Indoor Air Quality

Table 1: Acceptable range for specific physical parameters

Parameter	Acceptable range
(a) Air temperature	23 – 26 °C
(b) Relative humidity	40-70%
(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
	ppm	mg/m3	cfu/m3
Chemical contaminants (a) Carbon monoxide (b) Formaldehyde (c) Ozone (d) Respirable particulates (e) Total volatile organic compounds (TVOC)
	10 0.1 0.05 - 3	- - - 0.15 -	- - - - -
Biological contaminants (a) Total bacterial counts (b) Total fungal counts	- -	- -	500* 1000*
Ventilation performance indicator (a) Carbon dioxide	C1000	-	-

Notes:

• 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 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

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” 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.