A significant gas leak forced the evacuation of a downtown Fort Dodge building Tuesday morning and electricity was shut off to an entire block to prevent an explosion.

The gas leak occurred in the alley in the 800 block of Central Avenue. The gas seeped into The Boston Center at 809 Central Ave. That building, home to Olde Boston’s Restaurant & Pub on the ground floor and offices on the second through eighth floors, was evacuated.

“It was very lucky a disastrous explosion in this building did not occur,” Fire Chief Steve Hergenreter said. “The gas levels in the building were at the explosion level, it just did not find an ignition source to cause an explosion before it was contained.”

“This is a reminder that if a person smells a gas odor to immediately call 911 or MidAmerican Energy,” he added.

The gas began leaking last week, but the situation was not reported until Tuesday morning.

According to Fire Department reports, the leak was caused by an underground boring company that had been working in the alley on July 12. The leaking gas flowed along water and sanitary sewer lines into 809 Central Ave. People in the building reported smelling a gas odor over the last couple of days.

MidAmerican Energy was notified Tuesday morning and the Fire Department was dispatched at 10 a.m. Tuesday.

Utility company workers told firefighters that they were getting explosive gas readings in the basement of 809 Central Ave. The electricity to the block was shut off.

MidAmerican Energy crews located and contained the gas leak.

Firefighters vented gas from the building, a process that took three hours because of the size of the structure.