Sept. 9, 2010: a cool, breezy Thursday evening, not much different from most other weekday nights in San Bruno's Crestmoor neighborhood. Residents were arriving home, making dinner, hanging out with their families. Then, at the corner of Glenview Drive and Earl Avenue, came a blast so powerful that one resident said it sucked all the air from her living room.

The fireball that soared into the sky at 6:11 p.m. instantly transformed the neighborhood into a scene of chaos, with people dashing from their homes, first to see what happened, then to try to escape with their lives.

"When you're in a dream and you try to run as fast as you can but feel like you're getting nowhere, like you're in quicksand -- that's how it felt," Earl Avenue resident Tammy Zapata said later.

In the 50 minutes before the explosion, technicians at the PG&E natural gas terminal in Milpitas and workers monitoring the company's pipeline network were dealing with a crisis.

An electrical failure at the terminal, which helps regulate the network, had triggered an uncommanded increase in pressure to Line 132, a 30-inch pipeline carrying natural gas from Milpitas to the Peninsula and up to San Francisco. Alarms started to sound, warning of dangerously high pressure.

The electrical problem had also knocked out sensors used to monitor the network. As the pressure surge continued for 10, 20, 30, then 40 minutes, staff in Milpitas and in two monitoring centers struggled to understand just how high the pressure inside the pipeline really was and how to bring it under control.

At 6:02 p.m., a worker in one of the monitoring centers said, "We’ve got a major problem at Milpitas, and we’ve over-pressured the whole Peninsula."

As the surge continued, a section of Line 132 that ran beneath the Crestmoor neighborhood began to come apart. PG&E records showed that section of pipe was seamless. In fact, investigators later found, it was a badly welded collection of pipe segments installed in 1956.

When the pipeline finally gave way at 6:11 p.m., the gas it was carrying fueled an explosion that left a 72-foot-long crater and hurled a 3,000-pound segment of pipeline 100 feet through the air.

The blast was just the opening act. Firefighters, paramedics and police rushed to the scene as residents fled. But with no automatic shutoff valves on the pipeline, natural gas continued to roar from Line 132, feeding an inferno that kept emergency responders at bay and started to consume surrounding homes.

PG&E workers began to arrive. But confusion reigned amid reports that a plane had crashed or a gas station had blown up in the area. It took more than an hour before the utility was convinced the explosion had been caused by a pipeline rupture. It wasn't until 7:30 p.m. that three workers managed to manually close a set of valves, stem the flow of gas to the blaze and allow firefighters a chance to control it.

The explosion and fire killed eight people and injured 58 while destroying 38 homes and damaging 70 others. The community is still recovering from the trauma.

The disaster and all the subsequent investigations and disclosures prompt the question: Are Californians safer from a pipeline disaster now than the day Line 132 blew up in San Bruno?

Shock waves from the San Bruno disaster shook the foundations of PG&E and the California Public Utilities Commission, the state agency charged with regulating the company.

The blast exposed the utility's haphazard system of record keeping for its tens of thousands of miles of gas pipelines and its sometimes shoddy construction and inspection practices. The catastrophe prompted questions about whether the company was actually carrying out pipeline safety improvements that ratepayers had been charged for.

“This was not an accident," says state Sen. Jerry Hill, who represents San Bruno. "It was based on circumstances where you have a utility that diverted hundreds of millions of dollars from safety, from maintenance, from testing and from service."

The tragedy eventually led to disclosure of the close ties between PG&E's top executives and the officials in charge of the CPUC, a relationship that led to numerous back-channel discussions, including about the San Bruno blast and how the company and agency should respond to it.

“Really the most shocking part of this is the extent to which the [CPUC] was complicit in the negligence that led to the disaster here in San Bruno,” says San Bruno City Manager Connie Jackson. “You had the leadership of the California Public Utilities Commission essentially in bed with the utility. Dining, drinking, vacationing -- and making deals behind the scenes. Californians should be vitally concerned about the extent to which that behavior has compromised safety across our state.”

PG&E faces hundreds of lawsuits arising from the explosion, as well as federal charges of criminal negligence. Earlier this year, the CPUC fined the utility $1.6 billion in connection with the disaster -- the largest penalty ever levied against a California utility.

Five years after the disaster, the company is still in the midst of the laborious process of ensuring its pipeline network is safe. The company was ordered to perform complex pressure tests or verify the integrity of 1,800 miles of transmission pipeline. So far, it has completed testing on 673 miles of the massive pipes.

"I think we’re safer,” Michael Picker, the new president of the California Public Utilities Commission, told KQED News in an interview. “I don’t think we’re safe enough to satisfy me.”

