DYLINE, La. — The cleanup of 3,000 tons of explosives haphazardly stored at a munitions plant has frayed the nerves of residents who evacuated, closed the high school and spawned a criminal investigation of the company that owns the materials.

Authorities said about half the town's 800 residents had heeded requests that they leave during the cleanup that started Saturday, but some appeared to be returning to their homes. Some displaced residents were exasperated by the sheer volume of explosive material, which is more than authorities initially estimated. Adding to the uncertainty was a forecast of thunderstorms Tuesday that could slow efforts to move the propellant used in artillery shells to safer storage sites.

"We got outside the evacuation area when they said there was a million pounds. Now it's six million," said Frank Peetz, 71, who was staying with his wife in a camper at a nearby state park. "Maybe we ought to be up in Arkansas somewhere."

State police say some of the propellant was found spilling out of boxes crammed into buildings, and they have opened a criminal investigation into why the materials were not stored in bunkers at the state-owned site, leased by Explo Systems.

Weather could complicate the transfer of the roughly 6 million pounds of propellant. If lightning is spotted within five miles of the site, authorities will suspend efforts to move it, state police spokeswoman Lt. Julie Lewis said. No lightning was expected Monday, but the National Weather Service said there's a 30 percent chance of Thunderstorms on Tuesday.

Lewis said that as of late Monday, crews had segregated or safely stored 1.2 million pounds of the propellant since the cleanup started. The work has slowed because they are indoors moving the material, sometimes through narrow hallways.

State police said the material is stable and would need an ignition source to explode. Lewis said it would take something significant such as lightning or a brush fire — and not static electricity — to ignite it.

Col. Mike Edmonson, commander of the Louisiana State Police, said police weren't sure how much damage an explosion of the material could cause, even after consulting with Department of Defense officials.

"Nobody can tell you what 6 million pounds of explosives would do if it went up," Edmonson said in a telephone interview. "And I don't want to find out."

Police have checkpoints on roads leading into Doyline, though residents are allowed to come and go. The evacuation was voluntary, and some residents elected not to leave their homes in the town that has been used to film some scenes for the HBO vampire series "True Blood." The evacuation will remain in place at least until Tuesday.

Edmonson said that Explo Systems leases and controls about 400 acres of the 15,000-acre Camp Minden, a former ammunition plant that now is a state-owned industrial site and home to a National Guard training facility. He estimated that the M6 propellant was stored in an area of less than 10 acres.

It was discovered there, stored indoors and outdoors, sometimes in containers that had spilled open, by a trooper following up on an October explosion at the facility.

"It was stuffed in corners. It was stacked all over," Edmonson said.

Just outside the evacuation area, Doyline High School teacher Linda Watson stopped Monday to buy chicken strips at D&H Hardware, which has a small kitchen serving fare that also includes burgers.

Watson said she has not evacuated and has no plans to. Like some others around here, she's accustomed to living near an ammunition plant.

"I've been there the whole time," she said.

Her main concern is the school having to tack on days to the end of the year to make up for classes being out during the evacuation. The school was to remain closed Tuesday.

John Finklea, who was working the register at the store his family owns, said business is down because of the evacuation. He said there's too much being made of the situation.

"I understand people get scared," he said, adding that he considered leaving but ultimately chose not to.

Explo has not publicly commented on the investigation. Neither a company executive nor an attorney who represents the company returned calls Monday. Its website says the company has been in existence for seven years and that its management has been "demilitarizing" and recovering explosives and propellant for 15 years.

Authorities had initially estimated the total of M6 stored at the site at 1 million pounds after the first investigator saw cardboard boxes on long rows of pallets behind a building. Police found more stacked in sheds and warehouses when crews returned Saturday to begin moving the boxes into bunkers about two miles away on the former munitions site.

Lewis said the cause of the Oct. 15 explosion remained under investigation.

The company isn't currently allowed to manufacture any explosives, but can sell what it has. Authorities are hoping such sales could reduce the amount of the material in the area.

Webster Parish Sheriff Gary Sexton said authorities have still not been in touch with the company's owners, though police officials previously said a company manager was working with them. He didn't know how many people were still displaced but said the majority of people in shelters had left them.

Sexton said explosions weren't uncommon in the years that the munitions plant has operated, but he lamented the danger posed by the improper storage of the propellant.

"They not only put their people in jeopardy, they put our people and the people around here in jeopardy," he said.

Evacuees were allowed to stay for free at Lake Bistineau State Park, but ranger Marc Massom said only a few had shown up by midday. Masson, a Doyline resident who lives outside the evacuation zone, said some stayed at their houses because of fears about looting.

Lewis, of the state police, said that security was tight throughout the town with help from neighboring agencies, and that crime hadn't been a problem.

Peetz, the retiree staying in the camper with his wife, said there should have been more oversight of the munitions storage.

"I'd like to see more state and federal checks on who is there and what the hell they're making," Peetz said.