Air and Water Pollution
Prevention and Control Engineering
Indoor Air Pollution in Residential Structures
Bill Bardin
RPI – Fall 2013
Professor Gutierrez-Miravete
Air and Water Pollution Prevention and Control Engineering
RPI – Fall 2013
Professor Gutierrez-Miravete
Bill Bardin
Table of Contents
INDOOR AIR POLLUTION IN RESIDENTIAL STRUCTURES
1
INTRODUCTION
1
PRIMARY POLLUTANTS OF CONCERN
3
RADON
VOC’S
PM’S
3
3
5
MITIGATION
6
RADON
VOC’S
PM’S
6
7
9
CONCLUSION
9
REFERENCES
10
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Air and Water Pollution Prevention and Control Engineering
RPI – Fall 2013
Professor Gutierrez-Miravete
Bill Bardin
Indoor Air Pollution in Residential Structures
Introduction
Many of us realize, from first hand experience, that the outside air can be unhealthy and
polluted, but fewer people know that the indoor air quality can be even worse. Everybody
wants to believe that our home is a clean and healthy environment for our families.
However, an increasing body of research is pointing to very serious health concerns from
both short term and long term exposure to pollutants such as volatile organic compounds
(VOC’s), particulate matter (PM), and biological agents such as mold, pollen, animal
dander and bacteria. These pollutants are generated both inside the house and brought in
from outside. Problems can arise when homes are sealed to reduce infiltration of outside
air to increase heating or cooling efficiency. This can result in the build up of pollutants
from inside the home such as VOCs, radon gas, Carbon Monoxide (CO), etc. The
exchange of outside air is necessary to insure a safe interior environment and is also
inevitable no matter how well a home is sealed. So, the contaminates found in a home's
air will be a mix of particles from outside and those generated from within the home.
There are many varieties of pollutants in our homes. Ones from outside include industrial
sources, construction sites, combustion sources, pollen, and numerous other pollutants
that are found in the ambient air. Urban areas tend to have higher levels of pollutants due
to the general nature of the surrounding air. Conversely, homes in rural settings tend to
have lower levels of pollution from ambient sources. This does not preclude rural
dwellings from having high levels of pollutants if they are downwind of polluted cities,
coal or oil fired power plants, or industrial areas. Pollutants are also generated by all
kinds of normal indoor activity ranging from cooking, showering, and walking across the
carpet, pets, burning candles, wood stoves and fire places. In many homes, with forced
air heating and cooling systems, these pollutants are spread throughout the house.
Allergens, mold spores, bacteria, particulate matter (PM), VOC’s, Radon are all actively
moved throughout the structure either by the installed HVAC system, independent fans,
or just an open window.
The primary concern with these and other pollutants is the physical effect they have on
the inhabitants. Many of the pollutants present both short and long term concerns. The
primary route for entry into the body is through the lungs and although larger particles
are usually trapped in the upper respiratory system, many of the smaller particles and the
gases penetrate deep into the lungs where they can enter the bloodstream and have
devastating effects. I do not intend to address cigarette smoke in this paper, as it is too
large an issue and can easily be controlled in the indoor environment by eliminating it as
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Air and Water Pollution Prevention and Control Engineering
RPI – Fall 2013
Professor Gutierrez-Miravete
Bill Bardin
a pollutant. As a note, smoke released from cigarettes, cigars and pipes is composed of
more than 3800 different substances. Airborne particulate matter is 2–3 times higher in
homes of smokers.(1)
The Environmental Protection Agency (EPA) estimates we spend as much as 90 percent
of our time inside, mostly in our homes. In this study I will be taking a look at three main
areas of indoor pollution, radon, VOC’s, and PM’s and possible methods of controlling or
eliminating them.
