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Indoor Air Quality

Indoor air quality describes how inside air can affect a person's health, comfort, and ability to work. It can include but not limited to temperature, humidity, mould, bacteria, poor ventilation, or exposure to other chemicals. Indoor air pollution has received little attention in the past compared with air pollution in the outdoor environment. It has now become a matter of increasing public concern, prompted partly by the emergence of new indoor air pollutants, by the isolation of the indoor environment from the natural outdoor environment in well-sealed office buildings, and by the investigation of so-called Sick Building Syndrome.

Poor indoor air quality can lead to discomfort, ill health, and, in the workplace, absenteeism and lower productivity. Good indoor air quality safeguards the health of the building occupants and contributes to their comfort and well-being. [1] Well-established, serious health impacts resulting from poor IAQ include Legionnaires’ Disease, lung cancer from radon exposure, and carbon monoxide (CO) poisoning. More widespread health impacts include increase allergy and asthma from exposure to indoor pollutants (particularly those associated with building dampness and mould), colds and others infectious disease that are transmitted through the air, and “sick building syndrome” symptoms due to elevated indoor pollutant levels well as other indoor environmental conditions. These more widespread impacts have the potential to affects large numbers of building occupant and are associated with significant cost due to health-care expenses, sick leave and lost productivity.

In 2010, the Department has introduced the Industry Code of Practice on Indoor Air Quality 2010 to increase the compliance of designated workplaces. Activities regarding the issues of indoor air quality involve the investigation of complaints from workers. The procedure of handling any complaints can be found in the Industry Code of Practice on Indoor Air Quality 2010. Investigation usually involves five main activities, which are the preliminary site visit, measuring the level of contaminant in the area, data analysis, discussions with employers and the report writing.

Industry Code of Practice on Indoor Air Quality 2010 (ICOP IAQ 2010)


This Industry Code of Practice is known as the Industry Code of Practice on Indoor Air Quality 2010 approved by the Minister on 30 August 2010 and will replace the Code of Practice on Indoor Air Quality launched by the Minister on July 2005.

Good indoor air quality (IAQ) is required for a healthy indoor work environment. Poor indoor air quality can cause a variety of short-term and long-term health problems. Health problems commonly associated with poor IAQ include allergic reactions, respiratory problems, eye irritation, sinusitis, bronchitis and pneumonia. IAQ problems occur in buildings that are served by a mechanical ventilating and air conditioning (MVAC) system including air-cooled split unit. IAQ problems can be due to indoor air pollutants or to inadequate ventilation.

There are many sources of indoor air pollutants and among the common ones are environmental tobacco smoke (ETS) emitted due to burning of tobacco products; various chemical substances such as formaldehyde emitted from furnishings; volatile organic compounds emitted from the use and application of solvents; and ozone emitted from photocopiers and laser printers. It should be noted here that ETS has been recognized as a human carcinogen by the International Agency from Research on cancer (IARC) in 2002 and exposure to it will increase the risk of coronary heart disease.

This Industry Code of Practice has been drawn up to ensure employees and occupants are protected from poor indoor air quality that could adversely affect their health and well-being, and thereby reduce their productivity. It is the general duties of employers and self-employed persons to their employees as stipulated under Section 15 of Occupational Safety and Health Act 1994 (OSHA) while Section 17 of OSHA stipulated that it is also the general duties of employers and self-employed persons to persons other than their employees.

This Industry Code of Practice has been drawn up to ensure employees and occupants are protected from poor indoor air quality that could adversely affect their health and well-being, and thereby reduce their productivity. It is the general duties of employers and self-employed persons to their employees as stipulated under Section 15 of Occupational Safety and Health Act 1994 (OSHA) while Section 17 of OSHA stipulated that it is also the general duties of employers and self-employed persons to persons other than their employees. The Industry Code of Practice also emphasize on the duties of an occupier of a place of work to persons other than his employees stipulated in Section 18 of OSHA. An occupier is a person who has the management or control of the place of work. This duty is owed to persons who are not his employees but go to their premises to carry out work. Compliance to this Industry Code of Practice can be used as evidence of good practice in a court.

Physical parameters & list of indoor air contaminants and the acceptable limits

Table 1: Acceptable range for specific physical parameters

Acceptable range

(a) Air temperature

23 – 26 °C

(b) Relative humidity


(c) Air movement

0.15 – 0.50 m/s

Table 2: List of indoor air contaminants and the acceptable limits

Indoor Air Contaminants
Acceptable limits

Chemical contaminants

(a) Carbon monoxide

(b) Formaldehyde

(c) Ozone

(d) Respirable particulates

(e) Total volatile organic compounds (TVOC)



















Biological contaminants

(a) Total bacterial counts

(b) Total fungal counts









Ventilation performance indicator

(a) Carbon dioxide








  • For chemical contaminants, the limits are eight-hour time-weighted average airborne concentrations.
  • mg/m3 is milligrams per cubic meter of air at 25° C and one atmosphere pressure.
  • ppm is parts of vapour or gas per million parts of contaminated air by volume.
  • cfu/m3 is colony forming units per cubic meter.
  • C is the ceiling limit that shall not be exceeded at any time. Readings above 1000ppm are indication of inadequate ventilation.
  • *excess of bacterial counts does not necessarily imply health risk but serve as an indicator for further investigation.



Moulds Contamination

Mould Organism

Moulds are the most typical form of fungus found on earth, comprising approximately 25% of the Earth’s biomass. Other fungi include yeasts and mushrooms. Moulds are ubiquitous on our planet and are essential decomposer of organic substances necessary for sustaining plant and animal life. Moulds are made up of masses of filament-like cells called hyphae. Under appropriate conditions, hyphae would grow into long intertwining strings that form the main body of the fungus, or the mycelium. This mycelium is visible to human eye. Moulds reproduce via spores. However, moulds can also spread if a fragment of broken hyphae is transplanted to an area with adequate moisture and organic matter for food.

