A first responder walks by smoldering wood and a burning retaining wall near a home following a natural gas explosion at a pipeline complex, on Friday, April 29, 2016, in Salem Township, Pa. The explosion caused flames to shoot above nearby treetops in the largely rural area, about 30 miles east of Pittsburgh, and prompted authorities to evacuate businesses nearby.

Pipeline Building Boom Raises Safety Concerns

On the morning of April 29, a natural gas transmission line exploded in a field in Salem Township in western Pennsylvania. The blast was so powerful it ripped a 12-foot crater into the landscape, burned a section of the field with a quarter-mile radius and threw a 25-foot section of the 30-inch steel pipeline 100 feet away. At the time of the explosion, a 26-year-old man was in his house, a few hundred feet away. He was badly burned, and his home destroyed. When local fire chief Bob Rosatti arrived at the scene, the flames were so hot, he had to stay in his truck. “They were massive—I would say 300 feet at the least,” Rosatti says. “That was the biggest fireball I’d ever seen in my life.

A "pig launcher" at the Eighty-Eight Oil tank farm in Guernsey, Wyoming.

As Pipelines Multiply, Pigs Are Paramount

Pigs are used for cleaning pipelines, pipelines that carry natural gas, crude oil, waste water from energy producing areas to the places where that energy is used. Perhaps more importantly, they are used to inspect the millions of miles of pipeline that crisscross the country for corrosion and other problems.

The Invisible Network of a Million Miles is a TIME magazine map from January 1964. The pipeline network has expanded by more than a million miles since it was drawn.

Leaky Barrels, German U-Boats And 2.6 Million Miles Of Pipe

There’s an invisible network connecting every corner of the United States. Without it, cars wouldn’t start and lights wouldn’t turn on. At 2.6 million miles, if it were stretched out, it would reach around the Earth more than a hundred times. Chances are, you’ve never noticed it. The nation’s sprawling pipeline network is buried underground, out of sight and out of mind. But it wasn’t always the case that pipelines crisscrossed the nation, bringing energy where it was needed.