The majority of mass produced building products, finishes and furnishings contain
compounds and chemicals that may cause health problems through chronic exposure in the indoor environment. While knowledge of VOCs and other harmful building products has become more widely spread, it is difficult to gauge levels of these harmful products without a clear guidelines and
regulation to monitor their use. Even with EPA regulation on VOCs it is typically to prevent
environmental harm rather than health complications to humans in the indoor environment. Further, due to their presence in most finishes and furnishings it would be difficult to gauge how many harmful pollutants are in each individual house as the levels would vary significantly depending on where the materials are from and how many exist in each home.
SOLUTIONS:
There are usually a few options when you are trying to solve a human health problem;
prevention, mitigation or a combination of the two. The obvious solution to harmful direct exposures like VOCs, solvents and other chemicals would be prevention, to simply avoid using products which contain them. During the design phase, architects and contractors could work to choose building materials which contain little or no pollutants. With the current building methodology and materials which are typically used in Hawaiian residential architecture this would be incredibly difficult to achieve. Even with the proper design and concentrated effort on the part of design and building professionals to reduce the amount of negative health exposures in the building materials, it would still be nearly impossible to control inhabitant behaviors or commercial interests. Home owners may install or change their own finishes or buy furnishings which contain the pollutants and without a real system is in place to monitor and regulate these compounds and chemicals, homeowners will
continue to be at risk of exposure. Even though it is partially the purpose of this dissertation to choose building materials and construction methods which reduce harmful exposures, it is important to still have a design which can mitigate the potential contamination of the indoor environment.
We must also remember that not all building materials and finishes are equal in the levels of harmful pollutants that they expose people to in the air of the indoor environment. There are a few variables which can change the number of contaminants, given the same material and same VOC or
chemical. These are ventilation, temperature and humidity. Put simply, the indoor climate can and will affect the level of harmful indoor air pollutants.
Ventilation is probably the greatest determining factor as to the level of harmful exposures indoors. It does not require much specialized knowledge to understand that if the indoor air is exchanged with the outdoor air (in the case of natural ventilation) then the pollutants are temporarily reduced or removed from the indoors.65 The amount of air changes per hour (ACH) is usually the unit of measure which explains how often this air is exchanged, the more ACH the more often the air is refreshed. While there are some places in the world where the outdoor air is more polluted than the indoor air and in those cases different types of mechanical filtration and ventilation systems may be required, Hawaii generally has good air quality and we will be focusing on naturally ventilated spaces.
More information will be presented regarding ventilation later in this project.
Temperature and relative humidity are also important indoor climatic factors which effect VOCs and other chemical pollutants from being released into the air.
We must only look to the name of this category of
compounds to understand why. Volatile organic compounds are unsurprisingly, volatile. In chemistry, volatility is the propensity of a substance to vaporize or turn into a gas.66 While volatility usually is used to explain how liquids vaporize into gases, in many cases VOCs which off gas from solid building materials do so through a process of sublimation.
This is when substances vaporize from a solid to a gas without first turning into a liquid.67 VOCs, by definition have high vapor pressures at room temperature and therefore a low boiling point. Given that temperature and vapor pressure are factors in volatility and sublimation, it is known that VOCs will off gas more when temperature rises. For example, the boiling point of the VOC formaldehyde is –2 °F this means a material containing this VOC will off gas even at normal
65 Kang Hu and Qun Chen, “Ventilation optimization for reduction of indoor semi-volatile organic compound concentration based on the variational principle,” Building and Environment, 94 (October, 2015).
66 Canadian Centre for Occupational Health and Safety, “MSDS – An Explanation of Common Terms,” P96-1E, (Revised, 1996), accessed September 24, 2016 http://ccinfoweb.ccohs.ca/help/msds/msdstermse.html.
67 Merriam-Webster’s Online Dictionary, s.v. “sublimate,” accessed October 5, 2016 https://www.merriam-webster.com/dictionary/sublimation.
Figure 6.5: Air Purifying Respirator
Source: U.S. Centers for Disease Control and Prevention, 2005,
https://commons.wikimedia.org/wiki/File:Air-Purifying_Respirator.png accessed October 13, 2016
room temperatures. When the temperature increases so does the substances vapor pressure and therefore more off gassing occurs.68
Relative humidity also influences VOCs and off gassing.69 While not as directly correlated as temperature, relative humidity does play a role in the transport of VOCs around the indoor
environment.70 Humidity probably helps the transport of vaporized VOCs by capturing the compounds in their gaseous state in the saturated air making it more difficult to remove the contaminants from the indoor space. Humidity also plays a role in the movement of VOCs from the air to surfaces which inhabitants may encounter.
It should be noted that different VOCs and chemicals have different levels of volatility, minor increases in temperature and humidity will not affect all materials in the same way. However, the important point is to remember that controlling the indoor climate is not only for human comfort but to control the off gassing of any building material and overall VOC level in a home.
68 Peder Wolfoff, “Impact of Air Velocity, Temperature, Humidity and Air on Long-Term VOC Emissions from Building Products,” Atmospheric Environment, vol. 32, no 14/15, (1998). Pp. 2659-2668.
69 P. Markowicz and L. Larrsson, “Influence of relative humidity on VOC concentrations in indoor air,” Environmental Science and Pollution Research International, 5772-9 (April, 2015), accessed November 3, 2016 doi:10.1007/s 11356-014-34678-x
70 Ibid.