CALGARY, Alberta (Reuters) - Some 2,000 residents of wildfire-ravaged Fort McMurray, Alberta, will not be able to return home this week as planned because of the risks posed by debris and contaminants including "caustic" ash, Alberta Premier Rachel Notley said on Monday.
The city of 90,000 people was evacuated in early May as an uncontrolled wildfire ripped through some neighborhoods, destroying about 10 percent of the city's homes.
It also forced around a dozen oil sands projects in the region to halt more than a million barrels per day of crude oil production.
With the 580,000 hectare wildfire now burning away from populated areas, provincial government officials are planning to let residents start returning to Fort McMurray on June 1 in a phased re-entry program.
However, Notley said ash, soil and air tests carried out in Abasand, Waterways and Beacon Hill - three of the worst-hit areas of the city - showed that around 500 homes are unsafe for habitation, even though they were spared by the blaze.
"Unfortunately I have to report today that the outcomes of these tests indicate that undamaged homes in certain neighborhoods are not immediately safe for reoccupation," Notley said, adding residents may not be able to return until September.
The province's chief medical officer, Dr. Karen Grimsrud, said tests showed the ash left behind after the fire was caustic and could cause skin and respiratory irritation and burning, while heavy metals like arsenic were also present.
"We need to ensure that residents and their families are protected when crews begin removing debris that has toxic and potentially dangerous chemicals in it," she said.
Alberta has extended its state of emergency for an additional 28 days until the end of June as around 2,000 firefighters, including 300 just arrived from South Africa, continue to battle the blaze.
The wildfire is now burning to the east of Fort McMurray and has also moved away from oil sands projects. Suncor Energy, Canada's largest oil and gas producer, said on Sunday that it expects to partially restart operations at its facilities by the end of the week.
Editing by Alan Crosby