The blood of the five people who died of carbon monoxide poisoning in Porter Creek last year was full of deadly carboxyhemoglobin when the bodies were found.

In one case, they reached levels as high as 99 per cent.

A toxicologist testified Thursday in the inquest surrounding the deaths of Bradley Rusk, 45, his wife, Valerie, 37, along with their children Gabriel, 13, and Rebekah, 11.

They died in their Centennial Street home in January 2012 along with 47-year-old family friend Donald McNamee.

Carboxyhemoglobin is a mix of carbon monoxide and hemoglobin in the blood stream. High levels prevent oxygen from being carried through the body.

Toxicologist Walter Martz concluded that all five people living in the house had died from carbon monoxide poisoning.

Martz told the jury that the ratio of carbon monoxide in the blood is measured in percentages. A heavy smoker would have a carboxyhemoglobin of about 10 per cent.

Levels at 40 per cent or higher are considered severe. Levels at 60 per cent would lead to unconsciousness and likely eventual death.

McNamee's level was at 78 per cent, something that is "not survivable,” Martz said.

Bradley Rusk's blood reached 61 per cent, and his wife's 81 per cent.

The children's levels were found to be even higher.

Rebekah Rusk's carboxyhemoglobin level was 99 per cent. "Almost saturation,” the toxicologist said.

Her brother Gabe was at 94 per cent, "clearly a lethal level,” Martz said.

Had they been able to get medical help or even get outside their rented house, things would have improved, Martz said.

Removing carbon monoxide from the blood takes about three to five hours in outdoor air, he said.

Oxygen delivered at a hospital can cut that time down to 25 minutes.

Both the Rusks and McNamee had been complaining of flu-like symptoms in the days leading up to their bodies being found.

They missed work and school, staying home.

Experts have blamed a crumbling blocked chimney filled with ice and debris for trapping the deadly gas in the 40-year-old A-frame house.

The jury also heard from Marc Perreault, the chair of an oil-fired appliances working group formed later in 2012.

Perreault's group recommended better public awareness, better education and training and a legal act specifically targeting oil-fired appliances.

Perreault said he was surprised by the lack of public education in the Yukon. Many people told them they hadn't had their heating systems serviced in years.

They also heard from a lot of homeowners and landlords who didn't know what to look for when it came to safe heating and didn't know what their responsibilities were.

But Perreault's group was not the first to complete a report on oil-fired appliance usage in the territory and he will not be the only person to speak on the topic.

Though the inquest was on track to wrap up Thursday, family members have asked to call one more witness: Rod Corea.

Corea completed multiple reports for the Yukon government years before the Rusks and McNamee died. He was scheduled to give testimony by phone today.

The reports showed the vast majority of oil appliances in the territory are not up to code standards.

"As stated in all four previous reports, self-regulation has failed to provide the level of safety and environmental protection that is the aim of the B139 Fuel Oil Code,” Corea writes in the conclusion of his final 2010 report.

"The evidence — especially from the current survey regarding problems at re-inspected sites and new installations — strongly indicates that action must be taken as soon as possible to prevent an incident causing harm to person or property.”

Territorial court judge John Faulkner is presiding over the proceedings as a coroner.