.1 An audit should be conducted by the competent persons within six months after commencement of operation of the ACMV system. The information for such an audit is similar to that which is collected in (6.1)-(6.4) when investigating an occurrence of building-associated illness, but includes the entire building rather than focusing on any area with an identified problem.
9.2 During the normal operation of a building, an audit should be conducted by the competent persons at least every two years to ensure that the indoor air quality is acceptable and conforms to the specifications listed in Appendix E.
9.3 When indoor air testing is required to study if the air quality complies with the relevant specifications, the tests should be carried out by a laboratory accredited under the Singapore Laboratory Accreditation Scheme.
9.4 The necessary plans, drawings and specifications on the building and its installations should be kept by the owner or the management corporation of the building, and made available for inspection when necessary.
9.5 A formal record book containing adequate and accurate information on the ACMV system should be kept by the owner or the management corporation of the building, and made available for inspection when necessary. The information should include:
(a) description of the air-conditioning system;
(b) name of the building manager or person who ensures that proper records are kept;
(c) person or company who is responsible for the assessment of risk, and implementing and managing precautionary measures;
(d) person or company carrying out the maintenance programme; and
(e) details of maintenance, including:
(i) date and result of visual inspection;
(ii) date and type of cleaning/treatment works conducted; and
(iii) date and nature of any remedial works (if required).
