Five men are “very lucky” to be alive after high levels of carbon monoxide from an idling vehicle left three of them unconscious and the other two in “varying states,” according to Edmonton Fire Platoon Chief Gregg Menard.

Four of the five individuals were transported to hospital in critical condition after the incident on Sunday.

Three have now been released and the other two are also expected to also recover, according to one of the victims.

First responders who arrived at the home Sunday said a car had been left idling in the garage for more than 40 minutes and the door to the garage was half open, allowing the gas to build up inside the home.

Edmonton Deputy Fire Chief Russell Croome told CTV News Channel that the carbon monoxide level in the home when firefighters arrived measured 900 parts per million -- 18 times the acceptable level.

Carbon monoxide is an odourless, colourless gas that can be deadly when inhaled by humans or animals. It is produced whenever fuel is burned in automobiles, stoves, grills, fireplaces and furnaces.

Edmonton EMS Public Safety Officer Stuart Brideaux said the risk of carbon monoxide poisoning increases in winter because people are spending more time indoors and using furnaces.

Symptoms of exposure to high levels of carbon monoxide include headaches, dizziness and nausea.

The best way to protect against carbon monoxide poisoning is to install a battery-powered detector in your home, and check and replace the batteries whenever you change your clocks in the fall and spring, according to the U.S. Centers for Disease Control and Prevention.

With a report from CTV Edmonton’s Susan Amerongen