The deadly build-up of the silent killer gas, radon, in Irish homes is linked to 250 cases of lung cancer every year.
One non-smoking couple from Kerry both lost their lives to lung cancer because of the fatal levels of the invisible gas in their home.
Over-exposure to naturally occurring radioactive gas is second only to smoking as the leading cause of lung cancer in Ireland.
RTE's new flagship science show, 10 Things to Know About, investigates how the invisible, odourless gas occurs naturally in soil and generally dissipates harmlessly outdoors. However, in some places, it can leak into the house through the foundations and build, unseen, to potentially deadly degrees.
Senior scientist at the Environmental Protection Agency, Dr David Fenton, said the naturally occurring radioactive gas can be fatal. "Radon gas in homes is linked to 250 lung cancer cases each year, so it is something people need to be concerned about."
He told how one Kerry couple lost their lives while unknowingly living in their carcinogenic home which had deadly levels of the gas.
"It's a tragic story because the householders unfortunately died of lung cancer.
"One of the doctors treating them felt it was so unusual for two non-smoking people living in the same house to have lung cancer, so he said to get the radon levels checked. We found this huge level of radon in the house."
He said their North Kerry house had the highest levels ever measured by the EPA in a home in Ireland.
"It (had) 49,000 units of radon. Bearing in mind a safe level is below 200, this house had very, very high levels of radon in it."
The World Health Organisation has categorised radon as a carcinogen, in the same group as asbestos and tobacco smoke. The cancer-causing gas has no colour, taste or smell.
He said: "Your senses are blind to it. Radioactivity is quite natural. It exists in nature. You get doses from the sun and from space when you fly in aircraft.
"The radon is coming from radioactive elements in the ground called uranium and radium. It comes naturally out of the ground and can build up in people's houses to high concentrations."
Radon levels can be checked by buying a test kit for your home. If the levels are over 200 units then action should be taken. Radon levels can be cut easily by installing a pump which sucks the gas from under the floorboards and expels it outside.
Grandmother Christine Keaney in Galway told how she was shocked to discover a reading eight times the advised safe level when she tested her home for the gas on the advice of her son-in-law.
She said: "It was equal to eight chest X-rays per day. I had no idea. It was frightening."
On advice from the EPA, she used a sump pump to suck the gas out and expel it outside. When she re-tested the levels, they were back to the safe level.
'10 Things to Know About' will be shown on RTE One tomorrow at 8.30pm