ANCHORAGE, Alaska - BP Exploration (Alaska) Inc. workers were preparing to vacuum up about 4,200 gallons (100 barrels) of crude oil and a smaller amount of produced water that overflowed from a tank at a Prudhoe Bay oil-field facility, the Alaska Department of Environmental Conservation said on Tuesday.

The spill occurred Monday afternoon on the east side of the giant oil field, the department said in a statement. The affected tank is at a flow station, a facility that separates oil from natural gas and water, the department said.

Production at Prudhoe Bay, the nation's largest oil field, was unaffected by the incident, said Steve Rinehart, a spokesman for BP in Alaska.

BP is the operator of the field. BP's major Prudhoe partners are ConocoPhillips and Exxon Mobil.

All of the overflowed oil and produced water was caught in a secondary containment that surrounds the tank, state officials and Rinehart said. "It's got an impermeable liner," Rinehart said.

There were no injuries or environmental damage, Rinehart said.

The cause of the overflow was a failure of instrumentation and valves that are supposed to control tank volume, the Department of Environmental Conservation said.

BP has been monitoring air quality at the site, and will use vacuum truck to suck up the spilled crude when conditions are deemed safe to do that, the department said.

While officials have an estimate of the volume of released material, an exact figure was unavailable on Tuesday, partly because snow in the secondary containment had mixed with the oil and produced water, the department said.