Fort McMurray may well be the most heavily policed city in the country Wednesday when the first wave of residents begin returning home, four weeks after a wildfire called "the beast" forced 90,000 people to flee houses and businesses with only a few hours' notice.

Supt. Rob McCloy, the officer in charge of the Wood Buffalo RCMP detachment, says traffic is the biggest challenge police expect to face tomorrow. (Terry Reith/CBC) The RCMP will have more than 200 officers in the region, patrolling the streets of Alberta's oilsands capital or the highways leading into the city.

"Make no mistake, the RCMP will protect this community from harm," Supt. Rob McCloy said at a news conference Tuesday.

Highway 63, which links the city to the rest of Alberta, will be opened to traffic at 8 a.m. MT, said Scott Long, executive director of the Alberta Emergency Management Agency.

He warned those headed home in the first wave to make sure they have food, water and full fuel tanks, since gas stations in the region will have limited supplies.

More than 30,000 detailed information booklets have been delivered to homes throughout the city, said Long, who urged people to read them carefully and follow the instructions.

Residents will start going home to Fort McMurray on June 1 as planned, the province announced Tuesday. (CBC) Alberta officials insist most areas of the city are safe for people to live in, and that there is no evidence that ash from heavily damaged areas has contaminated other neighbourhoods. The province's chief medical officer of health, Karen Grimsrud, said air quality in the city was rated a one on Tuesday morning. The air quality measurement, which is normally reported on a 1-10 scale, had spiked as high as 51 in the days after the fire.

"Personally, I would feel quite comfortable to go back," Long said. "In my mind, the biggest risk would be people not following the advice and recommendations ... that we've outlined."

Long said Zone 1 residents who are scheduled to return Wednesday will have plenty of time to get back to their homes to start cleaning up.

"We do not want endless rows of vehicles on Highway 63 that are going to cause an immediate traffic snarl," he said.

Premier says 5 criteria met

Alberta Premier Rachel Notley said in a statement the five conditions established for the safe return of residents have all been met.

Those five criteria were:

Wildfire is no longer an imminent threat to the community.

Critical infrastructure is repaired to provide basic service.

Essential services, such as fire, EMS, police and health care, are restored to a basic level.

Hazardous areas are secure.

Local government is re-established.

"I am pleased to report today that these conditions have been met," Notley said, "and voluntary phased re-entry will begin June 1 as planned, with the exception of the neighbourhoods of Abasand, Beacon Hill and Waterways."

Grimsrud said soil and ash tests have been completed in most parts of the city. She was asked to respond to comments by one Wood Buffalo councillor who has said repeatedly the city is not safe to return to.

"I look at this sort of neighbourhood by neighbourhood," Grimsrud said. "And when you look at the neighbourhoods of Abasand, Waterways and Beacon Hill, and the amount of debris that's there as a result of these homes being destroyed, that's where the risk is, right?

"We knew that the ash was going to be contaminated, so it's the amount of ash, the amount of the destruction to me, is one of the key components when considering whether to return."

Some may not be home until September

People whose homes were not destroyed in Abasand, Beacon Hill and Waterways will not be able to return until all the debris in those areas has been cleared away, Grimsrud said. The plan is to have people return to those areas by September.

"In the other zones, you do have isolated areas where there were homes that were destroyed," Grimsrud said. "But they have been fenced off. I've also recommended for homes around those destroyed areas, that (residents) be taken to see their home with a municipal officer and then assessed for whether there's any risk to them at all."

Conditions in the region will be assessed each day and, if the situation changes, the re-entry schedule may be adjusted, she said.

Despite the significant work that has been done, Fort McMurray is not the city that residents left behind a month ago, the premier said.

A boil-water advisory remains in effect, some health-care services are not available, and many businesses will not be open.

The province is advising seniors, children under seven, and other at-risk groups to exercise caution when deciding when to return home. Anyone with a medical condition should not return until the hospital is fully operational.

"To residents choosing to return this week, I ask you to not go home without a plan," Notley said. "Bring food, water and any other supplies needed for the next two weeks."

Notley thanked residents for their patience.

"There is still a long road ahead of us, and we will travel it together," she said.