Tony Brake had seen tunnel fires before, and given the tower of black smoke and what he could see of the flames, he feared this one was going to be bad.

On a Saturday morning in July, a tanker truck carrying 8,700 gallons of gasoline flipped over, and the two-lane underpass connecting the northbound Glendale Freeway with the northbound 5 Freeway turned into a blast furnace.

If the tunnel — which supports the 5 Freeway — were to fail, the freeway would collapse. Traffic would be snarled for months, and for a region just emerging from a recession, the economic impact could be severe.

Brake, a senior bridge engineer for Caltrans, remembers walking through the tunnel two days after the fire. It looked as if it had been bombed. Crews had erected a bulwark running its length to support the ceiling, and the scorched walls were brittle and crumbling. A skeleton of rebar was laid bare.

At Friday's reopening of the tunnel, Brake stood amid a crowd of close to 50 fluorescently clad engineers, contractors and maintenance personnel, as politicians stood at a lectern and raised their voices against the freeway drone to praise the work.

"In California, we know how to make things happen when we need to," said City Councilman Mitch O'Farrell.

At about 10:30, an armada of Caltrans vehicles slowly traversed the tunnel and saw — nothing. All evidence of the inferno and the work that has defined Brake's life for the last six months had been erased.

Drivers too will notice little more than shiny guard rails, a new roadbed and signage, more than 200 LED lights and a coat of white paint that just might resist the efforts of local tagging crews.

For Brake, indifference is a sign of a success.

"After the work is done, no one really knows what we did," he says. "But that's OK. What is important is that we prevented a tunnel from collapsing, no one was hurt, the repairs were made, and we are able to move on."

Soon after Brake's initial walk-through, crews began searching deep into the walls for patches of concrete no longer able to hold up the freeway overhead.

Drills bit into the walls and ceiling, extracting up to 100 concrete samples, a process akin to taking a medical biopsy. The samples were injected with dyes that highlighted microscopic cracks, and they were placed in vises that compressed them to the shattering point.

Cameras snaked into small bore holes. A radar system analyzed swaths of the walls and the ceiling, and sensors recorded the sound waves of hammers struck against the surface of the tunnel.

When the results came in, Brake was relieved. The damage was not as bad as he had feared. Most troublesome were a series of outrigger beams on the north side of the tunnel. The beams had cooked in the fire, Brake thought, like chicken in a rotisserie.

Brake and two colleagues drafted a set of blueprints that specified the repairs. The design included 13 pages of structural work, one of the most complicated reconstructions that Brake had overseen.

By mid-November, demolition started on the compromised concrete.

Wearing a hard hat, yellow rain slicker and rain boots, with a blue bandanna over his face, Lance Higgins stood at a control panel of an ungainly, four-wheeled contraption with an articulating arm angled high against the side of the tunnel.

A machine, a Conjet Robot 363, "delivers 32 gallons a minute through a nozzle the size of a Starbucks' stir stick," Higgins said.

With the push of a button, the water pressure — about 18,000 pounds per square inch — tore at the brittle concrete, stripping off four inches and further exposing the rebar. Occasional rocks shot across the tunnel like bullets. Loud pops signaled the displacement of larger chunks.

The wall soon looked like a cliff at low tide, its mottled surface of aggregate dripping wet. A soggy rubble littered the roadbed.