Primary Pollutants of Concern
Radon
Radon gas has a significant pollutant potential in this part of the United States. Radon is
routinely found in granite deposits but can be found almost anywhere in the United
States. Even granite counter tops have the potential to contain Radium although the
National Safety Council has stated that is unlikely.(2) The average national indoor radon
level is 1.3 pCi/L. The average indoor radon levels of Fairfield County, as determined by
radon test results from Air Chek, Inc, is 3.9 pCi/L with 29% of the test sites yielding at
least 4.0 pCi/L and above, the EPA action level.(3)(4) Radon has long been associated with
an increased risk of lung cancer. The Radon itself is not actually that harmful, but it
decays into radioactive elements such as Polonium, which is potentially lethal. These
elements of decay have an electric potential that allows them to attach to duct particles in
the indoor environment. As these duct particles are inhaled, they carry along with them,
the products of radon decay. These elements emit alpha radiation, which has the potential
to damage cells in the lung. Alpha radiation can disrupt DNA of lung cells. This DNA
change can be the first step to cancer. Radon is the most common cause of lung cancer
among non-smokers and causes about 21,000 U.S. deaths a year, more than drunk
driving. (5)
VOC’s
Volatile organic compounds (VOCs) are comprised of carbon containing substances that
evaporate or off-gas at ambient temperature. A number of building and household
materials can be sources of VOCs. Carpeting, carpet backing, and adhesives; fabrics;
wood products that use certain glues (phenolic and isocyanates), finishes, and waxes in
the manufacturing process; and vinyl and engineered wood flooring and wall coverings
may all release VOCs into the air. Most of us don't think of furniture when assessing
indoor air quality, but if it is made from treated wood or particleboard, it probably
contains formaldehyde, which is the same chemical used in funeral homes as a preserving
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Air and Water Pollution Prevention and Control Engineering
RPI – Fall 2013
Professor Gutierrez-Miravete
Bill Bardin
agent. Short-term effects of exposure to formaldehyde vapors include eye, nose and
throat irritation as well as coughing, skin rashes, headaches, dizziness, nausea, vomiting
and nosebleeds.
Oriented strand board (OSB), used as sheathing in residential construction is comprised
of wood chips or strands of wood, combined under heat and pressure, with a phenolic or
isocyanate, typically methyl diphenyl diisocyanate (MDI), as the binder to form sheets or
structural components(6). The Structural Board Association reports that, when processed
properly, OSB panels are virtually free of phenol, formaldehyde and unreacted MDI.
Persons with isocyanate sensitivity may experience respiratory issues in some cases when
handling OSB, especially when exposed directly to sawdust from cutting operations.
The list of potential VOC sources in our homes seems endless. Cleansers, disinfectants,
waxes, glues, cosmetics, dry cleaning products, paints, varnishes and preservatives can all
contain VOCs. Gasoline, kerosene and other fuels also contain VOCs. VOCs are also
found in cigarette smoke and pesticides. Exposure to elevated levels of VOCs may cause
irritation to the eyes, nose, and throat. Headaches, nausea, and nerve problems can also
occur. Sensitivity to VOC’s varies from person to person. While one person may not
show ant effects from relatively high levels, other people may be hypersensitive and
exhibit symptoms at very low levels. An example of this hypersensitivity to VOC’s is the
sensitivity of some people to perfumes worn by coworkers. Even small amounts produce
a reaction that inhibits a person’s ability to function effectively.
Although VOCs are found in both outdoor and indoor settings, the levels of VOCs found
outdoors are usually much lower than those found indoor. This is the result of building
houses tighter and tighter in an effort to save energy and not properly addressing the
consequences. This can be most prevalent in homes of moderate age. These homes were
not designed to be “tight” because energy was not a critical factor at the time they were
constructed. As energy efficiency and conservation has moved to the forefront, there has
been a big push to “seal and insulate” these middle aged homes. As they are sealed and
air infiltration is reduced, energy use goes down but the indoor air quality can suffer as
the pollutant levels rise. Depending on what is used to seal a home, we can actually
introduce VOC’s to the interior environment. Great Stuff®, a single component
polyurethane expanding foam, contains isocyanates and a flammable solvent(7) as the
blowing agent. As we seal the windows and doors and cracks we are effectively pouring
VOC’s into the interior of our homes. A house that doesn’t have enough ventilation does
not allow potential indoor pollutants to escape.
Recent events with drywall imported from China have highlighted the effects of
compounds in construction materials that can have an adverse effect on indoor air quality.
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Air and Water Pollution Prevention and Control Engineering
RPI – Fall 2013
Professor Gutierrez-Miravete
Bill Bardin
Chinese drywall refers to drywall imported from China (from approximately 2001 to
2007), which contains extraneous metals and minerals, such as sulfur, strontium and iron.
