APEX, N.C. — Crews likely won't begin cleaning up a hazardous waste site where a chemical fire last week prompted the evacuation of thousands of local residents until next week, officials said Wednesday.

Only state, federal and insurance investigators have been allowed at the Environmental Quality Industrial Services site in recent days. They are investigating the cause of the fire last Thursday night.

The federal Chemical Safety Board wrapped up its work at the site Wednesday after interviewing employees and taking photos and video of the site. Once state and insurance investigators complete their work and the site is released back to EQ, the company will begin its own assessment so a cleanup plan can be developed, officials said.

But before the cleanup can begin, the state Division of Waste Management needs to approve the plan, which could take 24 to 48 hours.

Meanwhile, a contractor hired by EQ continues to monitor the air quality at 13 points around the perimeter of the plant site.

After waiting days for EQ to provide information on what chemicals were at the site at the time of the fire, Apex officials hired their own environmental consulting firm to gauge the impact on the town.

"I know professional toxicologists have a way of explaining it to make it appear minimalistic. But when you use words like cyanide, arsenic and sulfur, the man or woman on the street becomes alarmed about that, and I want to raise their comfort level," Town Manager Bruce Radford said.

Environmental engineers with Long Beach, Calif.-based Earth Tech will review EQ's chemical inventory list and help decipher the chemicals involved for town leaders. They also want to go over previous air and water quality testing results and collect some more samples for testing.

"We're trying to see how (the chemical fire) may have affected (the town), what the conditions are now and how it might impact people now," said Pat Backus, an environmental engineer with Earth Tech.