There are several types of mould exist in indoor environment such as:

  • Cladosporium
  • Penicillium
  • Alternaria
  • Aspergillus
Cause of Mould Growth

Moulds are incredibly resilient and adaptable. Moulds gain the nutrients they need through the decomposition of organic matter. Most moulds found in indoor air are saprotrophic, meaning they gather their food from dead moist organic matter such as wood, paper, paint, fabric, plant soil, dust, and cooked or raw foods. Moulds can also grow on surface of damp inorganic matter such as glass and bare concrete covered by an invisible biofilm.

In general, there are few factors as listed below that contribute to mould growth in built environment:
  • Mould spores – which are readily available in the air
  • Nutrient – such as dirt, dust cellulose and starch
  • Temperature range between 5°C to 50°C
  • Relative Humidity consistently above 70%
  • Oxygen
relative humidity
Figure 1: Mould Factors Diagram

Air with high moisture content constitutes one of the key elements for mould growth. Therefore, to prevent mould growth, all possible factors that can introduce moisture into a building should be identified and eliminated. Low surface temperature (below dew point temperature) of the air adjacent to the wall and/or floor slab would cause condensation on the surface and if left unattended, will become ideal breeding grounds for mould to grow.

All mould needs food source, undisturbed water and time to germinate and grow. Some moulds can germinate in as little as four to twelve hours. Left undisturbed, mould can grow and spread in 24 to 72 hours.

Endogenous mould problems generally occur after prolonged or repeated water damage to a variety of organic materials. Mould spores can be brought indoor from outside. Outdoor factors that seem to affect indoor mould spore concentrations include marked shade, increased levels of available organic debris and natural or basically uncared for property.

Floods, condensation, leaking pipes, leaking windows and leaking roofs are all potential sources of moisture that can lead to mould infestation. Increased ambient humidity as a result of inadequate ventilation or improper drying of flooded areas can also lead to mould growth

Potential Health Effects of Mould

Mould can cause a range of health responses in humans. The severity of the impact depends upon the type and amount of mould present as well as the susceptibility and sensitivity of the individual experiencing mould exposure. Humans are exposed to moulds via ingestion, inhalation, and skin contact with mould or mould infested material. Moulds produce acute health effects through toxin-induced inflammation, allergy or infection.

Sick Building Syndrome & Building Related Illnesses

Sick Building Syndrome

“Sick building syndrome” is the name that has commonly been used for illnesses that occur among occupants as a result of poor indoor air quality in building.

Sick building syndrome describe situation in which building occupants experience acute health and/or comfort effects that appear to be linked to time spent in a particular building, but where no specific illness or cause can be identified. The complaints may be localized in a particular room or zone, or may be spread throughout the building.

Some of these buildings may be inadequately ventilated. For example, mechanical ventilation systems may not be designed or operated to provide adequate amounts of outdoor intake air. People generally have less control over the indoor environment in their offices than they do in their home. As a result, there has been an increase in the incidence of reported health problems

Sometimes building occupants experience symptoms that do not fit the pattern of any particular illness and are difficult to trace to any specific source. This phenomenon has been labelled as sick building syndrome. Symptoms that have arisen among occupants of “sick building” have varied from eye and nose irritation, fatigue, cough, rhinitis, nausea, headache, sore throat or a combination of these.

Building Related Illnesses

A number of well-identified illnesses, such as Legionnaires’ disease, asthma, hypersensitivity pneumonitis, and humidifier fever, have been directly traced to specific building problems. These are called building-related illnesses. Most of these diseases can be treated; nevertheless, some pose serious risks.

Legionnaires’ disease is one of the building-related illnesses. It is a form of bacterial pneumonia that is characterized by fever, chills and dry cough associated with muscle aches and occasional diarrhoea. Legionnaire’ disease acquired its name when people attending an American Legion’s convention in Philadelphia in July 1976 were affected by the disease. Pontiac fever on the other hand is a milder form characterized by fever and muscle aches with no symptoms of pneumonia.

The bacteria that cause Legionnaires’ disease, legionella pneumophila will grow in any environmental reservoir in which its nutrient, water and temperature requirement are met, and enters the air when such sites are disturbed. The bacteria thrives in temperatures between 25°C and 45°C, with an optimum around 35°C. Although this organism is ubiquitous in the environment, airborne concentrations only occasionally reach levels adequate to infect otherwise normal subjects.

Water-cooling towers and warm water systems in buildings have been identified as major sources of this organism. Without treatment of the water or without adequate maintenance of the system, legionella can proliferate and then be distributed throughout the building by the air-handling system.

Guidelines on the Use of Personal Protective Equipment against Chemicals Hazards, 2005.

These guidelines is intended as a guide for employers in order to comply with the requirements pertaining to the use of approved and suitable personal protective equipment as stipulated under USECHH Regulations. This guideline only covers personal protective equipment that is related to protection against chemical exposures.

Click here to download the Guidelines.

Guidelines on Storage of Hazardous Chemicals: A Guide for Safe Warehousing of Packaged Hazardous Chemicals, 2005.

These guidelines propose safer ways to establish safe storage and warehousing of chemicals whether already existing or in a planning stage. Sound storage of chemicals can contribute to the safety and health of employees as well as protection of the environment.

Click here to download the Guidelines.


Tags: Chemical Management, Indoor Air Quality

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