SERGEANT BLUFF, Iowa (AP) — A 320-foot-tall structure that shoots flames into the air has been put into service at an Iowa nitrogen fertilizer complex.

CF Industries announced Thursday that the flare stack had been placed into service during commissioning of its new ammonia and urea plants at Port Neal, according to the Sioux City Journal (http://bit.ly/2dZy3Gq ). The stack is designed to safely combust gases during certain times at the plant. Flames can extend as far as 200 feet beyond the tip of the stack, when it's ignited.

Officials said the stack will be used intermittently, but will burn continuously for a couple of weeks as the new plants come online and production begins. The expansion is projected to produce nearly 2,500 tons of ammonia daily.

CF Industries has already alerted airport personnel, civic groups, local emergency responders and 3,000 households in an eight-mile radius of the facility of the flare stack project. Flare stacks are common in other areas of the country, but this is the first time a CF complex will be using one.

"When people see a 100-foot-tall candle on top of this 320-foot-tall structure, they're to think something's wrong. But in fact it's part of the design of the flare stack," CF Port Neal general manager and expansion project director Nick DeRoos said. "It's a safety feature."

The company is nearing completion of a $2 billion expansion.