Radon Gas Mitigation Solutions in Brief

While I do not personally perform radon mitigation, I wanted to share in brief what is generally entailed. The cost in the Dallas area for reducing radon below the EPA action limit of 4.0 pCi/l varies depending on the construction / size of the house and how high the levels are. In general, you can expect an estimate of anywhere from $2000 – $5000.

It is suggested that the solution follow the ASTM E-2121 standard for lowering radon and that information can be found in detail here:


While homes that contain excessive radon can be found in every state in the nation, many people (such as in Texas) are not aware that it is a problem, nor is testing / mitigation required by Texas law as of this writing. However it is not unusual for some relocation companies to require testing for radon gas first as a condition of a real estate purchase.

Bear in mind that radon levels do fluctuate with weather conditions and home ventilation, so before investing in a mitigation expense, it may be worth testing more than once.

The main idea behind mitigation is to ventilate the excess radon (which is heavier than air) to the outside so as to minimize impact to occupants. The method by which this is done depends on whether you have a basement (rare in the Dallas/Ft. Worth area) have a pier and beam or slab on grade foundation.

For slab foundations, sealing the interior spaces from the ground is generally not enough, and often a soil suction system is required to actively draw the radon out via a vent pipe and specialized fan. These systems are generally referred to as active soil depressurization, sub-slab depressurization or just simply soil suction.

In some cases, a heat exchanger or ERV (Energy Recovery Ventilator) can recover some of the energy lost in the process of exchanging the vented radon to the outside with fresh air.

For pier and beam foundations (houses with crawlspaces) you can cover over the base soil with a special heavy duty plastic sheet whose underside connects to a ventilation system similar to the one described above in a method known as sub-membrane suction.

Sub-membrane Suction Radon Mitigation

Sub-membrane Suction Radon Mitigation

MERV (Minimum Efficiency Reporting Value) Ratings and Filters

You generally cannot place a True HEPA filter in your air furnace because of the flow restriction would place too heavy a load on the blower unit. But you can get a higher efficiency MERV filter that can give some of the benefits of better filtration and indoor air quality without unnecessarily straining the HVAC unit or restricting the air flow.

But to get a good balance between clean air and not damaging your HVAC unit, consult with an air conditioning professional and / or consult with the manufacturer regarding the recommended MERV filter range that can be used in your particular model. Also, the higher your MERV rating, the more often you may have to check and/or change it as it will tend to clog faster.

MERV ratings are numbers that generally measure the quality of an air filter, but can be hard to understand without some context and this chart is a handy reference.


MERV Chart Air Quality

MERV Rating Chart with application comparisons   *Note – the pm size designations listed should be in um or microns

Allergens Air Purifiers

Air Purifier Guide to Size Ranges of Allergens in microns (millionth of a meter or um)

The MERV rating is a filter standard established by ASHRAE  (American Society of Heating, Refrigerating and Air-Conditioning Engineers) but when you shop for a filter online, you may also find references to MPR and FPR.

MPR (Micro-Particle Performance Rating) is a standard used by 3M (notably the Filtrete series) that rates filter performance with respect to the ability to screen out sub-micron (less than 1 um) particles, but can be confusing when comparing to MERV. Note that less than a micron is on the low end of the PM2.5 Fine particle range as designated by the EPA. (0.5 – 2.5 microns)

FPR (Filter Performance Rating) works a little like MERV numbers (but on a 4 – 10 color coded scale) developed by Home Depot for filters they sell including Honeywell.

To get a relatively close comparison, the following chart may be useful when shopping for a more suitable HVAC filter.

MERV MPR FPR Ratings Compared and Explained from www.airfiltersdelivered.com

MERV MPR FPR Ratings Compared and Explained from www.airfiltersdelivered.com (not endorsed by ScanTech)

While this chart is useful, it is not guaranteed to completely stop all of the biological and inorganic contaminants that are listed. Your mileage may vary.

MERV Filter Models


Composition of Dust Particles and Particulate Matter in The Air

When I test for PM2.5 and PM10 which are Fine Particle and Coarse Particle designations used by the EPA, I am often asked what is the nature of this particulate matter. These may also be referred to as TSP (Total Suspended Particulate) or RSP (Respirable Suspended Particulate) matter. While it is very difficult to tell exactly what it is without microscopic analysis and will vary depending on the environment, an educated guess can be made based on what sources are nearby and the potential contribution of those sources based on typical size regimes.

