The company that owns the Salt Creek oil field, a Casper consulting firm, and government agencies continue to monitor and find the source of the gas releases near Midwest School, Natrona County's Emergency Management Lt. Stew Anderson said Friday.

"In the school is where they did find pockets of carbon dioxide or CO2," Anderson said.

"They specifically did find there's some type of a small amount of flammable gas, also," he said. "They did rule out hydrogen sulfide or H2S gas, it is not that. They were going to grab some samples to figure out exactly what it was."

Hydrogen sulfide is a poisonous, highly flammable and explosive gas that occurs naturally in petroleum and natural gas. In high enough concentrations, breathing it is quickly fatal, according to the U.S. Occupational Safety & Health Administration.

The CO2 is emerging from a small gully just east of the school, and Anderson was shown where the gas line runs at the corner of the school property, he said. "They found nothing else around the school."

A map revealed an old well under the school's front yard, and crews checked it to determine it had been properly capped and not leaking, Anderson said.

The Irving, Texas-based Fleur de Lis LLC, (FDL) has a private safety firm from Casper that visited houses in Midwest, asked if residents were concerned, and tested the air and found no hazardous gases, he said.

FDL, which bought the oil field from Anadarko Petroleum Co. a year ago, has between 10 and 15 employees and the consulting safety firm has about five on the scene, Anderson said.

Natrona County Emergency Management used its code red system to notify Midwest citizens that the companies are still trying to find the source and people can contact FDL if they want testing done in their homes, Anderson said.

In a news release Friday morning, FDL said the company is still looking for additional point sources of gas and odors. "No additional incidents have been reported or discovered."

FDL will monitor the scene until the issue is resolved. The company also has a hotline --  (307) 462-9112 -- and asks area residents to call with questions and concerns, according to the news release.

Meanwhile, Midwest School will conduct its remaining classes at North Casper Elementary School until June 7, Natrona County School District spokesman Kelly Eastes said Friday.

The district announced Wednesday evening that a gas leak forced the school to close for Thursday, and then announced no staff or students would be allowed in the building.