Radon Gas

Introduction, Concerns, and Mitigation Methods

What is Radon?

Radon is a radioactive gas that occurs naturally beneath the earths surface. It is colorless, tasteless, odorless, and completely undetectable to humans.

    • 9 times heavier than air
    • Some studies link radon exposure to childhood leukemia.
    • At one time, the gas was used for radiotherapy cancer treatment
    • Below its −96 °F freezing point, it emits bright yellow luminescence
    • It used to be used in spas, when people thought it might confer medical benefits
    • Some studies indicate children are at higher risk from radon exposure than adults
  • 1400’s

    Recognition of an unusually high incidence of a fatal lung disease in miners.

    “Lung disease”, almost 500 years later is discovered to be lung cancer, which was reported to be the cause of up to 70% of death in miners.

  • 1898

    Radium was discovered by Marie Curie.

    Marie Curie was a Nobel Prize winning scientist. She’s also where we get the measuring term “Curie” in Pico Curies.


  • 1900

    Radon was discovered by Friedrich Ernst Dorn

    Radon, originally named Niton after the latin word for “shining”, was discovered while studying radium’s decay chain.

  • 1904

    Chemists William Ramsey and Robert Whytlaw Gray are able to isolate Radon.

    In doing so they measure it’s density and determine Radon to be the heaviest gas known to man.


  • 1949

    U.S. Public Health Service concerned about the potential hazard of miners.

    Measurements in ~40 mines in Utah and Colorado and confirmed high concentrations averaging over 2,500 pCi/L.

  • 1960’s

    ANSI takes action.

    The American National Standards Institute develop a standard to regulate radon exposure for miners. This standard is still in effect in mines in the United States.


  • 1984

    Watras Incident

    At a time when exposure was impossible due to the plant still being under construction, Stanley J. Watras, a construction engineer at the Limerick nuclear power plant in Pottstown, Pennsylvania, set off the alarm at a radiation monitor installed to make sure workers weren’t going home with unsafe levels of radiation on their bodies.

  • 1988

    International Agency for Research on Cancer listed radon as a known human carcinogen


Health Risks

Radon LevelOut of 1,000 non-smokersSame risk as…
20 pCi/l36 people would get lung cancer35 times the risk of drowning
10 pCi/l18 people would get lung cancer20 times the risk of dying in a home fire
8 pCi/l15 people would get lung cancer4 times the risk of dying in a fall
4 pCi/l7 people would get lung cancerThe same as dying in a car crash
Radon LevelOut of 1,000 smokersSame risk as…
20 pCi/l260 people would get lung cancer250 times the risk of drowning
10 pCi/l150 people would get lung cancer200 times the risk of dying in a home fire
8 pCi/l120 people would get lung cancer30 times the risk of dying in a fall
4 pCi/l62 people would get lung cancer5 times the risk as dying in a car crash

The number of radon deaths each year as estimated by the EPA and Surgeon General.

Cancer is a disease in which some of the body’s cells grow uncontrollably and spread to other parts of the body.

Laboratory studies have documented that an alpha particle can cause both single- and double-strand DNA breaks and can produce indirect genotoxic and nongenotoxic effects on both traversed and neighboring non- traversed cells. Experimental animal exposures to radon clearly demonstrate that radon decay products cause lung cancer.

When the atoms of an element have extra neutrons or protons it creates extra energy in the nucleus and causes the atom to become unbalanced or unstable. Radon is unstable and therefore spontaneously disintegrates into decay products.

Responsible for over 95% of the radiation dose to the lungs, Polonium-218 and Polonium-214 are solid metals with an electrostatic charge. This charge allows them to attach to other airborne particles such as dust where it can then be inhaled into lung and attach to the epithelium.

While the half-life of radon is 3.8 days, the half life of Polonium 218 & 214 is about 2.5-3 minutes. This means that if you could fill your cup up with radon gas then 3.8 days later half of it would’ve decayed into RDP’s.

2.5-3 minutes later when Polonium-218 & 214 decay they release ionizing radiation causing mutations in the lung epithelial cells’ DNA.

Cells respond to the induced damage and attempt to repair it, but sometimes the damage cannot be repaired or is misrepaired, which may lead to mutations. The modifications induced by low levels of radiation dose may be transmitted to daughter cells and may lead to uncontrolled cell growth and consequently cancer, the health effect of primary concern in the context of radiation.

Radon Pathways


Foundation wall cracks


Basement windows


Sump/Drain tile systems


Floor/Wall penetrations


Cracks in the slab


Water supply

Foundation floor and wall cracks

Radon gas can be pulled through cracks in the foundation.

  • Monitoring wall and floor surfaces for cracking.
  • Sealing as cracking occurs and monitoring for worsening.
  • The floor to wall joint should be sealed if not part of a dewatering system.

Water Supply

Radon can be absorbed by water underground where it can then be pumped into homes.

  • Radon in water is rarely a concern for public water supply, however in some instances problems have been found in well water.
  • If a radon system is installed and levels are still testing high, your measurement specialist may suggest testing a water sample.
  • When water is a pathway for radon, levels will be higher in kitchens and bathrooms where the water is agitated and gas is released.

Wall/Floor Penetrations

Radon gas can be pulled through unsealed penetrations in the walls and floor slab.

  • Unsealed penetrations should be sealed and maintained to prevent radon gas entry.
  • Sealant tends to break down over time and should be monitored for cracking or deterioration.

Drain Tile/Sump Systems

Drain tile systems provide an efficient way for radon to be pulled into the structure through underground perforated piping.

  • Sump pits should be sealed with an air tight lid to prevent radon gas entry.
  • Pump discharge lines may penetrate the foundation wall where sealing is also necessary.

Basement Windows

Due to their close proximity to grade level and perhaps sub-grade, radon can be pulled into the structure through basement windows.

  • Radon vent terminations should be 2′ above any operable window within 10′ to prevent re-entry.
  • Windows should be appropriately sealed and monitored.

Open Soil

Open soil provide an unrestricted radon gas entry.

  • Floor drains that drain to soil should have a one way valve installed or be sealed off.
  • Shower boxes should be backfilled with sand or gravel and sealed off with either cement or mortar.
  • Crawlspaces should have a vapor barrier installed at the soil to seal off the ground from the interior of the structure.

Foundation Type

Any structure can have a source, pathway, and driving force to allow for radon accumulation. This includes new construction, old construction, and foundations of all kinds whether on a basement, crawlspace, or slab.

Driving Forces

Wind Pressure
  • Air pressure is greatest on the windward side of the structure.

  • Air pressure is least on the leeward side of the structure.

  • Pressure can be decreased if the leeward side of the structure has more openings, surface area, larger leaks, etc.

Ventilation Pressure
  • Gas furnaces that draw combustion air from the interior.

  • Ventilation fans such as kitchen, bathroom, and whole house fans.

  • Clothes dryers and central vacuum systems.

Stack Pressure
  • Difference in interior/exterior temperatures.

  • Height of the structure.

  • Air leaks within the structure.

As radon is pulled into the structure it begins to accumulate at the lowest level due to its dense characteristics. As accumulation increases radon concentration levels rise until they meet a point of equilibrium.

Mitigation System Types

Radon Resistant New Construction

Passive System

Sub-Slab Depressurization

Drain Tile Depressurization

Sub-Membrane Depressurization

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