Possible sources are pollen, toxic mold spores, smoke, bacteria, pet dander, construction dust, etc.

There are some useful reference charts that not only talk about the ranges of certain pollutants, but also give an indication of different filtration mediums which are relatively effective in removing these contaminants.


Particulate Matter in Air Quality

Air Filtration with Regard to Particle Size

*NOTE – HEPA (High Efficiency Particulate Air) filters are typically rated at 99.97% efficiency for particles of 0.3 um or larger. At this time, I am not sure that a HEPA filter will remove more than 95% of particles which are 0.01 microns in size as this chart seems to imply.

Also, beware of filters and vacuum cleaners which claim to be “HEPA-like”, “HEPA-type” or “99% HEPA” as these are not true HEPA filters and are often inferior in quality with regard to air filtration efficiency.

BTW – the term DS efficiency mentioned in the Pleated Filter (40% DS ) refers to Atmospheric Dust Spot Efficiency which measures how well a filter removes staining dust from the air.


HEPA Air Filtration Particle Ranges

HEPA Filtration Particle Chart


Particle Filtration Size Chart HEPA vs. ULPA

Particle Filtration Size Chart HEPA vs. ULPA


Characteristics of Particles and Particle Dispersoids

Characteristics of Particles and Particle Dispersoids

This is a fairly technical diagram for general reference use.


Origin of Dust Particulate Matter

Origin of Dust Particulate Matter

Water Filtration Particle Sizes and Composition for Contamination Control

For aqueous media such as drinking water, here are some reference charts which compare ranges of relevant pollutants, and suggest different filtration mediums which are relatively effective in removing these contaminants.

Particle sizes thin film membrane filtration

Particle sizes thin film membrane filtration

*NOTE – there is an error in this chart at the very top. Instead of pm which is traditionally for picoMeters, the correct unit should be in um or microMeters. (Microns)


Water Filtration vs Particle Size

Water Filtration vs Particle Size


Water Filtration Particle Size Chart Common Contaminants

Water Filtration Particle Size Chart Common Contaminants

VOC (Volatile Organic Compounds) Air Contaminants and Health

Reference list on the plastics, pesticides and other solvent vapors which contribute to poor air quality, allergies, illness, airborne toxicity and carcinogenic risk.



VOCs – can be classified by boiling points (VVOC, SVOC, VOC and POM) or by chemical structure such as aliphatic / aromatic hydrocarbons or functional R group composition such as oxygenated / halogenated hydrocarbons. Low volatility, high potency organic compounds and those with high polarity can be expected to preferentially take on the form of solid particles rather than remain in a vapor phase. Settled house dust or respirable suspended particles (such as those in the PM2.5 and PM10 size regimes) can also serve as reservoirs for both vapor phase SVOCs and POMs by adsorption. Exposure can be through inhalation, digestion or direct skin contact.

May come from a variety of sources including building materials, pesticides, air fresheners / aerosols, carpeting and linens. (including drapes)

Ozone (O3) ppm

Sulfur Dioxide (SO2) ppm

Nitrogen Dioxide (NO2) 5-35 ppb

Nitric Oxide (NO)

Carbon Monoxide (CO) 0 – 30+ ppm

Carbon Dioxide (CO2) 400 – 1000 + ppm (acts as a respiratory stimulant / increases breathing rate)

Polychlorinated Biphenyls (PCBs) found in electrical equipment

Aldehydes – Because of their solubility in aqueous media and high chemical activity due to the carbonyl functional group, aldehydes tend to be strong mucous membrane irritants affecting both the eyes and upper respiratory tract. This irritation tends to reflexively reduce respiratory rates which will also decrease oxygen intake. Significant examples include acrolein, (major eye / throat irritant in smoke and smog) glutaraldehyde (a biocidal used in medical, dental sterilization as well as duct cleaning and carbon-less copy paper) and acetalaldehyde which is a relatively weak irritant, though it is a proven animal carcinogen and found predominantly in combustion by-products such as cigarette smoke and automobile exhaust gas.

Formaldehyde (HCHO)  0 – 0.5 ppm

Fungicide – Pentachlorophenol, (PCP – used to prevent wood decay)

Pesticides: Organochlorines (chlordane, heptachlor – termiticides, p-dichlorobenzene for moth control)

Pesticides: Organophosphates such as dichlorvos, chlorpyrifos, diazinon, malathion can cause acute neurotoxicity but dichlorvos (used in bug bombs, dog and cat flea collars) has been phased out since 1988 due to potential for animal carcinogenicity except for chlorpyrifos (used for termites, cockroaches and fleas) and diazinon which was phased out in 2000 because of potential exposures to children.

