SHERIDAN — The yellow haze rising from area mines may seem bad for the environment, but agencies work to ensure compliance with regulations to preserve air quality in surrounding communities.

The week before a group of fourth- and fifth-graders from elementary schools in Sheridan County School District 2 presented to Decker Coal Mine workers, a yellow cloud of smoke hung above the Spring Creek Mine 5 miles north of the Wyoming border. The sight sparked questions with visitors.

Yellow billows of smoke gathering above a mine indicate a recent blast in the mine. The yellow cloud is a result of incomplete combustion of all the blasting agents and the atmospheric conditions are such that the residuals have not dissipated, according to the Montana Department of Environmental Quality. The clouds are made up of nitrous oxide and are a result of using ammonium nitrate as an explosive; nitrogen dioxide causes the reddish-orange cloud.

Mines in the area, like Decker and Spring Creek mines, must follow regulations set forth by the DEQ. In Wyoming, DEQ air compliance inspector Tanner Shatto, who also serves as the District 3 manager, keeps track of blasts occurring at the mines and follows the residual to see where it dissipates.

Regulations require ideal conditions for blasting. Descriptions must be published 30 days before the blast to ensure compliance.

If mines do not properly follow blasting regulations, fear of the yellow smoke reaching Sheridan or popular recreation areas like Tongue River Reservoir.

Montana DEQ records indicated Spring Creek and Decker mines both followed emissions regulations and have not had violations. If citizens nearby have seen the colored cloud of smoke around the mines in the past, the emissions have come in under regulation.

Shatto said occasionally the pollutants entering the air come close to the maximum allowed, so the mines paying close attention to weather and wind conditions is an integral part of the blasting process.

Montana DEQ said blasting must be conducted by certified professionals and designed or implemented to prevent injury to people or damage to public or private property.

“When yellow clouds occur, they typically do not leave the mine site,” Montana DEQ said. “If a citizen observes a yellow cloud that leaves the mine property, they should avoid coming in contact with it and should contact DEQ immediately.”

If one of the mines were to violate regulations for blasting and air quality, DEQ completes a thorough investigation into the extent and conditions of the suspected violation. The DEQ’s process is dependent on what the violation is, the length of the violation and the extent to which the violation occurred, according to Montana’s branch that oversees both Spring Creek and Decker mines.

A Wyoming-specific regulation requires mines to ensure the wind is not blowing toward a community before they blast. If the wind does blow in the direction of a local community, mines are required not to blast that day.

While the colorful clouds over mines after blasting may cause some concern for surrounding communities, reporting and staying away from the clouds will help prevent any injury or unwanted contact with nitrogen dioxide.