As we all spend on average 90% of our time indoors it is important the quality of air we breathe and indoor air conditions we experience are good. We all like the air to be clean, and within a narrow band of comfortable temperature and humidity. So what are the sources of poor indoor air quality in buildings?
The comfort band varies from person to person but would generally be about 20-24 deg.C.room temperature and 40-60 %Relative Humidity for most people.
Clean air however can be more of a problem to get these days in urban locations where there are high levels of background air pollution. This pollution can be in either in solid particle or gas form.
In large public buildings there are contaminant sources from outside the building and inside the building. If the building is not well managed a high level of a contaminant or ‘cocktail’ of contaminants can cause bad health reactions from the building inhabitants leading to the term known as ‘Sick Building Syndrome’. It is worth considering the more common problem contaminants that lead to this situation.
Particles – Contaminated Air from outside may contain particles of dust such as fine combustion particles from cars, power stations and the burning of fossil fuels. Other inorganic particles found may be windblown sand or salt crystals, particularly in coastal locations. Fumes and smoke are usually solid particles while mists and fogs usually contain mainly liquid based particles. Smogs are often a mixture of solid and liquid particles and may also have an associated photo-chemical gas phase. Contaminant particles may also be sourced from inside the building. Asbestos fibres are a threat in many older buildings and may be exposed in alteration and refurbishment works. (Solution: Effective air filtration and investigate source)
A particle count of the supply duct system can reveal the quantity and often the type of external particulate contaminant coming into the building
Bio-aerosols can comprise of larger organic particles such as pollen grains and fungal spores but may be smaller bio-particles such as bacteria and virus. Apart from outside sources humans are a common source of bio-particle contamination when inside buildings. The variety is great and needs more detail given than is possible here. Critical environments such as hospitals and operating theatres especially need to ensure any sources of contamination such as breeding colonies of bacteria are investigated and dealt with effectively. The same principle applies in all offices, commercial and public buildings used by many people. (Solution: Effective air filtration and investigate source)
Gases – Gaseous contaminants problems occur when people in buildings are exposed to levels of gases that cause an adverse reaction. These would commonly be classed as Inorganic gases and Organic gases. (Although CO2 and CO contain Carbon they are normally grouped with Inorganic gases).
Carbon dioxide (CO2) is non toxic and exhaled naturally by people as part of their process of living, but it can cause asphyxiation when concentrations in air are greater than 35000 ppm. and drowsiness above 10,000 ppm. Generally experienced levels can be in the range 500 to 1000 ppm. It can come from boilers cookers and similar gas appliances.
If the CO2 level is constantly above 1000ppm. the ventilation air flow rate should be checked. A minimum advised supply of fresh air of about 10 L/s per person should be delivered to dilute CO2 in buildings to an acceptable level. (Solution: Dilution by increased ventilation and investigate source)
Carbon monoxide (CO) is highly toxic to humans even at low concentrations. Workers should not be exposed to more than 50 ppm. over a long work period or peak exposure short term of 100 ppm. Levels in houses should rarely exceed 5 ppm.
World Health Organisation guidelines are tighter and advise less than 25ppm over 1 hour and 10ppm over an 8 hour period is the limit.
Carbon monoxide blocks the bloods capacity to carry oxygen. It is an odourless and colourless gas so CO monitors and alarms should be placed near fuel burning appliances that could malfunction and produce this gas. It can also be produced from vehicle engines which should not be run in enclosed spaces with people present. (Solution: Dilution by increased ventilation and investigate source)
Nitrogen oxides NO and N2O are present in air often being produced in conjunction with CO when burning of fossil fuels is taking place. Fertilisers are thought to be another outside source. WHO N2O exposure limits 100ppb over 1 hour and 20 ppb annual limit. Solution: Effective Gas filtration and investigate source)
Sulphur dioxide – Produced from the burning of fossil fuels such as traffic and power stations but also from natural sources like volcanoes. WHO guidelines advise short term (10minutes) exposure of no more than 500µg/m3. Daily exposure less than 125µg/m3. Long term exposure less than 50µg/m3. (Solution: Effective Gas filtration and investigate source)
Ozone – This gas can often be found in outlying city areas and is a very reactive gas that can often be taken up by reaction with Nitrogen oxides. Indoor sources can include office equipment such as photocopiers and UV lights. It is harmful to human respiratory systems and exposure should be limited to levels not exceeding 120µg/m3 over an eight hour period according to WHO guidelines. (Solution: Effective Gas filtration and investigate source)
Formaldehyde –This usually comes from off-gassing of furnishings so is an internal source of pollution. (Solution: Effective Gas filtration and investigate source)
VOC’s – Volatile Organic Compounds are numerous in type and sources. Poorly burned fuels and household chemicals are two sources. (Solution: Effective Gas filtration and investigate source)
Radon – usually depends on the building location as it is a ground source gas that occurs in quite well documented locations around the country. It is a good idea to check the probability of Radon in the location being considered and testing if it is likely to be there. (Solution: Dilution by increased ventilation and investigate source)
All of these contaminants may present a problem. If there is a suspected problem that needs investigating it is worth calling in an expert to make a report and test for the more common problem contaminants we have mentioned and test for any other suspected ones. The HVAC plant itself can be a source of contamination if it is not well maintained. It needs to have the correct design and application of filters to clean the air with regular inspection and cleaning of the duct system on the intake and supply side. The air handling units also need cleaning with attention given especially to the coils and heat exchangers.