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CHARTIERS TOWNSHIP, Pa. (KDKA) – The sprawling MarkWest natural gas processing plant in Washington County was shut down Thursday night as a precaution, after a fire broke out, injuring four workers.

Marathon Petroleum, the parent company, said the fire — which neighbors said followed a big explosion — broke out around 6 p.m.

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The four burn victims were airlifted with to Pittsburgh hospitals — two to UPMC Mercy and two to West Penn. All four were employees of Markwest.

UPMC Mercy updated the conditions of the two patients at their facility, saying one is in good condition and one is in critical condition.

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A statement from MarkWest said there was “an incident near two temporary tanks that were on-site for routine maintenance, resulting in a fire.”

The fire started in a tank, which holds 200 barrels of liquid Ethylene Glycol plus hydrocarbons.

At least eight fire departments responded to the emergency along with HAZMAT and four ambulances.

Two STAT Medvac helicopters and two life flight helicopters also responded, according to Washington County 9-1-1. Washington County 9-1-1 also said there was no order to evacuate homes in the immediate area of the plant.

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“Our prayers are with our injured colleagues and their families,” the statement from MarkWest concluded.