A heavy layer of smoke has settled back over Fort McMurray, Alta., choking off oxygen, blocking out the sun, and painting the sky an eerie shade of orange.

Changing wind conditions and higher temperatures in the area have forced the evacuations of even more residents and oil workers, and brought thick, particle-filled smoke over the city.

The air quality became so bad, it endangered firefighters and crews working to restore services in the city.

Alberta's Air Quality Health Index readings are normally measured on a scale of one to 10. The reading in Fort McMurray hit 38 on Tuesday morning before later settling down to 13, which is still considered “very high risk.” Experts forecast that air quality in Fort McMurray will remain above 10 tonight and tomorrow. That’s because the thick smoke of the fires is leaving dangerous levels of carbon monoxide, sulphur dioxide and particulate matter in the air.

Dr. Karen Grimsrud, the chief medical officer of Alberta Health, said Monday she’s expecting those readings to remain high for the next few days, given what forecasters see ahead for weather and wind patterns.

The fires are doing more than just choking out oxygen; they are painting the sky rarely-seen shades of red and orange, creating what looks like a vibrant sunset in the middle of the day.

Some workers in the area have uploaded footage to YouTube and Facebook, showing the smoke-filled air and the sky turned dark red.

The bad air is not only forcing more evacuations, it’s also hurting work crews trying to restore utilities inside the city. Grimsrud says those workers are being told to wear disposable or cartridge-style masks or respirators, and limit their time outdoors.

“It’s an irritant in your lungs. So it’s going to cause you significant breathing problems, without a respirator, you’re taking in that air,” she said.

“Even if you don’t have any underlying diseases, it’s still going to make a difference in your ability to breathe.”

With a report from CTV Edmonton’s Bill Fortier