The dangers of the potentially fatal underground gas radon are being highlighted in one of its Welsh hotspots.
Warnings over the dangers of radon are highlighted in Flintshire
People living in Flintshire are being targeted first in the all-Wales campaign because it is particularly prone to the gas.
New properties built in the county must have built-in radon protection under strict new building regulations.
But there is concern that, along with other areas, people do not appreciate the dangers of the gas, which can cause lung cancer at certain levels.
Free testing is being offered to people living in the county to encourage them to take steps to deal with the gas in their homes.
Research carried out in Wales over the past 20 years to identify areas most at risk and shows that Flintshire, which is on the carboniferous limestone which gives off the gas, has "areas of concern".
"The assembly is concerned that the message about the health implications of radon has not had sufficient impact to encourage residents to have their properties tested and to take remedial action where appropriate," Flintshire councillors were told in a report.
"Previous campaigns with offers of free testing have only had a limited take-up."
In Flintshire there was only a 20% take-up when 10,000 homes were targeted.
"There also appears to be insufficient knowledge among the medical profession, builders, surveyors and solicitors," the report went on.
"This can result in a lack of expert help or advice being available to people who are considering having work done or who are buying or selling property in affect areas."
Radon is seen as a silent threat: you cannot see, hear, feel or taste it.
It is formed when atoms of uranium-238 decay. Radon will also decay, and, if it is inhaled, will emit alpha particles that can damage the internal lung surfaces.
The alpha radiation dislodges the electrons that hold DNA together which can trigger a series of chemical changes in the body that lead to cancer.
The radon concentration in the average UK home is about 20 becquerels per cubic metre.
Action to deal with the problem is recommended when the concentration reaches 200 becquerels per cubic metre.
The most effective way to deal with radon is to fit an air pump to a property to vent the gas into the atmosphere.
This is the first time that a major campaign, with free testing, has been launched and it aims to identify the majority of the 10,000 homes in Wales with radon concentrations at or above the action level, and to encourage people to tackle it.
Funding has already been allocated to Flintshire County Council to undertake the work and officials say the campaign should have a significant impact on the improving the safety of the environment for a large number people living in the county.