Radon is a naturally occurring radioactive gas that forms from the breakdown of uranium and radium found in the earth’s crust. It is entirely imperceptible to human senses, being colorless, odorless, and tasteless. This means a home can harbor dangerous concentrations without any obvious warning signs. Specialized testing is the only way to determine if this unseen hazard is present in an indoor environment.
The Invisible Nature of Radon Gas
Radon is a noble gas, meaning it is chemically inert and does not readily react with other substances in the air. This lack of chemical reactivity prevents it from creating any odors or being detected by smell or sight.
Radon-222, the most stable and common isotope, has a half-life of 3.82 days, allowing it time to migrate from the ground into buildings. As a gas, it is invisible; although heavier than air, it does not settle into a visible layer. Because this radioactive gas is undetectable, dedicated testing is necessary to protect occupants.
How Radon Enters Indoor Spaces
The primary source of indoor radon is the soil and rock beneath a building’s foundation, where uranium and radium naturally decay to produce the gas. Radon gas moves upward through the ground, driven by the difference in air pressure between the soil and the interior of a house. This pressure difference, often lower inside the home, effectively draws the gas inward through a process called advective flow.
Any house can be affected, regardless of its age, design, or foundation type (basement, crawl space, or slab-on-grade). Radon infiltrates through structural weaknesses in the foundation. These entry points include cracks in concrete floors, construction joints, gaps around utility penetrations, open sump pits, floor drains, and pores in hollow block walls.
Radon can also enter a home through well water, especially when the water is agitated during activities like showering or washing dishes. Once trapped inside a building, the gas can accumulate to harmful concentrations, particularly in lower levels like basements where ventilation is often poor. Since soil composition is the main factor, high radon levels can be found in homes right next door to others with low levels.
Essential Methods for Radon Detection
Testing is the only reliable way to measure the concentration of radon gas inside a home. Radon levels are measured in picocuries per liter of air (pCi/L), a unit that quantifies the rate of radioactive decay. The Environmental Protection Agency (EPA) recommends that action be taken to reduce radon levels if the concentration reaches or exceeds 4.0 pCi/L.
Radon testing falls into two main categories: short-term and long-term.
Short-Term Testing
Short-term tests typically run for 2 to 90 days. They provide a quick snapshot of the radon concentration and are often used for initial screening or during real estate transactions. These kits, which include charcoal canisters or alpha track detectors, are available for do-it-yourself use and require laboratory analysis.
Long-Term Testing
Long-term tests measure levels for 90 days or more, providing a more accurate average of annual radon exposure. This extended period accounts for natural fluctuations in concentration caused by seasonal weather changes, such as snow cover and ground saturation. Professional testing services using continuous radon monitors offer real-time data and are often the most comprehensive option.
Health Risks Associated with Radon Exposure
The hazard from radon comes from its radioactive decay products, known as progeny, rather than the gas itself. Once inhaled, the gas is mostly exhaled. However, these solid decay products—such as polonium, lead, and bismuth—attach to dust particles and become lodged deep within the lungs. These particles continuously emit alpha radiation, which directly damages the DNA of the cells lining the lung tissue.
This cellular damage, accumulating over years of exposure, increases the risk of developing lung cancer. Radon exposure is the second leading cause of lung cancer in the United States, following only cigarette smoking. It is also the leading cause of lung cancer among people who have never smoked.
The risk is significantly magnified when radon exposure is combined with smoking, creating a synergistic effect that raises the cancer risk higher than either factor alone. The EPA estimates that radon exposure is responsible for approximately 21,000 lung cancer deaths annually in the U.S., including nearly 2,900 among non-smokers.