When somebody mentions pollution, you probably immediately think of cars, planes and factories belching out toxic exhaust fumes. Whilst these are sources of outside air pollution there are a whole host of other pollutants which have a more direct impact on our indoor air quality and consequently our health.
We spend up to 90% of our lives indoors, maybe we should take more notice of what we are breathing in – both at home and at work. A recent study suggests that many schools in the London area have levels of indoor pollutants that are likely to be much higher than the level of pollution immediately outside. So this is a real and pressing issue which needs to be addressed.
Indoor air quality is defined by a number of factors, some well-known, such as temperature, humidity, CO2, odours and particulates (skin cells, smoke, vehicle fumes, fiberglass, dust), and others less talked about, such as combustion products (CO, NOx, SOx) and allergens (dander, dust mites, pollen).
Humidity levels affect indoor air quality
Whilst humidity in itself isn’t necessarily a pollutant, too much or too little humidity can cause problems. Not only can it be uncomfortable to be in a warm, humid room, but excessive humidity provides an environment in which mould, dust mites and fungi can prosper. These can have a serious impact on our health, with chronic exposure to damp air strongly associated with increased rates of respiratory disease in humans. Severe asthma with fungal sensitisation is estimated to affect between 3.25 and 13 million adults worldwide and contributes to the 100,000 annual asthma deaths.
The chart below shows how important the humidity and temperature of a room is for our comfort:
How CO2 affects our indoor air quality
Next on the list is carbon dioxide. CO2 is everywhere, but if its concentration builds up it can negatively affect our wellbeing and health.
It’s tempting to think that these concentrations only occur in unusual or specific circumstances, but studies have shown that carbon dioxide levels in a typical unventilated bedroom often peak above 1500 parts per million (ppm) overnight.
Toxic chemicals can be generated in the home itself
Another common range of indoor air pollutants are known as volatile organic compounds (VOCs). These are organic compounds with an initial boiling point of less than 250oC and are therefore very varied. Volatile organic compounds are found in building fabric materials (MDF, OSB, plywood, laminate), furniture, solvents and cleaning products. Short term effects include eye, nose and throat irritation, headaches, nausea/vomiting, dizziness, and asthma aggravation, while long term exposure at high levels can lead to cancer, liver & kidney problems and central nervous system damage.
Typical examples are propane, butane, methyl chloride, formaldehyde, d-Limonene, toluene, acetone, ethanol (ethyl alcohol) 2-propanol (isopropyl alcohol), hexanal, pesticides (DDT, chlordane, plasticizers (phthalates) and fire retardants (PCBs, PBB)). As they are so varied, both their effects and the concentrations to which we can be safely exposed can vary greatly depending on the substance. Some are completely safe, whereas others can be extremely toxic.
So, how do we deal with all these indoor air pollutants?
Well, the traditional way is to open windows and use the
extractor fans in our kitchens and bathrooms. Whilst opening windows is extremely effective, it’s not something we can do during the winter months when it’s cold outside, and extractor fans on their own simply won’t shift enough air to deal with the problem.
Homes in the UK also tend to be draughty, which helps provide what’s called “unregulated ventilation” through the gaps and holes in the property. But as energy efficiency requirements push our modern buildings to be renovated and built to be more airtight, relying on unregulated ventilation to help deal with indoor air quality is no longer possible.
Another alternative is therefore to introduce a more comprehensive ventilation system such as a Mechanical Ventilation with Heat Recovery system (MVHR). This provides fresh, clean air 24 hours a day at very low levels of air-flow, whilst recovering the heat that’s in the stale air before expelling it outside. Mechanical Extract Ventilation (MEV) uses a central extract system and Positive Input Ventilation (PIV) provides a constant flow of fresh air to do much the same thing, albeit less efficiently.
Enhabit have been gathering indoor air quality data from a number of different house types to see what works best. We looked at three different types:
– A traditional Victorian end of terrace relying on opening windows and extract fans
– A hybrid model which had a background MVHR system but also used natural ventilation (opening windows) as appropriate
– A newly completed EnerPHit project – a home refurbished to the Passivhaus standard to be almost completely airtight and fitted with a comprehensive MVHR system
Enhabit monitored all the key indicators of indoor air quality in each of these homes over a number of months. The summary of the results are below and show that our Victorian end of terrace performs pretty poorly, whilst the other two offer much healthier internal environments. The EnerPHit has slightly higher levels of VOCs than the naturally ventilated building, which is likely o relate to the glues and sealants used in the construction. However, these levels are still half those seen in the Victorian terrace. Unsurprisingly, the EnerPHit project wins out on minimising energy use even though the occupants tended to have the house at a higher temperature than the occupants of the naturally ventilated house.
Good indoor air quality is vital for our health
We spend much of our time breathing in air at home and at work, and
most of us probably have no idea what we are actually inhaling. It’s likely that, for some of the time, all of us are being exposed to a range of pollutants which at best might make us feel uncomfortable, but at worst could be seriously affecting our health.
There is a lot of ongoing research into this area at the moment and it is gaining increasing recognition as something which needs more attention during the design and construction of buildings.
We might not fully understand the levels of exposure and risk, but we do know that designing a proper ventilation strategy for our buildings will go a long way to ensuring that we live and work in a fresh and healthy environment.