ST. PAUL (AP) — Minnesota utility regulators have decided pipelines that carry carbon dioxide are hazardous and therefore subject to state approval.

The decision by the Public Utilities Commission Thursday affects two multibillion-dollar CO2 pipelines proposed to cross Minnesota and carry waste from several ethanol plants in the Midwest.

Commissioners interpreted a 1998 state law on pipelines that carry hazardous materials includes those transporting carbon dioxide. The decision initiates a rulemaking process that could take a year to complete. Actual approval of any CO2 pipeline could take months after that.

The companies seeking to build the pipelines disagree with the commission’s decision.

The Midwest Carbon Express, proposed by Summit Carbon Solutions, would run for 150 miles in Minnesota, connecting to seven ethanol plants. The Heartland Greenway, proposed by Navigator CO2 Ventures, would run for 12 miles, linking to one ethanol plant west of Fairmont.

Commissioners left open a possible exemption for Navigator’s pipeline since it only goes through one county, the Star Tribune reported.

The law “lists very specific materials” as hazardous for pipeline transport — and CO2 is not one of them, said Christina Brusven, an attorney representing Summit Carbon Solutions. “What I don’t want is for the commission to engage in a yearlong rulemaking process only to find out the commission doesn’t have the authority to regulate a CO2 pipeline.”

CO2 is heavier than air, so if a pipeline ruptures it can displace oxygen and potentially cause breathing difficulties, rapid heartbeat, vomiting, headaches and impaired thinking.