Under certain environmental conditions (typically warm, humid climates), the drywall
will emit sulfur gasses. These gasses create a noxious odor and corrode copper and other
metal surfaces, which can damage one's air conditioner, electrical wiring, copper
plumbing, appliances and electronics. Chinese drywall can also cause adverse health
effects, which are primarily irritant and temporary in nature. Long-term health effects are
unknown. The gasses emitted from Chinese drywall corrode copper and metal
surfaces. Corrosion of electrical wiring may hamper the effectiveness of smoke
detectors, which presents a safety concern. Low level arcing has also been observed in
some homes with Chinese drywall, which could cause an electrical fire.(8)
PM’s
If you live in or near a city, power plant, major roadway or busy street the level of
particulate matter can be increased greatly in the outdoor environment and that typically
translates into increased levels of PM’s indoors as well. A number of studies show a link
between particulate pollution and cardiovascular disease, respiratory disease, and cancer.
Studies of children show particulate pollution can retard lung function growth similar to
cigarette smoking with predictable consequences for lung health later in life(1). The
effects come from both long term and short-term exposure. Studies show in the shortterm mortality rates from a variety of causes rise on days with high particulate pollution.
Since the brachial passages of young children and infants are significantly smaller than in
an adult, a small percentage reduction in the passage opening due to irritation can have a
significant impact in their ability to breathe. Pets, especially those that spend part of their time outdoors can contribute to poor indoor
air quality in a significant way. All pets with fur, shed no matter what kind they are. They
also produce dander. If these pets are allowed free range in the house the problem is
prevalent throughout the entire house. Pets that are allowed to sleep in bedrooms or on
beds will increase the potential exposure. Other uninvited guests in your home such as
dust mites, insects, or rodents also pose a problem. If they are present, they will defecate
inside. When the feces dries up it can become dust-like and possibly airborne and
transported throughout the house if it is equipped with a forced air ventilation system.
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Air and Water Pollution Prevention and Control Engineering
RPI – Fall 2013
Professor Gutierrez-Miravete
Bill Bardin
Mitigation
Radon
Radon mitigation is a fairly simple process if done during the construction of a home.
The installation of a series of PVC drainage pipes in the gravel bed, which are run to
collector pipe(s) outside of the foundation footings, will provide a means of extracting the
radon from under the basement or crawlspace slab. By imbedding the PVC drainage pipe
in the gravel, air can be extracted from the entire area under the slab because of the
porosity of the stone. A continuous impermeable membrane is then placed on top of the
gravel and piping system. This membrane should be installed before, and extend beyond
the footings to insure complete isolation of the radon capture bed from the interior of the
home. This effectively isolates the radon-laden air from the interior of the home. A
standard concrete slab floor is poured on top of the membrane. The piping from under the
slab is combined into one or two stacks that are equipped with small fans. The purpose of
these fans is to provide a slightly negative pressure under the slab and insure proper,
continuous extraction of the radon gas. It should be noted that the presence of radon
could be very sporadic. Your neighbor may not have any significant amounts while your
home could be exposed to significant levels. Even when building in areas where the
probability of radon is very low, one needs to be diligent and monitor any rock or crushed
stone that is being shipped in for foundation and drainage purposes.
In existing structures there are a number of methods that can be used to mitigate the
exposure. In an existing structure it is usually a combination of methods that must be
used to correct the problem. One very common method for dealing with radon in existing
homes is to drill a hole or holes through the basement or crawlspace floor and insert a
large, 3 – 4”, PVC pipe. The pipe extends below the slab into the rock bed and is sealed
tightly where it penetrates the floor slab. This pipe is usually routed out of the house and
then extended up the side of the house to a point above the roofline. A small fan is
installed in the pipe, either in the home or at an outside location. This fan is designed to
run continuously and in many cases has a battery backup in the event of a power failure.
In some cases, multiple radon evacuation systems may be needed depending on the
condition of the sub-slab construction and/or the size of the slab being evacuated. In
conjunction with a sub-slab evacuation system, all cracks, seams and joints in the slab are
sealed with elastomeric sealers. In addition, walls, especially concrete block walls are
sealed on the inside with impermeable sealers. In extreme cases, basements and
crawlspaces are sealed from the rest of the structure and a continuous ventilation system
is installed to vent radon-containing air to the outside. In these extreme cases, an air-toair heat exchanger is usually employed to minimize the heat loss.
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Air and Water Pollution Prevention and Control Engineering
RPI – Fall 2013
Professor Gutierrez-Miravete
Bill Bardin
VOC’s
Generally, the air outside naturally dilutes VOCs from sources such as power plants,
automobiles, industrial operations, agricultural spraying, etc. Outside exposure to
increased levels of VOCs tends to be more common in urban areas from sources like bus
or automobile exhaust. It is highly unlikely that any of us can live, work, or go to school
in an indoor setting that is completely free of VOCs. However, there are steps that can be
taken to reduce exposure to VOCs.
