DENVER -- Welders working underground at a Denver Water reservoir and pump station facility started a fire Monday afternoon that burned through 150 feet of an underground pipeline.

The fire broke out at about 1:30 p.m. when a group of four welders were using welding torches to cut holes into a five-foot underground pipe.

The welders got out safely.

Dozens of firefighters, who fought the flames from the surface and from underground, extinguished the fire by 4 p.m. An expert team of three firefighters were lowered 15 feet under the ground to fight the flames up close. They were attached to a lifeline, which helped them get out because they could not see anything underground. The lifeline also provided extra oxygen in case their tanks ran out.

"These (fires) are extremely difficult to fight. These are the ones that really are a firefighter's nightmare because just like a basement fire, for example, it's very limited to get out of those basement fires. You can only imagine. Here -- there's zero visibility and you're going to have to find the access point to get out and they're very limited," said Denver Fire spokesman Phil Champagne.

The fire was burning at the Denver water facility at East 56th Avenue and Quebec in Denver. The underground reservoir had been drained prior to the welding work and there was no impact on customers, Denver Water said.