What is Radon?

Radon is a naturally occurring chemically inert gas. It comes from the radioactive decay of uranium in soil that enters a building directly beneath and a few meters around the foundation. Radon can enter all types of buildings, and the main concern is when radon has the chance to accumulate. Tight homes do not cause radon; they increase the likelihood of radon lingering instead of escaping through ventilation.

The Health Risk

There are over 20,000 annual deaths just in the United States directly related to radon decay product’s exposure. There is no safe level of radon.

Radon is an unstable atom and will break down into a family of elements called radon decay products. These decay products attach to the surface of dust and become logged in the lungs. When exhaled, the radon leaves, but the decay products remain in the lungs, which are known to cause lung cancer. The chance of lung cancer increases significantly for smokers as they may already have damaged, weaker lungs. The EPA suggests remediation at 2.0 pCi/L but makes the actionable level of 4 pCi/L when tied to a real estate transaction. 

How Radon Enters Buildings

There are many ways radon can enter a building. The main reason is that buildings naturally create vacuum effects. Vacuums are caused by either temperature-induced stack effects or mechanical exhaust systems. There are typically four ways radon enters a structure: Vacuum effects, water, diffusion, and emanation.

The Vacuum Effect (90+% of radon)

Mechanical Devices such as Stove Fan and Bathroom Fans

An excellent way to visualize is to imagine a bathroom fan or over-the-stove fan turned on and creating negative pressure in the home. If it is winter, the windows and doors in the house are closed tight so a lot of air is being drawn from the cracks and holes in the basement foundation to the radon-laden soil below. If your basement is a dirt crawl space, it can have a much more significant accumulation of radon gas.

Fireplaces

A fireplace will draw a small amount of air from your home and create enough vacuum effect to increase radon amounts.

Radon from Water

Radon can dissolve in groundwater and readily degases when brought into a building, causing an additional amount of radon to enter the air. On average, 10,000 pCi/L in water will add one pCi/L into the air. The health concern is from the additional amount of radon in the air, not ingestion.

Diffusion

Where radon diffuses from the soil through a slab due to concentration gradients. This is typically a small contributor.

Emanation

Emanation is when a building material contains uranium or radium and is brought into a building. This is also a low contributor but deserves attention.

Source: 

https://sciencedemonstrations.fas.harvard.edu/presentations/radons-progeny-decay