Herbicide 2,4-D risk factor for non-Hodgkin’s lymphoma

Biocides – hypochlorites, glutaraldehyde, alcohols, o-phenylphenol, quaternary ammonium compounds, mercury (Hg) in latex based paint until 1990.

Plasticizers (phthalic acid esters) used to make vinyl more flexible and commonly found in floor coverings. Tends to leech out over time. Some evidence that it contributes to asthma.

Radon (Rn-222) picoCuries / liter



Allergens (dust, pollen, dust mites, pet dander)

Bacterial Endotoxins

Fungal Glucans and Mycotoxins from Mold

Total Suspended Particulate (TSP) Matter or Suspended Particulate Matter (SPM) and Respirable Suspended Particles (RSP) measured in particles / cubic foot or micrograms / cubic meter. The size regimes classified by the EPA are Fine particles PM2.5 which are 2.5 microns in diameter or less and Coarse particles PM 10 which are generally 2.5 – 10 microns in diameter.


Heavy Metals – Lead and Mercury in latex paint



Respiratory / Mucous Membrane Irritation


Hypersensitivity Pneumonitis

Humidifier Fever

Legionnaire’s Disease





Candles & Incense (particularly if burned during pregnancy) can contribute to risks of childhood leukemia. Incense may produce benzo-alpha-pyrene, polycyclic aromatic hydrocarbons (PAHs), and sinapaldehyde. (nasal carcinogen)

Propane fueled forklifts and burnishers (Carbon Monoxide)

Control of Formaldehyde (HCHO) and VOCs in Indoor Air Quality

One of the first issues to address for pre-existing construction is proper selection of materials that have low VOCs and formaldehyde content (UF or Urea-Formaldehyde) and/or that outgas (release the noxious vapors) relatively quickly. Low emission products include:

  • Low VOC paints
  • Low VOC carpeting (though carpets tend to have inherent issues with collecting/releasing dust)
  • Other mastic (waterproofing putty) products that have low levels of 4-phenylcyclohexane (4-PC) which produces a characteristic odor
  • Pressed wood products that have low formaldehyde (HCHO) levels
  • Formaldehyde-free varnishes and lacquers
  • Softwood plywood
  • Oriented-Strand board
  • Decorative gypsum board
  • Hardwood panels
  • Pressed woods with PF (Phenol-Formaldehyde) resin release less HCHO than UF resins

You might want to AVOID:

  • Medium-Density Fiberboard (MDF) sometimes used in cabinets, furniture and doors
  • Hardwood plywood paneling
  • Particleboard
  • Pressed wood products with UF
  • UF-based Acid Cured Finishes
  • Homes insulated with UFFI (Urea-Formaldehyde Foam Insulation) though this is unlikely to be an issue
  • High humidity (keep between 40 – 50 % RH)
  • Occupying the home or property until a proper out gassing period has passed – preferably during hotter weather
Formaldehyde Emissions from variou Construction Materials

Formaldehyde Emissions from various Construction Materials

Then having an outgas period before occupation is good when possible. Preferably during hot, humid weather which tends to accelerate the exit of gaseous residues from the building materials. If you have an existing wood material that is emitting formaldehyde, then the can be treated with scavenging coatings or encapsulated with vinyl materials.

ASHRAE Ventilation Guidelines 2013

ASHRAE Ventilation Guidelines for Acceptable Air Quality – 2013

Another critical factor is having adequate ventilation, particularly during the initial outgas period. Many homes and multifamily dwellings are often built rather “tight” as a response to the desire for energy conservation and reducing moisture intrusion. If it is not a security issue, keeping the windows open even a crack on opposite sides to create a flowing cross-draft can assist out-gassing as well as opening chimney dampeners.

Factors in formaldehyde levels:

  1. Composition of building materials (formaldehyde potency in manufacture)
  2. Loading factor (amount of material in exposed surface area and volume)
  3. Material age
  4. Adequate ventilation taking into account occupancy and room size
  5. Environmental conditions
Indoor Air Exchange Rate Per Hour Table

Indoor Air Exchange Rate Per Hour Table


Formaldehyde Levels Indoor Air Quality

How Formaldehyde Levels Decrease Over Time

The use of sorbents (gas absorbent materials) such as activated charcoal can be used to remove relatively high molecular weight VOCs such as toluene, benzene, xylene and methyl chloroform.