In August, the CPUC approved Picker’s proposal to launch a new investigation into PG&E’s corporate culture, to determine whether the utility is living up to its promise to put safety above all else.

“We have fined them about as much as we can fine them,” Picker says. “So what else do we need to do?” The pending investigation, he adds, seeks to explore whether there is “real accountability at the top."

Danger has surfaced in other parts of PG&E’s natural gas distribution system since the San Bruno explosion.

In March 2014, for instance, a cottage blew up in Carmel after a utility welding crew accidentally punctured a plastic pipe, triggering a gas leak that fueled a blaze ignited by a pilot light. Last April, a PG&E pipeline blew up in Fresno County at a sheriff's gun range, injuring a dozen people, including jail inmates and a contractor who had been working in the area. The company said the pipeline had been inspected just weeks before the blast.

PG&E says it welcomes the dialogue that the CPUC's newest inquiry will bring. In an interview with KQED, spokesman Donald Cutler defended the company’s progress (Read PG&E's statement).

“The cultural shift that took place at PG&E has been drastic,” he says. “In the past, there were other things that came first. But today, it’s about safety.”

One of the major challenges in making the system safer is its age. Almost two-thirds of PG&E's transmission pipeline system –- the high-pressure backbone, which includes the segment that ruptured in San Bruno –- was installed before 1970. That's the first year federal law mandated that all new transmission lines undergo pressure testing to ensure their integrity.

“Metal deteriorates over time,” notes Steve Weissman, director of UC Berkeley’s Center for Law, Energy and the Environment and a former CPUC administrative law judge. “It can rust. There can be places where plant roots have dislodged things. High temperatures can speed up the deterioration of welds."

With proper maintenance, however, steel pipelines can remain in service safely for a long time, says Glenn Stevick, CEO of Berkeley Engineering and Research and an expert in analyzing pipeline failures.

"For the pipeline to be in a dangerous state — that takes a great deal of time, typically many decades," Stevick said.

But it's hard to see when a pipeline buried underground is deteriorating and becoming prone to failure. One way to know is through hydrostatic testing -- a process in which pipeline sections are filled with water at high pressure to detect cracks and other flaws. But when federal regulations went into effect, thousands of miles of transmission pipeline -- including Line 132 under San Bruno -- were grandfathered into operation without testing.

If any line in the whole state needed hydrostatic testing, the later investigations suggest, it was that one.

The pipeline segment that failed in San Bruno was poorly built when it was pieced together in 1956, with a poorly welded joint containing a visible crack that PG&E's quality control failed to detect. With Line 132 carrying gas at high pressure, the crack grew year after year until it was ready to fail. The pipeline was never pressure tested.

"If they had hydrotested that pipe initially, it would have ruptured during the hydrotest when it's full of water," says Stevick, who was asked by the state to investigate the Line 132 rupture. "We know this from basic calculations. The size of that crack was already in there at the time the pipe was made because they forgot the weld on the inside."

Soon after the 2010 pipeline explosion, a glaring problem came to light: PG&E didn’t have the records to identify with any certainty what exactly it had running underground. As the National Transportation Safety Board noted in its final report, the company's records indicated that the segment of pipeline that failed was seamless.

Throughout the system, the question arose: What other information was missing? Or wrong?

"The older the pipes are, the less likely you are to have really good information about what you have out there,” UC Berkeley's Weissman says.

Two days after the San Bruno pipeline explosion, CPUC Executive Director Paul Clanon emailed Brian Cherry, then PG&E’s vice president of regulatory affairs: “I’m not sure how confident I am that PG&E knows enough detail about every pipe segment,” Clanon wrote, referring to a request federal investigators had made for records demonstrating the integrity of the utility’s underground gas-pipeline network. “Do your people actually have the data?”

Cherry responded by sharing his “gut reaction.”

“God knows what is underground,” he wrote.

In the months that followed, the utility began tracking down pipeline records from decades past. PG&E staff collected documents from more than 46 offices. It took about 1,500 employees five days to sort through 100,000 boxes at the Cow Palace in Daly City.

Elizaveta Malashenko, the CPUC's recently named Safety and Enforcement Division director, described the scene:

“People just going through hundreds of thousands of documents of paper, and then scanning them and then putting them into a database. Then they did analysis of what they found, and said, 'OK, here’s where we think we’re good, we have the records for it. Here’s where we think we have issues.' "

Malashenko says much more is known about PG&E’s system today, but the project of pinning down all the data continues.

One of the eight people killed in the pipeline disaster was Jacqueline Greig, who worked in the CPUC's consumer advocacy branch. Her daughter, an eighth-grader named Janessa who loved theater and was student body president at St. Cecilia School in San Francisco, was also killed.

