Shawcity Limited

Indoor Air Quality

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Courtesy of Courtesy of Shawcity Limited

Indoor Air Quality-Makes Me Sick

EVM 7 measures it all


How often do you here ‘I need some fresh air’. Why do we say that? Maybe you simply want a break from the wife and kids or work colleagues! But it may be because the indoor air you are breathing in is contaminated. Indoor air contains significantly higher levels of contaminants than outside air.


The effects of these contaminants can be irritation, headaches, dizziness, fatigue or more seriously, asthma etc. We need to identify how to prevent poor indoor air quality. When air quality is unacceptable, corrective action is needed. But identifying contamination means that indoor air quality monitoring is needed.


Air quality monitoring usually begins with measurement of temperature and humidity. If  the temperature is too hot or cold we complain. Similarly humidity levels must be maintained at an acceptable level to establish thermal comfort. Because when it is too hot for one person it is too cold for another, this can be difficult!


After measurement of temperature and humidity the next most important measurement for most situations is Carbon Dioxide CO2. Levels of CO2 increase as the density of population increases. We all breathe in and consume oxygen O2 whilst breathing out CO2.

So the more people in a room means CO2 levels will inevitably climb. If the occupants are engaged in physical activity this is going to further increase the CO2 levels. The HSE, EH40 document specifies a limit value for an 8 hour average of 5000ppm (parts per million). But many people feel very uncomfortable at lower levels. The US, NIOSH organisation considers levels over 1000ppm indicate inadequate ventilation. In the UK the schools have a maximum target of 1500ppm, averaged over the full school day. When CO2 levels are high occupants will become drowsy and could suffer headaches. Performance or work levels are also affected.


Dust levels can also affect our health and many indoor facilities are affected. When ingested the dust will pass into the nose and mouth. Dust with a particle size of 100microns or less is inhalable and potentially harmful. If the size of the dust is 10microns or less it is thoracic dust and will pass through the nose and throat and may reach into the lungs. Smaller, 5micron and less dust particles will penetrate deep into the lungs and these smaller particles pose a significant risk to health as well as comfort.


Volatile Organic Compounds(VOC’s) are gases or vapours that are inevitably present in many indoor environments. Gas is emitted from solids or liquids that are used in the office or workplace. VOC’s are present because of adhesives, cleaning fluids, paints, building materials and other chemical based office supplies. All types of fuels are also going to increase the risk of high concentrations. As with dust, VOC’s pose a significant health risk as well as affecting comfort levels


Toxic gases can also affect indoor air quality. The most common toxic gas to pose a threat is Carbon Monoxide (CO). CO may be present as a result of faulty heating appliances, vehicle exhaust fumes or tobacco smoke. Smoke free areas have reduced the problem. CO is a colourless and odourless gas and at low levels you will become drowsy, get a headache and experience nausea. This happens because the CO deprives the brain the oxygen that it has displaced. Higher levels of CO and exposure over longer periods of time will lead to unconsciousness and possible death. The HSE EH40 document recommends a limit value regards exposure of 30ppm over an 8 hour average period.

Other gases including Sulphur Dioxide, Nitrogen Dioxide, Chlorine or Ammonia etc may also affect indoor air quality but are less frequently present.



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