Radon is a naturally occurring radioactive gas that forms from the decay of uranium found in soil, rock, and water. This gas is undetectable by human senses, being colorless, odorless, and tasteless. Understanding its characteristics is important because prolonged exposure to elevated indoor radon levels poses a significant health risk, primarily increasing the likelihood of developing lung cancer.
Understanding Radon’s Density
Radon is significantly heavier than air. Its atomic mass is 222, making it one of the densest known gases at standard temperature and pressure. For comparison, the average molecular weight of air is approximately 29 g/mol, composed primarily of nitrogen (about 28 g/mol) and oxygen (about 32 g/mol). Radon is roughly 7.5 times heavier than air.
This substantial density means that radon gas does not readily disperse upwards like lighter gases. Instead, it tends to settle and accumulate in lower elevations, especially in enclosed spaces without adequate ventilation. Its weight influences how it behaves once it enters a building, causing it to concentrate near the ground level.
Implications for Indoor Accumulation
Radon’s density directly influences its behavior within buildings, leading to its accumulation in specific areas. Its density causes it to collect in the lowest parts of a structure, such as basements, crawl spaces, and ground-level rooms.
Radon enters homes primarily through openings in the foundation that are in contact with the soil. Common entry points include cracks in concrete slabs, foundation walls, floor drains, sump pits, and gaps around utility penetrations like pipes and wires. The gas is drawn into the home due to a slight negative pressure difference between the indoor air and the surrounding soil.
Protecting Your Home from Radon
Given radon’s invisible and odorless nature, testing is the only reliable way to determine its concentration within a home. Homeowners can use either short-term tests, which provide results in a few days, or long-term tests, which measure radon levels over several months for a more accurate annual average. These testing kits are readily available and typically involve placing a small device in the lowest living area of the home for the specified period.
If testing reveals elevated radon levels, specifically at or above the Environmental Protection Agency’s action level of 4 picocuries per liter (pCi/L), mitigation is recommended. The most effective and common mitigation strategy is active soil depressurization, also known as sub-slab depressurization. This system involves installing a pipe through the foundation slab and connecting it to a fan that continually draws radon gas from beneath the house and vents it safely outside, preventing its entry and accumulation indoors.
Supplementary measures can also help reduce radon levels. Sealing major cracks and openings in the foundation can limit entry points for radon, though sealing alone is rarely sufficient to lower high levels below the action threshold. Improving general ventilation within the home can also help dilute radon concentrations, but it is not a substitute for a dedicated mitigation system when levels are significantly elevated.