The surviving Greig family members joined almost 500 plaintiffs in suing PG&E in the wake of the San Bruno explosion.

The Greig family managed to hold PG&E to unique terms in their settlement agreement, requiring the company to calculate a minimum safe life span for all pipes running beneath populated areas. It’s a small attempt to force PG&E to replace weak lines before they’re dangerous. But there’s an entire state agency tasked with ensuring that utilities like PG&E adhere to safe practices –- the CPUC.

“The regulators that we rely on to ensure that the utilities are doing their job appropriately and properly were not doing that,” Sen. Jerry Hill says. “They were pretty much in bed with the utilities, doing their bidding for them.”

Richard Clark was the director of CPUC’s safety and enforcement division when the San Bruno pipeline exploded. Now retired, Clark devotes more time to riding his Harley Davidson motorcycle and welding metal artwork in his home shop.

During an interview, he shows a picture of Jacqueline and Janessa Greig. He says he's still haunted by the deaths of his co-worker and her daughter.

Weeks after the disaster, Clark says he was preparing to testify about it before the U.S. Senate. But then something happened.

“Suddenly, on the runup to the hearing, I was replaced,” he explains. “I thought that was fairly curious.”

When a trove of 65,000 email records was released in connection with San Bruno’s lawsuit against PG&E, it was revealed that Cherry had contacted Clark’s boss, Clanon, to say PG&E was concerned that Clark might "blindside" company executives who were also appearing at the hearing.

Clanon responded to reassure Cherry: “We’re trying to get them to list me as ... the main witness.”

“Whew,” Cherry replied. “That should calm some nerves.”

Cherry was fired when his frequent behind-the-scenes contacts with the CPUC came to light. Clanon stepped down from his post of CPUC executive director last year, saying he planned to study jazz. Former commission president Michael Peevey — whose emails revealed, among other things, that he’d discussed commission business with Cherry “over two bottles of good pinot” at a vacation spot in Sonoma -- decided not to seek reappointment when his term ended at the end of 2014.

“I would be surprised if all the bad apples are gone,” Clark says. “I don’t think it’s an issue of bad apples, quite frankly.” Instead, he chalked it up to PG&E being “quite good at capturing its regulatory authority.”

While he was safety director, Clark said he had repeatedly requested two changes to make his safety division more effective: more safety inspectors and the ability to track how utilities were spending their money. While PG&E conducts its own pipeline inspections, CPUC’s regulatory staff audits that work and conducts field inspections.

According to CPUC president Picker, PG&E had been making layoffs in its gas safety operations in the years leading up to the San Bruno explosion.

Meanwhile, eight inspectors in Clark’s division were responsible for overseeing more than 200,000 miles of gas transmission and distribution lines in California. As state Sen. Joe Simitian, D-Palo Alto, pointed out to Clanon in a May 2011 hearing, that was more than five times the national average per inspector.

“You’ve had to assign staff to other duties, you’ve discovered that there’s a backlog and it’s gonna take a year to get people up to speed,” Simitian said, adding he thought more inspectors should be hired than the four Clanon requested. “Wouldn’t it make sense to get these folks on board?”

Emails also show that PG&E misinterpreted federal pipeline safety rules in a way that likely contributed to the disaster.

In early 2011, the San Francisco Chronicle reported that PG&E had "spiked" pressure on Line 132 to its maximum allowable limit.

PG&E officials later told federal investigators they believed the periodic increases to the maximum allowable operating pressure (MAOP) of 400 pounds per square inch were necessary to show that its Peninsula pipelines, including Line 132, were sound. But under the Chronicle's questioning, PG&E offered a series of contradictory explanations for the increase in pressure.

When the newspaper's story appeared, Clanon wrote to Cherry expressing uncertainty about the federal safety requirements and asking whether it was standard practice in the industry "to raise pressure up to MAOP ...?"

The practice was not standard, nor was it required by any regulation. In fact, the NTSB found that PG&E was the only utility in the country that was spiking pressure.

Clark told the safety board that “artificially raising the pressure in a pipe that has identified integrity seam issues seems to be a wrong-headed approach to safety.”

Failure analyst Stevick says the pressure spikes "almost certainly" damaged the pipeline in San Bruno.

It wasn’t until after Clark left that staffing was bulked up to the levels he’d requested. He sees the shift as a sign of progress. While Clark said it was rare for Peevey to sit down with him to discuss anything relating to safety, Malashenko described Picker as “very engaged. We meet with him on a regular basis.”