In reality, the best way to improve indoor air quality with respect to VOC’s is to not
allow them in the first place. Increasing ventilation by simply opening the windows and
doors to provide fresh air from the outside can do this. Installing exhaust fans in
bathrooms and kitchens and properly maintaining air filter systems will also help with air
quality. Use products that contain low levels of VOCs whenever possible. Many products
clearly advertise, in fact use it as a selling point, that their product contains low levels of
VOC’s. The California Air Resources Board (CARB) mandates that low, and in some
cases, no VOC products must be used in the state. Many companies formulate
specifically for California sales, and have another formula for the rest of the country.
Some companies manufacture a CARB approved product for sale throughout the Unites
States and some companies just don’t sell their products in California. Combustion
fumes can also be a source of VOCs, so it is important that furnace, chimneys and
stovepipes are in good condition. It is important to reduce the use of household
chemicals. Eliminate the VOC containing cleaning agents and consider using cleaning
products that do not contain VOCs such as baking soda, vinegar or borax. If you have
clothes dry-cleaned, air the clothes outside before bringing them into your home. Some
interior paints are solvent-free or contain very low levels of VOCs.
If you have to use VOC containing products it is important to read and follow the
directions for use on the label. Most products today come with or provide a link to a
Material Safety Data Sheet (MSDS) which contains valuable information about the VOC
content, personal protective equipment needed for safe use and proper methods of
disposal. To minimize indoor exposure to VOC’s, chemical products should not be stored
in the living space.
There are systems available that will scrub VOC’s from indoor air but they typically are
designed for commercial applications and are rarely adapted to residential constructions.
The simplest of the systems uses activated carbon filters that are installed in a way very
similar to standard air filters. The life of the media can be relatively short necessitating
replacement on a regular basis, which can result in significant costs. Some plants are
good at removing VOC’s from the air but this creates a potentially high maintenance
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Air and Water Pollution Prevention and Control Engineering
RPI – Fall 2013
Professor Gutierrez-Miravete
Bill Bardin
system that requires constant attention. There are some air cleaners that use ultraviolet
(UV) light to destroy pollutants in indoor air. These air cleaners are called ultraviolet
germicidal irradiation (UVGI) cleaners and photo catalytic oxidation (PCO) cleaners.
UVGI cleaners contain UV lamps that may destroy biological pollutants such as viruses,
bacteria, allergens, and molds that are airborne or growing on HVAC. PCO cleaners use
UV lamps along with a catalyst, which reacts with the light. They are intended to destroy
gaseous pollutants by converting them into harmless products, but are not designed to
remove particulate pollutants. These are not widely used primarily due to the cost and
maintenance requirements. Both UVGI and PCO air cleaners are used in conjunction
with standard particulate filters.
When buying new furniture, choose cabinets made from solid, untreated wood. Wherever
possible, phase out your particleboard furniture, such as shelving and office desks, and
replace them with pieces made of untreated natural materials.
Even the mattresses that we spend 1/3 of our life on contain considerable amounts of
synthetic and chemical-based foams, plastics and artificial fibers, and most box springs
are made with chemically treated wood and chemical adhesives. Next time you buy a
mattress consider one made from more health-conscious materials, such as natural fibers
and untreated wood. In the meantime, a mattress cover made of barrier cloth can help
isolate a chemical-laden mattress.
Look to organic fibers wherever possible. Cotton, one of the most used “natural” fibers in
the world can contain hazardous chemicals. Cotton production consumes 25% of the
pesticides used in the world today and processing them to be “easy care” can introduce
toxic chemicals like formaldehyde that can off-gas for long periods of time. Switch to
organic fibers and natural dyes to reduce VOC’s.
Even paints that are low or zero VOC don’t guarantee there won’t be issues. Very often
additives are introduced at the site to improve flow for the application process. These
additives can introduce VOC’ as well.
Eliminate synthetic carpets wherever possible since they can be a large source of VOC
emissions and act as a "sponge" for chemical and biological pollutants. Anything tracked
into the home is deposited on the carpets and will slowly release over time. This includes
pesticides from the lawn, oils from the garage and almost anything else you walk
through.
