When Steelers fans order chicken wings, hamburgers, French fries or fish sandwiches at Heinz Field, they'll soon be indirectly helping to fuel Pittsburgh's fleet of dump trucks, garbage trucks, fire trucks and ambulances and clean its air.

The city will convert all of its 300-vehicle diesel fleet to cleaner-burning, less-polluting bio-diesel within the next three years, using fuel produced on the North Side, some of it with waste vegetable oil and grease from Heinz Field's refreshment stands and restaurants.

The fuel switch will save the city money because bio-diesel is cheaper than regular diesel, and a state Department of Environmental Protection grant of $303,675 will pay for new fuel storage tanks at the city's refueling stations.

Mayor Luke Ravenstahl, at a news conference yesterday morning outside Heinz Field, said the city is committed to the bio-diesel conversion and thanked the state for the grant money and the Steelers for their grease.

"The grant will enable us to convert our refueling stations to bio-diesel," Mr. Ravenstahl said after arriving at the snowy news conference in one of the city's blue garbage trucks. "And the bio-diesel will help Pittsburgh become a cleaner city. I hope the city taking the lead will encourage other municipalities, the county and the Port Authority to get involved."

The city's fleet conversion will begin in April when city garbage trucks, recycling trucks and public works department vehicles will begin using bio-diesel, which will contain a waste vegetable oil component of from 5 to 30 percent. By the end of 2009, the city expects to use about 1.2 million gallons of bio-diesel a year, all of it made by United Oil, a bio-diesel producer on the North Side.State Department of Environmental Protection Secretary Kathleen McGinty said Pittsburgh is the largest city in Pennsylvania converting to bio-diesel fuels with the help of the state's Alternative Fuel Grants program. That program provides up to $6 million a year to producers of alternative fuels -- bio-diesel and ethanol -- and municipalities to help them cover fuel station conversion costs.

Other public entities converting fleets to bio-diesel are the Pennsylvania Turnpike Commission, the York County Transit Authority and Great Valley School District in Chester County.

"Homegrown diesel is cheaper than OPEC diesel," Ms. McGinty said. "This conversion will make the environment cleaner, the city treasury healthier and help big and small businesses prosper."

Because there are no mechanical changes needed for vehicle fleets to operate on the cleaner burning bio-diesel fuel, the switch is simple, and studies show that bio-diesel fuel reduces engine wear and maintenance expenses. Additionally, studies show that alternative fuels are cleaner than conventional fuels, emitting little or no soot, less carbon monoxide and fewer pollutants that contribute to ground-level ozone and smog.

Ms. McGinty said Pennsylvania is becoming a leader in alternative fuel production, and by August of next year, with the opening of Lake Erie Bio-fuels in Erie County, its bio-fuels production capacity will increase to 65 million gallons a year. Right now bio-fuel production in the entire nation totals 70 million.

"Pittsburgh's purchase," she said, "represents a far-reaching combination of environmental protection and economic development."