Commentary on this story on Saturday's Headlines Podcast .

Officials in Moore County kept a close eye Friday and Saturday on the developing situation in Apex, concerned about the possibility of noxious gas escaping from a chemical plant explosion.

The explosion, or series of explosions, caused a fire at an Apex chemical plant that continued to burn through Friday. About 17,000 people were evacuated from the area, and about 30 had to be treated .

Fireballs flew over a hundred feet into the air, as most Apex residents north of N.C. 55 fled. What exactly caused the explosion is still unclear.

As winds shifted Friday to blow from the north, there was a worry that a cloud of unidentified gas could float south toward Sanford and Moore County.

Scot Brooks, head of Moore County EMS, said that he had been in contact with North Carolina Emergency Management, which had been monitoring the situation along with the Department of Natural Resources to check the air quality.

Even in Apex, the organizations said they had not found any contaminants in the air, Brooks said.

"We're in a holding pattern," he said.

Jonathan Blaes, a meteorologist with the National Weather Service in Raleigh, said that a light wind was blowing out of the north overnight Thursday to Friday and said that the wind was expected to pick up late Friday.

Rain Friday may have helped to push contaminants to the ground, Blaes said.

Moore County's rescue workers stood ready to lend a hand, but Apex had plenty of help from nearby Raleigh. FirstHealth also volunteered to send teams north to help in case more people should see adverse health reactions, said spokesperson Meg Bigger, but hadn't been asked to assist by Friday afternoon.

The fire began Thursday night at Environmental Quality Co. Several explosions erupted. A chlorine cloud reportedly rose above the hazardous waste plant. No workers are believed to have been injured.

The plant dealt with hazardous chemicals including chlorine, pesticides, herbicides, sulfur and fertilizer and included paints and solvents.

The fire and possible contamination forced the closing of several roads and highways, including N.C. 55 between U.S. 1 and U.S. 64. N.C. 55 is used extensively during the morning Raleigh-area commute. The roads have since reopened.

Many residents of Apex had to leave their homes and stay in schools that were being used as shelters.

Firefighting crews let the blaze burn because they didn't know the specific chemicals that were fueling the fire and therefore didn't know how it would react.

The plant had been destroyed by Friday, but firefighters used infrared cameras to determine if and where there were hot spots of fire still burning within the rubble.

Officials said that the fire may take days to extinguish.

Officers discouraged sightseers from going to the area.

"People are going to want to come as sightseers at this fire scene," Apex Town Manager Bruce Radford told the Associated Press. "They will either get terribly sick or they'll be arrested."