Whenever possible use sustainably harvested natural materials, which are gentler to the
planet and can actually help promote healthier ecosystems, which can result in less need
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Air and Water Pollution Prevention and Control Engineering
RPI – Fall 2013
Professor Gutierrez-Miravete
Bill Bardin
to treat the air and water.
PM’s
There are two basic types of air filtering devices in use today for removal of particulates
in a home, mechanical air filters and electronic air cleaners. Mechanical air filters remove
particles by simply capturing them on filter media that is typically disposable. There are a
number of different media that fit into this category from the simple flat cardboard
framed filter to pleated filters that significantly increase the surface area to high
efficiency particulate air (HEPA) filters. The second category, electronic air cleaners
such as electrostatic precipitators use a process called electrostatic attraction to trap
charged particles. Air is drawn through an ionization section where particles obtain an
electrical charge. The charged particles then accumulate on a series of flat plates called a
collector that is oppositely charged.
Both of these system can be very effective, especially the higher efficiency models. There
is a maintenance requirement with either of these systems; one requires regular filter
changes that could be quite extensive if you live in a dusty area or one with high outdoor
PM levels. The electrostatic air cleaner is highly effective but again, requires regular
maintenance and is susceptible to environmental conditions. The electrostatic unit also
has a power requirement, which adds to the operating cost.
Conclusion
It is certainly possible to construct a home that is extremely airtight. Those currently
attempting to build extremely “tight” homes typically conduct air tightness tests at
multiple stages during the construction. While it is getting easier, and more cost effective
to build tighter and tighter homes as builders gain experience and materials evolve, this is
only a portion of the equation. While an airtight home could be built it would be almost
impossible to live in. We need to create a balance between all the components that make
up a home. While windows let in light, in the winter they also let out a lot more heat than
a wall. We can create a warm, clean and healthy indoor environment in the winter but as
soon as spring rolls around, the doors and windows open and in comes the pollen, bugs,
humidity and whatever is in the outside air. Here in Connecticut we typically have five
months, November through March when most people do not open their windows and are
running their heating systems on a regular basis. This is when you want a tight house the
most but this is also the time when even small changes in the indoor air quality are
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Air and Water Pollution Prevention and Control Engineering
RPI – Fall 2013
Professor Gutierrez-Miravete
Bill Bardin
noticed. The candles during the holiday season, all the cooking, all the people. Even
something as simple as an air freshener can introduce multiple VOC’s that can have an
effect on the occupants. Each one has a detrimental effect on the quality of indoor air.
Conversely, summers in Connecticut can be extremely challenging when trying to
maintain a stable indoor air quality. There are typically four to six weeks where air
conditioning is necessary. The rest of the time the doors and windows are open and
whatever is out there, is coming in, VOC’s and PM’s from the lawn care next door,
chemicals from the pool, anything you could imagine. The idea of controlling the indoor
air quality is literally “out the window”.
It is apparent the adage “there’s no such thing as a free lunch” applies here. You can have
great energy efficiency but you can also have a significant maintenance cost associated
with it. A third concern is the habitability of the home from a social point of view. If
maintaining a healthy home requires too much manual intervention it is less likely to
happen, especially over the long term. Automating the needed adaptations can be
effective but it doe introduce another layer of complexity (and maintenance costs).
It is readily apparent that making a home as tight as possible will significantly reduce
energy costs, but that energy efficiency can come at a price, indoor air quality and social
habitability issues. In the end, build it as tight as you can, ventilate it right, change your
buying habits and to a certain extent your lifestyle, and you will see the benefits in an
energy efficient home. (If you are thinking about building a “tight” home, you are already
changing your lifestyle.)
Reference
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
Strategies and technologies: Controlling indoor air Quality 23 July 2009 Anthony Bennett
http://www.nsc.org/Pages/NationalSafetyCouncil'sRadonHotlineOffersHomeownersTestKits.aspx
http://county-radon.info/CT/Fairfield.html
http://www.ct.gov/dph/lib/dph/environmental_health/radon/pdf/Basic_Radon__Facts.pdf
http://www.upi.com/Health_News/2013/01/08/Radon-causes-more-deaths-than-drunkendriving/UPI-11821357623380/#ixzz2iUAxHjQ5
http://osbguide.tecotested.com/pdfs/en/tb114.pdf
http://greatstuff.dow.com/pdfs/consumer_safety.pdf
http://www.chinesedrywall.com/index.html
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