Lung cancer is always a disturbing diagnosis. For a patient who has never smoked or had to put up with second-hand smoke, worked with asbestos or knowingly come in contact with radioactive material, such a diagnosis is not only disturbing, but perplexing as well.

How can you contract lung cancer if you've avoided all the major risks?

Exposure to radon gas could do it.

On July 21, 2009, a United Nations committee said radon gas in homes is directly linked to a small risk of lung cancer. Based on the report, the World Health Organization and other agencies are in the process of revising their recommendations on maximum radiation doses for homes and workplaces.

According to an earlier report by a government committee that was set up to review Canada's radon guidelines, lung cancer caused by exposure to radon gas killed 1,589 Canadians in 2001. It accounted for more deaths that year than accidental poisonings, homicides and drownings — combined.

What is radon?

It's a colourless, odourless gas. It is also radioactive. It's formed by the disintegration of radium, which is produced when uranium decays.

I don't come in contact with uranium. Why should I be concerned?

Radon gas and its byproducts occur naturally everywhere — in soil, water and air. Rarely does it occur in concentrations that you need to worry about. However, radon gas can accumulate in confined spaces such as basements and crawl spaces in homes. If the levels are high enough, it can be a health hazard.

As radon decays, it produces decay products called "radon daughters." They also decay rapidly and emit alpha particles. Your skin is normally enough to protect you from these particles. But when they become attached to dust and you breathe them in, you could be at risk.

What levels are considered safe?

It depends what country you live in. The levels that had been considered safe in Canada were substantially higher than in the rest of the world — as much as five times higher. They were equivalent to the exposure considered safe for someone who spent their working hours in a uranium mine.

But Health Canada reviewed those standards and recommended the level considered safe be reduced to at least match what's considered safe in the United States.

Radon gas levels are measured in a unit called the becquerel (Bq). One becquerel is described as one event of radiation emission per second. It is an extremely small unit. The old Canadian standard considered 800 Bq per cubic metre to be an acceptable level.

On June 8, 2007 — 15 months after the Federal-Provincial Territorial Radiation Protection Committee received a report recommending tightening the guidelines — the federal government announced a new standard of 200 Bq per cubic metre. That's a level considered safe by most industrialized countries, including Russia, the Czech Republic and China. The United States recommends a level of 150 Bq per cubic metre.

The Canadian report that recommended tighter guidelines noted that as people make their homes tighter and more energy efficient, they may also be inadvertently raising radon levels. The report suggested the government should explore a system of grants and subsidies to help homeowners with the costs of testing and cleaning up radon gas.

It also recommended that private homes undergo mandatory tests for radon levels as a condition of sale, as is the case in several American states. The new guidelines did not address that recommendation.

The report by the UN Scientific Committee on the Effects of Atomic Radiation, or UNSCEAR, used 20 studies in homes where concentrations of radon were very low, rather than relying on estimates of radon risk that were extrapolated from studies of uranium miners who were exposed to high levels of the gas.

"We can see a risk," in homes, Wolfgang Weiss, UNSCEAR's vice-chairman, told a news conference. "It is small, but it is certainly there."

How does radon get into my home?

Is your house airtight? Very few are, especially older homes — and especially if the foundation or any of the walls are built with concrete blocks, which are particularly porous to radon. But the gas can also seep in through basement floor drains, cracks in the floor or foundation, and under the furnace base. Radon can also become trapped in well water and released into the air when the water is used.

How do I know if there is radon in my house?

Where radon can enter homes. (Associated Press)Call a professional. They'll come to your house and take samples of the air in your basement. The most common method is to use a canister that contains activated charcoal. Activated charcoal absorbs radon gas. The unit will be left in your home for several days before being sent to a lab for analysis. You will receive an average radon level for the time the unit was left in your home.

The soil around your home can also be tested if it's suspected that there could be high levels of uranium.

What if tests show higher than acceptable levels of radon in my home?

You'll need to have the problem fixed. The federal government recommends that if the radon concentration in your home is greater than 600 Bq per cubic metre, work needed to reduce levels below 200 Bq per cubic metre should be completed within a year. If levels are between 200 and 600 Bq per cubic metre, the work should be done within two years.

The report recommending lower radon levels suggested that the federal government should offer some assistance to homeowners who need to have work done on their homes. The government's revised guidelines did not address that subject.

What can I do to minimize the risk of radon exposure?

If there are unacceptable levels of uranium in the soil around your house, the soil should be removed and replaced with clean fill. But this is extremely rare.

Steps you can take inside your home include:

• Sealing all cracks and openings in the walls and floors of your basement as well as around drains and pipes.
• If your basement floor has a sub-floor, make sure it is ventilated.
• Replace an earth floor with a concrete floor.
• Increase the ventilation in your basement or other enclosed space where radon may accumulate.
• Paint basement floors and walls. Use a sealant on top of the paint and add polyethylene sheets to basement walls.

What are the risks of developing lung cancer if I am exposed?

Not huge. But they're far greater if you are a smoker. At the proposed new stricter radon guideline, your risk of developing lung cancer increases by 17 per cent if you smoke and are exposed to radon. That's on top of your increased risk because you smoke. If you don't smoke, you have a two per cent chance of developing lung cancer if you are exposed to radon at 200 Bq per cubic metre.