Last Thursday, a terrible smell wafted over the city of Dimona. Kindergarten teachers closed their classroom windows, and municipal workers complained of headaches and a burning sensation in their eyes.

Mayor Meir Cohen called the Environmental Protection Ministry to determine the cause and was told that the source of the stench Rotem Amfert fertilizer company, a few kilometers outside the city.

"Last Thursday was a tough day in Dimona," he said. "It simply stank. We called the Environmental Protection Ministry and they started working, but the stink didn't go away."

Cohen said he was told by Rotem Amfert's environmental hotline told him that oil shale was burning underground but that it was not harmful.

"It was a smell of burnt oil hanging over all the neighborhoods in town," Avi Ben-Zikri, the Dimona municipal spokesman, said.

Moshe Levi, a local resident, said the smell was so strong he was convinced it was coming from Ramat Hovav, the main Negev industrial zone. "It was choking," he said. "It smelled like burnt rubber. We could still feel it yesterday morning."

Roi Alfasi, a Dimona fifth-grader, said children in his class covered their faces with their shirts. "It was so hard to breathe," he said. "We closed all the windows in the classroom."

An official at the Environmental Protection Ministry said: "Rotem Amfert has a phosphate mine that operates a six-megawatt power station that runs on oil shale. The rocks started to burn and the fire was in fact caused by cracks in the ground. People indeed complained of a burning sensation in their eyes, but there was no real health hazard. The factory took immediate steps to put out the fire and covered the cracks."

Neta Schoener, a spokeswoman for Rotem Amfert, told Haaretz that the factory had received no complaints but it was still checking the matter. She said that last week a spontaneous localized fire broke out underground from oil shale used to produce electricity. "This is a rare natural occurence in mines and reserves of coal and shale in various places in the world," she said. "The company immediately took steps to put out the fire by cutting it off from sources of oxygen."

She added that Rotem Amfert was unaware of any link between the oil shale burning and the complaints of stench in Dimona.