The U.S. Environmental Protection Agency (EPA) has made final its changes to the Clean Air Act regarding emissions from commercial and industrial solid waste incineration (CISWI) units and boilers.

The Washington-based EPA said in a news release that only about 1 percent of boilers in the United States will be affected by the changes.

The changes are designed to reduce air pollution, including mercury and particle pollution, from high-emitting boilers and incinerators. The EPA said those typically operate at refineries, chemical plants and other industrial facilities. The EPA is establishing more targeted emissions for those operations.

The EPA said the changes strengthen the original standard established in March 2011.

The EPA also issued its final amendments to the Non-Hazardous Secondary Materials (NHSM) rule, to make clear what types of secondary materials are considered non-waste fuels and provide greater flexibility in rule implementation.