On the utility side, PG&E’s gas-safety department has many new faces in 2015. A couple years ago the utility opened a $38 million control room facility in San Ramon. There, engineers monitor gas flow in real time and respond immediately to callers reporting the smell of gas.

Every control room employee must undergo extensive training in emergency-response protocols. In a simulation room, the slogan “Do the Right Thing!” is painted overhead in foot-high lettering.

PG&E has installed 208 automated valves that the utility can shut off remotely from the control room. And 14 automatic shutoff valves will kick in without human interference, for instance, if there’s a big earthquake. Now, it would take up to 20 minutes to shut off the gas, estimates Mel Christopher, director of gas operations.

Data, warnings and real-time maps scroll across a 90-foot video screen. Technicians monitor live feeds from Cal Fire, and watch as PG&E crews move throughout the state.

Out in the field, meanwhile, pipeline testing is underway.

It's a scorching August day in Felton, just north of Santa Cruz, but a thick layer of ice coats pipes and hoses connected to a hulking piece of industrial equipment at a PG&E job site.

Austin Hastings, a lanky engineer clad in a PG&E hardhat and orange safety vest, gestures to a huge contraption mounted on a flatbed truck. It converts super-cooled natural gas from liquid to vapor. Nearby, enormous pill-shaped LNG tankers are lined up.

After the liquid has been vaporized and a chemical added to lend its distinctive odor, the natural gas will be slowly consumed as some 44,000 area residents use their stoves, hot water heaters and other appliances.

Hastings and his crew worked for almost a year to figure out how to provide gas to so many consumers while a work crew performs hydrostatic testing on 5½ miles of a transmission line running parallel to Highway 1.

Since the San Bruno explosion, the company has hydrostatically-tested 673 miles of its transmission pipelines -- which can now be certified as safe. The company has at least 1,500 more miles to test, according to documents PG&E submitted to the CPUC to determine gas rates. In PG&E's 2014 safety report, the utility estimates it will take 12 to 15 years to finish strength-testing its entire transmission system.

This 1950s-era line near Santa Cruz is being tested because PG&E, under direction of federal investigators, has to test any pipeline that's still missing documentation.

It's just one method of assessing pipeline integrity. Operators also send gadgets known as "smart pigs” through the line to check whether the pipe is riddled with leaks or has welding defects like the one that caused the San Bruno explosion. All told, the utility has "pigged" nearly 1,200 miles of transmission pipeline. It has also conducted external assessments on another 885 miles.

“We’re looking for anything that shouldn’t be there,” PG&E spokesman Cutler says. “A dent, issues of corrosion. We live in California – the earth moves here. And so sometimes things are not exactly where we put them in the first place.”

Asked whether the pipeline test in Santa Cruz would be happening if it hadn’t been for the San Bruno disaster, there’s a long pause before Hastings replies, “No.”

In the last five years, PG&E has spent hundreds of millions on physical pipeline upgrades and other additional gas-safety measures. But all of that work doesn’t come close to addressing its entire 6,700-mile transmission system, let alone the sweeping distribution network. There’s much more work to be done -- and PG&E customers will foot the bill.

Bob Bea, once dubbed the "the master of disaster" by GQ Magazine, is professor emeritus of civil engineering at UC Berkeley. He's been all over the world analyzing the causes of high-profile disasters, including the Exxon Valdez oil spill in Alaska and the New Orleans levee breaches in the wake of Hurricane Katrina. He also served as an expert witness for the San Bruno plaintiffs who have sued PG&E.

“PG&E had multiple opportunities during 55 years to properly detect, analyze and correct the defects,” he says, but failed to act.

He says utilities and government aren't doing enough to upgrade aging infrastructure.

"The process of dealing with these infrastructure risks has become largely reactive," he says. "If the Bay Bridge falls down, we build a new one. In other countries, they can't afford an infrastructure disaster. They have to be much more proactive."

As San Bruno residents mark another year, PG&E, regulators and California ratepayers still face a long road before the utility's natural gas pipeline system is fully tested and modernized. The company says the work will cost $12 billion and last more than a decade. The company's customers are likely to pay the lion's share — though just how much is a decision that rests with the CPUC.

Jackson, San Bruno’s city manager, still believes that stronger reforms are in order before the utility and its regulators are really functioning properly.

“It’s been five years,” she says. “And I think that we in San Bruno and throughout California should be able to expect tangible demonstration of real, true reform that allows us to see that our regulators are on it, that they’re proactively demanding accountability and holding themselves and the utilities responsible in a real strong and clear way. We’ve seen progress, but we’re not there yet.”

Ericka Cruz Guevarra contributed to this report. Dan Brekke and Kat Snow edited.