For lower molecular weight (MW) materials such as formaldehyde (HCHO), ethylene, and acetaldehyde then potassium permanganate, (KMnO4) activated alumina or specially impregnated charcoal are better choices than regular activated charcoal.

Other special air cleaners may also be used – consult ScanTech for further information.

Indoor Air VOCs: Volatile Organic Compound Contaminants

Volatile organic compounds make up a very large group of chemical substances and are often sub-classified by boiling point temperature ranges which gives an idea of how likely it is to be found in liquid, solid, gaseous forms (or possibly more than one state) at various temperatures. The levels found in breathable air and how they affect air quality are strongly correlated with the boiling points. In general, the lower the boiling point, the higher the concentration that will be present in the air.

VVOC (Very Volatile Organic Compounds)   Boiling points:    less than 0 C to 100 C

VOC (Volatile Organic Compounds)  Boiling points:   50 C  – 260 C

SVOC (Semi-Volatile Organic Compounds)   Boiling points   260 C – 380 C                                        (includes many biocides)

POM (Particulate Organic Matter aka Solid Organic Compounds)  Boiling points exceeding 380C includes PAHs (polycyclic aromatic hydrocarbon compounds)

Carbon Monoxide Safety Levels and Indoor Air Quality

An important component of indoor air quality testing is measurement of abnormal levels of carbon monoxide.

Carbon monoxide (CO) is a result from all forms of combustible sources, from smoking and wood fires to propane and fuel-powered automobiles. Poisoning of a human subject comes in two forms – short term exposure to high levels which can cause severe illness or death, or longer term exposures at lower levels which may cause chronic symptomatology.

While actual death is relatively rare, there are far more cases that occur with sub-lethal exposures over a broad range of concentrations. (30 – 100 ppm by volume or ppmv) At the lower end (40 – 60 ppmv) headache and low levels of fatigue, and at higher levels (75 – 200 ppmv) nausea, vomiting and especially sleepiness.

Symptoms with Different Blood COHb Levels

Symptoms with Different Blood COHb Levels

Carbon monoxide and oxygen both bond to hemoglobin in the blood and will compete with each other over binding sites, but CO has the advantage as it binding sites have an affinity or preference of binding with CO that is 200 times greater than O2. (atmospheric oxygen) The result is decreased oxygen carrying capacity in the blood with the consequent neurological symptoms of oxygen deprivation as listed above as well as reduced oxygen to other body tissues. It also binds to intracellular proteins such as tryptophan oxidase, cytochrome oxidase,  myoglobin, and dopamine hydroxylase which may cause extra-vascular effects.

The result of CO combining with hemoglobin is to form carboxyhemoglobin. (COHb) Exposure to CO can be evaluated by measurement of the levels of COHb in the blood which is typically less than 1% for unexposed individuals. This is the % amount of blood hemoglobin bound with carbon monoxide. Cigarette smokers typically have a level of 3% – 8%. OSHA has a permissible exposure limit (PEL) of 50 ppmv over an 8 hour time-weighted average (TWA) in which case an individual would have a COHb level of approximately 5%. At 100 ppmv, it would be over 10%.

COHb Levels Resulting from Exposure Duration

COHb Levels Resulting from Exposure Duration

Even low level carbon monoxide exposures can cause issues in compromised human subjects such as those with cardiovascular disease. The lowest level at which COHb can show as a physiological symptom is 3 %- 4 % COHb. At 6 % COHb, arrhythmia may be induced in exercising patients with coronary artery disease with a risk of sudden death. There is also evidence that suggests that carbon monoxide exposure may contribute to atherosclerosis.

Studies have shown that those with flu-like or neurological symptoms had COHb levels of 10% or greater. (24% and 3 % respectively. Sub-acute carbon monoxide poisoning commonly goes unrecognized and is not diagnosed because it mimics other conditions and is present at the residence / workplace – not the doctor’s office.

Those at higher risk include pregnant women, young children, the elderly, individuals with conditions that already compromise O2 availability, and those that use certain medications and drugs.

For a discussion of CARBON DIOXIDE poisoning which is an entirely different phenomena, see the post here:

New Homes and Carbon Dioxide Levels: The Overlooked Indoor Air Quality Health Hazard

If you live in the Dallas / Fort Worth, Houston or Austin metropolitan areas and suspect carbon monoxide / dioxide poisoning or other indoor air quality issues, then contact ScanTech Technical Consulting for an evaluation.