Wyoming Refining Co.'s Newcastle refinery apparently experienced a power failure on Wednesday night, resulting in one or more releases of droplets of heavy residual oil, according to the Wyoming Department of Environmental Quality.

The refinery was forced to shut down operations after the power failure at about 10 p.m. Wednesday, according to a DEQ press release.

Droplets of heavy residual oil occurred as refinery personnel were restarting units early Thursday morning. The heavy residual oil is a tarry asphalt-like substance.

No injuries were reported, according to refinery officials.

Bob Neufeld, vice president of environmental and government relations for Wyoming Refining Co., said a thunderstorm was most likely the cause of the power failure. He said the oily substance hit the flare and caused residue to settle over the refinery and on nearby cars and homes.

"The flaring itself was quite a spectacular event," Neufeld said in a phone interview on Thursday. "We are dealing with local residents now as they clean their cars and houses."

DEQ said it will send staff to the refinery. The agency also indicated that local residents should contact the refinery for assistance in removing any oil that has been deposited on their property.

Neufeld said there is no human health risk associated with the oily substance. However, normal precautions should be taken as with any oil.

"Avoid contact with skin. Don't eat it," Neufeld said.

Earlier this year, Wyoming Refining Co. signed a cooperative agreement with the U.S. Environmental Protection agency settling alleged violations related to "past performance." The refinery agreed to buy $14 million in new pollution control equipment and pay an "assessment" of $150,000 under the cooperative agreement.

In 2008, the company reached a settlement with 47 current and former Newcastle area residents regarding pollution from the refinery and a 20-plus tons catalyst spill in 2002 that blanketed residential areas with the substance.

The catalyst spill cost Wyoming Refining Co. a $20,000 penalty, which was assessed by DEQ's Air Quality Division. An air quality task force was formed to monitor volatile organic compounds and other emissions.

Energy reporter Dustin Bleizeffer can be reached at (307) 577-6069 or dustin.bleizeffer@trib.com. Check out Dustin's blog at tribtown.trib.com/DustinBleizeffer/blog.