FAIRFIELD (CBS SF) - The six-alarm fire at Macro Plastics Inc. in Fairfield on Tuesday afternoon appears to have started when employees used an "open flame device" during maintenance work in a storage yard, Fairfield Fire Marshal Morgana Yahnke said Wednesday.

The fire, which sent a thick plume of black smoke into the air that was visible for miles, started about 1 p.m. at the facility, located at 2250 Huntington Drive in an industrial area.

Firefighting resources were scaled back at about 5 p.m. and the blaze was extinguished around 11 p.m., Yahnke said.

Firefighters from 15 Solano County agencies responded. They used water and foam to confine the flames to the storage yard, Yahnke said.

KCBS' Chris Filippi Reports:

"In the end, the fire burned itself out," Yahnke said.

Three firefighters suffered minor injuries but did not need to be taken to a hospital, Yahnke said.

At the height of the blaze, the response consisted of 120 firefighters and 30 to 40 fire vehicles, including trucks, engines and water tenders, Yahnke said.

A shelter-in-place order was issued for residents within a one-mile radius of the fire. The order was lifted around 6:30 p.m.

Yahnke said Macro Plastics Inc. is open for business Wednesday.

The company makes plastic MacroBins used for harvesting, storing and shipping fruits and vegetables. Yahnke said a Macro Plastics Inc. spokesman estimated there were 15,000 bins in the storage lot.

Photo Gallery: Fairfield Plastics Plant Fire

Air samples from the plant fire are being tested and ash fallout is light, which has environmental health officials saying that the type of plastic that burned should be no worse to the environment than a wildfire.

Solano County Environmental Health Manager Terry Schmidtbauer said the components of the plastic bins that are used in harvesting grapes are made with a less toxic type of plastic.

KCBS' Margie Shafer Reports:

"The chemicals are known as polypropylene and polyethylene, and that's fortunate because when those constituents burn the byproducts are pretty much similar to what we would see typically resulting from a wildfire," said Schmidtbauer.

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