On my way home from work yesterday I noticed a plume of black smoke rising over Superior, and at first I thought it might be another angry ex-wife, but I quickly realized it was coming from the oil refinery. So what caused that big puff of black smoke? Find out after the jump.

Dave Podratz is the plant manager and he explained to me it is very similar to the hot water heater in your house, it, like the oil refinery, has a relief valve and when unwanted pressure builds up, the relief valve lets that pressure out.

With your hot water heater the pressure would be released in the form of water on your basement floor, at the oil refinery the pressure is released in gas vapors through the "closed flare stack". You'll often see a fire burning on the flare to burn off small amounts of gas vapors, which is normal.

Yesterday they had a larger than normal relief event which resulted in some black smoke being produced in a very short amount of time, the plant quickly reacted and added steam to the flame, which quickly made the smoke disappear and reduced the flame size.

Basically the safety system in place at the refinery worked as designed and at NO time was anyone at the plant or in the surrounding community ever in danger. Dave and his crew work very hard to operate a safe and clean operation and what happened yesterday is a rare occurrence.