Indoor Air Quality

Thermal Comfort and Air Quality

Since the evolution of our species we have always been subjected to airborne pollution – from dust in the air, volcanic gases, and fire smoke for instance. However, since we’ve started to inhabit closed spaces, airborne pollution has become more of an issue.
 
These days, indoor air quality is a very big issue, so much so that all buildings have minimum ventilation rates set in law. Indoor air quality can be affected by a great number of pollutants, produced by ourselves and our actions, our choice of finishes and furnishings, the materials that our buildings are made of, and the wider world outside.
 
Metabolic pollutants are produced by ourselves and our pets, and include water vapour, carbon dioxide, and body odour. Although none of these might be considered dangerous to health in the quantities that they normally exist, they can have a detrimental effect to our comfort.
 
Water vapour levels inside are generally above those outside, particularly in our houses due to washing and cooking. Too little humidity and our eyes and throats become dry, and risks of respiratory infection increase. Too much and the resulting dampness can give rise to moulds and other micro-organisms that might cause more serious allergic responses in some individuals.
 
Carbon dioxide levels inside are bound to be higher than outside, and depend upon density of occupation and activity. However, even high rates of CO2 indoors are not known to cause negative health effects, although CO2 is measured to indicate the general level of ventilation and therefore other pollutants.
 
Body odour, and other odours, may be unacceptable but rarely, if ever, dangerous. However, their existence may be indicative of the existence of more hazardous volatile chemicals that might not have an odour, and therefore point to a lack of adequate ventilation.
 
Combustion pollutants are caused by the burning of fossil or carbon fuels. Carbon monoxide is produced by incomplete burning, which happens little in modern appliances due to  current regulations. However, insufficient air supply or ventilation can result in concentrations sufficient to cause death.
 
Nitrogen dioxide is produced during combustion. Its presence in the air might cause respiratory infection, although studies have been carried out comparing children from homes who cook with gas and those who cook with electricity, and the evidence is not conclusive.
 
A huge number of organic pollutants have been identified in our buildings, arising from many sources, including furnishings and finishes, smoking, combustion, deodorants, so called ‘air-fresheners’, and even the building fabric itself.
 
Emission rates and typical concentrations have been little measured, and health effects have largely been observed in commercial situations where concentrations are greater – very little is known about the long term effect of low concentrations.
 
However, formaldehyde is one such organic compound that has been proven to have negative effects, and the precaution principle suggests treating other organic compounds similarly and ensuring good levels of ventilation until more is understood.

Respirable Suspended Particulates (RSPs)

RSPs come in two forms – viable and non-viable.
 
Non-viable particulates include dust and dirt. They are generally of external origin, and  benign depending upon the nature of the particulate and concentration. Fibres also come into this category, which includes tiny bits of fluff from our clothes which are of little or no concern (some people might be allergic), but also asbestos. However, deaths attributable to cancer caused by asbestos are less than 1 in 700,000 and generally those who were subjected to occupational exposure.
 
Viable particles include micro-organisms such as tiny insects, protozoa, fungi spores, bacteria and viruses. Due to the vast range of potential particles and limited measurement techniques, knowledge of the typical types and concentrations in indoor air are sparse towards sketchy.
 
However, it is known that concentrations are dependent upon colonies being able to form. This is in turn dependent upon there being a suitable environment, largely controlled by location, humidity, and temperature. A range of allergies and infections from minor to deadly might broadly be attributed to viable particles in indoor air. The best form of control is to prevent their occurrence by ensuring the environment does not suit them.
 
Radon is a widely found naturally occurring gas, formed as radium decomposes in the earth’s crust – it is present in nearly all soil and rock. Miners have shown increased incidences of lung cancer, but the overall risk to the UK population is small – unless mixed with tobacco smoke with which it reacts synergistically to produce much higher risk.
 
The extent to which any or a combination of all of these pollutants become an issue to human health depends upon concentration and rate of production, rate of absorption or decay, and the rate and characteristics of ventilation and fresh air supply.
 
Hence the need for adequate ventilation!
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